Comments on: Design Monday #1 – Central Heating

By: Phil

Phil — Thu, 02 Jul 2009 14:16:14 +0000

As a heating engineer I have fitted a great many thermostats and programmers that do all of the above and more. I have also removed almost as many when human nature kicks in and a week later they pay me to take it out and fit the old fashioned dial type.

What is intuitive to use for a designer at a controls company may not be for an elderley couple. The controls are available to heat separate zones, outside temp compensation, etc, cost aside I could heat all your kitchen cupboards to different temperatures if you wanted. But people generally dont want that level of complexity because in a years time when their hours of work change they cant remember how to set the programmer and if they cant find the instructions they will have to pay for an engineer to come and switch it on or replace it.

You could fit the best controls in the world and regulate every room to a tenth of a degree but simply walking from room to room would destroy that and then the heating system would have to start all over again, I think you would use more energy moving heat around from zone to zone.

In most cases all the “fancy” controls on new boilers are bypassed and so that people can just use the room stat as an on/off switch, and hear that reassuring click in the process.

By: madteckhead

madteckhead — Thu, 12 Feb 2009 13:21:37 +0000

Perhaps a third button for ‘this feels good’, which keeps the room at the current temp.
Also i think the system should be automated… like smart fridges… that use sophisticated algorithms to learn what we like at different times. this should then be the default, with the three buttons for adjustment.
just my 2c after a glass of red

By: Kaleberg

Kaleberg — Tue, 03 Feb 2009 04:34:53 +0000

The default thermostat installed in American homes seems to be one of those programmable boxes with a system mode, desired temperature, current temperature and a couple of up/down buttons. Most have seven day programmability which tries to reach the desired temperature at the time you specify, so if you come home from work at 1730 you can leave the heat turned down and have it nice and toasty (or nice and cool) when you get in. Since I don’t have a regular schedule, this is worthless, but a lot of people like having the house warm in the morning, then again in the evening.
The algorithm is obviously tricky, since heating or cooling has to start at some time before 1730, and apparently they use predictive algorithms. There is one energy related trade off on heating if you have a heat pump. It is much cheaper to pump heat in from the outside, even on subzero days, than to use a resistive coil and generate heat. The latter process is faster. As it turns out, the units, even the under $100 units, have a hidden parameter which controls the threshhold for turning on the heating coils. To set it, you have to do some clever finger work on the touch pad, sort of like entering a cheat code in a gaming system. This gets you the extended control option set. Some of these parameters can damage your unit if they are set wrong. Luckily, the heating coil preference parameter is pretty straightforward.
I think there is room for improving this interface, but we haven’t tinkered with that parameter since we got it set right some years back.
I think there is a lot of potential for energy savings if systems were designed with multiple zones, or with mechanisms for simulating them. When you have several rooms in your house or apartment, you often want your sleeping area cooler than your living area. Right now, it is all or nothing, unless you pay the big bucks for a multiple zone system. I’m sure that this can be handled better with local in room controls and sensors. Given the costs of a new system, the marginal cost of putting in something beyond a basic heat register or radiator are probably low. If nothing else the sensor, computer and control system are likely to be modestly priced, and could communicate using WiFi or some other standard system if you don’t want to run wires.
I grew up in an old fashioned steam radiator building which meant it was overheated in the winter. Basically they set the boiler to blast the building with enough oomph to get the upper stories warm enough to satisfy the Board of Health. This meant that the lower stories were often horribly hot on the coldest days. (Granted, the Jack Frost frozen crystals on the single glazed window could be quite pretty, even if it was a sign of inadequate insulation.) Turning the heat down could be dangerous as it involved manipulating a hidden valve attached to a steam heated metal radiator. This kind of interface is still in use, for example in my sister’s 26 floor apartment building, and her place is hotter in the winter than in summer which implies some kind of interface breakdown, though I’m not sure of what.

By: Frankie Roberto

Frankie Roberto — Thu, 02 Oct 2008 09:27:06 +0000

We actually had a quite a lengthy discussion about whether it was better to leave the heating on permanently or not. A plumber had convinced James that it was more efficient to heat the home to a constant temperature, rather than allowing it to cool and then having to heat it up again. I can’t see how that can be the case though.
This link suggests having a ’set back’ temperature, to avoid cooling the house down completely and having problems with condensation: http://www.cmhc-schl.gc.ca/en/co/maho/enefcosa/enefcosa_004.cfm (mind you, this is for Canada, where it gets really cold).
I like the idea of using weather forecasts to have the timer come on early. The system would have to be able to calculate how long it takes to warm up from different starting temperatures though.

By: Evan Roberts

Evan Roberts — Wed, 01 Oct 2008 20:15:09 +0000

Actually thinking about it not switching the heating off is probably a huge waste of energy.
But it brings up another thought, should the central heating intelligently automatically come on earlier on those really cold days to make sure that the house is nice and warm when you get home.

By: Evan Roberts

Evan Roberts — Wed, 01 Oct 2008 19:19:42 +0000

As well as setting individual temperatures for each room/water-loop, it is not unusual to wish for separate on/off times as well. For example someone in at home may wish for their bedroom to only come on at night.
Taking it further, instead of on/off times you should perhaps be able to set different temperatures at different times. I guess this would all be controllable through the web interface.
Two functions we have here are “boost” and “advance”, the first switches for an extra hour
for each time you press it. “advance” which starts the next on cycle immediately.
A different question would be how much energy is actually saved by switching the boiler off during work/night, as the majority of the savings gained by being switched off are lost by having to reheat the house in the evening/morning. By having the heating always on (except for holidays), you could save in one respect by requiring a less powerfull heating system, and less radiators. Just a thought, probably not true. Depends on the power required for covering heat loss as opposed to increasing the thermal heat of the building.

By: Frankie Roberto

Frankie Roberto — Wed, 01 Oct 2008 17:23:43 +0000

Hi Tristan, sounds interesting – can you take a photo? I wonder why these more advanced types of interfaces don’t tend to be installed by default. Central heating systems are so expensive, you think it’d be a no-brainer to spend a bit more on a better interface.
I still think the ideal is to have a temperature display, and hotter/colder buttons in each room, so that you don’t have to worry about fiddling with individual radiator valves.

By: tristanf

tristanf — Wed, 01 Oct 2008 15:46:24 +0000

My thermostat does lots of that – it has a digital display showing the current temperature and +/- buttons to change the desired temperature (which is only shown as you adjust it). And it’s got a 7-day timer inc. settings for weekdays/weekends and individual days. You just leave the boiler on and then the thermostat is in series with it. It wasn’t particularly expensive, just bought from some DIY store and I even fitted it myself (which is impressive for me). But I like the idea of a web interface.