Groundwater Heat Pump Equipment Selection Procedures for

Utah State University
DigitalCommons@USU
Reports
Utah Water Research Laboratory
January 1980
Groundwater Heat Pump Equipment Selection
Procedures for Architects, Designers, and
Contractors
Calvin G. Clyde
Edward W. Vendell
Kirk D. Hagen
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Part of the Civil and Environmental Engineering Commons, and the Water Resource
Management Commons
Recommended Citation
Clyde, Calvin G.; Vendell, Edward W.; and Hagen, Kirk D., "Groundwater Heat Pump Equipment Selection Procedures for Architects,
Designers, and Contractors" (1980). Reports. Paper 526.
https://digitalcommons.usu.edu/water_rep/526
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Grou ndwat'er f}{eat 'PU1rl;P
Z'qu[foment SelectCon Procedures
for
Architect".s, D~sign~rs, e. Contractors
Utah State University, Logan, Utah 84322
Utah Water Research Laboratory
Extension Service
Mechanical Engineering Department
·.
.
~·~~~~-·-····-------"'9··
This publication was prepared under the Groundwater Resources Program
at the Utah Water Research Laboratory at Utah State University (project WR-61)
with funds provided by the State of Utah. Department of Energy (DOE) funds
were also provided through the Utah Division of Water Rights, Geothermal
Studies Branch, under DOE Contract No. DE-FC07-79-120 16. Project
personnel were Dr. Calvin G. Clyde, Professor of Civil and Environmental
Engineering (801+750-3174), Dr. Edward W. Vendell, Professor of
Mechanical Engineering (801+750:2834), and Mr. Kirk D. Hagen,
Graduate Research Assistant.
GROUNDWATER HEAT PUMP EQUIPMENT
SELECTION PROCEDURES
For Architects, Designers, and Contractors
Engineers at the Utah Water Research Laboratory and the Mechanical Engineering Department at Utah State University have investigated the use of groundwater heat pumps for residential space heating and cooling in the Utah climate.
They have found that this type of system conserves energy and may cost less for
Utah home owners to operate than many conventional heating and cooling systems. Since the use of groundwater heat pumps will probably become more widespread in the near future, building and heating contractors should become more
informed about what groundwater heat pump is and how it works. The purpose
of this publication is to answer some common questions about heat pumps and
help the contractor feel more confident about working with this relatively new
heating and cooling system.
a
How Does a Groundwater Heat Pump Work?
A groundwater heat pump operates in a manner similar to a household refrigerator. The major difference between the two systems is that a heat pump
can either deliver heat to or remove heat from an enclosed space by reversing the
flow direction of the refrigerant. Thermal energy is removed from the groundwater and is used to heat a home in the winter. Thermal energy is removed from
the home and delivered to the groundwater to provide cooling in the summer.
There are several different types of heat pumps commonly identified by
their heat source and heat sink respectively, such as air-to-air, water-to-air, and
water-to-water. A groundwater heat pump for residential use can be of the waterto-air or the water-to-water type, the water-to-air type being more common.
In Figure 1, a groundwater hea t pump extracts heat energy from incoming
groundwater and delivers heat energy(Hh) into the home. When the heat pump
is operating as an air conditioner, however, heat energy (He) is removed from the
home and delivered to the outgoing groundwater, which is usually discharged
back into a second water well drilled an appropriate distance from the source
well.
I
I
I
7'hn
1
---.I
Electrical
Energy (El
m
Ground Water
Source
Well
Discharge
Well
Water
Pump
Figure 1. How a groundwater heat pump works.
Heat Pump Cycle
The heat pump cycle is shown schematically in Figure 2 for the heating
mode. As the groundwater, which in this case acts as a heat source, passes through
heat exchanger (5), thermal energy is transferred from the warmer groundwater
to the colder circulating refrigerant thereby causing it to pass from a liquid to a
vapor. Mter passing through the reversal valve (1), the warm, low-pressure refrigerant vapor enters the compressor (2), which adds energy to the vapor in the form
of work and discharges the hot, high-pressure gas into heat exchanger (3). Air
from the fan is blown across the heat-exchanger coils to extract heat from the hot
gas thereby producing hot air, which is delivered to the living space; the refriger.ant gas condenses to a liquid as the air removes heat from it. Then, the moderately hot, high-pressure liquid leaves heat exchanger (3) and expands to a much lower
pressure in the expansion device (4). During the expansion process, a small fraction of the refrigerant flashes into a vapor thereby also cooling the portion that
remains liquid. Finally, the cold refrigerant completes the cycle by passing
through heat exchanger (5) where it once again absorbs heat from the warmer
groundwater.
When the heat pump system is operating in the cooling mode as shown schematically in Figure 3, the refrigerant flow direction is changed by switching the
2
Hot Air to House
Household Air-to-Refrigerant
Heat Exchanger
~
Fan
Compressor
Reversal Valve
Expansion
Device
4
Groundwater -to- Refrigerant
Heat Exchanger
Groundwater
Inflow
Groundwater
Outflow
t
Cool Water
Warmer Water
Hot Gas
Warm Liquid
Cold Liquid
Cool Vapor
Figure 2. Heating mode water-to-air heat pump.
3
a Vapor
Cold Air to House
Household Air-to-Refrigerant
Heat Exchanger
~.
FAN
Compressor
Reversal Valve
Expansion
Device
4
Ground water -to- Refrigerant
Heat Exchanger
68°F.
Groundwater
Groundwater
Inflow
Qutflow
f
CoOl Water
Warmer Water
Hot Gas
Warm Liquid
Cold Liquid
Cool Vapor
Figure 3. Cooling mode water-to-air heat pump.
