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heat load design question/icelyne foam

Wayco Wayne_2
Wayco Wayne_2 Member Posts: 2,479
and the articles. They were very helpful. Jerry I hear you on sealing the ducts. What about insulating them? I believe there will be no insulation between the ceiling and the attic. I use wrightsoft heat load software. I can add a cathedral ceiling and get the heat gain as if there were no ceiling. I want to be as close as possible in my design to avoid moisture /mold problems. Also how much do I add for mechanical infiltration? This areea is notorious for hot humid Summers. WW

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Comments

  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    This job has been

    undergoing design changes for several years. The Homeowner has named the house "Squirrel House." He is a madman with a sense of humour. He started years ago redesignong his bathroom. One thing led to another and now his family is living in another house and he has totally gutted the existing house, and added two additions. He is both intelligent and passionate. A bad combination for his family. It also makes for an interesting customer. My question has to do with his insulation. He is having icelyne foam blown in everywhere, including his roof trusses just under the roof. I am used to the insulation being on top of the ceiling, not up under the roof. Do I account for the heat gain in the attic as another room? Do I have to insulate the ductwork? He has suggested letting the ducts leak to condition the attic space. I've been trying to seal my ducts tight as long as I can remember. This idea goes against my instincts. I need the collective genius of the Wall on this one. I'm not certain how to approach this different type of heat load. Any input is appreciated. WW

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  • John Starcher_4
    John Starcher_4 Member Posts: 794
    Wayne

    I would treat the entire insulated portion of the structure as conditioned space, including the attic. I would still seal the ductwork, though, and insulate it to make sure all your btu's are going where they are supposed to!!!

    If the attic portion of the space needs cfm, then install an air outlet for this space.

    Starch
  • Brad White_19
    Brad White_19 Member Posts: 23
    For calculation purposes, Wayne

    I would take the attic as unconditioned space.

    I gather that the attic an unoccupied space, storage if anything and not overflow/playroom space.

    When calculating, I would treat the attic as an unconditioned space with no positive heating or cooling supplied. Not sure what calculation program or method you are using but I would consider the floor to be "partition to unconditioned space" both from a gain/loss to attic perspective and to the gain or loss to the conditioned space below that. (Does that make sense?) Yes, first calculate a load for the attic volume. That will help predict conditions although still an educated guess. Then you will have better design delta-T's for your conditioned space.

    The floor of the attic presumably is insulated hence blocks passive heating from the occupied areas. If the roof is insulated equally to the floor, I would think that the conditions would be about halfway between indoors and outdoors. Hotter in summer though due to solar gains. Cool in winter but better than an uninsulated attic for sure. If freezing is an issue, a little controllable (emphasis controllable) heat would be in order. I would never rely on leakage.

    On the ductwork issue, my short answer would be, yes, you should insulate the ductwork, no question about it, both supply and return. I would seal the bejeezus out of all ductwork as you have always done. (To recover 10% leakage by fan power costs 30% in horsepower; you never get that back.) I am bullish on duct sealing.

    Hope this helps-

    Brad
  • Constantin
    Constantin Member Posts: 3,796
    I'd treat it as inside the thermal envelope,

    ...therefore, the attic is not unheated. The effects should not be dramatic as far as the end results are concerned, if the roof isn't very steep, the insulation is thick, and the house underneath isn't one of those giant amoeba homes popularized by "house shall not be taller than two stories" building ordinances.

    I would not insulate more than minimal levels between the lower levels and the attic for the simple reason that any AH left up there can be safely forgotten come wintertime since the space won't get cold enough to crack a water-filled condensate pipe, even if the house is put into deep setback.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    The air handlers

    will be down in the basement. The heat is all radiant floors. We will also be putting in mechanical ventilation with heat exchangers for fresh air. I'm worried about removing enough moisture in the Summer, because of the low infiltration I'm expecting from the foam. WW

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  • S Ebels
    S Ebels Member Posts: 2,322
    Depends Wayne

    If he's insulating between the ceiling and the attic then I would not consider the attic to be part of the conditioned space. If there's no insulation between the two spaces then you would want to include the attic in your heat gain/loss calc.If you don't include the attic in the "uninsulated" scenario, you'll come up short for the space below due to heat loss through the ceiling. It's the same as an insulated basement or crawlspace. You have to treat it as part of the conditioned space or it'll screw up the rest of the calc.

