Carrier Infinity Hybrid System set-up

[Lucas4]

My 4 ton 25HNA948A300 heat pump and 58MVB080-F--20 was installed last month. Heat pump has been working great until outside temps dropped below 50 degrees F last week. Below 50 the house was not warming up (getting 67 degrees instead of 72) even though the heat pump was running - until the oudoor temp dropped below 40 for the gas furnace to kick in. I found out that the User Interface (UI) is set for the following outdoor lockout temps: furnace lockout is 45F and heat pump lockout is 40F. When my installer returned from his trip, he "fixed" it by raising the heat pump lockout temp to 44 and furnace lockout to 47. This means my furnace takes up the load for the heat pump sooner which increases my gas consumption. I have heard co-workers in my area (Virginia Beach ,VA) say that their gas furnace is set to take over from the heat pump at 38 degrees so why can't my 2007 model system perform to that standard? The heat pump manual says on page 3 that "continuous operation in the heating mode is approved to -30 degrees F". Thankful for your comments.

[aruddick]

I would have your heat pump checked out. we run ours down to 30 or 25 and they keep up fine. Sounds like you are not getting good performance.

[Lucas4]

What are your outside lockout temps set for in your user interface and what geographic area are you in? I'm looking for specific answers because the installer already thinks he "checked it out" and fixed it so your specific numbers will help me. Thanks for the quick reply. lucas4.

[geodude]

Did your installing contractor do a load calc on the building? I'm assuming your install was a retrofit. A load calc will determine the balance point ( the outdoor temp when back up heat should be allowed) If your contractor has not performed a load calc, then they may be assuming the first system was properly sized. But you cannot know for sure without doing a load calc. The brand of equpiment should not matter on performance, IF it is sized correctly. Have the system checked for leaks in the refrigerant system and have a load calc done.

[skippedover]

Your installer should have done a Manual 'J' calculation before specifying the size furnace and heat pump you need. The same manual 'J' can be used to determine when the heat pump can no longer keep up. I'm in Massachusetts and around here, a heat pump that is sized as it would be for cooling, e.g. 3-ton AC needed, 3-ton heat pump installed, runs out of capacity at about 38 to 40 degrees, depending on the manufactuer's specs. Based on that, I'd latch out the HP at 40. I don't latch out the gas furnace at all but rather keep it available anytime the heat pump might not be doing the job. If the C/B were to trip for some reason while I was away from the house for the day, even though it's 45 or 50-degrees, I'd rather have the furnace come on and heat the place than to come home to cold house. A little reduncancy never hurt, IMO. :D

[Lucas4]

Did your installing contractor do a load calc on the building? I'm assuming your install was a retrofit. A load calc will determine the balance point ( the outdoor temp when back up heat should be allowed) If your contractor has not performed a load calc, then they may be assuming the first system was properly sized. But you cannot know for sure without doing a load calc. The brand of equpiment should not matter on performance, IF it is sized correctly. Have the system checked for leaks in the refrigerant system and have a load calc done.

My installer was the only one out of about 7 who took the time to do a load calc right in my living room. He also was one of the few who quoted a 4 ton system vice 5 ton Goodman that I had. One contractor told me he was quoting me the 5 ton because he didn't want me calling him back when the outside temp was 100 degrees but I believe in the "bigger is not better" school of thought when it comes to hvac. He has checked for leaks and I guess I can get a "second opinion check" from another contractor but isn't the balance point the same temp for everybody in my city? Can you give any more leads? Thanks.

[Lucas4]

Your installer should have done a Manual 'J' calculation before specifying the size furnace and heat pump you need. The same manual 'J' can be used to determine when the heat pump can no longer keep up. I'm in Massachusetts and around here, a heat pump that is sized as it would be for cooling, e.g. 3-ton AC needed, 3-ton heat pump installed, runs out of capacity at about 38 to 40 degrees, depending on the manufactuer's specs. Based on that, I'd latch out the HP at 40. I don't latch out the gas furnace at all but rather keep it available anytime the heat pump might not be doing the job. If the C/B were to trip for some reason while I was away from the house for the day, even though it's 45 or 50-degrees, I'd rather have the furnace come on and heat the place than to come home to cold house. A little reduncancy never hurt, IMO. :D

My installer did the manual J before specifying the size furnace and heat pump I need. My old system had a 5 ton Goodman. I agreed with him that bigger is NOT better. If he had kept my furnace available all the time (like the way you do it), I would never have been alerted to this problem because the furnace would keep the house warm. Before I ask him to replace the heat pump, I want some technical reasons why my heat pump can't keep up with warming the house all the way down to 40 degrees. Thanks for your reeply.

