Tuesday, March 17, 2009

Thoughts on Thermostats

I live in Florida, which means that aside from a month or two in the winter it's hot and humid. Air conditioning is a must; much can be done by using tree cover, tall rooms and natural sources of cooling, but none of those apply to modern construction, so central A/C it is.

Now, my house happens to be two stories tall, which exacerbates the problem, but the same issue is commonly found with any manner of multi-room construction and central air conditioning: the room you're in isn't the right temperature, while other rooms, in particular the one with the thermostat, may be.

In every house I've lived in in Florida, and that's a fair number, there has been one thermostat situated by the return air intake. The logic makes sense: all the air has to pass by that location, so it's a pretty good indication if the temperature of the internal air. This logic, of course, suffers from a major problem: the air only moves past this point when the air handler is running. So when it's hot where you're at and cool in the core of the house by the thermostat, there is no relief. Instead of running the air handler (which moves the air; the A/C cools it) only when the A/C is active one can use the "fan on" setting and have air circulate all the time. This gets old, though, and costs a bunch in electricity, even though it turns out that the fan only consumes about 1/10th of the energy of the full system.

I've suffered with this conundrum for a while, figuring I'd just live with it, until my cohabitant mentioned being bothered by the same issue. This promptly turned on my "must fix it" mode and I went to research options.

The right way of doing this would obviously be to have a separate thermostat in every room, and a method of adjusting the individual temperature of each room. This option gets rejected as unworkably complex and expensive, even with adjustable baffles, not to mention the lack of HOA approval for installing a bunch more A/C units to do it right.

So, then, the next best solution, I figured, would be to move the thermostat to where it's hot (second floor). Due to the particular situation, this pretty much calls for some wireless magic, as running a cable anywhere from the current location would be a bit painful. No problem, it turns out! Honeywell has a nifty solution, and so do a few other vendors. If you can string wire, you're even better off. You can also expand some of these systems by adding external sensors and more than one indoor sensor that get averaged. Neat! But where would I put the remote sensor? There are three bedrooms to choose from.

I kept digging, and came upon a better (simpler) solution. There are a number of thermostats that run the air handler for a while if the cooling (or heating) cycle hasn't kicked in for a period of time. The idea is that this way the air keeps moving, but the fan isn't on all the time either. The centrally located sensor now makes sense again, since it guarantees a good sampling of real air in the house. Some of the Honewell TH8110U, TH8320U and TH8321U ones do this, as does the White-Rodgers 1F95-1277, Braeburn 5300, ClimaTouch CT03TSB, Hunter 44860 and the Lux Products CAG1500. Carrier and Lennox also have something similar; Lennox had by far the best thermostat I found, but you can't buy one off the street.

A number of these products are "professional installation only" type, which means they aren't dumbed down to the average consumer and may require a bit more careful reading of the manual to figure out. On the other hand, they tend to have pretty decent manuals and installation instructions and many more options than the Home Depot specials.

I spent a good while going over the manuals, since this feature isn't always advertised, and even when it is, finding out just how customizable it is and how long the fan may be inoperative was pretty tough. While at it, I found a bunch of really common sense features that made me wonder why they aren't more popular.

1) External temperature sensor. Not so big in Florida, but in other climates this is used by the thermostat to figure out if it can use the heat pump or if it's so cold outside that it needs to switch to straight electric heat. That, and it shows you the temperature inside and out, just like a thermometer. Magic!

2) Control of the A/C not just based on temperature, but also on humidity. Air too humid? Run A/C for a while. Alternatively, it can take humidity into account when figuring out the "feels like" temperature. If it's dry, it doesn't need to be as cool as when it's humid, since it feels cooler. Even if you don't control the A/C based on the humidity, the thermostat can still display it, so you can use it as hygrometer.

3) Adaptive learning: the thermostat figures out how long it takes to get down from one temperature to another. For example, if you've set your temperature to 80 during the day when you're gone, and 76 starting at 5:30 pm when you get home, the system figures out when it needs to start cooling down to reach 76 at exactly 5:30.

4) Remote thermostats and multiple thermostats. Carry one with you, and always be comfy!

5) Timed overrides. Instead of overriding to the start of the next program, or permanently, set the override for the next X hours. Some also had vacation modes where you could set an override for a number of days.

6) Energy meters. Every digital thermostat I've ever had has kept track of running time to remind you to change filters. I found that you can tell some models how many amps your A/C, your heater and your air handler pulls, and possibly even the cost of power. The thermostat then figures out how long it runs, how much power it draws, and gives you a running total of kWh or even straight up dollars. Obviously the runtime information is in all of the units, they just don't let you see it!

Note that so far everything has been done with dirt cheap electronics. Most of these features add a little logic to the thermostat, some use RF remote technology of the kind you can find in a $5 Wal-Mart wireless thermometer. Yet to get them into your house ends up costing you a bit. It's yet another example of charging for intellectual property. The technical cost of doing any of these things is pennies, yet to get them you have to dig fairly deep into your wallet.

I also started to think about all the neat things that a thermostat could do, but I didn't see anyone sell. Like hook up into Ethernet or wireless so you can connect to it from your computer, easily change programs, check run times, and change temperatures from afar. Or integrate into RFID/Bluetooth/alarm system/motion sensors to figure out when the house is or isn't occupied; no more need to be tied to strict programs -- if you stay at work late, no need to cool an empty house; if it's a day off, you get home early, or you're home sick, it knows not to let things get too hot despite it being the middle of a work day.