Balance Point Adjustment Question

[georgiaguy]

I have an Amana Ultron dual fuel heatpump with a Vision Pro stat. The installer set the balance point at 40 degrees. I've dropped it to 35 degrees (which is easy to do on the Vision Pro) and the system seems to be working fine with the house staying comfortable. I'm contemplating a drop to 30 degrees, but I'm not sure if it requires an adjustment to the defrost board. If so, I probably need to call the installer because I do not believe the stat controls the defrost call. Does any one know if a defrost board adjustment is necessary, or if it is handled by the stat?

[tecman]

You can drop the balance point further, if the heat pump can provide the heat demand. Some systems will do fine into the 20's.

No need to do anything with defrost. It is controlled by a board in the compressor unit and will work properly at the lower balance points.

paul

[dash]

The balance poit you refer to is the Thermal Balance Point,it can be calculated ,but what you are doing is fine.

There is also an economic balance point,meaning the temp at which the heat pump is costing more then gas would to heat you home.This can be calculated,using the cost of gas and electricity,effienecy of the furnace and heat pump.

[ruud-man]

I would think one should avoid the defrost cycle because it is a large energy user.

hat is probably why the contractor used 40dF. Of course defrost frequency is determine by many factors. Location is one of them. Relative humidity during the marginal heating periods is another.

Just some food for thought...

[dw1]

A heat pump icing up is normal, that's why they have some way of defrosting the unit. Agree that you want to minimize going into a defrost cycle.
"Most" heat pumps will have a COP above 2.0 at 17 degrees so you're getting $2 worth of heat for $1 of electricity. Even at zero degrees heat pumps have a COP above 1.1-1.2. (At 47 degrees the COP will be above 3.0.)
You can drive yourself crazy trying to figure the lowest cost for operating a heat pump with dual fuel gas furnace. Part of the problem is both utilities have a sliding scale on what you pay for kwh or therms on top of a fixed price to supply you with either utility. Depending on how the tiers are set up the only savings will be at the lowest rate!
Since moving your balance point from 40 to 35 can you maintain the temperature with out firing the gas furnace? You will have longer run times because as the outdoor temps drop you need more heat. Depending on whether your heat pump has time/temp defrost or demand defrost. With longer run times and time/temp defrost you could have more defrost cycles.
There's no easy answer. :rolleyes:

[glennac]

On dual fuel I prefer to set it at 40 or no lower than 38F especeally if you have a 93% eff furnance.

[georgiaguy]

On dual fuel I prefer to set it at 40 or no lower than 38F especeally if you have a 93% eff furnance.

I see you work in the Atlanta area. Any particular reason you prefer a 40 thermal balance point?

Thank you to all that have responded. My concern was principally limited to whether or not lowering the thermal balance point at the stat requires an adjustment to the defrost timer on the outside unit to account for the likely increased need for defrost cycles. I'm not sure how Amana's defrost is set up.

[heatermanbob]

I see you work in the Atlanta area. Any particular reason you prefer a 40 thermal balance point?

i didnt know it got that cold in Atlanta..