I've been thinking about heat exchanger design. In some earlier e-mail
you had mentioned that getting heat into the storage tank from the
glycol loop was relatively easy ... the heat energy arrives slowly, and
you have all day to move it. But getting the heat back out again was
harder. There are several issues:
1) The water from the city supply is under higher pressure.
2) Need to maintain pressure and flow-rate (so that showers
upstairs work acceptably).
3) Need to move a lot of energy quickly.
At first I wondered about inducing some turbulence in the
flow (to avoid the problem of the water at the edges of the
pipes moving slowing and picking up a lot of heat, while the
flow at the center of the pipe is rapid, and insulated by the
slow moving water at the outside ... thus lots of cool water
might get through the exchanger). This could be achieved
by adding some larger diameter pipe at intervals in the
heat exchanger (e.g. step up from 1/2" to 3/4" and back
down again) which shouldn't affect flow rate.
But then I realized that we just have a buffering problem.
We don't need to be able to quickly heat an arbitrary amount
of water. We can slowly heat a larger amount ... and if the
amount is large enough to meet typical domestic needs
(fill the washing machine, take a shower, etc.) then we can
take our time about warming the next batch of water.
I think that the capacity here probably needs to be 30gal
So now I'm wondering whether there is an economically
viable way to do this ... either we need to include one or
more water tanks as part of the heat exchanger. Or build
the exchanger from large diameter pipe (e.g. 4").