Electric Heat Pump

[SagaLore]

Originally posted by: CorCentral
I've read that most heat pumps lose their ability to heat efficiently when the temperature outside reaches in the low 30's.

I don't know about new pumps, but in general, heat pumps are more efficient at heating when there is more heat. That is why its by far more efficient to use heat pumps with ground pipe circulation, rather than with outside air.

 

[SagaLore]

Since we're on the topic of heat pumps...

I have an old central air gas furnace and ac unit. The ac unit is shot, and I have problems with the compressor. I've been told that if I were to replace the ac unit, the location of it is no longer to code for new units, so I'd have to put it on another side of the house, which would require a lot of re-ducting and wiring. That sucks.

The furnace is a horizontal unit that sits in the crawl space. I think they built the house over it. How big of a heat pump would I need to heat/cool 1700 sqft in NC weather? Could it also be installed in the crawl space, or am I kind of screwed either way?

 

[boomerang]

Originally posted by: MadScientist
Corcentral,
You stated that it got down to 10F last night but the house temp stayed at 65F. Did you have your thermostat set at 65F or 71F? Did the aux (gas/electric furnace) heat kick in?

Heat pumps are assigned two efficiency ratings, a SEER rating based on a unit's cooling efficiency and a HSPF rating based on a unit's heating efficiency.
SEER Rating
The SEER (Seasonal Energy Efficiency Ratio) rating is used to identify the cooling efficiency of both traditional air conditioners and heat pumps. The SEER rating indicates how efficiently the unit utilizes electricity: the higher the rating, the less electricity the unit requires to cool a given area.
HSPF Rating
The HSPF (Heating Seasonal Performance Factor) rating is used to identify the heating efficiency of heat pumps: the higher the rating, the less electricity the heat pump uses to heat a given area.
There's also COP. Link

The newer heat pumps are more efficient. I replaced my 22 year old Heil HP and electric furnace last summer with a Carrier Infinity 15 Seer/9.0 HSPF HP and matching electric furnace with the high end thermostat. The Heil still had its original compressor, but yearly maintenance costs were starting to rise and so were my electric rates. So far no problems with the Carrier and my electric bill has dropped. The installer, a former Heil now Carrier dealer, said my old Heil had a 7 SEER rating.

Here's a few sites to check out for further info: Link1 and Link2. The Halowell HP is discussed in a number of posts.

Originally posted by: boomerang
I've got a air to air HP here and had one at my last house.

I replaced the A/C and the furnace at this house and for a grand more, I went with a HP. I've got a Carrier system with one of their mega dollar thermostats. I can set the Lockout Temp (the minimum temperature at which the HP will run) as low as 5 degrees. When the system was installed the guy that did the work was unfamiliar with the system and left the thermostat set at the default which I think was 25 degrees.

This was way too low. The HP would heat the house and it was very comfortable, but it would run for hours and hours and hours. Finally, one Saturday morning I realized what was happening and bumped it up to 35 degrees. I have since bumped it up to 40 and now have it set at 45 degrees and am waiting for spring to see how it performs at this setting.

Bommerang,
Sounds like we have the same mega dollar Infinity Control thermostat. I checked my Install/Service menu and under Lockout Temp it gives me the option of None(Default) and +5F to 55F. According to the manual, this is the outside temp above which the the furnace will NOT run except for defrost. So with yours set at 45F, at 45F and under the furnace will kick on. Correct? This temp seems a bit high to me. Mine is set to None(Default). This morning it got down to 8F here in WV. I had the thermostat set to 66F and the HP alone, no aux heat, was holding it at 66F (the aux will kick in if there is a 2F difference between the thermostat settiing and house temp). The HP seemed to be in an idle type mode, very quiet, with the inside fan running very slow. Yes, it ran a long time between shutdowns due to decreased efficiency, but is it cheaper to run it this way or run my electric furnace at say a 15F or 20F lockout temp? At 25F outside temp my HP runs fine, staying on for about a half hour with the thermostat set at 69F.

MS

Yeah, we've got the same stuff. Correct on the interpretation on the temperature stuff. Now remember, my furnace runs on natural gas. So as I said, I'm trying to determine the most efficient way to use this system.

