Heat pump expertise

[hvacjb]

Hello all,

I really appreciate all of the advice that users of this forum have provided over the years. So far I have just been reader, but now I could really use some help, especially if you are particularly knowledgeable about Carrier Greenspeed models.

To give some background, I have a medium/large house that has always had a 5-ton "dual fuel" heat pump system. Until this summer, it was a Bryant single stage and the compressor died after 13 years. I did a lot of research and found generally very positive reviews of the Carrier Greenspeed heat pumps. My local contractor provided a couple choices and I chose to "go big" by getting what I think is near the top of the line. The SEER and HSPF ratings certainly indicated it was much better than my 13 year old unit. While everything seemed to work fine over the summer, I have been really frustrated by the performance this fall and need someone to confirm whether this is expected behavior or whether something is wrong.

On my old unit, I made a habit of recording the duct air temperature through a vent that is *very* close to the main unit. I realize that there will be some differences in performance numbers, but I would expect different installations to be at least within the ballpark of other systems. I have the set point set to 68 degrees always. On my old single stage heat pump I found that the blowing air temps were *very* dependent on the outside air temperature. And for the most, they were very consistent. If it was 50 degrees outside, I would expect about 105 degrees for the blowing air temperature. And for 30 degrees outside, I found the blowing air temp to be around 85 degrees. So, generally speaking I would see a temperature that was 55-60 degrees above the outside air temperature. And for my particular home, blowing temperatures below 85 simply didn't keep the house at 68 degrees. So, I would therefore run on propane when the outside temp was below 30 degrees.

This new unit is a "variable speed" heat pump. And in these cooler fall temperatures, it generally indicates it is running at 100% capacity all the time. I generally see the blowing air temp is about 82 degrees, no matter what the outside temperature is. Also, I'm not sure I've ever even seen it above 85 degrees. I know that heat pumps aren't as warm as burning fuel. Obviously I have lived with a heat pump for the last 13 years, so I thought I knew what to expect.

So, my main questions is, does 82-83 degrees blowing air temperature seem reasonable? Since my return air is presumably around 68 degrees, I just can't believe that the best that I can expect is a temperature lift of 14 degrees (from 68 degree return air to the 82 degree blowing air). That is just so incredibly far off from what I got from my 13 year old unit where I have always seen a 22+ degree lift for outside temps 30 and above. I read so many positive reviews from owners in much colder climates than me (midwest). I just don't understand this behavior or how others manage to heat their house with 82 degree air.

So, if anyone has a new Carrier Greenspeed and can measure the blowing temperature of the air to give me something to compare, I would be very grateful. Please let me know your set point as well as the outside temp when you make the measurement. Or, if any expert has read this and can provide any guidance, I would very much like to hear from you.

Thanks everyone!

[Restaurant Mech]

You can raise or lower the temperature coming out of the registers simply by increasing or decreasing the airflow at the air handler......
Temperature coming out of the ducts means very little as far as heat pumps go. Because you have only so many btus input.
So in other words slow moving air at 105 degrees will heat pretty much the same as fast moving air at 85 degrees.
The real question is.... does it maintain house temperature?

[comfortdoc]

There is a specific sequence to test the performance of that unit. 100% does not mean it is at full capacity. It means is at the highest capacity for the current conditions. The higher the temp outside, the slower the compressor will operate. It is a bit confusing.

The Greenspeed system is designed to operate nearly constantly. To achieve this it will adjust airflow and compressor speed to gradually maintain the comfort setting. It does learn over time and will definitely get “confused” in the shoulder seasons when the outdoor temp has large swings, or you are switching from cool to heat in the same day.

Is the 68 degree temp setting maintained with no drift? As Restaurant mech posted, your dealer can choose different airflow profiles to increase delivered air temperature.

[hvacjb]

No, it does not maintain the 68 set point even though it isn't particularly cold out now (low 30s). And there in lies the problem, a little. My house does have lots of windows. And I can't say how good a job they did with insulation. That's why I thought register temps would be better than discussing house temps. I mean, if it were blowing 100 degree air and I had all my windows open, the room temp wouldn't be 68 either.

