Anyone have any input on radiant cooling? I have radiant heat in slab already and was wondering if any systems were offered for cooling. Any input good or bad on the subject will be appreciated.
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In most climates there is enough moisture in the air that you will get condensation on the floors.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Cold air drifts downward - without some active form of circulation "in floor" cooling wouldn't work too well. Then there's that minor problem of water condensing on your cold floor...
The Gleneagles Community Centre by Patkau Architects uses radiant heating and cooling from floor slabs tied to a water to water heat pump. The slab never cools enough to have condensation problems, and because you aren't relying on cooling the air, you can still open windows without significantly affecting the system.
It is a logical and efficient way to cool. The Gleneagles project saved 40% over conventional mechanical systems.
Yeah, what the others said--I thought I had "the answer" when I thought of it, and happened to mention the idea in earshot of an old HVAC man and he told me the condensation made it a real bad idea. I suppose if you used in in a bathroom or something and channeled the water away--but I think even that would get musty.
I was just now thinking of something topping the tubes that is somewhat porous--like sandstone--that would sort of absorb the moisture and wick it so it could evaporate later. Maybe run the flooring under a wall to a greenhouse so the moisture would "flow" toward the hotter/dryer greenhouse and it could evaporate in there. Just thinking out loud. Maybe you could put channels and drains in the concrete and put cypress or teak or similar grid over it to walk on. I hate abondoning a good idea jsut because it seems to have some glitches!
We did it on one house. Ran a line from the well through the floor (on a loop pump so it was blended slowly with the constantly circulating water in the floor) and out to the submatic drip irrigation in the garden. We stole an old Levittown trick and used a rubber disk with a hole drilled in it to regulate the release of water to the garden and used a 24 V t-stat and valve to turn the flow on when the house warmed up and shut it down when it cooled off. It worked fine since the house had a ton of insulation in the roof and 36" overhangs so it didn't need much cooling but it did nothing at all for the humidity and if you accidently left the windows open in the morning and we had a summer shower in the afternoon you would come home to damp floors.
Final verdict, we never did that again but I can see that there might be some way to make it work if coupled with an undersized variable speed or zoned-bypass HVAC unit for dehumidification.
------------------
"You cannot work hard enough to make up for a sloppy estimate."
i think a better idea is passive air cooling. it has been talked about before in this forum how thomas jefferson's house had an air duct that traveled underground for enough distance (through servants quarters and root cellar/basement) to cool the air in a house that was designed with ventilation in the top to conduct or move the air.
the most efficient use of power to cool is with a fan to move the air. ducted systems that will move air that will be naturally cooled by the placement of the duct is the ticket. many times when working on a project in a crawl space or basement i am surprised at the difference in temperature. all you have to do is move the air through the cooler areas at a speed that wiil produce cooler temperatures in the desired space.
There are some recent high-rises that have used similar passive air cooling ideas. One I saw in Australia had a small wooded area with a pond at its base where the air intakes were located. The air then travelled underground before venting into a central atrium, where convection moved it upwards until it exited at the roof.
The architect claimed it was based on the cooling strategies termites use in their mounds. Much more likely he'd just been to Jefferson's house.
Check out http://www.bekausa.com for cooling applications. I don't have any practical experience with them.
Maybe I'm alone, but the title "Radiant Cooling" seems like the perfect oxymoron, at least in terms of basic thermodynamics.
Scott.
Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”
radiation is the method by which the panel draws heat from your body and the room, that's Radiant cooling, right?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Kinda, but technically, no.
The panel does not "draw the heat from your body", it absorbs the heat radiated from your body. The temperature difference between radiator and the absorbing surface, as well as surface qualities, drive the amount of heat transfer. Your familiar with MRT. If the MRT is lower than the body, heat transfer is out of the body; if MRT is greater than the body, heat transfer is to the body.
So radiant cooling is no more an oxymoron than radiant heating, it is the same process, just a matter of perspective.
that's a pretty semantical arguement. how exactly do you determine if I am pushing heat at a cool surface, or if the cool surface is drawing heat from my body, and what exactly is the differencein those mechanisms?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
It is not semantics, it is physics.
Energy is transfered from a higher energy state TO a lower energy state. You never actually cool anything, you transfer heat away. You're not pushing or pulling anything. You're simply allowing or preventing heat transfer. If you offer a "hot" object a means to transfer energy to a "cooler" object, it will do so. Always. In the absence of work, heat (energy in general) always moves from a higher energy state to a lower energy state, i.e. hot to cold.
"...how exactly do you determine if I am pushing heat at a cool surface, or if the cool surface is drawing heat from my body." You say this like heat is a material. Thermal energy is only a relative measure of the molecular kinetic energy of a substance or object.
