Recommissioning Guide for Indoor Public Pool Facilities in Minnesota

RECOMMISSIONING GUIDE
FOR INDOOR PUBLIC POOL
FACILITIES IN MINNESOTA
DECEMBER 2017
RUSS LANDRY
CENTER FOR ENERGY AND ENVIRONMENT
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
This project is supported in part by a grant from the Minnesota Department of
Commerce, Division of Energy Resources through the Conservation Applied Research
and Development (CARD) program. And with co-funding by CEE in support of its
nonprofit mission to advance research, knowledge dissemination, and program design in
the field of energy efficiency.
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Contents
Summary ........................................................................................................................................ 1
Purpose ....................................................................................................................................... 1
Scope ........................................................................................................................................... 1
How to Use the Guide .............................................................................................................. 1
Indoor Pool ReCommissioning Checklist .................................................................................... 3
General Notes for Indoor Pool Facility Recommissioning ........................................................ 4
HVAC Requirements & Types.................................................................................................... 4
Water Side Systems & Types....................................................................................................... 4
Site to Site-Variations in Systems & Opportunities ................................................................. 5
Monitoring Considerations ......................................................................................................... 5
Individual Measures ........................................................................................................................ 7
Pool Area Setpoints & Lighting .................................................................................................. 7
Optimal Relative Humidity [S1 in Appendix 1 has more information] ............................ 7
Confirm Humidity Sensor Accuracy [S2 in Appendix 1 has more information] ............ 8
Optimal Pool Water Temperature .......................................................................................... 9
Optimal Space Temperature .................................................................................................... 9
Lighting ..................................................................................................................................... 10
HVAC Measures ......................................................................................................................... 11
Dehumidifier Control [H1 in Appendix 1 has more information]................................... 11
Energy Recovery Ventilator Operation [H2 in Appendix 1 has more information] ..... 12
Outdoor Air Ventilation [H3 in Appendix 1 has more information] .............................. 12
Compressor Heat Recovery Operation ................................................................................ 13
Energy Recovery Ventilator (ERV) Retrofit ......................................................................... 13
Compressor Heat Recovery Retrofit ..................................................................................... 14
Water Side Measures .................................................................................................................. 14
Pool Cover ................................................................................................................................ 14
Pool Pump VFD [W1 in Appendix 1 has more information]............................................ 15
Correct Pool Filter Flow ......................................................................................................... 16
Operation of Pool Water Heat Source .................................................................................. 16
Pool Water Heat Source Retrofit ........................................................................................... 16
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Scheduling of Pool Feature Pumps ....................................................................................... 17
Appendix 1. Operator Inspection Instructions for Select Measures ....................................... 18
S1. Optimal Relative Humidity ............................................................................................... 19
S2. Confirm Humidity Sensor Accuracy ............................................................................... 23
H1. Seasonal HVAC Operation............................................................................................... 27
H2. Energy Recovery Ventilator Basic Check ....................................................................... 30
H3. Outdoor Air Ventilation Rough Check .......................................................................... 34
W1. Main Valve Throttling ...................................................................................................... 37
Appendix 2. Detailed Savings Calculation Guidance for Select Measures ........................... 39
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
SUMMARY
Purpose
This guide outlines for you as a
recommissioning provider the most important
energy saving measures that should be
investigated for every indoor public pool
facility in Minnesota. It outlines 17 operational
checks that identify no cost, low cost, and
moderate cost changes that can be made
without major equipment upgrades. It also
points out a few situations where more
expertise and/or a little higher investment
might be required to take advantage of an
energy cost saving opportunity or solve a
problem. The recommended actions are
conservative to ensure that pool and space
conditions are not negatively impacted.
This guide would ideally be applied with the
support of a utility-funded Conservation
Improvement Program (CIP). Some of the
measures addressed are eligible for traditional
utility equipment rebates (e.g. the installation
of a variable speed drive on the pool pump),
while many other items may be rebated
through utility recommissioning programs
(e.g. fixing a control programming issue that
causes excess energy use), a behavior change
program, or other progressive program design.
Scope
The focus of this guide is on energy saving
measures that require no or moderate capital
cost, and which are appropriate for
Minnesota’s climate. It is not intended to
systematically address water quality, air
quality, or moisture condensation issues. It
does not address all upgrades that might be
possible as part of major upgrades or
replacement of equipment.
In addition, this guide does not fully address
water side operations related to water filtration
and treatment that can impact energy use. This
specialty subject is already addressed by
numerous other resources, including the pool
operators manuals listed on the next page.
How to Use the Guide
While a one-time use of portions of this guide
can yield energy savings, you will most
effectively achieve long-term energy savings,
comfort and minimal moisture condensation
issues if:
• all applicable checks are conducted for a
facility, and
• data is collected over the typical range
of operating conditions—especially
seasonal outdoor temperature variations
and major variations in the pool
activities schedule.
While
each
measure
is
individually
worthwhile and written as a stand-alone item,
there is a level of interdependence that makes
completion of all applicable items significantly
more effective. It is recommended that you
follow these steps:
1. Systematically go through the guide to
determine the applicability of each item
for the facility being investigated.
2. Conduct all applicable measurements at
a range of outdoor temperatures.
3. Follow through on the energy cost
saving actions.
4. Confirm successful operation after the
implementation of measures, and take
any subsequent corrective action
required.
5. Provide operations staff with clear and
adequate
documentation
and
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
instruction regarding the improvement
measures.
The checklist on the following page gives a
summary of measures to be addressed in a
pool recommissioning study. A summary of
each of these measures appears in the
Individual Measures section of this guide. The
“Detail” column in the table also notes where
more detailed information is available for
many of the items. Some specific measures
have detailed instructions provided in
Appendix 1 of this guide. A two character
letter and number code is noted for each of
these measure detail items. Note that while
these measure-detail write-ups in Appendix 1
were designed for pool technicians, they still
provide
summary
and
investigation
information that you will likely find valuable
as a recommissioning provider.
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Indoor Pool ReCommissioning Checklist
Check
Identifying
How It Saves Energy
Pool Area
Optimal Relative Inspection & Keeping the humidity lower than necessary increases the
Monitoring evaporation rate and the energy usage of the dehumidifier.
Humidity
Confirm Humidity
Humidity sensors tend to fail quickly causing either
Inspection
unnecessary dehumidifier operation or high humidity.
Sensor Accuracy
Detail
S1
ASHRAE
S2
Overheating the pool increases the pool evaporation rate,
Optimal Pool
Inspection (&
heating energy and dehumidification needs. Lowering it within
Water Temperature Monitoring) the comfort range prevents this.
NSPF,Ch.12
Overheating the pool area air above the pool water temperature
Inspection &
causes excess air heating and evaporation. Reducing the air
Monitoring
temperature within the comfort range prevents this.
NSPF,Ch.12
Optimal Space
Temperature
Lighting
HVAC
Dehumidifier
Operation
Energy Recovery
Ventilator
Operation
Outdoor Air
Ventilation
Compressor Heat
Recovery
Operation
ERV Retrofit
Compressor Heat
Recovery Retrofit
Water Side
Inspection
LED lighting retrofits typically give a quick energy cost
payback, plus the reduced maintenance costs are substantial.
NRPA,10-3
ASHRAE
NRPA,20-5
ASHRAE
-
Inspection & Control problems can lead to over active dehumidification with
Monitoring excess energy use and equipment wear.
H1
Where an ERV is present, improper control or breakdown can
Inspection &
eliminate its energy cost savings—typically without any change
Monitoring
in space conditions that would draw attention.
H2
Bringing in too much outdoor air increases energy costs, while
Inspection &
bringing in too little can cause air quality problems, and
Monitoring
excessive dehumidifier operation.
H3
ASHRAE
All compressorized systems recover heat to reheat the
Inspection & dehumidified air, and some heat pool water as well. SubMonitoring optimal control coordination of heat recovery often significantly
reduces the savings achieved.
-
Using the exhaust air to preheat the fresh outdoor air provides
Inspection &
substantial savings when high continuous outdoor air
Monitoring
ventilation is needed.
-
Inspection & Adding or re-establishing heat recovery for pool water heating
Monitoring may be cost-effective
-
Pool Cover
Interview, Covering an unused pool to prevent evaporation is typically a
Inspection & large energy savings opportunity. The use of a liquid pool cover
Monitoring may provide savings in a similar say (although lower).
Pool Pump VFD
Oversizing of pumps is often compensated for by choking down
Inspection &
the flow. This uses more energy than slowing down the pump
Interview
with a variable speed drive.
NSPF,Ch.12
NRPA,10-5…
W1
Correct Pool Filter
Flow
Inspection & Turning the pool over faster than the required 6 hour time
Interview
frame required for most pools increases pump energy use.
NSPF, Ch.10,
NRPA, Ch.5,
Ch.8,Ch. 9
Operation of Pool
Water Heat Source
Long-term pool water heater under-performance can be masked
Inspection &
by overheating of the air above the pool, which leads to
Interview
excessive heating energy use.
NRPA, 10-2,3
Pool Water Heat
Source Change
Inspection,
Interview &
Monitoring
High efficiency condensing pool heaters (or condensing boilers
with a heat exchanger) can reliably provide substantial savings
-
Scheduling of Pool
Feature Pumps
Inspection,
Interview &
Monitoring
Pumps serving special pool features (e.g. water slide or play
features) may use much more energy than the circulating pump.
These should be turned off when not needed.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
General Notes for Indoor Pool Facility Recommissioning
HVAC REQUIREMENTS & TYPES
Typical primary requirements for indoor public pool air HVAC are:
1) Provide continuous outdoor air ventilation as needed to dilute and remove pool chemical
breakdown products.
2) Provide adequate heat to maintain the space at temperatures of up to 85°F.
3) Provide dehumidification to maintain the space at a relative humidity of 45% to 60%.
4) Keep the pool area depressurized with respect to the adjacent portions of the building.
Note that the majority of existing indoor public pool HVAC systems in Minnesota do not have a
means to provide comfort cooling only (e.g. the cooling coil’s compressor has all of its heat put back
into the pool area air through a fully condensing reheat coil). Those that do have cooling capacity
generally only use the cooling-only mode for a very small percentage of the summer hours.
Larger pool rooms (e.g. in a school or fitness center) tend to be served by a single compressorized
dehumifidifier that uses refrigerant based cooling and reheat. These larger units have a wider variety
of options and configurations that can include energy recovery ventilation, and outdoor condenser
for getting rid of excess cooling/dehumidication compressor heat, heat reclaim for pool water
heating and/or variable speed fans. Exhaust/relief air is often built into the single main air handler,
but is also sometimes provided by separate exhaust system. Most of these large units have some
capability to tie into a building automation system (BAS).
On the other hand smaller pool areas tend to have a single outdoor-air-only dehumidifier that simply
brings in a varying amount of relatively dry outdoor air and heat it as needed to maintain the
appropriate temperature in the space. Most of these have a direct-fired gas burner. The outdoor-air
only units are often paired with an exhaust fan that has a variable speed drive. While one product
line for smaller pool rooms does have a variety of options for heat recovery, heat rejection and remote
data monitoring/control, most do not and this specific product line does not incorporate a heat
source so that another, external heater is also required. It is also noteworthy that a small, but
significant percentage of smaller units use electric heat. Most smaller HVAC units are installed with
stand-alone controls that are not connected to a BAS in any way.