[skippedover]

There are actually two different balance points. One is for comfort, the other for economy. So again, the calculations need to be done. With the Carrier Infinity series, the contractor can check the history of the last 10-system faults as well as the general operating history. Have him check that out and see what the various faults are. Maybe the heat pump is tripping off due to low or hi pressures. It can also go into various lockouts for up to 4 hours at a time. There could very well be a mechanical reason the heat pump is not keeping up but just resetting the temperatures is not the best way to determine if there's a problem. Again, the load calcs should tell right away if the unit if properly sized and if it is, then there is definitely something wrong. If you can't get anywhere with the installing contractor, then contact Carrier yourself and they'll get you some help. They're very good about that. ;)

[geodude]

Every home is different when it comes to loads. The winter design temp or "wet bulb" will be the same for everyone in your area but you may have a different indoor design temp then somebody else. The load calc program is only as accurate as the info plugged into it. Ask your contractor to show you a copy of the load calc and explain it to you. If they are a reputable company they will have no trouble doing this for you. A detailed trouble shooting of the system may turn up a "gremlin" previously unnoticed. Keep a log of temps indoor and out thermostat settings and run times then show them to the tech, sometimes this will help the tech responding to the service call. Good luck!

[Lucas4]

There are actually two different balance points. One is for comfort, the other for economy. So again, the calculations need to be done. With the Carrier Infinity series, the contractor can check the history of the last 10-system faults as well as the general operating history. Have him check that out and see what the various faults are. Maybe the heat pump is tripping off due to low or hi pressures. It can also go into various lockouts for up to 4 hours at a time. There could very well be a mechanical reason the heat pump is not keeping up but just resetting the temperatures is not the best way to determine if there's a problem. Again, the load calcs should tell right away if the unit if properly sized and if it is, then there is definitely something wrong. If you can't get anywhere with the installing contractor, then contact Carrier yourself and they'll get you some help. They're very good about that. ;)

You're heading me in the right direction. I'll call Carrier. I wanted to say that I stood by as he checked the last 10-system faults - yes there were some "31-high pressure switch open" and "32-low pressure switch open" and "161-excess static pressure stagedown" and "zone 3 airflow limited stage down occured" events but his answer was to just increase the heat pump lockout from 40 to 44 degrees after he checked the charge in the system. That answer doesn't satisfy me and if my contractor is at his wits end, I guess I have to call carrier - we'll see how good their headquarters customer service is. If there is anything you care to add, please do. thanks-a-million.

[skippedover]

You're heading me in the right direction. I'll call Carrier. I wanted to say that I stood by as he checked the last 10-system faults - yes there were some "31-high pressure switch open" and "32-low pressure switch open" and "161-excess static pressure stagedown" and "zone 3 airflow limited stage down occured" events but his answer was to just increase the heat pump lockout from 40 to 44 degrees after he checked the charge in the system. That answer doesn't satisfy me and if my contractor is at his wits end, I guess I have to call carrier - we'll see how good their headquarters customer service is. If there is anything you care to add, please do. thanks-a-million.

Well at least now we've got a little more to go on. I'd guess from the fault history that the heat pump refrigerant circuit has some non-condensables in it. That can make the pressures go crazy as the NC's migrate from one part of the system to another. The "excess static pressure stagedown" events are not faults. Usually those are associated with zone damper movement. Apparently you've got a zoned system and sometimes the dampers don't move quickly enough to satisfy the blower needs, so the blower is commanded to slow down. But the high and low pressure faults are likely the cause of your discomfort with the heat pump. Full refrigerant recovery, new filter driers, thorough evacuation using a micron gauge and a full recharge with virgin refrigerant and I'm betting you'll have a nice system. ;)

[Lucas4]

Every home is different when it comes to loads. The winter design temp or "wet bulb" will be the same for everyone in your area but you may have a different indoor design temp then somebody else. The load calc program is only as accurate as the info plugged into it. Ask your contractor to show you a copy of the load calc and explain it to you. If they are a reputable company they will have no trouble doing this for you. A detailed trouble shooting of the system may turn up a "gremlin" previously unnoticed. Keep a log of temps indoor and out thermostat settings and run times then show them to the tech, sometimes this will help the tech responding to the service call. Good luck!

