Electric Heat Pump

[CorCentral]

I've read that most heat pumps lose their ability to heat efficiently when the temperature outside reaches in the low 30's.
It got to about 10f lastnight, but stayed at a decent 65f inside for most of the morning and is now sitting at 71.

QUESTION-- Is it true that there are newer heat pumps that can run efficiently into to mid teens (17f), or is this bs?

Not sure I'm wording this right, but someone that knows will understand.



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

 

[mrrman]

I have a heat pump in my house and there are no issues...it has been -12C outside(10F)and my place is a constant 71F(21C). It heats a 4000 sq ft house and I have an AC/heat pump unit. One thing for sure is that this unit is saving me alot on heating bills.

 

[Modelworks]

Heat pumps extract heat from the air outside, so as the temps fall there is less and less heat to extract and use to heat the home. Once that point is reached most homes have electric heat coils that work just like those in an electric dryer. They are also used if the temp inside and outside are too far apart . Some thermostats show that as aux heat, while others will use the resistance heaters without informing you , so you think it is all the heat pump outside.

 

[CorCentral]

Originally posted by: mrrman
I have a heat pump in my house and there are no issues...it has been -12C outside(10F)and my place is a constant 71F(21C). It heats a 4000 sq ft house and I have an AC/heat pump unit. One thing for sure is that this unit is saving me alot on heating bills.

What's the size of it? 4-5 ton?

I edited the details of what I have.

 

[zzuupp]

"geothermal" heat pumps wiki

Instead of outside air,
long loops of pipe are buried deep enough to provide a more moderate temperature for the heat pump to work with.

 

[CorCentral]

Originally posted by: zzuupp
"geothermal" heat pumps wiki

Instead of outside air,
long loops of pipe are buried deep enough to provide a more moderate temperature for the heat pump to work with.

But I'm talking about Electric Heat Pumps.

 

[Modelworks]

Originally posted by: CorCentral

Originally posted by: zzuupp
"geothermal" heat pumps wiki

Instead of outside air,
long loops of pipe are buried deep enough to provide a more moderate temperature for the heat pump to work with.

But I'm talking about Electric Heat Pumps.

I have read about some models in engineering journals that can go down to -20F and still be efficient, but they are not in production and are not likely to be. They cost more to produce than they return in savings.

Sometimes its just a matter of cost vs return, rather than what is most efficient to run.

 

[amdskip]

I don't have an answer for you but the heat pump in the one apartment I had sucked. It really ate up the electricity and the air felt cold when it kicked on. I have a normal forced air electric furnace now and it seems much much better.

 

[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?

 

[NL5]

We had high teens low twenty's here, and I'm all but certain, the aux heat never had to kick in on my heatpump. It's only 2 years old.

 

[zzuupp]

Originally posted by: CorCentral

But I'm talking about Electric Heat Pumps.

when you asked about something that worked down to 17 degrees or so, "geothermal" was the first thing that came to mind. I think I saw on This Old House.

As far as I know, at the temperature range something other than an outside air source has to be used.

 

[Rubycon]

Originally posted by: CorCentral

QUESTION-- Is it true that there are newer heat pumps that can run efficiently into to mid teens (17f), or is this bs?

Certainly its possible. Remember that an air to air system works just as an air conditioner - you're just swapping the condenser and evaporator positions. Systems have gained efficiency in the past years and do have the ability to run with lowered balance points. In addition house insulation and "tightness" have improved to lower heat losses. So while it is possible that balance points can be lowered from the mid 30 degree range of units made in the 1970's the achille's heel of the system still exists and climates found in higher latitudes will mandate the use of supplementary heat either in the form of gas/oil burners or resistance wire heat. Unless your thermostat has an indicator that your supplementary heating is active, you don't have any way of knowing this is the case.

Additionally, since the evaporator is located outside and its coils run with temperatures that frequently reach levels below the dew/frost point, they will accumulate frost/ice. If this is allowed to build up, airflow through the evaporator decreases and reduces efficiency. (too much liquid in the suction accumulator and lowered head pressure in the condenser which results in lowered register air temps!) The defrost cycle is used where the reversing valve (in systems that fail to heat the orange wire is switched high to engage it) is switched on to bring the system into cooling mode. This makes the outdoor coil a condenser. The outdoor fan is stopped during the defrost cycle to increase head pressure even higher. This makes the indoor coil the evaporator so to stop the air handler from blowing cold (and it would be VERY cold!) air the supplementary heat is engaged. The defrost timer starts counting down. If the system is working properly the frost will melt off in minutes. Once the timer runs out the system switches out of defrost mode and the reversing valve power is disengaged. The system reverts back to heat mode and head pressure builds once again now that there is good airflow across the evaporator once again.

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! :Q

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.

 

[Mojoed]

Acadia.
Read up! I don't have the time for an in-depth post right now. These systems cost more than traditional heat pumps, but are much more efficient.

