Heat pump questions Newbieeeeee

Okay, here goes.

Moved from the North East US where I had an oil burner/water baseboard radiator set up (Sounded like a Jet Engine) to the South East US where we now operate dual Heat Pump/AC configuration (brand unknown but purrs like a kitten in comparison).

Anyway a couple of questions. My units are about 5 years old, larger one blower unit in crawlspace handles the lower level. Smaller unit blower unit in attic handles upstairs. Both have fanned units side by side outside.

1) Its been cold here lately getting down to about 15 at night and around 35 during the day. About what temp does a unit loose effeciency and auxilary heat is needed? Both units have auxilary heat strips that can supplement heat and dramatically boost the temp at the registers. Both thermostats have dual mercury switches one for normal heat and one for "emergency heat".
It seems like the lower unit runs constantly on cold nights blowing air that is only a few degrees warmer than the room air if that much.

2) Sometimes, not always we get strange odors emitting from a few of the registers. The odors seem random sometimes downstairs in the bedroom, sometimes in the kitchen, sometimes here , there, etc. Sometimes upstairs and sometimes downstairs, sometimes not at all for a few days. It smells like the previous owner stuffed dirty laundry into the ductwork. (I hope not) I changed the filters and that seemed to help for about a week is all. Gross!!!

Please help if you can.

A lot of people can't get used to heat pumps because the air temperature expelled is very low compared to other forced air systems.

The point that your heat pump crosses over to emergency heat is usually set by the installer. It starts out at over 2 and reduces as the outdoor temperature goes down. It usually is not set lower than the temperature where the COP = 1(Coefficient Of Performance), which means that for 1kw electrical energy in, you get 1kw of heat out. If your emergency heat is not electricity, you may want change this setpoint to where the cost of that heat source equals the electrical cost.

The other way your emergency heat can come on is when there is too big a demand between the command temperature and the actual indoor temperature. Say if you setback to 55 at night and want 70 in the morning -- most systems would see this as too big a differential for the heat pump and turn on the emergency heat.

Welcome to the Forum Matt:
Air to air heat pumps decrease in efficiency on a curve from 40* down to 17*, after that there is not enough heat in the air to squeeze out. The auxillary heat kicks in when the air temp in the house is 3-5* lower than the temperature setting. Also when air to air units are running outdoors they have a tendency to frost or ice up. When that occours they momentarily reverse the flow of gasses allowing the hot gasses to defrost the outdoor unit.
Mine is a Geothermal Heat Pump with 'supplemental' heat that kicks in when the temp is 5* below the set temp and the 'auxillary' heat must be turned on at the thermostat. The ground temp remains very close to the same year-around, so there are few times we need to use the auxillary heat. Our supplemental heat kicks on about 3 or 4 nights a year because the heat pump can't keep up. That is no problem though because it indicates that the heat pump is sized correctly for the 'normal' outdoor temps we have here.
Glenn

Hi guys, can I revisit this question?

I am still getting odors from my heating system. The smell is of musty wet dog, old tennis shoe, dirty laundry, body odor type of smell. Thats the best way I can describe it. It is a moist smell at any rate. It does not happen all the time, but rather a few times a week and always when the heat pump has defrosted itself.

I say defrosted, but its not at all like the outside unit is caked with frost and needs defrosting. In fact I have never noticed an ice build up on my units. I can hear the pumps build up pressure, then there is a whooshing sound similar to a truck bleeding its airbrakes. It is at this point that the temp of the forced air inside my home rises by several degrees even though I know the aux heat is not engaged. It is also at this point that I get these awful stale odors.

I have shoved my vacuum hose as far as it will reach into each into each of the vents and pulled out various construction garbage like sawdust, scraps of drywall and wood, and a couple of soda cans but no laundry. The smell is always associated with the defrost cycle of the unit and always happens when the forced air is warmer and feels more humid right as the unit is defrosting.

Any help or suggestions here?
Thanks