February 2013

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Thermostat Wars

Hostilities on the home front

Steven R Calabrese

Steven R. Calabrese
Control Engineering Corp.

Contributing Editor

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The house that I live in is the house that I grew up in. It is a large two-flat bungalow with two fully separate living spaces and a basement that runs the length of the house. It was, as legend has it, built as a rectory for a church that was to be built in the adjacent lot. It is said that the church was never built due to the recession in the 1930’s, and so the empty lot is one big “backyard”.

My grandparents bought the house in the 40’s, when my dad was just an infant. Well, my dad ended up living there his entire life (until he passed in 1995). He married my mother, moved into the upstairs apartment, and had three kids (me being the oldest), all the while my grandparents lived on the main level. At some point in my youth he officially purchased the house from my grandparents, and took over all of the responsibilities that go along with owning a home.

Fast forward a bunch of years and I find myself on the same path as my old man. Meaning that I got hitched, moved my wife and I up into the by-then vacant upstairs apartment, and had a couple kids. As it stands, my family and I live upstairs, and my mom lives on the main level. The basement, I will note here, is all mine, and is truly the sickest mancave west of Chicago!

The heating system for the house is traditional hot water heating, with a boiler and two zone pumps. One pump serves the main level, and one pump serves the upstairs apartment. The boiler and pumps are of course located in the basement. The hot water supply and return pipes that serve the main level are run in a loop around the basement, with take-offs here and there going up to radiators and baseboard heaters. The basement itself is not heated “per se”, however whenever the main level thermostat is calling for heat, the hot water circulating through the mains provides plenty of radiant heat for the basement, as these pipes are not insulated. I don’t know for sure, but I think that that was an original design intent.

The heating capacity for the upstairs apartment is such that, when the main level is maintained at an indoor design condition of 72 degrees, the upstairs level can be maintained at 72 as well, even on a design day of -10 degrees.

Now we get into the “meat and potatoes” of the story…my mother is, by all measures, the opposite of most women, her age and any age, really. She likes it cold! I’m talkin’ a space temperature setpoint of 60 degrees! Seriously? When did she become an arctic warrior? I think that she thinks that she’s doing me a favor keeping her thermostat down and saving me money in energy costs. At any rate, this poses some interesting problems for the rest of us, as I’ll try to explain.

In the winter I spend a lot of time in my mancave, as this is where both my office and my studio are located. On any given night, barring any other family plans or commitments, I’ll come home from work and hit the mancave. First thing I do is, I go to the thermometer on the wall. 68 degrees?? No good, too cold! So I go to my “basement override thermostat”, which is an old snap-acting “farmstat”, and turn it up. Way up, until I hear it click and then some. Basically using it as an override switch, for the most part. Anyway, this stat is wired into the pump controller, and simply forces the zone pump serving the main level to run. Remember from above, that the hot water mains serving the main level are run around the basement, and do a darn good job of heating the entire space when that main level zone pump is running.

So the temperature in the basement comes up to my comfort level, and if I’m lucky, I’ll remember to go back to the farmstat and turn it back down. In the meantime the main level goes into an overheating scenario, if you call 70 degrees “overheating”! The bigger problem occurs when I forget to turn the farmstat back down, and the main level pump controller runs all evening and into the night. At some point my mom figures out that I left it on, and will go down herself to turn it off. Of course not without letting me know about it! Sorry ma.

Now, when it gets really cold out, we have a whole different problem. As I stated earlier, the hot water system has the capacity to heat the upstairs apartment to a comfortable room temperature, even on a design day, as long as the main level is also maintained at room temperature. Of course ma likes it cold, so when it’s zero outdoors, its 60 in her space, and the floors upstairs in our space are cold! To combat and exacerbate the problem, my lovely wife jacks up our stat to 80. Now I know that this in effect does nothing, because the zone pump for our level is already on, and what we get is what we get. I tell her, “Go ahead and feel the radiator, it’s hot!”. And her response is “Then why is it so cold up here…can’t you do something about it??”. So instead of asking my mom to raise her thermostat to 70, I skirt the situation by going downstairs in the mancave to my trusty override stat, and crank it up.

Control Solutions, Inc Now at this point, the main level zone pump starts, the main level space temperature begins its ascent, and the floors in the upstairs apartment begin to warm up. And we all go to bed. And come morning time the entire house is 80 degrees. Huh? Well, think about it. The main level zone pump never stops running, because I cranked up the farmstat to the max, and so the main level rises in temperature to a toasty 80 degrees, while my mom tosses and turns during the night, and thinks that she having “hot flashes”. And since the main level is warm and heat rises, and given that our upstairs thermostat has been set to 80, we also end up sleeping in a pool of sweat…well, at least I do!

So in the morning I get an earful from my mother, go down to the mancave and turn the farmstat back down, and instruct my wife to leave our stat at 72 degrees, regardless of how cold it gets in our space. I then instruct my mother to “reset” her setpoint upward as it gets colder outside, so that our floors stay warm and our living spaces remain comfortable throughout the winter.

Eventually we all seem to get it figured out. Ma comes to understand that, when it’s below 15 degrees outside, she needs to set her thermostat to a more reasonable setpoint. And my wife eventually takes my word for it, that turning up our thermostat to 80 will do no good if it’s only 68 in the space and the radiators are already hot. As for me, I always have the option of my trusty farmstat at hand, but use it less and less as the winter marches on. Heck, by springtime, we have it dialed in, and everyone is happy. And then I turn the boiler off for the summer, and we all forget about it, and come the following heating season, we start the battle all over again!

Tip of the Month: Reset boiler water temperature setpoint as a function of outside air temperature. My boiler is set up so that, when the outside air temperature is -10 degrees, the hot water temperature setpoint is 170 degrees, and when the outside air temperature is 60 degrees, the hot water temperature setpoint is 140 degrees. This saves energy, as the hot water pipes are not insulated, but also allows for more efficient comfort control, as 140-degree water in the pipes is a much better “match” to the heating load on a mild day.


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