With that said, our old unit would certainly maintain 68 down to 30. To me, that was the critical temp where I had to switch to propane. One of the things that coming up over and over again about the Carrier Greenspeed was how well it did at low temps. So, my hope was that we'd be able to maintain 68 even in the 20s. As it stands, it seems like I would need to go to propane at more like 40 degrees.

I do understand your point about airflow. I guess I'm just not sure how we can measure things to know whether things are actually delivering the BTUs we should be getting. Certainly the blown air doesn't feel like it is coming out of the register at a higher rate or the "sound" of the air is any louder.

I'm assuming my airflow and duct work are all what you would expect out of a typical higher-end home. Certainly none of the contractors said anything otherwise. And FWIW, I also put in a brand new furnace. So, everything on this setup is new. But the air temps after the coil are just SO low that I find it impossible to believe that others with this same setup haven't also questioned it. I mean, everyone knows that heat pump air doesn't come out "hot" like fuel-burned air. But 82? Does *anyone* ever measure register temps that low? How on earth could my 13-year old unit seem to do better than this state-of-the-art version?

I have read other posts that talk about temperature "differential" between the return air and heated air and they have *always* been way above my measured 14 degrees.

Thank you so much for your input.

[hvacjb]

There is a specific sequence to test the performance of that unit. 100% does not mean it is at full capacity. It means is at the highest capacity for the current conditions. The higher the temp outside, the slower the compressor will operate. It is a bit confusing.

The Greenspeed system is designed to operate nearly constantly. To achieve this it will adjust airflow and compressor speed to gradually maintain the comfort setting. It does learn over time and will definitely get “confused” in the shoulder seasons when the outdoor temp has large swings, or you are switching from cool to heat in the same day.

Is the 68 degree temp setting maintained with no drift? As Restaurant mech posted, your dealer can choose different airflow profiles to increase delivered air temperature.

I am not switching from cool to heat. We're in the midwest and it was low 30s all day today. The 68 degree set point was not maintained. The thermostat has basically shown 66 degrees all day, running the equipment at 100%.

Thanks for the info about compressor and the "100%". I did not know that. Still doesn't help me even get close to where we were with the old unit. With these "profiles", it sounds like you are saying I could have higher temps, but the air output would "slower" and hence less total heat. So, I do understand that. I just can't believe that the total heat produced is so much less than our 13 year old unit. That just doesn't make any sense.

[comfortdoc]

Which furnace was installed?

There is nothing for you to do to test it. Your installer needs to follow the step by step instructions in the installation manual for each piece of the system. If that is not done performance cannot be predicted. Get the installer back. Forget the delivered air temperature. It tells nothing without a lot of other information until it is proven the system is setup and adjusted properly. Then it could be an indication of change in performance, but it still is not easy to predict with this type system. If the unit cannot maintain the comfort setting at 30 degrees outdoor temp there is something wrong. Unless the windows or doors are open.

[pacnw]

"5 ton unit in a medium/large house"

Specifically where is the home located and square footage?

Why was 5 ton selected?

What killed the old compressor, they are killed by something and don't(usually) "just fail".

[hvacjb]

"5 ton unit in a medium/large house"

Specifically where is the home located and square footage?

Why was 5 ton selected?

What killed the old compressor, they are killed by something and don't(usually) "just fail".

- Home is located in Southern Ohio
- 5 ton matched the outgoing unit which was chosen by my builder 15 years ago. The 5-ton unit covers the first floor and we have another 2.5 ton unit covering our second floor.
- No idea what killed the old compressor. I had 3 different contractors come out and they all ran tests on it and came to the same conclusion. I could have replaced the compressor, but didn't think it made financial sense on a unit that was 15 years old.

[hvacjb]

Which furnace was installed?

There is nothing for you to do to test it. Your installer needs to follow the step by step instructions in the installation manual for each piece of the system. If that is not done performance cannot be predicted. Get the installer back. Forget the delivered air temperature. It tells nothing without a lot of other information until it is proven the system is setup and adjusted properly. Then it could be an indication of change in performance, but it still is not easy to predict with this type system. If the unit cannot maintain the comfort setting at 30 degrees outdoor temp there is something wrong. Unless the windows or doors are open.

