Both heating and cooling ducting?

[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.)

[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.

[cem-bsee]

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.

[marauderx]

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.

[airhead1164]

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

[fat eddy]

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

[keetoe]

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

[coolguysfl]

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.

[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). (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

[jacob perkins]

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.

[jacob perkins]

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?

[docholiday]

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.

[keetoe]

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

[keetoe]

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

[jacob perkins]

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.)

"to minimize laminar flow pertubation"

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!

Good luck.

[Murphcoair]

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.

[gillman-air]

I suggest getting an acca manual T. It will show you the flow characteristics of many different outlet/return placements.

[keetoe]

I.
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.

II.
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.

IV.
Gillman-air: Ordered the ACCA Manual T per you’re suggestion, but not here yet. Looks interesting from the description, thanks for the tip.

V.
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):

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

(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.

VI.
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):

http://comgrid.com/HVAC%20Stuff/Layout%20Sketches.htm

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?

Thanks, Keith



[Edited by keetoe on 03-02-2005 at 07:30 AM]

[pstu]

>>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:
http://www.tamtech.com/PDF/R.A.P.%20...L.%2008.02.pdf

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]

[pstu]

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