I’m building a new house and I’m using hydronic (in floor) heating and a geoexchange heat pump (not common in my area). I would like to use radiant cooling also. Does anyone have any advice for constructing radiant walls or ceilings for cooling?
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Where is "your area"? In most areas cooling of any sort is not possible without a plan for condensation. Easy enough with ducted AC, but much harder with radiant. In general there's no radiant cooling in the sense of radiant floor heating. Maybe in a dry, dry desert...
http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12470
Edited 7/7/2006 6:55 am ET by CloudHidden
I've seen drawings of hydronic cooling registers where there is a fan to move air over the fins AND and channel to catch the condensate drips on days when the dew point is higher than the cold water temperature in the pipe (happens even in dry climates). These registers are installed near the ceiling because that's where the hot air goes. IMO you would be better off using a traditional heat exchanger in a ducted system because there would be only one drain for condensate, and the moving air would improve the cooling effect.
I've seen valence systems for cooling, and I didn't like the look at all. I was talking of course about using the in-floor tubes for cooling, too, which in most cases is a non-starter.
Not knowing your location (fill in the profile) it would be difficult to know if it would work. In most cases, cooling with water in floor leads to condensation when humid air comes in contact with a cool surface.
A fan / radiator type exchange might be able to do it, but then you'd need ductwork and if there's ductwork, the heat pump would be the viable form for cooling.
And welcome to Breaktime.
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
I'm in northern Utah, a generally dry climate. I was planning on using a dehumidifer to try to maintain humidity below dew point, coupled with several humidity sensors in key locations such as bathrooms and kitchen. These would be linked to the central controller which would keep the temperature of the chilled water above the dew point or shut off specific zones. The water temperature shouldn't need to be lower than 50 degrees for my cooling load. Thanks for the feedback.
I am just north of you in Western WY. I have my small hydronic system set up so that I can run the cold water through the floor in the summer. I have not had ant moisture problems, but it is not usually alot of water going through the floor. I did one summer (when we had a long hot spell run the water to the outside sprinklers through the floor. It was nice on the feet but still no condesation. The floors are cement.
I was planning on using a dehumidifer to try to maintain humidity below dew point
There you go. Potential problem solved. Control your indoor humidity, like everybody ought to do anyway. Then you can do whatever with your floor.
Our concrete floor is a large part of our passive cooling system. The only one we need in a warmer climate (1131 cooling degree-days) than yours if you're around Salt Lake City (1047). Looks to me that you're greatly complicating things, but no reason not to work.
PAHS Designer/Builder- Bury it!
I also have a radiant cooling system, only mine is in humid Iowa. It works fine. Don't let the naysayers convince you it can't be done, it can.
You are on the right track with controlling humidity. In a well insulated and air sealed home you probably aren't going to need water that cold (e.g. I use 57*water at 95* ). You will benefit from constant circulation in this situation since it leads to warmer water temps.
Remember, much of a conventionally calculated cooling load is latent heat removal, not just sensible heat removal and you will need to take this into consideration when sizing the system since latent heat removal will be done through the dehumidifier.
The dewpoint will be the same everywhere in the house as long as the doors are left open. As long as the dewpoint is below 50* you should be fine (the voice of experience there). If you simply control your dewpoint to 50* with dehumidifier(s) and reset your water from outside air temp it should work.
What are you going to use for cooling your water?
Thanks for the info and encouragement. In my first radiant house I used culinary water to cool the floor when watering the lawn and it felt wonderful but it didn't get the temp down far enough.This time I plan to use a ground source heat pump for heating and cooling, with a backup condensing boiler to assist with snowmelt in the winter. I have triple pane (2 low E coatings) windows, insulated stucco, and very little solar insolation in the summer months so I suspect that my cooling load will be nominal. The numbers say that 50* water will work fine. I'm debating whether to put radiant ceilings or walls in now before the drywall goes in or just to use the floor for cooling. The numbers say that the floor will work and the consideration is comfort. I'm inclined to just use the floors but I've also considered running tubing under the kitchen countertops (granite tile) to help keep the kitchen comfortable for cooking. -SC
It will depend on your floor type/coverings but by using 3/4" wood and slate I had no issues with comfort using the floor tubing. The floors feel cool but not uncomfortably so, and this construction allows the water to easily stay above the dewpoint.
Just a side note, I needed to put a buffer tank between the chiller and the loop to keep the temperature in the water from fluctuating too much. I was able to get an electric hot water heater (with the elements removed) accepted but check with the inspector first.
