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Hey Ed, Explain the Difference Between Condition A and Condition B When Selecting a Heat Pump?

In this edition of "Hey Ed," Ed discusses the difference between Condition A and Condition B when selecting a heat pump.

Hey Ed, explain the difference between condition A and condition B when selecting a heat pump. In ACCA’s Manual S®, there are two paths, or two ways, that you can select a heat pump. And one goes based off of the idea, or I shouldn’t say one, I should say A. If you have a sensible heat ratio, a Manual J® sensible heat ratio of under 0.95, which describes the majority of heat pump installations, it’s quite simple. You follow the guidance for selecting an air conditioner. If you have a set of circumstances that qualifies under condition B, that means you have a house that has a sensible heat ratio of 0.95 or greater. You have either an extremely tight house that virtually gets no infiltration or latent moisture coming in from outside, or you live in an arid environment. This area would have what we refer to as negative grains. Negative grains are the infiltration that takes place or the air that comes from outside to inside that actually has less moisture in it. I live on the East Coast, and that’s almost more than my brain can take that that actually happens in some areas, but it does. So, there’s more wiggle room via Manual S® with condition B. Condition B says you can add an additional 15,000 BTUs. Round up a ton is in real life how it works for the size of the equipment, if it meets those specific bits of information that are listed in condition B. And that’s the way I see it.

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

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