On Jan 5, 12:43*pm, harry wrote:
On Jan 5, 4:43*pm, "
wrote:



On Jan 4, 9:15*pm, wrote:

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

I think the OP is already planning on putting it
on the return side. *He said he had a filter unit
that was not being used and he could put the
heat exchanger there. *On the return side is
the only place that makes sense to me.

- 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.

You'd always get maximum heat extraction with
the most airflow through the heat exchanger, so
why the need for a system of dampers to vary
the flow?

That is not correct.
The factors are Time, Turbulence and Temperature difference (between
the media)
All need to be maximised to get maximum heat transfer in any given
heat exchanger..

The media need to be in the heat exchanger as long as possible.

Are you trying to tell us you can get more heat out
of the same radiator system
with less air flowing through it instead of more? How do
you maximize the temperature difference if not by
using the maximum available air flow? Hmmm?? Air barely moving
results in the air being hotter in the heat exchanger and
less energy transfer. Air quickly moving results in
the air being cooler and more energy transferred.
Do they put part of the air through a furnace heat
exchanger, or ALL of it? Do they put part of the air
through an HVAC evaporator or all of it?

Turbulence does increase the transfer. You think you're
gonna get more turbuluence with reduced airflow?
Ever hear of a Reynolds number?



The media flow needs to be as turbulent as possible, (ie non laminar)

He isn't designing the heat exchanger. It's a simple
radiator. You want to make it into PHD thesis?


The temperature difference between the heating and cooling media needs
to be as high a practical, ie a counterflow system if applicable.- Hide quoted text -

- Show quoted text -

Uhhuh. And one way to get it as high as possible is for the max
airflow of the furnace to be going through the radiator. Anything
less than that for the same design and he gets less heat
transferred.