Heat pumps

[jk96]

LD lots of good information there.

I started this thread partly due to the fact that my power company routinely sends letters saying that I am using a gazillion% more electricity than other houses in my area. My house is roughly 1600 sq ft and last month I used 3900kwh. I don't know if that is excessive for an all electric house??? The house ,built in 1953, could probably use some additional insulation and we have landscape/security lighting that is on a lot.

One of the best things you could do is work on air sealing and insulation. Maybe someone else can chime in but I would think blown in would be better than bats for the attic. A blower door test will help you find the leaks and will be especially easy to find when its cold out. Given the size of your house I would think that you could get your usage down significantly with some work on the building envelope. If the landscape and security lighting is LED then the amount of usage that contributes is minimal. You could easily figure your KWH usage if you know the wattage and run time of the lights. My guess regardless of type is that its probably not a significant factor.

Our house is total electric however its new construction probably on the opposite end of efficiency from an older home, closed cell spray foam, geothermal, and fireplace for supplement heat. House is 3500 square feet, two water heaters, 2 adults and 3 kids so lots of showers, laundry, etc. Our latest bill showed 2640 KWH for the billing cycle, or about 88 KWH per day.

 

[LD1]

Our house is total electric however its new construction probably on the opposite end of efficiency from an older home, closed cell spray foam, geothermal, and fireplace for supplement heat. House is 3500 square feet, two water heaters, 2 adults and 3 kids so lots of showers, laundry, etc. Our latest bill showed 2640 KWH for the billing cycle, or about 88 KWH per day.

Thats about what my usage was at my previous 1300sq ft house. Only used propane when it was colder than 17. The rest was all HP. 2 adults and 2 youngins (baths everynight). I was also out in my shop tinkering alot on my days off. (3-4 days a week). That was running ~700watts of lights for 10hrs a day, plus equipment. Air compressor, welder, etc. Also had a 200w aerator, 200w pond pump and a 80w pond pump that all ran 24/7. And a 200w birdbath type heater that ran in the small pond when below freezing.

I think my highest ever was 3000kwh. Needless to say, when I moved to a similar sized house with baseboard heat only and no ponds or shop, and was pushing 150kwh a day before it even got real cold, something had to change. Basement was unlivable due to no heat at all, and was really expensive to heat upstairs. I am burning wood to get through this winter. But planning on a DIY geothermal this summer, once I get the bulk of the work done on building my shop.

 

[techman]

Be aware that the issue with heat pumps is NOT efficiency, it is capacity. A modern heat pump will still output more energy in heat than it consumes in electricity even in the single digits. As it gets colder out, the energy draw for the heat pump drops as well. The problem is that the amount of heat that it is generating also drops with temperature. This is due to the fact that the colder the air, the less heat that can be drawn from it. So in very cold temps, the electric heat is added as a SUPPLEMENT to the heat pump. So if you require 30,000 BTUs and the heat pump is only generating 15,000 at the given outdoor temp, the electric heat makes up the difference. So when the backup is on, the heat pump will still run and is still generating its portion of the heat at efficiency greater that straight electric heat. A a low temperature the heat pump will reach a point where is will generate less heat energy than it consumes. This point is generally zero or below for a modern heat pump. So it is normal for it to run, and usually run 100% of the time at cold temps. It is still giving you more than the electricity it is using.

paul

 

[Gary Fowler]

My all electric 2010 built home or 2380 sq foot averages about $160 per month winter and summer. We put extra insulation in all the walls and really overdid the ceiling for Arkansas when we put in R 52 rating insulation. We have a 19 SEER rated HVAC system which is far superior to the 13 SEER that the OP has. It would pay for itself in 2-3 year to upgrade that system to at least a 19SEER.

I agree 6" bat insulation is what is required in the southern states and is no where near enough for way up North. Check the requirements for your area, but I would guess that it requires at least 12" of bat insulation.

Some saving can be had by monitoring lights, TV's, etc to make sure they are turned off when not in use. My next door neighbor (3500 sq foot 2010 build house) complains about his electric bill being over $400 per month, but whenever I go over, there will be at least 2 and sometime 3 TV's on (just the 2 off them) plus lights on in every room, doors left open when they go outside for 5 minutes or more. His man cave (really nice about 2000 sq feet) usually has a TV on in it even if no one is around. Refrigerator doors stay open for 5 minutes or more when they are preparing food and a ship load of outside security lights that burn way into daylight hours. Lots of wasted energy there for sure even though it is well insulated, it doesn't help when doors are open for several minutes at a time.

