Setting up Dueal Fuel System for optimum performance

[hamons]

WOW - this is agreat site. Wish I would have known about this site 3 mos ago when I was researchign and bought a new system for my home. Although I think I would have made the same choice -- it would have been easier.

I wanted your help to see if I everything is setup for maximum efficiency.

The system is Bryant Dual Fuel Heat Pump System

Bryant 80% 2 stage 312aav Furnace and 13 SEER Bryant 650A Heat Pump controlled by Honeywell 8320 Thermostat.

My queestion is how should I se evenign set abck for max efficiency. I have never had a heat pump before and would assume that cooling off the house too much wills tart to harm the cost savings.

Is there a way to setup thermostat so mornign warm up happens with furnace and then temp is maintained with HP?

What temperature should the thermostats balance pointbe set too to go from electric to gas?

Any other pointers you suggest in using HP system?

[dan sw fl]

Originally posted by hamons
What temperature should the thermostats balance point be set too to go from electric to gas?

Depends on ..
Location ( operating hours .. AZ or Canada )
Gas & Electric $ RATES
and What the rate might be TODAY.
Equipment efficiencies
Load Calc ( duty cycle )

All factored together
in an Energy Co$t Analysis

Or Guess 33'F? ... Somewhere between 25'F to 41'F
for This week

OF Course, a knowledgeable LOCAL A/C firm ( or electric utility) would KNOW this 'off the top of their head'.
Knowledgeable ... being the operative word here.

WIDE range of electric rates in North America:
... $0.05 to $0.25 per kW.
... Time-of-day rates?


Nat Gas rate .. What day is it?

http://stockcharts.com/def/servlet/SC.web?c=$NATGAS,uu[h,a]daclyyay[de][pb35!b140!f][vc60][iLb14!La12,26,9]&pref=G

[Edited by dan sw fl on 10-12-2005 at 07:08 AM]

[BaldLoonie]

Usually you don't want a setback with a heat pump.

The Vision Pro won't bring on backup. If you want a morning warmup to occur with gas, you'll want a different control system.

[hamons]

Thanks for the replies

I live in Kansas City. Our WInter Electric rate is .043/kwh for the first 1000 and $.039/kwh after that. Good rates.

SO you don't think I should set the thermostatback at all in the evening?

68 deg is normally a comfort level for my family. In the past I set it back to 50 at night and warm up by 7am.

I had a very good installer put in my system -- but did not consider the thermostat to be there job.

[eeh]

posted by BaldLoonie
Usually you don't want a setback with a heat pump.

The Vision Pro won't bring on backup. If you want a morning warmup to occur with gas, you'll want a different control system.

Which systems or tstats will allow a morning warmup using gas when o/s temp is still above the balance point?
(gas & heat pump system)

[tpa-fl]

The VisionPro stat will work fine for this, as it was designed to work with dual-fuel systems. Using too much of a setback can cause the system to use the gas (more expensive) heat when used with the older setback thermostats, but the VisionPro stat automatically calculates for this and prevents the home from getting so cold that the HP couldn't catch up. By default, it assumes running the HP is more cost-efficient than the gas furnace, so it will do whatever it can to use the most efficient source. For example, I have my VP set to 85F for the cooling setback temperature. The occupied temp is set to 78F. There are many days where the stat won't let the room get above 83-84F because it knows it'll miss the 78F setpoint. Usually it accomplishes this with just the first stage of cooling, but I have seen the second stage kick in every so often, but in these cases the 2nd stage would be needed anyway.

There will be a time when the HP becomes near-useless b/c of a low outdoor temperature, but that's a question I'll defer to the experts on the forum. I'm a Florida native. Heat for us usually means a few heat strips slapped into the ductwork after the AC coil and it only really gets used ~2 weeks out of the year.

[BaldLoonie]

The Vision Pro will not bring on gas if outside temp is above the changeover point. So if you have your changeover set as low as possible, on a cold morning there will be no reserve capacity to warm the house back up.

The entire capacity of the heat pump will be used just to maintain the temp. 2 ways around that, set the changeover point warmer or use an old style dual fuel kit that will bring on gas to warm the house back up then return to heat pump.

[docholiday]

Eliminate the outdoor stat all together and let second stage control the gas. Thats how mine works. I dont use gas unless it needs to and if you turn off the setback logic your second stage would bring on the gas.