Below is a quote from their site.

As you?re probably aware, typical air source heat pumps lose their ability to heat your home when outdoor air temperatures drop below 30°F. At that point, they need to bring on supplemental heat which is usually in the form of inefficient electric resistance (also known as ?electric strip? heat) or a fossil fuel burner. The Acadia? does not require this supplemental heat, so you can continue to heat your home even when outdoor temperatures fall well below freezing using only the efficient refrigeration cycle. This is achieved through the use of our patented Opti-Cycle? Technology. The Opti-Cycle? Technology uses a second compressor in series with the main or primary compressor to ?boost? the system?s performance. When temperatures fall below 30°F, this booster compressor is engaged and we see a considerable jump in heat output while maintaining operating efficiencies of almost 300%.

These guys are small, but are growing fast. I've seen a few local news stories about these guys and it's been all positive.

 

[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.

I can't answer your question directly. I don't know how efficiently these things can be made and as a result at just how low a temp they can work efficiently. IMO, it's a balancing act. In my case, my 'supplemental heating' is natural gas. So, it's a balancing act between the cost of the electricity and the cost of natural gas. I would think that the type of climate you live in, the construction of your home, how airtight it is, etc., etc., would all factor in.

I don't know if any of this will be helpful to you or not.

 

[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.

 

[Itchrelief]

Originally posted by: grrl

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.

Pardon my butchering of the proper terminology, but he's not talking thermodynamic/work efficiency (<100%), but rather heating efficiency (>100%).

You don't get more work out than you put in, you just get more heat (which is what he wants).

I'm sure Rubycon can clarify this, as I'm just taking a wild guess.

 

[Modelworks]

Originally posted by: amdskip
I don't have an answer for you but the heat pump in the one apartment I had sucked. It really ate up the electricity and the air felt cold when it kicked on. I have a normal forced air electric furnace now and it seems much much better.

A lot of installers just put whatever they like without really doing a proper calculation on what the place really needs. I have heard a lot of people say they have an undersized heat pump.

I live in NC where it gets cold, but not really cold, about 20F at the worst on average. The heat pump on my apartment is a Ruud unit and the highest electric bill I have had in two years here is $74 .The apartment does have double glass on the doors and windows and is well insulated. I think you have to look at things overall like insulation, heat pump size, etc.

 

[dullard]

Originally posted by: grrl
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.

A heat pump uses electricity. Much of that electricity eventually ends up as heat in your house. But, you are correct, there is waste. Some of that electricity ends up as heat outside your house. If you put in 2000W of electricity, you might get 1800W of heat directly in your house. But, there is a catch. The purpose of a heat pump is to PUMP heat from outside (even if it is cold outside) to the inside of your house. You may very well pump in 4000W of heat. The end result may look like this:

Your electricity:
[*]Used 2000W
[*]200W lost due to inefficiencies (I just assumed 10% loss)
[*]Net: 1800W goes to heat your home

Your home:
[*]1800W of heat from the heat pump
[*]4000W of heat from outside
[*]Net: 5800W goes to heat your home.

Outside:
[*]200W of heat gained from heat pump inefficiency
[*]4000W of heat pumped into your home
[*]Net: -3800W of heat.

Reverse the 4000W part during the summer as you are pumping heat from your home to the outside (even if it is hot outside).

So, in my crude example, the pump was 90% efficient. But your house was heated with 5800W while you only paid for 2000W of electricity. Apparent efficiency is 290%. This doesn't break the laws of thermodynamics. The reason is that the extra heat came from the outside.

 

[CorCentral]

Originally posted by: Modelworks

Originally posted by: amdskip
I don't have an answer for you but the heat pump in the one apartment I had sucked. It really ate up the electricity and the air felt cold when it kicked on. I have a normal forced air electric furnace now and it seems much much better.

A lot of installers just put whatever they like without really doing a proper calculation on what the place really needs. I have heard a lot of people say they have an undersized heat pump.

I live in NC where it gets cold, but not really cold, about 20F at the worst on average. The heat pump on my apartment is a Ruud unit and the highest electric bill I have had in two years here is $74 .The apartment does have double glass on the doors and windows and is well insulated. I think you have to look at things overall like insulation, heat pump size, etc.

Yea' that's where I'm losing tons of money I believe......... Insulation!

It's a 1972 home/2000sq ft
I checked the attic and the insulation (cellulose) comes to the top of the ceiling joists. about 5.5 inches.

What is the ratio when calculating R rating per inches of cellulose?
3 R-value for 1 inch? Equals about 15-R......... should be closer to 40!

What's everyone else's take on it?

 

[Modelworks]

Originally posted by: CorCentral

Originally posted by: Modelworks

Originally posted by: amdskip
I don't have an answer for you but the heat pump in the one apartment I had sucked. It really ate up the electricity and the air felt cold when it kicked on. I have a normal forced air electric furnace now and it seems much much better.

