Hey Ed, What Is the Correct CFM per Ton on a Heat Pump?
In this edition of "Hey Ed," Ed talks about the correct CFM per ton for heat pumps.
Hey Ed, what is the correct CFM per ton on a heat pump? CFM per ton on a heat pump is a quest that I have been on to find the correct number for five years, and that’s not an exaggeration. I can find some stuff in an RSES SAM manual, going back to the 80s, where the number 450 per ton was published. And then periodically, I’ve seen it in other places. And I’ve finally come to the conclusion where I’m going to say it’s not a bad number. I can’t find anything in the design series that specifically tells me for a heat pump what my airflow is supposed to be. Beyond that, there is some verbiage Manual D® that says to keep in mind that if your airflow for your heating and cooling are going to be different, try to keep them close if you can. And I’m paraphrasing, but that’s essentially what it says. So, if I have an air conditioner that needs 450 a ton, I’m going to run my heat pump at 450 a ton. If I have an air conditioner that needs 350 a ton, I don’t have to go seasonally balanced. There’s a solid chance I’m going to run my heat pump at 350 a ton. Notice I purposely didn’t say 400 a ton. The big part of all of this, and again something that the practitioner has to understand, is that a heat pump is going to be at its most efficient; it’s going to have the highest COP when it runs the highest published airflow. So, if your major focus is you’re in a heating climate, and you want to get the most out of that heat pump, it squeezes every penny out of it; bigger airflow is better. And that’s the way I see it.
Ed Janowiak is the Manager of HVAC Design Education at ACCA.
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