1. Nick Kelly, Paul Tuohy, ESRU
SIMULATION-BASED PERFORMANCE ASSESSMENT OF PHASE-CHANGE-ENHANCED THERMAL BUFFERING FOR DOMESTIC HEAT PUMP LOAD SHIFTING
Building Simulation 2013
The 13th International Conference of the International Building Performance Simulation Association, Chambéry, August 2013
Nick Kelly, Paul Tuohy, ESRU

2. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Overview
in UK heat pumps (HP) promoted as low-carbon heating source and potential replacement for gas boilers
potential problem for low voltage network at times of peak demand
load shifting a possible solution
HP load shifting requires use of buffering
presentation covers performance assessment of buffered domestic HP subject to load shifting
buffering with and without PCM
single and aggregate performance compared to unconstrained, unbuffered operation

3. Why Load Shift Heat Pumps?
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Why Load Shift Heat Pumps?
shift
shift

4. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Previous Work
Hong et al. (2013) looked at ‘flexibility’ of HPs in UK dwellings
ability to time shift HP
without affecting end user
time shifts of hours with no buffering
6 hours possible but only with 500 L buffer and passive house insulation levels
Arteconi at al. (2013) found even larger volumes required for conventional UK housing – 800 L per hour of ‘autonomy’
key questions:
could the use of PCM improve the situation?
how does load management and buffering affect performance?
Hong J, Kelly N J, Thomson M, Richardson I (2013) Assessing heat pumps as flexible load, Proceedings of the IMECHE Part A: Journal of Power and Energy, 227 (1), pp
Arteconi A., Hewitt N.J., Polonara F. (2013) Domestic demand-side management (DSM): Role of heat pumps and thermal energy storage (TES) systems, Applied Thermal Engineering, 51, pp

5. Model Basis of work ESP-r model of a UK detached dwelling
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Model
Basis of work ESP-r model of a UK detached dwelling
136m2 of floor area
modest thermal upgrading (floor, loft, cavity wall insulation)
family of 4
equipped with buffered and unbuffered 11kWth ASHP heating system
replaces gas boiler heating system (retrofit)

6. Heat Pump System Buffered & Unbuffered
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Heat Pump System Buffered & Unbuffered

7. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Model - Storage
Padovan R and Manzan M, Development of a stratified tank storage component for ESP-r with embedded phase change material modules, Proc. of the IMECHE Part A: J of Power and Eng. 2013; v227;1: pp

8. Model PCM commercial inorganic PCM
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Model PCM
commercial inorganic PCM
PCM Products,

9. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Load Shifting Method
operating time of heat pump fixed to off-peak UK Economy 10 periods
size of tank and % of PCM (by volume) varied
performance simulated over cold winter week with northern UK climate
delivered space temperatures and DHW temperatures compared to no load shift case (% occupied time below 18oC and 40oC, respectively)
tank size and PCM % identified for near identical end user service provision (same service provision as no load shift case)
case of 50 buffered heat pumps operating freely and under Economy 10 investigated

10. Load Shifting Method Heat Pump Operating Periods Ref. 6-9hrs Reference
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Load Shifting Method
Heat Pump Operating Periods
Ref.
6-9hrs
Reference
16-23hrs
Economy 10
0-5hrs
13-16hrs
20-22hrs
Time 12 24

11. Technical Performance
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Technical Performance

12. Technical Performance
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Technical Performance

13. Technical Performance
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Technical Performance

14. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Overall Performance

15. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Overall Performance

16. Aggregate Performance (Economy 10)
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Aggregate Performance (Economy 10)

17. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Conclusions
the heating demand of a typical UK detached dwelling can be completely shifted to off peak (Economy 10) periods
significant amounts of buffering required (1200 L)
the use of PCM more than halved the volume of thermal buffering required for effective load shifting
but …
energy use was significantly higher than in the reference case (no buffering, no load shifting)
emissions are higher than with no load shifting
running costs are higher than in the no load shifting case

18. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Conclusions
population of 50 ASHPs constrained to operate in low-tariff periods
peak demand increases due to Economy 10 timings reducing operating diversity (esp. mid-day and evening periods)

19. Caveats … one case and one HP configuration NOT an optimised system
Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Caveats …
one case and one HP configuration
NOT an optimised system
scope for improvement in buffered system energy performance
emissions results based on 2011 CO2 intensity data
financial results based on existing Economy 10 tariff
relatively crude load shifting strategy employed in HP population study
more sophisticated load control would not give the same result

20. Kelly, Tuohy 2013: Load management of heat pumps using phase change heat storage
Thank You!
The simulation work described in this presentation was done with the support of the SUPERGEN Highly Distributed Energy Futures research consortium (HIDEF). The authors gratefully acknowledge the funding and support provided by the UK Research Council’s Energy Programme under grant EP/G031681/1.
The authors also wish to acknowledge the assistance of members of IEA ECBCS Annex 54 for their help and useful input to this work.