if your total price for electricity (dollars / kw's used) is only .063 cents. I would run that heatpump as much as possible. That electric rate is half of what mine is and I run my heatpump alot. Its still pretty reasonable.

jocoman

generally speaking, I agree with above poster's statement. run the heat pump until it is not comfortable and/or will not maintain your home's normal indoor thermostat setting.

you need to re-check your furnace's mdl number and provide the evap coil mdl number.

It must be said that while you have a very nice system, Trane/Amstd's condensers whether AC or HP have relatively mediocre performance/efficiency numbers when paired with VS furnaces.

if you want the "on the money" COP rating, you will probably have to go back to your dealer or AmStd distributor and they can give you the published number. If you will accept a down and dirty number, then take the HSPF number(found in AHRI directory) and divide by 3.4.

you are one lucky person to have cheap electric and gas rates. I will assume you have included all costs to get these rate numbers. I used a 2.5 COP and found on a BTU basis a HP is cheaper to operate by about 20%.

IMO

Here is a link that might be useful: Fuel Comparison Calculator

Yes, both utility rates include averaged delivery rates, ECAs, taxes, etc. My initial electric rate before the extras is $.052 for the first 1000Kw and $.039 for beyond. These rates are part of a program that my utility offers for purchasing high efficiency heat pumps and is only for date range of 9/15 - 5/15. A rate hike was announced recently that may effect that program but hey that's an advantage of duel fuel right? It looks like it might be better winter on the pocket book this year in the KC area regardless of electric or gas usage although the gas rates change almost every month.

tigerdunes,

Thanks for the input. My furnace model is AUH3D120ACV5VAB right off the plate so it looks like I cut off the "B". The coil model is 4TXCD064BC3HCAA.

I've used the divide by 3.4 method but from my understanding that gives an averaged COP correct? Really the only reason I need the numbers is to get the value at certain temps to determine the correct balance point. Is there a way I can calculate these for myself? I don't need it to be deadly accurate but good enough to set my stat. I've already done a good deal of math and used some tools I've found on the Internet but it seems that having these numbers is usually the best way to get it right.

I've read several things about the lower heating efficiencies on the Trane/Am Std. HPs, but honestly I must have bought a good one because I haven't experienced that. My only complaint is the loud sound it makes going into defrost but that's normal from what I've heard and read. Based on your own calculations and my current rates are you recommending that I set my HP cutoff really low and just let the system figure it out due to the cheap electric rates? Thanks again for taking time to respond.

jocoman

you are correct. that COP would be at 47 deg and obviously comes down as outside temp drops.

3221515 Discontinued Systems HERITAGE 16 AMERICAN STANDARD, INC. 4A6H6060C1 4TXCD064BC3 *UD2D120ACV5 56000 10.70 14.25 51000 8.50 31400

this appears to be your AHRI matching number although the mdl numbers are not identical to the ones you posted. you will note you don't get full BTU rating on a five ton for either cooling or heating. a big negative.

I did run across a spreadsheet the other day and I'll check to see if I can locate it.

what is your changeover set at now between gas and electric?

as far as cutoff setting, I think you may be overthinking your situation. It's nice to know economic and temperature balance point but I really think each homeowner must look for best balance of comfort and leveredged savings between gas and electric.

on an unrelated matter, I bet your dealer had to oversize you on furnace to get the 5 ton rated blower. this is a problem with Trane/AmStd.

IMO

tigerdunes,

Right now the stat is set like it was last year to lockout the HP at 20 and the furnace at 30. Depending on the windchill somewhere between 25 and 20 is where the HP will run consistently at second stage and sometimes upstage to the furnace if the timer expires. It sounds like this may still be the optimum setup and you're right that I may be overthinking it a bit. I'm and engineer and tend to overthink a lot of things...LOL. Comfort hasn't been an issue as the HP keeps my setpoint of 69 quite well in most cases. If anything when the furnace kicks on it seems too hot because we're so used to the lower temp supply air.

As for the sizing, I am slightly oversized. My load calcs per the dealer came out to requiring 4.5 tons and I could only get 4 or 5. So the blower speed was set at 350 CFM for the HP and 1850 CFM for the furnace to compensate for the sizing. I hope this is permissible. It's worked pretty much flawlessly for over a year now.

Thanks so much for your time.

jocoman

I understand about these engineers-they like numbers and sometimes can be a real PIA...LOL.

it seems that you have found or are close to the temperature balance point. if you look at the AHRI matching number I listed above, you will see that at 17 deg your system produces around 31.4 KBTU. now the question is what is the least expensive method-gas or electric at your temp balance point. you will get different opinions on this, but I have dual fuel system as well and don't like to see the HP condenser run continuously.

you may be losing some BTUs at that 350 CFM setting.

IMO