malachi constant
Senior Member
- Location
- Minneapolis
How should condenser w/ gas furnace systems be calculated? Condensing obviously unit falls under 220.82(C)(1). What about the furnace blower? It operates during heating and cooling seasons but doesn't really heat or cool - just blows air.
If you look at 220.82(C) (NEC 2008) a furnace doesn't fall neatly into any of the six Heating and Air-Conditioning Load categories. A strict reading of the code would probably dictate the furnace go into 220.82(B)(4) General Loads. This would effectively derate the furnace at 40%. But is derating the furnace blower really the intent of the code?
If you don't put it in (B)(4) then where does it go? In one or more of the following?:
* (C)(1) - nameplate rating of AC & cooling?
* (C)(2) - nameplate rating of heat pump?
* (C)(6) - "...other heating systems where the usual load is expected to be continuous at the full nameplate value"? This sounds promising, but is followed with: "Systems qualifying under this selection shall not be calculated under any other selection in 220.82(C)". You would think the furnace blower would count towards both heating and cooling, so to only count it once (or not at all actually, as the larger cooling load will effectively cancel out the smaller furnace blower load) doesn't seem right.
Related question - anyone familiar Packaged Air Conditioning Units (PACUs, Magic Packs, etc)? They provide both heating and cooling in apartments, and the heat can be gas or electric. If it is a gas unit, I've been taking the nameplate of the entire unit and plugging it into 220.82(C)(1). Now we're considering electric heat PACUs, with some units having a supplemental electric fireplace. How would I go about calculating that? I assume for cooling take the nameplate of the entire unit, and for heating take 65% of the nameplate of both the PACU and fireplace, then ignore the lesser of the two.
If you look at 220.82(C) (NEC 2008) a furnace doesn't fall neatly into any of the six Heating and Air-Conditioning Load categories. A strict reading of the code would probably dictate the furnace go into 220.82(B)(4) General Loads. This would effectively derate the furnace at 40%. But is derating the furnace blower really the intent of the code?
If you don't put it in (B)(4) then where does it go? In one or more of the following?:
* (C)(1) - nameplate rating of AC & cooling?
* (C)(2) - nameplate rating of heat pump?
* (C)(6) - "...other heating systems where the usual load is expected to be continuous at the full nameplate value"? This sounds promising, but is followed with: "Systems qualifying under this selection shall not be calculated under any other selection in 220.82(C)". You would think the furnace blower would count towards both heating and cooling, so to only count it once (or not at all actually, as the larger cooling load will effectively cancel out the smaller furnace blower load) doesn't seem right.
Related question - anyone familiar Packaged Air Conditioning Units (PACUs, Magic Packs, etc)? They provide both heating and cooling in apartments, and the heat can be gas or electric. If it is a gas unit, I've been taking the nameplate of the entire unit and plugging it into 220.82(C)(1). Now we're considering electric heat PACUs, with some units having a supplemental electric fireplace. How would I go about calculating that? I assume for cooling take the nameplate of the entire unit, and for heating take 65% of the nameplate of both the PACU and fireplace, then ignore the lesser of the two.
