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Old 01-13-2010, 08:17 PM   #1
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Trane Heat Pump Costing Me Mucho $$


I'm renting a 2200 Sqft house in Houston. It's new construction with nice double pane windows and decent insullation. I just got my electricity bill for December and it's $500.. I've had larger homes and never paid over $200 in Houston, and I wasn't even home for a week in December.

The bill shows 3000 kWh usage which is equivilent to running over 40 100W light bulbs 24/7 for the whole month. (I am pretty conservative on ussage, keeping lights and fans etc off most of the time)

I keep the thermosdat set on a modest 68 (on from 4:30pm to 7:30 AM - Off during the day time) and December was not a cold month here.
When the heater kicks on our lites dim slightly, and it seems to me that something isn't quite right with the unit, the wiring, or the breaker box.

It is running off two 60 amp breakers and up in the attic one of the power supply lines is slighty warm and the other isn't. I assume one is supplying the aux heater. Is this correct?

Should I get someone out to look at the unit? Is there some checks I can make? I'm fairly handy with some HVAC background.

The unit is aprox 7 years old.
Model # TWEO48C14FCO

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Last edited by Wadsworth; 01-13-2010 at 08:24 PM.
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Old 01-13-2010, 09:09 PM   #2
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Trane Heat Pump Costing Me Mucho $$


From what you are saying, what is likely happening is that the AUX heat is kicking in to get the house up to temperature.

Heat pumps generally prefer to be set and left.

Your thermostat is likely set to energize the electric heat when you turn the heat on if the set point is several degrees different than the current temperature.

Find the manual to your tstat and see if you can change that setting to a wider deadband.

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Old 01-13-2010, 09:20 PM   #3
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Trane Heat Pump Costing Me Mucho $$


If your living in new construction. Why is the unit 7 years old? It should be a new unit also.

Or do you mean you live in a 7 year old house.

If you are turning your heat off during the day. And then back on at night when you come home. You are making your bill that high.
The expensive electric heaters are coming on because you do that.
Its not a gas furnace. Setting themp back, or turning the heat off during the day won't save you money.

Heat pump with electric aux. Don't set back more then2 degrees. If your thermostat
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Old 01-13-2010, 09:40 PM   #4
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Trane Heat Pump Costing Me Mucho $$


Check the heat pump capacitor. Seven years is a long time for one to last anymore. That would dim the lights and could have the compressor not run causing the expensive elements to do all the heating. As already stated leave the heat on at a set temp so the hp does all the work at a third or less of the cost of elements running.
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Old 01-13-2010, 10:44 PM   #5
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Quote:
Originally Posted by Marty S. View Post
Check the heat pump capacitor. Seven years is a long time for one to last anymore. That would dim the lights and could have the compressor not run causing the expensive elements to do all the heating. As already stated leave the heat on at a set temp so the hp does all the work at a third or less of the cost of elements running.
if the outdoor unit wasnt running the unit would never shut off
when the second stage was satisfied there would be a cold blow from lack of an outdoor unit and system would blow cold till second stage made again. I might check all the high voltage connections for tightness especially in the main panel inc the main breaker(only if youre confortable doing so of course)
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Old 01-13-2010, 11:06 PM   #6
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Trane Heat Pump Costing Me Mucho $$


Can you make the auxiliary heaters (electric resistance heaters) stay off all the time at the expense of having the system take longer to heat up?

Try it that way and see if your electric consumption is significantly lower. Read the meter every day to get an idea of usage without waiting a whole month to see another electric bill.

Feel the heat pump unit to at least see that it is running in heat pump mode. If the "pump" stops when it would call for auxiliary heat, then stop the above experiment as the system will then never heat up without auxiliary heat.

By the way, the heat pump itself will run much longer to achieve a given inside temperature when the outside temperature is lower.
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Old 01-13-2010, 11:21 PM   #7
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Originally Posted by AllanJ View Post
Can you make the auxiliary heaters (electric resistance heaters) stay off all the time at the expense of having the system take longer to heat up?

Try it that way and see if your electric consumption is significantly lower. Read the meter every day to get an idea of usage without waiting a whole month to see another electric bill.

