Heat Pump Weirdness

[Doug]

I have a combination heat pump/ac unit in my garage. I've owned this place for 1 1/2 years and I've never been satisfied with either function of this unit. The heated/cooled space is 30x30 and is well insulated. The symptoms are these:

At a given temperature, the heat output can vary by as much as 15 degrees. I never know what I'll get, but the best heat comes out after a long inactive period. This morning I ran the heat (50 degrees outside and I had 86 degrees out of the vents. After it ran for a while it became 80 degrees (which is about what I normally see). I do have a differential of approximately 10 degrees between the output and the return. The filter is clean.

Occasionally the heat output is really warm, but that's a rarity (this is regardless of outside temperature.)

This is a Concept 2000 unit with an Emerson 47D01U-843 controller. I had a reputable HVAC company here to look at it a couple of weeks ago and the guy recommended replacing the controller with the one that was OEM to the unit. He had a real distaste for my controller. He made sure the refrigerant was correctly charged, cleaned the fins and checked my output/return temperature and said 'that's the way it is and get used to it.'

Under the current circumstances, this thing takes an eternity to raise the temperature 5 or 6 degrees even when it's 50 out. It's even longer when the temperature is 40-ish. (Also know that I keep the thermostat set at 60 degrees overnights.)

I think I'm spending way to much on electricity to get mediocre HVAC, given that the unit has to run so long to satisfy the thermostat. This is my first experience with a heat pump, so I don't know what to expect for performance.) Do my symptoms ring a bell with anyone? Thanks -

 

[Milton Shaw]

If the temp is raised more than 2 degrees on most heat pumps you are on heat strips which will use 3 times the electricity of the heat pump itself. That accounts for the temp difference you see with the initial temp higher on heat strips than later on the heat pump itself. Most heat pumps are made to set at a temp and leave it, for the most efficiency.

 

[Bert_]

Set it and forget it. If you want it 60* in there just leave it there. Don't do setbacks, manually lower the temperature or turn it off.

Most heat pumps also have resistive coils in the air handler. They will give you much warmer air and will raise the temperature in your space faster but, as said above, cost much more to operate.

If you are trying to raise the temperature often then you are using the resistive strips often. It may actually be cheaper just to leave it running all the time.

 

[dcg9381]

I
I think I'm spending way to much on electricity to get mediocre HVAC, given that the unit has to run so long to satisfy the thermostat. This is my first experience with a heat pump, so I don't know what to expect for performance.) Do my symptoms ring a bell with anyone? Thanks -

It sounds like something is wrong if in reasonable temps (say above 40 degrees) you're not getting consistent heat.

It's normal for heat pump output to vary in colder temps.. Here, you can literally see the coils freeze up on the compressor, the heat will lose performance, and then it will return to heating after the compressor de-ices. During defrost cycles, there is no heating.

It's not normal for heat output to vary that much in moderate temperatures.

Can you provide a performance chart for your unit?

There are heat pump units that are performant in really cold climates, but this certainly isn't the case with the units that I've installed (Daikin) and the residential units that have been in my home in Texas. Basically, below 30, the performance drops off pretty miserably. Below 20, you're not producing much heat at all and you're spending a lot of energy to run the compressor and defrost cycles... Northern climates really need heat pumps designed to perform in cold weather.

 

[metlmunchr]

If you want to set the temp back at night then you should add an outdoor heat pump thermostat. It will lock out the auxiliary heat anytime the outdoor temp is above whatever temp you set it to. As it stands now, you're doing most of your warm up with resistance heat which, as stated above, uses 3X the electricity to produce the same heat as the heat pump.

 

[u3b3rg33k]

I have a combination heat pump/ac unit in my garage. I've owned this place for 1 1/2 years and I've never been satisfied with either function of this unit. The heated/cooled space is 30x30 and is well insulated. The symptoms are these:

At a given temperature, the heat output can vary by as much as 15 degrees. I never know what I'll get, but the best heat comes out after a long inactive period. This morning I ran the heat (50 degrees outside and I had 86 degrees out of the vents. After it ran for a while it became 80 degrees (which is about what I normally see). I do have a differential of approximately 10 degrees between the output and the return. The filter is clean.

Occasionally the heat output is really warm, but that's a rarity (this is regardless of outside temperature.)

This is a Concept 2000 unit with an Emerson 47D01U-843 controller. I had a reputable HVAC company here to look at it a couple of weeks ago and the guy recommended replacing the controller with the one that was OEM to the unit. He had a real distaste for my controller. He made sure the refrigerant was correctly charged, cleaned the fins and checked my output/return temperature and said 'that's the way it is and get used to it.'

Under the current circumstances, this thing takes an eternity to raise the temperature 5 or 6 degrees even when it's 50 out. It's even longer when the temperature is 40-ish. (Also know that I keep the thermostat set at 60 degrees overnights.)

I think I'm spending way to much on electricity to get mediocre HVAC, given that the unit has to run so long to satisfy the thermostat. This is my first experience with a heat pump, so I don't know what to expect for performance.) Do my symptoms ring a bell with anyone? Thanks -

that's my favorite smart defrost unit. I would get another HVAC guy if he doesn't like it. all it does is decide when to defrost, (either based on temp sensors or time). it will have NO effect on heat output unless it's not defrosting properly and the outside coil is iced up. you should be able to verify that part pretty easily.

information we don't know:

• 
  unit tonnage.
  indoor temp
  unit setpoint
  load on the unit. 'well insulated' and 'garage' are typically excusionary terms.
  thermal mass in the garage?
  condition of outside coils? are they functionally attached to the coil? or are they rotted out?
  does the compressor run the entire time? is it cutting in/out? any icing on the compressor housing?
  across-the-coil ∆T. we care less about vent temp, there's a lot more variables there.
  what kind of metering unit do you have? cap tube? TXV?

cap tube systems need to basically have EXACTLY the right charge or performance will be terribad. this is often a "vacuum it out and fill by weight" fix, not a "pressures looked ok" deal.


for the money i'd probably throw in a 24k mini-split and call it a day. you can get a DIY one for not a lot of money (under $2k).