4
a
Vapor
position of the reversal valve (1). This flow reversal causes the heating mode
source and sink to become the cooling mode sink and source, respectively. Thus,
in heat exchanger (3) the fan blows unconditioned warm air across the coils and,
in the process, the air temperature is lowered as heat is absorbed by the colder
refrigerant, which is transformed into a vapor by the time it leaves heat exchanger
(3). The resulting warm, low-pressure refrigerant vapor then enters the compressor (2), which compresses it to a hot, high-pressure gas. After passing through
the reversal valve (1), the gas enters heat exchanger (5) where it is condensed and
leaves as a fairly hot high-pressure liquid. Then, in expansion device (4) the highpressure liquid expands to a lower pressure and emerges as a cold liquid mixed
with a small amount of cold gas. Finally, the circuit is completed when the cold
refrigerant again enters heat exchanger (3) where it is tra.nsformed into a vapor
while it cools down the air which is fan-driven acroSs the heat exchanger coils.
As indicated by the above description, one of the primary attractions of
the heat pump system is the fact that the same equipment components can be
used for either heating or cooling a conditioned living space.
Coefficient of Perfonnance
The coefficient of performance (COP) is a measure of heat pump efficiency
in the heating mode. The higher the COP, the more efficient the heat pump is.
By definition, the coefficient of performance is the heating or cooling output in
KWh divided by the electrical energy input in KWh. Referring to Figure 1, the
COP may be written as:
COP =Hh/E for the heating mode and
COP = He/E for the cooling mode.
Since groundwater heat pumps utilize electrical energy to remove "free
heat" from the groundwater, the COP normally exceeds 1.0. Typical air-to-air
heat pump COPs relate closely with outside air temperatures and range from
about 1.3 to 2.4 over an average year. The COP of a typical groundwater heat
pump ranges from about 2.7 to 3.4 and does not vary significantly with outside
air temperatures, but the COP varies with groundwater temperature, as indicated
in Figure 4. This graph, used in conjunction with Table 1, is for estima tion purposes only; actual COPs may be different for each manufacturer. Individual manufacturer's data should be consulted for actual efficiency values.
A groundwater heat pump is normally more efficient than an air-to-air heat
pump. It is estimated that groundwater heat pumps are about 37 percent more
economical to operate in Utah homes than air-to-air heat pumps and 70 percent
more economical than electric heating. Although a groundwater heat pump cannot presently achieve a significant cost savings over natural gas, the Utah homeowner may want to consider installing a groundwater heat pump system even in
natural gas service areas because of the strong possibility of large price increases
for natural gas in the future. Furthermore, if a well must be drilled for culinary
water for the home, a groundwater heat pump could also use the same well to
hea t the home.
5
•
~ 4.01-----------------------------------------~
()
I
lLI
()
Z
«
::E
a:::
3.5
o
LL
a:::
W
Q..
3.0
LL
o
I-
Z
W
() 2.5
li:
LL
W
o
()
2.0~--------~----------~--------~----~
40
50
60
70
INLET WATER TEMPERATURE (OE)
Figure 4. Heating/cooling efficiency.
Table 1. Utah groundwater temperatures for four selected cities.
City
Logan
Salt Lake City
Residen tial
West of Airport
Moab
St. George
Average Groundwater Temperature
Range
·53.6°F
48.2 -59 .ooF
57.6°F
77.4°F
63.0 0 F
66.2°F
509-64.4°F
73.9 -81.5° F
6
55.4-75.2°F
Wby Use Groundwater
Heat pumps that use groundwater as the heat source have two basic advantages over heat pumps that us~ air as the heat source. First, water has the highest
specific heat of any common substance; its specific heat is four times greater than
that of air. Second, groundwater temperatures are fairly constant the year round,
with annual temperature changes from 10 to 20°F in shallow groundwater. The
temperature variation for deep groundwater is even less. Air temperatures, however, are usually too low for economical use in the winter when heat is needed
and too high in the summer when cooling is needed. When an air-to-air heat pump
operates in these extreme temperatures its efficiency is reduced, and a greater
quantity of electricity is consumed.
A side advantage of a groundwater heat pump is that the water which leaves
the heat pump may be used to irrigate a lawn or garden provided such uses are
approved in the well permit obtained from the State Division of Water Rights.
This is another way of recharging the underground water formation. If the source
well water flow is large enough, it may be also used for drinking provided the water
is of good quality.
A common auxiliary feature of many groundwater source heat pumps is a
secondary heat exchanger coil to provide domestic hot water. A groundwater
heat pump provides hot water at the same efficiency as it does for space heating.
In addition, excess heat that is absorbed during the cooling cycle can be used to
heat water as a free by-product of air conditioning.
Heat Pump Reliability
One of the major concerns of the heating or building contractors is the reliability and maintenance of groundwater heat pumps_ Some contractors have undoubtedly already installed air-to-air heat pump units in Utah homes and have
probably had few installations or maintenance problems. Since the major components of a groundwater heat pump are the same as an air-to-air unit, groundwater heat pump maintenance requirements are similar. However, since a groundwater heat pump has a water-to-refrigerant heat exchanger through which groundwater flows, corrosion and scaling may occur in the heat exchanger piping if the
groundwater is of poor quality. Iron, calcium, magnesium, salts, and suspended
solids can result in corrosion, scaling, and encrustation. Some manufacturers
design their equipment to reduce the effects of poor water quality. One way to
prevent scale is to use cupronickel instead of copper tubing. The cupronickel expands and contracts with temperature, and its surface tends to flake off mineral
deposits and scale with each cycle.
The cOl\lpressor is an important component in any heat pump. Its main
function is to pump refrigerant vapor from a relatively low suction pressure to
a higher delivery pressure. The suction and delivery pressures are afunction of
the heat pump design and groundwater temperatures. Under a large difference
7
between the delivery and suction pressures, the compressor must work harder
for the same flow rate, which requires more electrical input, and higher mechanical stresses in a crankshafts, bearings, and valves. These high stresses often caused
compressor failures in the early heat pump models. In recent years, however,
compressors have been developed which have better bearings and improved
valving. Improved motor insulations have been developed, and better motor
cooling methods are being used. In short, compressors are much more rugged
and are protected by much better controls. In fact, the extra durability of today's heat pumps has lessened the requirement for numerous protective controls, and thus lowered the number of parts which can cause problems. For example, 20 years ago heat pumps had many relays; today, most have only three.
