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fake summer switch
Wednesday, March 30 2011
Temperatures reached into the mid-50s today for the first time in well over a week, and so finally the last of the snow melted away (with the exception of two piles created by repeated shoveling from the parking area and walkway over the winter). The willows in the Esopus valley have gone yellow with the promise of foliage, and there's even some greening evident in some of the non-oak trees that provide the summer screen blocking the view of our downhill neighbor. Aside from those vernal stirrings and the evergreens, the retreat of snow has left us a world of brown and grey.
Tomorrow I'd be leaving to visit my father down in Virginia, so I wanted to get some loose ends tidied up before my departure. One of those was to print out a guide to running the woodstove for Gretchen (who mostly leaves that job to me). The other was to devise a method allowing Gretchen to switch the solar controller over to summer mode should the weather improve and permit the shutting down of the boiler. (Summer mode is for when the sun is used to heat household water with a switchover to heating the slab should the water get too hot. Winter mode only uses the sun to heat the slab.) The solar controller is smart enough to switch to winter mode if the boiler should cut on, but it's harder for it to recognize when it should switch to summer mode. Every night at 1AM it switches to summer mode if outdoor temperature is above freezing and it's not January or February, only to switch back again should the boiler kick on. It also attempts summer mode if the hot water tank falls below 75 degrees Fahrenheit (meaning the boiler must have been shut off). But I didn't have any way to manually switch to summer mode in the middle of a beautiful day except by issuing commands from a computer (the command is "SS1" meaning "Set Season 1"). So today I implemented both an indication of season on the solar controller's LCD screen and a button that could be pressed to immediately send the controller into summer mode. I'd actually wanted to create a set of buttons for setting things at the controller itself (instead of relying on a computer attached via serial link), but that would require several cycles of programming, testing, and debugging, and for this I just needed a normally-closed push button switch attached to the hot water tank's thermometer. Depressing it would send a "less than 75 degrees" value to the solar controller, sending it immediately into summer mode.
For linking purposes this article's URL is:
http://asecular.com/blog.php?110330 feedback
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