Listers,
I need some help with the radiant floor heating system in my garage. The
system heats a 475 sf garage that is very well insulated:
- There are four loops in the floor to permit variations due to the
different floor thicknesses (some areas are new, some are old. A three inch
slab was poured over the whole floor area. The loops are mostly in that
slab.There are approximately 350 feet of Ipex 1/2 in. tubing in the floor.
- The system has a capacity of approximately 15 gallons of water/glycol
(50/50).
- The manifolds were fabricated from 3/4 in. copper pipe ("t"
fittings).
- Heat is supplied by two 5 gal hot water tanks in the overhead loft.
- Hot water is called for by an aquistat on the return side set at 80
degrees F.
- The aquistat controls two 2 way 3/4 valves equipped with actuators
that are normally closed (the valves open when powered).
- One of the valves is in the hot water line. The other is in the hot
water tank bypass. When the aquistat falls below 80 degrees, the bypass valve
closes and the hot water supply valve simultaneously opens (and vice versa on
temperature rise).
- The system is running at approximately 20 psi. If I run it at too low
a pressure, the air entrained in the water is released (I could hear the
bubbles). At 20 psi you can barely hear the pump running.
- There are two automatic vents in the system, one at the highest
point.
- The cushion tank is now set at 18 psi. It was previously set at 28
psi (It was pressurizing the system - not cushioning it! - could that have
damaged the pump?).
- The pump runs all the time. It is an Armstrong Astro30.
The pump failed once, possibly because it was not manually vented and air was
trapped in one end leading to rusting. It was repaired, but the damage has
left the pump a little rough and it does not always restart by itself (e.g.
after a power failure). I can get it going by turning it manually back and
forth to free it up and then giving it a good whack.
I need to replace the pump, but am concerned that the system may need
tweaking. For instance, it has been suggested to me that I should install a
flow switch to cut power to the pump if there is no flow through the pipes.
Presently, if the pump jams, it builds up tremendous heat because it is
stalled. The pump draws very little current but will eventually burn out if
left in that position. (But if there is no flow, how does the pump ever
start?) Is anyone familiar with these switches?
Another thought is that the two 3/4 valves should be normally "open", not
"closed". Originally I had one valve and a check valve. The check valve was
installed in such a way that it would never be subject to the head of water in
the tanks above to close it when the hot water tanks opened into the system.
Already having one actuator that is normally closed, I got another. They could
be replaced with two normally "open" and the aquistat wiring reversed. Should
I bother doing that? Would having them both closed starve the pump enough at
start up to be a problem?
I would sure appreciate any comments/suggestions. The system provides even,
comfortable and quiet heat when it works!
Thanks,
Dan
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Dan Harris daharris@interlog.com
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