Posted by nicksanspam on November 23, 2007, 4:25 pm
>> 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?
>... 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.
The thermal part might happen without a heat exchanger.
>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.
What's a thermovar? You might run the pump with a 3-way heatmotor zone valve
for mixing.
>The pressure helps keep oxygen out of the water for longer boiler life.
You might use a cast iron pump with a 1/2% solution of ACI-100 corrosion
inhibitor from D. W. Davies.
>Tarm's 800 gallon tank uses two 120' 3/4" coils of copper pipe in parallel.
An STSS tank.
>... Tarm voids the warranty above 180F.
The EPDM tank liner only works to 170, long-term.
Nick
Posted by Loren Amelang on November 20, 2007, 3:05 pm
On Mon, 19 Nov 2007 17:35:28 -0800 (PST), Randy
>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.).
Google "heat exchanger ntu technique"... That's the estimation method
I've found to be simple enough to use and still decently predictive. I
don't know how to add the effect of the fins you mentioned, but I've
had good luck with smooth pipe.
Loren
Posted by John Barry on November 24, 2007, 3:36 pm
Randy,
Another factoid of note (TM):
Counter-flow heat-exchanger will be much more efficient than "normal"
parallel-flow, in that, if properly sized for flows & temps, the
discharge temp of each loop will closely approximate the input temp of
the other loop. (This is common with air-air exchangers I've looked at.)
Downside: need (2 ea) loops w/pumps, to run the coldest of the cold
reservoir into the exchanger, with the discharge of that loop to the top
of the cistern.
HTH,
John
Randy wrote:
> 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
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>> the Tarm to heat the tank and through baseboard radiators or a fan-coil
>> unit (eg a car radiator :-) to warm the house?
>... 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.