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When the temp gets below about 25 degrees my heat pump doesn't work well either, it will run constantly all night long. If I know it's going to get that cold I usually just go ahead and switch it to emergency heat before going to bed. I never forget to switch it back in the morning because mine has a bright red light that comes on. Now if I were to set my thermostat to say, 85 degrees, and have the heat pump and heat strips working together, it would burn me out of here.
The refrigerant charge may be "off". While you may notice some ice on the unit during operation, it will usually disappear when the unit goes into defrost mode. You will usually hear a distinct sound when it goes into this mode, and the air coming out of the registers turns cold for a few minutes while the unit defrosts. This is normal.
Yep. Mine makes a "swoosh" sound when it starts to defrost. The fan outside will stop turning and a cloud of steam comes from it. The first time I saw it I thought the thing was about to catch fire.
Notice in this download the COP as temps drop. This is for a Goodman heatpump matching system. When you cut on your emergency heat and you have electric backup your COP is 1.00. Means you deliver 3.413 btu for each watt of energy used. Looking at the link I provided at -10*F you have a COP of 1.09. Which mean for every watt you use you produce 3.72 btu. So as you can see even when temps drop tremendously it's still more effcient to heat using the heat pump rather than the electric backup. There would probably be a different cost for gas backup. In general unless you don't mind paying for it the less you can use the electric backup the more money you will save.
In contrast when it's 60*F outside you have a COP of 3.8. or an easier way to look at it is 3.8 x 3.413 = 12.97 btu for each watt used. This would be for as properly installed/designed system that is properly charged and completely clean.
For example @ 70*F @ sea level the volume of air that it takes to make 1 lb is 13.33 cubic feet. The specific heat (amount of heat required to raise 1 lb of that item 1*F) of that air at dry conditions is .24 btu/lb. The more moisture in the air the higher the absolute heat is of that air and the more heat that is required to raise the temp of the air 1*f.
Water is the base for specific heat equation which is 1 btu to raise 1lb of water 1*F.
Notice in this download the COP as temps drop. This is for a Goodman heatpump matching system. When you cut on your emergency heat and you have electric backup your COP is 1.00. Means you deliver 3.413 btu for each watt of energy used. Looking at the link I provided at -10*F you have a COP of 1.09. Which mean for every watt you use you produce 3.72 btu. So as you can see even when temps drop tremendously it's still more effcient to heat using the heat pump rather than the electric backup. There would probably be a different cost for gas backup. In general unless you don't mind paying for it the less you can use the electric backup the more money you will save.
In contrast when it's 60*F outside you have a COP of 3.8. or an easier way to look at it is 3.8 x 3.413 = 12.97 btu for each watt used. This would be for as properly installed/designed system that is properly charged and completely clean.
For example @ 70*F @ sea level the volume of air that it takes to make 1 lb is 13.33 cubic feet. The specific heat (amount of heat required to raise 1 lb of that item 1*F) of that air at dry conditions is .24 btu/lb. The more moisture in the air the higher the absolute heat is of that air and the more heat that is required to raise the temp of the air 1*f.
Water is the base for specific heat equation which is 1 btu to raise 1lb of water 1*F.
I just figured I was saving some wear and tear on my compressor by not having it run continuously on those freezing nights.
It's totally your choice the air coming out will feel warmer with the emergency heat on for sure. In terms of thinking about wear and tear if installed correctly there should be practically nothing in the system to wear on the compressor. If properly maintained (and that means meticulous) there is no reason not to get decades of life out of a system. Unfortunately proper maintenance and instillation are rare things to see for the most part to the tune of 70% having some issue or another ending up in not so optimal conditions and the severity just depends on the various factors that are wrong.
Heat pumps don't work well when the outside air temp is below 35-ish. They are fairly efficient above 35, but terrible below and it will have to turn to a secondary system of some sort. This is why you hardly see any heat pumps in northern climates (north of Virginia on the east coast).
Tennessee (assuming you aren't in the top of the mountains of East TN - think Seivierville not Knoxville or Maryville) is somewhere where a heat pump will be great for 90% of your winter. But for those really cold night, it won't work. Also, if this is your first heat pump, the air doesn't come out feeling warm like it does with fuel-based heats. I'm in my first force-air oil house after years of heat pumps (I keep moving more north, started in TN), and I LOVE the warm air I've never had before.
I am in north Florida and have my heat pump backed up with propane heater,ranch home 1900 sq ft,helps heat pump in 23-30 nites.
The majority of problems that compressors die from happen outside normal operating conditions. Something like a leak that allows overheating of the compressor promotes the breaking down of the oil.
If someone were to be obsessively meticulous over the condition of the install and continual inspection and upkeep of the system I think it would surprise people how long the hermetic systems can last. Obviously time and money are the biggest factors in having someone maintain a system to that degree.
Mechanical failures obviously can happen but it's usually due to something happening outside of designed operations like continuous flood back from having a clogged evaporator coil or something similar. Or when it was installed the system was not properly evacuated/cleaned and the tiniest bit of moisture was allowed to mix with the ref. and oil which subsequently starts the breakdown of the windings resulting in a imminent death which a filter dryer usually takes care of small amounts of moisture trapping it in the desiccant.
Every system most certainly has a death time where it's bound to die and it starts the first second the system is started up. The best action that can be done after that point is to slow that death process down as much as possible with meticulous care through preventive maintenance like routine washing of the coils...etc.
The ability for mfg's to give longer warranties than previous times is in part due to the the growing trend of more safety items like low or high pressure switches being installed which tries to stop operation during those bad times when it might possibly operate outside of the typical or designed conditions.
That link above is a peak into how obsessive cleanliness can get and how important that cleanliness is. It's for commercial but typically the same practices should be used but on the commercial side the equipment is much more expensive and therefore it's life span is critical for business operations and downtime is obviously something that cost lots of money when the refrigerant system is critical to the operation of that business. The cost of having such dedication is usually the deciding factor for home owners as HVAC companies aren't cheap just like most other contractors.
Clean room conditions result in long life which are obviously impractical in the real world. The weird part about the story of "snowball" is it was returned for having failed and when Trane got it for warranty replacement they found nothing wrong with it and it ran for decades after the initial wrong diagnosis.
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