"Every home is different when it comes to loads" - from that perspective my contractor could be right by saying that my insulation is poor and thefore needs to raise the temp at which my furnace should take over from the heat pump. I know he did one so I'll get a copy of the load calc - then what do I do with the numbers - no pun intended? It will not change the fact that the heat pump can't warm up my house to 72 when outdoor temp is say 46. The discussion is useful and I'm thankful so hit me again.

[Lucas4]

Well at least now we've got a little more to go on. I'd guess from the fault history that the heat pump refrigerant circuit has some non-condensables in it. That can make the pressures go crazy as the NC's migrate from one part of the system to another. The "excess static pressure stagedown" events are not faults. Usually those are associated with zone damper movement. Apparently you've got a zoned system and sometimes the dampers don't move quickly enough to satisfy the blower needs, so the blower is commanded to slow down. But the high and low pressure faults are likely the cause of your discomfort with the heat pump. Full refrigerant recovery, new filter driers, thorough evacuation using a micron gauge and a full recharge with virgin refrigerant and I'm betting you'll have a nice system. ;)

:( ... Thanks Dr. Skippedover. That sounds like the panacea I need. I'll ask my contractor for that. I wonder what I should say when he protests, you know, many doctors don't like being told what to prescribe for you even though he has failed to prescribe the correct medication. Does his contention that my 1960 house probably has poor insulation (I could use more in the attic) hold any water? So I can get poor performance at lower outdoor temps because of NC gases? I'm all smiles. Thank you very much and good night.

[Dave-B]

Originally Posted by skippedover.
from the fault history that the heat pump refrigerant circuit has some non-condensables in it. That can make the pressures go crazy as the NC's migrate from one part of the system to another..... But the high and low pressure faults are likely the cause of your discomfort with the heat pump. Full refrigerant recovery, new filter driers, thorough evacuation using a micron gauge and a full recharge with virgin refrigerant and I'm betting you'll have a nice system.
:)
I just had this very situation this week. New biflow, tripple evac to 500 microns, fresh charcge and running great. Left both lockouts at 40.

[tag1956]

Sounds like its low on gas, When it was started was the charge adjusted by sub-cooling. I find this to be the best way for a correct charge

[mike d373]

codes 31 and 32 have to do with the furnace. Have a service tech check it all out.

[dash]

:( ... Thanks Dr. Skippedover. That sounds like the panacea I need. I'll ask my contractor for that. I wonder what I should say when he protests, you know, many doctors don't like being told what to prescribe for you even though he has failed to prescribe the correct medication. Does his contention that my 1960 house probably has poor insulation (I could use more in the attic) hold any water? So I can get poor performance at lower outdoor temps because of NC gases? I'm all smiles. Thank you very much and good night.

As the temperature drops the amount of heat needed to heat your home increases,and the amount of heat provided by the heat pump decreases.This can be graphed ,and where the two lines cross is the "balance point" at which you need to bring on the furnace.

Homes with better insulation,etc.,will have a much lower balance point then then poorly insulated,etc..No question about it.

Stage down can also indicate an undersized duct system.

Calling Carrier will cause a call to the distributor who will call your dealer.I'd just ask the dealer to get the distributor's customer service folks to help them out .

Maybe a call to the owner is all that will be needed.

[aruddick]

My 4 ton 25HNA948A300 heat pump and 58MVB080-F--20 was installed last month. Heat pump has been working great until outside temps dropped below 50 degrees F last week. Below 50 the house was not warming up (getting 67 degrees instead of 72) even though the heat pump was running - until the oudoor temp dropped below 40 for the gas furnace to kick in. I found out that the User Interface (UI) is set for the following outdoor lockout temps: furnace lockout is 45F and heat pump lockout is 40F. When my installer returned from his trip, he "fixed" it by raising the heat pump lockout temp to 44 and furnace lockout to 47. This means my furnace takes up the load for the heat pump sooner which increases my gas consumption. I have heard co-workers in my area (Virginia Beach ,VA) say that their gas furnace is set to take over from the heat pump at 38 degrees so why can't my 2007 model system perform to that standard? The heat pump manual says on page 3 that "continuous operation in the heating mode is approved to -30 degrees F". Thankful for your comments.

I did a little checking this morning and your 4 ton heat pump at 50 degrees should produce 50,000 btu and at 40 degrees should produce 40,000 btu of heat. The reason I feel it is a heat pump issue is that your furnace is only 80,000 btu. If you have over 40k heat loss at 40 deg. There is no way that furnace will heat at 0. As for where we are . Southern Indiana. A little north of where you are.