WATER SIDE SYSTEMS & TYPES
Continuous circulation of pool water at a turnover rate of 6 hours is required in public pool facilities
in Minnesota. This is for cleaning of the water through filters that have a significant pressure drop,
and this continuous recirculation water stream is also used for pool heating, as well as water quality
monitoring and treatment. This water flow rate is measured and recorded every day as part of a pool
operations logs, but the pool water heat source often has only a portion of this recirculation water
flow going through it.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Smaller systems tend use a commercial, packaged gas-fired pool heater with a simple burner on/off
control with a manually adjustable return water temperature setpoint that is displayed in degrees
Fahrenheit. Some spas and small pools may have a residential style heater without electrical power.
On the other hand, larger pools are often heated by a heat exchanger that receives heat from a steam
or hot water boiler system. Typically this boiler system serves other loads in the building, but in some
cases a dedicated pool boiler system uses a water to water heat exchanger.
SITE TO SITE-VARIATIONS IN SYSTEMS & OPPORTUNITIES
We found a very wide variety of both system designs, and site-specific modifications and operations
practices that have occurred since the original installation. This means that the preset list of potential
measures and investigation approaches described in this manual should not be considered as an
exhaustive list of what you should consider in your recommissioning efforts. An open-minded look
at the existing systems based on an appreciation of the key energy impact items will uncover other
site-specific opportunities. The typical list of recommissioning fundamentals apply, but with a slight
twist on many items. The following is a list of key energy impact factors to keep in mind with
recommissioning an indoor public pool facility:
1) Optimal outdoor air flow control balances its dehumidification potential against the need to
heat it to the high space temperature maintained in a pool room.
2) Dehumidification needs and actual humidity achieved vary seasonally because of changes in
outdoor air moisture levels and the surface temperatures of exterior windows and doors.
3) Evaporation represents the vast majority of pool heating load.
4) Scheduling opportunities are less than most facilities, but can still be worthwhile (especially
covering the pool).
5) The specialized and/or complicated HVAC systems for pools are often not optimally
controlled.
6) Heat reclamation opportunities are often worthwhile, but also often not optimally controlled
or maintained.
Both HVAC and pool heating trend data should be analyzed over a range of outdoor temperatures
and the variety of pool occupancy situations. Time series plots are valuable for observing control
sequencing while a combination of regression and BIN analysis (where relationships are not linear
over the range of observed conditions) is our recommended approach for the analysis of load and
system energy use variables. Also note that while the full on-off cycle length of pool heat systems can
be several hours, the actual burner on-time for gas -fired pool heaters tends to be only a very small
fraction of this full on-off cycle length.
MONITORING CONSIDERATIONS
Effective recommissioning of an indoor public pool facility may require the use of stand-alone data
loggers instead of the reliance on trend logs from Building Automation Systems (BAS) that is typical
for recommissioning. The specialized pool area HVAC units are often not linked into a BAS in a way
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
that provides adequate trend logging capability. Some sites do not have any link to a BAS, while
some very common pool HVAC units used in larger facilities have been found to have BAS system
integration issues across multiple sites and vendors. Pool facility specific tips related to the use of
dataloggers and the logging of pool water heating equipment operation are outlined in the following
paragraphs.
When choosing and installing datalogging equipment, careful consideration should be given to the
potential for greatly accelerated deterioration due to high humidity and the presence of corrosive
chemicals in pool area air. Sensors and/or loggers should be chosen accordingly. Where practical, the
most reliable arrangement is typically to have only the sensor(s) in the pool return duct or pool area,
and have them connect to a logger that is not directly exposed to the pool area air. However, pool
maintenance room air is often not much better than pool air in regards to corrosive chemical vapors.
If loggers are left in place for an extended period of time, the conditions of the sensors and loggers
should be verified monthly—including verification of data consistency over time or against a reliable
spot reading.
Gas-fired pool heaters only require a burner on/off status indicator via a connection to the burner
control or power signal. Pool water heating energy use can then be simply calculated using the buner
on-time fraction in connection with the burner’s fixed input rate. You may also run across a smaller
residential pool heater that doesn’t have electrical power. In this case, a temperature measurement in
the flue or vent (with a small gauge thermocouple read by a datalogger) can be used to tell when the
burner runs.
When a water to water (or steam to water) heat exchanger is used for pool heating, it may not be
possible to get a very accurate measurement of pool water heating energy use. There are some cases
with heat exchangers where reasonably reliable estimates can be made:
1) the water flow rate is known (either constant or logged) and the temperature rise (or
drop) of more than 6°F is logged with sensors inserted into the pipe; or
2) the boiler supplying water to the heat exchanger is dedicated to serving only the pool
heating load (and the energy use of the boiler can be determined as noted above for a
constant firing rate boiler or through logging of modulated firing rate).
The limited accuracy of individual water temperature sensors makes the measurement of smaller
temperature rises (or drops) relatively inaccurate. There are only limited cases where strap-on pipe
temperature sensors (with insulation wrapped around the outside) are useful in pool systems
because most pool water piping is plastic. The piping adjacent to a heat exchanger can sometimes be
an exception to this. While it is often easier to measure pipe temperatures on the boiler side of a heat
exchanger, it is usually difficult to accurately estimate the water flow rate on that side of the heat
exchanger. It is also common to not be able to reliably estimate the water flow through the pool side
of the heat exchanger because of many of the systems having only a fraction of the full, measured
recirculation flow going through the heat exchanger. The actual bypass flow rate tends to be constant
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
over time based on a manual bypass valve setting. This means that changes in pool heating load over
time can be compared through temperature rise measurements, but the assumption of constant
manual valve setting must be confirmed over the course of the monitoring period. Because of these
various site to site challenges recommissioning efforts will sometimes not be able to make reliable
direct measurement of pool water heating load and its dependence on multiple factors.
Individual Measures
For those checks on the checklist that have a single letter and single number code in the detail
column, a detailed check with that letter-number code can be found in this section. These specific
items were chosen based on consideration of significant potential energy impact and/or a shortage of
clear information available in other readily available pool technical resources. For a number of other
items, the checklist refers you to specific parts of the two most prominent pool operator training
manuals and/or an ASHRAE Handbook . These documents are:



NSPF: National Swimming Foundation, Pool & Spa Operator Handbook, 2012, 2014, & 2017
Editions.
NRPA: National Recreation and Park Association, Aquatic Facility Operator Manual, Revised
6th Edition.
ASHRAE: ASHRAE Handbook—HVAC Applications, Chapter 5, Pages 5.6 – 5.8, 2011.
Also note that the checks are broken down into three categories, which are described in greater detail
below.
POOL AREA SETPOINTS & LIGHTING
Suboptimal control settings and/or inaccurate sensors commonly cause pool systems to use more
energy than needed and lead to occupant discomfort. The measures in this section outline a few key
items that commonly provide cost-effective savings opportunities:
Optimal Relative Humidity [S1 in Appendix 1 has more information]
While pool operator training materials give guidance for pool room humidity based primarily on
comfort considerations, facilities in Minnesota may need to seasonally maintain lower humidity
levels to prevent condensation on windows, door frames, and other exterior surfaces. This
condensation issue is much worse in severe cold weather, so the low humidity that is needed in these
conditions does not necessarily need to be maintained at more mild conditions. Maintaining lower
than required humidity during mild weather can significantly increase energy use and wear on
dehumidification equipment. Also, in Minnesota the low wintertime moisture content of outdoor air
that is continually brought in will typically bring the relative humidity below the setpoint in cold
weather so relative humidity control setpoints may not even need to be based on the worst case
design dewpoint/condensation thresholds. The optimal approach is usually to have a low relatively
humidity setpoint when it is very cold out, and then to have the relative humidity increase gradually
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
to a higher relative humidity in warm weather. The ability to accomplish such setpoint variation
automatically will vary from site to site, but will more often be possible when a BAS is used. Where
not possible, operations staff can be instructed to manually vary the relatively humidity setpoint
seasonally.
Identifying and addressing envelope condensation causes may also allow the relative humidity to be
increased. Common areas of concern are door frames, window frames and structural steel or concrete
that extend all the way through the exterior envelope without thermal protection. This leads to cold
surfaces that can be below the dewpoint and have condensation. Having adequate supply air flow
rate over such surfaces can also minimize condensation by raising the surface temperature supply
airflow rate and diffuser distribution should also be investigated where there are doors, windows or
other envelope components susceptible to condensation.
Long-term monitoring of pool area temperature and relative humidity over the extremes of outdoor
temperature variation is recommended for investigation of this measure, as well as periodic spotchecking of controller humidity setpoints. Return or exhaust duct temperature and humidity may be
substituted for pool area values when these are more readily available. When available, trending with
a Building Automation System (BAS) is typically the easiest way to accomplish this (and setpoints
can also typically be monitored as well), but the accuracy of the temperature and humidity sensors
should be verified at the start of trending (see next item). If BAS trending cannot be used to capture
seasonal variations, dataloggers may be used. Note that the chloramines in pool area air can lead to
greatly accelerated corrosion, so sensors and/or loggers should be chosen accordingly. Where
practical, the most reliable arrangement is typically to have only the sensor(s) in the pool return duct
or pool area, and have them connect to a logger that is not directly exposed to the pool area air.
However, pool maintenance room air is often not much better than pool air in regards to corrosion.
Estimation of savings should take into account the site-specific relationships between dehumidifier
operation, outdoor temperature, and indoor relative humidity, besides the relationship between pool
area humidity and outdoor temperature. The use of theoretical calculations of annual impact of pool
area humidity changes should be conservatively with careful attention paid to assumptions about the
impact of seasonal outdoor air absolute humidity on the HVAC unit dehumidification load.
Confirm Humidity Sensor Accuracy [S2 in Appendix 1 has more information]
Humidity sensor accuracy is critical in pool facilities, and the general tendency towards humidity
sensor problems is greatly exacerbated in these facilities by the presence of chloramine gas in the pool
room air. The investigation should both confirm that the relative humidity sensors used to control
equipment is rated for a chlorinated environment and that it currently gives an accurate reading. As a
recommissioning provider serving pool facilities, you should use a handheld relative humidity
sensor with an accuracy of ±2% that is recalibrated within the manufacturer’s recommend interval.
Since relative humidity measurements are very sensitive to both temperature and absolute humidity,
it is crucial to have the handheld humidity sensor as close as possible to the BAS sensor or humidistat
during a humidity sensor accuracy check. If there is a small bias in temperature, the adjustment noted
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in S2 can be used; however, it is preferable to use a psychrometric chart or calculation when making
an adjustment for such bias. Relative humidity readings can be slower to respond than temperature
readings, so be sure and wait until both are steady before taking readings for a comparison between a
reference probe measurement and the HVAC system’s sensor. Also note that many humidity sensors
perform poorly below 15-20% RH or above 80-85% RH, so a repeat check on the accuracy of the
HVAC system sensor should be made at another time if the relative humidity is not between 20% and
80% at the time of verification. Use of a datalogger can be useful in situations like this or to compare
against trend log data, but the datalogger’s RH sensor accuracy should be verified against a
calibrated probe at the beginning and end of its deployment. Industrial grade dataloggers and
sensors are recommended to prevent premature failure due to exposure to high humidity and
chloramine gas.
