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Old 06-07-2010, 01:53 PM   #1
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Need ideas, power consumption mismatch between two heat pumps


Hello!

I know this is probably more complicated than this but here is what I do know:
  1. The North unit is brand new upgrade, Rinnai 75,000 BTU hydronic air-handler 2.5 ton 13 SEER heat pump. South unit is 3.0 ton Goodman Model CPL T36-1B, don't know SEER, but electric air-handler.
  2. South unit is existing unit, I am assuming it's sized properly.
  3. Both units are connected to separate Aprilaire 8870 thermostats with remote sensors inside of two separate bedrooms. Each are set at the exact same temperature.
  4. Both bedrooms are on the same side of the house, have same number and size of windows facing same direction and rooms are exactly the same size
  5. The North bedroom is above a conditioned basement, the south bedroom is above a non-conditioned crawlspace.
  6. Both bedrooms have lofts above them that communicate, i.e. no doors between sides of house.
Here's the problem? I have installed a TED 5000 we have two separate breaker panels one for each half of the house. Each unit is on one of the panels. The North half had 532 kwh of consumption and the south half older unit has 782 kwh of consumption. When neither unit is running house baseline is about 300-500 watts of power being used. Is it just an age of unit (SEER) that is creating the 250 kwh difference in consumption? I do feel that the new unit cycles far less. The older unit runs appreciably longer, but does cycle. Is this a sign it's not sized properly or just evidence of improving the SEER rating? I didn't get TED until after the new HVAC was installed so don't have reference for "before" state.

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Last edited by ChrisDIY; 06-07-2010 at 02:05 PM.
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Old 06-07-2010, 03:06 PM   #2
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Need ideas, power consumption mismatch between two heat pumps


Your comparing a 13 SEER 2.5 ton, to a 10 SEER 3 ton.

While the 3 ton may be cycling more then the 2.5 ton. The 3 ton may have a bit more load to handle. But a 2.5 ton may not be large enough to handle that load.

While the bedrooms may be the same size, and face the same direction. The rest of the load each unit has to do, may be very different. So you need to take that into consideration.

Next, is any of the power monitoring done when the 3 ton could have been in heat mode, and the electric aux heat came on?

I'm sure a new 13 SEER heat pump would use less electric then the current 10 SEER. In theory, it would only lower your KW usage by 30% max, which would only be 75KWH's less.

So a load calc, to see if its over sized. And a check to see if its low on charge, or has dirty coils should be done before just replacing it.

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Old 06-07-2010, 03:43 PM   #3
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Need ideas, power consumption mismatch between two heat pumps


Quote:
Originally Posted by beenthere View Post
Your comparing a 13 SEER 2.5 ton, to a 10 SEER 3 ton.

While the 3 ton may be cycling more then the 2.5 ton. The 3 ton may have a bit more load to handle. But a 2.5 ton may not be large enough to handle that load.

While the bedrooms may be the same size, and face the same direction. The rest of the load each unit has to do, may be very different. So you need to take that into consideration.

Next, is any of the power monitoring done when the 3 ton could have been in heat mode, and the electric aux heat came on?

I'm sure a new 13 SEER heat pump would use less electric then the current 10 SEER. In theory, it would only lower your KW usage by 30% max, which would only be 75KWH's less.

So a load calc, to see if its over sized. And a check to see if its low on charge, or has dirty coils should be done before just replacing it.
The new 2.5 ton cycles probably half as often as the old 3.0 ton. 3.0 ton was charged July of last year when purchased and moved in. Suction lines had been cut, maybe as attempt to steal unit as house sat vacant. There is a wacky return vent layout will need to post a picture. Maybe a cause but no clue how to remedy...
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