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  1. #1
    Join Date
    Nov 2007
    Posts
    47

    Questions about my proposed dual-fuel system.

    I have a few (OK, a lot of) questions for the experts here about the system I'm about to have installed. Basic info:

    40 year-old house in Northern Virginia, ~2600 square feet in two floors, plus an unfinished (and unconditioned) basement.

    Heat pump: Trane 4TWX6048B1000B
    Coil: 4TXCD050BC3HCA
    Natural gas backup / air handler: TUH2D120A9V5VA
    Humidifier: THUMD500APA00A
    Stat: Vision Pro IAQ

    I definitely like and trust the contractor, but for this kind of $$ it doesn't hurt to get additional opinions. Just to get past a few issues that usually get brought up in this forum:

    Yes, he's going to do a Manual J -- these sizes are his initial guess, but they may change once he's done the math.
    Yes, I really do want the 95% efficient furnace, even though I expect to be using the heat pump most of the time. I'm willing to spend the extra money up-front.
    Yes, I've considered other brands such as Carrier (the Infinity control is sweet!). I picked Trane as a result of picking the contractor I trust the most.
    Yes, I'm aware that larger Trane heat pumps are a bit low on the BTU range for the quoted tonnage.

    Now my questions:

    - Any obvious issues with this proposal?

    - My current furnace vents up the same chimney flue as my natural-gas fired water heater. Since I'll be going to a condensing furnace, the contractor says that they'll need to install a flue liner, since the water heater will be the only thing venting up the flue. I must confess I don't really understand the reasoning -- any opinions?

    - My current whole-house humidifier plugs into an electrical outlet on the outside of the furnace. This outlet is, I believe, switched to go on/off with the fan (or possibly fan + heat? I need to doublecheck). A humidistat in the return provides control. A pretty standard setup, I suspect. But is there a better way to do it when using the IAQ? I assume what many people do is ditch (or just disconnect) the humidistat in the return, and control the humidifier using the HUM1/2 contacts. Since the IAQ can be configured to operate the humidifier only when the fan (or fan+heat) is on, should the humidifier be plugged into an unswitched outlet? Or is it safer to stick with a switched outlet? Also, is it really OK to allow a humidifier to operate when fan is on but heat is not? Are there issues with condensation?

    - On the flip side, what about dehumidification in the summer? I've seen threads here that suggest removing the factory jumper between R and BK on the air handler, then running wire from R/BK to DHM1/2 on the IAQ, configured in NC mode. Does that sound right? Should Comfort-R mode be left enabled? Anyone have any experience with this setup?

    - How does heat pump defrost work? I have to assume it's under the control of the heat pump, not the thermostat. Do they run a line from the H.P. to one of the W terminals of the furnace, to allow the H.P. to force aux heat on? Does the H.P. handle the required sequencing and lockout timing of switching the reversing valve, cycling the compressor, etc?

    - I'm under the impression that the following connections (using the IAQ's labels) go to all three components (stat, furnace, and heat pump): R, C, O/B, Y, Y2, possibly AUX (see above). Is that right? Any others? I'm sure my contractor will get it right, but I really want to understand how it all works together.

    - Do contractors typically hook up the L (equipment monitor) line from the heat pump to the IAQ? Should I ask him to? Should I care?

    - OK I'm done

  2. #2
    Join Date
    Sep 2006
    Posts
    136
    I'm a lowly HO. I'm having an AS system almost (smaller sizing) like this installed next week. I have an existing Aprilaire 760 humidifier that I'm hoping to use, but I'm wondering how well it (and your choice) will perform on a heat pump.

    I came across a new steam unit that Honeywell just came out with called TrueSTEAM. And it connects perfectly to an IAQ as far as I can tell. There are a few threads on this board about it.

    BTW, your systems sounds great to me. But them again, I'm just a lowly HO.
    Thanks,

    Mark

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    I thought you said you were confident in the dealer you chose. What company did you choose?

  4. #4
    Join Date
    Oct 2004
    Location
    PDX
    Posts
    4,917
    Quote Originally Posted by dbb1 View Post

    Now my questions:

    - Any obvious issues with this proposal?
    Sounds OK, as long as the sizing matches up with the Man. J calcs.


    - My current furnace vents up the same chimney flue as my natural-gas fired water heater. Since I'll be going to a condensing furnace, the contractor says that they'll need to install a flue liner, since the water heater will be the only thing venting up the flue. I must confess I don't really understand the reasoning -- any opinions?
    Code requires it now a days. Plus you will insure that the WH will havet he proper draft going up the chimney. The condensing furnace is most likely going to be vented out the side of your home with PVC pipes. But both will not be in the chimney.

