220.82 load calc. regarding HVAC load

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1electricalgenius

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I am reworking a large house (14K Sq' +) which has 5 sub unit heat pumps with back up electric heating installed in each one (4 @10K 1 @20K), all bigger loads then their AC counter parts as well as a central boiler system (its motor listed per part B, line item 4). Which part of 220.82,C 1thru 6 would I use for this demand factor for the HVAC load. Is it the sum total of all the heat pumps, or just the biggest of all the heat pumps? And am I correct as I read this Art, it is only the biggest load of220.82C- 1 thru 6, not the sum of 1 thru 6 Then which multipler for this demand?

1electricalgenius


My greatand giving intelligents does not impede my ability to occasionally and spontainously do very stupid things!!!
 
Most heat pumps run the compressor and the strip heat at the same time. It is possible to wire them so they don't do that, but the home owners won't be happy with the cold defrost air or the high billls when its cold out. But I don't understand why there is a central boiler too. Is this a dual fuel heat pump system, or is it yet another separate HVAC system?

I think you need to use part (3). I believe "largest" refers to each of the six choices and not the largest of your 5 heat pumps. Heat pumps are a killer, and you need the MCA of the compressors and strip heat from all of them added together but you get the 65% factor on the strip heat. Finally, note that the strip heat nameplate value will have a 125% factor, so a 10KW heater will end up about 8 KW in the calculation.
 
220.82 calc per HVAC load

220.82 calc per HVAC load

1electricalgenius said:
I am reworking a large house (14K Sq' +) which has 5 sub unit heat pumps with back up electric heating installed in each one (4 @10K 1 @20K), all bigger loads then their AC counter parts as well as a central boiler system (its motor listed per part B, line item 4). Which part of 220.82,C 1thru 6 would I use for this demand factor for the HVAC load. Is it the sum total of all the heat pumps, or just the biggest of all the heat pumps? And am I correct as I read this Art, it is only the biggest load of220.82C- 1 thru 6, not the sum of 1 thru 6 Then which multipler for this demand? 1electricalgenius
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Hi 1eg,
If this is a remodel to an existing dwelling, section [220.83] can be more applicable to re-calculaltions if the existing service or feeder is sufficient capacity to serve the additional loads. Using 220.83(A) where no additional HVAC, or 220.83(B) for new HVAC is added.
The boiler motor, as mentioned is included with the Fastened-in-place NPR totals 220.82(B)(4) that exclude any HVAC equipment. Many other questions arise due to the separate boiler heating in relation to the use of the heatpumps along with heatstrips. Sounds like some energy management controls may be in order for zone efficiency of environment within a 14k sf residence.

Mark is correct regards to 220.82(C)(4) is applied to 100% of the compressor and refrigerant section (are these scrolled?) and 65% of the heat elements application. Now if the boiler is the prime heating source then the A/C load could be considered separately. The complexity arises as to how each heatpump is applied to the overall system and if they are all new and may become the prime largest source.

I would look at the system from a sub feeder standpoint to the heatpumps being zoned separately. More information is needed to make a better assessment. rbj
 
There are so many unique methods where an energy package can use zoned digital controls (i.e. for tier cycle off-loading) not normally applicable in smaller residential new construction.

Maybe the following can help. Could you describe the boiler system heating more in detail. 1. Is a gas heated boiler used for distributed wall radiant or hydronic recirculated floor radiant heating? 2. Is the boiler shared with a split exchanger? 3. What sf area heat coverage is the boiler distributed thoughout and what are the zones that utilize the heatpumps? 4. Type of heatpump equipment used...single or split systems or are these ductless wall mini-split pump unit retrofits being added? 5. Does a heatpump kick in when boiler cannot sustain adequate heat distribution by zone or room? rbj


rbj
 
piling on

piling on

FYI just because this wasn't complex enough.. We also are trying to install a Gen Set to run the place (listed in the national historic reg to give a hint at the $$$ at stake) in event of a power outage (during last ice storm they pipes froze and they now hvave a 75Kish repair bill) I like the idea of shedding some of this load with an energy management system. I wonder if I can "soft start" the HVAC compressors to eliminate that. The biggest comp. load has an RLA of about 30A but a LRC of 150A, does the gen set need to put out 150A to start the comp? I am musing about putting all the HVAC into a sep. pnl with soft start to reduce the KW needed to start em all from the Gen set, any recommondations of an specific model:rolleyes: , brand of EMS that may accomadate 75 kw HVAC load? As I ponder all this maybe my best solution is to be a plumber!!!
 
The generator will have to supply the motor inrush currents. Gen sets have ratings for that. If you can get a generator sizing program or get a generator sales rep to perform the service it would be good. The sizing software programs now include a soft start option for motors loads. I wonder if you could consider just having the electric heat running in emergency mode? That way the inrush issues are a lot less. Of course then on a 95 degree day when the power fails you will want to start the compressors for cooling. But the generator may still have enough capacity for that. Using the sizing software and running some "what-if" scenarios might be worthwhile.
 
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