Radiant Slab Cooling

[bpirger]

For those of us nerdy enough to be reading this during the summer.....a topic perhaps to kick around...inspired by the shoulder season thread.

Does anyone use their radiant floor for cooling during the summer? Biggest issue is likley condensation obviously....and I don't think there's much of a chance unless there is lots of massive concrete.

But I have that....6" floor that is 44x32. That's quite a mass. When it is nice and cool in the evenings, and no rain, so I can leave the windows open all night, if I can get the slab down to 66 or so....it does a remarkably nice job keeping the house cool throughout the next day. What happens though here in the north east is the 5 days or so of 90's temps with nights that dip maybe in the high 60's....and there's no much help cooling the slab it seems. That's when the big AC in an upstairs windows turns on...and spins that meter. The 55 degree air really does a nice job on an overnight "soak".

Sometimes I toy with the idea of plumbing things up so I can circulate well water (about 45 degrees at the house) through the floor to keep it cool during the day. Would have to plumb in some valves to make the switchover and disconnect the manifolds from the primary loop of the heating system....but doable. ALso, would be introducing fresh water into the heating system everytime I switched back over.....not a good idea either. So I have never bothered. But right now it is about 55 outside and clear, so when I hit the hay I will open all the windows...and the slab will be 65-66 in the AM. Easy enough to run the numbers and it seems like I have to run quite a bit of water through the system....and it would be dumped on the ground...quite a waste...but it might be overall cheaper than running the AC.

Running a few numbers it is in the realm of doable it seems, to perhaps keep the slab at at 65-66 degree temp during the day...which really seems to help cool the house....though I guess I have to really think about how much this cools the house as opposed to how long it just takes the house to heat up....

But if I only had to introduce say 1 gpm of fresh water into the floor, 60 gallons/hour, and I could get a 20 degree temp change, that's about 10,000 BTU/HR. Doesn't seem like much...not even one ton of AC. The well pump would be running every couple of minutes (pressure tank appears to still be behaving fine). So 60 gallons/hour used....for 8 hours a day...or 480 gallons. Maybe I could irrigate the garden with this.... Well pump at 240V * 10A (guess) but only at 5minutes/hour so just maybe 50 cents a day for 8 hours. Well should be OK to do this rate of water forever...though I did run it dry when I was sprinkling water on my garage floor (two big sprinklers running full bore for many hours straight......learned I had to go out and turn them off for awhile!)

So likely not worth all the effort and risk (to heating system, to well, well pump, and water waste, floor condensation/mold, etc).

But does anyone else have any cooling methods?

 

[jimbom]

Buried ground loop circulated directly through the floor? There has been some research. ASHRAE has published a panel cooling/heating graph. I have studied it quite a bit. It would work for me. We have a super-insulated house so payback is a stretch. That is always the issue with me. If it don't pay, I delay.

 

[Frozen Canuck]

Just a few thoughts.

Unless you have separate dedicated tubing for cooling, I would say no to pumping your potable water in the same tube that your boiler water circs through. Very likely there are things in your boiler water that you would not want contaminating your potable system & vice versa as I assume you have your boiler ph balanced to mfgr specs & the potable in the system would change that when you need to burn again in winter.

Run your numbers through an AC calc as it takes far more btu/sq ft to cool in summer than it does to heat in winter, I think you will find you need to pump a lot more water than your planning on. All the warm things in the house help in winter & hinder in summer (think people, stoves, showers etc).

Unless it pencils out to use a separate heat exch (a very big one for cooling) to cool in summer & try to eliminate contamination that way. Doubt it though as the pump would prob need to run on a continuos basis making your wire to water ratio very high.

Your efforts & money are probably better spent in venting (continuos soffit vent as well as continuous ridge vent) & insulating (think 14" blown in cellulose with proper insul stops) your attic & keeping as much of that excess heat from getting into your home in the first place as possible.

Sorry if it sounds like I am raining on your parade. FWIW some of the above is also why geothermal seldom pencils out, wire to water just gets to far out of line.

 

[ewdudley]

The old part of our house has radiant cooling in the basement, but it's not really habitable. I think that running cool water through your slab loops would tend to make your main living space more like a basement.

In your climate, if you have an abundance of cool water you'd probably be best served figuring out a way to exploit that resource to reduce the cost of controlling the psychrometry, as opposed to attacking just the sensible heat problem.

I can't remember all the details, but I believe there's a big college or university near you that pumps cool water out of the bottom of some big lake around there and uses it as a heat dump for their chillers.

--ewd

 

[jimbom]

Ya. The latent is the problem. I had to include a dehumidifier to make my design look like it might work.