Due to experiences in my day job I will always keep the potable water isolated from everything else (with an RPZ). The price of prevention is a tiny fraction of the price of the cure.
Chris
Hi,
This article might be helpful:
http://www.oikos.com/esb/53/hydroniccool.html
Gary
Ducted systems are notoriously leaky, which reduces system efficiency and indoor air quality. Forced air systems can harbor dust and organisms that reduce indoor air quality and might affect occupant health.
The Oikos people seem not to like forced air systems. Poorly installed systems are leaky!!!
If you run a dirty, humid house or have water leakage into your ducts (very rare), something "might' grow in the ducts. "organisms" or their spores are in every breath of air you breathe.....what's the big problem if some find their way into the dry ducts??
I recently visited a home under construction in Davis, CA which is right next to Sacramento and in the very hot and dry central valley. Talbott Solar (http://www.talbottradiant.com) was installing the radiant cooling in the ceiling. Look at the photos I took that day. The sheetrock ceiling nails over the assembly you see here in the photos. The source of chilled water is a heat pump. In the winter, the system will run hot water and the radiant heat will also come from this same set up in the ceiling. Talbott Solar has done several homes in our area this way and if you'd like to speak to the guy in charge, it's Dean Newberry. Just go to the website for more info. You will need to discuss issues like water temp vs. dewpoint.
Edited 7/16/2006 1:15 am ET by BarbaraD
"Radiant cooling" is an oxymoron. Those cold plates in the ceiling will never "radiate" cold, but they will absorb heat from the room below. They might work even better without a layer of wallboard in the way!As for heating in the Winter, why on Earth would anyone put the radiating elements in the ceiling behind a layer of wallboard? This whole setup looks like it was designed by a crank.
The metal plates transfer cold to the drywall ceiling by conduction mostly, because of the close contact. It is the drywall that then radiates cold to occupants in the room. Drywall (gypsum) has a remarkably high heat capacity, 38% higher than concrete which is commonly used as flooring for its coolness in the summer. Reference: http://en.wikipedia.org/wiki/Specific_heat#Specific_heat_of_building_materials
And yes the system does too work. There are quite a few installations in the greater Sacramento area. The main thing is, as an earlier poster said, you have to have low humidity in order to get a low enough water temp to effect the cooling.
Wow, who'd a thunk it -- sheetrock is now a candidate material for heatsinks! And it even "radiates cold" to other objects. This guy at Talbot Solar might as well book his flight to Sweden -- the Nobel Prize in physics is his for the asking!(BTW specific heat is not the same thing as thermal conductivity. That is why they make radiators out of copper or aluminum instead of gypsum and paper.)
Yep, the 'radiant cooling' phrase caught my eye too. Even worse than calling GSHP 'geothermal'.
Probably what is going on in Sacramento is like in WA state. A few years ago the legislatures 'legislated' energy efficiency, and the gobbledegook that transpired in the energy codes is marvelous (not) to behold. I have no doubt that a non-ethical PE with a stamp could manipulate the energy code sections to snow most the incompetents that run these state mandated 'energy savings' and go on to get a few $$ from the ignorant by virtue of floating a PE stamp past the just as ignorant local plan reviewers.... ..,, What state was it wanted to legislate the value of Pi??
"The metal plates transfer cold to the drywall ceiling by conduction mostly, because of the close contact. It is the drywall that then radiates cold to occupants in the room. "
I think part of the concern is with your terminology. Cold does not transfer by conduction or radiation, heat does. Cold is simply the absence of heat. Therefore the drywall does not "radiate cold" to the occupants, heat from the occupants radiates to the cold drywall.
As for heating in the Winter, why on Earth would anyone put the radiating elements in the ceiling behind a layer of wallboard?
This is done all the time with electric radiant heat!! 3 or 4 systems are available commercially. has been done a bit in the past with hot water radiant.