Optimal Pool Water Temperature
While the mid to low 80’s is the optimal temperature for comfort in most situations, pools that used
exclusively for lap swimming and competition are generally maintained at the low end of this range,
and sometimes in the very high 70’s. Heating the pool warmer than necessary greatly increases
energy use—primarily by increasing evaporation—so keeping it as low as possible without causing
undo comfort issues is important for minimizing energy costs. Depending on the relationship
between the capacity of the pool heating equipment and the pool water volume, it may be practical to
set back the pool water temperature during long periods of non-use or to change the temperature for
varying uses (e.g. senior aerobics class vs swim team practice).
Although it is generally very difficult to monitor pool water temperature with a temporary logger,
most operators keep long-term logs of water temperature and spot measurements can be made
quickly and easily. Pool operators are required to keep long-term logs of many pool water quality
indicators and nearly always include pool water temperature in their logs. Spot measurements are
useful as a reality check on the appropriate temperature and also to verify the accuracy of the pool
water sensor or controller. The plastic piping used for pool water makes strap on sensors inaccurate
(even if insulation is wrapped around it). Where pool water temperature is linked into a BAS, longterm trending can be useful.
Optimal Space Temperature
While a number of resources suggest keeping the pool room temperature higher than the pool
temperature, our findings indicate that energy use in Minnesota pool facilities is minimized with pool
area temperatures that match the pool temperature (or are even lower within comfort levels). It
appears that the assumptions behind recommendations in previous documents and calculators that
focus on dehumidification loads do not take fully into account some key realities related to the
annual operating season in Minnesota:
1) Outdoor Air Heating Loads. For the vast majority of the year in Minnesota, a pool space that is
kept at a much higher temperature than a typical occupied space must heat the fresh outdoor
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
air that is continually brought in to provide adequate air quality (and the outdoor air is seldom
cooled).
2) Humidity Often Below Setpoint. Previous analysis of pool evaporation and related energy use
has generally assumed that the relative humidity will always be right at the controller’s
constant humidity setpoint when the temperature is changed. However, just brining in the
minimum required outdoor air often causes the relative humidity to drift below the controller
setpoint during the heating season in Minnesota. This is because the cold outdoor air is very
dry (e.g. 25°F air has a relative humidity of 10% or less after being heated to 85°F). Therefore,
the constant relative humidity assumption overestimated the sensitivity of evaporation rate to
pool area air temperature for a majority of the operating season.
3) Average Activity Level Well Below Design Values. Activity levels used for worst-case design
evaporation rate circumstances lead to overestimation of evaporation rates—and the energy
impact of changes in evaporation rate—for the vast majority of the year.
The impact of these factors is reflected in our monitoring of the impact of space temperature on
energy use. Our monitoring generally suggests that keeping the heating season air temperature as
low as possible within an acceptable comfort range will provide the lowest energy costs. This is in
contrast to previous suggestions that the combination of HVAC and pool heating energy use is
minimized by keeping the air temperature 1°F to 4°F above the pool water temperature. We instead
suggest that minimum energy use is achieved with air temperatures up to 5°F below the pool water
temperature—especially during low and no occupancy periods. Of course minimum energy use must
be balanced against comfort considerations for occupants wearing only swimming suits and being
wet as they come out of the pool.
Using overnight setback in cool weather is a way to take advantage of the above relationship that has
been misunderstood, but care must be taken to prevent inadvertent overuse of the dehumidification
equipment. This is because with constant absolute humidity the relative humidity goes up as the air
temperature goes down. Over-dehumidification during setback can be prevented through the use of
dewpoint setpoint instead of relative humidity setpoint, or an increase in relative humidity setpoint
as the temperature setpoint is reduced.
Lighting
The replacement or upgrade of existing fixtures to LEDs is typically one of the best energy cost
saving investments with a quick return on investment. Substantially reduced long-term maintenance
costs are also a key benefit. This applies to both overhead (general area) lighting and underwater
lighting, although special considerations for each are noted below.
For overhead lighting in pool areas, only fixtures that are specifically designed for such a harsh
environment are recommended. Fixtures must be able to withstand possible splashing, high
humidity, high temperatures, and corrosive chloramine vapor.
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Our survey of existing facilities found that the actual use of underwater pool lighting can be
inconsistent (i.e. some facilities that have underwater lighting only use it for a small fraction of the
time, and some do not use it at all). When looking at the economics of underwater lighting upgrades,
be sure to specifically confirm the expected operating hours of underwater lighting separate from the
hours of overhead lighting and pool operation hours.
HVAC MEASURES
The specialized HVAC equipment and control requirements for indoor public pools are too often not
fully understood by designers, contractors, and operators. This can lead to a variety of energy
wasting HVAC operating conditions that can be identified and corrected through recommissioning
and subsequent implementation. The majority of cost-effective HVAC energy-saving opportunities
found at the study sites can be identified through HVAC investigation efforts focused on the general
issues noted in the checklist and repeated below. However, the large site to site variations in details
of the equipment and problems encountered means that the specific opportunities related to these
issues should not be limited to a pre-set list of possible corrective measures.
Dehumidifier Control [H1 in Appendix 1 has more information]
Indoor public pool spaces in Minnesota get significant inadvertent “economizer” dehumidification
much of the year. This is because the high amount of outdoor air needed for adequate dilution of
pool chemical breakdown products is relatively dry during cold weather (e.g. 25°F outdoor air has a
relative humidity of 10% or less when heated to 85°F). Having too low of relative humidity setpoint,
or numerous other control problems that lead to excessive operation of the dehumidifier, can greatly
increase energy costs and accelerate deterioration of the dehumidifier. While the previous “Optimal
Relative Humidity” portion of this document goes into greater detail regarding optimal seasonal
changes in humidity setpoint, this item focusses on determining if excessive dehumidifier operation
is occurring.
The information in check H1 in Appendix 1 should be used as a guideline for determining whether
dehumidifier operation can be reduced significantly. For recommissioning purposes, the actual
amount of dehumidifier operation over a range of outdoor temperature conditions can be obtained
through BAS trend logs in some cases, and will require the use of temporary dataloggers in other
circumstances. Where datalogger(s) are required for monitoring of a compressorized dehumidifier, a
CT (current transformer) on the dehumidification unit (or multiple CTs on individual compressors)
can be used with a datalogger to determine the operating state of one or more compressors. For
outdoor air only dehumidifiers, there are two approaches that might be possible depending on
details of the unit configuration. The first approach is to use a datalogger that measures tilt and attach
it to an appropriate portion of the damper actuator or damper. Where this is not practical, the second
approach is to measure the temperature of the outdoor air intake and the air stream it is mixing with
before and after the location where the outdoor air is introduced. Note that many dehumidifiers have
configurations that make the locations of these measurements different than the typical return air,
mixed air and outdoor air locations on other units, and/or make it impractical to measure a
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
representative average of all three of these temperatures (without a coil or heating element
introducing an additional impact on one of the temperatures). No matter which approach is taken to
monitor the operation of the dehumidifier, concurrent monitoring of pool room relative humidity
and temperature, outdoor temperature, and other dehumidifier control details (e.g. reheat) are
typically very important for understanding the cause and correction path should excessive
dehumidifier operation be found.
Estimates of energy impact should involve use of the actual monitored data of current operation
along with an educated estimate of the reduced dehumidifier operation that will be achieved. The
information in H1 can be combined with an engineering calculation of reduced dehumidification
loads if setpoint changes are to be made.
Energy Recovery Ventilator Operation [H2 in Appendix 1 has more information]
When an Energy Recovery Ventilator (ERV) is present, the information in check H2 should be used as
a guideline for a basic determination of whether or not it is operating as it should be. The Typical ERV
On/Off Operation Ranges chart in the Compare section of H2 shows the expected operation at different
outdoor temperatures, while the Investigate section of H2 describes how ERV On and Off operation
status is determined.
Of course recommissioning efforts should expand the spot determinations described in H2 to
monitoring over a range of seasonal conditions through either BAS system trend logging or the use of
temporary datalogger(s). Even though BAS or logger monitoring over time is important, direct
physical observations of ERV on-off status (i.e. turning of a wheel or the position of face/bypass
dampers) should also be done at least once for each status. Wherever possible, logged indicators of
ERV on/off status (i.e. wheel motor operation as determined by control signal or current measures or
a damper position indication) should be confirmed through concurrent data on the temperature of
the various air streams. While further optimization of control is possible through recommissioning
efforts, the vast majority of cost-effective savings from ERV recommissioning is obtained through the
correction of issues related to this basic on/off status control. One exception where further
measurement/investigation is recommended is the case of ERV units that have a variable speed drive
on the exhaust side. In this case, logging of data should be adequate to compare VFD speed and/or
exhaust side air flow against outdoor air flow and the total flow through the non-exhaust side of the
heat exchanger. Significantly unbalanced flows can make the savings of the ERV feature dramatically
less.
Wherever possible, estimates of savings from changes/corrections to ERV control should be based on
site-specific monitored data of the amount of heat recovered at or near the expected operating
conditions (as opposed to engineering calculations using rated effectiveness, etc.).
Outdoor Air Ventilation [H3 in Appendix 1 has more information]
Excess outdoor air and economizer operation are a typical focus of recommissioning efforts, and are
even more important in indoor public pool facilities, with some unique twists. Outdoor air can
provide “economizer” style dehumidification since it is dryer than the pool room for most of the year.
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However, the high pool room temperature also means that for the same outdoor air flow, the heating
load extends over many more hours and is greater at the same outdoor temperature than for other
spaces. Therefore, the review of the control of outdoor flow air variations above the minimum
required often identifies cost-effective improvement opportunities. Moreover, a high minimum level
of outdoor ventilation is also needed for dilution of contaminants, except when the pool is covered.
This high minimum outdoor air flow typically over-dehumidifies the pool room throughout much of
the heating season, which increases the pool water evaporation rate and heating needs. Therefore,
reducing the continuous outdoor air flow by even a modest amount can provide substantial energy
cost saving benefits, both directly and indirectly. As a result, measurements and/or logging to verify
that the minimum level of outdoor air flow is appropriate is critical in pool facilities. More
information related to outdoor air for pool facilities can be found in the H3 operator’s instructions
document found in Appendix 1.
When scheduled activity levels and/or the use of a pool cover allows, it may be possible to reduce
the outdoor air ventilation level at night. Using a variable speed drive on the supply fan with a lower
“unoccupied” speed setting may be a cost-effective way to both reduce outdoor air ventilation and
fan power.
