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Temperature-based cut-in for a Vaporstat?
I installed a vaporstat on my steamer last weekend and have been datalogging the flue temperature to get cycle time data. When maintaining temperature, the system runs for 20-25 mins, and never cuts out on pressure. On recovery from setback (60 to 67 degF), the burner runs for about an hour, then there are 3 or 4 pressure cycles of 1 min off and 3 mins on, before the thermostat is satisfied.
Operating pressure is 2 oz, v-stat cut-out is 3 oz, diff is 3-1/2 oz (it cuts in at a bit of negative pressure).
Those pressure cycles at the end of the burn seem like wasted fuel to me. If it cuts out on pressure, then the system is (or should be) filled with steam. And if the system is filled with steam, then I should let the latent heat do its job and shouldn't re-fire the burner until its spent.
The Tekmar 279 steam control has a "lockout differential" feature where it waits for a measured temperature on a condensate return to drop below a setpoint before letting the burner re-fire.
I've been kicking around a couple of ideas for doing something similar, to add a temperature-based cut-in when the vaporstat cuts out on pressure.
So I was wondering if anyone has done this already, or if it's even worthwhile to try, or if I should just save up and buy the Tekmar. :-)
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