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 are a couple of people who are throwing stuff at their computer screens, or they’re ready to toss their phones across the room. We size air conditioners for their air conditioning capacity, or what Manual S® specifically says is we got to meet the 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. 15 percent are single-stage compressors, 20 percent are two-stage, and 30 percent are 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 of you having 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 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 laundry list of things that you need to do to follow that path, and the short version of that long list is you've got to prove 100% 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, and 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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