WiFi and an generator
Friday, February 17 2006
The weather this morning wasn't unusual for this winter. It was sunny and temperatures were the 50s (Fahrenheit). But a cold front was on the way and during the late morning and afternoon the weather changed dramatically. As usual with such big changes, these were accompanied by fierce winds. They weren't strong enough to tear the solar panel off the roof, but they did break one of my laboratory deck's balusters free and cut the power to the neighborhood for hours. As temperatures steadily plunged, I stayed near the fire with a succession of laptops, using what remained of their battery power so I could write. Periodically I'd brave the gales and go out to my laboratory deck with the iBook so I could check my email and load a few web pages for indoor reading; the neighbors across the street have both WiFi and a generator.
Since last year I've noticed a problem with the house's boiler that causes it to vomit up a gallon or so of its hydronic fluid regularly. On these occasions the pressure manages to cross the 40 psi threshold, causing the relief valve to open. These days I catch all such regurgitations and, using my pressurized antifreeze supply, recycle them back into the system. (Propylene glycol antifreeze is expensive.) But I've never managed to figure out what is causing these overpressure conditions. At first I thought I might have a defective expansion tank, but replacing it did no good. So then I replaced the feed supply valve, but that didn't fix the problem either. Even completely closing off all sources of pressure into the boiler system hasn't stopped periodic boiler overflows. Eventually you would think that these overflows would bring the pressure down to a level where overflows would be an impossibility. (Eventually the system would run out of water if nothing else!). But I don't see any indication that these overflows have diminished since I cut off all forms of resupply. This led me to wonder: is there water entering the system from some other source? What source could that be? Short of another feed valve hidden in the boiler room ceiling, I couldn't think of any. But last night it suddenly occurred to me the pressure gain could be explained by a pinhole leak in the coil of stainless steel tubing running through the indirect hot water heater. For those who don't know how an indirect hot water heater works, let me explain. The heater consists of a big 53 gallon tank with a coil running through it carrying water (or, in the case of this setup, diluted antifreeze) from the boiler. The coil is like the primary of my fluid heat exchanger. The boiler fluid in the coil heats the 53 gallons of water around it indirectly but never mixes with it. Well, it doesn't mix unless there's defect, say a pinhole leak. But if there should be a pinhole leak, water will tend to flow into the heater coil from the 53 gallons of fresh water around it. Why? Because the 53 gallons of water is pressurized to 40 psi, whereas the water in the coil is at typical hydronic pressures (less than 20 psi). Such a defect would be a serious one and the only way to fix it would be to replace the entire hot water heater. And one symptom of it would be a gradual inexplicable pressurization of the hydronic system. So today I ran an experiment where I completely isolated the hydronic plumbing that passes through the indirect hot water heater and put a pressure gauge on it. Then I monitored this gauge for hours to see if there was any accumulation of pressure. Interestingly, the pressure did fluctuate from a high of 25 psi to a low of 10 psi, but it didn't seem to be heading in any specific direction. The changes were probably the result of temperature changes, which were fairly large given that the boiler was off for the entirety of the power outage.
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