Radiant cooling?

[djmcmath]

We've all heard of radiant heating, typically the in-floor kind. My house has the older kind, with the cast iron radiators in each room. It works great, in that it provides lots of heat. Controlling temperature is ... painful, but that's a different post. I think the right answer is to convert the control system over to something more like the modern in-floor systems use, where it maintains a relatively constant temperature. But that's not the question from this post...

Here's the question for the Pelican Brain Trust: Is there any way to adapt the heating system to be a cooling system? How cool would I have to cool the radiator water to make it effective, say, to keep the house below 80F on a warm summer day? Is there an affordable pre-existing solution that could, basically, replace the furnace in the loop and make the radiator water 50F instead of 120F? Is this a wheel that's been invented already, and if so, how many spokes did it have?

Thanks,
Dan

[Hugh R]

Won't work. Heat radiates, cold is the absence of heat. Think of a match which you can't too close to, and an ice cube. With A/C you're taking heat away from the space and dumping it somewhere else. I suppose you could put fans behind the radiators, and try and dump the heat somewhere else. You got a big heat sink called the earth. You could run some piping underground a few feet to act as a condensor.

[Taz's Master]

All I can think of is all the condensation on those radiators, and everything around them would be moist, warped floors, moldy walls and wet carpets...

[masraum]

I think in theory it could be made to work (it's basically what AC does), but for that, you'd have to have a way to pump all of the air in the house over the radiators through a duct (ala Air Conditioning). Basically, you'd have to turn the radiators into a huge condenser, and I don't think the radiators would have the surface area that a real condenser does. I don't really think that's feasible. Then, there's the water problem that Taz's Master brought up. I think for them to really make a dent, you'd have to be able to cool them to subfreezing temps (like 0* or less) which again, doesn't seem possible (the condensed water would freeze and insulate them).

The closest thing to what you're talking about is geothermal heating and cooling where you use a huge radiator in the ground to heat your house in the winter and cool it in the summer, but I think you need a climate that doesn't have too much of an extreme (hot or cold) climate for that to work well.

[rick-l]

Originally Posted by Hugh R

Won't work. Heat radiates, cold is the absence of heat. Think of a match which you can't too close to, and an ice cube. With A/C you're taking heat away from the space and dumping it somewhere else. I suppose you could put fans behind the radiators, and try and dump the heat somewhere else. You got a big heat sink called the earth. You could run some piping underground a few feet to act as a condensor.

Heat transfer is the transition of thermal energy or simply heat from a hotter object to a cooler object so if the water in the radiator was cooler than the surrounding air it would cool the air. Now the problems I see are:

1. part of the job of an air conditioner is to remove moisture from the air. Where does it go?
2. I think the circulation of water in a radiator is steam going up and water going back (gravity not a pump)

I was looking at the AC where I work and there is a massive compressor with a local loop of freon to a refrigerant-water heat exchanger. The chilled water is pumped to the various buildings. There are air handlers (cold water to air heat exchanges) in each area that filter the air and remove moisture.

[rick-l]

Originally Posted by masraum

The closest thing to what you're talking about is geothermal heating and cooling where you use a huge radiator in the ground to heat your house in the winter and cool it in the summer, but I think you need a climate that doesn't have too much of an extreme (hot or cold) climate for that to work well.

A friend of mine that lives out in the sticks uses a geothermal grid (tubing buried in the ground) to heat and cool his house (heat pump). The water circulating is a pretty constant 50 degrees year round in St Louis.

The freon is completely contained in the unit in the basement. Of course he has a pinhole leak in the condenser and is looking at $8000 to replace the whole aging unit.

[Heel n Toe]

Dan, what do you use to cool your place now?

[RWebb]

Originally Posted by Hugh R

Won't work. Heat radiates, cold is the absence of heat. Think of a match which you can't too close to, and an ice cube. With A/C you're taking heat away from the space and dumping it somewhere else. I suppose you could put fans behind the radiators, and try and dump the heat somewhere else. You got a big heat sink called the earth. You could run some piping underground a few feet to act as a condensor.

Not at all. And the first few sentences are completely wrong. Heat will radiate from the objects in the room (including you) to the exchanger that is full of fluid. Heat will also convect to the exchanger.

It will work, but is not practical. You would need a good working fluid as the fluid temperature would need to be quite low.

The idea to use the earth as a sink is a good one and such systems are all the rage now. They are not practical unless you are building a new house and have an excavator out there anyway - they dig trenches and lay piping, then cover it all over.

[ckissick]

In Dubai they are building a hotel on a beach. The beach sand will be kept cool with some kind of radiant cooling system under the sand.

[djmcmath]

The existing heating system has a pump. When the thermostat says it's cool enough, it fires off the furnace and a pump at the same time. The existing cooling system is just window AC units.

So the problems with radiant cooling ... condensation is definitely an issue. Drip trays are an ugly solution, but it'd be the only real option. Blech.

Temperature requirements? Hmm, good point. A rough approximation of the surface area of the radiators says I can get a delta-T of about 20C, which would mean I'd need to fill the radiators with water at something like freezing in order to maintain something like room temperature in the space.

Ok, so maybe not such a good idea.

Thanks for the feedback.

Dan

[Hugh R]

Originally Posted by RWebb

Not at all. And the first few sentences are completely wrong. Heat will radiate from the objects in the room (including you) to the exchanger that is full of fluid. Heat will also convect to the exchanger.

You're correct, incompletely edited post before I had finished my thought process.