The following stumper is presented in BPI's March Performance Matters e-Newsletter

 

A big thank you goes out to Jamie Clark of ARRONCO Comfort Air in Lexington, Kentucky for sending in this stumper! Jamie was called to an 18 year old, 2,500 sf, two-story home with a vented attic in Lexington that had a broken central air system. There were two air systems, one in the attic, one in a closet. ARRONCO decided to replace both systems with two ton Carrier® hybrid systems. After the project was completed, all the registers in the house started sweating. Jamie came back the next day to find the humidity level over 70 percent! The two stage systems were running on low most of the time which should have resulted in lower than average humidity (average in Lexington is 55 percent). ARRONCO inspected all the equipment to make sure it was installed correctly, and tested all the equipment. All air volumes were right, the equipment was perfectly sized, all duct work was sealed (with less than 10 percent leakage).

 

Question: Why was the humidity so much higher? 

 

Think you know the answer?

 

Figure out what is going wrong with the house, write it up along with your prescribed solution, and share your wisdom by posting your answer right here in our comments section. You can also send it to us at lmcdowell@bpi.org. If you’re the first person to get the right answer, we’ll feature you, your company and your answer in the next issue of Performance Matters!

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 Before an accurate assessment can be suggested, outdoor conditions need to be measured and a blower door test should be performed. Also, where are the returns located?  Damien Herold

Summer time conditions 85 degrees 75% outdoor humidity, central return filter grills in both up and down hallway, this was in 2008 prior to my adopting blower door so no numbers but I can tell you natural infiltration is not the answer.

Wet crawl space/basement or leaky/misducted returns would be my 1st 2 areas to look at.

Could be this: Running the air handler fan between condenser cycles will reintroduce the humidity removed by the air conditioning process. This combined with a tight home, high indoor humidity sources, and a humid climate could create this issue. Set the thermostat to FAN AUTO and watch the humidity drop.

March Stumper Revealed!

We are chagrined. We realize we should have given you more clues to last month’s stumper, sent in by Jamie Clark of ARRONCO Comfort Air in Lexington, Kentucky. (But we beg your forgiveness because it's a fine balance! If we tell you too much we give away the easy answer; tell you too little, and you don’t have the information you need to make an educated guess). Readers will recall that Jamie replaced two broken air systems with Carrier® hybrid systems only to find that after the project was completed, all the registers in the house started sweating, with the humidity level over 70 percent! All equipment was installed correctly, air volumes were right, the equipment was perfectly sized, all duct work was sealed (with less than 10 percent leakage).

Despite the gaps in information, we received several creative responses to the puzzle. Dean Smith of Santee Cooper in Moncks Corner, South Carolina came closest, guessing that the customer had the system’s fan in the “on “ position and the blower motor was picking up the condensate from the wet coil, which was being distributed back into the home. Well done Dean!

Jamie reveals what was really going on. When he went back to the house on the second visit, he visually inspected the duct work to make sure it wasn’t pulling in excessive air and humidity from the attic. But when he lifted the scuttle hole hatch it started to float; there were two full size attic exhaust fans in a 6,000 cubic foot attic. They put the entire house on such a negative pressure, they were sucking in moisture from the outside. Says Jamie: “It was like having a blower door on 24/7”. Important note: The first time Jamie visited the house for his initial assessment of the broken central air system, it was a cold and rainy day, so the attic fans weren’t running. To solve the problem, Jamie disconnected one attic fan and turned the other one to 120 degrees so it would only turn on in extreme heat.

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