    - My current whole-house humidifier plugs into an electrical outlet on the outside of the furnace. This outlet is, I believe, switched to go on/off with the fan (or possibly fan + heat? I need to doublecheck). A humidistat in the return provides control. A pretty standard setup, I suspect. But is there a better way to do it when using the IAQ? I assume what many people do is ditch (or just disconnect) the humidistat in the return, and control the humidifier using the HUM1/2 contacts. Since the IAQ can be configured to operate the humidifier only when the fan (or fan+heat) is on, should the humidifier be plugged into an unswitched outlet? Or is it safer to stick with a switched outlet? Also, is it really OK to allow a humidifier to operate when fan is on but heat is not? Are there issues with condensation?
    Have the IAQ control the Humidifier. Use the HUM terminal in the furnace to power the Humidifier. No mess, no fuss.

    - On the flip side, what about dehumidification in the summer? I've seen threads here that suggest removing the factory jumper between R and BK on the air handler, then running wire from R/BK to DHM1/2 on the IAQ, configured in NC mode. Does that sound right? Should Comfort-R mode be left enabled? Anyone have any experience with this setup?
    Run the dehumid wiring as suggested in the installation set up. If using the comfort-r settings, there is a set wiring sequence for that. I am sure you installing contractor is fully aware how this need to be wired.

    - How does heat pump defrost work? I have to assume it's under the control of the heat pump, not the thermostat. Do they run a line from the H.P. to one of the W terminals of the furnace, to allow the H.P. to force aux heat on? Does the H.P. handle the required sequencing and lockout timing of switching the reversing valve, cycling the compressor, etc?
    Yep, thats how it works. Couple that with an out door temp sensor, and the IAQ does all the rest.

    - I'm under the impression that the following connections (using the IAQ's labels) go to all three components (stat, furnace, and heat pump): R, C, O/B, Y, Y2, possibly AUX (see above). Is that right? Any others? I'm sure my contractor will get it right, but I really want to understand how it all works together.
    You have the gist.


    - Do contractors typically hook up the L (equipment monitor) line from the heat pump to the IAQ? Should I ask him to? Should I care?

    - OK I'm done
    I never do. Some others will chime in and probably say differently.

  5. #5
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    All things being considered, it looks like a good proposal. I like Trane equipment, and that's a good thermostat selection. You should be satisfied with your selection. I live in MD; what company did you go with? Maybe I've heard of them.

  6. #6
    Join Date
    Nov 2007
    Posts
    47

    trust?

    Quote Originally Posted by second opinion View Post
    I thought you said you were confident in the dealer you chose. What company did you choose?
    Is it considered OK to name specific companies here in reference to proposals? I wasn't sure, since in general my type of post could be viewed as an invitation to criticize the contractor...

    Let me address your general question, though. I trust him to do the job right, given a particular set of choices. I also trust him to make reasonable choices by default, and to tell me if he thinks I'm making bad choices. That doesn't mean I automatically assume he'll make the same choices I would, if I had the requisite knowledge. For instance, he quoted me the Trane 803 stat. I'm interested in features of the IAQ such as frost control, the ability to dehumidify without as much overcooling, etc, so I asked him to quote the Vision Pro IAQ instead. He was happy to do so. Was his original proposal wrong or bad in any sense? I don't think so.

    Finding the right contractor is the most important choice, but that doesn't mean you have to rely on your contractor to make all your choices for you. On the other hand, if you've picked the right contractor you should be *able* to say to him, "Please make reasonable choices for me", and trust that what he comes up with will be OK. I don't want to do that.

    I have the educational and job background to be interested and able to understand the general physics, electronics, and operation of my HVAC system, and to the extent possible I really want to. What I don't have is the specialized training and years of experience to even *consider* doing it myself. These forums are a great place for people like me who want to better understand what the choices even *are* -- the manufacturers seem to go out of their way to hide useful information from consumers.

    I hope this makes sense.

  7. #7
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    Is it considered OK to name specific companies here in reference to proposals? I wasn't sure, since in general my type of post could be viewed as an invitation to criticize the contractor...
    My email is in my profile if you want to email it. I'm just curious as to who you are going with and if I know them. I won't criticize them; from what I see in the proposal, it looks like they know what they're doing. I'm curious who sells the upper-end line of Trane like this company apparently does. Thanks.

  8. #8
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by oloenneker View Post
    Code requires it now a days. Plus you will insure that the WH will havet he proper draft going up the chimney. The condensing furnace is most likely going to be vented out the side of your home with PVC pipes. But both will not be in the chimney.
    Thanks. By the way, "Contractor B", when I asked him why *he* didn't include flue lining in *his* quote, said something like, "In my experience it isn't necessary". Since you say it's required by code, I'm even more happy with my choice of contractor. I could have just asked the guy I picked to explain this question to me, but it sometimes takes him a bit to get back to me (unlike this forum ).

