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Old 05-17-12, 01:38 PM   #230
Mobile Master Tech
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The pumps are virtually silent-an average whisper would drown their noise out from a few feet away. I do have a couple of places in our master BR that creak as the pipes expand when coming on from dead cold, but that is almost non-existent except for the first heating call of the day after several hours of dormancy as that is the only time they cool completely off. I chalk these noises up to the way I routed the pex for this room. Since I have two loops in this zone, I had them crisscross back and forth so each loop had one pipe per joist bay. I made a big deal of trying to have the hottest pipes at the perimeter of the room instead of the simplest routing. Because of all the routing issues this caused, plus obstacle clearance,the pipes touch each other, touch obstacles and make lots of passes through joists. I did the simpler "one u-loop per joist bay forming 2 pipe runs per joist bay" on the rest of the system and have not had noises there. The keys to a reasonably quiet floor: not having lots of friction where the pex has to change direction or go over/around obstacles, some sort of isolation surface like foam pipe insulation or cloth at contact points, align the plates in a reasonably straight line, have at least 5" of exposed pex from the end of the previous plate to the start of the next one, and don't constrain the end of each U-loop.

When the water heater is set for 140F, water is roughly 137-138F by the time it hits the first transfer plate and 105-110F by the time it returns from the loop once temps stabilize. It takes a minute or two to make the loop and takes at least 15 min of run time before the return temps stabilize-I don't remember exactly how long. Unless it is super cold or the first heating call of the day, the tstat cycles the zone off shortly after the return temps come up. If I turn up the pumps to full speed, the return is a little over 120F. I imagine with a good building envelope, 9" or tighter spacing, well done transfer plates, 120F water and quick enough circulation so you only have a 10F temp drop across the loop, a staple up system would work well for all but the most extreme climates.

With GSHP and solar for heat sources, both of which lose a lot of efficiency with higher deltaT between source and load, I believe a stratified tank system like I described in the solar tank thread (I have to figure out how to give a link to a particular post) has particular benefit. If you have around 6' depth, you can get around 25F stratification from top to bottom. For GSHP with a counterflow condenser and waterflows balanced well, you could probably return 130-135F water to the tank while the condensing temp the compressor "sees" is closer to the 105-110F you are drawing into the condenser from the bottom of the tank. This way you won't have such a COP penalty on your heat source and the radiant system doesn't have to be a slab type or oversized to get the heat flux you need.
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