"and what exactly is the differencein those mechanisms" Absolutely nothing. heat transfer is heat transfer. Whether you consider heat added or removed is perspective only.
yes, it's perspective only. so it's just as right to say radiant cooling as it is say radiant heating as it is to say radiant heat transfer. it depends if you are describing the process from the point of view of the object being heated, cooled, or outside the interaction entirely. so why is calling it radiant cooling wrong?If you actively pump heat energy out of an an object surface, I would suggest that you are ultimately drawing heat from a nearby object by cooling that surface. that's the relevant point of view. You are doing it by forcing this imbalance to occur in the direction you want it to, that is, you are actively cooling a space; you are doing it by radiant heat transfer; it is radiant cooling. If you are instead adding heat energy to a hot surface to cause it to heat up another object, that is radiant heating, and you are "pushing" the heat. That may not be the molecular interaction that is occurring, but that doesn't mean that it's a bad way to discuss it, nor imprecise.Finally, what exactly do you call transferring heat energy away, if not "cooling"? last I knew, that was the very definition of cooling.I didn't really mean to get into a big discussion about this, I just don't understand your objections to the term.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Maybe in stead of "radiant cooling", we should call it "radiant UN-heating".Would that be more PC ???(-:
You cannot strengthen the weak by weakening the strong.
First, I didn't say or mean to say that "radiant cooling" was wrong, I meant the terminology "drawing heat out of the body" is wrong.
"If you are instead adding heat energy to a hot surface to cause it to heat up another object, that is radiant heating, and you are "pushing" the heat. "
I need Frenchy to interpret. I know he's lurking out there somewhere.
"I just don't understand your objections to the term." I shouldn't have been so technical. So for the confusion.
So lets say you have a 3 story victorian house in the SF bay area region. Its going to be well insulated and it will have radiators on the top floor.
Would it make sense to 'radiantly cool' these radiators to cool the house?
Daniel Neumansky
Restoring our second Victorian home this time in Alamdea CA. Check out the blog http://www.chezneumansky.blogspot.com/
Oakland CA
Crazy Homeowner-Victorian Restorer
You are a mad scientist! I believe that if you got the radiators cool enough to cool the space they would condense moisture out of the air and drip on your floor. If you paired them with a good de-humidifier you might be able to use them to boost the dehumidifier but in Oakland you have so much humidity I think a zoned bypass heat pump or even a very small variable speed heat pump would be a more elegant solution. Just my thoughts from muggy Chapel Hill NC.------------------
"You cannot work hard enough to make up for a sloppy estimate."
Sorry Dan, I can't design a radiant cooling system ;)short answer is probably not. You need VERY low cooling loads, and lots of surface area, and good humidity control to do radiant cooling. Typically the best choice would be radiant ceiling, and even that, I'm told, is restricted to a 12 BTU/sq ft cooling load with humidity control in effect.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
You say this like heat is a material.
Yeah, phlogiston, right? You have an excess of it in one thing and it goes to where there is a lack of it. Gracious, I learned this at University when that upstart Newton was still in knee breeches!
Since we don't know where you are located (fill in your profile) radiant cooling may or may not be an option.
As other have pointed out, condensation could be an issue. You need to understand the terms "sensible" heat and "latent" heat. You might be able to archive a room temperature of 72* (sensible heat), but if the RH is high (latent heat) you are still going to be uncomfortable. Condensation problems will occur when the RH is high and surfaces within the home are below the dew point.
The suggestions about bringing air in through underground ducts sounds good and was used quite a bit--seems like as recently as the 70's and 80's people were doing that to cool air and to heat it in winter. But many found out that moist air through ducts ends up bringing lost of mold into the house and breathing mold spores wasn't sitting well with some people. If it were a completely separate system, or if you could filter the air, it may work.
I played with a house design that used the idea of turning concrete blocks on their sides to form a series of parallel "ducts." This combined with a solar heated greenhouse was supposed to help heat the house, but I was concerned with dust and dirt and mold getting in the block and blowing through the house. I think in one plan, I isolated that air in its own loop, so it went under floors to heat them, but the air itself didn't go into the house.
(Can't remember how I drew it up (never built it)--maybe went into attic and was vented or returned to greenhouse of went out to enclosed back porch. I remember it was pretty elaborate--had air vented from kitchen and baths blow under and through plant beds in the greenhouse to add heat and moisture. Would be intersting to see if any of those ideas would actually work! (Including garage doors, one to shield greenhouse from too much sun and to insulate on winter nights and another between greenhouse and house to insulate house at night or when greenhouse was too hot.))
jes82677
Cooling is a matter of insulation plus efficency..