Compressor Heat Recovery Operation
Sub-optimal control of compressor heat recovery and/or a lack of coordination of other heat sources
with heat recovery often reduce the savings achieved and provide a good recommissioning savings
opportunity in pool facilities. Identifying these control opportunities requires simultaneous logging
of compressor operation, heat reclaim operation, and primary heat source operation, and careful
review of the data. For example, we found that independent control of an electric supply duct heater
and hot-gas reheat increased the electric use. In this case, the dehumidifier could either reject heat via
an outdoor condenser or a hot-gas reheat coil located right after the cooling coil. During mild
summer weather when the compressor was cycling frequently, the unit was found to be rejecting
most of the heat through the outdoor condenser instead of the reheat coil causing the electric heater
in the supply duct to cycle on shortly after the compressor cycled off. Similarly, if heat is reclaimed
for pool water heating, using this reclaimed heat as a first stage of heating while holding off use of
the primary pool heat source until a second stage of heating is really needed to prevent an impact on
comfort will maximize the energy savings from having the pool water heat reclaim feature. In each of
the above cases, the key to finding these savings opportunities was to understand the HVAC unit
thoroughly—especially the heat reclaim features and the primary heat sources they are supplanting
when they operate—before beginning logging. This will ensure that the logging will capture all of the
data needed to spot situations where both heat sources are operating simultaneously and/or cycling
over the same time period.
Energy Recovery Ventilator (ERV) Retrofit
Although a recommissioning study scope typically doesn’t include such a significant design change
and capital-intensive equipment upgrade, the high continuous outdoor air ventilation rates and high
pool room temperatures may make an ERV retrofit cost-effective for an indoor public pool facility—
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
especially if there is a need to replace the dehumidifier anyway. When installed as part of a new or
replacement unit, the use of an ERV may allow the heating and/or cooling capacity of the unit’s
primary systems to be substantially lower than for a unit without and ERV. Site-specific logging of
outdoor air heating loads will yield a much more accurate energy cost savings estimate that design
and engineering calculations alone.
Compressor Heat Recovery Retrofit
For facilities with at least one dehumidifier compressor operating over the majority of the time in the
summer months, the addition of compressor heat reclaim for pool water heating might be costeffective. Actual logging of dehumidifier operation and pool heating energy use should be used as a
basis for determining the site-specific savings potential. Savings should be estimated based on the
lesser of each of the following values for each hour (or the average for those conditions when typical
equipment cycle length is longer than an hour :
1) The pool water heating energy use;
2) the calculated heat rejection from the cooling compressors; and3) the proposed pool reclaim exchanger’s capacity multiplied by the fraction of time that the
compressor operates in that condition.
Controls must be carefully integrated to use the reclaimed heat as the first stage of heating during
time periods that the waste heat is available (i.e. disable the primary heat source except when the
reclaimed heat can’t keep up). See the Compressor Heat Recovery Operation topic within this list for
more information about compressor heat reclaim control issues.
WATER SIDE MEASURES
This category addresses a number of items that can lead to more efficient operation of a pool facility.
Some of these require no capital cost while others are aimed at finding specific facility conditions that
may require significant capital, but which will typically yield a worthwhile return on the investment.
Depending on the applicability in a particular facility, a couple of these items should be worked into
regular operating procedures.
Pool Cover
Although they require a daily commitment to operate and are prone to repair needs, the use of pool
cover during unoccupied times is widely recognized by pool operators as providing substantial
energy cost savings. Before making specific plans to implement, you should ask about a facility’s
history with using a pool cover as a number have used them at one time and then abandoned the
practice due to problems with the cover, concerns about a lack of off-gassing of contaminants while
the pool is covered, and/or inconsistent follow-through on the use of the cover. Site-specific concerns
need to be recognized and addressed in order to achieve buy-in from the facility owner and staff.
Whenever possible, actual monitored pool water heating energy use during unoccupied times should
be used for estimating the site-specific energy cost savings of a pool cover. This is because the many
assumptions that go into engineering calculation estimates of pool evaporation rates and the
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subsequent energy costs do not always align well with the specific characteristics at a particular pool
facility.
Using a pool cover during unoccupied times also provides an opportunity to reduce outdoor air flow
rate, ventilation fan power, and the space temperature setpoint. However, ongoing care should be
taken to ensure that the HVAC unit operation keeps up with pool operational schedule changes. If a
BAS system is used, a reading of pool room humidity could be used as a backup to respond to times
when the pool cover is not used or the activity schedule is changed. After the pool cover is put in
place, continuous outdoor air ventilation will reduce the relative humidity of the space
substantially—especially during the heating season.
There is also a liquid pool cover product that appears to have the potential to achieve a significant
portion of a pool cover’s energy savings without the expense and daily operation of a traditional pool
cover. The liquid pool cover is thin film of clear liquid that floats on top of the water and acts as a
barrier that reportedly reduces the pool water evaporation rate to about half of what it would
otherwise be. During pool use it is relatively ineffective as it gets mixed in with the water, and then
returns to the surface to form a thin layer again whenever the pool is not used for a period of time.
While other studies1 and anecdotal information have suggested that this product does provide a
substantial benefit, our study of this in one recommissioned facility did show the achievement of
significant savings.2
Pool Pump VFD [W1 in Appendix 1 has more information]
The potential savings from adding a variable speed drive to the pool circulation pump varies
substantially from site to site. Current pool code in Minnesota is generally interpreted as requiring a
constant minimum circulation rate, so the primary source of savings potential is in using a variable
speed drive to balance the system to the minimum flow rate instead of throttling main line valves.
About one-quarter of sites surveyed were found to have the main line pump throttled at a 45 degree
angle, so the use of a lower pump speed with the valve fully open would reduce the pump’s pressure
drop substantially while still providing the proper flow rate. More than 10 percent of the facilities
surveyed were also found to have the pool circulation flow rate at least 20 % above the required flow
rate, which provides an opportunity for savings through reduced pump flow rate via a variable
speed drive reduction of pump speed. It is site specific instances like these where large variable speed
drive pump savings is possible. Most of the savings can be achieved through manual, one-time
adjustment during balancing.
When a variable speed drive is put in place to achieve better balancing, there is also some secondary
savings potential that can be achieved by automatically adjusting the speed in response to a flow
1
One such study that showed energy saving is another Minnesota funded CARD Grant study conducted by Michaels
Energy (Hotel Energy Efficiency: Market Potential for Minnesota’s Hospitality Center, Bruce Dvorak, et al., 2015).
2 It is hard to draw a firm conclusion from the combination of these two studies as the Michaels Energy study did not
carefully consider the confounding impact of seasonal changes, and CEE’s study could not definitively rule out the
possibility of unintended changes in outdoor air ventilation that may have impacted the results.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
measurement. This is because most systems use sand or similar filters that have a moderate swing in
pressure between backwash cycles. The magnitude of this swing can be seen by looking at the history
of pool operator logs to see the daily pressure and flow variations between backwash cycles that
typically occur no more than once a week, and often less often than that.
Correct Pool Filter Flow
It is common for public pool facilities to operate with a pool filter flow rate that is moderately or
significantly higher than required by the current Minnesota Pool Code. For typical pools (not wading,
zero, plunge or other special purpose) the code requires that the pool filter flow rate is adequate to
recirculate the the full pool volume in 6 hours. In the industry, this is typically referred to as a 6 hour
turnover rate. For public spas the required turnover rate is 30 minutes. Moderately or significantly
faster turnover rates often provide an opportunity for reduced pool pump energy use. Proper
balancing of the pool flow rate might be accomplished through simple balance valve adjustment, or
through the installation of a variable speed drive with either a fixed speed control or a control that
automatically adjusts the speed to provide the required flow rate (see previous checklist item for
more information). All public pools will have an indicator of pool filter water flow rate and log this at
least daily. Also, most pool operators either know the pool volume, or have it on reference material
that is easily at hand (e.g. printed on the pool log book). This usually makes it relatively easy to
determine the current pool turnover rate. When rates are higher than the code required level, there
should also be inquiries to pool operations staff and review of design documents to investigate
whether this pool has a special need for a recirculation rate that is higher than the code requirement.
Operation of Pool Water Heat Source
Although infrequent, we did find multiple indoor public pool facilities that had woefully
underperforming pool water heating. In these cases, significant overheating of the space
compensated for the lack of adequate direct water heating capacity, but with a high energy penalty
associated with the outdoor air heating load and increased envelope heat loss (as well as poor
comfort for occupants). In one case this inadequate water heating only occurred seasonally when a
different heat-exchanger was used, and the pool operations team did not appear to be aware of the
problem. Because of the long cycles of pool water heating (a heat source cycle may last hours with the
heat source only on for a period of minutes of that time period), this problem was identified through
long-term datalogging, and then confirmed through targeted follow-up spot measurements.
Pool Water Heat Source Retrofit
While the high capital cost of replacing heating equipment is beyond the scope of a recommissioning
study, it may be considered in certain circumstances. High efficiency condensing pool heaters and/or
dedicated high efficiency condensing boiler-heat exchanger combinations are often much more
efficient than existing pool heaters or central boiler systems. Besides having a higher efficiency rating
than the boilers in most central boiler plants, the operating conditions of dedicated pool heating
equipment make the achieved operating efficiency of high efficiency condensing equipment much
higher than a similar boiler serving typical building heat loads. This is because the low temperature
of the pool water compared to boiler water temperatures needed for most space-heating applications
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in Minnesota is ideal for condensing boilers and pool heaters. In one site, we even found an
opportunity to achieve substantial savings by simply using the boiler that was installed for summeronly operation (to allow the central boiler plant to be shut down) on a year-round basis. The results of
site-specific logging of pool water heating loads will provide much more accurate estimates of the
potential energy cost savings than engineering estimates.
Scheduling of Pool Feature Pumps
Pool features such as water slides, waterfalls, and play features require the use of pumps that are
typically even larger than the primary pump used for filtering the pool water. Limiting their hours of
operations to only those times that they are needed can provide substantial energy cost savings. This
savings is primarily directly through reduced pump energy use, but depending the type of feature,
the evaporation rate may be reduced substantially as well (e.g. air jets in a spa). Beyond shutting
features off during unoccupied times, a number of facilities limit the operation of specific features to
posted, scheduled times. For facilities that are not doing so, a recommissioning report should
quantify the potential savings from doing so to facilitate an informed decision by the facility owner.
Spot measurements of pool feature pump motor current or power is recommended to increase the
reliability of savings estimates. This is because the custom nature of pool feature design and pump
selection may cause the load factor (ratio of actual motor load to nominal rated load [i.e. brake
horsepower: nameplate horsepower]) to be substantially different from the typical 0.8 load factor
assumption.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Appendix 1. Operator Inspection Instructions for
Select Measures
The following documents were prepared for the purpose of providing pool operators and
contractors with guidance for spot-checking the operation of an indoor public pool facility to
see if there are opportunities to save energy through low or no cost operational changes. Much
of the material is also useful a useful reference for recommissioning providers. Specific
documents are referenced by their two character reference ID in the summary checklist and the
individual measure sections of the guide.
