Hello,

I just finished building my first super efficient house ( icf foundation, 6" spray-foam walls, 20" cellulose w/ advanced air sealing in attic ), I have a 3 zones in the radiant system (basement, 1st and 2nd Floors). Is there a simple way to use my existing radiant system to cool the house? the basement seems to to be very cool and i gotta believe that if i could run the circulators without the boiler and move the basement water through the other zones it would have to create some sort of temperature drop? has anyone done this? is there a simple means of doing this? am i risking creating a dewpoint inside the floors( alum pex, with spacers, radiant foil barrier, with 2-3" open cell foam under it below the sheetrock)

Thanks in advance,

Where are you?

it's unlikely that simply circulating through the basement would result in any significant cooling on an ongoing basement.

I have run cold water through my infloor radiant. It does not make a huge difference. I agree with Rob.

Since the basement slab is insulated, it doesn't really tap the thermal mass of the subsoil to circulate the water. Running the circulator may take the temp of the slab up a few degrees F, but the most it can do is move the heat around within the thermal envelope of the building, it won't remove heat.

To run into dew point issues by running the circulators the slab would have to be at or below the dew point, of the interior air (which is the same mass of air on all floors), and already condensing (not likely, eh?).

I have been told by one of our very highly paid National Research Council's technical people that running cold well water through the slab can cool the house nicely and very inexpensively. Well water runs around 10 degrees Celcius here in Ontario in the summer so there is a significant temperature difference comparing to the desired room temp of 21 C. Apparently, they have run these experiments in a "test house" with favourable results. I mentioned that I was concerned about the floors "sweating" when the warm moist house air meets the cool slab. His response was that you should be able to control the humidity well enough with a properly sized HRV with proper ducting and prevent the condensation problem. I'd say you have nothing to lose giving this a try. If it becomes a problem just stop doing it. The extra cost to plumb the well water into the system is only a few valves.
Has anyone tried this yet? What sort of results do you get?

The extra cost to plumb the well water into the system is only a few valves.

I know someone who put hose bibs on their radiant slab system. One for entrance and one for exit. During the hottest part of the summer, which is only a few weeks here in Western Washington, they run domestic water through their radiant system on it's way to watering the lawn or the garden. Outdoor temps would be considered very warm in the 80-90F range and the temperature of the entering water is probably about 53F-56F. They report it works very well and the cost is literally zero as they are using the irrigation water anyway. They report no condensation problems.

You will have an "open" system and need potable water components if you want the system to last.

Brass pumps and all brass fittings for the oxygen incorporated by opening the system?

-Rosalinda

Potable water rated; may be stainless, bronze, etc.

Congrats on your Green house ratings.

The main culprits would be iron and manganese. Since the loop is essentially only open at the end, the exposure of the water to oxygen is avoided and precipitation of the minerals is minimal. Smooth wall pex loops do not create alot of turbulence so I can't see alot of mineral build up in these areas. The main factor that creates mineral oxidation and precipitaion is heating. When you put the water through a heat exchanger and increase the temperature you start to cause problems, especially in the heat exchanger.
I think this idea of using the water for irrigation is brilliant and considering the only time you need to air condition is on hot sunny days, it's exactly when you need to irrigate so the two concepts go well together.
Now the important question remains, how to automatically control the system? Should we open the solenoid when the lawn needs watering or when the house needs cooling

I have a couple of points.

I have my radiant floor system hooked up so I can run my irrigation water through it. There are two things that make it problematic. Timing amount of irrigation water. For proper irrigation you need to be running this during the cool of the day not during the hot when you you would really need it. Second, it is a lot of water that you will need to run to make a big difference. That may be fine in my situation where I water pastures. I can not see on a small city lot.

What makes it work here in Western Washington is the relatively moderate weather. We only get temperatures hot enough to want your home cooled for about 2 to 6 weeks a year. It nearly always comes during a period when you can disable your normal heating so it represents a twice-a-year changeover event. The hottest times of the day come well after noon, during the late afternoon heat build-ups, particularly when the sun swings lower and strikes from the west. My friend gets off work at 4 pm so she can go home and set the watering hoses and sprinklers. Cooling the slabs gives immediate relief and keeps you from suffering into the evening hours, or in some cases, thorough the night. They have also set them in the morning with a simple hose timer that comes on if they aren't going to get home right away. They water pasture, lawn, fruit trees and a large vegetable garden.

Posted By mnelson61 on 06 Feb 2012 06:37 PM
I have been told by one of our very highly paid National Research Council's technical people that running cold well water through the slab can cool the house nicely and very inexpensively. Well water runs around 10 degrees Celcius here in Ontario in the summer so there is a significant temperature difference comparing to the desired room temp of 21 C. Apparently, they have run these experiments in a "test house" with favourable results. I mentioned that I was concerned about the floors "sweating" when the warm moist house air meets the cool slab. His response was that you should be able to control the humidity well enough with a properly sized HRV with proper ducting and prevent the condensation problem. I'd say you have nothing to lose giving this a try. If it becomes a problem just stop doing it. The extra cost to plumb the well water into the system is only a few valves.
Has anyone tried this yet? What sort of results do you get?

