I am confused with the heat pump and furnace portion of the question. I would have thought that the heat pump would heat to a certain level and if it gets colder than the furnace would turn on as well. I would have taken 100% of the compressor and 65% of the furnace for the demand load. Any thoughts?
You are partially correct. At lower temps, the furnace strips will kick on. But when that happens, the heat pump kicks off, since it no longer can function effectively. They are noncoincident loads. That's why you only need to calculate the larger of the two. At any given time, only one of the two loads will operate. There are situations where a heat pump may operate at the same time as furnace strips, but that is extremely rare. In fact, I've never heard of it in a dwelling - only special commercial setups. That's where 220.82(c)(3) would come in.
@@simply.electrical Thank you for explaining these as non-coincidental loads. I also would have done calc with 100% Heat Pump AND 65% of heat strip. Nobody else on TH-cam mentions this, and how are us electricians sposta know that until we are told!
@@rideoregonfirst The code is written with Formal Interpretation as the goal. See 90.6. In many cases, this makes it difficult to understand for the everyday users. The CMPs would serve the public better by writing in a more useful and obvious style, IMO.
I am confused with the heat pump and furnace portion of the question. I would have thought that the heat pump would heat to a certain level and if it gets colder than the furnace would turn on as well. I would have taken 100% of the compressor and 65% of the furnace for the demand load. Any thoughts?
You are partially correct. At lower temps, the furnace strips will kick on. But when that happens, the heat pump kicks off, since it no longer can function effectively. They are noncoincident loads. That's why you only need to calculate the larger of the two. At any given time, only one of the two loads will operate.
There are situations where a heat pump may operate at the same time as furnace strips, but that is extremely rare. In fact, I've never heard of it in a dwelling - only special commercial setups. That's where 220.82(c)(3) would come in.
@@simply.electrical Thank you for explaining these as non-coincidental loads. I also would have done calc with 100% Heat Pump AND 65% of heat strip. Nobody else on TH-cam mentions this, and how are us electricians sposta know that until we are told!
@@rideoregonfirst The code is written with Formal Interpretation as the goal. See 90.6. In many cases, this makes it difficult to understand for the everyday users. The CMPs would serve the public better by writing in a more useful and obvious style, IMO.