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Operator’s Guide to Energy Efficient Indoor Pool Operations
S1. Optimal Relative Humidity
While too high of humidity at the wrong time can cause familiar condensation problems, being
too aggressive at maintaining a low humidity can also significantly increase energy use and
make it feel uncomfortably cold for swimmers after they exit the water. Also, humidity far
above or below the setpoint can be a symptom of a problem that is preventing the HVAC
system from performing as intended or performing in a way that uses more energy than
necessary.
WHEN TO CHECK: EVERY 2 MONTHS
INVESTIGATE
COMPARE
ACTION
• Record
humidity
setpoint
• Actual humidity
vs. setpoint
• Adjust humidity
setting
• Setpoint and
value vs. typical
range
• Correct issues
(e.g. too much
outdoor air)
• Record
humidity value
→
→
• Record outdoor
temperature
INVESTIGATE
Record Humidity Setpoint ______% RH
• Depending on the unit and controls arrangement, the humidity sensor display may be
accessible at a few different locations.
• Often the humidity setpoint is accessed either through a control display at the HVAC
unit itself, on a control device attached to the return duct, or through a Building
Automation System (BAS) interface.
• Sometimes, a thermostat-like device in the pool room has an accessible setpoint,
although there would typically be a locking cover, or some other way to limit access. If
a device in the pool room displays humidity but does not have arrow buttons, a dial, or
a lever for adjusting, it is probably only displaying the current value and is not
displaying the setpoint.
Record Actual Humidity Value ______% RH
• Depending on the unit and controls arrangement, the current sensor reading may be
accessible at a few different locations.
• Often the current reading for the humidity sensor is visible either through a control
display at the HVAC unit itself, on a control device attached to the return duct, or
through a BAS interface.
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• Sometimes, a thermostat-like device in the pool room has a display that shows the
current humidity. If a device in the pool room has arrow buttons, a dial, or a lever for
adjustment, it may display the setpoint instead of (or in addition to) the current sensor
reading. If so, look carefully to be sure that you do not confuse the RH setpoint for the
current value.
Record Outdoor Temperature ______°F
• Outdoor temperature can be measured on-site via a BAS sensor or thermometer (in the
shade)
• Or, you can use a cell phone app (or website) to get a current nearby weather station
reading.
COMPARE
If the RH Setpoint and RH Value Differ by More Than 6%
 If there’s no compressor, the RH is above setpoint, and it’s above 60°F outside, the unit
may be functioning as designed, but it has a limited ability to maintain a RH well below
60% in warm weather. If the HVAC unit is bringing in its maximum possible outdoor
air (see H1 for more information), then no action is needed to address this discrepancy.
 If the RH is above setpoint and it’s above 75°F outside, the unit may be functioning as
designed, but it has a limited ability to maintain a RH well below 60% in hot, humid
weather. If the dehumidifier appears to be operating at its maximum capacity (see H1
for more information), then no action is needed to address this discrepancy.
 If the RH is below setpoint and it’s below 50°F outside, the unit may be functioning as
designed, but the dry outdoor air needed for air quality reasons is providing more
inadvertent dehumidification than is needed. If the HVAC unit is not trying to
dehumidify (see H1 for more information), then no action is needed to address this
discrepancy.
 If the RH is well above or below setpoint under other circumstances, take the associated
steps noted in the action list for this check.
Typical Humidity Control Chart
• The chart shows the typical range of pool area relative humidity setpoints and actual
values.
• The solid, dark blue lines show the suggested range of RH setpoint.
• The dashed green lines show the range of actual RH values that are somewhat common
to see.
• The higher observed humidity levels at high outdoor temperatures tend to occur for
outdoor air only dehumidifier systems. HVAC units with cooling coils and/or desiccant
dehumidification tend to control the humidity better at these extreme conditions.
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Typical Relative Humidity Ranges
Compare Humidity Setting and Value to Chart Ranges
 Setting the HVAC unit to provide a lower humidity than suggested by the “setpoint”
range significantly increases energy use, pool water evaporation, and wear on any
compressors. This should only be done to the extent that site-specific experience has
shown a need to do so to prevent condensation problems. Note that condensation
problems are far worse in very cold weather, when the inside part of exterior surfaces
can get cooled below the dew point of the humid, pool room air. So higher a RH
setpoint during mild winter weather may be fine in a facility that needs lower humidity
in very cold weather to prevent condensation problems. If a setpoint is unnecessarily
below the suggested range, see the associated action.
 Humidity setpoints above the range are not recommended due to the likelihood of
condensation and/or comfort issues. If a setpoint is unnecessarily above the suggested
range, see the associated action.
 Actual RH values below the range shown suggest that there may be more outdoor air
ventilation than is needed. Take the associated action to investigate and correct if
needed.
 Actual RH values above the range shown suggest that there may be less than the
needed amount of outdoor air ventilation. Take the associated action to investigate and
correct if needed.
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ACTION
If Direction to Action for RH Setpoint versus Value Discrepancy
 To degree to which it is possible, check on dehumidifier operation (see H1 for more
information) to see the extent to which it is actively trying to dehumidify.
 If the RH is above setpoint and:
 If the HVAC unit is not trying to dehumidify as much as possible, then a qualified
technician should inspect for what is probably a controls issue; or
 If the unit is trying to dehumidify as much as possible under conditions for which
it is expected to keep up, then a qualified technician should inspect for what is
probably an equipment issue.
 If the RH is below setpoint and:
 If the HVAC unit is not trying to dehumidify, check for excessive outdoor air; or
 If the unit is still trying to dehumidify when it is not needed, a qualified technician
should inspect for what is probably a controls issue.
If Directed to Action for a RH Setpoint Outside of Suggested Range
 Change the setpoint to a value within the suggested range.
 If the setpoint control is right on the unit or a thermostat like device, it will probably
have a fixed setpoint. This may need to be manually changed seasonally to get the
optimal balance between comfort, energy use, and condensation.
 Many BAS (and some stand-alone controllers) will have the capability to automatically
adjust the relative humidity setpoint in response to outdoor air temperature. If so, this
will probably provide the best approach. However, note that the control logic should be
verified as much as possible to confirming the proper setpoint on displays and that such
automatic control is also susceptible to any errors in the outdoor sensor readings and
should also be checked periodically.
If Directed to Action for an Actual RH Value Below Expected Range
 Check for excessive or inadequate outdoor air by first seeing if a motor-driven outdoor
air damper has a problem with the actuator or linkage that is causing it to be open or
closed farther than it should be based on the expected control. If so, have this corrected
by a qualified technician.
 If the outdoor airflow is a fixed value or at its expected value, it is suggested that the
airflow be checked by someone who is qualified to assess the desired minimum outdoor
air ventilation rate and measure the actual outdoor airflow rate. If outdoor air
ventilation is found to be significantly above or below the amount needed, have it
corrected.
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S2. Confirm Humidity Sensor Accuracy
Relative humidity sensors are notorious for failing and leading to control problems. For pool
areas humidity control is more critical than in many other situations, and the presence of
chloramines and high humidity make humidity sensor life even more problematic in pool
systems. This check gives detailed guidance on how you should regularly confirm the
accuracy of the humidity sensor used to control the pool dehumidifier.
WHEN TO CHECK: QUARTERLY
INVESTIGATE
COMPARE
ACTION
• Purchase
hygrometer
• Controller RH
vs. handheld
RH
• Have sensor
calibrated
• Record control
sensor RH
→
→
• Have sensor
replaced
• Record
handheld RH
INVESTIGATE
Obtain and Maintain Hygrometer (i.e. Relative Humidity Meter)
• A handheld hygrometer that measures RH with an accuracy of ±3% can be purchased
from many different industrial suppliers or retail suppliers for less than $150. If the pool
area’s humidity sensor has a case that can hold up a small desktop type hygrometer, the
price may be even lower.3
• DO NOT STORE THE HYGROMETER IN THE POOL EQUIPMENT ROOM. Doing so
would greatly accelerate the failure of this meter. It is best stored in a conditioned
indoor environment that does not experience extremely high humidity levels.
• The accuracy of the handheld hygrometer should be checked periodically. A convenient
way to get a rough confirmation of a handheld hygrometer is against a nearby weather
station reading obtained from a website, news report, or mobile phone app. Don’t do
this comparison if the outdoor RH is below 15% or above 80%. Also note that the RH
reading is dependent on temperature, so this comparison will only give a close match if
the meter’s temperature reading is within 2°F to 3°F of the weather station temperature.
A hand-held sling psychrometer is a moderately lower cost alternative that will not need to
be calibrated. During each use of a sling psychrometer, the sock on a wet-bulb thermometer
must be wetted and the thermometers must be spun for a few minutes until the wet-bulb
temperature stops going down. Then the relative humidity is found from the wet-bulb
temperature and a dry-bulb temperature (on the same device) using a slide rule that is on the
psychrometer, or that comes in the same package.
3
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Also note that site-specific conditions (e.g. sunny versus cloudy or a nearby lake) can
cause discrepancies between the weather station and the handheld hygrometer.
Record Handheld Hygrometer Humidity and Temperature Values ______% RH ______°F
• The dehumidifier will have a humidity sensor either in the pool room itself or within
the ductwork that returns air from the pool room to the HVAC unit. If the sensor is in
the room itself, measure the RH right where the sensor is located. If the control sensor is
in the return duct, hold the handheld sensor as close to the return grill as possible.
(Although return grills are often near the ceiling so you may not be able to get very
close.)
• Note that humidity sensors can be sensitive to temperature or RH fluctuations caused
by your breathing or body heat. Take care to avoid breathing on the device and
whenever possible stand at arm’s length while taking the reading.
• If there is a convenient and safe place to set the portable hygrometer on top of the
control sensor case, set it there for at least five minutes before taking a reading. If that’s
not possible, hold the portable device as close to the control sensor as possible and wait
at least two minutes to record the values. If either the RH or temperature are still
changing every few seconds, wait until they are both steady (being careful to breath
away from the sensor).
Record Control Sensor Humidity and Temperature Values ______% RH ______°F
• Take the control sensor readings as soon as possible after taking the handheld meter
readings.
• Depending on the unit and controls arrangement, the current sensor reading may be
accessible at a few different locations.
• Often the humidity sensor is visible through a control display at the HVAC unit itself,
either on a control device attached to the return duct or through a BAS interface.
• Sometimes, a thermostat-like device in the pool room has a display that shows the
current humidity. If a device in the pool room has arrow buttons, a dial, or a lever for
adjustment, it may display the setpoint instead of (or in addition to) the current sensor
reading. If so, look carefully to be sure that you don’t confuse the RH setpoint for the
current value.
• Humidity sensors can be sensitive to temperature or RH fluctuations caused by your
breath or body heat. If you are taking a reading directly from the display of a
thermostat-like device in the pool room, take care to avoid breathing on the device and
whenever possible stand at arm’s length while taking the reading.
COMPARE
Put Inputs into RH Comparison Calculations Below
• Enter the temperature and RH measurements you recorded above into the blanks by the
blue highlighted labels in the first calculation table below.
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Operator’s Guide to Energy Efficient Indoor Pool Operations
• Use the control sensor RH value to find the “adjustment factor” from the calculation
table on the right hand side. Enter this “adjustment factor” into the calculation in the
blank below the orange highlighted label.
