Tuesday, 11 September 2012

What could smart heating controls do for me?

We had our question time on home heating last Thursday and I still can't say I fully understand heating systems but judging by the questions I don't think very many other people do either, even though every home has one and its function is so very important for our personal comfort. Heating systems have evolved drastically over the last few decades and they are now more efficient and controllable than before. We started with timers and a room thermostat, then we added thermostats on the radiators for per-room control. The current building regulations require at least two heating zones, each with a separate timer and thermostat so you can run your bedrooms and your living or work areas differently. At the top end you can now get smart controls which turn down the heating when there is no one in the room, interlock with doors and windows to reduce heat loss when they are open, prioritise areas with high heat demand and automatically adjust the radiator temperature according to heating requirement. These controls are not just gimmicks: smart controls have been shown to save 20% of heating costs [1]. Much of what they do we could do for ourselves if we took the trouble. However, most of us would rather not have to give the heating that much of our attention.

Space heating uses on average 2/3 of our home energy and, although many people use gas which is relatively cheap and low in carbon emissions, this is still a very significant portion of our fuel bills. Before central heating it was usual to heat only a few rooms - perhaps just the kitchen and living room. With central heating the default is to heat the whole house but this uses a lot of fuel. Turning down the thermostat by just 1C is supposed to save you up to 10%. Dropping the temperature by 2C in half the house would save a similar amount. If you put a programmable valve (for  example from Pegler Yorkshire) on all your radiators you can run every room independently - effectively each room is a different zone - and save more.

There are different ways to manage the heating so that you can control the timing and temperature independently in different rooms:
  • Manually - by twiddling the radiator valves up or down as you enter and leave the rooms
  • On a programmed timer - using zone controls
  • Automatically in response to your activity - using smart controls with presence sensors in each room
Unfortunately none of these arrangements are perfect and which is better for you depends on your activity and preferences as well as your house.

The trouble with the manual system is that it requires frequent attention. Also you would have to get to know your house quite well, so that you can know how much you can turn down the radiators without the room getting so cool that you can't heat the room again reasonably quickly. Heating the air in a room takes very little time - the problem is that you have to heat the walls, floors and ceiling and everything in the room too. The structure and contents of houses are very variable and some houses take much longer to warm up than others. You can shorten the reheat time by adjusting the radiator temperature to be hotter - but this will make your condensing boiler run less efficiently. You don't want to be fussing with the boiler thermostat as well as the radiators.

The programmed timer system works well only if you are consistent in your patterns of room use - and if you can understand the programming system. Most people find this quite hard because controls usually have appalling user interfaces. [2]

The smart control system is better than the manual system in that you don't have to keep remembering to do things, and the reheat problem can be partially solved by a load compensation system which increases the radiator temperature just for a short while until the room is close to the target temperature.

Suppose you are going out for the evening. If you do this 2-3 evenings a week you could make significant savings by not heating the house when it is empty.
  • If you rely on a manual system, you could turn down the central thermostat or even switch the heating off altogether. You have to remember to do this, and you will come back to a cold house.
  • If you are using a programmed timer, then if this is a regular event you could incorporate this into your program and even arrange to have the house warm again before you get back. If you are not so predictable and you haven't programmed this in, then by default you will heat the empty house.
  • If you are using a smart control system, your absence will be detected and the heating turned down a bit (though probably not as much as with the timer). When you come back the house will be a bit cool but should warm up reasonably quickly.

Smart controls are probably better for most people and perhaps not quite as expensive as you would think even though a lot of wiring is involved. I have been advised the cost would be around £1500 to retrofit in an average house. Given that the average heating bill is around £700, a 20% saving would pay back in about 10 years. That is comparable with solid wall insulation [2] and distinctly better than double glazing but poor compared to cavity wall or loft insulation which pay back typically in 1-4 years.

Your actual savings would depend also on how you use your house. If you have children who spend most of their time in their bedrooms then you use most of the house most of the time and you won't be able to save very much. On the other hand if there are only one or two of you, and especially if you are sociable and spend a lot of time together, or out of the house, then you could save a lot.

If you don't want to splash out on smart controls, then it is probably worth poring over the instruction manual of your heating controller or watching the videos [2] because getting good performance from a condensing boiler manually is a balancing act and not something you want to be fussing with throughout the day. Let's not all try to be heating engineers. If you don't have a condensing boiler - well then you presumably aren't too worried about energy efficiency anyway.

[1] The EN 15232 standard defines different levels of heating control and how much fuel savings you can expect at each level. The reference standard is C which includes thermostatic valves on radiators and a boiler control system with weather compensation - setting the radiator temperature higher when the weather is very cold, and lower when the weather is mild. Level A including coordinated room heating with presence sensors, interlocks with doors and windows has been shown to save typically 20% in a residential setting or a school. It saves even more in offices and retail/warehouses. Here is an overview of the standard from Leonardo Energy.

[2] Here is a depressing discussion thread about boiler controls on the diynot forum:
Combi Heating Control Programmer advice
Some controller manufacturers like Worcester Bosch and Heat Miser publish video demonstrations of how to use their systems, perhaps for advertising, but presumably also in an effort to reduce the number of support calls.
The e-TRV electronic thermostatic radiator valve www.etrv.co.uk is another example. This device gives you remote control of your thermostatic radiator valves; with just a single button push you can switch your radiator temperature to 'low', 'eco' or 'comf' . You can also configure those settings and set up a program timer. However, the remote control has no display screen - all the feedback on the settings comes from flashing leds on the valve: one flash for Monday, two for Tuesday ... A time check involves a sequence of 4 sets of flashes and pauses. A temperature readout involves red flashes for the actual temperature and green flashes for the set temperature: 1-8 flashes for 16-18C.

[3] Energy saving Trust on Solid wall insulation

1 comment:

  1. Have you seen http://www.nest.com/ ?
    Supposedly very good at learning, with a simple UI. Expensive, and American-centric, but it will be interesting to see if comparable EU devices follow.
    (Can be used in the UK, but not simply - http://diy.stackexchange.com/questions/12620/would-the-nest-thermostat-work-outside-us )


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