I don't know what to set this at. I've asked the dealer that installed it and all I get is a blank look. I called Carrier and they referred me to my dealer. Now, I just dialed it up to 45 degrees recently. I had it set at 40 degrees. As I said, I was waiting to see what happens late winter or early spring when the temperature rises. Are you dialing down during the night? I've got mine dialing down 3 degrees at night and it takes about one a half hours to get up to temp in the morning. This seems like an awfully long time to me.

My house is 20 years old. It's 1550 sq. ft., 2x4 construction with full insulation and 1" of styrofoam on the outside surround by Tyvec. I don't remember the R value in the ceiling but there is batt insulation covered by blown in. I have double pane casement windows. The point being that my house may not be constructed as efficiently as yours.

There are so many variables in this that I am just overwhelmed and it appears I have no one to turn to that can tell me anything with any certainty.

I'd be really willing to exchange some PM's on this if you'd like. Take the discussion out of the thread. I'd like to exchange some ideas. I know that I expected to get far lower heating and cooling bills, but then again there are a lot of variables. Price per KWh for electric and price per Cubic Foot of gas and so on.

Edit: spelling

 

[boomerang]

Originally posted by: SagaLore
Since we're on the topic of heat pumps...

I have an old central air gas furnace and ac unit. The ac unit is shot, and I have problems with the compressor. I've been told that if I were to replace the ac unit, the location of it is no longer to code for new units, so I'd have to put it on another side of the house, which would require a lot of re-ducting and wiring. That sucks.

The furnace is a horizontal unit that sits in the crawl space. I think they built the house over it. How big of a heat pump would I need to heat/cool 1700 sqft in NC weather? Could it also be installed in the crawl space, or am I kind of screwed either way?

I'm far from an expert on this and if you read my post above, that will confirm it. I'll add what I can to try and help you out.

You really need a HVAC company to come out and do a survey of your home. That's the true way to determine what you need. The take into effect the construction, age and condition of the home, the sun load, exposure and so on and so forth. I can just about guarantee that your replacement can't go in the crawl space. For these units to work effeciently, they need a lot of airflow. It may need to be on the other side of the house to take the sun load off of it too. Is it on the South side now?

As I said earlier, I upgraded to a HP from just having A/C because as a portion of the total cost it was not that great. I'm in SE Michigan and it's debatable whether that was really a cost-effective thing to do. Where you're at, I would think it makes perfect sense to go with a HP. Edit: I should add that part of what influenced my decision to go with the HP was federal tax credits that were in effect at that time.

Hope this helps some.

 

[NoShangriLa]

Electric Heat Pump

You mean air source or geothermal heatpumps?

Airsource heat pumps ultilize outside air temperature to exchange heat energy with indoor temperature.

Geothermal heat pumps ultilize ground/water to exchange heat energy with indoor temperature.

Heat pumps sizing depend on the volume, R or U factor, and windows/doors of the space being heated/cool.

Efficiency depends greatly on outside temperature & humidity vs. indoor set temperature. SEER valve is the rating of efficiency of heat pump (higher mean better), therefore heatpumps energy consumption varied from model to model.

Most air source heatpumps (ASHP) energy return compare to electric heater in mild coastal climate can be as high as 3.5-3.7:1 return (3.5W out to 1W in) in ideal situation. However in real practice it is somewhere between 1.5-2.5:1 return (pending SEER rating, and refrigerant level).

As temperature drop efficiency drops, most ASHPs require emergency heat (backup heat source) to kick in at -1C to -3C if sizing correctly and pending SEERs rating (at -1C to -3C most ASHP is around 1.5:1, and efficiency quickly drop off after that ). Refrigerants efficiency of heat transfer at 1:1 usually approach up to -22C, pending refrigerant type, condenser & evaporator size, and compressor efficiency.

It is possible to design very high SEER (such as 24-25 SEER) by over size condenser/evaporator and high quality compressor, but the return is relatively low in energy saving compare to the extremely high initial install fee. Today price vs. efficiency sweet spot is 18-22 SEERs.