Perform the Calculations as Laid Out
• Be careful to carry and negative (minus) sign from one box to the next. If both numbers
being multiplied together are negative, the adjustment value will be positive.
• An example calculation appears immediately after the blank calculation table.
Compare Adjusted Handheld RH to Control Sensor RH (Two Value on Bottom Row)
• If there is less than a 5% discrepancy, no action is needed.
• If there is a 5% to 8% discrepancy, you should consider checking again soon and
making the seasonal dehumidifier operation check to see if it contributes to unusual
control.
• If the discrepancy is more than 8%, take action as noted in the next subsection.
Humidity Comparison Calculations
Control Sensor Temp
Handheld Temp —
=±
Handheld RH
Adjustment ±
Adjusted Handheld RH =
°F
°F
°F
Adjustment Factor
(From Table)
X —
% per °F
%
%
%
Control Sensor RH
VS
%
=
±
Adjustment
%
Control
Sensor RH
< 40%
40 - 50%
> 50%
Sample Humidity Comparison Calculations
Control Sensor Temp
Handheld Temp —
=
84 °F
81 °F
3 °F
Handheld RH
54 %
Adjustment ± -4.5 %
Adjusted Handheld RH = 49.5 %
Adjustment Factor
(From Table)
X
-1.5 % per °F
=
Adjustment
-4.5 %
Control Sensor RH
VS
48
%
ACTION
If >20% - 25% discrepancy
• Replace the humidity sensor.
• Adjust control setting to compensate in the meantime
If 15% - 25% discrepancy
• Calibrate or replace the humidity sensor.
• Adjust control setting to compensate in the meantime
• Repeat checks on this sensor more often than the typical frequency.
If 8% - 15% discrepancy
• Have the humidity sensor calibrated.
• Adjust control setting to compensate in the meantime
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Adjustment
Factor
-1 % per °F
-1.5 % per °F
-2 % per °F
Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
• Repeat checks on this sensor more often than the typical frequency.
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Operator’s Guide to Energy Efficient Indoor Pool Operations
H1. Seasonal HVAC Operation
Indoor public pool facilities in Minnesota get adequate “free” dehumidification much of the
year. This is because a certain amount of outdoor air must be continuously circulated through
the pool area to keep the air fresh, and for most of the year the outdoor air is much dryer than
the humid pool area air. Some HVAC systems dehumidify a pool area by simply bringing in
enough dry, out outdoor air to keep the indoor humidity in check, while others use air
conditioning compressors to cool and then reheat the air. Whichever, approach is used,
excessive operation of the dehumidifier in cool (dry air) weather can cause both excessive
energy use and accelerated deterioration of the dehumidifier. Here’s how to check for this
excessive operation.
WHEN TO CHECK: QUARTERLY (EXCEPT IN THE SUMMER)
INVESTIGATE
COMPARE
ACTION
• Record outdoor
temperature
• Determine if
dehumidification
is occurring

• Check RH
setting
• Check RH
sensor
• Have an expert
evaluate
→
Typical
humidifier
range vs.
overserved
operation
→
INVESTIGATE
When to Measure
• It’s best to check when there hasn’t been unusual activities that increase load.
• Wait until at least two hours after unusually high activity levels to do your check.
Record Outdoor Temperature ______°F
• Outdoor temperature can be measured with a BAS sensor or thermometer (in the shade)
• Or, you can use a cell phone app (or website) to get a nearby weather station reading.
• If dehumidifier operation is monitored over a period of time, record the outdoor
temperature periodically (being sure to get a high and low reading).
Record HVAC Operation Status
• For systems with variable outdoor air dampers, observe outdoor and return air
dampers.
Outdoor Air______% open;_Return Air______% open
and/or exhaust fan variable speed drive (if it has) ______Hz ÷60 Hz = ______% speed
• For systems with compressors, observe which compressor(s) run and roughly the
percentage of time that they run [see compressor observation tips].
#1______% on; #2______% on; #3______% on; #4______% on
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
COMPARE
Typical Dehumidifier Operation Chart (below)
• The chart shows how the typical dehumidifier load varies seasonally in Minnesota,
where the fresh outdoor air needed for ventilation is cold and very dry in the winter,
but carries in more moisture in warmer weather.
• Dehumidifiers that use compressors are represented on the left. [See “Compressor
Observation Tips” for more information about how to know if a compressor is running
or cycling.]
• Dehumidifiers that vary the outdoor airflow to dehumidify are represented on the right.
Compare Actual Dehumidifier Operation to Chart
• Does the actual compressor/outdoor air match chart closely? Okay as is.
• Is the actual compressor/outdoor air > chart (or <<)?
Take Action to save
• If Outdoor Air % Open + Return Air % Open ≠ 100% (±20%)
Typical Dehumidification Operation Chart
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Take Action to save
Operator’s Guide to Energy Efficient Indoor Pool Operations
ACTION
Check Humidity Control Settings [see S1]
• If it’s lower than it needs to be, adjust and repeat observations to confirm reduced
dehumidifier operation.
• If it checks out okay, continue on to the next action on the list.
Check the Humidity Sensor for Accuracy [see S2]
• If it’s inaccurate, replace and repeat observations to confirm reduced dehumidifier
operation
• If it checks out okay, continue on to the next action on the list.
Have an Expert Evaluate the System for Other Issues and Solutions Such As:
• Not enough outdoor air to ensure good air quality.
• Minimum outdoor air is too high (likely if compressor runs much less than chart).
• Damper actuator failure.
• Suboptimal control sequencing.
SAMPLE OF SAVINGS — FITNESS CENTER
$20,700 PER YEAR
One fitness center had poor control of the hot water
heating coil that caused the compressor to run
continuously in the winter for heating purposes. Besides
dramatically increasing the energy costs, this was causing
the compressor to fail an average of every two years at a
replacement cost of $30,000.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
H2. Energy Recovery Ventilator Basic Check
Energy recovery ventilators (ERV) provide dramatic energy cost savings for public pool
facilities because of the need for high continuous outdoor air ventilation rates. When present,
ensuring proper operation of an ERV is typically the most important energy saving check. This
is because, although they have a dramatic impact on energy use, their failure usually doesn’t
cause any other adverse effects that would alert an operator of a problem. Another heating
source typically picks up the slack without there being any impact on pool room conditions.
This check outlines how you can quickly confirm that an ERV is operating as intended.
WHEN TO CHECK: QUARTERLY (EXCEPT IN THE SUMMER)
INVESTIGATE
COMPARE
• Record
outdoor air
temperature
 ERV on/off
status vs.
expected status
• Observe ERV
on/off
operation
 Track over
range of
outdoor
temperatures
→
• Alternatively,
observe ERV
supply
temperature
ACTION
• Check/correct
physical
breakdowns
→
• Check/adjust
control settings
• Have expert
review control
logic
INVESTIGATE
Record Outdoor temperature ______°F
• This can be measured on-site via a BAS sensor or thermometer (in the shade), or you
can use a cell phone app (or website) to get a current nearby weather station reading.
Fixed Plate ERV Face and Bypass Damper Control ______On (face) or Off (bypass)
• Fixed plate ERV units turn the heat recovery “on” or “off” by having air flow through
the heat exchanger (i.e. face) or around the heat exchanger through an alternative
airflow path (i.e. bypass). When an ERV is “on,” the face damper is open to allow air to
flow through the heat exchanger, and the bypass damper is closed.
• The face/bypass damper arrangement is usually on only one air stream — either the
fresh outdoor air stream or the exhaust air stream.
• Some systems will vary the ERV capacity with an “on” condition that allows a portion
of airflow through both the face and bypass dampers at the same time. If this is
observed, record: ______% open to heat exchanger and ______% open to bypass.
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• BAS displays will often have a graphic that notes the intended damper position. While
this can provide a good indication of the intended control, it is recommended that you
make a direct observation of the dampers to the degree that this is possible. On some
systems, opening a specific panel will provide a clear view of damper positions. Clear
indications of damper positions might also be possible by looking at the damper
actuator and linkage assembly.
Recovery Wheel Control _ On (Wheel Spinning) or Off (Wheel is Still)
• Systems with wheels for recovering energy turn “on” or “off” by having the recovery
wheel rotate or not. Complex systems may even vary the wheel rotation speed instead
of having it simply on or off. If the control system displays a wheel speed, record that
here: ______wheel speed as % of maximum.
• BAS displays will often have a graphic that notes the intended damper position. While
this can provide a good indication of the intended control, it is recommended that you
make a direct observation of the wheel itself to confirm that it is actually rotating or not.
Alternative ERV Recovery Status Observation
On or Off
• If direct observation of the face/bypass or recovery wheel operation is not possible, it is
sometimes possible to get a good indication of its operation status by looking at a BAS
or control panel readout of the preheated (or precooled if in hot summer weather) air
temperature after the recovery section and before any other heating or cooling coils.
• It is typically possible to get a BAS readout on a “preheated” temperature for recovery
wheel units. However, this is often not possible on plate ERV units because a true
indication of the preheated temperature for plate ERV units can only be observed after
the face and bypass airflows mix together. Many units have a heating or cooling coil
immediately after the heat exchanger and this changes the air temperature before the
face and bypass flows mix back together. Any heating or cooling provided by this coil
makes it impossible to get a true “preheated” air temperature that is a representative
average of all of the fresh outdoor air coming through the unit.
• Where a representative “preheated” air temperature is available, you can tell the ERV’s
on/off status by comparing this temperature to the outdoor and pool room
temperatures. If the “preheated” air temperature is closer to the pool room than to the
outdoor temperature, the ERV is “on.” If the “preheated” temperature is closer to the
outdoor temperature, then the ERV is “off” or operating at a reduced capacity
COMPARE
Typical ERV On/Off Operation Ranges
• The next figure shows when a pool ERV should be “on” or “off”.
• While the ideal exact transition points will vary somewhat based on site and equipment
specific details, operation that is clearly inconsistent with this should be addressed.
ERV On Ranges
• During most cold weather periods and very hot weather periods the ERV should be
operating to preheat or precool the outdoor air. The energy savings that can be achieved
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
by operating during these time periods is the reason that an ERV is installed. If there is
significant ERV “off” status in these ranges, take action to correct this.
• Depending on the HVAC unit arrangement, a failure of the ERV to operate in cooling
mode can cause comfort problems with either the humidity or temperature drifting up
beyond the desired range, and action should be taken to address this.
ERV Off Ranges
• Significant operation of the ERV in the “ERV Off: Frost Control” range could lead to
problems with icing up of the ERV that cause damage, prevent adequate ventilation, or
greatly reduce the ability of the unit to recover heat. Some units will vary the capacity in
this range to allow for some heat recovery without frost problems. In either case, watch
for ice build-up and take action to correct if there are signs of frosting.
• The “ERV Off: Free Cooling” zone of operation is more variable based on site and
system details. If the ERV is “on” in this area, it is not necessarily a sign of a problem.
The possible drawback is overheating, which could either cause the pool room to be
warner than desired or cause extra compressor use for cooling. If either of these issues is
suspected see “Have Control Evaluated By and Expert” section within the action items.
