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  1. #66
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Quote Originally Posted by tigerdunes View Post
    I would want to see the operational BTU cost of the propane versus electric heat strips.
    What would I need to determine that besides the LP cost of $3.13/gal and electricity cost of $ 0.089/kWh?

  2. #67
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,185
    Quote Originally Posted by pclausen View Post
    What would I need to determine that besides the LP cost of $3.13/gal and electricity cost of $ 0.089/kWh?
    These results are from a fuel comparison calculator that I like to use. Plugging in your costs which I will assume are accurate and all inclusive, I used a COP of 3 for the HP and 95% eff for propane furnace.

    Here are the results and should be used as a guide only.

    Cost per 100,000 btu of useable heat

    Electric baseboard: $2.37
    Heat pump: $0.88
    Propane: $3.60

    Obviously straight electric without the HP condenser is substantially less than propane.

    One thought though concerns your generator capacity. Obviously the propane furnace would not take much power to use compared to an air handler with heat strips and HP condenser. Someone would need to put the numbers to the paper not to mention other appliances like refrigerator that you would want to run.

    Just some thoughts to take into consideration.

    IMO

  3. #68
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Wow, it would seem that propane is not at all the way to go for generating heat in my situation! Yes, the figures I gave were all inclusive and reflect the total amount I pay for each energy type by unit.

    If I'm understanding the results correctly, a TAM8 air handler with electric heat strips would be a more efficient solution given my energy costs. I guess I should also look at replacing that Polaris water heater with an all electric unit. Or am I missing something?

    I have a load shedding transfer switch on the generator, so I'm not too concerned about burst in energy consumption that heat strips would result in, as long at they won't consume more than 10kw for extended periods.

  4. #69
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,185
    I would think you would require at a minimum 15 KW in heat strips that should be staged. That would yield about 51 KBTUs provided from heat strips alone.

    You need to understand your generator's capacity to handle all the appliances including HVAC. I would call the installing dealer for your generator to make certain your generator's capacity is adequate for what you plan on running. Not certain it is.

    IMO

  5. #70
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I have 400A service coming into my house. One 200A panel it tied directly to the utility meter base, the other goes through a 200A transfer switch. Looking at the installation manual for the 15Kw heating module for the TAM8, it appears to be feed via one 40A one 20A 240V circuit. So I can have them wire the 40A circuit to the panel feed by the transfer switch, and the 20A to the panel not protected by the generator. This way, during a power outage, I'd loose the 3rd 5kw stage, but stages 1 and 2 would work fine.

    I'll consult the generator installer/electrician to make sure, and also with the Trane installers to make sure the air handler doesn't do something stupid like shutting down all the way if it senses no utility power on the 3rd heating element.

    The more I think about it, the more I feel a TAM8 air handler is the way to go over the modulating furnace. I have already asked the installer to quote me for the TAM8. I can't imagine that it would cost more than the modulating furnace, even with the 15kw heat strips.

    That cost per 100,000 BTU of usable heat has been a real eye opener for me. I'm very surprised the sales rep did not ask me about my energy costs and just assumed going with another propane furnace was the most energy cost effective way to go. It appears to clearly not be.

    We were about to get a new dryer and I was leaning towards paying the extra $80 for the gas model over the electric, I guess I need to reconsider that as well.

  6. #71
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,185
    Defintely an electric dryer as long as you have panel capacity. In fact I would suggest weaning yourself off propane as is economically feasible with goal of only the propane fueled generator.

    With that said, I still remain concerned about generator's capacity and suggest this be thoroughly researched with all appliances including HVAC before deciding on TAM8 air handler with electric backup heat strips. Dealer will need to help you with heat strip size recommendation.

    In other words, cover your bases.

    I would also want to know the pressure on electric rates where you live. No doubt though you have a great deal of economic leverage with electric versus propane.

    IMO

  7. #72
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,619
    you could go with a tam8 air handler and hot water coil plumbed to your polaris for auxilary and emergency heat,also remember most hvac companys sell you whats best for them not you
    We really need change now

  8. #73
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Going the hot water route would certainly eliminate any electrical concerns with the generator.

    I'm still a little scared about the cost of heating water using propane given the cost figures presented above.

