SB: Tubing in the Floor

[Speireag Alden <Joshua.M.Alden.91@alum.dartmouth.org>]

Hallo, all.

     The demands on my time these days are such that I haven't spoken 
up much, but I still monitor the list and contribute occasionally.  I 
thought that I'd throw this thought out:

     Some of you may remember that I advocate putting PEX in a slab 
when you're pouring it, even if you don't think that you'll use 
radiant heat.  I reason that it's so darned inexpensive to put $200 
of tube in the slab that you might as well do it and cap it off, 
because you never know what you'll do down the road, and retrofits 
are expensive.

     Most people only think of such tubing for heating the house. 
However, I have discovered a side benefit by accident, which 
represents a substantial energy savings in any area where the ground 
temperature is less than the internal temperature of the house.

     In my house, I have an open heating system, where the radiant 
heat is not separated from the hot tap water.  In order to make sure 
that the system is flushed constantly, all water going to the heater 
(tankless) must first go through the single radiant loop.  So, 
whenever I turn on a hot water tap anywhere, cold water enters the 
loop and makes its way through to the heater.  That loop is embedded 
in a very massive earthen slab, so there's a lot of stored heat. 
There's insulation under the slab, which separates it from the 
ground's cold temperatures.  In the summer, the slab and other 
thermal mass in the house regulates the internal temperature of the 
house.  We have no air conditioner here in New Hampshire.  The slab 
never drops below 18°C (65°F), and it's seldom below 21°C (70°F).

     How do I know?  I have thermometers on the system where the tube 
enters and leaves the floor.  Our groundwater comes out of the ground 
at about 10°C (50°F).  So it's cold when it enters the floor.  It's 
about 21°C when it leaves the floor, *before it gets to the heater*. 
This is just ambient heat, which the floor absorbs from the summer 
air.  The floor is massive, so it never drops more than a few degrees 
at the pipe, even if I run the hot water for a long time.  When I say 
"at the pipe", I mean that the only part of the floor which cools 
much is the material within an inch or two of the pipe.  If I run the 
hot water for a long time, then wait an hour or so and run it again, 
the water comes out warmer again, and there is no perceptible 
difference when I touch the floor.

     In the winter, this all comes out in the wash; I drive hot water 
through the floor to heat the place.  If I demand hot water, then the 
floor cools slightly but the hot water is pre-heated and therefore 
costs less to heat.  So there's no net loss.

     What does this have to do with the price of tea in China?  Well, 
in the non-heating months that temperature gain represents about 25% 
of the heat which goes into my hot tap water.  And I get it 
absolutely free.

     So, regardless of how you heat your water or how much you use, if 
you live where the groundwater is cold and you'd like to save energy, 
consider routing the hot water line prior to the heater through the 
slab.  What have you got to lose?  $200 in tubing will pay itself 
back pretty quickly.

-Speireag.

-- 
Recently, I was asked if I was going to fire an employee who made a 
mistake that cost the company $600,000. No, I replied, I just spent 
$600,000 training him. Why would I want somebody to hire his 
experience? -Thomas J. Watson, industrialist (1874-1956)

-------------------------------------------------------------------------
To unsubscribe from the list, send a message to:
   <strawbale-unsubscribe@crest.org>

or for the digest to:
   <strawbale-digest-unsubscribe@crest.org>

Please send any list administration questions to
strawbale-owner@crest.org