Typical ERV On/Off Operation Ranges
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Operator’s Guide to Energy Efficient Indoor Pool Operations
ACTION
Check for Physical Malfunctions
• For fixed-plate ERVs, check that ERV face and bypass damper linkages are all securely
attached and that there are no visible problems with the damper assemblies. As
necessary, have an expert evaluate damper actuators and linkages.
• For wheel-type ERVs, check for a loose or broken belt or gear assembly and make sure
that the wheel motor is operational. As needed, have an expert evaluate and/or repair
the wheel rotor assembly.
Check/Adjust ERV Settings
• See if the frost control settings or economizer settings are significantly different from
expected in the previous table. If so, make adjustments and/or work with a qualified
expert to make control changes.
Have the Control Evaluated By an Expert
• ERV controls often do not have the frost control and/or economizer control logic clearly
shown on BAS system screens or other control diagrams, so it may be difficult to
determine what the controls are trying to do.
• As necessary, consult an expert to evaluate and correct ERV controls that are causing
significantly different operation (more than 10°F variance from outdoor temperature
ranges) than what is outlined in the table.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
H3. Outdoor Air Ventilation Rough Check
Continuous outdoor air ventilation to a certain degree is required in pool rooms to prevent air
quality problems. Having too much outdoor air ventilation can greatly increase energy use
and cause comfort problems, while not providing enough outdoor air can contribute to air
quality problems and condensations issues, as well as extra dehumidifier energy use and wear.
Here is how you can check to see if this is an issue.
WHEN TO CHECK: QUARTERLY (EXCEPT IN THE SUMMER)
INVESTIGATE
COMPARE
ACTION
• Record outdoor
air %
 Current outdoor
air cfm vs.
original &
common design
outdoor air cfm
• Fix broken
damper control
• Record total
HVAC flow
• Look at pool
and deck
dimensions
→
 Covered cfm vs.
uncovered
• Have expert
evaluate
→
• Better optimize
damper control
• If covered,
observe
overnight
ventilation
INVESTIGATE
Observe Current Minimum % Outdoor Air Damper % Open Outdoor Air Damper
• For systems connected to a BAS system, a careful look through the display screens may
clearly show the minimum outdoor air damper setting and current intended damper
position. A manual observation of the damper position should be carried out to confirm
the actual current percent outdoor air.
• If the weather outside is cool, the system is likely already at the minimum outdoor air
so there may be no need to do anything special to observe the minimum outdoor air
control condition.
• If necessary, the dehumidifier control can typically be temporarily set to a humidity
setpoint that is 15% to 20% RH above the current sensor reading. This should disable
any dehumidification efforts by the HVAC unit and may cause it to operate at the
minimum outdoor air. However, some economizer control features will make it difficult
to force the unit to temporarily control to the minimum outdoor air, especially in mild
weather.
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Operator’s Guide to Energy Efficient Indoor Pool Operations
• For systems with variable outdoor air dampers, observe outdoor and return air damper
temperatures
Outdoor_Air______% open;_Return Air______% open
• Note that some HVAC units are not designed to bring in 100% outdoor air even when
the outdoor air opening is fully opened. If the outdoor air opening has a smaller area
than the supply duct, record the dimensions of the outdoor air opening ______inches by
______inches; and supply duct ______inches by ______inches
Find Pool HVAC Unit Total Design Flow
(cfm)
• The HVAC unit total supply flow may be shown on the equipment’s nameplate, on
plans (look at the mechanical schedules which are usually the last M pages), equipment
documentation within a 3-ring binder, or on a BAS display screen.
• If it cannot be found by any of the above means, find the unit’s manufacturer, model
number, and serial number from the nameplate and contact the manufacturer to find
out (start with a local manufacturer’s representative if available).
Obtain Pool and Wetted Duck Dimensions _______ft by ______ft
• Do not include spectator areas, which are generally meant for people that are not
swimming; only measure the area of the pool and around the pool that is designed for
swimmers to occupy.
If Pool Cover is Used, Investigate Outdoor Air Control during the Covered Pool Time
• If there is BAS control of the HVAC unit, there may be an indication in the BAS screens
or documentation about the intent to control outside air differently when the pool is
covered. If so, it is still recommended that you actually observe that the system follows
this intent at a time when the cover is in place and the ventilation is to be reduced.
COMPARE
Current Minimum Outdoor Air Ventilation Rate
• If the outdoor air opening is smaller than the supply duct, calculate the ratio of opening
sizes:
    (_____ℎ × _____ℎ)
= _____%    ()
    (_____ℎ × _____ℎ)
•
Calculate current outdoor air flow:
 _____ ×  _____%  ×    ____% = _____  
Common Design Outdoor Air Ventilation Rate
• Calculate the wetted pool area as the product of the pool area dimensions:
square feet.
• Calculate a current typical outdoor air design flow (not considering spectator area):
Wetted pool room area ___ square feet X 0.5 cfm per square foot = Typical _ OA cfm.
• If the actual outdoor air cfm and typical outdoor air cfm are more than 20% different,
the take action to have an expert determine if a change is warranted.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Other Indicators of Possible Outdoor Air Amount Issues
• An inability to keep adequate pool area temperatures, or low discharge air
temperatures, could be symptoms of the system providing too much outdoor air.
• Also, if Outdoor Air % Open + Return Air % Open ≠ 100% (±20%), take action to save
energy and reduce control problems.
• Indicators of potential over- and under-ventilation are also noted in the S1 check.
Compare Pool Covered Ventilation to regular Occupied Ventilation
• If the outdoor air ventilation rate is not reduced significantly during most of the time
that the pool is covered, take action to take advantage of this opportunity.
ACTION
If Referred to Action Because of Improper Combination of Outdoor Air and return Damper Positions
• Inspect any linkages between dampers to look for loose connections. If simple
tightening of a linkage doesn’t provide a solution, have a qualified technician check the
damper actuators and controls to identify and solve the problem.
If Mismatch between Actual and Typical Design Outdoor Air cfm, Consult an Expert and Possible
Adjust Outdoor Air Damper Control
• Providing adequate outdoor air ventilation is critical so a qualified expert should be
consulted to confirm the potential to change the minimum outdoor air flow, if this was
suggested by the comparisons.
• The minimum outdoor air position is typically set via automatic modulating damper
controls that receive a signal from a central BAS system or controls that are at the
HVAC units. Where a comparison has found improper outdoor air flow control, modify
the setpoints and/or programming to correct the issue.
• Sometimes the outdoor air is manually controlled or fixed with an opening that only
has a manual balancing damper or no damper. If adjustable, this damper can be
adjusted to obtain the proper outdoor airflow.
• Where sizable spectator areas are present, this can cause a need for higher ventilation
rates during the events when a large number of spectators are present. A means to
automatically or manually provide adequate outdoor airflow during these infrequent
events should be provided. However, the needs during these infrequent events should
not cause the pool area to receive more outdoor air ventilation than is needed during
the rest of the year.
If Referred to Action for Not Reducing Ventilation When the Pool is Covered
• Explore options for reducing the outdoor air ventilation rate when the pool is covered.
• Ideally, a reduced, pool-covered, ventilation rate would be enabled and disabled by a
reliable form of feedback about whether or not the cover is being used. An interlock
with the pool cover mechanism is ideal.
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
W1. Main Valve Throttling
Many public pools end up with pumps larger than what is actually needed because of safety
factors in design and the limited selection of pump and motor sizes. For example, going from a
1 HP motor to a 1.5 HP motor (the next largest size) is a 50% jump in capacity. When dramatic
oversizing occurs, the pool water flow rate is usually still limited to the minimum needed for
adequate turnover by severely choking down the flow with a throttling valve. In such cases,
the pump must work against a high pressure caused by the throttling and it uses much more
energy than is really needed. Here’s how to see if your system has severe throttling that may
be worth correcting through pump motor control and/or replacement.
WHEN TO CHECK: ANNUALLY
INVESTIGATE
COMPARE
ACTION
• Record valve
throttle %
• Throttling % vs.
typical throttling
Get help
evaluating:
• Record
horsepower (HP)
→
• Look @ possible %
savings given and
horsepower (HP)
→
• Variable speed
pumping
• Replace
pump/motor
INVESTIGATE
Locating Main Line Valves
• Although main line valves that may be throttled are typically located near the outlet of
the pump, they could be anywhere along the main piping line that comes the pool to
the pump, from the pump to the filter, and from the filter to the pool.
• Ignore throttling of valves along the main line that are used to force some water
through smaller bypass lines (smaller pipes located just before and after the valve) that
divert some of the main flow to the heater. (See Valve Throttling Reference for more
detail.)
• Ignore any throttling of valves in the piping of a booster pump.
Record % Throttled for Each Valve: # 1 ______%; #2/Spa______ %; #3______%; #4______%
• Note the percentage closed above for each main line valve based on where the valve
handle points between perpendicular to the pipe (100%) and parallel to the pipe (0%).
• See “Valve Throttling Reference” for more detail on valve position.
Record Pump Horsepower (HP)
• Record pump nameplate HP (look on the pump or motor nameplate) for the pump
corresponding to each valve noted above Valve # 1______HP; Valve #2______HP;
Valve; #3______HP; Valve #4______HP
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
COMPARE
• If any main line valve is throttled 25% or more, use the table in “Valve Throttling
Reference” to estimate potential annual kilowatt-hour (kWh) savings using the percent
throttling value in combination with pump horsepower.
• Also use the table if a pump larger than 5 HP has a valve throttled 10% or more.
• Estimate potential cost savings by multiplying the kWh savings by $0.11 per kWh (or
another available representative utility rate that includes usage and demand savings).
• If the potential energy savings is significant enough, take action to save energy.
ACTION
• Consider the installation of a variable speed pump or the addition of a variable speed
drive to the pump motor. Operating at a lower pump speed with the previously
throttled valve wide open can provide the required flow while using less energy.4
• If the economics of the variable speed drive retrofit based on the above estimate is
questionable, have an engineer or other qualified individual perform a detailed analysis
of the potential to replace the pump and/or motor with one selected to provide the
design flow without significant throttling.
Example of a Variable Speed Drive for a Pump
More information about variable speed pool pump control can be found in NSPF, Ch.10 and
NRPA, 7-6 to 7-7.
4
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Appendix 2. Detailed Savings Calculation Guidance for
Select Measures
The following pages provide detail regarding recommendations related to energy savings
calculation recommendations for the measures listed below:
Recommended Minnesota TRM Manual Additions
1) variable speed pool pumping
2) high efficiency pool heater
3) pool cover
Recommended Savings Calculation Approaches
4) reducing outdoor air
5) modifying pool room temperature control
6) modifying pool room humidity control
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
RECOMMENDED MINNESOTA TRM MANUAL ADDITIONS
1) Variable Speed Pool Pumping (Commercial)
Site Specific Savings
For site-specific estimates of savings for variable speed pool pumps, follow the energy savings
calculation procedure for the measure Electric Utility Infrastructure - Variable Speed Drives (nonHVAC) in version 2.1 of Minnesota’s TRM with the following modification.
a) Calculate the Energy Savings Factor as the difference between the current and proposed
conditions in the Table of PLR Values below. (This replaces the use of the TRM’s Table 5
with multiple load factor and % of design flow values per the format of the TRM’s
Tables 1 and 2.)