Most of the controls and protective devices necessary for efficient and safe
groundwater heat pump operation are provided by the manufacturer and are
located within the heat pump enclosure. Usually the only control for which the
contractor is responsible is the room temperature thermostat (recommended or
supplied by the manufacturer) which the contractor must install, connect, and
adjust. If a water storage tank is installed, the contractor must also install the
tank temperature controL Most of the electrical connections are self-contained
and prewired within the heat pump unit. Most heat pumps require a 220V, 60Hz
power supply from a separate circuit breaker at the main box. Individual manufacturer's electrical ratings should be consulted.
The reliabihty of heat pumps is clearly improving, as evidenced by a preventative maintenance and service program conducted by the American Electric
Power Company (AEP) in which detailed maintenance reports have been shared
by individual heat pump manufacturers on a regular basis since 1961. The important results of the program are summarized in Table 2. Annual maintenance costs
for four different manufacturers are compared for the in-warranty period (first
five years) and the out-of-warranty period (next five years). The average for all
manufacturers is also compared. Annual maintenance costs have decreased substantially for all manufacturers except manufacturer D whose data were erratic.
As far as the reliability of individual components of the heat pump, compressor failure constitutes the major percentage of maintenance costs, as indicated in Table 3. Fans have the next highest maintenance cost percentage, followed by refrigerant leaks and flow controls. The prime targets for improved
reliability continue to be compressors and fans, especially fan motors and compressor controls.
Another indication of improved heat pump reliability is its sales volume
history. Shortly after 1952, the year heat pumps were made commercially available, sales were slow but increased steadily until about 1963. Then, as a result of
a high number of heat pump failures in the 1950s models, sales growth nearly
came to a stand still. No one wanted a product with such low reliability and high
service costs. But the heat pump industry perservered; improved designs were
Table 2. Heat pump maintenance-cost trend-line values, five-year intervals, in 1976 dollars. a
In Warranty
Model
Year
1957
1961
1966
1971
1976
IQ
Out of Warranty
All
MFG.
MFG.
MFG.
B
MFG.
MFG.
All
MFG.
A
C
D
MFG.
A
$131
109
83
56
29
$150
96
57
35
22
$214
121
60
29
14
$109
94
75
55
36
$34
42
93
93
$228
201
168
135
102
$271
163
87
46
25
MFG.
B
MFG.
MFG.
C
D
$270
189
121
$369
242
143
85
50
$59
179
180
77
49
a Actual dollars spent on maintenance were less, depending on the year analyzed. Adjustments to 1976 dollars were necessary for comparison purposes.
Table 3. Heat pump component failures, percent of total cost.
Major Group
First 5 yrs.
(0-4th yr.)
Next 5 yrs. Last 5 yrs.
(l0-14th yr.)
(5-9th
Average
(0-9 yrs)
Average
(9-14 yrs)
52%
Compressors
(Mechanical, Electrical,
Controls)
43%
57%
55%
50%
Fans
18%
16%
19%
17%
17%
Refrigeration Leaks
15%
9%
9%
12%
11%
7%
7%
6%
7%
7%
6%
4%
5%
5%
5%
11%
7%
6%
9%
8%
Refrigeration Flow Controls
Supplemental Heating
Misc.
developed, components were made more rugged, and installations were improved.
The industry had corrected its faults and was ready to push forward after eight
years of readjustment (Figure 5). As a result of the heat pump industry'sgreat
push to improve :their products, heat pump shipments rose sharply in the early
1970s and have skyrocketed ever since.
Water Wells and Groundwater Availability
The wells and well pump are an integral part of a groundwater heat pump
system. The first questions that come to mind are, "Is there enough groundwater
available in a particular location for use by a groundwater heat pump?" and
"How deep must the wells be drilled?" An experienced well driller is probably
best suited to answer both questions. The map in Figure 6 can serve as a rough
guide in locating major groundwater formations in Utah. Groundwater also may
be found in many other more localized areas throughout the state. The homeowner should realize that the deeper the wells must be drilled to reach groundwater the more costly his total heat pump system will be, and he should decide
for himself whether or notdrilling deep wells is economically feasible.
It is necessary to obtain a well permit for a groundwater heat pump system.
To acquire the well permit (water right) the home owner must file an application
with the Utah Division of Water Rights and receive approval of the application.
The normal period for suchan application is about 120 days.
Where water rights are not being permitted for consumptive purposes, no
such auxiliary uses as irrigation could be made from approved groundwater heat
pump wells.
A good feature of a groundwater heat pump system which utilizes a source
well and a recharge well is that there is no net depletion of the groundwater
aquifer. The same water which is pumped from the source well and enters the
water-to-refrigerant heat exchanger is discharged into the ground via a second
well. The only change is a slight increase or <decrease in temperature depending
upon whether the heat pump is cooling or heating the house. Of course, the two
wells should be spaced a sufficient distance apart to prevent large amounts of recycled water from being pumped again around through the heat pump thereby
decreasing its efficiency. A minimum well separation distance of about 50 feet
should be adequate to prevent recycling, for most groundwater formations.
Most building lots should be able to accoinmodate two wells 50 feet apart within their boundaries. The wells need not be close to the house, and since the
water is at ground temperature it is not necessary to insulate the pipes. The
pipes should be buried deep enough to prevent freezing in the winter.
A decrease in the amount of well water used by the heat pump system
results from the addition of an underground tank immediately adjacent to the
well in the surrounding soil. The heat pump then uses the water stored in the
10
z
Source: American Refrigeration Institute
700
o
IJJ
a..
a..
