On Wed, 04 Jan 2012 17:01:32 -0500, RBM wrote:

On 1/4/2012 12:53 PM, JIMMIE wrote:
My son has a home that he added a solar water heater to a few years
ago. Works great , too great. The unit far exceeds his demand for hot
water. He wants to add some coils to his forced air HVAC system so he
can use the solar heated water to heat his home. He was expecting
there to be a coil he could place in his HVAC system but cant find
what he is looking for or knows what to ask/google for. Any help would
be greatly appreciated.


We call that a "Hydro-Air" system. The hot water coils are inside the
air handler along with the cooling coils. I think he could make his
solar system assist the boiler, but I don't think I'd rube the air
handler to do it. Possibly if he T'd the solar loop into the boiler loop
where the go into the air handler, and set up some solenoid valves, so
whenever the thermostat called for heat, an aquastat on the solar system
would open it's solenoids as long as the water temperature was hot
enough. It would also have to turn on a circulating pump for the solar
loop. When the temperature isn't hot enough, the aquastat would close a
circuit, opening the solenoids from the boiler loop and it's pump, and
fire the boiler.
The problem with doing something like this, is that the only guy who
will know how to service it, is the one who built it. If anything
malfunctions, he could be without heat for a while

Personally, I'd go at it a little differently. Since this solar assist
is not the PRIMARY heat source, I'd install the solar hydronic loop in
the RETURN air to the furnace - and to avoid excessive restriction I
would put it in PARALLEL with the existing return air duct . Properly
designed, the heat exchanger could have very little more restriction
than the open return, and a system of dampers could restrict the
airflow on either side to extract the maximum heat from the solar
loop.

Because the delta T is higher on the return side than on the heated
side, you would get more heat ( in absolute BTUs) out of the solar
assist than if it was being used on the outlet side.