Geothermal run off ground/water temperature pending area constant ground temperature 4' below frost level. But most high SEERs should see a constant 2-3:1 energy return. Geothermal becomes very economical over traditional heating or ASHP in extreme hot/cold climate.

Search older threads for gas, electric, and wood heat source that I have posted for more information on traditional heat sources.

 

[NoShangriLa]

EDIT: One thing I forgot to add, is that the heat pump is well underrated for the size of my house. It's a 2ton unit/2000sq ft

As posted above heatpump sizing greatly depends on volume, R or U factor of said house. A modern home with adequate insulation, and in mild climate ASHP can be rate as low as 1 ton per 1000 square feet at 97.5% standard seasonal rating. Over size doesn't mean better, it might get your house cool quickly in AC mode, but it just mean that the heatpump cycling more often which translate to poor efficency and possibly lower the service life of the heatpump.

Correct sizing of heatpump is critical for efficiency, and emergency backup heat source (generally electric heating coils on the supply line within the first 2' of air handler ducting) is there to pick up the slack for the 2.5% occasion that temperature drop below seasonal standard.

 

[NoShangriLa]

If your system occasionally blows very cold air this could indicate a problem with your supplementary heating as it not engaging during a defrost cycle would mean air at least 20 degrees F cooler than ambient out of the registers!

Finally a non functioning supplementary heat is very bad when temperatures drop to levels where the heat pump on its own cannot sustain a comfortable indoor temperature. Total failure of the heat pump altogether with no working supplementary heat results in a total loss of ALL heat.

Look up icing of coils & compressor.

 

[Rubycon]

Originally posted by: NoShangriLa

Look up icing of coils & compressor.

😕

Heat pumps should have a rather large suction accumulator to prevent winter slugging. This vessel can freeze if repeat cycles don't remove all ice or ice is at the bottom of the coil (vertical wraparound coils are most vulnerable) and suction pressure is lower than normal, etc. Slugging should not occur prior to LPS cutout! 😉

But the aux heat contactor is supposed to be energized during the defrost cycle!

 

[NoShangriLa]

How big of a heat pump would I need to heat/cool 1700 sqft in NC weather? Could it also be installed in the crawl space, or am I kind of screwed either way?

Depends on how well the house insulated and how drafty it is.

If it is an older house, and not having seen it nor test it I would say at the very least 2 ton, but more likely 2.5 ton. There are many make & models that can accomodate vertical or horizontal install. Duct work in crawspace isn't that difficult to mod to accomodate airhandler and location. Older furnace setup supply duckwork is slightly smaller than require for heatpumps, but it isn't a problem if you don't mind higher friction rating calculation (slightly noisier air flow than correct calculation for residential application), however the installer must find or resize return air opening to make sure that it can satisfy the blower CFM rating. Undersize return air can lead to inefficency and/or not fully ultilized the heatpump capacity.

 

[NoShangriLa]

Originally posted by: Rubycon

Originally posted by: NoShangriLa

Look up icing of coils & compressor.

😕

Heat pumps should have a rather large suction accumulator to prevent winter slugging. This vessel can freeze if repeat cycles don't remove all ice or ice is at the bottom of the coil (vertical wraparound coils are most vulnerable) and suction pressure is lower than normal, etc. Slugging should not occur prior to LPS cutout! 😉

But the aux heat contactor is supposed to be energized during the defrost cycle!

In ideal situation all of the failsafe work according to design, but in real practice they can fail that lead to slugging/icing of compressor. An experience tech can tell if icing has occured with out the need to open the heat pump for inspection by the hum of the compressor and the clacking noise of ice. If the situation is prolong and failsafe didn't kick in, the compressor will fail and the replacement of compressor is almost as much as the purchase of a new heatpump :Q

😉

 

[Rubycon]

Originally posted by: NoShangriLa
An experience tech can tell if icing has occured with out the need to open the heat pump for inspection by the hum of the compressor and the clacking noise of ice. If the situation is prolong and failsafe didn't kick in, the compressor will fail and the replacement of compressor is almost as much the purchase of a new heatpump :Q

😉

What if he is deaf? 😛

Pressures would be key. 😉

Also it would depend largely on the compressor type. Recips can be damaged a lot easier than scrolls or swash plates.

