Monday, January 09, 2006

Too Hot Here, Too Cold Then, Too Little Control!

I think we've probably all experienced that situation of having one room too hot, another too cold, and the house being heated when not needed, and not heated when we want it!

So, one area I can attack is to find out what I can save by improving my central heating control system. Let's start by having a look at what I've got, what it does, and what I'd like it to do.

I currently have digital thermostat controller with the following features:
  • it allows me to programme 6 different time periods at different target temperatures for each of 7 days of the week,
  • "holiday mode" - sets a constant reduced temp of my choosing for however many days I specify)
  • "sick mode" - press a button, and it'll use Sunday's settings for the rest of today - rather dumb considering that none of my days of the week is the profile I'd have if in all day!
  • "party mode" - extends the last time period by however many hours you want, so if you have a party, you can just add some 'warm hours' to the day.
In addition, each room radiator has a reasonably modern thermostat (radstat), that with a bit of effort I can get to behave.

Unfortunately, it's not designed as a system! It has the following notable drawbacks:
  • The main digital thermostat is in my hallway, so it relies on the hallway radstat being open a reasonable amount for other rooms to get warm.
  • The radstats are simple and have no variation... they're completely independent of the main controller.
  • The main controller, while being very clever, and the best I've ever had, is too clumsy to operate (and it's good by comparison). It's rather like old video recorders.
What I want is a heating control system that does the following:
  • It senses where people are and prioritises heating to those rooms, allowing other rooms to stay cooler, and therefore loose less heat through the walls.
  • In each room, it integrates with the alarm clock, warming the room ready for when a person gets up (and poss lighting the room or opening blinds). A simple wall mounted interface would allow the alarm clock to be silenced once out of bed, so it can learn when the target temperature is needed. Or, a motion or floor pressure sensor would detect when someone is out of bed.
    This alarm clock feature allows the heating to be set without even realising we're changing it. And... on a weekend, when no alarm is being set, a default could kick in at a lower target temperature.
  • Morning routine is complimented by having other rooms in the house, such as the kitchen warmed up in time for the earliest riser of the household.
  • Once people are up, a daytime mode starts, where the system detects who is where, and maintains a comfortable room temperature in the active rooms. Naturally, the bedrooms would probably be left to cool.
  • Control panels in all rooms would allow simple room by room overrides, allowing the occupant to indicate to that controller that they want the room at a given temperature for a given amount of time.
  • Lastly... budget. The heating control system would preferably be able to be given a budget (e.g. 20% less gas than last month), and adapt temperatures and timings accordingly. A system that fits within hard boundaries would be excellent for having people learn to do the obvious (go to bed earlier in winter, put on a sweater, indulge in some heat generating activity, etc.)
  • And... measurement. An intelligent control system should be able to measure heat delivered to each room (volume of water * temperature difference from one end of radiator to the other). This can then indicate which rooms are consuming the most heat, and would therefore most benefit from improved insulation. This in itself could be a system that can be temporarily installed once someone is using an intelligent system. Also, if the valves are all controlled centrally, then having only one open at a time would allow the proportion of flow to each room to be measured, and the temperature change could also be measured at the boiler. In effect, the control system heats only one room at a time, and either measures the temperature difference at the boiler, or the gas flow rate. All that would be needed is a flow meter and two temperature sensors. The rest is just maths.

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