Experience with Heat Pump in Really Cold Weather?

[brucet999]

Has anyone used MY heat pump in really cold weather?
Anyone know what ambient temperature is too low for HP to work effectively?
If there is a backup resistance heater, I'm not sure whether a user could even tell if HP is working.

 

[jstjohnz]

I have wondered about that also. A typical residential heat pump's efficiency makes it impractical to use much below 20-30F. I haven't seen any mention of backup heat coils but there must be something like that since the system has to work well below 0 degrees.

 

[Barrygold]

Watch this. Look like 0 degrees F is when the heat pump will lose its efficiency and then become as efficient as the previous resistance heating technology in the Model 3/S/X.

 

[mongo]

Has anyone used MY heat pump in really cold weather?
Anyone know what ambient temperature is too low for HP to work effectively?
If there is a backup resistance heater, I'm not sure whether a user could even tell if HP is working.

From the patent, the compressor motor and electronics can be run inefficiently to act as a resistive heater (along with the addition of mechanical work). So it can work at any temp, just with lower efficiency.
The blower fan can theoretically do the same, and there are two low voltage heaters in the cabin (for split temp).

 

[SSedan]

I have wondered about that also. A typical residential heat pump's efficiency makes it impractical to use much below 20-30F. I haven't seen any mention of backup heat coils but there must be something like that since the system has to work well below 0 degrees.

I run my Fujitsu home system as low as -25f though it begins having trouble keeping up with the losses in my 1970s house below about -15f, and this saves us money overall vs the old baseboard electric. I am sure it loses a lot of efficiency at those temps but it does work. Was told it functions to -28f.

 

[Barrygold]

I run my Fujitsu home system as low as -25f though it begins having trouble keeping up with the losses in my 1970s house below about -15f, and this saves us money overall vs the old baseboard electric. I am sure it loses a lot of efficiency at those temps but it does work. Was told it functions to -28f.

That makes sense, that refrigerant boils at -15 F.

 

[Bill Price]

That makes sense, that refrigerant boils at -15 F.

Really? Who told you that? Whomever told you that couldn't be more wrong.

 

[Barrygold]

Really? Who told you that? Whomever told you that couldn't be more wrong.

It’s on the YouTube video above and Google search returns similar results. I am not an engineer however. Simply regurgitating info.

 

[mongo]

It’s on the YouTube video above and Google search returns similar results. I am not an engineer however. Simply regurgitating info. View attachment 595324View attachment 595325

The piece of information missing is that boiling point is dependant on pressure. That table is 14.7 psi data (1 atmosphere) versus what the high and low pressure sides run at.

 

[brucet999]

From the patent, the compressor motor and electronics can be run inefficiently to act as a resistive heater (along with the addition of mechanical work). So it can work at any temp, just with lower efficiency.
The blower fan can theoretically do the same, and there are two low voltage heaters in the cabin (for split temp).

I get how the energy provided by the compressor can be used to provide heat, but how can the blower fan make heat?

 

[mongo]

I get how the energy provided by the compressor can be used to provide heat, but how can the blower fan make heat?

The same way as the drive unit motors and compressor motor, they use an inefficient drive waveform that results in extra current flow in the stator windings generating heat through resistive losses.

 

[Darmie]

The same way as the drive unit motors and compressor motor, they use an inefficient drive waveform that results in extra current flow in the stator windings generating heat through resistive losses.

Couldn't said it better than myself. All joking aside, I often thought this is very similar to how resistive heating is done. Instead of just heating up a coil, they're heating up a winding. I take it that it's more efficient since they are using same power to turn motor as well.

 

[brucet999]

The same way as the drive unit motors and compressor motor, they use an inefficient drive waveform that results in extra current flow in the stator windings generating heat through resistive losses.

That might work for an in-line fan, but not a squirrel cage blower where the motor is outside the air path.

 

[mongo]

Couldn't said it better than myself. All joking aside, I often thought this is very similar to how resistive heating is done. Instead of just heating up a coil, they're heating up a winding. I take it that it's more efficient since they are using same power to turn motor as well.

Capturing the motor heat is advantageous during heating modes, but the extra heat is still a COP of 1 like resistive.

That might work for an in-line fan, but not a squirrel cage blower where the motor is outside the air path.

The air path can still be routed around the motor on a squirrel cage type.

Note: the fan as aux heat was mentioned in the patent, but I have not seen confirmation of it being used.

 

[brucet999]

Capturing the motor heat is advantageous during heating modes, but the extra heat is still a COP of 1 like resistive.


The air path can still be routed around the motor on a squirrel cage type.

Note: the fan as aux heat was mentioned in the patent, but I have not seen confirmation of it being used.

 

[brucet999]

"The air path can still be routed around the motor on a squirrel cage type."

With about 60% reduction in air flow, perhaps. If their patent claims heat from blower motors, then they must be axial.

 

[mongo]

"The air path can still be routed around the motor on a squirrel cage type."

With about 60% reduction in air flow, perhaps. If their patent claims heat from blower motors, then they must be axial.

If the motor is in the plenum/ air space it will provide heat (either pre or post blower), no need to go directly through the side of the cage. Or am I missing something here?

 

[brucet999]

If the motor is in the plenum/ air space it will provide heat (either pre or post blower), no need to go directly through the side of the cage. Or am I missing something here?

What you are missing, I think, is any experience with squirrel cage blowers. The air path never comes close to the motor, whose long shaft has the blower wheel mounted to it.

 

[mongo]

What you are missing, I think, is any experience with squirrel cage blowers. The air path never comes close to the motor, whose long shaft has the blower wheel mounted to it.

Have experience. Still don't see a reason why the motor can't be in the ductwork connected to the blower outlet.

Or why it can't be in the inlet like this style: [Hot Item] 48VDC Squirrel Cage Dual Inlet Centrifugal Blower Fan with 146mm Impeller

 

[brucet999]

Have experience. Still don't see a reason why the motor can't be in the ductwork connected to the blower outlet.

Or why it can't be in the inlet like this style: [Hot Item] 48VDC Squirrel Cage Dual Inlet Centrifugal Blower Fan with 146mm Impeller
View attachment 595714

That could work. Never saw one like that. 48VDC - where would a thing like that be used, I wonder?