Service Calculation for Heat Pumps

[jcarter052496]

Background:
Existing 2600sf building. Adding 1400sf (4000sf total).

Existing service is (2) 200A panels with mains, 120/240V, 1-phase. Utility has the peak at 50A.

Our task was to compare bringing gas to the building or keep the heat pump type design.

We have 13.5KW (56A) of auxiliary electric heat in the building. This is non-peak for gas heat (summer is peak load), but can't be deducted with a heat pump.

Our calculations:
Gas heat: connected=61KVA, demand=47.5KVA (200A)
Heat pump connected=91KVA, demand=93KVA (390A)

I tweaked some loads and got each panel to be exactly 200A demand. I just realized I forgot a load making one panel 205A.

Am I missing something in the NEC?

Typically the code calculation is about 1.75 times of what's needed. In this case, I'm at 5 times!

Any help would be greatly appreciated.

Joe

 

[gndrod]

DF

DF

Hi Joe,

Check out Art 220 calculations for load factoring. Demand reductions for service load will reduce final service capacity required. (i.e. T 220.54, T 220.55, and 220.61 HVAC DF for a start) rbj

 

[suemarkp]

Is this a dwelling or not? If so, there is a demand factor for heat pump electric resistance heat of 65% if you are using the Optional Calculation method.

Load calculation would be:
For heat pumps only - Sum of compressor load and aux electric heat loads.
For gas heat - the higher value of compressor for summer cooling or your electric heat loads.

What does "Utility has the peak at 50A" mean?

Finally, how can your heat pump demand load of 93 KVA be higher than the connected load of 91 KVA?

 

[jcarter052496]

It's a Credit Union, so dwelling units don't apply.

 

[jcarter052496]

It's a Credit Union and Art. 220 doesn't help (that I've found).

Joe

 

[jcarter052496]

Sorry, didn't read far enough:

The Electric Utility Company told me that the peak load seen on the building's meter in the last 5 years is 50 amp.

The demand load is larger because the lighting is 125% of connected and HVAC is +25% of largest. The only time demand would be less is for receptacles (50% over 10KVA) or seasonal/non-peak.

 

[MikeGee]

Can you use the heat pump and have second stage heat be gas. In a space that big I'm not sure a heat pump is really suitable. Unless you are in Florida or something. Hey I could be wrong just continuing the conversation.

 

[bob]

Background:
Existing 2600sf building. Adding 1400sf (4000sf total).

Existing service is (2) 200A panels with mains, 120/240V, 1-phase. Utility has the peak at 50A.
We have 13.5KW (56A) of auxiliary electric heat in the building. This is non-peak for gas heat (summer is peak load), but can't be deducted with a heat pump.

Is this an existing 13 kw heat that will stay when the heat pumps are installed?

Our calculations:
Gas heat: connected=61KVA, demand=47.5KVA (200A)
Heat pump connected=91KVA, demand=93KVA (390A)

Would you list the heat pump compressor load and the strip heat load.
Will there be 1 heat pump or 2? Since there are 2 - 200 amp mains, I thought there may be one HP on each.

 

[jcarter052496]

No gas will be available in the building.

I'm not a mech. eng. but we have a 4-ton and 5-ton heat pump.

On a different note, is there anywhere in the code that says I can add a multiplier? Can I put the following note:
"I'm a licensed professional electrical engineer and I'm taking 75% of the load for my design load because I know better and this seal says so"?

What about diversity factor? Does the NEC say anywhere I can issue one?

 

[bob]

Background:
Existing 2600sf building. Adding 1400sf (4000sf total).

Existing service is (2) 200A panels with mains, 120/240V, 1-phase. Utility has the peak at 50A.
We have 13.5KW (56A) of auxiliary electric heat in the building. This is non-peak for gas heat (summer is peak load), but can't be deducted with a heat pump.

Is this an existing 13 kw heat that will stay when the heat pumps are installed?

Our calculations:
Gas heat: connected=61KVA, demand=47.5KVA (200A)
Heat pump connected=91KVA, demand=93KVA (390A)

Would you list the heat pump compressor load and the strip heat load.
Will there be 1 heat pump or 2? Since there are 2 - 200 amp mains, I thought there may be one HP on each.

Seems like I did this twice. Sorry

The Electric Utility Company told me that the peak load seen on the building's meter in the last 5 years is 50 amp.

The demand load is larger because the lighting is 125% of connected and HVAC is +25% of largest. The only time demand would be less is for receptacles (50% over 10KVA) or seasonal/non-peak.

If you are using the 50 amp demand in the service calculation, you add 25%. You also add 25% for the largest motor. Is this what you are indicating?

 

[suemarkp]

The demand load is larger because the lighting is 125% of connected and HVAC is +25% of largest. The only time demand would be less is for receptacles (50% over 10KVA) or seasonal/non-peak.

What nameplate value are you using for the HVAC compressor -- MCA or a sum of RLA's? The MCA value already includes a 125% factor, and I'd hope you don't don't have to apply this factor twice. I also wonder if that 125% factor could be removed from the smaller unit since you normally only need to apply this to the largest one.

 

[bob]

What nameplate value are you using for the HVAC compressor -- MCA or a sum of RLA's? The MCA value already includes a 125% factor, and I'd hope you don't don't have to apply this factor twice. I also wonder if that 125% factor could be removed from the smaller unit since you normally only need to apply this to the largest one.

That information applys only to the ckt to HVAC unit.

 

[jcarter052496]

13kW auxiliary heat is new (with the new heat pumps) for a mezzanine and back employee entrance.

4-ton: 230V, 18.3A compressor RLA, 17.4kW electric heat, overall-116FLA
5-ton: 230V, 25A compressor RLA, 17.4kW electric heat, overall-128FLA

(2) Heat Pumps, yes, one on each panel.

Not using the 50A demand since the whole interior is new. I've calculated like it's a new building. So, continuous load get multiplied by 125%, 25% of largest motor is added to the HVAC load.

 

[jcarter052496]

Demand reducing variables:
The only NEC rules that reduce the demand load for commercial buildings is receptacles (50% after 10KVA) and seasonal (non-peak, non-coincedental), right?

And there are no seasonal reducers with a Heat Pump since the heater can be on with the compressors during defrost mode in the winter. Or, winter is the peak season and the compressors are ON during the winter.

The NEC requires us to take the full load of the heat pumps (59 KVA) + auxiliary heat (13 KVA) + remaining loads (18kVA) = 90 KVA, right?

The building will use only require 19 KVA.

I can't believe the NEC hasn't provided some type of reducing demand factor for Heat Pumps! It's not like heat pumps are a new technology.

 

[Keri_WW]

The plans reviewers in my area have always had me take heating loads with a demand factor of 1.0. From there I have to use 220.87, taking 125% of the maximum demand and add the new load to it.

 

[suemarkp]

Demand reducing variables:
I can't believe the NEC hasn't provided some type of reducing demand factor for Heat Pumps! It's not like heat pumps are a new technology.

You only have two don't you? If the building cooled down in winter, it is conceivable that both systems would need to run with full aux heat for a while (especially if properly sized and not oversized). Shouldn't the load calculation design for that?

I could perhaps see a demand factor if there we a bunch of them and all the spaces were controlled separately (like a multifamily dwelling). There is also the demand factor electric heat strips for even a single unit in a dwelling, but it looks like you don't get to use that in commercial service.