Page 3 of 9 FirstFirst 123456789 LastLast
Results 27 to 39 of 116
  1. #27
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by Carnak View Post
    Return location will have next to no impact on comfort. What it can do is follow where air stagnates

    Try this http://www.price-hvac.com/content/flash/ptm/ptm.asp?Section=Space Air Diffusion

    If it does not work, then try this link and select "Space Air Diffusion" http://www.price-hvac.com/media/trai...ule.aspx#flash
    Carnak, that is an EXCELLENT link. Thanks for posting it.

    The training material at the link above seems to agree with ACCA Manual T in that although returns have little effect on room air circulation, they are best placed where the room stagnant zones are anticipated to be. For cooling, this would be near the ceiling, and for heating it would be near the floor. A high and low return system could accomplish this end, but my gut feeling is the return location should be based on the prevailing climate condition....a cooling or heating climate. Cooling climates would call for high returns, with heating climates having low returns.

    In my neck of the woods the return location is determined mainly by equipment type. An upflow furnace/air handler on a slab foundation with ducts in the attic above or a soffit get low returns. Attic horizontal furnaces/air handlers get high returns.

    For a dual return arrangement to be effective for most homeowners, if the extra cost could be justified, an automatic shift between high and low intake would be necessary. I'm just not sure it is worth the extra effort. Good supply air distribution overcomes a lot of thermal problems within a room, yet so many residential installations in my area use cheap stamped steel supplies either on the walls or ceilings (most common) and blast the air down into the occupied zone, leaving stagnant pockets everywhere else. Couple this with leaky thermal envelopes (walls, windows, doors, and ceilings) and marginal HVAC system installs, and is it any wonder we read posts such as the OP asking how to improve their comfort condition?

  2. #28
    Join Date
    Feb 2007
    Location
    SW Virginia (Roanoke)
    Posts
    48
    Quote Originally Posted by shophound;1772853i
    s it any wonder we read posts such as the OP asking how to improve their comfort condition?
    I never mentioned comfort, although I should have. I'm also concerned with wasting energy maintaining a thermal gradient in a room with a 15' ceiling.

    I'm currently recording that thermal gradient, but today's OAT is in the high 50's.

  3. #29
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by pstu View Post
    I am a homeowner too, therefore an amateur. I hate to believe you cannot find some issue more significant than this! So many duct systems have too-small returns in the first place, in such a case adding another would be helpful but not for the reasons you are thinking.

    In simplistic terms as I understand it yes hot air rises when air is still, but... because of your supply vents blowing air into the room the air is supposed to be mixed already. This has been said already by a couple of professionals and I cannot find any fault in what they say. I also believe the ACCA manuals address this issue and disprove the usefulness of summer/winter return switching.

    Lots of AC systems have things wrong about them, such as leaky ductwork in unconditioned space (e.g. attics). Or poor match between coil and condensor leading to lousy efficiency and/or poor humidity removal. Or returns which are too small and restrict airflow. Or even fan speed set wrong which also results in poor airflow. All of these are from my own experience, I am not complaining as these have been problems found and fixed. But to worry about a 2nd set of returns just for seasonal use, in my best opinion that is dwelling on trivia.

    Hope this helps -- Pstu
    Pstu, I think you'd be well served to click on the link in this thread that Carnak has posted regarding air distribution. Granted, it is aimed toward the office/commercial environment, but the principles discussed are no less applicable to a residence.

    I do not see tigerdriver's post or question as trivial. To dismiss it as trivial without suggesting a more effective solution to his concern is misguided, IMO. I think his motivation for posting the question initially is that he is not satisfied with the comfort level of the room shown in the photo. My replies to this thread have been along those lines, given I think there's more going on than even some in the HVAC trade may be aware of. Stack effect caused by leaky penetrations of wall and ceiling areas adjacent to an attic contribute significantly to discomfort within a room. Improper air distribution on the supply end is another factor. If the return shown in the photo is undersized, the entire system can't deliver the amount of air the room needs to stay comfortable, winter or summer. If the supplies are in similar condition, same result. If the grills are improperly chosen for the room geometry, yet again we'll have the same result. Discomfort.