    I wonder if the ultimate in efficiency would be to get a hybrid (heat pump based) water heater once the polaris gives up the ghost? I wonder if such a unit would be able to keep up with the demands of a TAM8 water heat coil?

    Being that emergency heat will hopefully only be used on rare occasions, perhaps the hot water coil would be the most practical solution?

    I'll discuss both the electric and hot water coil options with the dealer tomorrow. You guys have been great and I feel much more informed now than before. I should have posted *before* going with the current solution, but I'm very glad they are willing to change out what I have right now. The tam8 might be stretch, but maybe not if they have to disconnect the line-set from the coil anyway to swap out the furnace. From my measuring, the line set will not need to be extended to be connected to the tam8 since a plenum pedestal is needed below it anyway for the return. The tam8 sure would make for a lot cleaner looking setup.

  9. #74
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,185
    Please followup with whole house media filter cabinet and additional return.

    Good Luck
    IMO

  10. #75
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Thanks. I'll be sure to do that. I'm keeping my fingers crossed that a tam8 + heat strips is less expensive than a XC95m + coil and that the budget will then allow for adding another return and media filter. I know price discussion is not allowed, but a hint as to which is more expensive would be appreciated as I negotiate with them tomorrow.

    I found a fuel cost calculator at purdue.edu. This ones includes an adjustment to be made to the HSPF based on location. For me, the closest city is Richmond, VA, and the adjust is to change the HSPF rating from 9.0 to 7.6.

    The numbers I then get to generate 100,00 btu of heat are:

    $1.171 Heat Pump
    $2.608 Heat Strip
    $3.607 Propane

    So heat pump is still the obvious choice for primary heat and electric for backup as opposed to propane. It seems that the only reason propane would make sense is during an extended power outage where having an alternate local source of energy could be advantageous.

    Another interesting bit of data the purdue calculator has, is that the ASHRAE design temp for Richmond, VA is 18F, not the 5F they used.

  11. #76
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    the supply runs are two close to the end of the trunk .
    the way trunk systems work is off back pressure.the air should hit the end of the trunk and pressurize it. with runs at the end as in the pics it cant build pressure . a simple fix would be to add an 18" long piece of trunk to the end . Then all supply runs could recieve equal pressure or as needed some could be dampered down such as small load rooms baths ect.

    ps this looks like a comon install still only 1 pipe , as is likely why the didnt add the second on the new change out it was easy to just go with what was there

  12. #77
    Join Date
    Sep 2008
    Location
    New York
    Posts
    131
    Quote Originally Posted by energy star View Post
    I to thought five degrees was low as a design temp.
    Manual J design temp for central VA. should be 17-19 for heating and 90 for cooling.
    You can tell on the manual J report that the design temps were changed by the fact that the font is in bold type.

    There could be a justified reason for this, I don't know your area well enough to say for sure. There is a reasonable possibility your equipment is still over sized.

    With that small return and restrictive filter, it's unlikely that the system could actually deliver 4 ton of cooling.
    "The only way in which a human being can make some approach to knowing the whole of a subject is by hearing what can be said about it by persons of every variety of opinion and studying all modes in which it it can be looked at by every character of mind.
    No wise man ever acquired his wisdom in any mode but this."
    John Stuart Mill

  13. #78
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I didn't get a chance to talk to my rep yesterday as he was on vacation. I'll get with him tomorrow. I'll be sure to discuss the restricted return with him, and also see is he can add an extension at the end of the supply run to allow pressure to build up.

    Looking at the run history from yesterday and the day before, I was wondering if it is normal for the heat pump to be running 60-70 percent daily to maintain 71/72 degrees inside, when the temp is in the 30's outside?



    I have the propane furnace set to not come on at all unless it gets below 20 outside, but I was curious if it is normal for a heat pump to run almost constantly when temps are in the 30s outside. If temps drop into the 20s for a full day or more, based on what I'm seeing now, it will mean that the heat pump will run for 24 hours straight.

    Maybe there's more to this than just the cost to generate 100,000 btu of heat? Even though propane is more expensive, if it can deliver that heat in short intense bursts, perhaps that is more economical than having a heat pump droning away all day everyday in the winter time?

    I'm having a hard time deciding if a TAM8 is better or worse than a propane fired furnace, in my situation...

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