Controlling Heating/Cooling on a Complex Schedule?

Controlio asks: "I've just replaced my furnace, air conditioner, and humidifier last week, in a house that I am rebuilding almost completely from the studs. With the outrageous cost of heating oil, I looked at saving some money by installing a programmable thermostat. However, my work schedule is too complex for most programmable thermostats. The one benefit I have is knowing my schedule a month or two in advance. So, the most practical option seems to have some sort of computer-controlled system that can accept calendar-based setpoints. This would also allow me the opportunity to VNC to the computer from work and change the schedule, in case of last-minute scheduling changes. The ideal solution would be able to control the heat and air conditioner, plus have the ability to do humidity setpoints (though it's not required). Also a system that could control two furnaces would be beneficial, since I plan on installing a heater in my garage this year. Does anyone know any hardware and software combination available to accomplish this?"

Comments

Nothing for sale in a reasonable price range...

[ivan256]

As sombody who's doing the same thing to a house,(So far I've cleaned up a fuel oil spill, insulated, replaced all the plumbing, the furnace, the windows (22 new construction windows... Ugh.), the bathrooms, fireplace enclosures, siding, most of the interior trim, and refinished the wood floors), first let me congratulate you and (if you're doing the work yourself) give my condolences for the loss of all your free time from now on.

The pickings are slim, and short of a multi-thousand dollar (probably more than you paid for your furnace, and certainly more than you'll save in heating costs over the next five years from the programibility) home automation system, you're not going to find anything remotely suitable for what you described. Even then it's not going to be as flexible or open as you're hoping. You can build something yourself, but there are three things you should remember.

First, you use the most fuel transitioning from your low temperature setting to the high temperature setting. You don't want the low to be too much lower than the high or you'll actually increase consumption, and you don't want to transition too many times per day.

Second, the more complex you make your program the less change you'll notice in usage. Complexity provides deminishing returns. (At least it should if your house is insulated properly).

Lastly, and absolutly most important is that you never, ever want your thermostat to fail. As sombody who has just replaced all the plumbing in a two story house, and delt with the concequences of 4' of water in a basement (happened before I bought the house... Got me a good deal.) take my word for it when I say you don't want to do that. Especially if you have oil heat. The bottom rusting out of your oil tank is not fun for anybody. So if you want to make it programable from your computer, that's fine, but make sure it can still turn your heat on and off without your computer, or that you have a secondary manual thermostat that won't let the temperature drop below 50.

When it comes right down to it though, every ounce of effort and every dollar beyond $100 you spend on this would probably be better spent on insulating. There are some great thermostats off the shelf at home depot like places that have four or five week long programming sets. Get one of those, and on your way out the door every morning, or every monday, pick the program that fits your day.

Re:Nothing for sale in a reasonable price range...

[BigBlockMopar]

So if you want to make it programable from your computer, that's fine, but make sure it can still turn your heat on and off without your computer, or that you have a secondary manual thermostat that won't let the temperature drop below 50.

Absolutely agree with you. My little trick, which I do whenever I'm installing a programmable thermostat, is to take the old mechanical thermostat and mount it in the utility room (or wherever else the majority of the plumbing is). Set the old thermostat to its lowest setting and connect it in parallel across the heating leads on the new thermostat (R-W wires only).

This way, if the new thermostat fails (ie. dead battery), the furnace will kick on before the pipes freeze. Would work doubly well if you've got your computer controlling the heat - even FreeBSD can crash from time to time.

Another issue - why not consider using small motion detectors to adjust the temperature? If there's no motion, you're either out or asleep, right?

Insulation is super-important; my house is 600 square feet (tiny WWII veteran's home) in Ottawa, Canada. Each exterior wall was 2x4 originally; when redrywalling a few portions, I've screwed 2x2s onto them to allow the use of 6" thick insulation. With the new windows and a load of fiberglass in the attic, my Trane XV90 rarely kicks on even in the winter; computers and household activities (cooking, etc) keep the house warm enough most of the time.

Aside: love my Honeywell CT3500. It's a simple 5-2 programmable.

Yikes!!

[Anonymous Coward]

Excuse me -- you're a mammal. You can survive if you come home, the thermostat hasn't kicked in yet and you need to manually turn the heat up and wear a sweater for ten minutes. I'm glad you at least realize you can tolerate some marginal deviation in humidity.

Does it really need to be that complex?

