I've got the full Grumman system, never before used, including
electric-element storage tank, heat-exchanger, two 5x9' panels to be
plumbed in parallel and the manual.
I want to plumb the warmed solar water from the solar heat exchanger
into the cold water intake on my existing propane boiler, essentially
pre-heating or actually heating the water before it hits the boiler
thermostat. That way, if the solar panels can heat the water (via the
heat exchanger) to the set boiler temp (currently 150F) then the propane
burner need not ignite, and the mixing valves and the zone pumps can
still work as designed, heating the radiant floor zones and the potable
The storage tank itself is designed to be wired into the Grumman Heat
exchanger so that when the tank water reaches temperature some magic
occurs in the heat exchanger to keep the water below boiling...or to
kick the heat exchanger into action when the temp drops below set point.
Does it make sense to pre-heat the cold-well-water with the output of
the Grumman Solar Exchanger before it gets to the boiler without using
the storage tank? I think not, but it's another option.
Should I plumb the hot water out from the solar storage tank to the
biodiesel tank loop and have it return to the tank, so that the in-tank
sensors tell the heat exchanger to keep going because the heat in the
storage tank is being "drained" by the biodiesel tank loop?
In other words, I'd hook up the system as recomended in the manual (I've
got it in PDF if anybody needs it) and cut a section out of the cold
water pipe from the well input pipe into the boiler, running the cold
well water through the Grumman heat exchanger and plumbing the output of
the heat exchanger into the storage tank, with the output of the storage
tank plumbed into the boiler cold water input, where it would enter the
boiler essentially pre-heated. I recognize that I may need a bypass
valve in case the boiler calls for more water but the Grumman heat
exchanger unit valve isn't open, leaving the propane boiler starved for
water...but that can be handled in an automatic fashion somehow.
I've also got a need to heat a coil in my barn that surrounds a 3000
gallon 8' diameter round cylindrical biodiesel tank. I intend to wrap
the tank solidly with Pex radiant floor tubing (mine is red) and if I
can do what I intend, I want to extend a zone so that it includes the
biodiesel wrap. That way, if the solar panels are having a rough time,
the propane boiler will pick up where the solar panels failed and keep
the biodiesel tank above 50F. I recognize that a mixing valve and also
several shutoff valves will be necessary for summer operation.
I am concerned about the load on the existing zone motors as they get
pretty hot when operating, though I know the boiler itself can handle 2
more zones and the boiler is way over capacity for the house in terms of
Should I run the closed loop of glycol from the panels around the
biodiesel tank before it enters the Grumman heat exchanger?
Should I simply tap into the hot-water out from the Grumman heat
exchanger before it enters the boiler with a mixing valve and run it
around the biodiesel tank and have it return into the house storage tank
with heat lost but still a bit of pre-heating, which has the
disadvantage of not permitting the propane boiler to chip in to heat the
biodiesel tank when necessary?
Should I add another zone to the boiler and use that for the biodiesel
loop? (I've currently got two radiant floor zones plus a third "zone"
for potable hot water?)
Many thanks in advance.
Once the biodiesel gets up to temperature (about 60F) I don't expect a
dramatic fluctuation at night, since it will be greatly insulated and
the liquid mass will hold the heat quite well. The biodiesel tank is
about 20 feet away in a barn so I'm going to have to bury the insulated
pex under the frost line to make the biodiesel tank loop.
I guess my question is from where do I draw from the system to heat the
biodiesel tank loop, and secondly is it OK to preheat the boiler water
with solar to burn less propane?
Again, I've got the Grumman Manual in PDF format along with photos of my
exchanger and tank if anybody's interested.
kjcrandall _at_ svaha dot com