We are getting sidetracked here - sorry for the HIJACK guys! :Q

 

[MadScientist]

Yeah, we've got the same stuff. Correct on the interpretation on the temperature stuff. Now remember, my furnace runs on natural gas. So as I said, I'm trying to determine the most efficient way to use this system.

I don't know what to set this at. I've asked the dealer that installed it and all I get is a blank look. I called Carrier and they referred me to my dealer. Now, I just dialed it up to 45 degrees recently. I had it set at 40 degrees. As I said, I was waiting to see what happens late winter or early spring when the temperature rises. Are you dialing down during the night? I've got mine dialing down 3 degrees at night and it takes about one a half hours to get up to temp in the morning. This seems like an awfully long time to me.

My house is 20 years old. It's 1550 sq. ft., 2x4 construction with full insulation and 1" of styrofoam on the outside surround by Tyvec. I don't remember the R value in the ceiling but there is batt insulation covered by blown in. I have double pane casement windows. The point being that my house may not be constructed as efficiently as yours.

There are so many variables in this that I am just overwhelmed and it appears I have no one to turn to that can tell me anything with any certainty.

I'd be really willing to exchange some PM's on this if you'd like. Take the discussion out of the thread. I'd like to exchange some ideas. I know that I expected to get far lower heating and cooling bills, but then again there are a lot of variables. Price per KWh for electric and price per Cubic Foot of gas and so on.

Edit: spelling

Our houses are very similar. Mine is 26 years old, 1800 sq. ft., same construction and insulation, double pane windows, except I have ~12" fiberglass insulation batts in my attic. That's about an R factor of 38, which is about the minumum for my area. How much insulation do I need?. You may not have enough attic insulation. Blown in insulation has a R value per inch less than fiberglass batts.
I spoke to the HVAC dealer that installed my system about raising the Lockout Temp. He suggested I leave it at the None (Default) setting and that at 8F it is still pulling some heat out of the air. I find that hard to believe, but my HP still runs fine at 8F, and the guy has been in the HVAC/plumbing business for 35 years, but if the temp gets lower than 8F here I think I'm going to set it at 10F.
With the price of gas being what it is, I would suggest you lower your Lockout Temp and run your HP as much as possible and not your gas furnace.
I programmed my thermostat to 66 at night and to raise it to 68 in the morning. It takes about 1/2 hour to get it to 68.
Are you getting any ice build up on the outside coils? I would have the installer come out and check if you have any refrigerant leaks and if he filled the system with the right amount.

 

[boomerang]

Originally posted by: MadScientist

Yeah, we've got the same stuff. Correct on the interpretation on the temperature stuff. Now remember, my furnace runs on natural gas. So as I said, I'm trying to determine the most efficient way to use this system.

I don't know what to set this at. I've asked the dealer that installed it and all I get is a blank look. I called Carrier and they referred me to my dealer. Now, I just dialed it up to 45 degrees recently. I had it set at 40 degrees. As I said, I was waiting to see what happens late winter or early spring when the temperature rises. Are you dialing down during the night? I've got mine dialing down 3 degrees at night and it takes about one a half hours to get up to temp in the morning. This seems like an awfully long time to me.

My house is 20 years old. It's 1550 sq. ft., 2x4 construction with full insulation and 1" of styrofoam on the outside surround by Tyvec. I don't remember the R value in the ceiling but there is batt insulation covered by blown in. I have double pane casement windows. The point being that my house may not be constructed as efficiently as yours.

There are so many variables in this that I am just overwhelmed and it appears I have no one to turn to that can tell me anything with any certainty.

I'd be really willing to exchange some PM's on this if you'd like. Take the discussion out of the thread. I'd like to exchange some ideas. I know that I expected to get far lower heating and cooling bills, but then again there are a lot of variables. Price per KWh for electric and price per Cubic Foot of gas and so on.

