Isn’t that COP for AHRI matched systems, is that what you have, a AHRI matched system? You don’t have electric heat come on during 2nd stage Heat or while it goes into defrost?

Been involved with installing many single stage HP with electric heat and the Heat Pump runs all the time, no lockout in New England.

The question is: would it harm the heat pump running straight 16 hours a day.

Pretty normal if not even longer run times the lower the OD temperature you go from our many years of observation.

Judgement call how you want to set up your system IMO, running HP real long times, more wear and tear, subject to sooner breakable? running less, depending on electric rate in your area, could get expensive? If system is down for repairs do you subtract the service fee from your energy savings on whichever way you go to get optimal energy saving cost effective methods?

Guessing your a young person as you don’t seem to mind the cool supply air temperatures coming out of the supply grilles ( with no electric heat coming on ) at say 18 degree OD temperatures, what do you have a basic single stage HP?

 

Hi Bazooka Joe,
Thanks for your reply. I do have a matched system. The heat pump coil is inside the furnace's air handler. Auxiliary heat does turn on when the actual temperature is lower than thermostat set point by more than 1 F approximately, or when heat pump goes in defrost mode.
I live in Montreal, where climate similar to New England I suppose.
I do have a basic one stage heat pump.

I read the wrong COP figure from my heat pump peerformance table in my previous post. The COP at -6 F should be 1.6 and not 1.3.

In any case, when the outside temperature is -6 F , the air coming out of the floor registers, while heat pump in operation, and when no auxiliary heat in operation, is as low as 4 F warmer than the average indoor temperature. Not very warm, I agree, though the air being convected is not uncomfortable for us. This air temperature rise of 4 F is not enough to maintain the house at the desired set point in the thermostat. At these temperatures, if there is no sun ( no solar heat gain), and neither no internal heat gains, then the auxiliary heat will come on approximately 16% of the time, or 5 minutes every 25-30 minutes or so. The electric elements in the furnace (auxiliary heat) provide 20kW of heating power.

I like your idea of making a judgment call, trading off electricity savings VS the risk of more wear and tear and repair costs on the heat pump. Our electricity rate is low at $0.11 per kwh. I guess the potential savings generated by running the heat pump longer times in colder temperatures does not justify the risk of repairs.

 

If operating properly the worse the COP is 1.1 : 1

 

You are right, the installer is wrong and his advice will waste you money. Get rid of the heat pump lockout entirely.

 

^^^^^^^^^ what he said.

Also as you said the set back is a killer for you. Generally with a heat pump it is not recommended to set back over 5° and most don't even recommend that much. have you thought about closing the register in the bedroom and let the rest of the house stay warm, just close the bedroom door. Now having said that you will need to make sure that your airflow is adequate for the system with that register(s) closed.

 

The heat pump coil is inside the furnace's air handler.

A more common terminology would be you have a regular Air Handler with a heater kit installed or you have a modular blower is nothing more than a box with a motor and a cased coil is attached to the modular blower assembly and the heater kit is located in the modular blower box.

https://m.media-amazon.com/images/I/61axeFCIAOL._AC_SX679_.jpg

 

Modern equipment is rated for continuous operation. Your installer is ignorant.
Most heat pumps are more efficient than resistance heat down to 10° or lower. I recommend eliminating the cut off.

I suggest you eliminate the setback at night. I doubt the heat pump can recover from the setback so you're using the expensive resistance heat to warm the house. Just leave the temperature setting the same for day and night. If you want the bedroom to be colder, close the register.


Having said that, some heat pumps turn themselves off at low ambient temperatures because the suction pressure is lower than the low pressure safety. That's when your system will rely on the resistance heat alone.

 

You don't state what your 16 hour runtime temperature setting is.

Most system controls will bring on the backup/auxiliary heat source if there is a 3° difference between set point and room temperature. This plays a role in calculations for energy saving, too.

 

My thermostat is set to 72F during the day ( 16 hours ). I lower it to 65F during the night. ( I love sleeping in cool rooms). I know this practice kills most of the savings the heat pump normally generates because in the morning I am recovering to normal room temperature of 72F with the resistance elements of the auxiliary heat kicking in. I am looking for ideas to mitigate this fact, but this is another topic in itself.

The thermostat is a Honeywell T6 pro. I can adjust the delta between the setpoint and room temperature above which the aux heat will kick in. 3F gap feels a bit too wide a gap for comfort.

 

Yes, the heat pumps are more efficient well below zero IF you don't factor in spending upwards of 10 minutes an hour in cool mode. Goodman, like most, uses timed defrost. Every 30/60/90 (whatever you set to) you defrost and if below zero it may stay in defrost for the full 10 minutes. That chews up much or more of the savings for not shutting off your heat pump in bitter weather.

 

Speaking only on heat pump use.

It is designed to run 24/7 with no harm to it.

 

Yes, closing the 2 registers in my bedroom, closing the bedroom door, maybe slightly opening a window, and setting back the thermostat no more than 5° F, will be my strategy for the night.

Hard to say if my airflow is adequate. I have a 2200 sq. ft. cottage, 2 stories and a full finished basement. The temperature on the second floor tends to be 1 to 2 ° F higher than on main floor.

Getting back to the topic, there is a consensus here about getting rid if the heat pump low ambiant temperature sensor cut-off switch.

 

Yes, closing the 2 registers in my bedroom, closing the bedroom door, maybe slightly opening a window, and setting back the thermostat no more than 5° F, will be my strategy for the night.

Hard to say if my airflow is adequate. I have a 2200 sq. ft. cottage, 2 stories and a full finished basement. The temperature on the second floor tends to be 1 to 2 ° F higher than on main floor.

Getting back to the topic, there is a consensus here about getting rid if the heat pump low ambiant temperature sensor cut-off switch.

Generally this is a setting in the thermostat so it is just having him change the setting. If it is an actual switch then yes have it removed.