Comparing electric bill to temperature

[wahoowad]

I added a programmable thermostat this Fall and am now looking at my electric bill. I used 5% less kWH this past billing cycle compared to last year. But, for all I know, this past month could have been milder than last year. Is there a website that can provide specific or general info so I can see how the weather was last year?

 

[velvetfoot]

I think you want degree-days but I'm not sure how to use that.

 

[Sandor]

This link will give you directions on how to compare, and there is an embedded link to obtain historical data for your area.

http://www.usatoday.com/weather/resources/askjack/2004-12-16-heating-degree-days_x.htm

 

[wahoowad]

Sandor, you are THE MAN!

That link gave me exactly what I was looking for! Here is what I found:

Oct-billing-cycle-2005: 245 heating degree days
Oct-billing-cycle-2006: 359 heating degree days

A heck of a lot more heating degree days this year but my usage was much lower this year. I know it also depends on my other uses of electricity but I can't think of any significant differences. And, I actually think I am running my thermostat a tad higher this year (70 compared to 68 last year) too. Maybe that programmable thermostat is helping me out more than I think. Cool!

 

[daninohio]

Yes, thanks. That is a great source of data. Here the difference was 384 HDD v. 304 last year.

 

[Sandor]

I added a programmable thermostat this Fall and am now looking at my electric bill. I used 5% less kWH this past billing cycle compared to last year. But, for all I know, this past month could have been milder than last year.

Perhaps it was implicit, but I didn't READ that electricity was your alternate mode of heating.

It's not too much of a stretch to believe that one could use more electricity with a programmable thermostat.

I do believe that electricity was his primary mode of heating, via the heat pump. All heat pumps have an emergency/auxilliary mode, which is basically a heating coil. The coil is a backup mechanism, in case the heat pump fails- this is called emergency heat. In auxilliary mode, it supplements heat output during extreme outdoor temps where the heat pump cannot keep up with heating demand.

That being said, I agree with you 100 percent that a programmable thermostat could acutally cause an increase use of electricity. That may be happening in this case. Leaving the thermostat at a constant temp may never invoke aux mode, but asking the system to raise the temp from 62 to 70 may/will cause a prolonged period of auxilliary mode operation.

Since electric heat is basically 100 percent efficient, heat pumps are maybe 180 percent efficient.

I would like to help Wahoo, because I think there is a great deal of savings to be had.

Damn Dylan, ya make me think too much!..... but thanks for pointing this out.

 

[EatenByLimestone]

It's ben colder here too.

http://www.nyserda.org/Energy_Information/nyepk.asp

 

[wahoowad]

I noticed my aux heat kicking in a lot before I ever switched to a programmable thermostat. I chalked it up to a weak heat pump that did not produce warm air fast enough and causing the system to think it needed the aux heat. I now have the same problem but it minimized by not kicking in as much. I know what you mean that I could be letting the house get too cool, and thus using more electricity by creating too large of a differential. In my case, I think it would kick in anyway due to my weak heatpump so I'm still better off. At least until I fork over $4k (?) for a new unit and some duct work.

 

[begreen]

Depending on the thermostat and heatpump, there may be a lockout temp for the aux heat. I think it is set to 35 deg. on our system. There is an outdoor sensor that regulates this.

 

[Sandor]

Depending on the thermostat and heatpump, there may be a lockout temp for the aux heat. I think it is set to 35 deg. on our system. There is an outdoor sensor that regulates this.

More efficient units usually have this feature. Does yours also have a frost sensor?

 

[pgmr]

... All heat pumps have an emergency/auxilliary mode, which is basically a heating coil... Leaving the thermostat at a constant temp may never invoke aux mode, but asking the system to raise the temp from 62 to 70 may/will cause a prolonged period of auxilliary mode operation.

Actually, some hp systems are dual fuel (hp & gas/lp furnace) and have no coil. The furnace runs, as you said, when the hp can't keep up or raise temp fast enough and also when hp is in defrost to temper the air going to the house and send heat quickly to outdoor coil. I believe that the coil aux heat does the same during the defrost cycle, so most hp systems will use their aux system regularly.

The furnace in a dual fuel will not run while hp is in heating mode to prevent pressures from getting too high at the compressor.

I quit doing setback on our Bryant Evolution because it was using the gas to provide recovery heat and since gas has gone up so much in price, that was defeating the "trying to save money" purpose of a setback...plus my wife likes 68 much better than 60!

 

[Sandor]

... All heat pumps have an emergency/auxilliary mode, which is basically a heating coil... Leaving the thermostat at a constant temp may never invoke aux mode, but asking the system to raise the temp from 62 to 70 may/will cause a prolonged period of auxilliary mode operation.

Actually, some hp systems are dual fuel (hp & gas/lp furnace) and have no coil. The furnace runs, as you said, when the hp can't keep up or raise temp fast enough and also when hp is in defrost to temper the air going to the house and send heat quickly to outdoor coil. I believe that the coil aux heat does the same during the defrost cycle, so most hp systems will use their aux system regularly.

The furnace in a dual fuel will not run while hp is in heating mode to prevent pressures from getting too high at the compressor.

