Heat Pump calling for heat

[Ian Page]

Gentlemen

For those living in extremely warm summer climates...and I mean consistently well above 100 degs. How do you check, or do you, the heating side of a heat pump?

I ask because a recent inspection, the ambient air temp was over 105 degree at 10.30 am. The heat pump cabinet itself measured 119 and water supply somewhere in between. The cooling side ran okay and 'cooled' to about 85 as long as it was running. When not, indoor temps quickly reached into the high 90s and rising fast. Humidity was low, initially but also rising. Temps would only have increased by waiting, giving time for the system time to 'normalize'.

The hp was old - 30 years, data plate completely unreadable so I can't give any information about it. Due to age and temps I disclaimed it due to possible damage and whether it would have heated to any measurable degree.
Thoughts and advice welcome

[Mark Reinmiller]

With heat pumps I typically check either heat or AC and state what was tested and why. I do check the electric resistance backup regardless of outside temperature.

[Vern Heiler]

Gentlemen

For those living in extremely warm summer climates...and I mean consistently well above 100 degs. How do you check, or do you, the heating side of a heat pump?

I ask because a recent inspection, the ambient air temp was over 105 degree at 10.30 am. The heat pump cabinet itself measured 119 and water supply somewhere in between. The cooling side ran okay and 'cooled' to about 85 as long as it was running. When not, indoor temps quickly reached into the high 90s and rising fast. Humidity was low, initially but also rising. Temps would only have increased by waiting, giving time for the system time to 'normalize'.

The hp was old - 30 years, data plate completely unreadable so I can't give any information about it. Due to age and temps I disclaimed it due to possible damage and whether it would have heated to any measurable degree.
Thoughts and advice welcome There is no danger in harming the heat pump by going into heating mode. The highest head pressures are already there in the cooling mode, the pressures will be lower in the heating mode. Only bad side is the house gets hot if you leave it very long.

[Michael Chambers]

If the heat pump is operating as it should in A/C mode, doesn't that demonstrate that the unit works okay? Is it really necessary to then run it again in heat mode? Same thing in cold weather. If it's working as it should in heat mode, is it necessary to run it in A/C mode? I guess you might be checking to make sure that the thermostat will signal the unit to reverse, and I guess that by also checking in heat mode, you could then make sure that the emergency heat coils are putting out heat when asked for. I'm concerned however, with causing damage to the unit by switching from one mode to the other without letting internal pressures equalize. What would be a reasonable resting period for the unit, from shutting it down in one mode, to reversing it to the other mode?

[Jeff Zehnder]

When you run a heat pump in the ac mode you are not checking the operations of the three way valve or the back up heat.

[Jim Luttrall]

If the heat pump is operating as it should in A/C mode, doesn't that demonstrate that the unit works okay? Is it really necessary to then run it again in heat mode? Same thing in cold weather. If it's working as it should in heat mode, is it necessary to run it in A/C mode? I guess you might be checking to make sure that the thermostat will signal the unit to reverse, and I guess that by also checking in heat mode, you could then make sure that the emergency heat coils are putting out heat when asked for. I'm concerned however, with causing damage to the unit by switching from one mode to the other without letting internal pressures equalize. What would be a reasonable resting period for the unit, from shutting it down in one mode, to reversing it to the other mode?
Pressures do not need to equalize on heat pumps before restarting when switching modes. This is precisely what happens when the unit goes into defrost, the reversing valve switches while it is running. The unit is designed to operate. You might or might not have a delay built into the control circuit, but beyond that, don't worry about waiting. I would not operate any longer than absolutely necessary in heating mode during summer but a couple of minutes to prove it functions properly won't hurt anything.

[Nick Ostrowski]

I have been under the understanding that you can run a heat pump in either AC or heat mode base don the outside air temperature. Above 60 degrees, AC mode only. Below 60 degrees, heat mode only. This is the practice I have gone by for testing the system. I will test the auxiliary backup mode regardless of outside air temperature.

So some of you are saying a heat pump can be tested in heat mode regardless of what the outside air temperature is. Does doing this risk any type of damage to the condenser, particularly older ones?

[John Kogel]

So some of you are saying a heat pump can be tested in heat mode regardless of what the outside air temperature is. Does doing this risk any type of damage to the condenser, particularly older ones?Ask 10 inspectors, get 10 different answers.
Ask 10 HVAC guys and then pick one of those 10 answers.

