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  1. #14
    Join Date
    Mar 2004
    Posts
    1,042
    I wouldn't dream of using propane in this case.

    People talk about how dual fuel is the best of both worlds with regard to heating comfort. I think that argument is way overdone.

    With dual fuel, you can run the heat pump OR your furnace, but not both at the same time. When you're below the point at which the heat pump can keep up, of course, the furnace does a good job of providing toasty hot air. When it's mild outside, the heat pump can provide fairly toasty air. But when you're right at the balance point, especially if the balance point for your house works out to be pretty low for your house, the heat pump discharge air temperatures can get a bit low (maybe 85-90 degrees). The air movement can feel a little bit drafty in comparison to what you get from a heat pump in milder weather (95-100) or from fossil fuel heat (120+).

    With electric backup, the comfort results vary. Either way, in mild weather, the heat pump can do fine by itself. As it gets colder, it runs basically nonstop, and again, discharge air temperatures can get a bit low. Then as it gets colder, the thermostat starts adding in strip heat as the heat pump isn't keeping up anymore. Then everything starts to depend on the setup of the thermostat and the heat strips. There are lots of variables that determine how comfortable you are in this situation.

    A big help in these cases is to have a variable speed air handler in conjunction with a thermostat that's aware of outdoor temperature (this is most common in Carrier equipment, as far as I know). You not only get rid of the cold blow issues, but the right system can also slow down the indoor blower when it gets below a certain temperature outside; that helps keep the discharge air warmer when the heat pump's output would otherwise start to feel a bit drafty.

    If you use mid-sized heat strips (or big strips wired such that you don't get the full wattage unless you're in emergency heat mode), the strips run a lot of the time in cold weather. Still, they have to cycle off here and there, so there are some periods of drafty heat pump heat with no strip heat added in. If you just run big strips, they cycle on for a few minutes here and there, and you end up with mostly drafty-feeling heat pump output, interspersed with bursts of rip-snorting-hot air here and there. But if you run *multistage* heat strips with a stat that can control them, you can do nifty stuff, like run the strips at a low wattage steadily, staging in more and more strip heat as needed. By having the stat control the staging, though, you can do a lot to make sure that anytime you need some auxilary heat, you get to use a small enough element that you can run it pretty much nonstop, which keeps discharge temperatures up. Then you can add any additional heat that's needed with a big second stage heat strip.

    The traditional heat pump setup not only had the cold blow issues, the thermostats were stingy with backup heat. If you set them to 70 degrees and the heat pump wasn't keeping up, it might let the temperature get down to 67-68 before it would turn on the strips, and then it would cycle the strips on only enough to maintain that setpoint. Yet as soon as the heat pump could keep up again, the room temperature would get back up to 70. When the strips did come on, they would come on for a big blast of heat, and then stay off for a good long time again. No wonder people didn't like them!

    That's why I'm so impressed with the Carrier Infinity air handlers. They have variable speed blowers, three-stage heat strips, an outdoor temperature sensor, and a control system that knows exactly what to do all those goodies. The results are really outstanding. The system adjusts blower speed to suit outside temperature so that discharge temperatures never drop below what is comfortable (regardless of whether you're above or below the balance point). It keeps the wattage of the strips as low as possible when they are on, so that they can run slow and steady, instead of needing to cycle on and off and leave you feeling chilly during the off cycle.

    If you had a more economical source of fossil fuel on hand, you would be OK with a dual fuel system like mine. Then you just run the heat pump until it either 1) can't keep up or 2) is starting to feel drafty. Below that temperature, you just burn gas and don't worry about it. But the cost per BTU of my backup heat is less than half of what yours is. As it was, the only reason I bothered with gas backup here in Atlanta was because of electrical service issues (the gas line was already run, the electric wasn't, and it wasn't going to be easy to change that). A nice heat pump will do swimmingly as far as comfort goes, will be cheaper to operate, and cost a bit less to install than a nice dual fuel system.

    You may still want to have propane around for other reasons (stove, water heater, gas log or other heat source that doesn't require power). I just don't see where using it for space heating works to your advantage in a case where strip heat is cheaper than very efficient burning of propane. In fact, I take back that comment about the water heater; you can heat water for less with electricity at those rates!