Feel the heat pump unit to at least see that it is running in heat pump mode. If the "pump" stops when it would call for auxiliary heat, then stop the above experiment as the system will then never heat up without auxiliary heat.

By the way, the heat pump itself will run much longer to achieve a given inside temperature when the outside temperature is lower.
another thing you could try is just putting up a lightswitch instead of a thermostat
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Old 01-13-2010, 11:35 PM   #8
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is your stat set on heat or emergency heat?
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Old 01-14-2010, 05:14 AM   #9
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Can you make the auxiliary heaters (electric resistance heaters) stay off all the time at the expense of having the system take longer to heat up?
Depending which thermostat he has. Heat can set it up that it doesn't use aux at all.
Of course. If the outdoor temp drops below balance point. The heat pump won't be able to maintain temp.
And when its just above balance point, it could take 12 hours to recover.
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Old 01-14-2010, 07:50 AM   #10
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Trane Heat Pump Costing Me Mucho $$


3,000 Kwh for December is not bad for a house that size. But paying $500 for 3000 Kwh is rather steep. That almost 17 cents per Kwh. Perhaps the billl includes some past payments the owner did not make? Or a service charge for reconnecting the power?
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Old 01-14-2010, 09:09 AM   #11
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Thanks guys, I'll try a couple of things.
My rate is 15.74 cents. Recently went up when my one year contract ended. Actual ussage charge was $463.39 (2944 x 15.74).

The average daytime temp outside my house in December was proabaly around 60. When I get home at 4:30 it would generally take less than 30 minutes to get the house up to the thermosdat setting.
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Old 01-14-2010, 09:46 AM   #12
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With average temps in the 50's in December I paid about $280 for electricity and $60 for natural gas with a heat pump and dual fuel. A mild spring or fall month and electricity would be about $150 to $180 with a bit of air conditioning, and maybe a bit of heat. Nat gas during the summer is about $40 to $50 and stays pretty much there till the December bill. I don't know what the rate is but thinking its about 11 cents per KW. I suspect your heat strips are running more than it should. It could be as simple as the heat pump needing some freon.
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Old 01-14-2010, 03:35 PM   #13
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Trane Heat Pump Costing Me Mucho $$


When I get home at 4:30 it would generally take less than 30 minutes to get the house up to the thermosdat setting.

Turning the heat back when at work could be your problem. During the day there is not much savings from the setback because it is relativly warm, but the temperature drops enough that the heat strips kick in when you get in, which kills any savings from the setback and then some. If you want to set it back then get a digital setback thermostat that will calculate how long it will take the heat pump to recover and start it up before you get in. Or an old fashioned approach would be to use a outdoor thermostat that prevents the heat strip from coming till the outdoor temp drops below the crossover temp. Usually below 30 degrees. They would still come on for defrost though.
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Old 01-14-2010, 03:41 PM   #14
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Yep.

if your heat pump has 20KW of aux heat. Then in that 30 minutes of recovery time the aux alone used 10 KWHs.
And if you set it back when you go away at night, or the weekend. It uses a lot of electric to recover for those times also.
Just leave the temp set and your electric bill will be much cheaper.
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Old 01-14-2010, 04:58 PM   #15
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Quote:
Originally Posted by Wadsworth View Post
a 2200 Sqft house in Houston.
It's new construction with nice double pane windows and decent insullation.
The bill shows 3000 kWh usage
469 HDDs for Dec. for Houston
http://www.degreedays.net/
so your avg. Dec. temp was = 65 - [HDD/31] = 50F

2200 sf
3000 kwh = 10.2 therms

10.2/2200 = 4700 BTU/sf
4700/469 = 9.9 BTU/[sf-HDD]


Here's my samples of BTU/[sf-HDD] heat loss. Note that sample size is relatively independent of the size of the underlying population of 110 M resi. HVAC units. From an indep. source I know that 6 is avg.

1.7[low] 3.8 4.0 4.4 5.7 8.0 8.0 8.8 11 [high]

9 =number of samples
6.16 =sample average
5.70 =sample median
2.97 =sample standard deviation

3000 kwh seems high to me but there might be a flaw in this analysis. I'll post back if I think of one.

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Last edited by Yoyizit; 01-14-2010 at 05:09 PM.
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