Heat Pump Not Keeping Up. What Do I Do?

 
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Old 01-18-2005, 08:08 PM   #1
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Heat Pump Not Keeping Up. What Do I Do?


Let me start off by saying I purchaced this house a little over 2 years ago. I had a home warrante at the time. The heat pump wasn't working properly. I put a digital thermometer in the vents and when the heat kicked on the temp would rise out of the vents. Then the unit would turn on the outside unit and the warm air turned into 60 degree air. Needless to say I had many cold days. I had a contractor from my home warrante place come out. It took 2 techs later to figure out some little wire was never hooked up to the outside unit. After that it worked much better.

To date. It seems that maybe my unit is too small, or just cant keep up. I know I obviously need to replace some windows with bad seals on them. But the air coming out of the vents doesnt seem warm to me. Let me get you my unit #'s and maybe that can help.

The unit is a carrier
inside unit 40Aq030300BB
outside unit 38qno24310sm

The house is 1120 sq ft. My basement is also finished with a full 1120 sq ft. The basement is 3/4 in the ground with a walk out if that makes any difference. The people that lived here tapped into the floor ducts and pulled air vents into the basement rooms. I have almost eliminated all of these. It is cooler in the basement but now it is a little warmer in the main floor.

I have 2 returns 1 on the main floor in the hall. 25x20 and one 20x20 celing tile vent in the basement with a 6 in. duct coming off of it.

I hope I gave some helpful insite to my house. If their is anything I left out please ask.

The last 2 days it has only been around 20 degrees outside. My unit is running NON-stop. On the little control box it doesn't even kick on to Emergency heat. If I do it manualy I GET HEAT. Normal setting produces a whopping 77 degrees coming out of the vent. If I bump up the temp on the thermastat it goes into AUX mode and gives me a whole 80-81 degrees. Now if I put it on EMER. I get 100+ coming out. Now I know that is probably extreme and I can't expect that all the time without paying for it. I still feel I should have better that 80 coming out of the vent with normal heating shouldn't I.

Not that it may matter or not. But in the summer when it gets around 95 degreees. The house can't seem to get cool either. I have good insulation in the roof. Still I know I have to replace windows and that is coming this spring. I do have double pain glass windows. Some of them are leaking.

What gives? Do I need to upgtrade my unit? units? What should I look for if I want to stay with a heat pump.

Sorry for all the questions, and the long post. This has been bugging me for 2 years or better now.
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Old 01-18-2005, 08:24 PM   #2
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Re: Heat Pump Not Keeping Up. What Do I Do?


Here are some pics of the inside unit and outside unit.
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Heat pump not keeping up.  What do I do?-carrier.jpg   Heat pump not keeping up.  What do I do?-carrier2.jpg  

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Old 01-19-2005, 12:19 AM   #3
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Re: Heat Pump Not Keeping Up. What Do I Do?


A What are your current temps? Heat pumps were touted as the BIG thing during the energy crisis of the 70's and have since faded into oblivion.
I have had a few and realized little difference unless it really was cold and then it did nothing.
I have a personal opinion and little expertise. Doc will be along.
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Old 01-19-2005, 07:15 AM   #4
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Re: Heat Pump Not Keeping Up. What Do I Do?


Your supply air temp. will vary depending on your return air temp. Generally speaking a heat pump becomes inefficient to operate under about 30 degrees F. There is not enough heat in the outside air to justify running the outside unit. Under 30 outside you should just run emergency heat. That way you get the most bang per kilowatt hour.
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Old 01-19-2005, 10:17 AM   #5
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Re: Heat Pump Not Keeping Up. What Do I Do?


Your heat pump should be more than 100 percent efficient down to a temp somewhere around ten below zero F. The point that is typically around 30 degrees F where the heat pump is not able to keep up in a standard construction house is called the balance point, where the heat load of the house is equal to the amount of heat the heat pump is able to supply. Below this temp, which varies from house to house depending on insulation, heat pump size, etc, the heat pump cannot keep up and needs assistance from the strip heaters.

