So the results of the initial heating system analysis are in…for this analysis I haven’t carried out any behavioural or zoning analysis or changes to the shower heads.  The model therefore has the whole house heated to 21 degrees – 2 heating times during the week and one longer one on weekend days.  For each system I have modelled putting in modern controls appropriate for the system i.e. thermostats, radiator valves, boiler interlock

To begin with I looked at 9 different major changes to the current heating system (electric storage heaters supplemented by gas room heaters on the ground floor):

1. A top specification condensing combination boiler for a radiator heating system and hot water
2. As 1. but with the addition of a weather compensator
3. A top specification condensing boiler with a modern fully lagged 200litre cylinder and lagged pipework for a radiator heating system
4. As 3. but with the addition of a weather compensator
5. As 4. but underfloor heating
6. An air source heat pump system for the heating and hot water (coefficient of performance used – 2.5)
7. As 6. above but using the average coefficent of performance found during recent Energy Saving Trust fieldtrials – 1.94)
8. As 7. above but with the heat pump for heating only.  The hot water being provided by an electric immersion heater.
9. As 7. above but with an estimate of the Renewable Heat Incentive payments based on original consultation figures.

Here I have compared the different predicted total CO2 emissions for each type of system. Again it is worth stressing that the rest of the building remains unchange – i.e. superUNinsulated! What this shows us is that the gas boiler systems are predicted to roughly half the emissions (or over half when you take into account that some of the emissions are due to lighting and appliances). The air source heat pumps are predicted to reduce the emissions by about about 2/5 unless the hot water is provided by an immersion heater.

Another way of showing this is to concentrate on the CO2 savings – these are expected to range from between just over 6 to around 8 tonnes (excluding the immersion heater for hot water no.8). This really highlights why the strategy of working out the heating system and then including in the base before evaluating other insulation measures is a good idea.

The boilers obviously use gas and the air source heat pumps uses electricity. The system being replaced uses gas and electricity for heating and gas for hot water. This chart shows the expected savings from the different options. The higher coefficients of performance of the air source heat pumps are offset by the much higher cost of electricity compared to gas. Option 9. stands out as an outlier and is very high as it includes a large annual payment that might be possible under the Renewable Heat Incentive. This payment will come from the ‘energy companies’ who will have to pass it on to all consumers. We’d be interested in your thoughts on these payments taking into account the large capital costs that only some people will be able to afford.

I’ve taken some rough estimates for the different heating and hot water system options. These are obviously rough estimates as I haven’t yet been able to really investigate the property and work out exactly what is required. The gas boiler with radiators is the cheapest and the air source heat pump with underfloor heating is much more expensive.

Here is the results of dividing the estimated cost by the estimated savings. The gas boilers with radiators have a payback range of between about 13 and 15 years. The air source paybacks are positive when the manufacturers COP is used but negative when the average COP from the EST field trials are used – and that is compared to the current heating system. The potential Renewable Heat Pump payments skew 9 considerably.