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View Full Version : How much difference does it make?

09-12-2011, 08:56 AM
I inspected an air handler unit at a church.

Someone at the church decided it would be easier to maintain the filters if the cover was left off the filter housing (sucking hot atic air into the AHU!)

The inlet air temp to the AHU was 79deg
The outlet air temp immediately after the A-coil was 71.2deg

I covered the filter housing with tape and the outlet air dropped to 69.0 deg.

Charged the unit with 3 lbs of freon and the outlet temp dropped to 59.0 deg

Ok- barring the need for freon, how much was the 2.2 deg increase because of the missing filter cover costing these people. They have 10 air handlers in the attic and NONE of them have the filter housing covers on. The units are obviously working harder and longer to make up the temp difference, but I wanted to understand the theory behind this. It's a 2.5 tons unit. How much money are they losing per year? Can anyone point me to the right resources?

synergy
09-12-2011, 06:30 PM
Your resourses are a phycrometric chart a calculator an amprobe and some test and balance reading material. Your example is poor due to the unit malfuctioning.There are also to many variables in your question But going by your 2.2 increase in air temp you could calculate from a phycrometric chart the the entalpy differances between the two numbers. Multiple the pounds of air per minute you are circulating by deviding the unit CFM by 13.7 the standard cubic feet of air per pound. Convert the pounds per minute and enthalpy differance to tonnage. Convert the tonnage to watts. Figure the killo watt hours and use the standerd .08 cents per killo watt and do the math. That number would be your wasted energy. If your fan runs contiusally then you also need to calculate the sencible heat gain of attic air compared to the space temperature. You would need to know the cubic feet of area served and figure out the amount of air chages it takes to raise the temperature of the space and bring the unit back on. That amount of time would also be wasted energy. Your question is complicated. My answer may not be 100% accurate as I am going from memory but you get the idea. There is no rule of thumb for your question.