1. Comfort-taking, rebound and backfire Jenny Love UCL Energy Institute PEB:D3 29 November 2011

2. Modelling retrofit of dwellings a) Heat loss parameter W/m 2 K or b) Heating system efficiency % or Total efficiency of dwelling = a/b Heating energy use KWh/year

3. Heating behavioural variables Heating period(s) Number of heated rooms Setpoint temperature Physical variable Fabric heat loss parameter or Heating system efficiency or Heat loss/heating system efficiency Dynamic model (Energy Plus) Heating energy use Now visualise the results… Window-opening (later) Variables

4. Fabric heat loss parameter (HLP) = 71 W/KFabric HLP = 437 W/KFabric HLP = 634 W/K Building fabric heat loss 23°C 20°C 16°C Results: varying fabric efficiency

5. Results: varying heating system efficiency

6. Results: varying overall efficiency

7. Summary graph

8. Longitudinal trajectories – i.e. retrofit Partial retrofit could lead to energy saving, no energy saving, or increased energy use. Deep retrofit should lead to energy saving whatever the change in heating behaviour. The green line ‘bounds’ energy use.

9. Caveat: Window-opening behaviour Caveat to caveat: this piece of modelling contains so many assumptions it is now quite far removed from data. Heating energy use KWh/winter Efficiency of dwelling

10. Conclusion There is potential for heating energy use to increase as we make dwellings more efficient. Retrofit deeply to try to achieve robustness against behaviour change – either as a result of retrofit, or change of occupancy, or evolution of behaviour. Window-opening behaviour needs more data before being able to be realistically modelled, but an initial attempt yields large potential variation in energy use which could undermine efficiency measures. Thank you