Edit: spelling

Our houses are very similar. Mine is 26 years old, 1800 sq. ft., same construction and insulation, double pane windows, except I have ~12" fiberglass insulation batts in my attic. That's about an R factor of 38, which is about the minumum for my area. How much insulation do I need?. You may not have enough attic insulation. Blown in insulation has a R value per inch less than fiberglass batts.
I spoke to the HVAC dealer that installed my system about raising the Lockout Temp. He suggested I leave it at the None (Default) setting and that at 8F it is still pulling some heat out of the air. I find that hard to believe, but my HP still runs fine at 8F, and the guy has been in the HVAC/plumbing business for 35 years, but if the temp gets lower than 8F here I think I'm going to set it at 10F.
With the price of gas being what it is, I would suggest you lower your Lockout Temp and run your HP as much as possible and not your gas furnace.
I programmed my thermostat to 66 at night and to raise it to 68 in the morning. It takes about 1/2 hour to get it to 68.
Are you getting any ice build up on the outside coils? I would have the installer come out and check if you have any refrigerant leaks and if he filled the system with the right amount.

I'm really glad I posted in this thread. It's great to have somebody with a similar system to talk with. What I've just done is set everything back to defaults. I think that my natural curiosity and the fact that I like to tinker with things led to my changing a bunch of settings I should have left alone.

IIRC, the Infinity system with the Infinity thermostat has enough intelligence to make some smart decisions on when to run what. I'm going to let it do it's thing and see what happens.

Quite the coincidence today. I got home from doing some running around and the house felt kind of chilly. I ignored it for some time and eventually looked at the thermostat and the temp had dropped to 64. I normally have it at 70. I checked and there are 2 system events recorded. I ran the checks in the thermostat menu and everything checked out OK and the system began heating and it's working fine now. I called and a tech is scheduled to come out tomorrow. I'm still within the parts warranty and the dealer wants $79 for the service call. I guess I'm going to go ahead and have him come out.

As far as the coils, well the HP hasn't run for the last 6 weeks or so and I never really paid any attention. Today I had to go out and knock 8 to 10" of snow off the top of the condensing unit and beat on the top to get the snow off the fan blades. Once I changed the settings in the thermostat I knew it was going to start up. I went outside and the motor on the fan was stalled due to all the snow. I got there just in time.

You may have missed it but I have blown in over the batts.

Edit: In the morning, have you ever noticed if the system is running solely off the HP or if the supplemental heating is kicking in? I'm going to look at this tomorrow now that I've set everything back to defaults. My thinking is that if the HP alone cannot raise the heat at a satisfactory rate, that the supplemental will kick in to get the temp up.

Maybe I'm thinking too much again? 😀

What pissed me off was the dealer I dealt with was very happy to sell me the system and install it. But his knowledge is very limited. I asked him what that was all about and he started bellyaching that Carrier wanted him to send his guys to factory training and he didn't want the expense and lost time. I really wish I'd had the forethought to ask him this before I signed on the dotted line.

I want to apologize to the OP, we've really taken over his thread. Let us know if it's a problem and we'll move it elsewhere.

 

[MadScientist]

Getting back to one of the OP's questions about HP size. A 2 ton unit for a 2000 sq ft older house could be undersized. You need to get a good reputable HVAC contractor to calculate your house's heating load. The standard measure of a heating load is a Manual J calculation, and it takes into account your house's insulation, size, amount of shade, and many other factors. HVAC Sizing Calculations.
My HVAC contractor calculated I needed a 2.5 to 3 ton unit for my 1800 sq ft house, and that we needed more return air to balance the system. We went with the 3 ton unit and he added another return air duct.

Boomerang,
In the morning the system is running only off the HP. The only time I have seen the aux heat come on is when we are away for a few days and I turn the thermostat way down and then kick it up more than 2 degrees; or if the wife gets her mitts on the thermostat.
Don't mean to be critical but why did you buy a HP if you let it sit for 6 weeks idle? The snow and ice that accumulated on and in it probably caused the 2 system events.
When the dealer makes his service call I would have him also check out the Infinity thermostat to insure you have all the right settings.
I was just about to ask why the $79. service charge until I read my warranty. It states that the warranty does not include labor or other costs incurred for diagnosing, repairing, installing, shipping, servicing or handling of either defective parts, or replacement parts. It only covers the cost of a new or remanufactured part. WTF, that sucks.

Good Luck!

