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Thread: Water Furnace

  1. #14
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    548
    Quote Originally Posted by Jkb79 View Post
    Well job looks very nice. One small thing though, the variable speed blowers require a min. Of 18 inches of the plenum height to be the same size as the opening on the top of the unit. The reason why is because the blower needs to have the resistance of the pressure of the duct as it try's to find the proper speed. The transition ( while nicely done) will not allow this to happen and you will experience harsh " huffing " noises and uneven airflow. This can cause the loss of capacity and motor damage. Other than that nice job.
    Thanks

    Good to know

    To the OP, nice work by the way

  2. #15
    Join Date
    Dec 2008
    Location
    NW Iowa
    Posts
    125
    Jkb79-What do you mean by "huffing" noises?

  3. #16
    Join Date
    Jan 2013
    Location
    Champaign Illinois
    Posts
    97
    Well most variable speed fans regulate speed based on the back force or pressure of the air on the blades ( air causes resistance on the motor). When there is not enough back pressure on the fan it will want to speed up till it finds the resistance it is looking for. If motor speeds up to full speed it will ramp back down and then try again. This is the reason for the seemingly small opening on the packaged units. The plenum is kept this size for about 18" ( you can get away with12" if need be). The static pressure gained will allow the blower to find the resistance it is looking for. The term "huffing" is just a term that I use I guess the reason I use this term is because if you are watching the ductwork or observing air flow with meter it fluctuates up and down like the blower is " huffing and puffing". I don't know how we'll I have explained this sin aero I guess it makes more sence if u see it for yourself. Probably a better person to ask for a more scientific explanation would be an Emerson motor rep. I do know that if you look at the install instructions for the geocomfort packaged units it does or used to show a diagram of the plenum construction. P.S. sorry if this info has upset anyone again the photo of the job does look like a very nice job well done, I just wanted to share some info on an issue that I have run across and who knows maybe one of u will experience this issue and know how to solve without tearing your hair out.

  4. #17
    Join Date
    Aug 2012
    Location
    Palmyra, Missouri, United States
    Posts
    224
    Gracias

  5. #18
    Join Date
    Dec 2008
    Location
    NW Iowa
    Posts
    125
    Thanks for the info. The reason I asked was I installed my ground source about 7 years ago and I have always thought the fan sounded loud. (A Lot of air noise) It is a two stage system which only uses two fan speeds also, and I don't believe it senses air pressure in any way. It did however have a small plenum opening, so I wondered if it may have made a difference if I had kept it this size for the 18". I think it may have more to do with putting a heat pump on old duct work. I have had no problems with it and the elec. bills are very low in the winter, just a bit noisey.

  6. #19
    Join Date
    Jan 2013
    Location
    Champaign Illinois
    Posts
    97
    Another minor air flow issue I have ran across with the packaged units is when the. (rectangular) return drop is brought strait down and attached directly to the air coil/ filter rack. The air will tend to just be sucked in at the upper third of the coil ( this can be seen when dirty filter is removed and only the upper part has dirt). I feel that while the system will operate in this arrangement the uneven dispersment of air can cause some noise issues as well as effect efficant heat transfer. The best solution would be to use a double radius shoe and or turning veins. I've never tryed the veins but they may help. The problem I think a lot of people have is that it's hard to find a store bought fitting with the right dementions and is just easier to use the rectangle duct ( I make my own shoes). Like I said I see the rectangular application all the time and it works but if you have thies minor issues this may be a solution.

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