In the last blog I mentioned calibrating the customers expectations by providing them with a simulation showing what they can expect from their system. Occasionally, a customer will not realize the savings they should and they expect you to fix it. Under the right circumstances it is possible to install a solar heating system and see only a small fraction of the savings that should be delivered…

One such situation is when the customer uses a solar tank to pre-feed an indirect gas or oil fired tank that operates as the back-up to their system. When using a boiler fed tank as the back-up, it is possible to intermittently not achieve the desired temperatures in the indirect tank thus requiring the boiler to cycle on. If this is in the summer time when the boiler is only used to service hot water (and not heat the house) this means that all of the losses and waste associated with starting up and shutting the boiler down is still there. How can we eliminate (or at least minimize) the intermittent cycling of the boiler when the solar tank is already hot?

One way to reduce the boiler cycling is to tie the solar tank together with the indirect tank in such a way that any excess heat in the solar tank is shared with the back-up tank thereby reducing the demand on the boiler. This can be accomplished simply with an extra connection between the tanks, a pump, a check valve, and a differential control. When the solar heated tank exceeds the temperature in the back-up (indirect) tank the circulator turns on and causes the two tanks to be mixed together in such a way that the heated solar water moves into the back-up tank. By tying the tanks together in this manner you have accomplished several things including: reduced the firing of your boiler increased the overall efficiency of the solar collectors (by keeping the tanks at a lower overall temperature) significantly reduced the customers overall energy bill in the summer time. made the solar system more robust and resistant to overheating (glycol systems)

While this technique will not hurt in any way it’s greatest benefit will be seen during the summer when the solar system is capable of producing the extra energy. It is possible to totally eliminate the customer fuel oil usage in the summertime with this scenario.

Click here for a sample drawing