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Hey Ed, Is There a Difference Between Sizing an Air Conditioner and a Heat Pump?

In this edition of "Hey Ed," Ed discusses the difference between sizing air conditioners and heat pumps

Hey Ed, is there a difference between sizing an air conditioner and a heat pump? There is no difference currently in the ACCA Design Series when it comes to air conditioners or heat pumps. And I’m going to just put it out there right now. There’s a couple of people that are throwing stuff at their computer screen or they’re ready to toss their phone across the room. We size air conditioners for their air conditioning capacity or what manual S specifically says is we got a meet to sensible, we got to meet the latent, we’re not supposed to oversize that system by more than 15, 20 or 30 percent depending on the compressor technology. The 15 percent single-stage compressor, 20 percent, two-stage, 30 percent is the VRV systems. If you have a heat pump you are supposed to size it the exact same way. There is currently no path in manual S that says yeah go ahead and oversize the heat pump. And if you want to yell what add there’s condition B. You’re right but the likelihood if you have a sensible heat ratio for that structure of 0.95 or greater is almost non-existent. If you want to yell at me from Arizona or Phoenix or someplace like Utah where it’s really dry, yeah I might agree with you but that’s a very very small part of this whole process or the marketplace. So I’m going to stick with my statement that you size heat pumps for air conditioners. Now there is some stuff that’s going to come out in the next hopefully within the next 12 months that says something and it’s July of 23 so maybe by the end of this year the new manual S there is some guidance for sizing based off of the heating requirement but there’s a whole laundry list of things that you need to do to follow that path and the short version of that long list is you got a 100% prove how you’re taking care of that latent load. If you’re taking care of the latent load I don’t care what size system you put in. Well I do but my whole thing is managing moisture as long as you’re managing the moisture and you can prove it I’m on board and that’s the way I see it.

Ed Janowiak is the Manager of HVAC Design Education at ACCA.

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