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  1. #1
    Join Date
    Feb 2005
    Posts
    7
    Any hints for designing/installing a cooling duct network (ceiling registers) and also a heating duct network (registers near floor) and using a single heat pump with damper/valve for summer/winter? (I live in an area where summers are often over 100-dry, and winters in the 30s, so we want to put the conditioned air where it belongs. We're doing an Owner-Builder dream house.)

  2. #2
    I would recommend if going to the cost of a dual system tou use a radiant floor heating system uses water with no ducts then use air to air exchanger for ventilation, cooling ducting in the ceiling.Tats what high end homes are using. If you did use a dual duct system you would only need dampers in the branches not two entire duct systems wit one large damper I think that system would be an abortion.

  3. #3
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    wsteful to condition air above 7ft

    with proper design & proper installs, it makes insignificent difference for placement of registers, except for blockage by furniture, window & wall treatments, misguided HO installing diverters.

  4. #4
    Originally posted by fat eddy
    I would recommend if going to the cost of a dual system tou use a radiant floor heating system uses water with no ducts then use air to air exchanger for ventilation, cooling ducting in the ceiling.Tats what high end homes are using. If you did use a dual duct system you would only need dampers in the branches not two entire duct systems wit one large damper I think that system would be an abortion.
    Yes, do the radiant floor heating. You can also get special add-ons that can heat your towels when you take a shower (HW passes through the towel holder before hitting the shower mixing valve).

    A dual duct system would be an abortion these days, and if they are separate systems they will end up fighting one another - like a humidfier and dehumidifier next to one another.

    If you have special spaces, or are that concerned with how the systems will operate call up a local Mech engineer and weasel some answers or get a really good price to have them design a superior system that has more controls than NASA.

  5. #5
    Go to http://www.naturalcooling.com then you can heat and cool with out much duct at all. This would be a true cadilac system. Looking at it real seriously for our new home. Or I would do the radiant floor and a high velocity ac such as unico or space pak then your ac duct doesn't have as much of an impact on your home. JMHO. Brian

  6. #6
    I would be concerned about a derivative effect on that system, how fast can it makeup a large temp swing

  7. #7
    Join Date
    Feb 2005
    Posts
    7

    . Further information

    Thanks folks for the suggestions,

    More on the specifics of this (dual duct) system.

    1. The local approach to HVAC in this town is generally one or two heat pumps: Interfaced to outside air on one side, forced air inside. The indoor system shares the same ducts for warm and cold air, with the pump operating mode determining which. The duct system typically feeds ceiling registers in each of the rooms, with the blower in the attic. Any "zoning" is crudely done with manual register dampers. These systems are fine for AC, but awful for heating. Granny's feet are always freezing while the rest of us are glassy-eyed since the system is upside-down for heating. Btw, the neighborhood is upscale with all custom homes, so a reasonable investment for comfort is realistic.

    2. Oh yes, the city is all electric unless a propane tank is installed. Indeed, some houses have propane furnaces. Resistive radiaton heating is expensive and the power company sends "love notes" to those who significantly exceed their KWh quota. And geothermal is impractical also since the terrain is almost solid rock. Strangely, solar isn't popular despite the "Sunny California" stereotype.

    3. So, instead of getting creative with system design, all I'd like to consider is a second set of ducts to the floor area for the heat pump in heating mode. What I need (if such a thing exists) is a duct "switch" at the outgoing plenum of the blower. Again, this is not a diurnal issue, only annual, so the "switch" is moved only twice a year, just as the heat pump thermostat mode switch is.
    ---
    Again, thanks for you're inputs.
    (Stay tuned for the next fantasy!)
    Keith

  8. #8
    Join Date
    Nov 2004
    Location
    Naples, Fla.
    Posts
    1,403
    keetoe, cembsee is correct in design issues.