  2. #15
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,210
    Very, very nicely put, wyounger. Your choice of words make, even, me, appreciate my Carrier 38YZA heat pump and my FV4 fan coil and Thermidistat all that much more. I don't have the Infinity though, it came out a year or two after I had my system installed. I do have the outdoor sensor, too! I just got my Hydro bill today and it was $175.00 for 35 days. This includes all my hot water (60 gallon electtric tank) and all my lights and stove and fridge etc. Now I do run a direct vent gas stove in my downstairs family room only when we are down there which is mostly afternoon's and evenings. I have not got that bill yet, the previous month it was $ 45.00, so I'm anticipating a little more then the previous month. I just got my gas bill for the last 30 days, and it's $50.90, and the number of degree days is 598.

    Nevertheless, that was a great explanation you made there, bravo!

    Thorton

    [Edited by thorton on 02-15-2006 at 02:29 PM]

  3. #16

    Smile

    Very good info. Thanks to all and again, my apologies for appearing to be impatient. I've just been really stressed the past couple of weeks and started to panic a bit.

    Anyhow, it's interesting that wyounger mentioned the carrier system I'm installing, ie. Infinity with variable speed. 38ydb unit I believe.

    Sounds like I'll be placing the order to the heat pump with electric backup tomorrow.

    I did learn today that the power company has a fuel surcharge that actually runs up the rate to around 9.5 cents per kwh, but that doesn't seem like it will make much difference in this situation.

    I lot has been made about not being as comfortable with this setup as opposed to gas, but I feel confident that if my wife isn't warm enough, I can just turn up the heat a bit.

    Further, we'll have a couple of gas logs in the home that can be used to supplement if it is really, really cold.

    Thanks again to all

    Joel

  4. #17
    I can speak for Central MD, not VA.
    Electric rates are going to SPIKE big time in June 2006. This is due to artifically low rates due to lock in in 1999 of electric commodity.
    We're talking 60-75% increases. This will make nat gas look very appealing again.
    The governor has already entertained rate increase caps but more than likely it will be up to the PSC which will laugh at such caps.
    I believe duel fuel will pay for itself easily with the volatile nature of the markets , especially in the Northeast.
    Bottom line is YOU AND I DON'T KNOW what next year or the next 10 years will bring.

  5. #18
    Good point and thanks for the info. However, electric rates in VA are locked til 2010, unless the General Assembly should change that of course, which I beleive is unlikely.

    Further, if I had natural gas available as oppossed to propane, I probably would lean that direction. You're right no one knows what will happen to any of these costs for the various fuel sources, but I'm concerned that propane will remain rather high indefinitely because it is closely tied to the cost of crude oil and with all the various factors contributing to crude oil spikes, I can't see how it could come down very much for an extended period of time.

    Thanks,
    Joel

  6. #19
    Join Date
    Mar 2004
    Posts
    1,042
    Originally posted by gooberjkf

    Anyhow, it's interesting that wyounger mentioned the carrier system I'm installing, ie. Infinity with variable speed. 38ydb unit I believe.

    Sounds like I'll be placing the order to the heat pump with electric backup tomorrow.
    Good stuff. Keep in mind that you don't absolutely have to use the two-speed Infinity heat pump to get the vast majority of the "Infinity system" benefits. I have actually not used one of those two-speed Infinity outdoor units yet. Rather I used the "Performance 13" YXA-series single speed heat pumps. In so doing you drop the two speed operation and the self-diagnostic features in the outdoor unit that can communicate through to the Infinity control's display. Depending on the exact application, that can be a good way to trim cost without sacrificing much function or efficiency.

    Make sure your contractor knows you want the multistage "identifying" heat strips so your Infinity control has direct control over the heat strip staging. With the wrong heat strip it won't have direct control and will just have to do on-off control, which to me sacrifices a lot of the beauty of this setup.

