heat pump defrost cycle triggering heat strips
acrobaticnurse_Eli
| Posted in General Questions on
After installing an emporia energy monitor to see how much electricity my heat pump’s air handler was using I realized that when my heat pump goes into defrost mode it triggers 10kw heat strips for 2-5 minutes. This was a surprise as I didn’t think the air handler had heat strips. The paperwork that came with it listed them as an option and had a section the installer was supposed to check if they were included, and it was blank. Had I not installed the energy monitor I might have never known that a 10,000 watt resistance heater was running for 2-5 minutes every hour or two once the temperature gets into the 30s despite the heat pump being fully capable of handling temps well below that and the heat strips are expressly optional.
I looked into how to disable the heat strip activation during defrost and learned that while the thermostat has no control over it, it is simple enough to disconnect the white low voltage thermostat wire from the defrost panel of my heat pump without doing any damage. The heat strips are utilized for occupant comfort while the heat pump basically goes into AC mode to defrost and aren’t necessary for the defrost process itself. Since disabling them for the defrost cycle I haven’t noticed any comfort problems and I no longer see them activating on my energy monitor. If anything the air feels a little better as it’s no longer being cooked by a 10kw resistance heater every hour or two. Had it been a comfort issue it would be easy to reconnect the wire that is currently safely capped.
I was most concerned about a 10kw load overwhelming my inverter generator if/when I ever need to run my heat pump in a power outage, but now I’m glad to have eliminated a large electrical load that I’d been unaware of. I’d been watching videos of people installing microair easy starts to soft start their central air/heat pump in the summer with a less than 10kw generator, and realized that doesn’t work in the winter if heat strips are getting activated. Now I want to see if I can squeeze an emporia into my main panel.
Note: I made sure to shut off power to both the heat pump and air handler before touching any wires, and if I were going to get close to the capacitor I’d discharge it first. My post is simply to share the joy of energy monitoring.
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Replies
Your situation is pretty common. On some systems where the heat strip is configurable and disabled, some units revert to this mode when there is a power loss. It is annoying as it is a fair bit of power and really doesn't make any difference in comfort if the air handler is off during the defrost cycle.
The other way to disable is simply to turn off the heat strip breakers. Not an option for an install that needs the heat strip for cold weather but in most cases where it is only for backup it can work. The side benefit of disabling the breaker is that you find out right away if the heat pump has issues well before you receive a $1000 electricity bill after running on heat strip for a month.
My issue was that the heat strips apparently share a 60 amp breaker with the air handler. Aside from the low voltage wiring there's only one 6/2 cable going to the air handler. I thought the circuit was just oversized due to the old wiring being reused since that's what the contractor paperwork stated, but with the heat strips it genuinely needs that much. The air handler itself says it only needs a 6 amp circuit without the optional heat strips and I only see it use a little over 2 amps.
One thing I appreciate about my electric provider is that they email me if my bill ever seems higher than usual, and I can track whole house energy use down to 30 minute intervals via their app.