[Black Adder]

Sounds like an excellent way to set it up Doc... I have a variable speed two stage furnace and Heat Pump. With my vision pro I think I will set it up with 3 stages of heating and maybe do away with the outdoor sensor for a while and see how that works out.

[inturmoil]

Eliminate the outdoor stat all together and let second stage control the gas. Thats how mine works. I dont use gas unless it needs to and if you turn off the setback logic your second stage would bring on the gas.


Awesome Doc. Here I was thinking outdoor sensors, if X then Y, relays and stuff. I might have complicated a simple situation.

[wyounger]

Whoa, whoa!

"I wanted your help to see if I everything is setup for maximum efficiency. "

"Is there a way to setup thermostat so mornign warm up happens with furnace and then temp is maintained with HP?"

These two don't go together. If you want best efficiency/operating cost, use relatively small setbacks during vacant/sleeping periods and use the VisionPro to *maximize* how much of the work the heat pump does- whatever heat you can get out of it comes much cheaper than heat from the furnace. You only want the furnace to run when absolutely necessary.

Researching this question made me realize there is a difference in how the VisionPro does dual fuel as opposed to how the Carrier stats do it.

On the Carrier units (dual fuel programmable and Infinity stats) you get to control two variables, not one.

1. Maximum ambient temp for using the furnace (above this temp only the heat pump is allowed to run, period).
2. Minimum ambient temp for using the heat pump (below this temp, only the furnace is allowed to run, period).

If you set these two parameters to the same temperature, it acts as a simple "balance point". At that temperature, you switch fuels, period. That is how the VisionPro works. If you want to have enough reserve capacity to recover after a setback, you have to keep the balance point a little higher than you would otherwise. If you set the balance point lower, you will miss recovery sometimes because the heat pump doesn't have any reserve for recovery- even if the balance point you set is actually the real balance point.

I prefer the Carrier setup, though, because having a simple balance point gives the thermostat no discretion to choose fuels based on demand when you are close to the balance point. It also leaves you using more furnace heat than you would otherwise. And finally, your outdoor temperature sensor is usually close to your heat pump, like it or not, which tends to mean that after the unit starts up in heating mode, your outdoor temp signal drops a couple degrees. If you have zero discretion at the stat to decide which fuel to use based on demand, the stat will have a tendency, when you're near that balance point, to start up on heat pump, see the ODT drop, and then switch to furnace. Not efficient. If you can consider demand along with the temperature, it's less likely to act indecisively.

Instead, I like to give the thermostat a window in which it gets to choose. For example, you set the furnace so that it's not allowed to run when it's over 40 degrees, and the heat pump so that it's not allowed to run when it's under 30. If it's 31 degrees and running the heat pump nonstop is meeting demand, you want it to do so. If while it's 31 degrees out, you raise the setpoint a degree, or you need to recover from a setback period, the stat recognizes that it will never get there with the heat pump (demand is too great), and uses the furnace. This way you can use the furnace down to the real balance point instead of fudging the balance point up to an artificially high outdoor temperature (40, 45). The numbers will vary depending on your application, but these are the ones I've had luck with around here.

A lot of pros think I'm crazy when I tell them that both of my houses had balance points right at 30. They're used to using 40 or 45 because of the reserve capacity issue. If you give the stat credit for the intelligence it's got, though, you can use the heat pump down to colder ambients than you would expect for maintaining temp, and rely on it to know when the heat pump isn't going to be enough to make a decent recovery. The intelligent recovery will figure out in short order how quickly the heat pump can achieve recovery in outdoor temps near the balance point and will start making pretty good decisions on what to do. If it can recover by starting the heat pump way early, it will do so; if it's going to take unreasonably long, it will wait longer and start the furnace at the right time for the furnace to hit the recovery just right.

With either setup, you still don't want a large setback, because the more ground you have to cover in recovery the more often you will have to use the furnace to do it. I've had good results using 2-3 degree setbacks. In a colder climate (one where you may see dual fuel operation more in fall/spring and basically furnace only in the winter), you might want to use larger setbacks for the dead of winter, since the heat pump isn't coming into play.

[Edited by wyounger on 10-13-2005 at 11:06 AM]

[hamons]

That sounds great Wyonger.

Heat pumps are new to me -- fairly uncommon in this area -- until Dual fuel became more common. But with low electric rates and mostly mild temps -- it seems to fit.

When I asked my installer about this he said set it back to 58 degrees at night for atleast 8 hours. He siad the VisonPro is so advanced that it makes large setbacks with Heat pumps workable.