Table of PLR Values
Min %
of
Wide
Open
Flow
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
To
To
To
To
To
To
To
To
To
To
Max %
of
Variable
Wide
Throttle Speed
Open
Valve
Drive
Flow
PLR
PLR
10%
0.8
0.05
20%
0.81
0.06
30%
0.82
0.09
40%
0.83
0.12
50%
0.85
0.18
60%
0.87
0.27
70%
0.9
0.39
80%
0.93
0.55
90%
0.96
0.75
100%
1
1
b) The following equations will apply with Wide Open Flow being defined as the pool
water flow rate at full pump speed with any throttling valves wide open
 = ℎ , − ,
%     = %     ×
  [  ]
 []
=

60 [
] ×   [ℎ]
ℎ
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
c) Reference the current Minnesota Swimming Pool Code for the maximum time to run
the pools entire volume through the filtering and treatment system. The table below
summarizes the maximum turnover time requirement in the code volume published in
2009 and in force as of December of 2017.i
Table of Code Turnover Time
Pool Type
General
Wading
Spa
Dedicated Plunge
Zero Depth
Max Turnover Time
6 hours
2 hours
0.5 hours
1 hour
2 hours (for area < 3 feet deep)
d) For indoor pools in hospitality buildings, fitness centers, and other buildings that keep
the pool open year-round, assume 8,760 operating hours per year and a coincidence
factor of 1. For schools and other facilities with seasonal pool shutdown, base the hours
and coincidence factor on the facility’s reported schedule.
Preliminary Program Level Savings Estimate
For building type-specific estimates of savings of variable speed pool pumps, follow the
energy savings calculation procedure for the measure C/I HVAC - Variable Speed Drives in
version 2.1 of Minnesota’s TRM with the following modification.
a) Use the following values for Energy Savings Factor (ESF) in place of the TRM’s Table 3.
ESFhospitality, multifamily = 0.45
ESFschool, fitness = 0.51
The potential number of applicable facilities should be based on an assumed 35 percent
of pools (same value for all building types).
b) For indoor pools in hospitality buildings, fitness centers, and other buildings that keep
the pool open year-round, assume 8,760 operating hours per year and a coincidence
factor of 1. For schools assume 7,665 operating hours [i.e. pool shut down for 1 ½
months] and a coincidence factor of 0.78.
2) High Efficiency Pool Heater (Commercial)
For indoor public pool heater savings in Minnesota, the following savings calculation should
be used.
1
1
 [ℎ] = _ × [
−
]
 ℎ
Where:
BTUH_In = maximum input rating of the new pool heater [in units of BTU per hour]
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
Effbase = Baseline pool heater efficiency (78% [0.78] code minimum for new heater)
EffHigh = Efficiency of the new high efficiency pool heater efficiency [as a decimal value (e.g.
0.95 for 95% efficiency)]
3) Pool Cover (Commercial)
For indoor public pool cover savings, the following savings calculation should be used for
Minnesota.
0.9 [ℎ⁄ 2 ]
 [ℎ] =
×   [ 2 ]
  
If the pool heater efficiency is not known, it should be assumed to be 80% (0.80).
For the use of a liquid pool cover, the preliminary suggestion is to assume 50% of savings for a
traditional pool cover—as calculated above. However, it is recommended that additional
measurement and verification be conducted before using this assumption for large-scale
program implementation.
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Recommended Savings Calculation Approaches
4) reducing outdoor air
5) modifying pool room temperature control
6) modifying pool room humidity control
For these last 3 measures addressed by this appendix, we recommend a particular, rigorous
approach for CIP program savings calculations (e.g. custom rebates or recommissioning
savings estimates). In particular we recommend that savings estimates be based on detailed
hourly or BIN calculation models that address the real interactions between these factors—
plus the pool evaporation rate—with assumptions that have a sound basis in the actual design
and operating conditions. A degree of iteration needs to be used to accurately estimate the
savings from changing any one of these factors because each of these key pool room or HVAC
system parameters has an impact on the others. Because of these interactions, some
assumptions that have commonly been used in engineering calculations can cause misleading
savings estimates. For example, the actual relative humidity may be higher or lower than the
setpoint leading to a poor estimation the pool heating and dehumidification loads. Thus,
setpoints should be used as a starting point for iterative analysis of the actual conditions as
they are influenced by the other operating conditions and system limitations. The key
interactive effects that need to be taken into consideration are outlined below, as well as
guidance and references to detailed formulas and tables from Chapter 1 of the 2017 ASHRAE
Fundamentals Handbook.ii
Key Interactive Effects
a) Impact of Pool Room Temperature & Relative Humidity on Pool Room Humidity
Ratio. While relative humidity is the most commonly used indicator of moisture level in
the air for purposes of comfort discussions, humidity ratio is the measure of the amount
of water in air that is ultimately used in most engineering calculations. This is because
humidity ratio gives a direct indication of the amount of water vapor in air. It is defined
simply as the ratio of the mass of water vapor to the mass of dry air. On the other hand,
relative humidity indicates the ratio of how much water is in the air compared to the
maximum amount of water vapor that air can hold at its current temperature.
The humidity ratio of air can be calculated from the relative humidity, temperature, and
atmospheric pressure. As one might expect, increasing the relative humidity for a given
temperature increases the humidity ratio proportionally. However, the humidity ratio
also goes up with the air temperature if the relative humidity is held constant. The
warmer the air is, the more sensitive the humidity ratio is to changes in temperature (if
the relative humidity stays constant). Below are the steps for calculating humidity ratio
using equations in Chapter 1 of the ASHRAE Fundamentals Handbook.
i. Using the temperature, calculate the partial vapor pressure of water vapor in air at
saturation [the point where water starts to condense out of the air], pws, using Table 3 or
equation (6).
ii. Using this pressure, pws, and relative humidity, ø, calculate the actual partial vapor
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
pressure of water in the air, pw, using equation (22) [ø=pw/pws given here due to a
handbook error in some versions].
iii. Using this pw and the atmospheric pressure [in units of psia and can be estimated
from Table 1 in the handbook], p, calculate the humidity ratio, W, using equation (20).
b) Impact of Pool Temperature, Pool Room Humidity, and Pool Room Temperature on
Pool Evaporation Rate. Pool water evaporation rate is a key determinant of a pool
facility’s energy use for both pool heating and dehumidification. Although it happens in
a less intense process, evaporation of water at any temperature draws about as much
energy from the surrounding water as boiling water does from its heat source. This
energy needs to be made up via the pool water heater. Likewise, the water vapor that
evaporates must be removed from the pool room with a dehumidifying HVAC unit to
keep the room’s humidity in check. Therefore, the evaporation rate is the primary
determinant of the loads on the both pool water heating and pool room
dehumidification equipment.
The two key inputs for calculating the evaporation rate of an indoor pool are pool
temperature and pool air moisture level. Here the steps for calculating the pool water
evaporation rate following the ASHRAE Fundamentals Handbook and the Natatoriums
section within Chapter 5 of the ASHRAE Applications Handbook.iii
i. Using the pool water surface temperature, calculate the saturated vapor pressure of
water at the pool surface, pw, using Table 3 or equation (6) from Chapter 1 of the
ASHRAE Fundamentals Handbook [ignore the difference in subscript for p].
ii. Find the pool room’s partial vapor pressure of water in the air, pa, calculated from ii
in a) above (using pool room temperature and relative humidity).
iii. Based on the pool type and activity, choose an appropriate activity factor, Fa, from
the table right after equation (2) in the Natatoriums section of the ASHRAE HVAC
Application Handbook. (This ranges from 0.5 for an unoccupied pool to 1.5+ for special
water features.)
iv. Using the above vapor pressures and activity factor--along with the pool area--to
calculate the pool water evaporation rate, wp, using the equation below [equation (2) in
Natatoriums section of handbook].
 [⁄ℎ] = 0.1 ×   [ 2 ] × ( −  )
This pool evaporation rate can be used directly to calculate the evaporation impact on
pool water heating rate [in units of Btu/hr] by multiplying the evaporation rate by 1,000
[BTU/lb.]
c) Outdoor Air Flow and Humidity Ratio Impact on “Free Dehumidification” and Pool
Room Humidity Ratio. In Minnesota’s climate the outdoor air is usually much dryer
than pool room air. This means that the high, continuous outdoor air ventilation needed
to dilute and remove pool off-gassing provides significant “free” dehumidification
throughout most of the year. The amount of dehumidification provided by the outdoor
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Recommissioning Guide for Indoor Public Pool Facilities in Minnesota
air flow can be calculated using the steps outlined below.
i. Using the outdoor temperature and humidity, calculate the outdoor air humidity
ratio, WOA, following the calculation steps i through iii outlined in a) above.
ii. Using the outdoor air flow rate along with pool room and outdoor humidity ratios,
calculation the moisture removal rate with the equation below.
   [⁄ℎ] =    [
 
 3

] × 60 [
] × ( −  )
] × 0.075 [

 
ℎ
If the above calculated dehumidification provided by outdoor air (i.e. moisture removal
rate) is greater than the pool water evaporation rate, then the assumed pool room
humidity level should be lowered until these two values match. If, however, the
calculated dehumidification provided by outdoor air is less than the pool water
evaporation rate, then the remaining dehumidification load will be the difference
between these two. If outdoor air ventilation is the only (or first, economized) source of
dehumidification, then the outdoor air flow rate would be increased (up to the system’s
maximum outdoor air flow rate) so that the calculated moisture removal rate matches
the pool water evaporation rate. If the moisture removal rate calculated from the
outdoor air, plus any compressorized dehumidifier at its maximum capacity, is less
than the calculated pool evaporation rate, then the pool room humidity level must be
assumed to increase until these two calculated values match.
Note that as outdoor air flow increases to provide dehumidification, the energy needed
to heat the outdoor air also increases. The relationship between outdoor air flow and
energy used to heat the outdoor air can be reasonably approximated with the equation
below.
   [⁄]
= .  ×    × ( −  )⁄
where Eff = heating efficiency (90% for a gas direct-fired make-up air unit)
The above relationships often need to be used iteratively to find what the actual conditions
and loads will be. Depending on how the HVAC system capacity and operation matches the
loads, the modeling will generally use the pool room setpoints as a starting point, and then
adjust them where outdoor air flow and system limitations will lead to a drift above or below
the setpoint. Note that while it only happens for very few hours in the year, the pool room
temperature may similarly increase above the setpoint due to outdoor air being brought in that
is warmer than the pool room temperature.
References for Appendix 2
Minnesota Administrative Rules, Section 4717.2560 Recirculation Rate. The Office of the
Revisor of Statutes. May 11, 2009.
ii ASHRAE Handbook 2017 Fundamentals (I-P Edition). ASHRAE, Atlanta, GA.
i
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iii
2011 ASHRAE Handbook HVAC Applications (I-P Edition). ASHRAE, Atlanta, GA.
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