    The end goal of hvac systems is human comfort. If it cannot deliver on that promise, it is not living up to its potential. Same goes for a house structure. Both of these when done well deliver on that promise, and do so with energy use reduction.
    Last edited by Shophound; 02-25-2008 at 05:32 PM.

  4. #30
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Quote Originally Posted by tigerdriver View Post
    I never mentioned comfort. I'm more concerned with wasting energy maintaining a thermal gradient in a room with a 15' ceiling.

    I'm currently recording that thermal gradient, but today's OAT is in the high 50's.
    The link that Carnak posted includes a segment on thermal gradients, and what is acceptable within the "occupied zone" (also defined in the training modules). Above six feet you're not too worried about the temperature gradient, because you don't live up there (unless you're exceptionally tall! ) You want the temperature gradient where you live to be acceptable. IIRC, the ASHRAE standard gradient for a seated person is no more than three degrees between the floor and the person's head. For a standing person it is no more than five degrees between floor and head.

    You are right to be concerned about energy efficiency. Good hvac system design and a good thermal envelope of your house can deliver to you that goal handily.

  5. #31
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    Tigerdriver, now that I see your concern, I'll attempt to speak more directly about your situation vs. general talk.

    The supply registers in your room...do they throw the air straight down toward the floor, or are they two or three way registers with angled blades (with no curves to each blade)?

    Are all the supplies located along the outer walls?

    Do you find not enough warm air gets down where you live in the room?

    With the room architecture shown in the photo, and if the supplies are indeed along all the perimeter walls, it seems to me the most productive air introduction strategy is to throw the air down and toward the walls. It will then glide down toward the floor, inducing room air with it. When it hits the floor it will spread out, dispersing any stagnant, cooler air with it. The air coming down is warmer than the air in the center of the room, so it will tend to warm the air in the center and then that air will begin to rise toward the return on the far wall over the nice cabinetry work.

    How's that sound so far?

  6. #32
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,090
    Quote Originally Posted by tigerdriver View Post
    The other side of the wall is my garage, whose walls are finished. I would surface-mount the duct to the new return, then build a soffit to hide it.

    ..
    Joe
    Ok, that will work.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #33
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by tigerdriver View Post
    I never mentioned comfort, although I should have. I'm also concerned with wasting energy maintaining a thermal gradient in a room with a 15' ceiling.

    I'm currently recording that thermal gradient, but today's OAT is in the high 50's.
    Running the ceilig fan in reverse might do more.

    If you do add the return please check and post the gradient improvment at both ends of the room.

  8. #34
    Join Date
    Feb 2007
    Location
    SW Virginia (Roanoke)
    Posts
    48
    Quote Originally Posted by shophound View Post
    Tigerdriver, now that I see your concern, I'll attempt to speak more directly about your situation vs. general talk.
    Thanks.

    The supply registers in your room...do they throw the air straight down toward the floor, or are they two or three way registers with angled blades (with no curves to each blade)?
    See attached photo. I think of them as binary: on/off. When the slide lever is in the "on" position, air is dispersed parallel to the walls via the vanes on the cover. If you look at the attached photo of the Great Room, you can see several of the eight registers in the ceiling.

    Are all the supplies located along the outer walls?
    See photo.

    Do you find not enough warm air gets down where you live in the room?
    Marginally. There's a palpable temperature gradient between my arm-chair and the bottom to the return register. If I can distribute the thermal mass more evenly, I can increase my comfort somewhat and reduce my heating bills.

    Other INFO

    We like our rooms on the cool side-- 67-68 degrees, and we usually don't have much trouble maintaining that. Our Great Room is a recent addition to the home, the rest of which is heated by an oil-fired furnace pumping hot water to finned baseboard radiators. If I set all the downstairs and Great Room zones to 67 degrees, the upstairs zone call for heat only during wake-up in the morning and when the weather gets very cold.