Conduct from Pipe to plate.Conduct from plate to Drywall.Drywall radiates heat.That's why you would put a heating element behind the drywall as shown. it's a low temperature, very powerful form of heating as the resistance of drywall to heat transfer is much lower than wood or most other floor coverings, you don't have to worry about even surface temps, you don't have to worry about furniture and throw rugs, and it cools more effectively than a radiant floor system does.Also it's less than half the cost of most radiant floor methods and installs twice as fast.Let me know if you need any more reasons ;)-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
"Conduct from Pipe to plate."One would hope so. So far, so good. "Conduct from plate to Drywall."Now what about the air gap between the plate and the ceiling? Or are the aluminum plates bonded to the drywall with thermal paste? If not, the effeciency of conductive transfer falls dramatically. Radiative transfer will warm the drywall somewhat because it's emissivity is high. Radiation will of course also warm the attic above the plates. Where I live we try to avoid heating attic spaces, maybe it's different in Sacramento."Drywall radiates heat."Here's an interesting experiment. Take a heat lamp, place it behind a piece of drywall with the bulb facing the panel and turn it on. Now hold your hand on the other side and see if you can detect any radiated heat. That's right, drywall is not very transparent at those Infrared wavelengths. The drywall will eventually reradiate heat that it absorbs from the other side, but let's not forget that both sides of the ceiling are radiating this energy, so half is again going upwards into the attic space!What you describe may work after a fashion, but it is probably the least efficent way I could think of to heat or cool the living areas below.
Wouldn't "Absorbant Cooling" be more correct? When something is cold, it doesn't radiate anything, it absorbs heat from its surroundings...
I know, I know, I'm nitpicking...
Yes absobant cooling is what they describe. For marketing purposes though they might consider "RG" cooling, as in Rube Goldberg.
Hi Soultrain,
for Radiant Cooling the math is the same as heating just change the sign from + to -.
Basically when the ceiling is cooler than the room, the objects and surfaces in the room radiate to the ceiling.
Imagine walking from the sidewalk into L street parking garage on a summer afternoon. The themal mass of the garage keeps the mean radiant temperature around 80 when it is 100+ in ths sunshine. It is much more comfortable in the garage than in the sun.Why don't we cool from the floor??
We can remove heat from the space, but cannot achieve comfort.
Imagine walking from the parkin lot at Oregon Creek down to the river on a summer afternoon. It's hot, the sand and rocks are hot. Step into the river, your feet cool off nicely, and the mean radiant temperature is lower because the surface of the river is close and covers a significant area around you. But you still feel uncomfortable. Many people have including myself have built radiant cooled floors, in good house designs, even a basement, and while it is cooler than without chilling, it still isn't comfortable. Chilled ceilings produce satisfied clients, as do heated ceilings. I don't think we know why exactly, but it does work.
I never understood the idea of radiant heat in the ceiling anyway. I guess you could compensate for some of the heat loss by insulating heavily above the heating tubes & transfer plates, but even if that weren't an issue, I don't understand how radiant ceilings would be comfortable.
Radiant flooring is comfortable (when done right) because it radiates heat directly to people & objects in contact with it. It also heats the air in close proximity to it which then rises providing convective heating as well.
Since no objects (save the occasional light fixture) are in contact with the ceiling, it would seem to me that you'd need hotter temperatures (like those nasty heat lamps in the entry ways of those warehouse clubs like Sam's & BJ's) for people to feel the radiant heat. Plus the air in close proximity to the ceiling would heat up & then stay in contact with the ceiling. Seems to me that you'd end up with a hot head & cold feet.
Radiant is comfortable because of radiant heat transfer, not because it's conductive to objects only in contact with the floor. The floors radiate, as the name implies, to all objects in the room.Ceiling does the exact same thing, because radiant energy is omni-directional.As I just posted in another post, you do lose the convective transfer. But resistance to heat transfer is much lower with drywall.Think low-level sunshine. As long as the ceiling's surface temperatures and proximity to your heat (edit: head) is considered, radiant ceilings can be very comfortable indeed. My clients who have it all agree. And in many cases in mild climates, low load conditions and/or superinsulated homes, radiant floors don't even get noticeably warm to meet load. How much would you be willing to pay to actually notice a warm floor for a few weeks a year? What if you can have the comfort and efficiency of radiant for much less with no appreciable difference in performance? Never have to worry that your wife is going to want to come home with some big oriental rug for that dining room? Forget any possible wood floor issues?Ceiling has a lot of benefits. In many cases, it's not *quite* as great as floor, but it's pretty darn good and it's certainly much more affordable.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Edited 7/11/2006 12:51 pm ET by NRTRob
Electric radiant heat in the ceiling is not uncommon in the Portland, OR, area (low electric rates means electric heat is very common). I lived in an apartment with electric radiant celing heat and it was surprisingly comfortable and heated up reasonably quickly. It was much more comfortable than a similar apartment where I lived in Berkeley, CA, that had a gas wall heater (that clanked lowedly every time the thing heated up and the sheet metal expanded). The electric ceiling heat was about the same as what I paid for heating other similar apartments, probably slightly less than what I paid in Berkeley during similar temperatures.
