| Lots
of insulation is
certainly the most
important key in building a warm house, but thermal mass and solar
input
can still make a big difference.
One
thermal
mass system is the thermal
rock bed. Air is warmed in a
solar panel and blown through a
rock bed
beneath the house. This is essentially the "forced" air method of solar
heat, where the warmth is stored until needed, then blown inside the
house.
One of
the
best ways to use thermal mass
is in the form of a radiant
floor. A radiant slab
is any masonry
floor with embedded pipies for hot water heating. Most other heating
systems
warm only the air, leaving cool surfaces throughout the house that feel
like they are sucking the heat away from you. Comparatively, a warm
slab
underfoot gently releases a steady flow of heat, so the atmosphere
feels
comfortable even when the air is slightly cooler than normal.
|
Radiant
floors
are about the nicest heating
systems available, but they fell out of favor decades ago due to
problems
with the copper piping corroding in the concrete. The leaks were
difficult
and messy to fix. Today there are many new, long-lasting alternatives
to
copper, so there is a resurging interest in radiant floor heat.
A
radiant heat
system can be as simple
or as complex as you want it to be. A simple system includes plastic
tubing,
a few valves, a pump, a source of hot water, and a centralized
household
thermostat. |
Plastic
tubing
for radiant floors varies
in size from 3/8-inch up to 3/4-inch, but 1/2-inch diameter tubing is
the
most common.
The most
popular types of tubing for radiant
systems today are PEX and Entran 3 polyethylene. The latter has three
layers
for maximum strength, including DuPont plastics and Goodyear rubber,
with
rayon or aramid mesh for reinforcing. The tubing resists freezing and
abrasion,
and may be warranted for up to twenty-five years, alhtough
realistically
it should last much, much longer.
Before a
concrete or
soil-cement floor is poured, the tubing is laid
out in loops spaced no more than 12 inches apart. The length of each
run
or "zone" should be relatively equal in size. The tubing can be tied to
the rebar or wire reinforcing to hold it in place for a concrete pour
or
temporarily weighted down with large rocks if you are pouring an
unreinforced
soil cement floor.
|
Hot
water
from a
solar panel or tank comes through a "header" made with
copper pipe, where the flow is split to each of the zones. Each zone
should
have its own control valve, preferable a brass ball valve, before
connecting
to the rubber tubing. The pump is placed at the end of the run where
the
water is coolest to avoid problems with overheating. A radiant floor
with
a gas or electric boiler system is controlled by a centralized
household
thermostat. Typically the boiler has it's own thermostat, so there is
always
hot water available. The household thermostat turns the pump on to
circulate
the hot water through the floor. Swing check valves may be needed if
the
system is cycling water from one floor level to another. |
In a
solar heated
system the pump can be powered by a photovoltaic panel,
without the need for a thermostat. If the sun is shining bright enough
to produce hot water in the solar panel, then it is also bright enough
to generate the electricity to run the pump that circulates the water
through
the floor. |
