The 9000 vision pro will see that the runtime has been too long for the heat pump to make up and switch, however, the 8000 will merely wait for emer. heat to be enacted or for the lockout point to be reached.

 

Another issue to consider is that we used to pay $4 a gallon for gas, and it's now about 1.75. Do you think that the people driving hybrids are mad? Probably not, because in two to four years if the price goes back up to $4 a gallon, they are saving considerable money. The advantage of a dual fuel system is that you can prioritize whichever system is most cost effective relative to fuel rates. I put a very similar system in my house in anticipation of the energy rates going back and forth.

 

...in two to four years if the price goes back up to $4 a gallon,...

I doubt it will be 2-4 years before the prices escalate substantially. As soon as the world economy begins to bounce back, the price of fossil fuels is going to rise quickly, if not before. This is definitely the time for smart people to invest in new energy efficient equipment and systems, while they have the money they would have spent on higher priced products. People need to see that by investing now, they will be making it more difficult for the producers of fossil fuels to increase the prices. It's all supply and demand so if people would now invest in high efficiency, the demand is then constantly decreasing and the prices will stay lower longer. If they just start thinking, "Whew, it's over. Now I can forget about high fossil fuel prices." they're just sticking their heads in the sand. It's a monster lurking in the closet or under your bed (whereever it was when you were a kid, remember?) and when it comes out, if you're not prepared, it's going to be one ugly, scary, monster that will really hurt you!

 

the Vision Pro IAQ has an furnace upstage timer option which means that unless the balance point is met or 2deg. droop is met(if the droop option is enabled) the time you set for the upstage timer will always run 1st stage heat for that time programmed before calling for 2nd stage. Default on the upstage timer is 60mins. You can set it for zero.

 

Thanks for the responses!

Re: VP-8000 Stat. That sucks. Should I upgrade to an IAQ? Also, does anyone have any recommendations about an INSTEON compatible dual fuel thermostat?

Re: Fossil Fuel prices.

I have no doubts whatsoever that prices will go back up; also, in my long term plan, I intend to install a grid-tie solar system next year.

However; right now, for this winter, it seems as if I should lockout my heat pump around 50F.

That's what I'm looking for a math check on ;-)

I'm only frustrated with a little "f"; I'm very happy with my high efficiency equipment purchase, however, I believe that I'm currently better of running my high efficiency furnace than my high efficiency heat pump, simply because of the relative costs of each system.

 

More Info

Given the COPs for your unit and your very low natural gas cost, your heat pump's cost for a therm of heat will not be cheaper than your furnace below approx. 45 degrees. This economic break even point (not to be confused with the balance point), is different for every HP. Yours is rather high, so you'll get less benefit from your HP than those folks (like me) who live in areas where gas is more expensive.

Your Goodman unit is a single stage HP with a two stage furnace. The VP 8320 T-stat (the one for dual fuel heat pumps) CAN handle the coordination of HP and furnace heat. It all depends on what components you installed along with the basic HP. This coordination of systems can be done via an outdoor temp sensor OR a fossil fuel kit + outdoor t-stat. If you use an outdoor temp sensor (installed on the side of the house and connected to the VP 8320) the settings are all handled indoors using the T-stat wall interface. If you have a fossil fuel kit with outdoor T-stat (the kit is an extra circuit board installed in your furnace), then the 8320 will switch back and forth between the HP and the furnace depending on how well the HP can handle the current heat demand. This switching back and forth takes place ABOVE the break even cutoff point. BELOW the cutoff, all heat demands are met using the furnace. The cutoff temp is set outdoors on the compressor unit's control panel.

BTW: Use setting "13" on setup code "0170" to get 3heat/2cool HP coordination.

 

Don't forget...your economic break even point is not static. It will go DOWN to lower and lower temperatures as your natural gas prices go UP. Your HP may not be able to supply all the heat you need at those lower temps (due to your balance point --- which is static), but it may still be economical to use the HP for PART of your heat load if the HP's cost per therm is cheaper. That is why coordination of the systems is very important BELOW the balance point but ABOVE the economic break even point. It's important because you get to milk every bit of cheap heat out of the HP for as long as it is cheaper to do so.

 

Outdoor T-Stat and fossil fuel kit

I have a similar question to the above. I have a very similar system with a Goodman variable speed gas furnace. It has a goodman fossil fuel kit, which I can find little info about. What is the approximate temperature I should set the outdoor t-stat at, and is there an easy way to determine setting vs. relative gas and electric prices.

Sorry I did not supply as much info as above, but I am just looking for something approximate. Units are about 1 year old, and fairly high efficiency.

Thanks in advance.

EARL

 

I have a similar question to the above. I have a very similar system with a Goodman variable speed gas furnace. It has a goodman fossil fuel kit, which I can find little info about. What is the approximate temperature I should set the outdoor t-stat at, and is there an easy way to determine setting vs. relative gas and electric prices.

Sorry I did not supply as much info as above, but I am just looking for something approximate. Units are about 1 year old, and fairly high efficiency.

Thanks in advance.

EARL

novendeh:

First, go the Goodman site and obtain the COP (Coefficient of Performance) list for your heat pump from the spec sheet. There is a different COP for every temperature interval listed. That's because your air-source HP becomes less efficient and therefore more expensive to run as the outdoor temperature goes down.

http://www.goodmanmfg.com/Home/Products/HeatPumpSystems/tabid/216/Default.aspx

Second, your gas bill is probably quoted in therms, so find out what the current cost per therm is. Multiply that amount by the percentage efficiency of your furnace (.80 or .90 or .95). The result is your cost per therm of furnace heat. It is the same no matter what the outside temperature is.

