Re: "Doc Holiday's" suggestion of floor instead of attic ducting.
OK Doc, What you've said is certainly true. (Attics are typically very hot in summers, making attic duct branches and the equipment subject to increased losses for cooling.) The attics here are virtually unbearable in the summers, even with lots of insulation, pro design, and maybe forced attic ventilation. So why are ducts and Eq. put in the attics when A/C is essential for many 100+ days?
Because ducts CAN'T go in the crawl space or basement, since most houses, even the $upscale ones, are build on a slab on the ground! Thus the lossy attic location.
HOWEVER, our "Dream House" (not quite a nightmare yet, but may be if it doesn't stop raining which has made all construction around here halt) is an "upside down house" configuration. That is, the main floor (which has all of the essential rooms on it) is at street level, but the "2nd" floor is underneath it, for now as an unfinished basement. And it's way cool there. So, using "under" (the floor) ductwork sure makes sense.
Keep up the good suggestions guys. This house project will have several innovations ("experiments?") built in, like fancy lighting controls etc. Perfect for a frustrated retiree to tinker with. I'll gladly let y'all know how things work out.
ps to Jacob: System Efficiency is obviously a "desirement," but comfort (cold feet) is the primary thrust here. Interestingly, the power bills in this all-electric community don't seem that bad, maybe $200-300 during solstices, so energy-saving gymnastics aren't worth it if they cost much.
ps to The Doc: Unfortunately we don't have money to burn, but sometimes it seems it gets burned anyway!
Thanks to all, Keith
"to minimize laminar flow pertubation"
Originally posted by keetoe
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.)
Uh,sure I know what that means...
I was trying to reverse directions of supply and return airflow with the seasons.I think that would be the most practical distribution system.
If you are capable of making drawings like that,then sketch a layout of your design and post it.We would like to see it and learn from your successes(or mistakes).You are sure get some useful knowledge from these guys!
You could use HI-LO stack heads , these will give you a low wall and high wall supply on each branch, once a year you switch over , winter you open the low and close the high grill , summmer its the opposite open the high, close the low, returns should be a combination of high and low.
I suggest getting an acca manual T. It will show you the flow characteristics of many different outlet/return placements.
Please step AWAY from the condensing unit.
Disclaimer: There is discussion elsewhere on the forum about who’s who: HVAC Professional, DIY, HO etc. I’m merely a one-time owner-builder looking at potential improvements to the rote HVAC system our architect/engineer drew into our plans. Professional yes, but in a not-to-distantly-related field. I’m not here for freebies, just gleaning you’re expertise, so please bear with.
Project status: Today doing final pour before framing (3/2/5), serious HVAC coming soon.
III. Jacob: “Laminar flow” is borrowed jargon for idyllic smooth air flow in ducting (efficient). Such things as sharp corners and gizmos in the ducts (perturbations) introduce eddies and meanders in the flow (inefficient). Lingo, just lingo.
Gillman-air: Ordered the ACCA Manual T per you’re suggestion, but not here yet. Looks interesting from the description, thanks for the tip.
Murphcoair (“look at HI-LO stack heads”) and Jacob Perkins (garden hose duct-switching analogy): The HI-LO approach is attractive and fairly easy to incorporate for us. Good tip.
VI. IMPORTANT QUESTION: Is there any reason (other than complexity/cost) to avoid reversing flow in a duct system? That is, swap HI-LO duct networks winter/summer for distribution/return reverse directions? If not, here is a sketch of an “X-Bar Switch” (akin to those used in microwave waveguide plumbing for combined parallel/serial redundancy):
(An update/expansion on Jacob’s thoughts and Murphcoair suggestion).
The houses we’ve lived in over the years utilized a single return register (typically a single crude “duct” in the framing). Seems to me this is a potential improvement situation. Why isn’t much attention paid to return air passage? The house we’re in now (tract home rental) has distribution ducts to each room as usual, but a single ceiling return register. Closing, say, a bedroom door produces objectionable drafts under the door and even whistling sounds. The pressure delta is significant, doors slam if the blower is on. Admittedly, this is a 35 year old cheesebox and obviously little thought was given to the HVAC system.
