Residential Load Calc for Heat Pump Question

bwise863

Member
Location
Sacramento area
I've done a couple of Load Calcs (practice) for homes with Heat Pumps and want to make sure I'm doing this correctly. The only question I have is regarding the Heat Pump. I think the rest of the calcs I have down. I've attached 2 pics (Name Plates) of the Inside FAU and the Outside Compressor for the exact reference to numbers. I"m only focusing on the Heating load since that is larger than the cooling in this case.
Calculations Follow:
Outside Unit has a compressor and fan. From the Name Plate the VA I'll use is: 7314 VA (31.8X230)
Inside Unit has a fan and a Heat Strip. The heat strip is 5kw. FAU Minimum Ampacity is 7.5amps/230 volts. Gives 1725 VA (7.5X230) Plus 5000 VA for heat strips.

So the Total Heating Load is 7314 VA + 1725 VA + 5000 VA = 14,039 VA.

Did I take the correct numbers from the name plate....logic correct? Thanks for your input!
 

Attachments

topgone

Senior Member
Heating and cooling do not go ON at the same time. Just choose which one is greater than the other and use that heat requirement value to compute for the total maximum load requirement.
 

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
Not sure but I beleive the heat strips and the compressor do not run at the same time. Usually the compressor runs if it can't keep up with the heating load or the outdoor coil ices up it shuts down and brings on the heat strips which are usually considered emergency heat. Check the control sequence
 

bwise863

Member
Location
Sacramento area
Heating and cooling do not go ON at the same time. Just choose which one is greater than the other and use that heat requirement value to compute for the total maximum load requirement.
Maybe I'm missing the logic behind this. However, I'm pretty sure the compressor in the outside unit works when it is heating or cooling. So, I'm taking the minimum ampacity from the Compressor unit outside either way. The difference is the Heat Strips. Those are only activated when it is really cold and the reverse flow from the compressor isn't doing the job.

Thanks
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
@bwise863

Check the control sequence. I Think when the heat strips are activated the compressor will shut down and you just heat with the heat strips
The heat pump can be configured either way. If the heat pump is still working efficiently but the current temp is greater than some number of degrees from set temp the resistance heaters may still turn on too. Not just when heat pump is unable to work efficiently.
When heat pump is outside its operating range it will shut down and use just the resistive heating.
One reason heaters are usually on a separate circuit.

Sent from my Pixel 4a using Tapatalk
 

retirede

Senior Member
Location
Illinois
35 years ago, heat pump controls were pretty simple. The thermostat had two set points. When temperature in the house fell below the highest set point, the heat pump would run, if it fell below the lower set point, the resistance heat kicked in.
Additionally, once the outdoor temperature fell below a certain temperature, the heat pump would shut off.
It was definitely the case that both would run concurrently.
I’m sure it’s more complicated today.
 
Top