    As far as the duct goes, seal it as normal and install a register in the attic. You can then advise the customer that they can regulate the temp as they wish. It's the right way to handle your situation.
  • Brad White_19
    Brad White_19 Member Posts: 23
    I agree

    especially the variable of what insulation is in the attic floor. And yes, the register gives the HO control, not by chance. Good call.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    How much to add

    for duct insulation. I usually add 15% to 20% for duct losses when traveling through an attic. This will be different. WW

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  • You could calculate the loss of the attic to the outside, and divide that loss up into the adjacent rooms (ceilings) to estimate the additional load on the other rooms. Say if it were over 3 equal sized rooms, you would divide that loss by 3 and add it to each adjacent room.

    ASHRAE has a more scientific method than that for buffer space calculation, but that would get you in the ballpark.
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    my take

    You need to calculate the heat loss based on the surface area of the roof including any pitch. Once that's done, you can portion that out the the rooms below.

    You absolutely do want to seal the ducts. Just because it's insulated doesn't mean it's efficeint to leak air.

    Unless there is a room being built up there, I wouldn't add any air up there. I haven't seen any problems doing it that way with my house, but that may not be a real answer.

    jerry
  • gasfolk
    gasfolk Member Posts: 392
  • gasfolk
    gasfolk Member Posts: 392
    References...

    A little light reading (as if you have free time)...

    BuildingScience.com: Cathedral Roofs

    BuildingScience.com: Roof Design

    gf
  • gasfolk
    gasfolk Member Posts: 392
  • gasfolk
    gasfolk Member Posts: 392
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Cathedral Roofs, especially pages 2 to 6

    BuildingScience.com: Roof Design, especially pages 4 to 6

    A little light reading (as if anyone has free time for it)...

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6

    BuildingScience.com: Roof Design, especially pages 4 to 6

    A little light reading (as if anyone has free time for it)...

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6

    BuildingScience.com: Roof Design, especially pages 4 to 6

    BuildingScience.com: Roof References on Unvented vs. Vented Attics and Cathedral Ceilings,

    A little light reading (as if anyone has free time for it)...

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6

    BuildingScience.com: Roof Design, especially pages 4 to 6

    BuildingScience.com: Roof References on Unvented vs. Vented Attics and Cathedral Ceilings,

    Interesting reading, and we hope it's useful.

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6

    BuildingScience.com: Roof Design, especially pages 4 to 6

    BuildingScience.com: References on Unvented vs. Vented Attics and Cathedral Ceilings,

    Interesting reading, and we hope it's useful.

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6.

    BuildingScience.com: Roof Design, especially pages 4 to 6.

    BuildingScience.com: References on Unvented vs. Vented Attics and Cathedral Ceilings.

    Interesting reading, and we hope it's useful.

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6.

    BuildingScience.com: Roof Design, especially pages 4 to 6.

    BuildingScience.com: References on Unvented vs. Vented Attics and Cathedral Ceilings.

    Interesting reading, and perhaps (we hope) useful.

    gf
  • gasfolk
    gasfolk Member Posts: 392
    References

    BuildingScience.com: Unvented Roofs, especially pages 2 to 6.

    BuildingScience.com: Roof Design, especially pages 4 to 6.

    BuildingScience.com: References on Unvented vs. Vented Attics and Cathedral Ceilings.

    Interesting reading and perhaps (we hope) useful.

    gf
  • Constantin
    Constantin Member Posts: 3,796
    Hmmmm....

    Well, if infiltration is no longer an issue due to a tight envelope, I propose that your real issue will be the removal of excess humidity generated inside the home, not outside. The right fans and an HRV or two should solve that problem.

