Originally Posted by warholic
So - pros and cons of propane hot H2O versus flate plate. Any/all comments appreciated.
So I know this is an old thread, but I was investigating how the SMB heat exchangers were utilized. I had previously designed a solar heater system using rooftop PVC along with a heat exchanger and circulation pump to add additional heat content to the "luke warm/hot water supply for the sink and outside shower.
As has been discussed here, you get more hot water out of your system with a circulation pump, but the thought occurred to me to do better than that if you have a hot water tank heater. It doesn't necessarily need to be a water heater but perhaps just an insulated water tank (e.g. 2- gallons).
In the attached figure I'm assuming there is a heater water tank and the idea is that that tank contains pressurized water from the fresh supply. This probably does not do much of anything for a "Tankless" water heater because of the overly limited storage capacity.
So the use case for this is that while you are on your way to your campsite, and have a hot engine. You can flip on the temperature controller which will recirculate the hot water supply through a Normally Closed Solenoid valve till the outlet water hits a predetermined temp.
You could also locate the "T" where the recirculation draws water directly from the sink so you won't be wasting water reheating the water line to the sink/shower. The net result will be that your hot water tank/heater will be full of hot water and the hot water line to the sink/shower will stay hot but you would not waste any water because the water gets recovered by the freshwater supply (from the NC solenoid valve).
Even for a tankless system, the recirculation temperature control is a way to skimp on the water since you will have instant hot water at the point that you "T" off from the hot water supply.
This is still in the concept phase. Since my new build has a Tankless water heater, the heat exchanger may be unnecessary but the recirculation would still offer a nice way to save on fresh water.
One other feature of this system is that by adding a second temperature controller (they are cheap) you could use the circulation system with a tankless system to keep the cold water supply from freezing. Depending upon your system configuration you could sense temperature at the coldest spot and set the temperature accordingly. Just wire the Temp Controller output together in parallel. The low temp circulation would be powered off of House power that is constant ON.