 

[bpirger]

Indeed, Cornell pumps a huge amount of water up the hill from Cayuga lake....All sorts of issue I think within the lake, but being Cornell and a very big fish in a small town, they get what they want. Much bigger fish they are then those in the Lake.

Like I said above, I don't think it would work very well....just looking at numbers....let alone all the risks. But it is a curious thought. Burying a line for a "closed system" isn't feasible up here. Too much woods to clear and too much rock. About 1' of dirt and then all shale. Though apparently there is lots of natural gas just a few thousand feet down....just below the water we all drink and take for granted! But I'll stop that discussion right there!

Psychometry? Is that like thinking it to be cool and then it IS cool?

I know the garage floor will actually condense a bit on very humid days following a cool snap, when presumably the slab is below the dew point. At least it appears dark and damp.... Certainly wouldn't want that in the house....and I assume it would happen in the house if it was as open as the garage. Insulating that is another project, likely to happen in 2012.

 

[bigburner]

slab cooling requires two systems -1 for the latent heat & 1 for the specific heat. You got to walk the fence with the dew point.

 

[ewdudley]

Indeed, Cornell pumps a huge amount of water up the hill from Cayuga lake....All sorts of issue I think within the lake, but being Cornell and a very big fish in a small town, they get what they want. Much bigger fish they are then those in the Lake.

In the course of geological and ecological history, defenders of Gaea's perfect eternal balance would look a lot less foolish if they chose battles more sensible than that of taking up the cause of pretending to know what the temperature and phosphorus concentration of the Six Mile Creek delta should be in some idiotic Platonic sense.

Psychometry? Is that like thinking it to be cool and then it IS cool?

As if I didn't type it correctly the first time. Frickin' spell check needs step aside once in a while.

Got home from from vacation last night and the house was in the high sixties. Turned on both the heat and the air conditioner for a few hours and let them fight it out. The heat won, and it was a dry heat.

I know the garage floor will actually condense a bit on very humid days following a cool snap, when presumably the slab is below the dew point. At least it appears dark and damp....

Somebody on here was advising under-slab insulation even for an unheated garage, which sounded like a pretty good idea.

 

[DaveBP]

Somebody on here was advising under-slab insulation even for an unheated garage, which sounded like a pretty good idea.

I have no heated slabs of the 5 on my property. I have styrofoam under 4-and-a-half of them. Guess where it's dark and damp in muggy or rainy weather.

I can stack bags of grain on the slab in my rodent-proof room (insulated but not heated) and they never get mildewed against the floor.

Whoever said it, I can agree with conviction based on experience.

Also from experience, I would say in arid climates NOT to insulate under a slab. When I was a kid I stayed with my grandparents out at their place in the Mojave desert. When it was really hot I just laid down on the concrete to cool off at night. Earth temperature probably wasn't all that cool but everything is relative.

 

[pybyr]

For those of us nerdy enough to be reading this during the summer.....a topic perhaps to kick around...inspired by the shoulder season thread.

<snip>

But does anyone else have any cooling methods?

Chilled beam?

see, e.g.-

http://web.mit.edu/newsoffice/2009/greening-beams-0528.html

 

[bpirger]

My entire garage floor does have 2" of insulation underneath....the entire thing. It also has tubing, though I haven't hooked it into the system yet. So there's more to it than just insulation. Might just be the cool slab from the cold soaks during the cool nights? Mostly it is in the shoulder seasons....I haven't seen it happen since we are warm. I don't yet have the place insulated and button up...so some soffits are open, trusses are all wide open, etc.

 

[jimbom]

For those of us nerdy enough to be reading this during the summer.....a topic perhaps to kick around...inspired by the shoulder season thread.

<snip>

But does anyone else have any cooling methods?

Chilled beam?

see, e.g.-

http://web.mit.edu/newsoffice/2009/greening-beams-0528.html

What likely was edited from the MIT article: All required ventilation air is completely dried before being introduced into the space. So, the only moving air is required minimum ventilation. Thus the ducts are very small relative to regular HVAC. This process removes the latent heat from the structure. The chilled water beams remove sensible heat without condensation because: Relative humidity is controlled by the very dry ventilation scheme. Far be it from me to correct MIT, but I am sure the engineer who designed this system did not write this article.

 

[ewdudley]

For those of us nerdy enough to be reading this during the summer.....a topic perhaps to kick around...inspired by the shoulder season thread.

<snip>

But does anyone else have any cooling methods?

Chilled beam?

see, e.g.-

http://web.mit.edu/newsoffice/2009/greening-beams-0528.html

What likely was edited from the MIT article: All required ventilation air is completely dried before being introduced into the space. So, the only moving air is required minimum ventilation. Thus the ducts are very small relative to regular HVAC. This process removes the latent heat from the structure. The chilled water beams remove sensible heat without condensation because: Relative humidity is controlled by the very dry ventilation scheme. Far be it from me to correct MIT, but I am sure the engineer who designed this system did not write this article.

