set back stat or lower water temp

joel_19

ok I've had lots of customers trying to set back their stats WAY back while running reset. I've been fairly able to explain that isn't a great idea as if they want a 10f set back the water temp will be much higher. Does anybody have a source article explaining this so it can come from someone other than me??
Thanx veddy much.

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Mike T., Swampeast MO

If you're willing to somewhat read between the lines, this Tekmar Literature at least alludes that the best way to conduct setback is via reducing the supply temperature, not the thermostat setting. Conversly it at least alludes to the notion that if you're using a "tight" reset curve, the only reasonable way to achieve setback recovery is to increase the reset curve above what is actually required.

While they go at it from greatly different methods, the only two mod-cons I know of that incorporate "setback via reduction of the supply curve" are the Viessmann Vitodens and the Buderus GB (both German by the way).

Ever since a DOE study during the first "energy crisis" in the 1970s determined a VERY rough guideline that you get X amount of savings for each degree of once-daily setback, nearly all levels of government as well as thermostat manufacturers have nearly brainwashed consumers into believing not only that "dadily setback ALWAYS saves", but that "the more daily setback, the more savings". Unfortunately they completely ignore the fact that the original study not only said up to X savings, but that they found the entire subject was extremely complicated and that generalities were impossible. The general construction, the insulation level, the degree of weatherization, the type and condition of the heating system and even the weather itself are all extremely important factors when it comes time to determine savings from setback.

I have found one and only one way to convince homeowners that they are using too much setback, but it does require that they believe one thing:

If you turn off the heat completely and let the room temp fall, the turn the heat full on to get back to the original temperature it took at least as much energy to recover as was saved on the way down. The only time you get savings is when the heat has to turn on to maintain the lower room temp.

Many electronic setback thermostats have a built-in, resettable run-time function that's used mainly as a "filter replacement" reminder. If you reset the function right after your setback period begins and examine it before recovery has begun and see zero or a very few minutes, people will actually understand that they're using too much setback. Unfortunately though the amount of setback varies inversely with the weather--the colder it is, the more setback can be used. Not only that, but the time-of-day matters as well. Space temp tends to fall faster at night than during the day--not only is the outside temp generally warmer during the day, but on fairly clear days our friend the sun both adds energy and reduces radiant losses from the outside walls while on fairly clear night you get that nasty "nighttime re-radiation" phenomenon whereby the outside walls loose more heat via radiation to the cosmos...

Matt_67

While I generally agree with the post and the statement that there are many factors that contribute to the overall savings potential. I must point out that the following statement. “If you turn off the heat completely and let the room temp fall, then turn the heat full on to get back to the original temperature it took at least as much energy to recover as was saved on the way down.” Does not address the fact that for the time that the temperature is below the day set point on the way down and back up to the set point; the heat loss, which is a function of the delta T across the building envelope, is reduced. It is the heat loss that equates to energy consumption.