Heat Storage

 Hi,

I have a Tarm wood furnace. I want to run the output of this furnace
(hot water) into my cistern (a large, to be insulated, water tank in
the basement, not used for anything right now)  I'm looking for some
information on DIY heat exchangers (water to water) and have not had
much luck. The basic concept is a copper pipe, or coil of pipe, but
how do I determine the effectiveness (ie. how long a length, flow
rate, BTU transfer rate, etc.).

I have a number of hydronic baseboard heaters that I could use. Would
these be more effective in water than in air? I have the specs for
them - how would I determine (short of experimentation) their
performance in water? Is there a rule of thumb?

I have searched under every term I can imagine and have found very
little practical information. Surely I am not the first person down
this road. If you could point me in the right direction, I would be
very appreciative.

Thanks,

Randy

 

Type Tarm wood furnace
then key heat storage with your mouse at the
Tarm site.
They tell you whether you need a 600 gal or 1200 tank with a 200'
of 1/2 inch copper(probably K series) tubing with your model.
The insulated tank size and flow rate is more important than tubing area.
The next question is do you have a circulation pump,popoff, and check valves
for this system.
You already have the hydronic wallboards and controls installed?
Do you know how to braze/silver soldier copper,since you are doing that for
both the connections and
coil holder rods.
Liquid is better than air on heat transfer.
Tarm also has a installer's corner on that site that has prints for your
piping ,etc.
If you can read plumber's blueprints .....you are in business on your DIY
project.
They make a really good product....as long you have it installed right.

 

Why use water-water heat exchangers, vs circulating tank water through
the Tarm to heat the tank and through baseboard radiators or a fan-coil
unit (eg a car radiator :-) to warm the house?

With one pump and a Taco 561 3-way zone valve to bypass the baseboards?

Nick

 

    I'm still very impressed by the heat of fusion of glauber's salt being
released at 90*F; think I'd throw a buttload of that into my plans
somewhere, if I was him.

 On Nov 20, 7:15 am, nicksans...@ece.villanova.edu wrote:

Well, for burning efficiency (i.e. no smoke or creosote) the Tarm
likes to run around 180F and 10-15 psi. They recommend an automatic
thermostatic valve that mostly recirculates the boiler water until the
input is up to temperature. This also protects the boiler from the
thermal shock of a sudden cold input. Don't know whether their
thermovar would be up to the task of continuously dribbling cold
cistern water through the boiler. It could perhaps oscillate and cause
damage.

The pressure helps keep oxygen out of the water for longer boiler
life. Copper, iron, or oxygen barrier PEX piping is recommended for
water going through the boiler.  It would be difficult to pressurize
or keep oxygen from a large storage tank.

Tarm's 800 gallon tank uses two 120' 3/4" coils of copper pipe in
parallel.  Each is about 3' high and 2' diameter. They are used in
both directions, a  flap valve keeps water from the boiler when the
heating loops are  circulating.  Each is rated 26,400 BTU/hr at 3gpm
for 120F tank water.  Probably one coil would suffice if you burn
softwood. But it also depends on  the max temperature you want to run
the reservoir at - Tarm voids the  warranty above 180F. Don't forget a
thermosyphon loop to extract  heat if  the power fails!

Car and truck radiators work well, but discarded round air
conditioning  condensors are more attractive and make toasty
footstools :)