They seemed careful enough to point out that the system is aimed at sensible heat removal. I'd bet that you are correct that make-up air is dehumidified before being introduced to the controlled space.

According to Cooper, the beams are useful in offices, laboratories and other 
spaces where equipment and sunlight generate a significant amount of heat.

 

[DaveBP]

My idea of a good Chilled Beam starts with a glass and some ice cubes.

 

[jimbom]

My idea of a good Chilled Beam starts with a glass and some ice cubes.

Point of Order. Mr. President, I propose a toast to Jim. Mr Jim Beam.

Gentlemen. Mr. Beam. Assembly, Mr. Beam. Glug.

Point of Order. Mr. P.......................................to Jack. Mr. Jack Daniels.

Repeat ......

 

[ewdudley]

My idea of a good Chilled Beam starts with a glass and some ice cubes.

Point of Order. Mr. President, I propose a toast to Jim. Mr Jim Beam.

Gentlemen. Mr. Beam. Assembly, Mr. Beam. Glug.

Point of Order. Mr. P.......................................to Jack. Mr. Jack Daniels.

Repeat ......

I would say that sounds neat, but I suppose not ;-)

And to Joseph, Mr. Joseph Washington Dant. And don't forget the eminent Mr. George A. Dickel himself!

 

[jimbom]

My idea of a good Chilled Beam starts with a glass and some ice cubes.

Point of Order. Mr. President, I propose a toast to Jim. Mr Jim Beam.

Gentlemen. Mr. Beam. Assembly, Mr. Beam. Glug.

Point of Order. Mr. P.......................................to Jack. Mr. Jack Daniels.

Repeat ......

I would say that sounds neat, but I suppose not ;-)

And to Joseph, Mr. Joseph Washington Dant. And don't forget the eminent Mr. George A. Dickel himself!

That is how it goes. Soon, nobody recognizes the names, but who cares. The object quickly becomes to go to the head. Fortunately, Mr. President is generally the oldest, so his bladder gives out first and he announces the smoking lamp is lit. At which time everyone runs for the head. The good old Navy days. Fond memories of Dinings In(without spouse).

With spouse is Dining Out. The tradition is the bagpiper pipes in the roast beef. He marches in with the chef following with the beef on a cart. The second in command, Mr Vice samples the beef and declares the beef is fit for consumption. At which point, the piper is rewarded with a shot(of whiskey). At one dining out, the alternative was demonstrated. An alternative which I was unacquainted. Mr Vice sampled the beef and said this beef is not fit to eat. And, suddenly pulled his pistol and shot the piper, who collapsed. The ladies screamed, members of the mess were shocked, but the pistol report was weak and as I was processing the scene, the piper got up laughing along with the XO and CO. Needless to say, we were all had.

 

[benjamin]

In the past I have tried running groundwater through my floors with mediocre results. No condensation problems on the floor but not that cool either, just more comfortable than outside.

On Friday and Saturday of last week I had 30+ relatives over for the hottest muggiest days we're likely to get this summer, so I hooked up the well water to run through the floor loops with the circulator pump running also, some of the water from the return manifold was bled off to go through a water source heat pump running in AC mode. On Friday it was running at 5 GPM, 52 degrees F from the well, 62 degrees F going into the heat pump, and 78 degrees F out of the heat pump. On Saturday the flow was lower for some reason so the temp rise was higher. This roughly doubled the capacity of the heat pump for virtually no extra power consumption.

It worked excellent, the heat pump removed humidity well and then brought down the temp, and the cool floors provided a great comfort factor. The only problem was condensation on the exposed cold water piping before it went into the floor. And the solar hot water was unable to work at the same time with my setup.

A radiant heated floor is typically designed with many short loops for a high volume at low head, a cooling floor might work better with a longer loop to extract more heat at the cost of more pressure drop in order to use less water. I turned on the circulating pump in order to circulate the cold water around, but that mixed the fresh cold water with the warmed cold water to some extent. I didn't try it without the circulator turned on, but I suspect that the well water would have filled some of the loops with air and not circulated evenly. Another option would be to turn down the balancing valves evenly to encourage a more uniform flow.

This isn't terribly elegant or efficient considering the possibilities with water that cold, but it worked for me.

 

[jimbom]

....This isn't terribly elegant or efficient considering the possibilities with water that cold, but it worked for me.

Seems very elegant and efficient. Passing the water through the floor for sensible heat extraction and then downstream using it in a water source heat pump. Now if you had a still downstream of the heat pump. And a garden full of corn downstream of the still. Hmmm.