Air Conditioning System Performance Audit Instructions
Draft February 16, 1998
Depending on weather conditions it might be advantageous to modify the order of the 3 tests that comprise this audit (Fan Power, Dry Coil Air Flow, and Air Conditioning Performance). If the weather is such that the air conditioner has been cooling, the coil is likely to be wet and the condensate pan full. If this is the case, then task III ("Evaluate Air Conditioning Performance") should be performed first, followed by tasks I and II.
I. Evaluate Fan Power (No heating or cooling)
1) Turn system fan to "On" at the thermostat. Prepare small holes in the duct system, before and after the evaporator coil, being careful to avoid a location just above the coil which will allow the temperature probe to "see" the heat elements. Insert digital thermometer probes into center of air flow stream. Read values; the supply temperature should be higher than the return temperature because of fan heat. If Tsupply is less than Treturn, the coil is still wet. Wait five minutes after Tsupply is greater than Treturn and is stable over a minute (typically it will be 0.2 to 1.5oF or higher). If the coil is wet initially, it will often take 20 minutes to dry totally. Record return/ supply temperature difference [D].
2) While the fan is running, record the site, AC manufacturer and model data and obtain the utility meter Kh; it will usually be 7.2 Wh/rev; some units may be 3.6. Place exterior temperature probe at the inlet to the condenser coil. Avoid placing the probe in direct sun.
3) After 5 minutes perform Test#I. Inform the occupants that the indoor power will be off for a period of about one hour to complete the tests. Turn off all household breakers except for the air handler to insure that the only power draw is from the air handler fan. Go back to the utility meter and using a digital stop watch, start timing when the black band passes to the front of the meter and stop when it reaches this position again. Record the number of revolutions [A], and the elapsed seconds [B]. Then calculate the fan power [C]. It should typically be 200 - 600 W.
II. Evaluate Dry Coil Air Flow (Heating)
Caution: For heat pumps, turn system off and wait several minutes before switching to heating mode if in cooling mode.
1) Turn the system to heating mode at the thermostat if the unit has strip heaters; if it is a heat pump it must be turned onto "emergency heat" so that only the strip heat is activated. Set the thermostat to the highest value; noting the original setting so it can be returned to this point at the end of the test. If it is a gas furnace, flow can only be obtained by using a flow hood; the heating system cannot be used to obtain flow. Allow the system to run for five minutes to come into equilibrium. The strip heat can be confirmed to be "on" if the condenser is not running (confirmed by visual inspection) and if the power meter is moving quicker than it would be if only the air handler was running.
2) After five minutes, record the dry bulb temperatures before and after the coil. Then, with the stop watch, record the seconds [F] requires for ten revolutions [E] of the power meter.
3) Estimate dry coil air flow [G]. It should be approximately 350 - 425 cfm/ton (12000 Btu/h) although many units may show lower values.
4) Turn the heating system off at the thermostat.
III. Evaluate Air conditioning Performance (Cooling)
Caution: For heat pumps, turn system off and wait several minutes before switching to cooling mode if in heating mode.
1) Put the unit in cooling mode, and turn the thermostat down to its lowest setting. Allow the cooling system to operate for approximately 20 minutes until condensate flows at a consistent rate from the unit. Be sure to create a condensate "trap" to assure steady flow in the condensate drip. Set a timer and collect condensate for exactly ten minutes into a convenient vessel. Carefully pour contents into graduated cylinder and record milliliters of condensate water collected [M].
2) While condensate is being collected, use the stop watch to measure the time [K] required for 10 revolutions [J] of the utility meter.
3) Record the dry bulb temperature before and after the cooling coil and their difference [N].
4) Wet the cotton bulb over the two wet bulb temperature probes and insert in the return and supply air streams being careful that the wetted cover remains over the probe during the test. Wait five minutes and record values. Also record the outside air temperature at the condenser on the worksheet.
5) Compute power [L], sensible [O], latent heat [P] and system performance (EER) [R,S].
6) Note any unusual findings from the audit: (e.g. a gurgling sound during cooling operation; no condensate produced etc.). Turn the household breakers back on and reset the thermostat to the original setting.
7) Seal all holes made in the duct system; clean up all tools and return all things altered to their original condition. Thank the occupants for their cooperation before leaving.
Space Conditioning System Performance Audit
Site ID_____________________ Technician _____________________________ Date/Time_____________
Address____________________________________________________ Utility meter Kh: ________________
Nameplate Information Unit Type _________________________________ (Heat pump, AC or furnace)
|Indoor unit (if split)|
(See attached instructions for completing this form)
I. Fan Power (No heating or cooling)
|A||B||C||D||Original thermostat setting °F|
|Revolution||Time||Power (W)||T (oF)|
|Number||Seconds||A * kh * 3600 / B||Tsupply - Treturn|
|Revolution||Time||Power (W)||T (oF)||Air Flow (cfm)|
|Number||Seconds||E * Kh * 3600 / F||Tsupply - Treturn||G * 3.27 / H|
III. Air Conditioner Performance (Cooling)
|J||K||L||M||N||Dry Bulb Wet Bulb
Tsupply °F °F
Treturn °F °F
|Revolution||Time||Power (W)||Condensate||T (oF)|
|Number||Seconds||J * Kh * 3600 / K||Milliliters in 10 min.||Tsupply - Treturn|
Outdoor temperature by condenser inlet ______ F
|N * I||M * 14.04||O + P||Q / L||O / L|