Trane XL15i w 4TEE Air Handler

[Jammindude]

I was wondering if anyone knew when / how to shut out the compressor in heat pump mode (I have electric backup). The system is heating the house (1500sqft / one floor / southern Delaware) to 68 degrees without drop to Auxiliary into the low 20's. However, the heat pump is running continuously from the low 20's on down (and basically noticeable longer below 32 degrees... the balance point at full rating is supposedly 37 degrees).

The reason that I ask is that (even without doing the math), I know that the heat pump is still working alone when it is costing more to operate than electric alone. Say at 22 degrees, the electric runs (aux) for about two minutes 6 times an hour by itself, in the same conditions when the heat pump is running continuously by itself. The electric strips (both at the same time) is 15.36KW/h and the heat pump, I believe is 3.6KW/h. The heat pump stops cycling in the low 20's and just runs (producing heat the entire time, albeit progressively more expensive). I'm not sure if I'm figuring it out right, but this would suggest that the heat strips will hit the equivalent of a 15.36KW/h in 6 hours, where the heat pump will hit the equivalent of a 15.36KW/h (heat strip equivalent) in 4.27 hours. So even though the heat pump is still doing it's job, it's costing money at the lower temperatures. To add insult to injury, below 17 degrees the aux heat is kicking in regularly with the heat pump basically running around the clock at the same time. This is the standard Trane installation scheme.

Trane just want's to talk about hybrids under 32 degrees. But there is usuable heat generation under 32 degrees. We seem to have alot of time in the heat pump grey zone here (still working well, but under balance point). I'm just not clear on where to cut it off (or if I can). Like use an external sensor and cut off the compressor at 25 degrees (for example).

Even running in the standard Trane configuration mode, we have saved significantly in the last year over our old heating (propane) and electric A/C 2 Ton central Rheem system (10 years old).

Any ideas?

[hvactech126]

in a heatpump system with electric backup, the heatpump should not shut off when it calls for auxiliary heating. its not trane, its all manufacturers design to have the heat pump run. you may need to change the cycles per hour in the thermostat though, and this will help keep it from running "around the clock"

[Jammindude]

Trane XV15i with 4TEE

I forced the heat pump off so I could measure the time on and off the 15KW heat strips operated alone so I could do an apples to apples comparison of the power consumed by a continuously running heat pump at 22 degrees and the power consumed by the heat strips running alone. What I find is that even though the heat strips take 4 times the power of the heat pump, the heat strips are only running 1/6 of the time. What it suggests, if I'm doing my math right is that when the heat pump is running continuously, you are saving little if anything, because it is using more power than the heat strips do (because it is running so much longer when doing the same work). The heat pump is holding the temp at 68 @ 22 degrees when running continuously, aux isn't required, but the heat pump doesn't quite get the internal temperature to the point of cycling off.

I was considering staging the heat strips in 5KW at temperature "X", the 10KW at temp "Y" and 15KW at temp "Z" (if I can even do that), instead of waiting for the temperature to drop for aux to kick in.