Heat pump troubleshooting

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My last heating bill was excessively high and I am trying to figure out what is going on.
I have two heat pumps. The first unit is a 3 ton Goodman (seer 13) that produced a delta T (air duct outlet temperature-inlet duct temperature) of 20 when the outside temperature was 52. The second unit is a 2.5 ton Goodman (seer 13) which produced a delta T of 24.
Do these number make sense. What temperature rise should I expect at this outdoor temperature? I would expect the units to be efficent under these conditions. I am well aware that at low temperatures the efficentcy drops.
Thanks for the help.
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noname87 wrote:

I am sure you will get some useful answers but for my part, don't troubleshoot the damn thing just shoot it. Heat pumps are the power companies answer to low winter time power usage.
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I would love to but I really don't have an option. In theory, heat pumps worrk well above 40 and for cooling. The problem is when you have cold temperature. Below 30, the meter starts going crazy.
My area does not have gas. Propane might be an option but the conversion cost would be high. I don't think is available. Even if it was oil isn't cheap. In my area it is heat pumps or gas if you have it. Some have hybid system that swith from heat pump to gas when necesary.

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We are both in the same boat. I also have a heat pump and would love to have some other option, any option. If I am ever forced to go with another heat pump I will give very serious consideration of using a buried exterior coil system even if the initial cost is substantially higher. Trying to extract cool for hot air or heat from cold air is just short of foolish. At least with gas heating you are getting the maximum efficiency. The efficiency range for heat pumps is just too narrow to be effective except in temperate climates like Southern California.

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I gave a thought of a trench system. That should not cost all that must either. Dig a hole, lay pipe.
I have gas heat. My brother has oil, and since the oil went up, he uses electric which seems cheaper than oil. I get annoyed when my electric bill goes about $60 a month. I use the air conditioner in summer which does not seem to affect the bill much. Figure a trench should stay about 50 degrees year round. heat pumps usually shut off and go strictly resistive heat much below 40.
greg
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You need hundreds of feet of trench and it needs to be pretty far down to escape the temp variations of the surface soil. Several feet to as far as 8 feet deep depending on your location. Figure a hundred feet a ton as a swag for length. If you own your own trencher and have a decent field in the back of your house, ok. Otherwise it's cheaper and easier to just have a well driller put a ground loop or two in for you.
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I would love to but I really don't have an option. In theory, heat pumps worrk well above 40 and for cooling. The problem is when you have cold temperature. Below 30, the meter starts going crazy.
My area does not have gas. Propane might be an option but the conversion cost would be high. I don't think is available. Even if it was oil isn't cheap. In my area it is heat pumps or gas if you have it. Some have hybid system that swith from heat pump to gas when necesary.
+++++++++++++++++++++++++
I'll ask you what I asked someone here who posted about their heat pump last week:
What temp do you set your thermostats to ? If above 68, consider lowering to 68.
Do you have digital, programmable thermostats with temperature recovery?
If no, do you manually adjust the temp setting?
If yes, do you set the temp lower for overnight and when at work ? Consider lowering a few degrees above the higher setting.
When the outside temp falls below 20F and you notice the aux heat kick on frequently, do you change the heat mode from normal to Emergency Heat ? If not, you should until the outside temp rises back to 20 and climbing, or when you have to leave for work.
Last week's poster indicated their temp is set to 73 !!! You want that warm, you pay.
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oump is produce very little but I thought I read that even at that point it is cheaper than pure electric resistive heat. Based on my daily monitoring, it looks like my sysyem works well until the night temperature falls to about 25.
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I have a heat pump but I don't know much about a solution for you. I am curious about what you consider excessively high. I get antsy when my electric bill gets over $200 in the winter but if that was my only heating cost it would be excessively low.
-C-
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. What temperature rise should I expect at