Not at all.First, you have firm backers (strapping) behind at least a good portion of the plates, so it's pressed pretty firmly against the drywall. Probably a bit tighter conduction then you'll get in the majority of radiant installations out there today, in fact. Maybe not over the whole width of the plate though, I agree. But then, you never do get perfect conduction across the whole area of a plate.The drywall may re-radiate upwards, but then, you've insulated the ceiling properly, right? You could say exactly the same thing about any radiant install. They all have what is called "back loss". That's why we have insulation. You may have a warmer than necessary airspace between the plate and the ceiling insulation, depending on when and how the insulation was installed, but if that really bothers you, instead of more strapping use 3/4" polyisocyanurate foam. You'll shave a few degrees off of your supply water temps. Personally, an inch or two of warmer air over the drywall bothers me not at all, as long as the cavity itself is insulated properly. Just as an inch of space under a subfloor doesn't bug me, as long as the joists or ends of the joists are insulated properly. It's not heat loss until it leaves the envelope. Trying to heat a piece of drywall with pure radiation (heat lamp) is not even in the same ballpark as conducting heat into the drywall. If you want to wait long enough for it to actually heat up though, you'll see what I'm talking about. We're not trying to "shine" through it. We're heating it up to act as a radiant emitter, exactly the same way we heat up a floor to act as a radiant emitter. You lose some convective transfer compared to floor, but your resistance to heat transfer is cut by 50% or more depending on your finish floor choices.In most cases, running a 110 degree ceiling system is going to be at least as efficient as a higher temperature joist system, if not moreso. Of course poor insulation ruins everything, floor or ceiling.do you live in an area where you don't insulate ceilings, or for some reason you insulate them less well than you'd insulate your floors?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
"Trying to heat a piece of drywall with pure radiation (heat lamp) is not even in the same ballpark as conducting heat into the drywall."But that is exactly what the system shown in those photos is doing. There is no way for those large aluminum plates to have intimate contact with the paper covering of the drywall panels below. There is an air gap of probably 50%-75% between the plates and the panels and the only way energy can jump that gap is by convection or radiation. You cannot compare this system to a floor installation where the heat tubes are actually embedded in concrete or mortar.I could accomplish the same thing by moving my hydronic baseboards to the attic and covering the whole mess with two feet of cellulose insulation. The ceilings would be warm and "radiate" to the rooms below, but I suspect my utility bills might be a bit higher...
I just looked at those pictures closer, and I'd say you're probably right in that installation detail his conduction is pretty crippled. He will be radiating from a very, very close distance though and radiative power is the inverse square of distance so I don't think it'll kill the system. Water temps might be a bit higher than they have to be though.Generally we use single groove plates with a 3" line of strapping on both sides of the tubing groove so that's pretty solid conduction (since the drywall is screwed firm to the strapping), with pretty good contact in between the straps and probably minimal "pull up" on the outer edges.Obviously if you are pouring a slab the cheapest and easiest and most effective thing to do is put pipe in concrete. No one would ever argue that (though there are very select circumstances where that is not desirable). But if you aren't already going to do that, a thin pour on deck is some serious expense. And if floor coverings/unavailable floor are an issue (as they often are), you can easily require water temperatures higher than a good ceiling install would require, which does not have such obstructions to deal with. I see it all the time.Of course the ultimate system is polished concrete. You can't beat an emitter with NO resistance to transfer between itself and the room. You can get close with something like Warmboard, but then your cost is even higher.The ceiling install would be easily 30% of the cost of a thin pour on deck that isn't otherwise needed except for heating. I run these numbers every day. Slabs are great, but trust me, ceiling works and it works well.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
If you've properly insulated above, the area between drywall and the above insulation is effectively an oven -- it will achieve a constant temperature everywhere, and the only place the heat will "escape" is through the drywall.You could have 10" of concrete instead of the drywall, and, with enough insulation (and patience), it would still work. Heat doesn't evaporate -- it has to go somewhere. So you just limit where it can go.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Hello Rob,
I hope I'm not taking your comments (see below) out of context.
One of our other issues concerns the pod with the basement that will house our 3 plastic water cisterns. In that area (pressure treated wood walls), we are contemplating running the heating tubes behind the drywall because we figure we'd have trouble running the tubing beneath the water cisterns. Does this make any sense to you?