Z
C/)
600
500
C/)
rZ
400
:::::>
IJ.. 300
o
C/)
0200
Readjustment
Period
z
«
~ 100
o
i=
1954 56
58
60
62
64
66
68
70
72
74
76
YEAR
Figure 5. Industry shipment of unitary heat pumps.
tank and from the heat exchanger the water is returned to the tank to be reused
by the heat pump. In the heating mode, for example, the heat pump would extract heat energy from the water in the tank until the water temperature is lowered to a predetermined lower limit, say 40 degrees, then a heat sensor would
signal the well pump to begin adding warmer groundwater to the tank, thus displacing the colder water which would be returned to the aquifer. The well
pump would continue pumping warmer water into the tank until a higher selected temperature was reached. Of course, the advantages of using a storage
tank system are the smaller water requirements from the aquifer and the smaller
amount of electricity consumed by the well pump. In fact, during the spring and
fall seasons, the heat pump can often operate solely from the water in the tank
since the house is heated at night and cooled in the daytime. A general rule for
sizing the storage tank is one gallon per square foot of living space to be conditioned.
Heating Load Calculations
The heat that flows through a given residential building component may be
estimated by means of a simple formula
11
UTAH'S KNOWN AND PROBABLE:
GROUND-WATE:R RESERVOIRS
,
w:::~!~~:~:~:,/;;!:~~!:,,~:ii:
fJl
W"I.r
Figure 6. Distribution of groundwater aquifers in Utah.
12
lmr ,JOt
i-I
(~!Jvvl~",J
,
aMQ,n.d k~m bf4~i)tt.
where:
q
U
A
::: heat transmitted in Btu/hr
= the overall heat transmission coefficient in Btu/hr sq. ft. of
area in sq. ft. measured perpendicular to the direction of heat
flow
tj
inside design temperature in of
to
outside design temperature in of
The usual direction of heat flow in a residential building is perpendicular to a
window or a wall or a roof or a floor. The value of U depends, in general, upon
the kinds of materials through which the heat flows. Table 4 contains values of
U for a variety of typical Utah residential building components. The value of the
inside design temperature, ~, depends on the season for which the load estimate
is being made: the U.S. Department of Energy recommends 65 OF in the Winter
and 78°F in the Summer.
The value of the outside design temperature, to' to be used in the heat
transmission formula depends not only upon the season but also upon the locality and upon whether or not the component is above grade or below grade
(soil level). For above grade walls, windows, or roofs,
for heating season as given in
Table 5
for cooling season as given in
Table 5
The design values listed in Table 5 for T c and T H are based on average yearly climatological data records for a variety of Utah towns at a variety of altitudes. It
is in teresting to compare values of T c and TH for St. George and for Woodruff to
see the extremes in Utah.
The degree day information given in Table 5 is useful for estimating the fuel
requirement during the heating or cooling season. The degree day may be defined
in the following way: DUring one day, there are as many degree days as there are
degrees Fahrenheit temperature difference between 65°F and the average outdoor
air temperature for the day. Thus, if the average outdoor air temperature is 40°F,
25 degree days would accrue during that day. The formula for calculating the fuel
requirements is
F :::
where
F
DD
q
quantity offuel required for period desired (units depend on H)
degree days for period desired (from Table 5)
::: total heat loss in Btu/hr (found using q::: UA (tj - to»)
13
Table 4. Approximate transmission coefficients, U (Btu/hr - sq. ft. - Of).
Item
Descri ption
A. Walls with 1/2 in. gypsum wall board (sheetrock) on inside:
(1) 8 in. concrete block, 1/2 in. mortar, 4 in. brick,
(a) no insulation in core
(b) mineral wool or vermiculite in core
(2)
(3)
(4)
(5)
U
~
J
0.1710
0.1402
2 x 4 studs, 16 in. centers, no insulation, plus:
(a) 1/2 in. plywood, 3/4 in. wood siding
(b) 1/2 in. celotex, 4 in. brick
0.2834
0.3167
2 x 4 studs, 16 in. centers, R-ll insulation, plus:
(a) 1/2 in. plywood, 3/4 in. wood siding
(b) 1/2 in. cclotex, 4 in. brick
0.0713
0.0736
2 x 6 studs, 16 in. centers, R-19 insulation, plus:
(a) 1/2 in. plywood, 3/4 in. wood siding
(b) 1/2 in. celotex, 4 in. brick
0.0494
0.0506
2 x 6 studs, 24 in. centers, R-I9 insulation, plus:
(a) 1/2 in. plywood, 3/4 in. wood siding
(b) 1/2 in. celotex, 4 in. brick
0.0465
0.0475
Notes: (i) Walls (1a), (2a), and (2b) were typically used during 1950-1960
home construction in Utah.
(li) Thickness changes of up to 1/2 in. will not change U values significantly.
B. Windows:
(1) Single sheet, fixed (non-opening)
(a) without storm window
(b) with storm window, 3/4to 4 in. air gap
(2)
(3)
(4)
(5)
1.1000
0.5500
Single sheet, movable, average fit
(a) without storm window
(b) with movable storm window
2.2000
0.7400
Two sheets, fixed, 1/4 to 1/2 in. air gap
(a) without storm window
(b) with storm window, 3/4 to 4 in. air gap
0.6200
0.3538
Two sheets, movable, 1/4 to 1/2 in. air gap
(a) . without storm window
(b) with storm window
0.9140
0.3846
Three sheets, 1/4 to 1/2 in air gap, no storm window
(a) fixed
(b) movable
0.3500
0.5160
Note: The estimated U-values for movable windows exceed those of fixed windows because infiltration losses have been included.
14
II
n
]
Table 4. Continued.
Item
I
U
C. Basement wall, heated, 8 in. thick:
(1) No insulation
(2) Fiber glass. I in.
(3) Polyurethane foam, 1 in.
(4) Fiber glass, 3.5 in.
0.6462
0.2270
0.1282
0.0866
D. Basement Floor, 8 in. thick concrete, vinyl floor tile plus
(1) No insulation
.
(2) Fiber glass, 1 in.
(3) Polyurethane foam, 1 in.
