use of energy by hvac - is there a crankcase heater?

I've been trying to work on energy efficiency at my house and have over the years noticed the use of energy by crankcase heaters for my heat pump/AC systems:

http://en.wikipedia.org/wiki/Crankcase_heater#cite_note-6" onclick="window.open(this.href);return false;
http://hvac-talk.com/vbb/showthread.php?444262-Crankcase-Heaters" onclick="window.open(this.href);return false;

It appears to be necessary to run this, in order to prevent damage to the system. The draw on my home energy seems to be something on the order of 20-30 watts. Not sure if it's continuous 24x7, or if it's only a portion of the day (1/3?) as one person indicated. Maybe it depends on the system.

This got me to wondering if there is a crankcase heater in a vehicle's HVAC system and, if so, whether in a BEV or PHEV it is a significant draw on energy when the vehicle is on, or off.

I haven't seen any mention of any (compressor) crankcase heater in the leaf, or for any car for that matter. Cars use R-134a which might have different properties than R-22 when it comes to interacting with the oil.

I've heard it's a good idea to run a car AC system once a week for a few minutes to make sure everything stays properly lubricated. With most (all?) modern cars running the AC system when in defrost mode, I imagine this is well taken care of.

JeremyW said:

I haven't seen any mention of any (compressor) crankcase heater in the leaf, or for any car for that matter. Cars use R-134a which might have different properties than R-22 when it comes to interacting with the oil.

I've heard it's a good idea to run a car AC system once a week for a few minutes to make sure everything stays properly lubricated. With most (all?) modern cars running the AC system when in defrost mode, I imagine this is well taken care of.

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Ok, thanks. Maybe it's a matter of that R-134a vs R-22.

No it is a manner of how they operate, in a residential system you have a large oil sump that the refrigerant migrates to and absorbs into the oil, on start up this will cause foaming and liquid hammering on top of thinned oil. Very damaging to the system. The motor and pump both reside in this oil bath and there will usually be over 500Ml of oil

In an automotive system the driving motor is external to the pump and the valving is more rugged, so even if the oil foams there is little impact to the unit, and there is far less oil in the system as well less then 500Ml.

XeonPony said:

No it is a manner of how they operate, in a residential system you have a large oil sump that the refrigerant migrates to and absorbs into the oil, on start up this will cause foaming and liquid hammering on top of thinned oil. Very damaging to the system. The motor and pump both reside in this oil bath and there will usually be over 500Ml of oil

In an automotive system the driving motor is external to the pump and the valving is more rugged, so even if the oil foams there is little impact to the unit, and there is far less oil in the system as well less then 500Ml.

Click to expand...

Ok, thanks for the additional clarity on this. I guess the related question is what is it about the smaller automotive system that allows for a different approach to HVAC than a larger system such as a residence or office.

smaller volume of pipe work. and the fact the drive motor is not inside the compressor housing.

Due to small oil charge it leaves much less to worry about.

XeonPony said:

smaller volume of pipe work. and the fact the drive motor is not inside the compressor housing.

Due to small oil charge it leaves much less to worry about.

Click to expand...

Ok, thanks.

jlsoaz said:

It appears to be necessary to run this, in order to prevent damage to the system. The draw on my home energy seems to be something on the order of 20-30 watts. Not sure if it's continuous 24x7, or if it's only a portion of the day (1/3?) as one person indicated. Maybe it depends on the system.

Click to expand...

It definitely depends on the system - and it's one thing that drives me crazy on my heat-pump system, especially in my mild climate where I don't need to run the A/C or heat very often. Quite a large vampire draw when you consider how many HVAC units are out there. I usually disconnect my compressor completely when I won't be home a while and make sure I don't use the HVAC for 24 hours afterwards.

drees said:

jlsoaz said:

It appears to be necessary to run this, in order to prevent damage to the system. The draw on my home energy seems to be something on the order of 20-30 watts. Not sure if it's continuous 24x7, or if it's only a portion of the day (1/3?) as one person indicated. Maybe it depends on the system.

Click to expand...

It definitely depends on the system - and it's one thing that drives me crazy on my heat-pump system, especially in my mild climate where I don't need to run the A/C or heat very often. Quite a large vampire draw when you consider how many HVAC units are out there. I usually disconnect my compressor completely when I won't be home a while and make sure I don't use the HVAC for 24 hours afterwards.

Click to expand...

Yes, everything you say is what is on my mind about my own new multi-zone system, including the part about contemplating the vampire draw during lengthy stretches of temperate weather. However, if I turn it off (whether due to temperate weather or because I am traveling), I am concerned that when I turn the circuit back on I will forget to leave the whole thing alone for a day or so (or whatever the recommended number of hours is).