Air change per hr

Constantin

... do a blower door test on a cold day to see what's happening.

Terry Larsell

Air change per hr

I'm doing a heat loss on a shop and the default air change per hr is .5 This room has high ceilings and a lot of air. If I bump the number to one it adds almost 10,000 btu's to the heat loss. What is a good number for air change on a shop or a house for that matter. How can you tell? This is one variable that is giving me grief trying to come up with a number without using a blower door.

Terry

steven E.HEAT

ach

be careful. Recently i did a job and it was a great room above a garage reno but full gut like new and i figured a .75 achr @75 deg. 0 deg. out .then i got a call from the contractor on the coldest day this yaer and room only reached 67 @9 deg.out . I thought my calcs.were sparring but the brand new insul. job was garbage. So at my expense i added 14 ft. of ci.bb.to satisfy cust.my heat loss calc. is h.d.t. seigenthahler.i been using it for 8 years no prob. till this disaster. The next day i ordered a thermal image cam.the next time, they will pay not us. p.s. that day i noticed there was absolutely no snow on the roof!

gerry gill

well, i use hvac calc

and haven't had a problem when letting the computer deside ac per hour, it just asks if its poor, average or tight...but if in dought, here is what the old timers would do..this info is in the 1934 hoffman data book, page 71..if one wall exposed 1 ach, if 2 walls exposed 1.5 ach, if 3 or 4 walls exposed 2 ach..add 1 ach if the room has a fireplace..subtract 1/2 ach if the windows has weatherstripping...when all else fails, i do what the elders did..

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Greg_40

I would seriously recommend a blower door test. I did one at a shop recently that was only 42 x 60. It leaked so severely that the door/fan couldn't reach 50 Pascals. No vinyl wrapped insulation, no butyl sealant at metal seams. The entire building was insulated with foil-faced rigid foam that was labeled only R-3. Someone convinced the owner that the foil was going to give him all sorts of benefits. Concrete firm convinced him that insulating the slab perimeter was not necessary, even though the HVAC firm requested it. The HVAC guy was convinced into using foil/bubble insulation and that this product would pay dividends also. This shop was a travesty of one piece of misinformation after another.

The next shop I tested a few days later was proven to be so much tighter than I would have given it credit for- complete opposite of the previous one! You may get by with assumptions much of the time, but if you don't test, you're really just taking a guess. Also make sure important things such as insulation and building tightness products are installed as they are supposed to be and make it clear that your system was designed to work with "X" specifications. If the building is not insualted or sealed as it was supposed to have been, that your system is not to blame. It's a game of communciation all the way around.