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It seems like folks have a difficult time understanding heating concepts and our jargon but we all seem to understand cars and trucks so I try to relate heating to motor vehicles. I think about this stuff while I travel around in my GMC Sierra pickup,
hence: "Tales from the Sierra".
What does cruise control have to do with heating; what does outdoor responsive heating controls have to do with cars?
Try to imagine driving your car at 55 mph (60 is illegal in most areas) and all you have are two throttle positions, idle and full. We know this is difficult, uncomfortable, and uses a lot of fuel. Cruise control eliminates the problems, it's easy, it's comfortable and it saves fuel. It works so well because cars have variable engine speed.
Outdoor responsive heating controls (outdoor reset) does the same thing as cruise control. Remember the goal is to keep the living space comfortable and save fuel. By modulating the water temperature going to the heat output device (fin tube, radiant panel, in floor radiant) based on the outdoor temperature; just as your car adjusts the engine speed based on the load required, up hill, down hill or flat; we can maintain a constant temperature in the space. There are limits to the control because of the thermodynamics of components (cruise doesn't work well under 25).
We can make almost any hot water system more comfortable and save fuel, some we can make a lot more comfortable and save a lot of fuel. Most domestic boilers limit the return water temp to 140 degrees; fin tube baseboard needs about 130 degree supply temperature to initiate the convection, different output devices have different output ranges. The more sophisticated the heating system,e.g. Viessmann boilers and full radiant heating, the more comfort and more fuel savings we can achieve. The lower the water temperature and the longer the circulator runs are the keys.
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