0.5128
0.2080
0.1219
E. Ceiling and Roof: Flat or pitched cathedral ceiling
(U values for pitched case are based on horizontal ceiling area.)
(1) 1/2 in. gypsum, 2 x 4 or 2 x 8 ceiling joists, 5/8 in. plywood
deck, built-up gravel or asphalt shingles or wood, shingles, no
insulation
(2) As above, 1/2 in. insulation board
(3) As in (1) plus 1 in. polystyrene insulation
(4) As in (1) plus 1 in. polyurethane insulation
0.3058
0.2212
0.1345
0.1050
F. Ceiling and Roof: Pitched roof over flat ceiling: asphalt shingles,
2 x 4 ceiling rafters, 1/2 in. gypsum, 5/8 plywood deck plus:
(1) No insulation
(2) R-9 insulation
(3) R-11 insulation
(4) R-I9 insulation
(5) R-30 insulation
(6) R-38 insulation
0.2183
0.0868
0.0739
0.0465
0.0308
0.0247
1/
fi
Description
tj
to
H
24
utilization efficiency of heating/cooling unit (1/ = COP for heat
pumps, 0.75 for gas furnace, 1.0 for electric resistance heating)
= inside design temperature in OF
= outside design temperature in OF (from Table 5)
= heating value of fuel, Btu per unit volume (H = 3413 Btu/KWH
for electricity)
= 24 hours per day
Monthly heating and cooling degree days are given in Table 6 for four selected
Utah cities. For example, the quantity of natural gas required by a home in
Salt Lake City during the month of February assuming a utilization efficiency of
75 percent and a total heat loss of 60,000 Btu/hr is
F = 24 hrs/day x 664 deg. days x 60,000 Btu/hr
0.75 x (68-5)OF x 1,000 Btu/cubic feet
15
Table 5. Annual Utah weather design data for heating/cooling load calculations.
City
Alpine
Alton
Blanding
Bluff
Cedar City
Coalville
Delta
Duchesne
Emery
Fillmore
Green River
Heber
Kanab
Laketown
Levan
Logan
Manti
Moab
Monticello
Morgan
Ogden
Panguitch
Price
Provo
Richfield
Roosevelt
St. George
Salt Lake City
Scipio
Spanish Fork
Tooele
Tropic
Vernal
Wendover
Woodruff
Zion Nat! Park
Elevation
ft.
4935
6980
6036
4320
5618
5550
4653
5520
6250
5160
4070
5580
4985
5980
5315
4785
5740
3965
6820
5070
4350
6720
5680
4470
5270
5104
2760
4222
5306
4720
5070
6280
5280
4237
6315
4050
Design
Heating
Temp.,
TH'
OF
Heating
Degree
Days,
HDD
4695
5355
4720
3600
4215
4956
4467
4817
5239
4223
4038
4946
3639
5589
4526
4888
4695
3647
5216
4840
4592
5090
4684
4550
4436
4866
2889
4487
4361
4382
4362
4925
5217
4608
5580
2946
2
3
7
9
1
-8
0
-9
3
3
-1
-9
9
-6
0
2
-1
9
4
-7
9
-8
1
1
-1
-5
19
5
-9
7
9
5
-6
11
-19
17
Design
Cooling
Temp.,
TC'
OF
89
84
90
95
89
89
95
89
85
95
98
89
94
86
90
90
88
97
85
91
93
86
92
93
92
92
102
95
91
94
91
88
90
95
85
100
Cooling
Degree
Days,
CDD
608
160
600
1155
819
124
764
386
252
909
1057
166
982
99
624
584
367
1521
260
278
946
97
644
681
407
537
2047
927
449
892
859
306
342
1137
34
2067
Note: Design temperatures and degree days have been corrected according to ASHRAE
correction factors.
16
Table 6. Monthly heating and cooling degree day nonnals for four selected Utah cities.
City
Jui.
Aug.
Sep.
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
Jun.
Annual
734
664
596
471
650
590
458
365
394
356
208
155
206
178
56
27
85
64
4
1
4888
4487
3647
2889
Heating
Logan
Salt Lake City
-
Moab
St. George
0
0
0
0
6
4
0
0
106
79
16
5
325
302
192
106
616
583
511
417
844
807
769
657
922
860
837
685
Cooling
-.l
Logan
Salt Lake
City
Moab
St. George
245
207
56
6
0
0
0
0
0
0
13
57
584
363
505
598
300
425
546
99
173
303
11
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16
56
11
30
108
152
124
283
363
927
1521
2047
29
so, F =20,236 cubic feet of natural gas. Using 1979 Mountain Fuel Supply Co.
natural gas prices, the fuel bill for the month would be $37.0B.
The quantity of electricity required by a groundwater heat pump (COP
=3.2) for the same home during February is
F = 24 hrs/day x 664 deg. days x 60,000 Btu/hr
3.2 x (6B-5)OF x 3413 Btu/KWH
so, F = 1390 KWh of electricity. Using 1979 Utah Power and light all electric
home rates, the fuel bill for the month would be $47.36.
If the building component being analyzed is below grade, then
540F for Logan
58°F for Salt Lake City
° { 63°F for Moab
66°F for st. George
are the recommended values for four typical Utah locations; these values of to
are taken to be equal to that of the average local groundwater temperature.
Since the heat transmitted through below grade structures is usually such a
small fraction of the total for a given building and since groundwater temperatures do not vary significantly with the season or greatly with the geography,
one may choose from the four listed temperatures a value of to that corresponds with a similar climate. Also note that below-grade heat transmission is
comparatively small because design values for to are close to inside design
temperatures.
t
=
In practice, one applies the heat transmission formula separately to each
of the building components and then the total heating or cooling load is simply
the summation of the separate parts. Table 7 is a worksheet that is designed to
aid in the calculation procedure. Use of the worksheet is mainly self-explanatory.
As already noted in Table 4, the U-values for pitched roof-ceiling combinations
are based on horizontal ceiling areas.
