Reverse Radiant Heat

[D L Bahler]

In floor radiant heating works on the principle that hot air rises (or more properly, colder air sinks to replace warm air), thus the most efficient means of heating a room is from the bottom up. So these rooms heat the floor, which can then radiate their warmth into the air.

I am designing a room that must be kept cool. around 55 degrees all year. This means that cooling is the primary concern and heating is not much of a problem.

I had considered using a radiant system, but it struck me that I am designing in the opposite direction that these systems are usually intended for. Yes, they do make in floor systems that also cool, but if I am designing specifically for cooling it would be better to optimise my system for that.

So It struck me to reverse the system, place my radiation pipes is the ceiling, rather than the floor. (In this room, the pipes could be exposed to the air, strapped to the ceiling.) If I run liquid through them cooled to 40 to 45 degrees, they will cool the air in the top of the room which will sink down, bringing the warmer air to the top, etc. This would then become a radiation/convection system.

Another alternative is to instead place the pipes along the walls.

[Dave Shepard]

Wherever you put them, they will have plenty of condensation on them.

[D L Bahler]

In this environment, it is to be assumed that there will be condensation on anything and everything.

This is for my cheese aging room. 55 degrees and 85 to 95% humidity. A cold and very wet space.

It is just assumed that there will water dripping from everything.
Everything is enclosed in a moisture barrier, made to deal with water.

[danreed76]

There are several systems out there that do, in fact use radiant cooling (radiant floor, wall, ceiling, and chilled beam systems.  The difficulty you might have would be keeping your humidity up to the levels you're trying to reach with such a system.  If the room is to always have a high humidity and a low temperature, you need a system that can move a LOT of BTU/hr, essentially pulling down the sensible load (temperature) without removing the latent load (humidity).  It's the same effect that it has if you've ever been in a house that has an oversized air conditioning system; it gets cold and clammy because the system doesn't run long enough to condense the moisture in the air.

Depending on what the source of heat and humidity is (humidifier, ground, outside environment, the aging process of the cheese) and where it is located, you should be able to plan your radiant system to have the majority of the heat absorption located away from these sources which should create some natural circulation.

Do you need a certain amount of air exchange/circulation?

[D L Bahler]

One reason behind using a radiant cooling heat transfer system is to prevent the moisture loss that occurs with a regular cooling unit.
There is also an issue of aesthetics, I do not wish to put a large modern-looking cooling unit in plane sight, and have little space for it on the interior. Also the noise is undesirable. I won't get into why that is now, but there is a very good reason for it.

Required air exchange is minimal, though I will have to bring in a certain amount of fresh air as the bacteria in the cheese do consume oxygen and release gasses including CO2 and ammonia. (in very minimal amounts. Just walking in and out every day will probably be good enough to exchange enough air)

The room is right now open to the roof. While I will insulate and seal the ceiling, it will still be peaked. The plan is to put cooling pipes near the ridge, with a drip pan underneath to catch dripping condensation and drain it to a single location.

I have a very good HVAC guy I work with, he knows his stuff and is also very creative and intuitive. He works with modern systems all day, but isn't afraid to try something new or different. (He does a lot of work on the air systems for the control rooms in cell phone towers, very precise work due to the extreme sensitivity of the electronics)

The plan is to have a reservoir tank with a mixture of water with alcohol and propylene glycol (to prevent bacterial growth, algae, etc. and to keep the liquid from freezing) with a cooling coil or a cooling plate that will hold the water between 35 and 40 degrees. It is then cycled through the pipes, back to the tank.

[r.man]

Sounds like it should work although you still might have to humidify if the drip catch is too successful. Make sure the drip tube is reasonably large or removable for cleaning. Gunk can cause blockages in that sort of thing and your room might be more susceptible to it. Easy to build in, hard to modify.

[scsmith42]

For maximum temperature transfer, I think that you would want to used finned tubing for the ceiling portion of your run, and have some type of gentle air flowing across them.  Otherwise the system would be fairly inefficient.

In a slab, the fact that the concrete has full contact with the tubing promotes heat transfer between the two.  The large surface area of the slab then radiates the temperature upward. 

You won't get this same effect just off of some tubing in the ceiling though. 

If you route them to something like an automotive radiator with a fan pushing some air through it (or even an air handler from an old AC unit), it would be much more efficient.

[Al_Smith]

The basic idea of this is about the same principal the old TETCO geothermal units worked on .Cold water was pumped though an A coil and a fan blew through it .Ground water ,pond ,river ,lake at 50 some degrees .It did dehumidify because water condensate would collect on the coil .

The way that unit worked for heat was with refrigeration ,same as units built today .Only cold water was used on the cooling portion .

For a pump I suppose if a person were inclined they could use a windmill .I saw a bunch of them in Iowa and Nebraska on a recent road trip .

[LittleJohn]

You might be able to get around the humidity issue if you just run a dehumidifier that is hooked to a humidity sensor; might not remove all the condensation, but it should remove a good chunk of the moisture from the air.

[Dave Shepard]

The crux of the problem is that he needs the high humidity for aging the cheese.

[Al_Smith]

Oh he'll have enough humidity  if he's drawing in warm outside air once it hits those cold pipes .Probabley be able to grow mushrooms while aging the cheese .Double crop so to speak .< capitol idea ,hmm .

[Gary_C]

You are oversimplifying when you say radiant heating is all about heat rising. Radiant heating in the floor is more about thermal mass than convection.

When you heat or cool a large thermal mass in the room instead of just heating the air, you can maintain your controlled temp and humidity settings much easier than if you are just heating or cooling air. With a relatively low thermal mass system like you are proposing in the ceiling, you are going to need far more than natural convection to maintain cold temperatures and humidity.

You need to consider three things for your cold room. First is super insulation, second is creating a thermal mass of cold, and third is creating enough circulation to prevent temperature gradients in the room. Cold air is dense and hard to move naturally so you cannot rely on convection to prevent warm spots in the room.