SB: radiant floor pumps

[Carolyn Hoagland <choagland@connectec.com>]

Hi,
 We are getting down to the nitty gritty of self installing a radiant
adobe floor in our SB house/office/school.  We are installing about 1700
feet of 7/8 I.D. tubing 16" o.c. (in 8 separate 210' loops coming off of
a larger manifold) and are going to be heating about 2,500 sq ft of
floor as a single zone in a moderate climate (near Chattanooga, TN) with
4" of blueboard around the perimeter of the foundation.  The loops will
be buried about 4" under the surface of the floor (on top of a vapor
barrier) and there is no insulation underneath (I'd like to bury the
tubing a little deeper, but the subfloor is already heavily compacted
clay and would have to removed by hand with a pick axe or jack
hammer.....  We eventually expect to run solar heated water through the
loops and are hoping to build up a deep heat sink to carry us through
cloudy days.

Since we are off the grid, every electron we create and store is
precious, and I am curious about circulation pumps.  My radiant supplier
says the pumps (whatever kind you get) probably run less than 10 minutes
per hour, once the slab is brought up to temperature.  The smallest
grundfos 120v pump (1/25 horsepower) still takes about 80+ watts (and I
am told is only about 30% efficient in terms of
power_to_wire:water_moved ratio).  So I calculate:
80watts *1/6 hour *24 hours per day = 
         like running an 80w lightbulb for 4 hours   
(that's a lot of electrons!)

Have any of you had experience with this or other pumps (el sid,
dankoff)?  Can you tell me some basic parameters of your system, how
often your pumps run, what brand and size, are they on a timer or
thermostat?  What water temp are you running on the supply side? (I
assume the pumps can run less if your water is 130 degrees than if it is
90 degrees?) We can easily go DC or AC, depending on what type of pump
has the best wire:water ratio.

At this point we are just trying to get the tubing in the floor so that
we can proceed with the adobe stomping, and we want to make sure we are
not forgetting something before it is too late.  All of our tubing runs
end in a basement, so the manifold and pumps and timers/thermostats can
be added later?  I've been reading that a lot of systems use a computer
module that senses the temperature dropping outside and turns the pumps
on ahead of time (before you start to feel cold) - Is all this really
necessary?  We were hoping to use just a single programmable timer that
could store several pump timing routines, so we could just look at the
weather report for the next 24 hours and choose a routine (until the
weather changes and we choose another).  Someone is here in the building
almost all the time and we are used to moderate temperature swings (we
currently heat with wood and sunshine) and are hoping to keep the
control part of all this extremely simple (and inexpensive)!

Any of your thoughts about pumps, timers, controls and their suppliers,
or errors in our plans will be appreciated.

Thanks in advance,
Carolyn

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