I grew up in a house that had forced air gas heat (its now 60 years old). It had floor ducts. (Michigan, cold winters and it had a basement.) It ALSO had return registers in most of the rooms. The air flow/temperature was quite localized (“zoned” is the current vernacular, right?) by room, instead of the return air meandering through the house via circuitous paths to a single register or being sucked through cracks and chinkies from outdoors. Thermal striations and drafts were practically unnoticeable. "Zone control" was adequatrly provided by a (manual) register damper on incoming air in each room.
Again a Jacob suggestion: “. . . sketch a layout of your design and post it. We would like to see it and learn from your successes (or mistakes).”
Okay, I put together some very top level sketches of our project from the actual building plans as meat for HVAC discussion. See this site (and scroll down):
The house is an anomaly for this area (So CA inland, nearly desert climate). Most homes are built directly on a slab, use heat pumps (outside-air heat sink/source) for both AC and heating, with the blower/condenser/ducting located in the (very hot) attic.
Instead, we will have a basement (subterranean unfinished rooms) and can readily implement the recommendation of Docholiday (see earlier messages): Locate ducting (and equipment) under the (main level) floor which is much more benign than the 130+ degree attic. The sketches are only suggestive of thoughts so far, and will be expanded/updated as we progress.
So, y’all, any comments/criticisms?
[Edited by keetoe on 03-02-2005 at 07:30 AM]
>>Why isn’t much attention paid to return air passage? The house we’re in now (tract home rental) has
>>distribution ducts to each room as usual, but a single ceiling return register. Closing, say, a bedroom door
>>produces objectionable drafts under the door and even whistling sounds.
>>The pressure delta is significant, doors slam if the blower is on.
In modern times attention IS paid to return air paths, you just haven't yet been hearing about it. One common technique is to have a return duct to each bedroom, of course this is in not-the-cheapest homes. State building code for Florida requires pressure equalization within about 3 Pascals, to meet this standard requires paying attention to returns. There are several methods which will do the job, here is a treatise from one vendor:
Your symptoms are pretty clearly telling you *that* house needs more paths or capacity to get air from supply registers to the return registers. Absence of that slamming would mean the problem is limited. A cheap solution would be undercutting the doors, personally I find that looks ugly. My house used to have that symptom, and I installed a thru-the-wall vent (sealed of course) which routed air back to the main house section. That helped a lot. Later added a return for each bedroom, as much for capacity as for pressure reasons.
In certain climates (not necessarily yours) there could be a problem of moisture getting into walls due to too much or too little pressure vs. the outdoors.
Joe Lstiburek of Building Sciences Corporation has written on this subject as well. Do a Google search on his name spelling it correctly and you will find lots on various topics, including this one. Everything with Lstiburek's name on it is worth reading!
Hope this helps -- P.Student
P.S. I've measured room pressure differences as about 6 Pascal, and published case studies have measured approximately 11 Pascal. Occasionally on Ebay you will find a Dwyer manometer for sale cheap, which can be the tool to measure this.
All year I had a thermometer probe in my attic to see just how hot it gets. I don't think I ever saw over 120 degrees air temperature, this is in S. Texas on sunny days. Absolutely I don't want to trivialize the human health hazard of *people* being in hot attics, after all your body is in big trouble if you get up to 105 degrees internal temperature. But I wonder about those casual claims of 130 or 140 degrees in the attic.
In addition, you NEED to be talking about radiant barrier if you worry about attic temperatures, this can reduce cooling load about 10% for the whole house according to studies I have seen.
[Edited by perpetual_student on 03-02-2005 at 10:29 AM]
Keetoe, your idea is novel but I wonder if you might be better off with the KISS principle. I admire innovative engineering but one has to know when to keep things simple. Ductwork is expensive, any future buyer might deride it as Rube Goldberg. You have a manual adjustment which will need to be made every time the house needs change from heating to cooling -- probably several times a week in spring and fall.
Would not ceiling fans do the job of distributing air from top to bottom?
