RE-solar space heating storage tank size [RE-wrenches]

Ken Schaal ken at commonwealthsolar.com
Fri Mar 19 14:03:04 PST 2004


Hello to all,-- from a new guy to the list,

Some thoughts on storage tanks using ICF's, from someone currently building
tanks using EPS [ expanded polystyrene] as the insulating form--round and up
to 8' tall-- with tension band for support and flexible liner to hold the
water.

ICF's will make a fine structure but the temperature is limited to 167* F-
at which point the foam will begin to melt! Up to that temp. the foam,
either expanded or extruded, will be very stable and durable. There may be
some compression depending on  load, and the density of the foam. I
recommend at least 1.25 # , and use 1.5#  for my tanks.

Since collector efficiency is greatly affected by the inlet water temps, I
prefer a drainback system with no heat exchanger. If the collector loop is
thru a heat exchanger it will be about 20*, maybe more, warmer than the
coolest water in storage, and that is a significant loss of efficiency.
If at all possible use the full 8' height .with solar heating the bottom of
the tank, and the boiler [which does better with warmer temps--cleaner heat
transfer surfaces], heating the top.

Solar BTU's , from a good selective surface collector, would be much closer
to 900BTU's/sq.ft./d with clear dry air at 45-55*,bright sun, and inlet
fluid temps at 70-100*, which is also in my experience a good temp to
circulate thru the slab. If the space air temp is comfortable between 50-70,
then the floor slab needs to be about 60-80.

There are several other details but I'm to slow a typist to continue, so
feel free to contact me off list or give me a call any evening.

I hope this is useful.  And thank you all for sharing your knowledge and
experience!

Ken Schaal
CommonWealthSolar.com

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