Proceedings of "Energy Programs Evaluation:Uses, Methods and Results"
1991 International Energy Progra, Evaluation Conferences, Chicago, Illinois
Paper dated: August, 1991
Prepared by: John Proctor, Proctor Engineering Group
The development of this test allows substantial improvement of any audit, savings or other calculation that involves furnace efficiency. Decisions between furnace replacement and repair can now be made based on measured results rather than guesswork. The predictive ability of FAST is enhanced substantially the the use of tests at three different cycle lengths.
What is Furnace Efficiency and Why is it Important? Decisions on furnace replacement, furnace retrofit, and in some cases the potential savings due to shell measures, are based on the installed efficiency of the furnace. In the absence of an adequate field furnace efficiency test, utilities and weatherization agencies have used "educated guesses." The result is inaccurate savings predictions and compromised program decisions. The efficiency of a furnace is simply the Btu's of heat delivered by the furnace divided by the input Btu's to the furnace. The efficiency would be 100% if there were no energy losses so that all the energy input was delivered as heat
There are two fundamentally different approaches to measuring the efficiency of a furnace. The most common method is to measure or estimate the loss, convert it to a percentage, and subtract the result from 100%.
The most common measure is the "steady-state" efficiency, which merely reports the on-cycle stack loss after a long furnace run (20 minutes is needed). The "steady-state" efficiency therefore represents an idealized picture of the operation of the furnace at one particular point in time.
The second approach to determining the efficiency is to measure the output of the furnace over complete cycles or longer time periods and divide that quantity by the energy input over the same period. This procedure obviously gives a more complete picture of furnace efficiency. When the efficiency is measured in this manner for a whole cycle the result is called "cycle efficiency."
FAST determines the efficiency of furnaces in the second, more complete manner. The energy output of the furnace to the distribution system is measured from the beginning of the cycle. The input is measured at the same time. At any point in the cycle, FAST defines the cumulative efficiency as the total energy output of the furnace divided by the total energy input up to that point in the cycle.
Also see Impact/Process Evaluations and Energy Efficiency Research
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