I guess bottom line is I'll have to play with it. Lots of varaibles to mess with though.

Setback temperatures and balance point.

Right now balance point is set to 30 degrees.

[BaldLoonie]

Black, you can't do 2 stages of gas backing a heat pump with the VP. At least the way they have it designed. If you want to do some crazy wiring you might be able to jury rig something. I have an old Robertshaw 9720 and a DPDT relay. Pump is stage 1, gas backup is 2 & 3 though normally I have gas backup shut off via a toggle switch. A White-Rodgers 1F90 with 3 stage heat will do the same. The VP won't.

[hamons]

So I am not getting any benefit out of having a 2 stage furnace?

[wyounger]

Originally posted by BaldLoonie
Black, you can't do 2 stages of gas backing a heat pump with the VP. At least the way they have it designed. If you want to do some crazy wiring you might be able to jury rig something. I have an old Robertshaw 9720 and a DPDT relay. Pump is stage 1, gas backup is 2 & 3 though normally I have gas backup shut off via a toggle switch. A White-Rodgers 1F90 with 3 stage heat will do the same. The VP won't.

Looks like Loonie's right- I just checked the VP manual. I hadn't thought about that issue.

Blackadder, it looks like you *could* do (other than using the furnace board to control its own staging):
-configure it for 2H/1C with your second heating stage as low fire, and emergency heat as high fire. About the same effect as a toggle switch, but tidy enough to not annoy the missuz.
-use an outdoor thermostat to control furnace staging...?

It's a shame it's so hard to get a single stage furnace with variable speed (Nordyne or bust?) A two stage furnace in conjunction with dual fuel is kinda redundant, and frequently control systems can't handle all the stages anyway. And just watch out if you're looking at a two stage heat pump and a two stage furnace... not much will handle that. Infinity systems can do it.

Y'know, I just went looking, and apparently the Thermidistat can do four stages? I've never tried it, but it looks to me like they can handle a two stage heat pump with a two stage furnace. In fact they even let you program it to choose whether you want low fire or high fire for defrost tempering. It's not as pretty as a VisionPro, but in some ways I still like its bells and whistles better.

And the regular Carrier dual fuel stat can certainly handle three stages in dual fuel, either with a two speed furnace or a two speed heat pump. I have to say, Carrier's dual fuel stat was way ahead of its time when it was released.

[Edited by wyounger on 10-13-2005 at 02:24 PM]

[wango]

So if I have a HP with a two stage furnace with a VS motor I would be stuck with the HP and firststage heat only.

The VP model I have has 3heat and 2 cool.

Is it the VP that controls the 1st to second stage adjustment or is it the furnace?

[docholiday]

Originally posted by hamons
So I am not getting any benefit out of having a 2 stage furnace?

Yes you are. Not financial but comfort. The full fire is probably not needed. Mines a two stage furnace under a heat pump. Works great.

[inturmoil]

BaldLoonie
Associate

Registered: May 2000
Posts: 13299
Black, you can't do 2 stages of gas backing a heat pump with the VP. At least the way they have it designed. If you want to do some crazy wiring you might be able to jury rig something. I have an old Robertshaw 9720 and a DPDT relay. Pump is stage 1, gas backup is 2 & 3 though normally I have gas backup shut off via a toggle switch. A White-Rodgers 1F90 with 3 stage heat will do the same. The VP won't.


Yes you can. There are at least a couple of ways.
With a trane you could just jump w1-w2 and there would be a 10 min timer for 2nd stage gas heat.
I put in a Trane 16i (two stage) heat pump and did it with a vision pro. Use your imagination.
Jason

[dan sw fl]

Originally posted by hamons
I guess bottom line is I'll have to play with it. Lots of variables to mess with though.

Setback temperatures and balance point.

Right now balance point is set to 30 degrees.

With those VERY LOW electric rate$,
maximize heat pump use.
28'F " seems " just about right.

I didn't realize anyone is as low as $0.04/kW
(except Time-of-Day rates).

[wyounger]

That is really, really low. Is it really 4 cents total in KC? I know these things can be easy to misinterpret... utility rate structures can be absurdly complicated.

I know if you go looking for Georgia Power's winter rate, it looks like 4.something cents per kwh, but if you read the fine print, their is a separate "fuel cost recovery schedule" that adds another 2.6 or so cents per kwh to cover the cost of the fuel for the plants. The four cents covers everything else.