    The downstairs hot-water radiant zone works fairly hard, but, as you can see from the attached photo, the Great Room works hardest because its wall-space is 60% windows. While these are high-quality, double-paned windows and doors with excellent insulation and weather seals, they have their limits.

    it seems to me the most productive air introduction strategy is to throw the air down and toward the walls. It will then glide down toward the floor, inducing room air with it. When it hits the floor it will spread out, dispersing any stagnant, cooler air with it. The air coming down is warmer than the air in the center of the room, so it will tend to warm the air in the center and then that air will begin to rise toward the return on the far wall over the nice cabinetry work.
    It's certainly worth a try. Two questions:

    1. Can I purchase registers that allow adjustment of the direction of the air flow at Lowes/Home Depot?
    2. Considering that three of the four walls are windows, will forcing air over them create more heat loss than blowing it straight down?


    Thanks for your rational approach.

  9. #35
    Join Date
    Feb 2007
    Location
    SW Virginia (Roanoke)
    Posts
    48
    Quote Originally Posted by dash View Post
    Running the ceilig fan in reverse might do more.

    If you do add the return please check and post the gradient improvment at both ends of the room.
    By reverse, I assume you mean the direction that moves air from floor to ceiling?

  10. #36
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by tigerdriver View Post
    By reverse, I assume you mean the direction that moves air from floor to ceiling?
    Yes ,it will bring some warm air down the walls and prevent stagnent air .


    Did you check out the link Carnak posted??

  11. #37
    Join Date
    Feb 2007
    Location
    SW Virginia (Roanoke)
    Posts
    48
    Quote Originally Posted by dash View Post
    Did you check out the link Carnak posted??
    I started watching, but it's that time of day when I get brain-fade, so I've to postponed it until tomorrow morning--when I'm again capable of spelling kat.

  12. #38
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by shophound View Post
    Carnak, that is an EXCELLENT link. Thanks for posting it.

    The training material at the link above seems to agree with ACCA Manual T in that although returns have little effect on room air circulation, they are best placed where the room stagnant zones are anticipated to be. For cooling, this would be near the ceiling, and for heating it would be near the floor. A high and low return system could accomplish this end, but my gut feeling is the return location should be based on the prevailing climate condition....a cooling or heating climate. Cooling climates would call for high returns, with heating climates having low returns.

    In my neck of the woods the return location is determined mainly by equipment type. An upflow furnace/air handler on a slab foundation with ducts in the attic above or a soffit get low returns. Attic horizontal furnaces/air handlers get high returns.

    For a dual return arrangement to be effective for most homeowners, if the extra cost could be justified, an automatic shift between high and low intake would be necessary. I'm just not sure it is worth the extra effort. Good supply air distribution overcomes a lot of thermal problems within a room, yet so many residential installations in my area use cheap stamped steel supplies either on the walls or ceilings (most common) and blast the air down into the occupied zone, leaving stagnant pockets everywhere else. Couple this with leaky thermal envelopes (walls, windows, doors, and ceilings) and marginal HVAC system installs, and is it any wonder we read posts such as the OP asking how to improve their comfort condition?

    You're welcome. There are a few good modules on that site. If anyone knows how air moves it is the people who make the diffusers.

    We used to do slab on grade with a central return high sidewall

    Furnace in the basement, returns were low. In a cold climate the last thing you want is attic ductwork.

    A reversable ceiling fan is what the original poster needs.

  13. #39
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by tigerdriver View Post
    I started watching, but it's that time of day when I get brain-fade, so I've to postponed it until tomorrow morning--when I'm again capable of spelling kat.
    That's because you have the attention span of an electrical engineer. Table 310-16 and pay day is friday

Page 3 of 9 FirstFirst 123456789 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event