    Installing the HRV/ERV into an attic space may be a great option as it'll allow you to exhaust out of the bathrooms and back into the AC ducts.

    I'd take a close look at the sensible/latent ratio/load that Wrightsoft or whatever package you like to use calculates and then go a-huntin' for a condenser/AH combination that has the right capacity and ratio to suit your design day needs. For example, we oversized our AHs by 1 ton over the condensers to increase their sensible heat removal capacity.
  • gasfolk
    gasfolk Member Posts: 392
    Wrightsoft, Version 6

    Version 6 automatically accounts for duct leakage based on your specifications. To specify duct leakage:

    1. On the "Drawing Screen", right-click on a room to open the "Property Sheet".

    2. Select the "Room" tab.

    3. Left-click on "duct heat loss factor" to open the "Duct Loads" dialog box.

    4. If you select "Conditioned space" that will zero out all of the duct losses. Or make other choices as appropriate.

    5. To modify all the rooms on (for example) the First Floor, right-click on "First Floor" in the list of Sheets and Layers, move the pointer over "Select" and in the sub-menu click on "Rooms", which will select all of the rooms on that floor. Now right-click on any room and go to step #1 above.

    6. To include or exclude the attic in calculations, follow step #5 to select all the rooms on that floor, then go to the "Property Sheet" and choose "no" for "Include in calculations".
  • gasfolk
    gasfolk Member Posts: 392
    Wrightsoft, Version 6

    Wrightsoft, Version 6 automatically accounts for duct leakage based on your specifications. To specify leakage for ducts in a single room:

    1. On the "Drawing Screen", right-click on a room to open the "Property Sheet".

    2. Select the "Room" tab.

    3. Left-click on "duct heat loss factor" to open the "Duct Loads" dialog box.

    4. If you select "Conditioned space" that will zero out all of the duct losses. Make other choices as appropriate.

    To modify all the rooms on (for example) the entire First Floor:

    5. Right-click on "First Floor" in the list of Sheets and Layers, move the pointer over "Select" and in the sub-menu click on "Rooms", which will select all of the rooms on that floor. Now right-click on any room and go to step #1 above.

    To include or exclude the attic in calculations, follow step #5 to select all the rooms on that floor, then go to the "Property Sheet" and choose "no" for "Include in calculations". So, if you create a top floor, you can see how much (or little) it will add to heating and/or cooling.

    Watch out though. If the top floor is under a pitch roof, and you do a detailed job creating the roof, you may have to set the wall height of those rooms to zero. As a double check, make sure the Ceiling Height for the top floor is what you expect (for example, about four feet for a 12 over 12 roof).
  • gasfolk
    gasfolk Member Posts: 392


    Double check the average ceiling height for a given floor at the top of the Right-J Worksheet.

  • Bob Morrison_3
    Bob Morrison_3 Member Posts: 54
    inside, seal, infiltration (BM)

    I agree with Steve E.: include the attic in the load calc. and condition the space. You might want to have a higher design temperature for the area (less cooling load). Definately, seal the duct and install a register- a register can be closed (controlled), but a leak is constant. I would insulate the duct, because you will can not be certain that the attic air state (temp. and humidity) will be outside the non-condensing range.

    I assume you mean mechanical ventilation (not infiltration) , such as from an ERV or HRV. I would assume the unit's flow rate (e.g. 200 CFM) as raw ventilation air and not discount its load because of heat recovery.

    I (as the design engineer and installing contractor) did all of the above for my own house.

    Bob Morrison


  • why would you ignore heat recovery?
  • Bob Morrison_3
    Bob Morrison_3 Member Posts: 54
    HR maintained effectiveness? (BM)

    I would not include the benefits of a heat recovery (HR) from an HRV (or ERV) when sizing plant equipment (boilers, condensing units) nor terminal equipment (radiators, outlets). The unit's actual heat recovery effectiveness is a guess, with a maximum value being in the low 60% range for an HRV in heating mode and 10-20% range in cooling mode.