    To get the highest possible efficiency from the YDB unit in three ton size, by the way, they need to order the special "037" variant. There is a regular three ton "036" model that is basically the same capacity; the 037 model has a few special parts in it to boost efficiency. When they say that this unit is "17 SEER", the one that achieved 17 was this special 037 model. I'm not sure if you're getting a three ton or not, but if you are and you want to shoot for the moon, talk to your contractor about the difference between the 036 and 037 model.

    [Edited by wyounger on 02-15-2006 at 04:14 PM]

  7. #20
    Join Date
    Feb 2006
    Posts
    5

    A reply and question for der_panzer

    I went with the dual fuel so that I could use a small generator during a power failure. Set it to gas only and you only need enough power to run the blower.

    der_panzer, I also got the 48XZ. When it switches to gas and the blower at a higher speed I have a roar/thumping noise hard to explain wondering if you notice that in yours. Thanks


  8. #21

    Exclamation Update

    Funny that you mention the generator. I'm actually starting to re-think the heat pump and electric for several reasons, one of which is the generator.

    I'm convinced that the electric is going to be more cost effective than propane, however, since we average about 30 days per year below the balance point, I probably won't use either type of backup very often. In addition, I also want to install an automatic whole house generator which requires propane to run. Further, my house will have two sets of gas logs that need propane to run. Therefore, I have to have propane on the premises regardless. I still prefer the electric, but perhaps with all this I may be better off with propane as the secondary.

    Lastly, I'm a bit concerned about my wife during cold spells with electric as the secondary. My HVAC contractor says that the air from the electric secondary will be considerably cooler than the air from propane. My wife, like most, is very cold natured.

    Thanks,
    Joel

  9. #22
    Join Date
    Aug 2004
    Location
    Midwest
    Posts
    105
    I have 2 38YDB systems, a 3T with 15KW of strips and a 2T with 9KW of strips. Both have FE fan coils and Infinity controls.
    I replaced 2 dual fuel systems that used propane.

    WOW are these systems nice! You really need not worry about the supply air temp, any time it is cold enough that the system is calling for aux heat the supply air temp is going to be every bit as warm as a condensing furnace.

    These controls will allow you to make these systems run any way you would like but the best is to let it do what it wants to.
    I am heating 4600 sq ft and had a total elec bill last month of 148.00. I admitt my power is fairly cheap at approx .045 KWH.
    My hot water tanks are still on the propane but I would change that also if they were not so new and I would have to upgrade my service to a 400 amp meter can.

    Infinity= Cadillac

  10. #23
    I think I would go with the duel-fuel and make those fireplaces burn wood instead of gas, gas logs burn alot of gas with little or no heat, most of the heat gose straight up the chimney. And the one thing that you forget, if your wife is cold natured, the sofa is cold and lonely place if the wife ain't happy


    “Tell me and I forget. Teach me and I remember. Involve me and I learn.”

  11. #24

    brjones

    What part of the country do you live in? How are your temps?

    Thanks,
    Joel

  12. #25
    Join Date
    Aug 2004
    Location
    Midwest
    Posts
    105
    I am in KS and it is 10 deg right now and it was -5 last night. BUT this has been the 2nd warmest winter on record overall. It has really been a perfect heat pump winter with lows in the 20's and most days in the 40's.

    Last night was the coldest it has been since I installed these new systems. Just to see how it would do this morning I locked the aux heat out and let the HP run on high. The 3T system had 1101 CFM air/flow and 88-90 deg supply air temp with the ambient temp of 0-5 deg. Not bad. Of course this was below the balance point so I did not leave the aux heat locked out. It ran the 1st stage aux(5KW) most of the night and used the 2nd stage (10KW) a little. The only time I have seen it need all 3 stages of aux is during a defrost when HP is running on high speed.

    I have never thought the supply air was too cold but if I did the Infinity lets you select "Comfort" and reduce the air/flow therefore increasing the supply air temp.

    I do agree that you would not have to have the 2 speed cond units to get most of the benefits of the air handler and Infinity control system. I expect to get more benefit out of the 2 speed function in the summer.

  13. #26
    Just curious, but why did you replace the dual fuel? Was it due to operating costs, or was it worn out.

    Thanks,
    Joel

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