In northern parts of Utah the heating load will be dominant and will thus
determine the size of the heat pump unit.
Choosing a heat pump unit that is smaller than the heating load calls for
will mean the unit cannot supply enough heat some of the time; choosing a unit
that is larger than calculations call for will cause the unit to run only part of the
time even during maximum heating periods, thereby resulting in reduced efficiency. The heat pump should therefore be sized as close to the calculated value
as possible. Heating loads shouid be used to size the heat pump for any Utall climate because the heating load exceeds the cooling load for virtually all regions of
the state.
18
Table 7. Heating/cooling load calculation worksheet.
Location
----------------------
Design tj
OF
Altitude
\Q
II.
U-Value
(Table 4)
Area,
ft 2
tj - to
OF
q,
Btu/hr
Ceiling/Roof Combination
Vertical External Walls
Horizontal Foundation Overhang
Vertical External Basement Walls
Windows, Fixed
Windows, Movable
Doors, Wooden
Doors, Sliding Glass
Miscellaneous:
Below-Grade Structures: Use to from Table 6.
A.
B.
C.
III.
--------------------
Above Grade Structures: Use to from Table 5.
A.
B.
C.
D.
E.
F.
G.
H.
I.
-
Season
DeWeeDays ________________
Design to
Item
I.
OF
Vertical External Basement Walls
Basement Floors
Miscellaneous
Total Load:
Note: The above calculations neglect solar loads which are usually negligible during the heating season but may be significant during cooling season.
After the heating load calculations have been completed and the heat pump
sized, this information should be shared with the manufacturer from which the
customer is purchasing the heat pump so that the proper size unit can be selected.
Some manufacturers may even require a set of construction plans on the home so
that they can perform the heat load calculations and size the unit themselves. In
either case, contractor and manufacturer should be in close contact so that the
proper equipment can be selected.
Once the heat pump has been selected, the proper duct sizes must be determined. Since heat pumps circulate warm air at lower temperatures than do conventional gas and electric furnaces, a larger volume of air must be circulated to
provide the same total heating requirement. This calls forlarger air ducts than
conventional furnaces require. Figure 7 shows the typical range of cubic feet per
minute (cfm) of air required for a range of heat pump capacities in Btu/hr. This
graph, which is based on actual groundwater heat pump manufacturers' data, can
be used to estimate the approximate cfm required once the heat pump size has
been determined.
To obtain the proper duct size for a specific cfm value, use Table 8 which
lists the proper supply diameters, rectangular duct choices and return diameters
for a range of airflow values. Suppose that a duct must deliver 2000 CFM of air.
This means that the supply diameter would need to be around 18 inches. The approximate rectangular duct choices are 8 x 40,10 x 30,12 x 24,14 x 20 and 16
x 17 inches. The proper retum diameter is 22 inches, and the rectangular choices
for the return are 12 x 36, 14 x 30, 16 x 26,18 x 23 and 20 x 20 inches.
Calculation of Water Flow Requirement
In order for a groundwater heat pump to operate at its specified heating and
cooling capacity and efficiency, the proper groundwater flow rate through the
water-to-refrigerant heat exchanger must be maintained. The groundwater aquifer,
well and pumping system must be able to supply the required flow rate. A rule of
thumb for estimating the required water flow rate is 2;1 to 3 gallons per minute
(gpm) for every 12,000 Btu/hr of heating or cooling required. This flow rate also
depends upon the groundwater temperature to some extent, but we will use the
standard 3 gpm/ton in all flow rate calculations for the example problem. Based
on this value, the flow rate can easily be obtained using Figure 8. For example,
suppose the heating load is 30,000 Btu/hr. From Figure 8, the required flow rate
is 7.5 gpm. If the manufacturer specifies a lower flow rate than 3 gpm/ton, use the
manufacturer's value for the calculation.
Well Pump and Supply fRetum Pipe Sizing
An important component of any groundwater heat pump system is the well
pump. Ifthe heat pump is to operate properly and efficiently, the well pump
must be able to supply the required volume of water to the water-to-refrigerant
3000
o
~ 2000
::::l
a
LI.I
a::
-
E 1000
u
20,000
60,000
40,000
80,000
Btu/hr.
Figure 7. Typical airflow required (heating and cooling).
Table 8. Duct sizing guide.
i
l
Req'd
cfm
Supply
ilia.
In.
35
60
100
150
210
225
280
305
395
410
655
680
995
1325
1450
1750
2000
2250
2600
2900
3400
5
5
6
7
8
8
9
9
10
12
12
14
14
16
16
18
18
20
20
22
22
24
26
Return
ilia.
In.
Standard
Rectangular Choices
2'4x 10
2'4x 10
3'4x 10
3'4x 14
4 x 15
4 x 15
5 x 15
5 x 15
6 x 15
7 x 18
7 x 18
8 x 22
8x 22
8 x 30
8x 30
8x 40
8 x 40
lOx 38
10 x 38
12 x 36
12 x 36
14x 38
16 x 38
3x 8
3x8
4x8
4 xlI
5 x 12
5x12
6 x 12
6 x 12
7 x 13
8 x 16
8x16
9 x 19
9 x 19
10 x 22
lOx 22
10 x 30
10 x 30
12 x 30
12 x 30
14 x 30
14 x 30
16 x 32
18 x 32
3Yzx 6
3Yzx 6
5x6
5 x 8Yz
6 x 10
6 x 10
7 x 10
7 x 10
8 x 11
9 x 14
9 x 14
10 x 17
10 x 17
12 x 18
12 x 18
12 x 24
12 x 24
14x 26
14x 26
16 x 26
16 x 26
18x 28
20 x 30
4x%
4 x 5Yz
5Yzx5Yz
6x7
7x 8
7x8
8x9
8x9
9x 10
10 x 12
10 x 12
11 x 15
11 x 15
l4x 16
14 x 16
14 x 20
14 x 20
16 x 22
16 x 22
18 x 23
18 x 23
20x 25
22 x 24
5x5
5x5
6Yzx 6Yz
8x8
8x8
8V2x 8Yz
8Yzx 8Yz
9V2x 9Yz
llxll
11xll
12 x 14
12 x 14
15 x 15
15 x 15
16 x 17
16 x 17
18 x 19
18 x 19
20 x 20
20 x 20
22x 22
24 x 24
5
6
7
8
9
10
10
12
12
12
14
14
16
18
20
20
22
22
24
24
26
heat exchanger. There are two main factors which determine the proper size for
the well pump: water flow rate and lift (height which the pump must lift the
water out of the ground). The following formula is used to calculate the correct
size (horsepower) well pump to use:
hp
where:
hp
Q
H
e
=
= QH
QH
2637
(3956)e
= well pump horsepower
wate·r flow rate gallons per minute
lift, feet
pump unit efficiency (typically 0.67)
j
=
For ease of use, this formula is presented in graphical form in Figure 9. To illustrate the use of Figure 9, assume a water flow rate of 10 gpm and a lift of 200
feet. For this example, the required horsepower is found to be about hp. In
practice it is better to oversize a well pump somewhat than to undersize it. An
oversized well pump will be more rugged and will compensate for friction losses
in the pipes, fittings, elbows, and heat exchanger.
