Heat pump loads

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Fred B

Fred B

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Location
Upstate, NY
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Electrician
I have a customer approach me about setting up the electrical for a large heat pump system. Just got the list from the environmental company showing loads, total of all loads are 214 amps if all loads are cumulative, I dont know if that is how its calculated. If it is, that is a lot on an already overloaded system just based on number of fully loaded panels. Main service is only 200A from meter, main panel plus 3 sub panels, (2 - 100A and 1 - 60A). Are loads from heat pumps cumulative? And will this overload the service?
 
You really need to know exactly how they came up with 214 amps. I'm going to go out on a limb here and say that the 200 amp service is too small unless there is a large error in their calculation.
 
infinity said:
You really need to know exactly how they came up with 214 amps. I'm going to go out on a limb here and say that the 200 amp service is too small unless there is a large error in their calculation.
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They provided a list of individual components with associated amperages, I added them up, that was part of my question as to whether the individual loads are cumulative, or is there a total system load that might be different than the cumulative load. No other numbers were given from environmental company other than the component loads.
 
Fred B said:
They provided a list of individual components with associated amperages, I added them up, that was part of my question as to whether the individual loads are cumulative, or is there a total system load that might be different than the cumulative load. No other numbers were given from environmental company other than the component loads.
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Sounds like you may be adding in the backup heaters as running at the same time as the heat pump.
 
gadfly56 said:
Sounds like you may be adding in the backup heaters as running at the same time as the heat pump.
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Not sure but they list 4 units they called GSHP @ 30.1A and 2 units called ASHP DHW heater @27.5A. Several other 1 - 5 amp loads and loop pumps, load pumps, and hydronic distribution pumps loads.
 
GSHP is ground source heat pump. ASHP DHW is air source heat pump domestic hot water.

What type of building is this? Dwelling, commercial? If a dwelling, it must be huge to have multiple large GSHPs.

I think you're going to need a bigger boat (service).
 
suemarkp said:
GSHP is ground source heat pump. ASHP DHW is air source heat pump domestic hot water.

What type of building is this? Dwelling, commercial? If a dwelling, it must be huge to have multiple large GSHPs.

I think you're going to need a bigger boat (service).
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Huge house 7000 sq ft, single family, 3 story, 9 bd room, 10 bath, 2 jacuzzi, ball room, library, solarium, 8 fireplaces, multi car garage, not to mention the gardens with its fountains gazebos and lighting, and a seperate carriage house with guest housing above it(seperate service). Old 1800 mansion. So huge? Yes.
Bigger boat was my initial thoughts as well. Before adding the heat pumps I thought the system was undersized. Thoughts on sizing for the addition of the heat pumps? And was my math wrong to come up with 214A just for the geo?
The additional loads for geo beside what I itemized post #6 are the loop pump 240v 13.4A, load pump 240V 4.2A, hydronic distribution pump 120V4A, the rest seem to be electronics totalling 120V 17.35A
 
4 ea 30+A GSHP!?
WOW, that is 500,000 BTU/hr for decent SEER GSHPs.

Even for 7000 sq ft somebody really oversized heating system unless the 'old mansion' has no insulation updates and leaky windows. Maybe greenhouse heat, e.g garden?

Own house is 5300 sq ft and a single 16.3A GSHP ehich has never failed to keeps it warm (albeit in mild Seattle area) over the last 20 years.

That said, If owners have t-stats set lower for night sleeping, it is highly probably the 120A GSHP plus 55A ASHW will come on at the same time quite often, assume pumps are part of GSHP operation, that puts you at an actual 200 A already.
If a couple of coffee makers and microwave ovens and fridge come on at same time (again likely first thing in morning) you are over 200 A and close to tripping main breaker.

Like Infinity already said, bigger service needed or intertie the GSHP tstats so not all can come on at same time.
HO not likely hurting for $$ if they can order 4 each 10Ton GSHPs?
See if 3 phase from poco available, may allow a more efficient GSHP to be selected by env. company.
 
PS: re: old leaky house -- Suggest to HO that Env. company, if they have not done so already, give them options on improving insulation envelope before huge GSHP install.
 
That size house I'm surprised they got by with a 200 amp service. I'd be concerned about adding a window air conditioner much less a heat pump system.
 
junkhound said:
PS: re: old leaky house -- Suggest to HO that Env. company, if they have not done so already, give them options on improving insulation envelope before huge GSHP install.
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The few things I've already done on wireing found no insulation in walls. Probably why they had 8 fireplaces. Insulation has been suggested, they are waiting until they are doing the siding replacement.
augie47 said:
That size house I'm surprised they got by with a 200 amp service. I'd be concerned about adding a window air conditioner much less a heat pump system.
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I've told them in past that it needed upgrading. But like most, if the lights are coming on they think, why? I've got other things I want done like the heat pump. Lights dimming or flicker they blame on the POCO, Not undersized system.
 
You may be able to reduce the calculation a bit. Heat pump compressors are added at 100% no matter how many you have. You can get a break on heat strips, but you may not have any with a ground source system. I'd use the Optional calculation for sure, and the water heaters may fall under the 40% section (the same as everything else that isn't heating/cooling and over a 10KW floor is cut to 40% nameplate). You may have a hard time fitting all of this in a 400A service.

I had a heat pump at my last house. I added a bunch of insulation and double paned windows first because without I was going to need an 8 ton heat pump and a lot of aux heat strips. After doing that, I was able to install a normal 5 ton heat pump and 20KW of heat. Still needed a 400A service because of what else was in the house (it was all electric - no gas, and had 2 kitchens and a pool heat pump). They may want to assess energy efficiency once you tell them what a 600A service is going to cost.
 
If they insulate after putting in all that new heat, they're going to be double unhappy. An 1800's house brought up to even 1970 insulation standards is probably going to drop the heating requirements by 90%. Heating systems that are that over-sized will be very inefficient and the components may experience unacceptable thermal cycling, leading to shorter system life. They should do the siding and insulation now and go through a full heating and cooling season and get their loads recalculated.
 
Depending on how controls work, back up heat may or may not be able to run at same time as the heat pump. Back up heat should be the bigger load if they can't run at same time.

NEC basically requires you to use rated load amps for calculations. Reality is it won't draw that much if things are in good condition. I have 3 ton GSP two stage. Been a while since I took amp reading but on heat mode low stage it was only drawing about 6 amps. Does typically draw more in cool mode, still typically well below RLA though.
 
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