Humidifier Bypass

Discussion in 'HVAC Heating & Cooling' started by mcnauge, Jan 9, 2010.

  1. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    I doubt very much if the performance would be lowered by as much as 50% by not installing it in the most ideal location, but even if it was lowered as much as 50%, the effective amount would still be a lot better than not installing it at all.

    And I still maintain that as long as it is installed within the main air stream it will help increase the humidity within the home.

    Get it ?
  2. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    What I get is that you haven't bothered to consider the numbers on relative humidity to get a feel for just how bad an effect this would have. I've seen this sort of mistake made before on analagous systems, passed off with the same reasoning you are applying now.

    However, I neglected to point out another problem. If the bypass is before the coil it will reduce airflow across the coil, thereby reducing the efficiency of the heat pump. Even though the flows to the registers may be the same in the end, the heat pump coil in your scenario will see a reduced flow because you've created an internal bypass stream BEFORE it.

    You've said:
    and
    Neither of which are true.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,924
    Location:
    New England
    This is a furnace with a/c, not a heat pump situation, so especially if installed with a damper to shut off that bypass during the cooling season, it would not make all that much difference where it was tappped in. Yes, you will get more vapor per pass if the tap is into hotter air. If you locate the sensor well, you can control this.
  4. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    The issue being discussed at this stage was the placement on a heat pump system. That's what SteveW correctly pointed out and Hube disputed.

    I don't really need the sensor in mid winter. With temps running below 10 F daily average for a week the humidity dips down to the mid 20% range with the humidistat set to call for water the whole time. I can tell by touching both sides of the bypass piping that the evaporation is cooling the bypass gas stream greatly. It would barely work at all if it had zero preheating.

    I won't claim the house is tight, but it is considerably tighter than when I moved in.
  5. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    At least the Moderator(Jadunashua) got it right...."we are not talking about a heat pump system at all.
    But even if it was a heat pump forced air system it can be installed any where on either the return air or the supply air plenums or main trunks.
    Also,the fact still remains that if the Humidifier is allowed to put air into the main air stream no matter where the by-pass is located, the home will still have humidified air injected into it via the supply ducts,etc
    Now do you get it?
    Last edited: Jan 14, 2010
  6. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    You still don't get it. The flowsheeting and heat/material balance issues have escaped you.

    One could do the same thing by putting a bypass takeoff loop in between the furnace exchanger and blower. And it wouldn't work as designed (contrary to your opinion.) Where the humidifier bypass is connected does matter. Just anywhere won't cut it.
  7. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    been there, done that.
    Obviously you have not.
  8. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    That explains your defense of a poorly considered installation. It is one that WILL reduce the efficiency of the units, both for humidifying and for heating.
  9. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    Again, as long as it is installed anywhere within the systems main air stream it will help to raise the humidity within the home.

    (this is a recording....recording,...recording, recording ..etc,etc...
  10. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    So will hanging a wet towel on a rack... The point is it is a lousy way to do it.
  11. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    Is this towel within the main air stream???
    If it is, it would probably help to some very small degree.
    But since most towels that are on a rack are NOT within the main air stream.
    Or do you wish to argue that point too?
    Last edited: Jan 20, 2010
  12. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    Why would the towel have to be in the air stream? Water vapor (like basically everything in nature) moves from higher concentration to lower concentration. The increase may be small, but is there. Bison is trying to point out that there are many ways to add humidity, but not all methods are a smart way of doing it.
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,924
    Location:
    New England
    There are various configurations of humidifers...in-line and bypass are the two more common as I see it. Steam doesn't seem to be that common on residential units. An in-line one works best in the air duct after the heat exchanger. A bypass unit needs to have the inlet and outlets in different pressure regions of the ductwork so that air is moved across it. If you can put one end after the heat exchanger and the other side before the fan, it would be the most efficient, but as long as there is a pressure difference between the two sides, some air will cross through and pick up moisture. There are lots of places in a typical system where you can tap in to do a bypass, some are more efficient than others. Same is true with an in-line system, but the thing could even be put in the cold air return and still insert moisture...it would work better in the output because the heated air can hold more moisture. In this case, it may not need to run as long and be able to satisfy the demand quicker.

    To help keep stratification down, I run my variable speed fan constantly, which also enables the humidifer to work. It's a Trane air handler, and when not calling for heat or a/c, the fan runs on speed 1 of 16, so you don't hear it and the power draw is minimized at the expense of increased wear. It'll die one of these days, but has been running for nearly 15-years now.
  14. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    The Poster(McNauge) said he has no heat pump, just an normal furnace with a A/C coil installed in the plenum.I have been saying that as long as the Humidifiers moistened air is introduced into the main air stream that is going to give some humidification into the home via the supply ducts. Sure there are ideal plces on the plenums or main ducts that parts of this humidifier can be installed, and then there are not so ideal places that they can be installed.So what I have been saying is IF you cannot install it in the ideal location at least by installing it in an not so ideal location at least you will get some benefit out of it at the least.
    Having installed many, many various types of humidifiers over my 48 years of being in the Hvac trade, if there was no room to mount it on the return pleum, then it would be mounted on the Supply plenum. If there was no room on either of the plenums then the MAIN supply and return duct trunk would have to do . Sure, the IDEAL installation for the drum is on the return with the supply air running INTO the drum, but either of the other not so ideal ways will do as long as humidified air is introduced into the system and then sent to the various rooms of the home it is going to help increase the humidity level in the home to some degree.Maybe not as good as the best way, but if the best way cannot be achieved, then something is still better than nothing at all.
  15. mcnauge

    mcnauge New Member

    Messages:
    12
    Location:
    Ontario, Canada
    Work Completed

    Hey,

    Well i have got the humidifier fully installed and it works great, only took about 5 hours to bring the whole house humidity up to the requested range.

    I installed the Flow through humidifier onto the narrow side of the return plenum and the flexible bypass line to below the AC Coil about 6" below the level of the intake on the humidifier (total flex line length only 12" or so). Installed a dampner on the connection to the Supply side and soldered on a new valve on the cold water line and plugged it all in.

    Works like a charm.

    Thanks for the help everyone, on to the next project.

    Erik
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