*
The pipes which deliver the groundwater to the heat pump and back into
the discharge well must have a large enough inside diameter to accommodate the
required water flow rate and to allow for friction losses. Figure 10 shows the
relationship between the minimum required inside pipe diameter and the previously calculated flow rate. Figure 10 applies to schedule 40 steel pipe and includes 6.44 ft. of friction loss per 100 f1. of pipe. If smoother pipe such as copper or plastic is used, Figure 10 should probably be used in most cases even
though the friction loss is lower. This will allow some extra capacity to compensate for any additional friction losses without adding greatly to the costs.
Design Example
Now that all the basic design procedures for a groundwater heat pump system have been outlined, we will go through a complete design example. In order
to calculate the heating load using the formula q = UA (ti - to)' we must know the
total square footage of those areas of the house that will be actively heated. The
inside and outside design temperatures must also be known. Let's use the following data for our "design house":
Location
House style
Floor area
Basement
Walls
Salt Lake City, Utah
rectangular, one-story
1500 sq. ft. (30 x 50 ft.)
1500sq. ft. heated
1024 sq. ft., 2 x 4 studs on 16 in. centers, R-l1
insulation, 1/2 in. plywood, 4 in. brick
22
BASE D ON 3 gpm/ton
I ton =12,000 Btu/hr
24
21
-E
COl
18
15
LtJ
I<t 12
a::
3=
9I.i..
9
6
3
12,000
36,000
60,000
84,000
Btul hr
Figure 8. Well water flow rate required.
6.0~--------------------------------------~
5.2
a::
LtJ
3:
0
a..
4.5
3.75
LtJ
CJ)
a::
3.0
0
J:
a.. 2.25
:!:
::>
a.. 1.50
0.75
0
0
50
100
150
200
LI FT (ft.)
Figure 9. Minimum well pump horsepower required. (e
23
b
=0.67)
250
21---------------------------~~--~
Source' Standards of the
Hydraulics Institute
,.!..
2
,...
c::
-0
Applicable for SCH. 40 steel
pipe per 100 ft Nn.
~
I.JJ
N
Design velocity,5 fps.
CI)
Friction loss' 6.44 ft per
100 ft run.
I.JJ
n: t
0-
0
0
10
20
30
40
50
FLOW RATE (gpm)
Figure 10. Supply and return well water pipe size required.
Windows
Basement walls
above grade
Basement walls
below grade
Basement floor
Ceiling and Roof
200 sq. ft., two sheets, fixed without storm window
56 sq. ft., single sheet, movable, without storm
window
160 sq. ft., 8 in. thick, polyurethane foam, 1 in.
960 sq. ft., 8 in. thick, polyurethane foam, 1 in.
1500 sq. ft., 8 in. thick, polyurethane foam
1500 sq. ft., pitched roof over flat ceiling, asphalt
shingles,2 x 4 ceiling rafters, 1/2 in. gypsum, 5/8 in.
plywood deck, R-19 insulation
Groundwater depth 100 ft.
From Table 5, the outside design temperature for Salt Lake City is 5°F.
The inside desigu temperature is a matter of choice and depends upon the occupants' desired level of comfort. Let's use 68°F as our inside design temperature. From Table 4 the U value for the walls is 0.0736; for the two-sheet windows, 0.6200; for the single sheet windows, 2.200; for the basement walls above
and below grade, 0.1282; for the basement floor, 0.1219; and for the ceiling and
roof 0.0868. Now we are ready to calculate the total heat loss using the formula
q UA(t j - to)' Table 9 summarizes the calculation.
Therefore, the example house requires a heat pump that is rated at 35,000
Btu/hr, or approximately 3 tons.
24
Table 9. Summary of calculation.
Walls
Windows
Basement walls
above grade
Basement walls
below grade
Basement floor
Ceiling and roof
(2 sheets)
(1 sheet)
U
A
ilT
0.0736
0.6200
2.200
1024
200
56
(68-5)
63
63
0.1282
160
63
1,292
0.1282
0.1219
0.0868
960
1500
1500
(68-51)a
(68-51 )
63
2,092
3,108
8,203
Q
4,748
7,812
7,762
Total heat loss =35,017 Btu/hr
aWinter groundwater temperatures from Table I are used for outside design temperatures when calculating heat loss through basement walls below grade and basement floor.
Next we will determine the required size of ducts. We see from Figure 7
that for a heating load of 35,000 Btu/hr the required air flow is around 900 cfm.
Referring to the duct sizing guide in Table 8, a supply diameter of 14 inches is
needed which can be satisfied by rectangular duct choices of 8 x 22, 9 x 19,
10 x 17,11 x 17,11 x 15 or 12 x 14inches. The proper return diameter is 16
inches which can be satisfied by rectangular choices of 8 x 30,10 x 22,12 x 18,
14 x 16 or 15 x 15 inches.
