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12-04-2009, 10:09 AM #1
Inspecting & Testing an A/C's Performance
For air-temps, use a digital air-probe TH with a precise increment reading.
I've worked HVAC as a licensed Tech since before the mid-1970's.
The HVAC inspection is extremely important to the buyer.
This may appear a bit overboard, but is information & testing that can be helpful to you & the buyer. Few Techs know or use these important performance testing methods.
There is always a proper testing sequence for determining if the HVAC system is functioning up to par. Too low an airflow through the evaporator is very common!
1.) Determine if the condenser coils & fins, the indoor filter(s), blower wheel blades & indoor coil are clean. They have to be reasonably CLEAN or all other testing will be distorted.
2.) Actually when you check Model numbers, Tonnage Rating & SEER Ratings' of the condenser, then checking the temp rise is an excellent indicator of the amount for total BTUH, both sensible & latent, being transfered to the outdoors. Yes, even my HVAC ARI textbooks support this condenser split test. The higher the SEER the lower the acceptable Temp-Split.
"Air Conditioning System Sizing for Optimal Efficiency"
(Right Click Link & open in New Tab)
3.) You need an anemometer to ballpark check airflow velocity from the diffusers. CFM= (Velocity in FPM X's sq.ft area of the duct), or the diffuser' "Ak" listed sq.ft open-area is best to use.
4.) Total BTUH= (CFM X's 4.5 X's Enthalpy Change) Chart Link:
(Right Click Link & open in New Tab) Print the chart.
This test alone will ballpark the BTUH of the A/C.
You need an instrument to quickly check wet bulb temps along with ballpark accuracy airflow CFM to rooms.
Figuring round duct sq.ins. = 7" rd duct sq.in. area= 7X's 7=49 X's .7854 = 38.4846-sq.ins. / 144= 0.2672541 sq.ft area. X's say 600-FPM VEL = +160-CFM airflow. Say, seven runs all equal for this example; 160-CFM times 7= 1120-CFM, or 448-CFM per ton of cooling, a bit high but acceptable with some low humidity conditions for a 2.5-Ton A/C. (425-CFM per-ton with a wet coil is most acceptable.)
Well, anyway that is the easiest & fastest way to ballpark check an A/C or heat pump's actual BTUH Output Performance. After you do it a few times it becomes second nature. The home buyer will thank you for doing a thorough check on their central A/C or heat pump.
Practice figuring all this on paper. Using proper test instruments these testing procedures can be performed in a relatively short time span.
Do Google searches among others' for, Hart & Cooley & J&J Register "Performance Data," you will see the "Ak" you can use listed on some of the diffuser's performance Data. - Darrell