chores in the chilly outdoors
Monday, January 24 2011
Average peak cold in this area comes on January 22nd, and that's always when we have our worst cold-related troubles. On January 24th 2004, our shallowly-buried well line froze and required $400 worth of professional well work (damn you, Michæl Schn3113r!). And by early February of 2009, our house was plagued with ice dams (as I keep fearing it will be this year). This morning temperature dipped to -8 degrees Fahrenheit, the lowest it has fallen in a couple years. It was still in the low single digits when I went out this morning to get an armload of wood from the woodshed. The sun shining proudly through the dead frozen air still carried considerable energy, as demonstrated by a sudden "Whoosh!" from the hydronic solar array. The deck-mounted pressure relief valve had discharged a cloud of steam. This almost never happens; it was an indication that there was no open path for fluid to flow between the solar deck and the basement, where a pressure relief valve with the same release pressure is located. Being 30 feet below the solar deck, the basement pressure relief valve is usually the one that discharges in an overpressure "event." For there to have been no open path between the solar deck and the basement suggested that the pipes were blocked by frozen hydronic fluid. I'd assumed that fluid would be able to flow even several degrees below zero, but evidently I'd assumed wrong. From my computer, I monitored the readings from the thermocouples located along the solar loop, and I could see that, though the pump was running, the fluid was not moving. (This phenomenon wasn't entirely new to me; there's even an algorithm in the Arduino-based controller that looks for this condition and turns off the pump for awhile if it is detected.)
I didn't think to perform a test with that fluid until this evening, when I set a cup of it out on the laboratory deck as temperatures plunged from today's high of 12 degrees down to just below six. At those temperatures, the fluid turned into a slush, one that should have at least been able to flow. But at negative eight, who knows? I consulted a Cryo-tek antifreeze jug (I like to cut their tops off and use them as storage containers) to see what should happen at various dilutions and was alarmed to find that what I'd assumed was a behavior at a 50% dilution actually required a 66.6% dilution (only one third water). Still, the only fluid I add to my hydronic network is Cryo-tek antifreeze; I never add water, so it's possible it is at 66.6%. Still, it's a little scary thinking that solar-expanded fluid might not be able to flow freely through the pipes. What if the fluid couldn't respond to a solar-induced change in pressure in one of the panels by making it to the one decktop pressure relief valve? Of course, there is a big difference between a fluid being pumpable and a fluid being pushable by enormous pressure. The panels should be able to handle 80 psi and it's doubtful it will ever get cold enough for an antifreeze slush plug to hold back that kind of pressure. Still, just to monitor the situation, I've attached a pressure gauge to one of the panels. It's the kind with a little red hand that records the highest pressure attained. I'll be curious to see if it ever goes above 30 psi (the rating of the relief valve). If so, that would be a potential problem.
In other crappy activities conducted in the bitter cold, today I replaced the front passenger-side wheel and tire on the Honda Civic. Somehow I'd missed how terribly bald it had become on its inside half. There was so little rubber remaining that in places some sort of mesh (fiberglass perhaps) was showing through. Gretchen had just driven to central Massachusetts and back through the snow on that tire.
As I worked, I was kept warm by listening to the latest This American Life podcast, the one featuring the suspenseful tale of a gentleman who plotted to kill the man who had raped him back when he was a little boy (and his rapist had been a teenager). I knew it was going to be good when Ira Glass introduced it by first shooing away all of his child listeners.
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