Annual fuel utilization efficiency
The annual fuel utilization efficiency (AFUE; pronounced 'A'-'Few' or 'A'-'F'-'U'-'E') is a thermal efficiency measure of combustion equipment like furnaces, boilers, and water heaters. The AFUE differs from the true 'thermal efficiency' in that it is not a steady-state, peak measure of conversion efficiency, but instead attempts to represent the actual, season-long, average efficiency of that piece of equipment, including the operating transients.[1] It is a dimensionless ratio of useful energy output to energy input, expressed as a percentage. For example, a 90% AFUE for a gas furnace means it outputs 90 BTUs of useful heating for every 100 BTUs of Natural Gas input (where the rest may be wasted heat in the exhaust). A higher AFUE means higher efficiency.
The method for determining the AFUE for residential furnaces is the subject of ASHRAE Standard 103. A furnace with a thermal efficiency (ηth) of 78% may yield an AFUE of only 64% or so, for example, under the Standard's test conditions. When estimating annual or seasonal energy used by combustion devices, the AFUE is the better efficiency measure to use in the calculations.[2] But for an instantaneous fuel consumption rate, the thermal efficiency may be better.
| Fuel | Furnace/boiler | AFUE |
|---|---|---|
| Heating oil | Cast iron (pre-1970) | 60% |
| Retention head burner | 70-78% | |
| Mid efficiency | 83-89% | |
| Electric heating | Central or baseboard | 100% |
| Geothermal heat pump | see COP | |
| Air-source heat pump | see HSPF | |
| Natural gas | Conventional | 55-65% |
| Mid-efficiency | 78-84% | |
| Condensing | 90-97% | |
| Propane | Conventional | 55-65% |
| Mid-efficiency | 79-85% | |
| Condensing | 88-95% | |
| Firewood | Conventional | 45-55% |
| Advanced | 55-65% | |
| State-of-the-Art | 75-90% |
[edit] See also
- Coefficient of performance (COP)
- Energy efficiency ratio (EER)
- Seasonal energy efficiency ratio (SEER)
- ASHRAE
[edit] References
- ^ Systems and Equipment volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, USA, 2004
- ^ Heating and Cooling of Buildings, Kreider and Rabl, McGraw-Hill, New York, 1994
- ^ Canada Mortgage and Housing Corporation, ed. (2008) [1993], A Guide to Residential Home Heating (2008 ed.), ISBN 978-0-660-19848-4, http://www.cmhc-schl.gc.ca/en/co/maho/enefcosa/upload/wood_heating_EN_W.pdf, retrieved 2009-03-23
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