Generac Load Shedding

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readydave8

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I have had very little experience and would like to know more on this subject

The Generac comes able to shed 4 loads. I have 2 heat pumps wired to 1 and 2 (I chose to interrupt all control voltage versus just the heat strips because I was worried about how it would handle defrost without heat strips)

After generator runs for a few minutes, and both heat pumps are running, a load kicks in (I think strip heat) and it sheds both 1 and 2

Is it supposed to drop all 4 loads and bring them back one at a time? (Like it's doing) rather than drop one load at a time until it's satisfied?
 
readydave8 said:
I have had very little experience and would like to know more on this subject

The Generac comes able to shed 4 loads. I have 2 heat pumps wired to 1 and 2 (I chose to interrupt all control voltage versus just the heat strips because I was worried about how it would handle defrost without heat strips)

After generator runs for a few minutes, and both heat pumps are running, a load kicks in (I think strip heat) and it sheds both 1 and 2

Is it supposed to drop all 4 loads and bring them back one at a time? (Like it's doing) rather than drop one load at a time until it's satisfied?
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Not sure but sounds logical it would work that way. AFAIK it uses drop in frequency because of loading conditions to initiate those responses and not actual current conditions.

As far as defrost (without heat strips) all most heat pumps do is switch to cooling mode to move heat from inside to outside to do the defrosting. They kick on heat strips to lessen cooling effects. If you have extra shedding contacts you could use higher priority to turn the compressor(s) back on first then heat strips last.

Around here many times the generator not large enough to run heat strips unless nothing else is running, unless you happen to have a 5 kW bank in there. I'd likely not even connect any the strip heat to the transferred load, or put on a relay that disables strips any time on generator power, but connect the compressor lead to the load shedding contacts in many instances.
 
readydave8 said:
Is it supposed to drop all 4 loads and bring them back one at a time? (Like it's doing) rather than drop one load at a time until it's satisfied?
Click to expand...

Depends on size of the load on the generator. It’s apparently enough that it needs to drop both hvac units.

And yes it is frequency based.


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kwired said:
As far as defrost (without heat strips) all most heat pumps do is switch to cooling mode to move heat from inside to outside to do the defrosting. They kick on heat strips to lessen cooling effects. If you have extra shedding contacts you could use higher priority to turn the compressor(s) back on first then heat strips last.
Click to expand...
My {personal} heat pump has LP furnace rather than strip heat. Gas ran out once, when heat pump went into defrost, it never did start heating again, blower just blew unheated air. Only way to get heat was to turn off breaker, then it would heat again until the next time it cycled to defrost, etc. That's why I was reluctant to interrupt heat strips only on this job (for customer}

Yes I have extra shedding contacts, but right now it's shedding all contacts.
 
readydave8 said:
My {personal} heat pump has LP furnace rather than strip heat. Gas ran out once, when heat pump went into defrost, it never did start heating again, blower just blew unheated air. Only way to get heat was to turn off breaker, then it would heat again until the next time it cycled to defrost, etc. That's why I was reluctant to interrupt heat strips only on this job (for customer}

Yes I have extra shedding contacts, but right now it's shedding all contacts.
Click to expand...
Something must have malfunctioned, defrost termination logic/sensors? Only reason to run backup heat is to compensate for the fact it goes into cooling mode during defrost, which takes heat from indoor air and moves it to the outdoor coil and ultimately heats that coil up to defrost it. With most electric strip heaters for the backup, they aren't even on the supply side of the indoor coil so they won't directly put heat into the refrigerant to assist with defrosting.
 
readydave8 said:
so if size of load on generator was smaller, it would just drop one load? and then the 2nd load if still too much?
Click to expand...

yes it should drop them in order of priority, but if its an instant high load it will likely drop them all because of the frequency drag. Thats to prevent the circuit breaker in the generator from opening.
 
brantmacga said:
yes it should drop them in order of priority, but if its an instant high load it will likely drop them all because of the frequency drag. Thats to prevent the circuit breaker in the generator from opening.
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Thank you!

Sorta gotta has to be heat strips then, seemed to be consistent 3-5 minutes after heat pump outdoor unit started
 
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