Thermostat settings for a heatpump

Jimbo65 · 12-13-2011, 06:18 PM

I have an older Rheem heat pump (10 seer) that uses a Hydrokinetiix hydrocoil for auxilliary heat. I just replaced my old analog thermostat with a Lux LTX 9600TS programmable touchscreen thermostat. The thermostat is compatible with heat pump systems with single stage cooling and 2 stage heating. The install was easy and everything works fine. My question is regarding some of the settings on the thermostat. Specifically the settings for Swing ( .25 to 2.25 Deg. in .25 increments) which I currently have set to 1.25 Deg. , Offset ( 0 to 9 Deg. in 1 Deg. increments) which I have set to 1 Deg. There is also an option to enable the thermostat to utilize "smart recovery" to achieve the desired temp at a specified time by anticipating the time necessary to increase/decrease temp and doing so in the most efficient manner. I guess this means it tries not to use the auxilliary heat when raising the temp in heat mode. There is also a setting in which the thermostat doesn't initiate any changes for a period of either 2 or 5 minutes. I have it set to 5 which is the default setting. I understand the principle of operation for a heat pump. I understand what these various settings do. What I don't know is what settings are going to be the best choice for my particular system. I'm not used to seeing a thermostat not shut off the heat when the desired temp is reached (swing) not turn heat on when temp goes below set point (swing). I wonder if it would be more efficient to let a heat pump that uses a hydrocoil for aux heat to utilize it earlier on since I have already paid to heat the water in the first place (offset). I would really appreciate any input from an HVAC professional. I could do without the "Get a more efficient heatpump" suggestions. I don't have the money to upgrade. I'm just trying to get the most efficient use out of the system I have. Thanks in advance.

**beenthere** · 12-13-2011, 09:03 PM

With a Hydrokenetic as aux. Its 6 one way, half a dozen the other way. While you already paid to heat the water, if you don't use it, you still lose heat to the basement from the tank even though it has a 2"thick insulation around it.

A 1 to 2 degree drop in temp before bringing on the aux is ok, and so is using just the heat pump for recovery. It will save a little on the electric bill.

Jimbo65 · 12-13-2011, 09:34 PM

Quote:

Originally Posted by beenthere

With a Hydrokenetic as aux. Its 6 one way, half a dozen the other way. While you already paid to heat the water, if you don't use it, you still lose heat to the basement from the tank even though it has a 2"thick insulation around it.

A 1 to 2 degree drop in temp before bringing on the aux is ok, and so is using just the heat pump for recovery. It will save a little on the electric bill.

To be certain I am understanding your answer, are you saying a 2 degree offset is good? What do you recommend for a swing setting with a heat pump? I never measured the insulation on my storage tank but it seems thicker than 2". One thing for sure, when the water is heated to 170 degrees, the tank insulation is still cool to the touch. While I am certain the tank obviously loses heat eventually, I do know it will hold temp for an entire day if the Taco doesn't circulate it. I always go downstairs and check to see if the 10 kw heaters are kicked on. If not used they stay off for a long time.

**beenthere** · 12-13-2011, 09:42 PM

Yes, 2 degree offset is good for efficiency. On swing, 1.5 degrees gives good comfort.

The hydro tank will stay hot for a long long time if its heat is not used. The small tank as i recall is 400 gallons. For its temp to drop 20 degrees, it would need to lose over 66,000BTUs of heat.

Jimbo65 · 12-13-2011, 10:16 PM

Sounds like you know your way around RTS systems. It is a 400 gallon tank. The reason I began to worry about these setting so much is because after I set the thermostat to enable the smart recovery capability it seemed to take a long time to bring the house up to temp. I have the thermostat kick down to 55 at 10 pm when I sleep. I have it set to come to 63 at 5 am. I thought it was nice to have the house at temp for my wife when she gets up at 5am instead of just having it starting to raise temp at 5. The thermostat has a energy usage mode that can be reset. It shows yesterday's usage, todays usage and total usage for the month. After I enabled smart recovery, I reset the hour meter. The next 2 days I was able to determine it is taking 3 hours to get to 63 by 5am. It has been low 20's here at night since I installed the Lux. Even though the thermo is set to 55 at 10pm, the house never goes below 58 if it starts at 63. I just began wondering if it's more efficient to let the pump raise temp on its own for 3 hours turn of recovery mode and let it use the hydro to get to temp at start raising temp an hour earlier? Also I don't know at what temp a 10 seer pump can even extract heat.

**beenthere** · 12-13-2011, 10:26 PM

Even at 20, a 10 SEER can still extract heat efficiently. In three hours of run time with the outside temps at 20, the heat pump will only use about as much electric as the hydro in about an hour an a half, to an hour and 45 minutes.

Jimbo65 · 12-13-2011, 10:31 PM

Quote:

Originally Posted by beenthere

Even at 20, a 10 SEER can still extract heat efficiently. In three hours of run time with the outside temps at 20, the heat pump will only use about as much electric as the hydro in about an hour an a half, to an hour and 45 minutes.

So leave it alone and let the heatpump eat for 3 hours. Will do. Thank you very much!