    Have the IAQ control the Humidifier. Use the HUM terminal in the furnace to power the Humidifier. No mess, no fuss.
    Not sure I totally understand. Is the HUM terminal in the furnace a 24VAC supply or a switched AC supply? I was under the impression that the humidifier comes with a standard 3-prong AC cord preattached -- is that correct?

    Also, could anyone expand a bit on my question about humidifiers in fan-only mode? I guess the same question applies to heat-pump operation, depending on outside air temps. Stated generally, is there any danger/problem in running a whole-house humidifier in situations where the supply air temps are not very high?

    Run the dehumid wiring as suggested in the installation set up. If using the comfort-r settings, there is a set wiring sequence for that. I am sure you installing contractor is fully aware how this need to be wired.
    I don't doubt it. I'm asking the question here because I'm trying to verify that this is even possible. Namely, can this combination of equipment make effective use of the dehumidification control of the Vision Pro IAQ, in which (if I understand correctly), blower speed is reduced to increase dehumidification. If I just wanted dehumidification by straight overcooling, the Trane 803 / VPro 8000 would do that.

    In case you're wondering: Although I did talk to my contractor about installing the VPro IAQ, I haven't actually talked to him about this specific issue (utilizing the IAQ's more advanced dehumidification features). I certainly will talk to him about it when I get the chance, but in the meantime I thought I'd come here and educate myself.

    I also ask because I have seen other threads here in which there seems to be some uncertainty as to whether Comfort-R is compatible with or makes sense with this type of setup. That's where I came up with my very specific questions about removing factory jumpers, etc.

    I'd still love to know if anyone can confirm this works. Thanks!

  9. #9
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    I can unequivocally answer all of your questions, but I will wait to see what other posts you gather. Right now you have at least three misconceptions. I will alleviate part of one for you now. The 803 and the IAQ follow the identical algorithm for dehumidification by overcooling.

  10. #10
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by second opinion View Post
    I can unequivocally answer all of your questions, but I will wait to see what other posts you gather. Right now you have at least three misconceptions. I will alleviate part of one for you now. The 803 and the IAQ follow the identical algorithm for dehumidification by overcooling.
    I certainly appreciate any advice you're willing to give. Is there any particular reason you would want to tell me that I have misconceptions (which I don't doubt in the slightest, otherwise I wouldn't be here) but not tell me what they are? In particular, I hope I didn't say anything in my reply to your other post that offended you -- it certainly was not my intention.

    In regard to dehumidification by overcooling. I am aware that the IAQ supports the same up-to-3-degree overcooling method used by the 803. I was under the impression that the IAQ *additionally* can slow down the blower (with a compatible air handler) so that you'll get more dehumidification, when it is needed, without as much air temperature drop. Thus my phrasing, "the ability to dehumidify without as much overcooling". I am unclear, from my reading, whether the IAQ will do this only once the temp set point has been reached, or whether it will also enter this mode when neither the temp nor humidity set points have been reached, based on its prediction as to whether the humidity will still be above setpoint when the temp setpoint becomes satisfied. I'm guessing the former.

    If I've got it wrong, please don't hesitate to tell me

  11. #11
    Join Date
    Jan 2004
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    The IAQ will slow down the blower when humidity is above set point when the A/C is running weather temp set point has been reached or not.
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  12. #12
    Join Date
    Aug 2007
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    Northern VA 38 degrees N by 76 degrees W
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    Your dealer was correct in recomending the Tcon 803 for your application and using Comfort R. You can use the Vision Pro IAQ with your equipment if it is set up properly.

    Depending on what type of chimney you have you may not need a chimney liner.

  13. #13
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by second opinion View Post
    Your dealer was correct in recomending the Tcon 803 for your application and using Comfort R. You can use the Vision Pro IAQ with your equipment if it is set up properly.

    Depending on what type of chimney you have you may not need a chimney liner.
    Thanks for the info. If I understand you properly, you're saying that in your opinion, either the 803 or the IAQ are reasonable choices. That matches my impression and the feedback I got from my dealer as well. I do think that the IAQ has some nice features beyond what the 803 provides -- would you disagree? Or stated the other way, do you think I'm making a mistake in asking my dealer to configure the IAQ to control dehumidification? He seems quite comfortable and familiar with using the IAQ in this mode, but if you feel there are drawbacks I'd welcome your expertise.

    I'd be interested in any details you're willing to provide in regard to your comment about chimney types. I can tell you that it appears to have been the victim of many years of flue gas condensation, based on observed rusting and water marks on the exhaust duct between furnace and flue. That and the piles of what look like rust flakes that get deposited inside and around the old furnace.

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