    Assume a 200 CFM unit in heating mode, which recovers 60% at design (say 5 deg F outdoors): that's about 7.75 MBH of recovery on a 13 MBH ventilation heating load. It's a benefit, but most likely less than 10% of the total building heating load. And that's if the unit is working well. In a real case, I'd bet the effectiveness is half what the manufacturer claims, since the unit will not be maintained as new and will be fouled with drywall dust on one side of its coil and pollen on the other. Moreover, an HRV in cooling mode will not reduce incoming humidity (most of the time) and has negligible sensible cooling effect, compared to the load.

    As a designer, I'd neglect the HR equipment benefit in the loads, because the effectiveness is unreliable and most likely has negligible affect on the total load anyway. I am hoping to take a few measurements on my unit (Fantech SHR2005R) this winter and check its performance.


    Bob Morrison
  • Brad White_22
    Brad White_22 Member Posts: 15
    I agree

    especially on heating, there is no inexpensive "Backup Plan" should HR fail or fall short. Only on some cooling systems with enthalpy/total energy recovery, and where cooling is not a critical function would I take credit to reduce system capacity.

    When you ignore the "saved cost of tonnage not installed" as the ERV vendors would have you do, the paybacks do not seem as attractive, but are still worth evaluating on an "energy saved only" basis.
    Good call.

    Brad
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    late in responding

    WW,

    sorry, I didn't catch the questions.

    I'm just this side of an insulation fanatic. I did go with insulated ducts, just to cut down the risk of surface condensation during cooling. Also, I hate to put any energy where I don't need it.

    Moisture is handled with an ERV combined with good ventilation around moisture spots. Broan makes a bathrrom ven that runs automatically based on sensed humidity. Remind them to always use the hood when cooking.

    As for the infiltration value, it's all about the details. Every place you have two pieces of wood touching, you need to seal it up. Top plates, trimmer studs, bottomplates to subfloor... Icenene does a pretty good job of stopping infiltration where it is sprayed. With careful detailing of everything, you could see <.2 ACH for infiltration, plus the ERV exchange rate times it's loss (1-efficiency).

    Spent a summer in DC. This is my image of the discussion of where to put the capital. "I don't want to give up good land for this, my constituents will have my hide." "Mine too." "I know, let's put the capital in a swamp that no one wants anyway."

    jerry
  • gasfolk
    gasfolk Member Posts: 392
    Jerry,

    Would you also insulate the returns?
  • gasfolk
    gasfolk Member Posts: 392
    Also Jerry,

    Our contractor's team is returning Monday to finish installing A/C ducts inside conditioned space (Icynene-cathedralized roof), but behind an uninsulated kneewall. There may still be time to ask for insulation on the returns (none of the kneewalls have been built)--if you think it's important and worth paying extra.

    Thanks,

    gf
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    I doubt it's important

    I did it just to have one less type of ducting in the system. Probably won't have any issues with it inside the envelope.

    Make sure you put returns in all rooms except those that have mechanical venting. If you put it in those as well, you can pull the air out of the return plenum rather than the room.

    jerry
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Very true

    about our forefathers locating the Capitol in a swamp. It gets very humid here in the Summertime. A lot of office buildings have multiple banks of Sump Pumps in the lowest levels. WW

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  • gasfolk
    gasfolk Member Posts: 392
    Thanks!

    > I did it just to have one less type of ducting in

    > the system. Probably won't have any issues with

    > it inside the envelope.

    >

    > Make sure you put

    > returns in all rooms except those that have

    > mechanical venting. If you put it in those as

    > well, you can pull the air out of the return

    > plenum rather than the room.

    >

    > jerry



    Spoke with our contractor this morning, and he had assumed we would always be leaving the bedroom doors open. Since the walls and attic floor are still open, for a small extra cost they will install three more returns.
  • gasfolk
    gasfolk Member Posts: 392
    Thanks!

    Spoke with our contractor this morning, and he had assumed we would always be leaving the bedroom doors open. Since the kneewalls and attic floor are still open, for a small extra cost they will install three more returns.

    Thanks again,

    gf
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