    On the use of radiant cooling, (the posted link) you'd have to have a death wish. Radiant heat yes - radiant cool NO. You have'nt had a good time until you have mold & condensation (if you're lucky enough to get below the dew point.

    I would make the suggestion that while a well designed duct system properly installed will handle the home, I have found in two story or homes in locations of radical temp swings that a dedicated RA system for cooling (located in lower areas & dedicated RA system fo heating (located in higher locations) takes advantage of natural air currents and stratification issues.

  9. #9
    Join Date
    Feb 2005
    Posts
    7

    What constitutes a

    Hi Again,

    OK, it has been mentioned that a well designed and installed system works independent of where the registers are located (near the ceiling or near the floor). (Cem-bsee and coolguysfl.) Let's reduce this to a hypothetical simplistic case: We have a relatively large great room; essentially a big box of 35' x 60' with a 10' ceiling. Assume it's well insulated and no windows (for simplicity). We'll use a single heat pump for service. (Recirculated air indoors via ducting, and an outdoors air interface outside.) Conditions are essentially opposite in summer and winter. The pump is used to cool in the summer, then reversed to heat in the winter (it's a dry climate). The energy loads are about equal for both seasons. (The typical electric bill in this neighborhood has similar peaks and duration for both seasons).

    Now then, do we place the registers near the ceiling or near the floor? And where would the return register go?
    ---
    I know the real world is complex, with many case-specific design aspects to consider, but I'm looking for a simple answer to improve the typical heat-pump-single-duct-network systems used around here. Btw, I thought "heat" rises in a fluid medium? Ever turn you're lava lamp upside-down to see what happens?

    This is fun, and thanks again for ye'alls participation.
    ---Keith

  10. #10
    Join Date
    Nov 2004
    Posts
    2,927
    Okay,I will play along with your idea...

    Actually,I too have wondered how this could be done.The best way I could think of is also the simplest.

    We will have to use our imaginations.Imagine two lengths of garden hose in your hand.These are two feet long. Lay them on your desk side by side. Now, place your left hand on the two left ends and hold them stationary. Place your right hand on the two right ends.Make the two right ends alternate spaces by twisting a half turn... are you with me?

    Okay,your left hand represents where your return and supply are entering the floor to connect with all other branch ducting. Your right hand is where the ducts will connect to a "package unit"out side.There will be a rotating gadget to easily change sides with a half turn.
    You will use heavy duty flex duct for this...
    Good luck.

  11. #11
    Join Date
    Nov 2004
    Posts
    2,927

    Re: What constitutes a

    Originally posted by keetoe
    Hi Again,

    OK, it has been mentioned that a well designed and installed system works independent of where the registers are located (near the ceiling or near the floor).
    That is true.

    But what is your priority, system efficiency or comfort?

    Sometimes there are compounding complexities of multiple variables that are not intuitively obvious

  12. #12
    Join Date
    Apr 2004
    Posts
    7,680
    I would think a well designed system dictates where you put the registers. If it only gets to 30 outside, I wouldnt waste my money on radiant floor unless you just have money to burn, granted it is the most comfortable, no doubt, but ultimately your cost would be more than really needed for all the colder it gets.

    Frankly if you have the choice of over or under ductwork I would select under, her is why. Attic ductwork has a greater loss in cooling than does crawl or beasement. Your attic will reach temps of 130-140, the crawl space will not.

    The duct design is critical but if given the choice, I would select floor over attic, if you dont have the choice, then so be it, the placement of registers, throw patterns, and correct volume of air, insulation on a properly desinged system can make it work either way.

  13. #13
    Join Date
    Feb 2005
    Posts
    7
    Re: Jacob comment:
    (On you're garden hose analogy)
    Here is a sketch of what I think you had in mind (click the link):

    http://comgrid.com/HVAC%20Stuff/Jacob_Idea.htm

    Later in the discussions, "Doc Holiday" hit on what seems to be an excellent suggestion for my particular application. See reply to his note . . . Keith

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