Most central A/Cs aren't very efficent they use ducting intended for the furnace and let out cold air at ground level.. Hot hair rises cold air settles! That's why they aren't efficent..
I used a well insulated Home (built with ICF's and SIP's ) and instead put small window A/C in the wall.
That way I could put them up high where they work really well. I can pull them out in the winter and plug the hole with the cutout or make a insulated box to cover the unit..
The really great part is they are at least as efficent as central A/C and I only have a couple of hundred dollars in them. If more efficent A/C comes out I can buy new units very easily!
Most central A/Cs aren't very efficent they use ducting intended for the furnace and let out cold air at ground level.. Hot hair rises cold air settles! That's why they aren't efficent
In your neck of the woods, true enough. 'Round here, all forced air is eithe high wall or ceiling registers, so that the cold air can "fall" to floor level. With only 7-8 weeks of heating season, the "backwards" heating system just gets tolerated.
Now, half way in between, say around Wichita, dunno what they do, with about equal HDD & CDD . . . Occupational hazard of my occupation not being around (sorry Bubba)
CapnMac,
So A/C has seperate ducting in your neck of the woods?
So A/C has seperate ducting in your neck of the woods?
Nope, only the one set of ducts, always in the attic, optimized for cooling only.
Millions of houses where the warm air in the heating season is pushed out of the ceiling to puddle right there until the heat gets down far enough to trip the stat.
Thoughts of insolation much on my mind with heliogee coming up Friday after next--will be 89.37º at solar noon, dawning 29.36º N of East and setting 29.36º N of West that day.Occupational hazard of my occupation not being around (sorry Bubba)
CapnMac
Interesting!
I've a friend in SanDiego (and I've spent a lot of time there as well) and I've never seen a high exit cooling ducts. Everything I've seen is low for heating.. Considering how temperate the climate is That's interesting..
OOP's I have seen those mini ducts up high in some newer high end homes both there and here..
Interesting!
Ain't it though? What boggles my mind are the number of installations where the return air is also in the ceiling. Now, that does save having to fish retun air ducts down walls. But against that is the potention to "short-circuit" the air circulation.
Ducting habits in SD probably go back to when only heat was installed, so that's the way "everybody" did it, and that's passed down to the present time. But that would be a guess. My aunt's old house actually had a reversing damper so that the returns were supplies during heating season. Which was probably better in that transitional time there in SD semi-analogous to "spring" or "autumn" where a person needed both heating and cooling in the same day.Occupational hazard of my occupation not being around (sorry Bubba)
I lived on the left side for over 5 years and fought with a number of HVAC guys over ducting.
In short, they don't give a shid where the duct goes. Only that it is easy to do and it's done - somehow.
Seriously. I threw two guys off the job over it. And the owner of the third told me when I objected to them using 14" insulated flex as a return, pushed in and bunched up inside a 90 degree turn of the soffit (very little flow was possible as a result), "I'm providing a flow. If you build your soffit so it doesn't work that well, that's your issue. An upgrade to a sheet metal trunk return would be $2500."
16' across the front of the garage. When it was wide open. 10 years ago.
As many have alluded to in one fashion or another, radiant cooling is certainly possible, but has potential challenges that require some level of accomodation.
Using the hydronic slab to remove heat from your house is a good idea, if you have a source of cool water, and a means to regulate the surface temperature. If you live in area where dehumidification is important, that has to be addressed or the floor will sweat. That is a matter of keeping the surface temp above the air dew point temperature. In a humid environment, that means 65 degrees or higher.
What is the source of cool/chilled water? If its a well, don't do it. This would be a colossal waste of clean water. A small air cooled chiller? They're around, but not too prevalent. Water-to-water heat ground source heat pump? That's a real viable option.
In a commercial building with a large atrium, south or west wall of glass, chilled water system and good air handling, cooled slabs are frequently utilized to remove a large incident sensible heat load. In a residence, seldom worth the trouble, but cetainly possible.
I have a "radiant cooling" system in place at home and it works. I have customers with "radiant cooling" and it works. However, there are a few "gotchas". One needs to have a thorough understanding of latent and sensible heat and be very familiar with a psychometric chart and what change causes what effect.
As others have said, dehumidification is the key to the puzzle. It is not a set and forget system like ducted usually is, the owner needs to be a tinkerer at heart. We live in humid Iowa so vapor sealing the house is critical to keep humidity out. We also have a vestibule to provide a "buffer" when coming and going when the weather is more extreme.
You need to fill out your profile so You can get more better info.
Chris