 

[joemd11]

First, I have to say that you guys are the best. It never ceases to amaze me the depth of knowledge and expertise found on this forum. Thanks to all of you for your contributions.

LD1,
I'll have to enlist the help of my brother, an electrician, to run the tests you suggest (wow, thats a lot of math). He is retired now and usually looking for something to do. The question I posed in this thread was just one that I always pondered when I was outside on really cold days and would see the HP running. Thanks to you I now have a better understanding of whats going on.

Gary,
I agree that I need more insulation in the attic. We moved into this place in 95 and it only had 3" of rock wool insulation in it at that time. I thought I was really improving the situation when I tore that out and replaced it with the 6" fiberglass bats. One more thing on my "to do" list will be to add more insulation to areas that I can access. The house is cape cod style so some areas (i.e. dormer ceilings or behind knee walls) are not accessible from inside.
Insulating the walls would be a bit of a problem as the exterior is brick. I know insulation could be pumped into the walls, but I'm leery of going that route. I wouldn't want to create a moisture problem. Also, my HP is a 16 seer as opposed to 13 and about 7 years old. Don't know what seer they are up to now but it will probably be several years before we upgrade our system. Really wish I could get a natural gas furnace/HP combo but we have no gas lines nearby. I guess geothermal would be another option to investigate.

techman,
Thanks for your informative post on HP operations. I feel better now knowing my system isn't grossly out of whack.

 

[LD1]

The only thing an electrician is really needed for (and not even then if you have an amp clamp) is figuring out what amps your HP is using.

Everything else is just measuring temps and putting the numbers in. You cannot get all of your answers in a single day. It takes weeks of checking at different outdoor temps. But the HP amps only need checked once, thats a constant. Same with blower CFM. Once that is figured out you are good. All you have to do is check inlet and outlet temps of the vents, figure the BTU and COP, and make of note of the outdoor temp. You will find a time at which it makes sense to have the HP shut off. But without this, there is no way of knowing if that number is 25 degrees, or -5 degrees

 

[Country Geek]

To give you an idea, my 15 year old 10seer HP, that point was 17 degrees vs propane AUX. Since propane is cheaper than electric per BTU,

Don't assume that's the case for everyone. You need to plug your local rates and efficiency ratings into here to find out: http://www.eia.gov/tools/faqs/heatcalc.xls

I found that in my area, propane is more expensive than electric when it's more than $2.20 a gallon. Which it has been for quite a while. Might be cheaper know, but I blissfully don't know... put in a geothermal heat pump system this past fall and haven't bought propane since then.

 

[LD1]

Don't assume that's the case for everyone. You need to plug your local rates and efficiency ratings into here to find out: http://www.eia.gov/tools/faqs/heatcalc.xls

I found that in my area, propane is more expensive than electric when it's more than $2.20 a gallon. Which it has been for quite a while. Might be cheaper know, but I blissfully don't know... put in a geothermal heat pump system this past fall and haven't bought propane since then.

I wasnt assuming anything. Just citing my experience. In the OP's case it doesnt matter and the numbers are easier, since both the HP and the strips are powered by electric that cost the same per Kwh

 

[kenmac]

Check to see how many times the unit is going into defrost..At 0 temps.. the unit is probably going into defrost more often.. When the unit goes into defrost you get no heat ,but the unit still uses energy.. your aux heat (heat strips) come on during the defrost cycle.. note.. when your HP goes into defrost mode..You are in A/C mode..the heat strips come on to off set the A/C mode so, you don't get cold....You are using energy that you can't use (for heat) every time it is in defrost mode.. Depending on your elect. rates.. you may be better off with HP vs propane.. Glad we don't get 0 deg temps here

 

[grsthegreat]

i got suckered into the installation of a heat pump about 8 years ago. luckily i insisted on the 95% efficient gas propane backup emergency heat option. That system never worked well when temps fell below 35F outdoors. the system was always cycling and going into defrost. i could see ice build up on it. Had it looked at by 3 different warranty HVAC guys. wasnt worth the dynamite to blow the thing up with. House was never warm in the deep winter unless i manually placed it in emergency heat mode.

when the A/C started giving us problems on the hottest days..i ripped out the heat pump compressor and my HVAC guy installed a regular air conditioner. he reprogrammed the tstat as a standard gas furnace and elect a/c compressor. Now i love the system. My fuel bills are actually less this last winter and the house is warm. was nice and cool last summer also.

heat pumps might be nice in temperate climates....but no one will ever convince me there right for cold northern climates. no one. Im out about $6,000 on this failed test.