Typically, the heat pump coefficient of performance(COP) is somewhere around 2 at 30 degrees f, meaning the heat pump is still 200% efficient, and still cheaper to run than the strip heaters, which are 100 % efficient. So dont turn the pump off at this pump, just let the thermostat determine how much help the heat pump needs from the strip heaters.
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Old 01-19-2005, 10:47 AM   #6
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Re: Heat Pump Not Keeping Up. What Do I Do?


This is ironic that you posted this just after my posting asking about what temperature a heat pump has a COP of 1.0 My new ICF house with a heat pump has surprised me from how easy it is to heat. But I built the whole thing myself, and made sure everything was done right, including good doors and windows, and a well insulated flat attic.(R50 Cellullose)

You state that your unit was running non stop, and not kicking in your strip heaters. But was your house maintaining temperature? If you were right at your balance point, and maintaining temp, the strip heaters would not kick in, and your unit would run non-stop. If you have an electronic thermostat, they will bring in the strip heaters if the house temp falls about 1.2-1.5 degrees below the set point. Some of the old mercury controllers allow a larger drop, around 3-5 degrees before they kick the strip heaters in.

Your problem could be one of 2 things, either your pump is undersized or not operating at 100%, or the heat loss of the house is excessive. You say you have good insulation in the attic, what is it? I personally prefer cellullose, it is more effective than fiberglass. Fiberglass looses its insulation value the colder it gets: at minus 8 degrees it has loss half of its insulating value. I blew in 16 inches of cellullose in my attic to get R-50. Anything less than that is not enough as far as I am concerned. If you have fiberglass in your attic I would cap it off with about 8-10 inches of cellullose. This is something you can do yourself, and do it cheap, probably around 400 dollars.

Uninsulated basements are another big heat sink, 8 inches of concrete has an R value less than 1, same as a single pane window. Sounds like a lot of yours is exposed. You say it is finished, I wonder how much insulation it has in it. So if you basement is not well insulated, that would be another loss. Even though you have a lot of air flow blocked off to the area now, it would still hurt you to some degree.

So I would attack this problem from both angles. I would make sure your compressor is fully charged to maintain its power and efficiency and get the controls checked out. But I would also reduce the heat loss of your house. A lot of electric companies will come to your house and do a heat loss study for free, I would get this done if at all possible.
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Old 01-19-2005, 11:17 PM   #7
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Re: Heat Pump Not Keeping Up. What Do I Do?


I wouldn't say heat pumps have run their course, still many going in around the country. And, technology and efficiency has improved vastly over the past 20 yrs. That being said, I agree with what has been said about getting the unit gone through top to bottom and even trying to reduce some of the heat loss you might have. Heat pumps are critical in sizing for the fact too many contractors size them strictly on the a/c side of it alone. So if they come up with a 5 ton heat gain on the a/c end, they just automatically assume it will need 60,000 BTU worth of heating. If you are considering replacement of the system (and frankly even if you aren't) I would get a Manual J load calculation done on the home. This is more than just X tons per sq. ft rule of thumb, it takes into account your insulation, roof composition, windows, doors, etc. and gives a very accurate picture of what your house needs for heating and cooling. I would also have your ductwork checked using a Manual D to make sure there is proper return and supply for the system.
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Old 01-21-2005, 08:39 PM   #8
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Re: Heat Pump Not Keeping Up. What Do I Do?


WOW Thanks for all the replys. I was thinking this site would email me when I had a reply....I just checked in to see what was going on and I had all of these responces. You guys are great.

Now for the constant running of the unit. I figured that out. The wife had the gas fire place on. So she flipped on the fan on the heatpump. So it would pull the warm air out of the living room and push it in other rooms. My living room is only 14x14 with a small gas fire place. So needless to say it gets warm very fast in that room. Fortunately the return is just outside this room and can pull the heat.

Someone asked for the temperatures. It's been in the 10's at night and mid upper 20's during the day. The heat pump still runs, and it does kick on the AUX heat. I assume this is the strip heaters you guys are talking about. Are those heaters the same that is used for the EMER. heat. But just those and no outside unit. Just curious and trying to figure this stuff out.