MS

 

[boomerang]

Originally posted by: MadScientist
Getting back to one of the OP's questions about HP size. A 2 ton unit for a 2000 sq ft older house could be undersized. You need to get a good reputable HVAC contractor to calculate your house's heating load. The standard measure of a heating load is a Manual J calculation, and it takes into account your house's insulation, size, amount of shade, and many other factors. HVAC Sizing Calculations.
My HVAC contractor calculated I needed a 2.5 to 3 ton unit for my 1800 sq ft house, and that we needed more return air to balance the system. We went with the 3 ton unit and he added another return air duct.

Boomerang,
In the morning the system is running only off the HP. The only time I have seen the aux heat come on is when we are away for a few days and I turn the thermostat way down and then kick it up more than 2 degrees; or if the wife gets her mitts on the thermostat.
Don't mean to be critical but why did you buy a HP if you let it sit for 6 weeks idle? The snow and ice that accumulated on and in it probably caused the 2 system events.
When the dealer makes his service call I would have him also check out the Infinity thermostat to insure you have all the right settings.
I was just about to ask why the $79. service charge until I read my warranty. It states that the warranty does not include labor or other costs incurred for diagnosing, repairing, installing, shipping, servicing or handling of either defective parts, or replacement parts. It only covers the cost of a new or remanufactured part. WTF, that sucks.

Good Luck!

MS

I've reset mine for a two degree drop in temperature overnight. I had it at three so I'll see what happens. However, in looking through the manuals, there is a setting that allocates ninety minutes for the system to slowly ramp up the temperature after being turned down according to the schedule. So, with mine being enabled as it is, it's actually functioning exactly as it should.

The HP was not running because I had set the cut off temp too high. My own mistake because I kept fiddling around with it. As I said, it's all back at defaults and so far the HP seems to be doing its thing as would be expected. The HP would not run regardless of the snow buildup, because it was locked out from running by my setting the thermostat the way I did. The system events are furnace related. High pressure switch open and inducer fault.

Part of the problem is that the dealer is clueless. Remember I said that he didn't know anything about the Infinity system and when I called Carrier they said I must talk to the dealer. A Catch-22 situation. Maybe the dealer has gotten smarter in the two and a half years since the install.

As I mentioned earlier, I've read through the manuals to refresh my memory. There is somewhat conflicting information, but it appears that the thermostat will notify me in the event of a problem. I had to look through the menus to find these system events, they did not pop up on their own and there are others in there going back several years. I think I'm going to cancel the appointment. If I don't get a repeat of the problem, or an actual error message on the thermostat, I'm going to ignore it for the time being. I'm thinking it might not be a bad idea to power off the system and unplug and plug back in every connector and board. Additionally, there is an amber light on the circuit board in the furnace that is designated to flash codes. There are no stored codes. It will store codes for 72 hours and that time period has not passed. I think what I had going on would be termed an intermittent problem.

Thanks for all your input.

 

[SuperjetMatt]

Originally posted by: jagec
What do you mean by "efficiency"?

If you're using a heat pump to heat your house, OVER 100% of the energy consumed will be found in your house as heat, but this number drops closer and closer to 100% as the outside temperature falls. (Depending on where the compressor is, perhaps some of the heat will escape outside, but it shouldn't be much)

The lowest efficiency that a heat pump system will achieve is when it's operating on backup electric coils, and that is 100%. Not bad, eh?

True only from a 1st Law of TD point of view, and that's no way to rate efficiency.
Go by 2nd law, and it'll be much lower.

 

[SuperjetMatt]

Originally posted by: grrl

Originally posted by: jagec
What do you mean by "efficiency"?

If you're using a heat pump to heat your house, OVER 100% of the energy consumed will be found in your house as heat, but this number drops closer and closer to 100% as the outside temperature falls. (Depending on where the compressor is, perhaps some of the heat will escape outside, but it shouldn't be much)

What are you talking about? How can you get more energy out than you put in? No mechanical system is perfectly efficient, there is always loss.

With a heat pump, the heat comes from the outside air.
You put some electric power into the heatpump system (compressor, fan, etc), but it's a small portion of the total heating energy put into the house.
I.e., the heat pump itself may only use 1kW electric energy, but the house gets 30kW heat.