Hope this helps -- P.Student
1.Pulling unfiltered return air thru the ceiling grilles and duct ,used as returns ,in the winter,then blowing supply air backwards thru them in the summer.The reverse for the floor grilles and ducts.
I'd think that dust will be blown back,when changing seasons,and filters at each grille to prevent this ,is not a good idea,due to the restriction.
2.Your rotating fitting,will need to be air tight,as the static pressure will be near it's highest points ,on the supply and return,in that fitting.The pressure drop (static )thru this fitting and changing the air flow from floor to ceiling and vice-versa,will be a lot of pressure (static)loss as well.This can be accounted for in duct design,the result will be much "larger" ducts.If not accounted for,by a Pro,you'll have a disaster.
3.The design of a typical ceiling grille ,may not be well suited for reverse air flow,not sure what the pressure drop would be,but I know mfrs. ratings aren't printed from this.
4.Returns are not allowed in baths and kitchens,with standard design ,no problem,this air is pulled back by a return in an adjacent room,with a return sized to do so.In your design the supply would become the return,a code violation.
The other design(Jakobs),is much better,if you insist on doing this.The gain in comfort ,for reversing the suppies may be worth it,but reversing the returns will produce little effect.Trust me on the returns ,I did it in my own home,11 years ago.After looking forward to feeling a difference,today I just leave both retuns open.Since they are ducted from the attic,the high one pulls almost all of the air.
It seems we've come to a plan to press on with. After looking at several fantasies (some good, and some dumb like mine) we've focused on a mostly traditional approach for heating/cooling our "dream house:"
We'll stick to the heat pump systems typical in this neighborhood for both heating and cooling. (One for the big open mostly-daytime-use "Great Room" and another for the bedroom area.) The units, however, will be located under the main floor, in the basement, instead of the attic (per docholiday). The ducting will be a hybrid of dual ducting with a manual winter/summer “switch” (per jacob perkins) and in some areas HI-LO stack heads (per Murphcoair). Multiple return paths (ducts) will be used (per perpetual_student) and maybe all left open (no switch or dampers) (per dash).
As noted, this project is somewhat of an experiment for me (being newly retired), and we’re able to play around with schemes easily (access from big attic and also basement and lots of open behind-the-wall potential duct add-on space). So, if the nominal approach has a couple of undesirable “special features” like drafty areas or hot/cold spots, we can tweak the system empirically, post facto. That sounds wimpy and hedging, but this place does have several quirks in the real design. Several strange “architectural festoonaments” such as massively and uniquely contorted ceiling dropdowns (perfect for hiding grillwork but kinky in terms of flow patterns), a three-story spiral stairway/round staircase, a greatroom-near-centrally-located large kitchen island/”sushi bar” where registers can be placed chest-high and/or at the feet etc.
Is this design-by-committee? No, but a collection of good suggestions/guidance to stimulate/interview our HVAC pro soon to be chosen.
Here are some further notes:
Dash: Great assessment/rationale for why my idea of reversing duct flow is really, really dumb. Oh well, it was good brain food.
perpetual_student: a) KISS is agreed, especially the last “s” part, b) Hey Rube Goldburg is a hero in my book; his contraptions always work!, c) Ceiling fans absolutely. Very popular here for stirring things up and also chasing flies away. d) 130+ attic temperatures isn’t a casual claim, this here’s real desert and 117 degrees in the shade isn’t uncommon, it’s the land of melted dashboard plastic., e) In situ instrumentation/measurements I like, and the simpler the devices the better. Case in point: for establishing uniform and code-conforming elevations of footings we’ve had subs with fancy gear like laser gizmos, GPS, and transits whom couldn’t agree precisely. The equalizer was a water level: a garden hose and some clear tubing. Archimedes was one smart cookie and Mother Nature doesn’t lie, usually.
gillman-air: The ACCA Manual T came and indeed it has great, easy to read material full of practical ducting information. Will stir in several of the design features/guidance.
Thanks again folks. More notes coming in the future when we get things fired up and find out what the real world is.
"Always changing is the future." -Yoda