I had a local insulating company come out last spring/summer. I had him look into my insulation in the attic. He said it is sufficien, but he would be more than willing to take my money to add more. He was very honest. He said take this $600 for insulation and put it towards new windows. My windows are getting replaced. It was supposed to be done by a friend last fall, but you know how some friends can be.....Looks like spring will be the time for them now.

I do have insulation in my walls in my basement. I have floor trusses, and those are insulated around the outside of the walls too. I just read the R value of them It is R13. I poped the tile and it is still warm. I pulled the little piece of insulation on the outer wall to get the r value and it was cold on the paper side. So It is working good.

My unit was cleaned last year the coils were sprayed, pressures were checked and all was good. I thing (with my non expert opinion) that my unit was sized for the house upstairs and not downstairs. Origonally the downstairs was bare and open.
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Old 01-22-2005, 08:00 AM   #9
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Re: Heat Pump Not Keeping Up. What Do I Do?


Sounds like you are in fairly decent shape except for your windows. The insulating contractor sounds like a really honest person. He is right in that windows are a big area of heat loss and a top priority for money spent. I would still climb up there and check out the insulation for myself, sounds like you know what to look for.

The problem is this: 98 percent of the contractors out there think that r-38 fiberglass insulation is fine. In my opinion(for what little that is worth) it is not. I think r-50 using anything that does not convect air is needed. If you want to stick to fiberglass, that is fine but you would need to add r-38 unbatted over whatever you have now to come close to being equal to r-50 cellullose.

In summary: If you go up in your attic and see r-38 fiberglass, or less, you need more insulation. If you see cellullose and it is less than 14 inches deep, you need more insulation.

Sorry for getting off the HVAC trail, but the heat load is part of the equation.
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Old 01-22-2005, 11:18 PM   #10
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Re: Heat Pump Not Keeping Up. What Do I Do?


Ohh no you are not off track. It is all realative to my issues. i will check the insulation. As a matter of fact. I'll do it now. I have pull down stairs.

R-30

Well I guess that may answer a few questions. I did some reading on homes in my area, and what the insulation R value should be. I did check it at the time and it was good. We do get some cold months here in Southern Maryland. Usually around 30 for a low good 2 months. Mostly up around 40 though. Then in the summer we get upper 90's for a good few days-weeks depends, mostly lower 90's for about 2 months I guess.

Looks like I should get some of that insulation... :Thumbs:
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Old 01-23-2005, 08:35 PM   #11
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Re: Heat Pump Not Keeping Up. What Do I Do?


I didnt realize you guys had that fewer degree heating days than us here in southern indiana, but looks like Harford County Maryland shows about 4600 degree heating days, whereas we are about 5200 dhh. Sounds like prime heat pump climate to me. A little bit of cellullose blown over the fiberglass couldnt hurt. I blew about 16 inches in my home.
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Old 01-23-2005, 08:47 PM   #12
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Re: Heat Pump Not Keeping Up. What Do I Do?


Ohh so you could look up my needs for my area. That is cool. A little more insulation my be the ticket
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Old 01-26-2005, 03:39 PM   #13
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Re: Heat Pump Not Keeping Up. What Do I Do?


From that M # it looks like you have a 2 ton unit (024 = 24,000 BTU's @ 12,000 BTU's per ton)

I am in southern NJ. Rules-of-Thumb are no substitute for proper engineering calculation and design. Nonetheless; let's ramble about this thing for a bit -

Around here it takes about 1 ton of A/C to cool about 500 - 600 square feet of floor space. Which makes you about right for cooling if it's like NJ weather where you live.

And it takes about 20-25 BTU's per square foot of space for heating.

The real problem with applying an air conditioning unit as a heat pump to provide heating is that the typical heating and cooling loads requirements are so different.

Humidity control is critical to cooling performance and so the A/C sizing needs to be right on the money. The heat pump is almost always too small and it's heat output must be added to with some other form of heat. Most often this is done with electric elements.

Now; a heat pump, when heating, provides about 15,000 BTU's per ton under ideal conditions - say on a 50-55 degree day. This output reduces radically at lower temperatures. I would have to see the performance curves on your equipment to project exactly where the 'zero return' point is, but it's likely about 10-15 degrees outdoor temp.