[Camaro]

I know energy is damn expensive these days, but do you really need to adjust it that often? Do you think you'd really save enough to cover the cost of such a complex system by fine-tuning that precicely? Perhaps I'm misinterpreting your needs but if I were in your shoes, I'd go over my schedule and find some common points at which to set temperatures and leave it at that for the period of your known schedule, if that is possible. Just pick the programmable thermostat to fit those needs. I'd go nuts trying to fine tune a system as you're envisioning.

As for the garage, if you're not going to spend every day in there, I'd suggest a generic theremostat or even a power switch on the furnace. Just turn it on before you want to work in there. If you plan to heat it, you plan to insulate it, so it should heat pretty quickly.

Maybe it's just me (I'm just a geeky farmer), but I just don't see the point of a complex system.

Re:Does it really need to be that complex?

[N3Bruce]

The better the insulation, the greater effect thermal mass will have on your house. I recently had built a new modular house with Energy Star windows, R-30 in the ceiling, R-19 in the walls, and an R-6 Mylar faced insulating blanket on the basement walls extending from the joists to below the frostline, and am heating with a Trane high efficiency heatpump backed up by propane. Because of the good insulation, even if it is in the 20's outside, the temperature only drops a degree an hour or so if I turn back the thermostat. If you want to keep the house at 70 during the morning breakfast hours, cool at 60 when away, and 65 at night, the temperature does not really have an opportunity to settle at your programmed levels, at least not for very long. I have thought about getting a programmable thermostat, but I am lazy and just keep the house at 70 all the time, unless I am going to be away for a couple of days or more.

Keeping the house at a constant temperature has advantages in itself. Because of the lag in warming the walls, floors, etc. compared to the air, keeping the temperature at a constant compromise setting insures that those surfaces you touch feel warm as well. If the air is 72 degrees, but your desk is 65, you will have cold hands, and that isn't even talking about how cold the bathroom floor feels at night after cutting back the heat. By the time the floor, counters, and desk are warm, you are well onto your way to work.

The house itself also tends to benefit from constant temperature as well. I found out the hard way that temperature swings can make drywall crack after I heated the house back up after cutting the heat back to 50 when I went away for several days. Frequent temperature variations also start to work loose fasteners such as nails and screws as well, and can eventually result in squeaky floors, cracked grout, and nail pops in drywall as well.

Because of the improvements in windows, doors, heating systems, and insulation built into newer houses, my new house has about half the energy cost of my old 1946 vintage farmhouse, despite being 20 percent larger and built on the same windswept hill as my old house. One thing that is important when doing major energy efficiency upgrades to insulation and windows is to optimize the heating system for the new heat loss characteristics of the house. Just as a big pickup truck needs a V-8 to move it along as well as a Civic with a 4 banger, a house with major improvements to doors, windows, and insulation will be able to get by with a smaller furnace as well. If you are replacing an oil furnace with another, keep this in mind if you have the opportunity to replace the furnace. If the furnace has been recently replaced, you might still be able to tweak some things like nozzle size, fuel pressure, etc. to optimize what you have.

Another thing to consider if the furnace is on the "to do" list is to investigate Geothermal Heat Pumps . They are not for everyone, and the capital investment can have a fairly long payback period, but if you are blessed with suitable soil, a large enough lot, or a nearby body of water, they can cut your heating and air conditioning bills to a fraction of the cost of heating with oil or other fossil fuels. I made the decision not to go with the Geothermal heat pump because of the extra cost and a rapidly tightening construction budget, but with the recent increases in the price of propane and looming increases in electricity, it is one decision I might have reconsidered.

Way too much work

[linuxwrangler]

Wow this sounds like a lot of work. I think I'll stick to my current "system":

1. Too chilly? Turn on the heater for a few minutes.

2. Too hot? Open the windows/turn on a fan.

But you're right - energy is getting expensive. I just broke $100 for gas/electricity last month.

Materials....

[Anonymous Coward]

If the original poster is from America, most likely his house is wood from the sill up; wood is still relatively cheap in the US. Concrete construction in single family homes is much more common in Europe than America, and plumbing/heating systems in Europe reflect that difference.

Insulation technology for wooden houses has improved immensely in the last 20 years, and it's probably a better investment of time and money to figure out how best to button up the house, and get a nice programmable thermostat that will let you change between some pre-programmed schedules. Or come up with a system (sticknotes?) that will remind you to turn the manual thermostat down when you leave the house.