View Full Version : Auxillary for a Heat Pump
03-02-2010, 04:04 PM
I thought I would pass on my experience with my Trane XL16i 4 ton heat pump.
I had my heat pump set up to bring on 10k electric anytime the heat pump could not heat my house or raise temp fast enough and the last 10k to come on below 20 degrees. This worked fine until this winter when it was just so cold all the time.
I found out that using the full 20k could bring the temperature up about 3 degrees setback in 20 minutes at 24 degrees and 10k would take about 1 hour.
So I called and had the HVAC Installer change my setpoint to 30 * instead of 20*. I actually think this will be more efficient even though I am using 20k instead of 10k but recovery time is much faster. I set my stat back 3 dergrees at night.
Does this make sense to anyone? Also, my Trane XL16 i has worked like a charm the past 2 years and has been very efficient and I am in a very cold climate in the winter.
03-02-2010, 04:50 PM
With electric back-up, you want your HP running as much as possible. Chances are it's much more efficient than strips, even at 20 degrees or less.
Ask if your installer can stage the strips to supplement the HP while it's running.
Many HP systems are more efficient when not using a set-back - it avoids using the strips to recover.
03-02-2010, 06:46 PM
The new way you had it set up is not more efficient.
Now you will use more electric coming out of set back when the outdoor temp is below 30.
If your heat pump uses 4 KW an hour.
And with 20KW of aux you can recover 3° in 20 minutes. Then in that 20 minutes that the aux heat is on. You are using as much electric for the aux to recover that 3°F as if the heat pump had ran for an extra 1 hour and 40 minutes to maintain the higher temp all night.
So your probably not saving anything, and may in fact be costing yourself more money to recover.
I would just hit hold and have the second stage aux set to come on below 20F as it was configured before.
If any aux heat is required for recovery, setting back is counter productive. Avoid using electric re$i$tance heat as much as possible.
The system should be wired in stages, 1st is heat pump, the idea in the high efficiency heat pump is to let er run alot.........
03-03-2010, 08:59 AM
My heat pump is staged. It first starts out in low stage heat pump only, then high stage heat pump only, then auxillary if neither can satisfy stat.
The first 10k will now only kick in above 30* and 20k will only kick in below 30*.
I may not need to use a setback at night to 68 and raise at 6am to 71 but I like to sleep with it cooler. I am sure if I left it at 71 all the time the aux heat would not kick in near as much.
My worst power bill was 256.00 last month for around 2300 sq feet and I doubt the outside temperature averaged 30*. I have a 1 1/2 story with high ceilings.
The comfort has been outstanding with this heat pump as it does run a lot and keeps the temperature even. I might should have left the setting at 20* to kick in the full 20k but I thought I would try it and see what happened.
03-03-2010, 11:15 AM
A 3 degree setback at 45F ambient will probably not need aux heat to recover. At 25F ambient or so, differrent story: Aux heat is needed to recover.
Keep an eye on the ambient temps to recover from setback without using aux heat.
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