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re: passive solar help actively needed
15 mar 1999
techwriter wrote:
>hi all;
hi jim,
>...forgive me if this topic has been beat to death.
i'd say it's been insufficiently beaten :-)
>i will transform a deck into a sun room this summer.
sounds interesting.
>-its foundation is concrete block, 18-24 inches tall.
you might add some painted foamboard insulation on the outside.
>-my hope is to find a way to collect heat in the floor and have it
>release at night.
it's tough to passively store solar heat "under the floor" unless
the floor is transparent. seems like some fans are needed here. or
lots of thermal mass in the sunroom and some way to insulate the
glazing at night, eg filling the space between two layers of glazing
with tiny cold soap bubbles at night and on cloudy days.
where would you like to "release the heat at night"? heating a sunroom
with lots of solar glass at night is inefficient because of the low
thermal resistance of glass without insulation. better to let the sunroom
get cold at night (why look out the windows at night, except on special
occasions?) and release the stored heat to the house at night or
on cloudy days.
>i will replace the wood decking with a concrete floor and wish to find
>the best option to collect heat under this floor, in the 'sealed off
>crawlspace' or some other way.
concrete is a poor insulator, and it has lots of thermal capacity, so
it will store daytime heat and keep the sunroom warmer at night, wasting
a lot of the stored heat. how about covering it with some foamboard and
darkish carpeting, or just covering the wood decking with some foamboard
and carpeting?
for storing heat, i'd fill the crawlspace with sealed containers of
water and put a couple of powerful fans in the floor near the glazing
with some lightweight foamboard dampers above them that are hinged on
the south edge and closed in the horizontal position. when the fans
are turned on (by a cooling thermostat near the peak of the room),
the dampers open to about a 45 degree angle and draw air out of the
crawlspace that is replaced by warmer air drawn down from the north
peak of the sunroom.
the north wall of the sunspace should be darkish. a layer of darkish
greenhouse shadecloth hanging along the north wall with a 1' airgap
behind it would make this more efficient by keeping the solar-warmed
air away from the cool glazing and allowing the air that goes into the
heat store to be warmer than might be comfortable in the sunroom.
as an alternative, you might remove the wood decking and replace it
with some playground mulch over black plastic film on the ground, and
build a tall solar heat store in part of the sunroom, something like an
8' cube completely surrounded by insulation with some sealed containers
of water inside and an inward-moving plastic film one-way damper in
the wall near the top of the cube and a couple of exhaust fans in the
wall near the bottom.
this could store heat at a higher temperature if the fans and dampers
were on the south side, behind another layer of glazing, with some
darkish shadecloth in the air gap between the glazing and the insulated
south wall of the cube. that makes it a solar closet :-)
numbers can help with design details and performance predictions...
nick
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