It is my intent to use a combined passive/active radiant heating and cooling system. The floors in both of my buildings are concrete, which is an excellent medium to use radiant heating in the floor. Additionally, water cooled polypropylene mats will be installed in the ceilings. In the studio building is will be cast directly into the bottom surface of the floor assembly to cool the space below. Radiant cooling works best when the cooled surface has a direct ‘line of site’ to what needs to be cooled. (People) In the residential building the mats will be installed in a dropped ceiling system that will be more appropriate for a residential application.
Typical radiant heating systems are supplied by hot water that is heated by either a gas or electric water heater. Considering the lengthy southern exposure (200’+) of my building I plan to use a passive solar water heating concept. On the roof there is a ‘mechanical’ penthouse, which will contain fairly thin storage tanks, that will be heated by the sun. These tanks will supply the radiant heating… I intend to maintain an auxiliary electric or gas fired source at the end of the storage system which will monitor the temperature of the water, and should additional heat be needed the conventional source will kick in. Keep in mind though that the water that is being heated will still need much less energy to get to the required temperature to heat the spaces. Here is a link to a website where a guy built a ‘shed’ specifically to do this. www.builditsolar.com
Below is a description of radiant cooling that I got from the website www.toolbase.org
Radiant cooling systems rely on chilled water pipes to distribute cooling throughout a building rather than a conventional system that uses chilled air and ductwork. Radiant cooling systems rely mainly on the direct cooling of occupants by radiative heat transfer (heat transfer through space like the sun’s warming effect on an object in its direct path) because the pipes, which are commonly run through ceilings, maintain the surface at temperatures of about 65°F. Through radiative heat transfer, people in the room will emit heat that is absorbed by the radiant cooling surface. To manage indoor humidity levels and air quality, a separate ventilation system to supply fresh air is needed. Due to the ease of controlling water flow, independent control of areas of the home is relatively simple.
There are at least three methods of delivering chilled water in radiant cooling systems. The panel system is the most common of these. Aluminum panels that carry tubing can be surface mounted or embedded on floors, walls, or ceilings. Another, the capillary tube system, consists of a mat of small, closely spaced tubes that are embedded in plastic, gypsum, or plaster on walls and ceilings. Or, similar to hydronic heating systems, a concrete core with embedded tubes can provide the conduit and thermal storage capacity for a cooling system. In each of these systems, the water is mixed with glycol and cooled by an air-to-water heat pump, a cooling tower, a ground-source heat pump, or even well water. Because the radiative surface is typically a whole floor or ceiling surface, the water can be as warm as 65ºF and still provide comfort.
The specific product I plan to use is KaRo by Radiant Cooling Corporation. This system consists of very small polypropylene tubes that are supplied by larger tubes. Check it out here These 'mats' will be cast in place in the bottom of the cast in place concrete floor/ceiling assembly.
As noted in the opening description the system can be cooled by ground water due to the fact that it isn't necessary to cool the water to a temperature that forced air is typically cooled to.
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2 comments:
Karrick, I like your thinking, but would encourage you to have a serious discussion with Chris. I’m skeptical that your current design with the long north/south exposure allows you to reduce the cooling loads to the requirements stated by KaRo:
For any building envelope, perimeter thermal loads and interior heat generation can be designed to reduce the cooling load below 25 btu/sq. ft. is a candidate for radiant cooling/dedicated outside air system.
The heating on the other hand should be no problem, on a sunny winter day I would expect you would be cooking in the classrooms – no additional heat needed. The overcast days would simply use the auxiliary heating… do you even need solar collectors, as the good weather conditions would provide enough direct heat, and at times, when the sun doesn’t hit the class room windows, you also don’t get heat in the collector. Or do you provide storage tanks that are sized to hold enough energy to make up for “day-night” or “overcast period”?
Karrick, have you found somewhere to get the capillary tubing at a reasonable cost? I've contacted radiantcooling, I think it was them at least, and they seemed very uninterested in selling the product for any kind of DIY project.
I was quoted over $2500 for the capillary mats for one room that's about 14 x 20 ft! That's without any fittings, installation, etc...
I'd really like to use this to retrofit my home to radiant heat / possibly cooling, but at what price?
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