20929 Bridge Street, Southfield, MI 48033

20929 Bridge Street, Southfield, MI  48033
20929 Bridge Street, Southfield, MI 48033
4121 Brockton Drive SE, Grand Rapids, MI 49512
6200 Baron Drive, Bridgeport, MI 48722
6910 Treeline Drive, Suite A, Brecksville, OH 44141
Serving the industry since 1927
Phone: (800) 589-6120 - Fax: (248) 354-3710
www.deppmann.com
October 26, 2009 ~ Monday Morning Minutes:
Using Part Load Heating Data and Turndown Ratios
in Condensing Boiler Applications by Dave Shugars with edit by Norm Hall
Last week we defined turndown ratio. Turndown ratio is defined as the ratio of
the maximum input to the minimum input. It is an expression that translates to a
minimum percentage of firing rate the appliance is designed to operate at. The ability to
modulate infinitely from the minimum to the maximum translates to improved seasonal
efficiency by being able to match the actual load requirements.
The vast majority of systems rarely operate at the design temperature, since
most of the time the system is at part load. In fact, ASHRAE (American Society of
Heating, Refrigerating and Air Conditioning Engineers) publishes what is called “Bin”
weather data. This report identifies the amount of hours a specified location
experiences varying outdoor temperatures for a given geographic area.
This information helps us to understand the amount of time that the system
operates in the Part Load condition. This information will help you in the evaluation of
your final selection and optimum turndown ratio for a project using condensing boilers.
For example, the Aerco Benchmark BMK-2.0 boiler has a design input of 2,000,000
BTUH and has a 20:1 turndown ratio. In that case, it can modulate from 2,000,000
BTUH down to 100,000 BTUH WITHOUT having to cycle off and on to match the part
load condition.
This cycling, in particular short cycling, can have dramatic affects on equipment,
seasonal efficiency and carbon emissions.
 The equipment affects can include stress on the heat exchanger resulting in
premature failure and (b) wear and tear on controls decreasing longevity.
 Seasonal efficiency is reduced by the extra cycles of pre-purge and post purge
operation, wasting valuable heat to the atmosphere without return on investment.
 Carbon emissions (from start-up) are increased, due to the temperature
overshooting that short cycling causes.
(continued on page 2)
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many
years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions
that result from this information. Please feel free to contact us if you do have any questions.
20929 Bridge Street, Southfield, MI 48033
4121 Brockton Drive SE, Grand Rapids, MI 49512
6200 Baron Drive, Bridgeport, MI 48722
6910 Treeline Drive, Suite A, Brecksville, OH 44141
Serving the industry since 1927
Phone: (800) 589-6120 - Fax: (248) 354-3710
www.deppmann.com
The ability of a high turndown boiler to match the Energy input to Actual Heating Load, contributes greatly
improved seasonal efficiencies. The lower input potential will follow the inverse efficiency curve. Not only is less fuel
burned, it results in better unit efficiency, since the heat transfer surface remains constant. Precise temperature control
allows system designer to take full advantage of latest boiler and control technology offered by Aerco and Laars
For the design professional who is seeking sustainable solutions to their clients concerns, look no further than the
condensing products offered by the R. L. Deppmann Company. Next week we will look at two examples.
Thank you for using products sold by
R. L. Deppmann Company in Michigan and Ohio!
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many
years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions
that result from this information. Please feel free to contact us if you do have any questions.
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