Post the model numbers for the Goodmans. I may be available to find the specs for Delta T at a given OD temp.
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To answer some of the questions:
The main unit (GSH130361AO) is set at 68 during the day and set back to 66 at night. I have a programable thermostat (Honeywell RTH7600D) which does have a recovery mode. At low temperatures the Aux heat does come on. The compressor is roughly 3 years old and the air handler is 1 year old. I have not try running on emergency heat only at low temperatures.
The second unit (GSH130301AB) is set at 66 during the day and 64 at night. Unit is three years old. Same thermostat as above.
The house is roughly 2400 sqft and with cathedral ceilings in the living room, master bedroom and master bath. House was rebuilt in 2007 so insulation is at least average. Windows are thermopane. Unfortunately the previous owner (we move here last year) didn't seem too concern about enery cost. I do have excessive windows on the side of the house that faces west. Great during the day. Poor at night.
Our bill lasy month was higher than the previous owners worst bill by 20%. What has me concern is that it was significantly higher than last year when the main unit failed and we were running on emergency heat for at leatst 2 weeks. By high, it was over $700. We do heat all day since my daughter is home schooled. This has been one of the coldest winter in the last 20 years. However so was last year. Our cooling bill was significantely lower than the previous own by about 30% and it was a hot summer.
I am trying to get a HVAC technivian to come out to check things out. I have also scheduled an energy audit. I know I have some leaky door seals and too many windows but I believe something else is going on. Since moving in I replaced most of the light bulbs with CF and drop the hot water temperature from 150 to 125. Needless to say, the heat is driving the bill.
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Here are the heating performance tables for the heat pump units that Goodman lists. They are specific to the particular condensing (outside) unit and the indoor coil/air handler.
http://i5.photobucket.com/albums/y174/bashful24/Scan10295.jpg
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Thank you. Did this come from their web site?

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Yes, the dealer side of their website.

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What is the rational behind this? Granted at low temperatures the heat pump produces very little but I thought I read that even at that point it is cheaper than pure electric resistive heat. Based on my daily monitoring, it looks like my sysyem works well until the night temperature falls to about 25.
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Sounds about right but your unit is also working real hard. the wear and tear also has to be taken into account. When my unit had electric strips for backup heat the change over point was about 32 degrees when I went to NG backup they recccomend 40 for best economy. I understand we may be getting net metering soon. If this happens the night electric rates may be only about 3 cents per KWh. In that case using heat stripps would be a bargain at night.
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the COP (coefficient of performance) is at least 2.2 or more even at 25 F. outside temp. So the heat pump is still electrically efficient, meaning you're getting 2.2 times the heat with the heat pump versus resistance heating. But you're getting a lot less total heat from the HP because the thermal efficiency goes down as outside temps go down, and the electric resistance supplemental heat is quite expensive depending on where you live and your utility rates. Folks up north usually have a dual fuel system where the HP shuts off at say 30F. (varies) and the furnace turns on to provide the heat at the colders temps (they don't run at the same time).
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Thank you explaing the COP numbers. The data you sent explained a lot. What started this whole disscussion was that my last bill was $200 higher than my bill for last January. During January of last year, my main heat pump failed and I was running on 100% resistive heat for at least half a month if not longer. Prior to the repair, I was unable to get the house up to temperature.
I am in NC (not in the mountains).

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Sounds like you know you need to keep an eye on it since going into emergency heat is expensive. Excessive cold temps will cause it to run the aux strips as well. When they are running your cost is going to be high. You did not post where you are?
Propane is not nearly as cheap as natural gas so there might not be a lot of savings in that direction. It's certainly cheaper than resistive electric though and in more northern areas heat pumps with backup propane is probably the most economical solution. The heat pump runs in moderate outdoor temps and the propane kicks in when the temps get more extreme. But replacing your existing air handlers with propane furnaces will not be cheap. That assuming that your current heat pumps can be adapted to the dual mode.
Geothermal heat pumps are also very econimcal to run but they have not been popular enough to drive the cost down. It's also difficult to find people that can install and maintain them properly.
If you have a lot of windows I suggest you get some layers to put on them. Folding blinds and heavy draps that are made with backing. When it's cold outside close both. Check for airleaks and add some of that self adhesive foam where windows don't close completely. Usually you can add a strip at the top and that will lower the entire window unit a little making the bottom seal tighter. Check the attic insulation as well. Adding insulation in the attic is cheap and easy to do.
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I was wondering I could change the settings on my thermostat to "heat pump without AUX heating". This should prevent the thermostat from ever turning on the emergency heat. This would allow me to set the temperatur at night lower and allow the heat pump to bring the temperature up in the morning without turning on the AUX heat. I would only do this when the outside temperatures are above 40. Currently, I have only a minor setback at night because the thermostat calls for AUX heat if if sees the teperature difference greater than 1 or 2 degrees which happens if I set the temperature back more than 2 degrees at night.
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