Heating Older Houses

As some will be aware I am in the process of monitoring my domestic heating system, with the intention of developing a heating controller that offers better performance than the existing timer/thermostat one that is fitted.

The Navitrino has now been running for a few days, logging the outside temperature, the living room temperature and controlling the boiler so as to keep the living room temperature between comfortable limits.

The graphs show the variation in inside and outside temperatures over 31st October and 1st of November. On the 31st we had the woodstove blazing - not a very controllable heatsource - thus the peak of 24C and the slow cooling back down to 18C over a period of 16 hours. During this time outside temperatures were fairly mild - between 6 and 12C.

I believe that the thermal demands are unique to each property, which coupled with widely different lifestyles and levels of occupancy mean that there is no "one size fits all" solution to domestic heating control.

I have already written some control software, to control the heating, and found it convenient to split the day up into 3 time periods - loosely called Day, Evening and Night corresponding to periods of occupation and activity. For example in the evening when the living room is normally occupied, 20C is a comfortable temperature, whilst during the day 19C may be more appropriate. At night time, when the livingroom is unoccupied it may be acceptable to relax the temperature requirement to 17C, which allows more economical use of gas, but allows for a relatively quick warm-up.

The first stage is to monitor the thermal profile of the house, and the boiler behaviour and gas usage, for different external temperatures and generate a simple model of the thermal behaviour of the property.

My house has solid 9" walls and 4" internal brick walls. The living room has a large chimney breast which also retains a fair amount of heat.

What I hope to establish is a series of warm-up times, based on a given starting room temperature and setpoint versus the outside temperature.

Once the thermal mass of the room has been warmed up, the house will take much less heating power to keep it at the comfortable temperature.

For example, yesterday lunchtime between 12 and 1pm, it took 27kWh of gas to raise the room temperature from 17C to 20C. Once warmed up, the 20C room temperature could be maintained for the rest of the day and overnight with just 3kW heat (57kWh energy). During this time, the outside temperature varied between 12C and 9C - so not particularly cold.

The intention is to repeat these measurements for a range of outside temperatures. What is likely is that the 1 hour/ 27kWh "boost" heat will become longer in duration and use more kWh as the outside temperature falls.

I should mention that the heating system at the moment consists of 3 room radiators - with TRV, a bathroom towel radiator and 25m2 of underfloor heating. This heats the living room, kitchen, bathrom, my work room and 1 bedroom on TRV set to low. These rooms we consider to be the core of the house, leaving hall, and unused spare bedroom not directly heated.