The furnace is a Carrier Infinity Gas Furnace Model#59TN6B120C241122

While there are certainly no open doors or windows, the house has lots of big windows, tall ceilings, and lots of "outside walls". So, I understand why it would be harder to heat than a typical house. I just don't understand why the 13 year old heat pump would blow lots of air at ~87 degrees (at 30 degrees outside) when the new unit feels like the same volume of air, but is only 82 degrees. I know people have said not to get hung up on air temps, but that is the only thing I can easily measure. I can't measure air throughput.

I do have the installer coming next week to look at it again. I was just hoping to get as much info as possible so I could be an informed consumer. I will certainly update the thread if I learn anything.

Thank you all for your continued help and advice!

[kdean1]

- Home is located in Southern Ohio
- 5 ton matched the outgoing unit which was chosen by my builder 15 years ago. The 5-ton unit covers the first floor and we have another 2.5 ton unit covering our second floor.
- No idea what killed the old compressor. I had 3 different contractors come out and they all ran tests on it and came to the same conclusion. I could have replaced the compressor, but didn't think it made financial sense on a unit that was 15 years old.

A builder has no business choosing a heat pump size. That’s up to the contractor (or engineer if one is involved) by calculating by means of Manual J. Since most new home HVAC contactors base sizing on floor area, they get it wrong.
You may also need a blower door test to measure and locate house leaks that increase the load.

[hvacjb]

A builder has no business choosing a heat pump size. That’s up to the contractor (or engineer if one is involved) by calculating by means of Manual J. Since most new home HVAC contactors base sizing on floor area, they get it wrong.
You may also need a blower door test to measure and locate house leaks that increase the load.

I apologize for probably mis-speaking. It was not the builder that made the decision. It was the HVAC contractor that our builder used who made that decision. I just tend to lump every contractor under the umbrella of "the builder". FWIW, I have already had a blower door test to identify leaks and make energy efficiency suggestions. That analysis didn't lead to any kind of "you should have had a different size HVAC system". So, I will continue to assume that the unit was properly sized.

Out of curiosity, are you suggesting that somehow a smaller unit (like 4 ton or whatever) would somehow be better? That it could produce *more* BTUs? Since they don't make 6 ton units, if nothing else, wouldn't this just be overkill? I apologize if I have overly simplified things.

[pacnw]

7.5 tons of cooling is HUGE for residential.

120Kbtu furnace is HUGE for a single residential unit and then you have another.

Yes, based on lack of information, size is a concern!!!!

Too big is worse on the equipment than too small.
Too big can easily be the cause of the first unit's demise.

There are calculations to determine the size of equipment needed and then the ductwork is sized to match that equipment.

This equipment is quite sophisticated and can limit itself to minimize doing damage to itself. Maybe that is what is happening, but it could just as easily be something else.
You really need a qualified tech on this type of equipment. It is specialized and many techs don't really understand how this works or what to look for.

[hvacjb]

I don't really know what to say. My builder, who has a great reputation, used his long-time HVAC contractor when the house was built 15 years ago. From reading online and talking with all the new contractors I asked to do a replacement estimate, it seems like 14 years for a heat pump is about average. All of the new contractors claimed to have spent time recalculating our needs, measuring ductwork, etc. and all of them came to the same conclusion that a 5 ton unit was appropriate and what they proposed. Our house is unconventionally long. The "left half" of the house is one story with high ceilings. The right half is more like a traditional 2 story. Total SF is about 3500. We do have an unfinished basement as well.

I am having someone out to investigate, so I will update when I learn more. Thanks again to everyone for the help!

[Adlerberts-Protege]

Ductless!!!

[pacnw]

"Total SF is about 3500. We do have an unfinished basement as well."

Again, 7.5 tons of cooling and 120Kbtus(plus whatever the upstairs unit is) of heating seems like too much.

If the ductwork is sized properly, then fine.

And I would agree that, on the average, you got good life from a heat pump.