Here's my theory - it won't damage some, but it might damage some. ;)

[Nick Ostrowski]

Ask 10 inspectors, get 10 different answers.
Ask 10 HVAC guys and then pick one of those 10 answers.

Here's my theory - it won't damage some, but it might damage some. ;)

Yep.

I'm not changing my inspection routine. Just curious as to what others do. I read in an older thread where some guys say they will run it in heat mode for only a minute or two just to make sure the reversing valve works but that you run the risk of damage if you run it too long. No thank you.

Due to high ambient air temperature (75 degrees) at time of inspection, heat pump system could not be tested in heat mode

[Ian Page]

Pressures do not need to equalize on heat pumps before restarting when switching modes. This is precisely what happens when the unit goes into defrost, the reversing valve switches while it is running. The unit is designed to operate. You might or might not have a delay built into the control circuit, but beyond that, don't worry about waiting. I would not operate any longer than absolutely necessary in heating mode during summer but a couple of minutes to prove it functions properly won't hurt anything.

Jim and others, thanks for your input.
"...functions properly..." Implies you are feeling/sensing/recording heat coming out of the registers. In this instance where ambient indoor temp. is in the high 80s and rising, outdoor temps already at 105, are you saying heat from the heatpump in operation (via registers) could still be established without damage to an old unit?

[Jim Luttrall]

Jim and others, thanks for your input.
"...functions properly..." Implies you are feeling/sensing/recording heat coming out of the registers. In this instance where ambient indoor temp. is in the high 80s and rising, outdoor temps already at 105, are you saying heat from the heatpump in operation (via registers) could still be established without damage to an old unit?
As with any refrigeration system, there are limits to information and operation. If you don't know what you are doing, learn more until you become comfortable with the reasons behind what you are testing and what the dangers are. (i.e.I don't test garage door operator safeties when a car is parked under the door, just because of the chance of a malfunction and damage."
Stuff happens and I am not comfortable taking the chance.

By the same token, I am well versed in A/C and I do not see any unreasonable risk in my procedure. Can I overheat a compressor, etc? Probably if I am stupid. Can I test for "normal temperature differential", no because you are outside of normal operating parameters but I can tell if the reversing valve works and if its produces heat in about a minute or less. The temperature differential from the cooling mode is a good indicator. If it does not cool, then there is no reason to proceed since it needs service.

The only caution I would give is to remember that all hermetic compressors rely on the cool gas on the suction side to provide motor cooling. The longer you run a compressor with insufficient cooling gas the hotter the compressor motor becomes and you can trip on high heat or internal bypass. When it is 105 outside and 85 inside there becomes a problem with cooling the compressor, but it is not an instantaneous problem. I run the compressor long enough to verify that heat is being produced by the heat pump and switch to emergency heat to verify the condensing unit shuts down and the backup heat begins producing heat. The entire process is usually two minutes with the compressor running and another 2-4 minute to verify the strip heaters (in most cases) are energized and producing heat.

[ROBERT YOUNG]

As with any refrigeration system, there are limits to information and operation. If you don't know what you are doing, learn more until you become comfortable with the reasons behind what you are testing and what the dangers are. (i.e.I don't test garage door operator safeties when a car is parked under the door, just because of the chance of a malfunction and damage."
Stuff happens and I am not comfortable taking the chance.

By the same token, I am well versed in A/C and I do not see any unreasonable risk in my procedure. Can I overheat a compressor, etc? Probably if I am stupid. Can I test for "normal temperature differential", no because you are outside of normal operating parameters but I can tell if the reversing valve works and if its produces heat in about a minute or less. The temperature differential from the cooling mode is a good indicator. If it does not cool, then there is no reason to proceed since it needs service.

The only caution I would give is to remember that all hermetic compressors rely on the cool gas on the suction side to provide motor cooling. The longer you run a compressor with insufficient cooling gas the hotter the compressor motor becomes and you can trip on high heat or internal bypass. When it is 105 outside and 85 inside there becomes a problem with cooling the compressor, but it is not an instantaneous problem. I run the compressor long enough to verify that heat is being produced by the heat pump and switch to emergency heat to verify the condensing unit shuts down and the backup heat begins producing heat. The entire process is usually two minutes with the compressor running and another 2-4 minute to verify the strip heaters (in most cases) are energized and producing heat.

Jim,
Great post.
Much thanks.

[ROBERT YOUNG]

Emmerson technologies (http://www.emersonclimate.com/en-ca/products/compressors/hermetic_compressors/pages/hermetic_compressors.aspx) material on Hermetic Compressors.