Radiant Walkway Cooling

endenhall

A religious organization I have worked with in the past asked me about how to solve a problem they are having at a temple they are building in India.
People visiting the temple are required to remove their shoes at the entrance to the temple grounds. The walkways are 3cm white marble laid over a reinforced concrete slab. The problem arises in the summer when the outside temp can be 125 degrees. The walkways get so hot that they have been using mats to cover the stone to make it possible to use.
I suggested a radiant cooling system imbedded in the reinforced concrete cast over 2-3" foam board. The idea is to make the walkways just cool enough to be useable in the summer and maybe warm them a little in the winter season.
My thought was to treat the walkway like it needed a snow melt system. I am waiting for dimensions at the moment before any load calc can be attempted.
My question at the moment would be do you think it might be feasible?
Thanks

the_donut

Dew point is pretty high in India. How much cooler are you looking to achieve?

GroundUp

That's a tricky subject. It has been done but the dewpoint needs to be addressed to keep the slab from sweating. I've done a few of them on the install side, and yes they are just like a snowmelt in terms of piping arrangement. The controls however, I know nothing about except that the dewpoint needs to be adjusted for

endenhall

In the summer, when the cooling would be necessary it is the dry season. The humidity level is about 15-20%. This is northern India. Humidity is high during the monsoon and in winter.

endenhall

Keeping the walkway below 100 degrees in the summer season would be the goal. Warming it to above 60 degrees in the winter.
It does not freeze in this area, temps in winter go down to 40-45 degrees.

Leonard

Just curious. What's the air temp? How are you dumping the heat? , ground water, water/air heat exchanger , A/C pump....

endenhall

Summer temps can get to 125 degrees in the shade.
Right now there are a pair of 200ton absorption chillers used for AC. So, that is one possibility.

hot_rod

My question also, what to do with the heat from the walk way? Certainly not enough temperature to run absorption chillers, any DHW load?

I lived in Phoenix one summer and noticed the walks around some pools had an exposed, fairly rough aggregate finish, not as friendly to walk on but the voids kept them just cool enough compared to smooth finished walks.

The smooth finished walks had soaker hoses running to cool them. At least until the water shortage years came about.

Mark Eatherton

Dew point will be the least of your concerns. I wouldn't cool the slab any lower than 85 degrees F, which is the humans outer skin surface temperature. No sense in wasting energy. Is freezing a concern at all for this location?

I have drawings for a side walk snow melt system that can also harvest the free energy falling on the slab during the summer to preheat the DHW. I nick named it the "Why Not" system.

Theoretically, I can harvest more energy preheating DHW for a family of 4 than the snow melt system will use on an annual basis.

And, if a person weren't worried about the potential of slime, you could chill the slab so low that it WOULD condense the moisture out of the atmosphere to "water" the xerescape plantings along the side of the sidewalk.

Yes, you can absolutely chill it and warm it.

ME

endenhall

Thanks for all of the comments.
I still do not have a dimension for the walkway, my understanding is several thousand square feet.
My idea was to cool the walkway just enough to make it useable. In the peak of summer if it can be kept below 100 degrees F that would be a success.
As for dumping the heat, there are several options. The bigger problem is having the electric power needed to operate which ever machines are finally chosen. The local grid is less than reliable. So, space for the equipment plus a gen-set is required.

Mark Eatherton

How deep are the aquifers in this area? Thinking of a pump and dump from a deep well aquifer would be more than adequate to cool the walk way down. The Japanese did this many years ago for snow melting a large parking area. Only parasitic cost of operation was the pump, which compared to conventional energy, was negligible.

ME

hot_rod

If the cooling is only needed when it is warm and sunny, a small PV array could power low energy ECM circulators.

endenhall

I am leaning toward pump and dump myself.
There is one deeper aquifer that might do the trick.

Leonard

What's aquifer temp. Think ground water is average of summer and winter temps. Likely usable, but might not be that cool.

I'm used to winter city cold tap water being 43 degs (last night). In past, on vacation did my laundry in a motel near Miami in January. Thought they were being cheap with no hot water to the machine. Turned out "cold" tap water was warm there, maybe 70.
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Alternate..... Maybe Vacuum tube thermal solar panels to provide main heat to drive absorption chiller?? Don't know how hot they require. And solar PV to power pumps and controls. Neice-in-law just put in 5kw of solar in Maine, only~ 18 panels on small roof.

Gordy

Think evaporative cooling with the low humidity, and anything below 85 degrees from an aquifer would do the trick.

I’d question the effect of water on the surface would have on porous white marble however. Especially if the aquifer contains certain minerals, or metals. Marble stains easily.

endenhall

Right now I am waiting for dimensions. Then a calculation can be made. Spraying water on the walkways is not going to be practical because of the dust during the dry season.
Anyone have a line on manufacturers that make manifolds for larger diameter pipe? Say 3/4 to 1".

Mark Eatherton

Uponor.com

In fact, they can probably help you with load calculations and pump sizing, pretty much everything you'd need.

ME

endenhall

Thanks ME.