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Using a modulation boiler to control water temp in snow melt system
I am designing a driveway snowmelt system for new construction. I used the Wirsbo snowmelt design manual to come up with 12" PEX tube spacing, 160KBTU/hr boiler, 40 % Glycol, 9 zones, R10 under the slab ---etc etc. This will be a stand alone system , the boiler will not be used for anything else. I would be using a modulating/condensing boiler. There would be a flat plate heat exchanger to keep the glycol out of the boiler. My question: Instead of using a mixing system (either injection or a mixing valve) why not use the capabilities of the modulating boiler? They typically can run at 30 to 100 % of output and can be controlled with a 0-10Vdc input signal to modulate the delivery water temperature. You can buy PID temperature controllers from Omega and others for around $150. These controllers can take inputs from a number of types of sensors (in this case a sensor in the slab) and generate a 1-10Vdc signal that corresponds to the difference between the sensor temperature and the set point. These controllers even allow you to control the rate of change of the temperature. I would not do this for an underfloor heat system because the boiler would be running all the time but since a snowmelt system is used intermittently it would seem like this would work. What am I missing?