[Lucas4]

Originally Posted by skippedover.
from the fault history that the heat pump refrigerant circuit has some non-condensables in it. That can make the pressures go crazy as the NC's migrate from one part of the system to another..... But the high and low pressure faults are likely the cause of your discomfort with the heat pump. Full refrigerant recovery, new filter driers, thorough evacuation using a micron gauge and a full recharge with virgin refrigerant and I'm betting you'll have a nice system.
:)
I just had this very situation this week. New biflow, tripple evac to 500 microns, fresh charcge and running great. Left both lockouts at 40.

Thanks for the additional INSIGHT! I'll request this specific service recommended by you & skippedover. I'll be plenty satisfied to leave both lockouts at 40. Sure will be nice to have guys like you around - a huge credit to your profession.

[Lucas4]

Sounds like its low on gas, When it was started was the charge adjusted by sub-cooling. I find this to be the best way for a correct charge

I'll find out if "the charge was adjusted by sub-cooling" but can you please elaborate on how to do this. Is it important to also ask my dealer if the new lineset connected to my new heat pump was "purged with nitrogen"?

[RyanHughes]

I'll find out if "the charge was adjusted by sub-cooling" but can you please elaborate on how to do this. Is it important to also ask my dealer if the new lineset connected to my new heat pump was "purged with nitrogen"?

This has nothing to do with whether or not your lineset was purged with nitrogen. I'm not sure why a new lineset would be flushed with nitrogen anyway. Give your installing company a call and have them come out, hook up gauges, and check the pressures of the system.

[Yeah]

I have woken from a very deep sleep, have lots to share.

[tag1956]

Sub-cooling is done at the condenser, you take your pressure an temp at the high side service valve an convert the pressure to temp most manufacture's want a 12 degree temp change. That will give you the right charge,an the best performance. You said line set I hope they pulled at least a 500 micron vaccum on it before opening the service valves,especially if its a 410 system

[aruddick]

Sub-cooling is done at the condenser, you take your pressure an temp at the high side service valve an convert the pressure to temp most manufacture's want a 12 degree temp change. That will give you the right charge,an the best performance. You said line set I hope they pulled at least a 500 micron vaccum on it before opening the service valves,especially if its a 410 system

On that Carrier 19 seer heat pump you can only get an accurate subcooling reading in cooling mode. If you try that in heating it won't be even close to corret charge. They do come with a heat referance chart on the door.That will give an idea of how the unitis running

[RyanHughes]

Tag1956: Don't the necessary superheat and subcooling readings vary depending on the ambient conditions? I thought a wetbulb measurement determined what they should be. Any clarification on this would be appreciated.

[codywatkins]

Is your thermostat set at one temperature and you leave it there. Or are you trying to have the heat pump recover from a set-back?

I know my heat pump was driving me absolutely crazy a few months back with the furnace always coming on, but that was because I still had a 5 degree C setback. Once I changed it to a 1 degree C setback, the heatpump never calls for the furnace lately. It can usually handle the 1 degree C rise. (Carrier Performance 25HPA)

Oh, and you shouldn't be questioning your insulation as the heat load calculations should have taken your exact insulation situation into account?

[dash]

"Stage down can also indicate an undersized duct system."

Check this out.

[hvacrmedic]

As the temperature drops the amount of heat needed to heat your home increases,and the amount of heat provided by the heat pump decreases.This can be graphed ,and where the two lines cross is the "balance point" at which you need to bring on the furnace.

Homes with better insulation,etc.,will have a much lower balance point then then poorly insulated,etc..No question about it.


I'm going to call that into question. If the systems are correctly sized for two neighboring houses, and if the systems have identical performance curves, then the balance points will be very close to equal. One house may be well insulated and the other poorly insulated.

In the real world poor insulation won't typically be accounted for correctly by the installing contractor, leading them potentially to undersize the system. It is this human error that leads to higher thermal balance points rather than the poor insulation of the house per se.

[tag1956]

Tag1956: Don't the necessary superheat and subcooling readings vary depending on the ambient conditions? I thought a wetbulb measurement determined what they should be. Any clarification on this would be appreciated.

Yes the readings do vary,But 12 degrees is a good starting point. Now if its 50 deg. out you'll be looking for around 6 to 8. most units will have a graft on the control panal with ambient temp an what they want in cooling mode. Now this is best done in warmer weather for a correct charge but that ain't allways the way