Quote:
Originally Posted by cbearden
I've been using 1/2" pex spaced 12" apart for heating our slab.
And our 1st and 2nd floor is roughly about 900 sq ft.
I was thinking that just having the plain pex circulating cooler water in-between floors like that, would take away some of the heat during the summer. But I don't know much about the numbers for the cooling side of things.
Does anyone have any suggestions for how I need to do the calculations and best way to install this?
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You are the first person on this forum to show any substantial interest in radiant cooling.
Since cooling is your primary season, you might want to give some thought to efficiency.
So here's what I know...
What you're trying to do is called "
high temperature cooling" and also "
low exergy cooling". You might try searching on those terms.
You might have to modify your understanding of what heating and cooling are in pursuing your project, and be mindful of comfort rather that the readings from the thermometer.
Our bodies are covered with sensors that have evolved to keep us alive. We generate some amount of heat and that heat must be gotten rid of or we will die... so we have an evaporative cooling system to assist us. When our bodies are able to get rid of heat easily we feel comfortable. If the heat can not be gotten rid of easily we experience discomfort and become restless and miserable and motivated to seek shade under a tree or want to jump in to a glittering blue swimming pool, or some other way to cool off.
Looking at heating for a moment, you have probably experienced the feeling, when standing next to a window on a very cold winter night, of the warmth being 'sucked out of you'... well, that's exactly what was happening. If you had double or triple glass windows, you'd notice that the expected 'heat suck' experience was not there... in other words, you would feel comfortable.
The reverse is also true... if you are in a climate where heat predominates and on a particularly hot day, you go into a tin-roofed structure, you immediately feel the opressive heat radiating onto your skin, and your body senses that it's heat load cannot be dumped and that lethal conditions could be forthcoming... you experience discomfort.
The Germans are using radiant cooling with great success in office buildings. They are using continuous panels that conduct cooled water, in the ceilings. The panels have sensors that monitor dew point, so that it doesn't start raining on the office workers.
You could cool your slab too, but you'll need to monitor dew point.
If it were me, I'd use fairly close spaced PEX with aluminum spreader plates that physically contacted your ceiling material, probably sheet rock.
Using the high temperature cooling approach, you could gain greater comfort in a room that a thermometer would tell you shouldn't feel so comfortable but you'd be save money on cooling.
Humidity will play a big role in this scheme, in maintaining comfort. But the amount of dehumidification will be lower.
Overall, you should save money.
But in all honesty, the very thing that makes convection heating problematic, also makes convection cooling work well. Stratification of air temperatures with hot on top and cool at the bottom, where people lounge about.
You could also cool interior walls, etc.
But all in all, I think your strategy is a good one. You'll probably still need some amount of A/C, but it would be less, and your overall cooling cost will be lower.
Keep us posted as to how this goes.
Best,
-AC