Using the general rule of 3 gpm per 12,000 Btu/he of heating required, we
see from Figure 8 that the required Water flow rate is 8.75 gpm.
As for the well pump, Figure 9 indicates that for a 100 ft.lift and a flow
rate of 8.75 gpm, the required horsepower is about 0.375 hp.
And finally, from Figure 10, the minimum required inside supply and reo
turn pipe diameter is approximately 1 inch.
Summary
The future looks promising for groundwater heat pumps in Utah-especially
in the southern portion of the state and in areas where natural gas is not readily
available. Groundwater heat pumps are more efficient than conventional furnaces, and they provide cooling as well as heating. The major disadvantage of a
groundwater heat pump system is the initial cost. Nevertheless,a typical groundwater heat pump having an average COP of 3.2 will pay for itself in as little as six
or seven years as a result of the cost savings over conventional electric heating. A
2S
l
groundwater heat pump is also more efficient than an air-to-air heat pump because of the high heat capacity of water and groundwater temperatures remain
fairly constant the year round. The reliability of heat pumps has improved greatly since they were made commercially available in 1952. Compressors, which are
the heart of heat pumps, remain the major source of maintenance troubles, but
they too have been much improved over earlier years. Groundwater availability
and depth depend on the location, so local groundwater experts or well drillers
should be consulted. USing the information and methods described herein, adequate heat pump equipment can be selected for home heating applications.
References
1.
Groundwater Heat Pump - An Efficient Way to Heat and Cool Your Home.
Utah Water Research Laboratory, Mechanical Engineering Department,
Utah State University, Logan, Utah (free brochure available through U.S.U.
Extension Services) 1979.
2.
A Groundwater Heat Pump Anthology. National Water Well Association,
500 W. Wilson Road, Worthington, Ohio 43085, $3.00.
3.
The Unitary Heat Pump Industry - 25 Years of Progress. Joseph A. Pietsch,
ASHRAE J oumal, July 1977. (See the reference librarian in any University
library.)
4.
Heat Pumps. ASHRAE Journal, September 1979.
5.
Heat Pump Technology for Saving Energy. M. J. Collie, Editor. Noyes
Data Corp., 1979, Noyes Building, Park Ridge, New Jersey, 07656, $39.00.
6.
Heat Pump Technology, June 1978, U.S. Department of Energy, Division
of Buildings and Community Systems,Washington, D.C. 20545.
7.
Demonstration of Building Heating with a Heat Pump Using Thermal Effluent, May 1977, Peter W. Sector. Directorate of Military Construction
Office, Chief of Engineers, Washington, D.C. 20314.
26
Water Source Heat Pump Manufacturers
l
Company
Utah Distributor
American Air Filter
215 Central Avenue
Louisville, Kentucky 40201
(502) 637-0325
Midgley-Huber, Inc.
44 W 8th South Sheet
Salt Lake City, Utah 84101
(801) 322-2537
Carrier Corporation
Carrier Parkway
P.O. Box 4808
Syracuse, New York 13221
(315) 432-6000
Continental Air Conditioning, Inc.
2861 W 2700 S
Granger, Utah
(801) 972-4014
Mammoth Division
Holland Plant
341 East 7th Street
Holland, Michigan 49423
(616) 392-7021
Long-Deming-Utah, Inc.
80 West Louise Avenue
Salt Lake City, Utah 84115
(801) 487-0808
McQuay-Perfex, Inc.
13600 Industrial Park Blvd.
Minneapolis, Minnesota
(612) 553-5330
AAMaycock
3300 W 7th Street
P.O. Box 36
Salt Lake City, Utah 84101
(801) 364-1926
Solar Energy Resources Corp.
10639 Southwest 185th Terrace
Miami, Florida 33157
(305) 233-0711
(No Local Distributor)
International Energy Conservation
Systems, Inc.
1775 Central Florida Parkway
Regency Industrial Park
Orlando, Florida 32809
(305) 851-9410
Gunther's
31 N 100W
American Fork, Utah 84003
(801) 756-9683
Thermal Energy Transfer Corp.
5515 Old Three C Highway
Westerville, Ohio 43081
(614) 890-1822
(No Local Distributor)
27
Utah Distributor
Company
Weatherking, Inc.
4501 East Colonial Drive
Box 20434
Orlando, Florida 32814
(305) 894·2891
Andrew Mang Co.
P.O. Box 666
1465 Boston Street
Aurora, Colorado 80040
(303) 366-5453
Wescorp, Inc.
15 Stevens Street
Andover, Maryland 01810
(617) 470·0520
Alan Posen & Associates, Inc.
1942 Market Street
Denver, Colorado 80202
(303) 534·3577
Vanguard Energy Systems
9133 Chesapeake Drive
San Diego, California 92123
(714) 292·1433
(No Local Distributor)
York Division
P.O. Box 1592
York, Pennsylvania 17405
(717) 846·7890
Ted R. Brown & Associates, Inc.
1401 Major Street
P.O. Box 1356
Salt Lake City, Utah 84110
(801) 486·7241
Gervais Equipment Energy Company
9295 Fargo Rd.
.
Safford, New York 14143
(716) 343-0352
ENSCO,Inc.
P.O. Box 280
Monroe, N. Carolina 28110
(704) 289·6431
Phoenix Envir·Temp.
651 Vernon Way
El Cajon, CA 92020
(714) 579·3884
28
Utah Information Sources
1. Any Utah State University Extension Office. Phone 801+750·2200 for
the location of the nearest office.
2. Contact the personnel in the Geothermal Studies Branch, Utah Division
of Water Rights, 231 East Fourth South, Salt lake City, Utah 84111.
Phone 801+533·6071.
3. Contact either Dr. Clyde or Dr. Vendell; their USU phone numbers
are given inside the front cover.