A lot of installers just put whatever they like without really doing a proper calculation on what the place really needs. I have heard a lot of people say they have an undersized heat pump.

I live in NC where it gets cold, but not really cold, about 20F at the worst on average. The heat pump on my apartment is a Ruud unit and the highest electric bill I have had in two years here is $74 .The apartment does have double glass on the doors and windows and is well insulated. I think you have to look at things overall like insulation, heat pump size, etc.

Yea' that's where I'm losing tons of money I believe......... Insulation!

It's a 1972 home/2000sq ft
I checked the attic and the insulation (cellulose) comes to the top of the ceiling joists. about 5.5 inches.

What is the ratio when calculating R rating per inches of cellulose?
3 R-value for 1 inch? Equals about 15-R......... should be closer to 40!

What's everyone else's take on it?

Found this:
http://www.ornl.gov/~roofs/Zip/ZipHome.html

 

[CorCentral]

Originally posted by: Modelworks

Originally posted by: CorCentral

Originally posted by: Modelworks

Originally posted by: amdskip
I don't have an answer for you but the heat pump in the one apartment I had sucked. It really ate up the electricity and the air felt cold when it kicked on. I have a normal forced air electric furnace now and it seems much much better.

A lot of installers just put whatever they like without really doing a proper calculation on what the place really needs. I have heard a lot of people say they have an undersized heat pump.

I live in NC where it gets cold, but not really cold, about 20F at the worst on average. The heat pump on my apartment is a Ruud unit and the highest electric bill I have had in two years here is $74 .The apartment does have double glass on the doors and windows and is well insulated. I think you have to look at things overall like insulation, heat pump size, etc.

Yea' that's where I'm losing tons of money I believe......... Insulation!

It's a 1972 home/2000sq ft
I checked the attic and the insulation (cellulose) comes to the top of the ceiling joists. about 5.5 inches.

What is the ratio when calculating R rating per inches of cellulose?
3 R-value for 1 inch? Equals about 15-R......... should be closer to 40!

What's everyone else's take on it?

Found this:
http://www.ornl.gov/~roofs/Zip/ZipHome.html

I'd think about changing that link. It just closed all my open browser windows.

 

[Modelworks]

Originally posted by: CorCentral

Originally posted by: Modelworks


Found this:
http://www.ornl.gov/~roofs/Zip/ZipHome.html

I'd think about changing that link. It just closed all my open browser windows.

hrm, no problems for me using firefox.

Not sure why it would do that. From the page:

Requirements for running the ZIP-Code Insulation Program:

This program requires a minimum screen size of 800 x 600 pixels. To check or change your screen size, start the "Display" program in the "Control Panel" folder or right click the mouse in an unused area of the desktop window and select "Properties". The screen size is on the "Settings" tab. Your web browser must be restarted after changing the screen size.

This program also requires that the SUN Java Runtime Environment (JRE) be installed as an addon to your browser. Really old versions of Java, including the now defunct Microsoft Java, may not work with the 2008 version of this application. If you do not see a white box above that allows you to enter the first 3 digits of your zip code, please refer to the SUN Java JRE downlaod and instructions page.

Alternately, you can use the R-Value Recomendations Calculator which has less options than this program but does not require Java. Another option is to use the 2002 version of the ZIP-Code Insulation Program, which uses 2002 cost data but runs on very old versions of Java.

If you are using a Windows computer and have the Java JRE installed and are still having trouble running this program in Internet Explorer, you may need to adjust the security settings to enable Java. An easier solution might be to install the Mozilla Firefox browser.

Link to other calculator that doesn't use Java.
http://www.ornl.gov/sci/roofs%...insulation/ins_16.html


Link to page on how to calculate R value for attic:
http://www.ornl.gov/sci/roofs%...insulation/ins_06.html

 

[amdskip]

Oh you need to add insulation to your attic. You should add blown in fiberglass (the white fluffy stuff) instead of adding more cellulose which is dirty and settles. The fiberglass does not settle. I added it to my attic a couple weekends ago and I now have 20" of insulation. You probably do need about an R40. I could tell a big difference right away after adding the insulation. Make sure you add the styrofoam air vents so air can still travel underneath your roof from the eaves.

pics: http://www.facebook.com/album....23&l=cf0ee&id=30402409

 

[CorCentral]

Originally posted by: amdskip
Oh you need to add insulation to your attic. You should add blown in fiberglass (the white fluffy stuff) instead of adding more cellulose which is dirty and settles. The fiberglass does not settle. I added it to my attic a couple weekends ago and I now have 20" of insulation. You probably do need about an R40. I could tell a big difference right away after adding the insulation. Make sure you add the styrofoam air vents so air can still travel underneath your roof from the eaves.

Baffles for the soffits....... check 🙂

Yapple Dapple!

 

[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