Thanks,
Puzzle"Conduct from Pipe to plate.
Conduct from plate to Drywall.
Drywall radiates heat.That's why you would put a heating element behind the drywall as shown. it's a low temperature, very powerful form of heating as the resistance of drywall to heat transfer is much lower than wood or most other floor coverings, you don't have to worry about even surface temps, you don't have to worry about furniture and throw rugs, and it cools more effectively than a radiant floor system does.Also it's less than half the cost of most radiant floor methods and installs twice as fast."
you mean you want to make a radiant wall?That works, but you then have to be concerned about whether or not anyone is every going to screw anything into the wall.We recommend strapping across the face of the studs and using the strapping as backers for the plates. Is this primary heat or just "bonus" heat?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
In that area, yes.
See, our house consists of 3 pods - each 20' x 20' with basements, laid out in a triangular formation.
Then the living/dining area is on a floor that is suspended between the pods about 7ft. up in the air- there will be a dry gully running under this area between the pods.
The basement of one of those pods will house our 3 cisterns , each housing 1250 imp. gallons of water, which we get trucked in. Something like 18 tons of water, which we figure wouldn't be good to have on top of the tubing as I imagine it would suck all the heat out of the tubing (at least for a time...)This city water apparently
Then the other two pods are connected to each other by a hallway.
Sorry, I was interrupted and lost my place. The city water apparently arrives at a temp of 55F, summer or winter.
We won't be hanging pictures in that room, it serves only as a utility room.
That room however is below the master bedroom, so although we don't want to heat it a great deal we also don't want it to cool off the MBdrm (in winter).
We were trying to figure out if it is possible to use this water mass as a sort of ground source of heat in conjunction with a heat pump. i.e run pex pipes through the tanks...
See why my head hurts?
thanks,
Puzzle
Stop, stop, you're making my head hurt too!!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I told you we have a number of issues!
Sorry, didn't mean to hurt you!
So, then this goes back in a circle to where we were looking for a heat transfer medium for the living room floor. I think we've determined that we'll use sleepers on the floor to which we'll fasten the transfer plates.
Does it mke sense then to put strips of drywall between the sleepers to hold/transfer the heat?
I hope you won't be needing therapy after this discussion!
Puzzle
heck no. use a continuous 3/4" plywood infill of strips with a 1" gap between strips to house the tubing and plate tubing groove.Also, use PEX-AL-PEX for that application to make sure you don't have expansion noise issues.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
hmmm, don't have pex Al pex, are we speaking primarily of expansion in terms of the length or width of the tubing?
length. pex expands 1.1" per ten degree rise per 100'. measure each straight run and half will go to each end.So if your runs aren't too long and your water temps not too high, you might be ok, just make sure the bends have a little room to expand into.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thank you!
I notice you didn't care to weigh in on the topic of geoexchange through the cisterns!
that's a little beyond what I have time for on a forum, sorry!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Well, radiant cooling is NOT an oxymoron, though actually accomplishing it to a large degree is difficult. Cooling is the removal of heat, and if a "radiator" captures more IR heat than it throws out then cooling will occur. But the effectiveness of such a system drops with temperature (and of course is also affected by surface color).And radiant heat in the ceiling (behind wallboard) is certainly common. So long as the area above is appropriately insulated it's reasonably efficient.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Thanks for the photos and info -- very helpful.-SC
Hello DocC
A plan to remove humidity is necessary in most cilmates. A simple system puts a fan coil first in line in series with the radiant panel. The loop temperature sensor is located between these terminal units. Set the chilled water loop temperature to 55F in most climates. Operate the fan when the indoor humidity goes above 50%.
Return Chase should be in a central location, small duct system out to each room for dehumidification. In very humid climates the outdoor humidity can condense on the back of the emitter plates.
Radiant Cooling is experimental. Be absolutely clear about that with your clients. There have been many failures, some don't condition the space, some condense, many do both.
Current designs are informed by experience in passive roof pond systems and hydronic radiant heating systems. The key to these systems is to design a building that is easy to heat and cool in the first place. Control of solar and internal gains is critical, as is very good building envelope design and construction.
The Bible for this industry is the Radiant Heating and Cooling Handbook. by Watson adn Chapman. Published by McGraw Hill. It can be special ordered by your local bookstore or purchased from the Radiant Panel Association or ASHRAE.