Absolutely false!

An HRV does not remove the humidity from the ventilation air, and thus cannot reduce the humidity of the interior air below the outdoor dew point, which at times will be fairly high in July/August- high enough to limit how low you can take the slab.  You would almost certainly need mechanical dehumidification to be able to deal with the sensible load via the slab in most southern Ontario locations.

The mean July/August dew point in Toronto is ~17C, which isn't bad, but the peaks during the hottest-stickiest weather can be north of 22C, so if you tried to cool the house by taking the slab down to 18C, if relying only on the HRV for humidity control you'd end up with a surface temp not lower than 22C, with a film of condensation on it, accumulating over time.  Any rugs would be absorbing significant moisture, increasing the mold risk.

You can still cool with the slab in dog-days of summer but you'd have to LIMIT, rather than increase the ventilation rate on the HRV, and dehumidify via other means.  But with the relatively modest outdoor dew points if one sets the HRV to a minimum rate a single portable 70-pint room dehumidifer can keep up with the latent loads of a small to mid-sized house.

Further north & west the outdoor dew points are a bit lower (eg. Thunder Bay's mean July/August dew point is only 13C, with shorter & lower peaks.)

In Calgary or Vancouver the summertime dew points are lower still (rarely breaking 15C for the PEAK) and is a perfect climate for cooling the house with a chilled slab.

Resources like WeatherSpark are very useful for determining if YOUR local climate is suitable for cooling with slabs, or whether you would need dehumidification beyond what can be delivered with HRV.  You have to enable the dew point graph and zoom out to view the whole summer, and use the cursor to estimate the mean.  Locations with midsummer dew point averages above 60F/15C will surely need other forms of dehumidification, but if the mean dew point is well below 55F/13C you can do most of the cooling with just the slab.

Posted By ICFHybrid on 07 Feb 2012 09:26 AM
What makes it work here in Western Washington is the relatively moderate weather. We only get temperatures hot enough to want your home cooled for about 2 to 6 weeks a year. It nearly always comes during a period when you can disable your normal heating so it represents a twice-a-year changeover event. The hottest times of the day come well after noon, during the late afternoon heat build-ups, particularly when the sun swings lower and strikes from the west. My friend gets off work at 4 pm so she can go home and set the watering hoses and sprinklers. Cooling the slabs gives immediate relief and keeps you from suffering into the evening hours, or in some cases, thorough the night. They have also set them in the morning with a simple hose timer that comes on if they aren't going to get home right away. They water pasture, lawn, fruit trees and a large vegetable garden.

I guess in the Pacific Northwest where water is abundant you can waste it by irrigating during the day or afternoon. Here in Wyoming we just can not do that.

In the Pacific Northwest the cooling loads are much lower than in WY too.

In parts of WY you 'd be able to cool with well water in a loop system, discharging the water into an adjacent well geothermal-style without much risk of the well going dry.

In my part of Wyoming, western mountains at 6500 feet the cooling load is probably less. Add the cost of drilling another well at about 25000.00 dollars or more. Not feasible.

Posted By jmagill on 07 Feb 2012 12:03 PM
In my part of Wyoming, western mountains at 6500 feet the cooling load is probably less. Add the cost of drilling another well at about 25000.00 dollars or more. Not feasible.

Your pumping power costs may exceed the value of the cooling attained too. 

For that kind of money you could buy a pretty good high efficiency heat pump and enough grid tied photovoltaics to make it operating-cost negative.

I guess in the Pacific Northwest where water is abundant you can waste it by irrigating during the day or afternoon

It's not wasted. We have a certain amount of reputation for humidity that we need to maintain. ;-)

In any case, we use flood and drip irrigation here quite a bit.

But you're right; as much as anyone has abundant water, we do. Don't tell anyone. They'll want to come here.

Posted By ICFHybrid on 07 Feb 2012 02:56 PM

I guess in the Pacific Northwest where water is abundant you can waste it by irrigating during the day or afternoon

It's not wasted. We have a certain amount of reputation for humidity that we need to maintain. ;-)

In any case, we use flood and drip irrigation here quite a bit.

But you're right; as much as anyone has abundant water, we do. Don't tell anyone. They'll want to come here.

I am from there. A bit north though, Vancouver and Whistler. I remember what it was like to have endless water.

In the Pacific Northwest the cooling loads are much lower than in WY too.

Yeah, I don't think central AC is very common here. But, that's what makes a kludge like this so sweet - when it works to give you a few seeks of comfort and costs NOTHING.