Third, take the current cost per KWH from your electric bill. Then do the following computation for each temperature interval from your Goodman HP's spec sheet:

( (Cost per KWH*100,000)/3,413) / COP )

Fourth, you now have a cost per therm of HP heat for each temperature interval. Compare HP costs per therm to your furnace's cost per therm until you find the outdoor temperature at which the cost for a therm of furnace heat is cheaper than a therm of HP heat. That is your break even point, aka your economic balance point. Below that point, you should cut out your HP and rely solely on your furnace.

Fifth, quite unrelated to the above is the so-called balance point. The balance point refers to the outside temperature at which your HP can no longer provide 100% of the BTU's needed to maintain a given heat setting for your home. If you have an all-fuel kit installed (aka fossil fuel kit), then your aux heat will supplement your HP at temps between the balance point and the break even point. However, in this spectrum, it is still economical to use your HP for whatever portion of the heat load that it is able to provide. The balance point is probably above your break even point, so if you want to maximize economy, set your HP cutoff temp closer to the break even point. Installers often set the cutoff too high, not only above the break even point but also above the balance point. Be sure it is set to what you prefer.

 

Goodman Heat Pump

Thanks for your detailed response. I've learned alot from it. In addition, after I submitted my last reply, I did a google search and found a wonderful xls calculator to do all the calcs for me. Much easier.

If one uses google and searches on heatcalc_Vsn-C_1-08, you can download this calculator.

Many thanks and great site. My installer could never have figrued this out.

 

Thanks for your detailed response. I've learned alot from it. In addition, after I submitted my last reply, I did a google search and found a wonderful xls calculator to do all the calcs for me. Much easier.

If one uses google and searches on heatcalc_Vsn-C_1-08, you can download this calculator.

Many thanks and great site. My installer could never have figrued this out.

novendeh:

I looked over that EPA spreadsheet and it offers a single generic HP calculation based only on KWH cost and HSPF. That spreadsheet cannot tell you when you're HP is cheaper to run and when it isn't. Without that info, you can't determine where to set the HP cutoff. Which means, you won't know how to get the most out of your HP. You can do better than that by using the steps I mentioned below. Good luck whatever you choose to do.

 

Heat Pump

I'm not sure he has correct gas prices. Pittsburgh is pretty cheap, and gas prices are almost double what was used in his calc. If I remember correctly, it was 0.83/therm.

 

But if you use the spread sheet you posted.
Does that spread sheet come up with 3.7 COP the HP is cheaper.
Or does it say higher or lower.

And there are a fair number of areas that NG is less then 30 cents a therm.

Lowest I've seen is 23 cents a therm.

 

Just a tip if you want to stay on top of your economic balance point. Calculate your price per therm using this nice fuel cost comparison tool.

http://www.warmair.com/html/fuel_cost_comparisons.htm

I reuse that calculator every month when i get my updated NG costs and electric rates.

 

Where to locate evaporator on dual fuel application

Hello all, new to this.
Am getting an installation ready, and am wondering about whether to put the evaporator upstream or downstream of the furnace/blower. I might like to run the gas furnace during the defrost cycle, but know that the evaporator cannot be downstream and defrosting while the furnace runs, due to oil/refrigerant separation and compressor damage. For this, then, it needs to be upstream. I've also read that I shouldn't do that due to possible furnace heat exchanger corrosion during cooling cycle. Installer doesn't really have an opinion, so am looking for some thoughts. Knoxville, TN application, probably looking at about a 20 F changeover point on thermostat, which is Honeywell VisionPro 8000 series. So...evaporator upstream or downstream, and why?

 

slambson.

Get a new installer.

Ones that reads the install instructions.

 

Still need help

That's not particularly constructive.
The equipment is sitting in my attic, and I've read the install instructions myself. Believe it referenced the evaporator downstream. However, the furnace manual and the heat pump manual both appear written with the supposition that it is not a dual fuel installation. The installer, who will be installing in 2 weeks, has always only installed downstream, and has said that he's never heard a complaint from a customer about cold air blowing during the defrost cycle, since in Knoxville that cycle tends to be short, and that there is therefore no need to run the furnace during defrost. While I understand that, I believe that we may at some point have another cold winter, and would like to have the option, if it is not otherwise inadvisable.
Also, since I see conflicting opinions in reading this site and others, there must be some debate going on. I'd still like to understand the pros and cons of each approach, if there are any.

Thanks.

 

Its more constructive then you think.

Coil after furnace.

If your contractor can't explain why. Do you really think you picked the best one for the job.

 

Using existing 1994, (Trane XE78 Furnace)

I've just stumbled onto this board a few days ago, and really got into the efficiency discussion with COP and therms cost for HP and Furnaces. Thanks for all the great info.

In the spring, I tore down a rotten chimney, and with it, the flues for my fireplace and my furnace. FP was ng non-vented so no problem. A neighbor had a similar furnace but had it horizontally vented with a power ventilator, so I decided to not rebuild about 16 feet of chimney and use the power ventilator or get a new efficient HP system. Since money is tight now, I've decided to put off the purchase of a new efficient HP system till next year and use the tax credit. My current system for the 1st floor is a Trane 2 Ton compressor ('94) XE1000 (SEER 10?) with a XE78 (78% efficient?) furnace.

I bought a Tjernlund power ventilator($), and will be hooking it up shortly. Since NG is cheap right now, and I live in Raleigh NC where winters aren't too bad, I wanted to know I could insert my old furnace inline with a new High efficiency HP system I plan to get next year? I don't want to have to use the heatstrips, but don't think it would pay to get a really efficient furnace. Elect rates here are approx .10/kw and .98 to 1.04 for therm of NG.

Also, I was wondering if the power ventilator decreases the efficiency of the furnace alot verses just a draft flue?

Hotrocks