I quit doing setback on our Bryant Evolution because it was using the gas to provide recovery heat and since gas has gone up so much in price, that was defeating the "trying to save money" purpose of a setback...plus my wife likes 68 much better than 60!

You are correct. The aux heat will engage during the defrost cycle. That is why high efficiency units employ frost sensors to determine whether the defrost cycle is actually needed, rather than just on a timed basis.

 

[pgmr]

You are correct. The aux heat will engage during the defrost cycle. That is why high efficiency units employ frost sensors to determine whether the defrost cycle is actually needed, rather than just on a timed basis.

I know our system has an outdoor coil temperature sensor, which it uses in conjunction with a timer. If the coil is below freezing at the end of the timer interval, it will go into defrost. While better than a straight timer, it is somewhat disconcerting to hear it go into defrost when there is no frost on the coil. One would think they could base it on amp draw on the outdoor fan, airflow through the unit, etc. rather than just time and temp, which really doesn't indicate anything about ice on the coil.

Maybe some of the other manufacturers use a different method than Carrier/Bryant.

 

[wahoowad]

I looked at my electricity usage again this month and compared to heating degree days. Last month is above. This month I had 4% fewer heating degree days than the same time last year, but my overall kWH usage was 27% less. That's a significant drop to which I attribute both the programmable thermostat and my use of the woodstove.

The difference for me is only $24 (total electric bill was $102 and I use a heat pump), but a couple months of that will pay for the thermostat I purchased.

 

[kevinlp]

Last year I used 1 gallon of propane for every 6.8 degree days. Note: The propane does heat, hot water and cooking

So far this season it is 1 gallon of propane for every 9.4 degree days. A 38% increase.

There have so far been quite a few days where we didn't use the stove cause it wasn't colder enough but did use the propane.

The september to october fillup was 1 gallon of propane for every 15.7 degree days. We dipped to 9.3 degree days for october - early november. In the october - early november period we had added a thermostat to our infant's room as the main thermostart won't reach temp due to the stove. We also closed all the vents except for the bedroom. I think that cause the furnace to be slightly inefficient as it only had to run for a minute or two to get our daughter's bedroom back to temperature.

We just found a small electric space heater that is quiet enough to use in her room. Going to try that a couple night and see how much it actually runs by checking the electric meter before bed and first thing in the morning. 1500 Watts is only 15 cents per hour.

 

[DavidV]

We did a system upgrade for our dual fuel system this year. Probly should have just put in a heat pump....would have been cheaper. I'll never save enough to pay off that thing. I am using a lot less electric though....at least in summer. on average I was using 500kwh less permonth(example 2900 instead of 3500) and the house was just as comfortable....and if I am not mistaken it was hotter this year also. I'm putting A/C in my shop this summer so we will see what happens. I used about the same amount of gas last month as the month before. More than anything I think that is attributed to the fact that I have eased up one the energy nazi thing with the family....but, the wife has surprised me recently when we came home and the fire had died down. I loaded some wood onto it and kicked the thermostat up to heat the house back up....she kicked it back down and handed me a sweatshirt.

 

[Rhone]

Another point, wasn't it a special heat pump programmable thermostat purchased? Those use formula's to minimize aux heat.

 

[jjbaer]

Sandor, you are THE MAN!

That link gave me exactly what I was looking for! Here is what I found:

Oct-billing-cycle-2005: 245 heating degree days
Oct-billing-cycle-2006: 359 heating degree days

A heck of a lot more heating degree days this year but my usage was much lower this year. I know it also depends on my other uses of electricity but I can't think of any significant differences. And, I actually think I am running my thermostat a tad higher this year (70 compared to 68 last year) too. Maybe that programmable thermostat is helping me out more than I think. Cool!

Make sure the billing cycles you're comparing have the same number of days...if they don't, you'll have to ratio them up or down to make them equivalent

 

[ChrisN]

DavidV wrote:

I am using a lot less electric though....at least in summer. on average I was using 500kwh less permonth(example 2900 instead of 3500) and the house was just as comfortable

2900kwh/ month Dave? Holy crap, mine is closer to 500 to 600 / month for my 4 bedroom house. Here in CT, 2900kwh would run about $520.00.

 

[jjbaer]

We did a system upgrade for our dual fuel system this year. Probly should have just put in a heat pump....would have been cheaper. I'll never save enough to pay off that thing. I am using a lot less electric though....at least in summer. on average I was using 500kwh less permonth(example 2900 instead of 3500) and the house was just as comfortable....and if I am not mistaken it was hotter this year also. I'm putting A/C in my shop this summer so we will see what happens. I used about the same amount of gas last month as the month before. More than anything I think that is attributed to the fact that I have eased up one the energy nazi thing with the family....but, the wife has surprised me recently when we came home and the fire had died down. I loaded some wood onto it and kicked the thermostat up to heat the house back up....she kicked it back down and handed me a sweatshirt.

Dave,

You saying your average electricity bill was 3500 KW-HR per month? If so, what size house do you have? You must not have that much (or any) insulation unless your house is HUGE!