Hot Water Solar & HVAC controls

[jdurand]

Our hot water solar collector shares water with our house heating boiler. The system has been rebuilt over the decades as parts wore out and to meet updated building codes.

We originally had off the shelf controls for the solar collector, tank backup heat, and house heating loops. That stuff was ...err... less than satisfactory and died after a short time in the 1980s. I replaced it with a PLC that also handled our house cooling system (swamp cooler that was switched into the heating ducts with automated 16 inch Y valves). That had separate 24VAC, 24VDC and 120VAC circuits to accommodate all the different things. That lasted until 2007 and then started acting funny.

By this time we were designing microcontroller systems so my wife and I designed this controller which has been happily running ever since. ;It's just a simple 16 bit microcontroller with 4 thermistor inputs, a 24VAC input from the heat demand thermostat, and four 120VAC relays for solar pump, heating pump, backup pump, and boiler. It has a supercapacitor which keeps the clock running for about 2 days without power.



I happened to mention it to the owner of the company* we were buying some new hot water panels from (old ones started leaking). He wound up ordering a bunch of a custom version for a power company trial.

Funny how things go.

* those replacement solar panels have been working great for many years, they were made IN CALIFORNIA by these guys
https://solarroofs.com/