As the temperture falls outside two things happen -

1. You house requires more BTU's to heat it.

2. Your heat pump is able to supply less BTU's to heat your house.

First you need to make your heat pump work it's best and so minimize the time that you have to use addditional heat.

I'm going from memory here but I would think that 80-90 degree discharge air is about normal for a heat pump system.

the outdoor unit has a temp sensing function that tell the inside portion when to add more heat. This may be set wrong on yours. At 20 degrees I would think it should have been enabled already.

We'll come back to thermostat functioning, but first tell me if you have a digital thermostat?

PHM
-------------------------------------







Quote:
Originally Posted by RKM
Let me start off by saying I purchaced this house a little over 2 years ago. I had a home warrante at the time. The heat pump wasn't working properly. I put a digital thermometer in the vents and when the heat kicked on the temp would rise out of the vents. Then the unit would turn on the outside unit and the warm air turned into 60 degree air. Needless to say I had many cold days. I had a contractor from my home warrante place come out. It took 2 techs later to figure out some little wire was never hooked up to the outside unit. After that it worked much better.

To date. It seems that maybe my unit is too small, or just cant keep up. I know I obviously need to replace some windows with bad seals on them. But the air coming out of the vents doesnt seem warm to me. Let me get you my unit #'s and maybe that can help.

The unit is a carrier
inside unit 40Aq030300BB
outside unit 38qno24310sm

The house is 1120 sq ft. My basement is also finished with a full 1120 sq ft. The basement is 3/4 in the ground with a walk out if that makes any difference. The people that lived here tapped into the floor ducts and pulled air vents into the basement rooms. I have almost eliminated all of these. It is cooler in the basement but now it is a little warmer in the main floor.

I have 2 returns 1 on the main floor in the hall. 25x20 and one 20x20 celing tile vent in the basement with a 6 in. duct coming off of it.

I hope I gave some helpful insite to my house. If their is anything I left out please ask.

The last 2 days it has only been around 20 degrees outside. My unit is running NON-stop. On the little control box it doesn't even kick on to Emergency heat. If I do it manualy I GET HEAT. Normal setting produces a whopping 77 degrees coming out of the vent. If I bump up the temp on the thermastat it goes into AUX mode and gives me a whole 80-81 degrees. Now if I put it on EMER. I get 100+ coming out. Now I know that is probably extreme and I can't expect that all the time without paying for it. I still feel I should have better that 80 coming out of the vent with normal heating shouldn't I.

Not that it may matter or not. But in the summer when it gets around 95 degreees. The house can't seem to get cool either. I have good insulation in the roof. Still I know I have to replace windows and that is coming this spring. I do have double pain glass windows. Some of them are leaking.

What gives? Do I need to upgtrade my unit? units? What should I look for if I want to stay with a heat pump.

Sorry for all the questions, and the long post. This has been bugging me for 2 years or better now.
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Old 01-26-2005, 03:45 PM   #14
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Re: Heat Pump Not Keeping Up. What Do I Do?


John,

I do heat load calculation fairly often and I have noticed that the different factors for a double paned window and a single glazed window with a decent storm window is not all that much different. <g>

PHM
---------------------------------





Quote:
Originally Posted by John
Sounds like you are in fairly decent shape except for your windows. The insulating contractor sounds like a really honest person. He is right in that windows are a big area of heat loss and a top priority for money spent. I would still climb up there and check out the insulation for myself, sounds like you know what to look for.

The problem is this: 98 percent of the contractors out there think that r-38 fiberglass insulation is fine. In my opinion(for what little that is worth) it is not. I think r-50 using anything that does not convect air is needed. If you want to stick to fiberglass, that is fine but you would need to add r-38 unbatted over whatever you have now to come close to being equal to r-50 cellullose.

In summary: If you go up in your attic and see r-38 fiberglass, or less, you need more insulation. If you see cellullose and it is less than 14 inches deep, you need more insulation.

Sorry for getting off the HVAC trail, but the heat load is part of the equation.
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Old 01-26-2005, 04:17 PM   #15
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Re: Heat Pump Not Keeping Up. What Do I Do?


No good old mercury thermastat. I put a level on it. It is perfect. It is a box not the round one.

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