Thermostat plan

[MrGibbage]

I was thinking about adding some extra thermostats to my house. In particular, my upstairs sools and heats so irregularly, the temperature in one room can easily be five degrees hotter or coller than another room. I am fine with letting the thermostats directly control my HVAC--I don't think I need my Elk to do it. So, can't I use regular thermostats (instead of the Aprilaire and other expensive thermostats) and have my Elk switch thermostats on and off as selected by the user? I was thinking about using the output expander to switch them in and out. Since each of the relays has an NC and NO contact, this seems pretty practical.

Thoughts???

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[DavidL]

Is your HVAC system zoned now? Doesn't sound it. If not, the issue won't be a matter of detecting the temperature, the issue will be in balancing the heat around the home. If you have the furnace look at the "cold" thermostat, then the hot area will also just get hotter as the cold area is brought temperate. You will still be out of balance.

A zoned heating system has means to control how much heat goes to Area A vs. Area B. In forced hot air systems, this can be an electrically controlled "butterfly" valve that shuts off air flow to the hot area (during heat season). So the BTUs goes to the cold area. Each area has a means to determine the temperature and then the zone controller then processes which valves to open vs. close.

One thing to look out for is that if too much air flow is constrained due to poorly designed system then the fan can get overtaxed. There are pressure relief valves to prevent damage from this. The valve typically connects the output side of the furnace to the input to relieve the output pressure.

You might want to start simpler by mechanically balancing the system (shut off dampers in hot areas, and opening same sq ft in the cold areas). You can also put a booster fan in the ducts going to the cold areas that tends to put a higher percentage of the btus to the cold area.

for a cheap way to get temperature only, you can look into using a 1-Wire network where you can inexpensively monitor temperature in all areas (one sensor per room) and then have a control system (like a PC) then allow for temp monitoring at a minimum, and even to manage the balancing. I typically don't recommend this to control the overall temperature, especially in cold zone climates that can have big issue if the plumbing system were to freeze.

I was thinking about adding some extra thermostats to my house. In particular, my upstairs sools and heats so irregularly, the temperature in one room can easily be five degrees hotter or coller than another room. I am fine with letting the thermostats directly control my HVAC--I don't think I need my Elk to do it. So, can't I use regular thermostats (instead of the Aprilaire and other expensive thermostats) and have my Elk switch thermostats on and off as selected by the user? I was thinking about using the output expander to switch them in and out. Since each of the relays has an NC and NO contact, this seems pretty practical.

Thoughts???

Skip

 

[MrGibbage]

Actually, we are zoned. It's a 3000sq ft house, with a separate zone for upstairs and downstairs. The family room and foyer both extend up to the second floor. The upstairs thermostat is in the hall, which is also open to downstairs, if you know what I mean. The funny thing is, there are no AC vents anywhere near the thermostat. So the actual temperature there more closely matches the temperature downstairs. So, the temperature in the bedrooms will get all out of whack with the temperature at the thermostat. In fact, I have a feeling that if I did install a thermostat in my bedroom, I'd probably leave that one on all the time, and probably wouldn't ever switch it off.
Fortunately, I ran a CAT5 to each of the thermostats, and I have a spare CAT5 behind the keypad in my bedroom, so adding a thermostat in there will be pretty easy.

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[pete]

the temperature in one room can easily be five degrees hotter or coller than another room.

as I mentioned in a previous post

your system(s) needs to be balanced (most residential contractors don't do this !!) . . by this I mean you need to adjust air flow to the different spaces to achieve uniform temp through out . .

you should have manual dampers on the branch duct runs (hard duct or flex to each individual outlet), usually a small handle locked with a wing nut . . if not, get a local hvac contractor to install them . . then with a couple (3-4) instant read thermometers (one in each room) make adjustments until all rooms are cooling evenly . .

make take a little time and effort to get it right, but will do wonders for your comfort level . .


also, the t-stat is usually best in the return air path, you don't want it to be in the air-flow comming out of one of the registers as this will cause short-cycling of the system . .


Pete C