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Dr Anne Stafford
MSc Materials Technology, PhD Fuel Cell Technology (Napier)
Research Fellow
a.stafford@leedsbeckett.ac.uk

Dr Anne Stafford

Anne has a background in Physics and Materials with technical research experience in a number of renewable energy technologies, including solid oxide fuel cells, photovoltaics and heat pumps. Current interests are focussed on technology field trials, performance and energy monitoring, refurbishment strategies and thermal comfort.

She is the author of the Welsh PV Solar Energy Road Map, and also the UK PV Solar Energy Road Map (the latter produced in conjunction with the Photonics Knowledge Transfer Network).

PUBLICATIONS

Electrical Load Characteristics of Domestic Heat Pumps and Scope for Demand-Side Management. P. Boait and A. Stafford, Proc. CIRED 21st Int. Conf. on Electricity Distribution. Frankfurt, June 2011.
Abstract:
Domestic heat pumps are a key part of the UK Government’s decarbonisation strategy and are expected to form a substantial part of national electrical demand by 2050. This paper reports on the practical performance and electrical load characteristics of a group of ten heat pumps over an annual cycle. The variation of electrical load with ambient temperature and domestic hot water usage is explored and useful opportunities for demand side management are identified. 

Performance and Control of domestic ground-source heat pumps in retrofit installations. P.J. Boait, D. Fan and A. Stafford, Energy and Buildings 43 (2011) 1968–1976.
Abstract:
Heat pumps are an essential technology for decarbonisation of domestic heating in the UK. This paper reports on the performance in use of a group of ground-source heat pumps, and in common with other UK studies finds that the seasonal performance is not as good as that reported in trials from continental
Europe and that the system controls are unsatisfactory. Control improvements are investigated via a model of the dwelling and heat pump as a combined system, from which the thermal time constant of the building is identified as a critical factor that needs to be considered in retrofit projects incorporating
heat pumps. The validity of the conventional practice (and advice from installers to users) of allowing heat pumps to run continuously is tested and bounded. Techniques for improving control are outlined and reasons for the poorer performance in the UK examined with the conclusion that heat pumps need
to be better matched in capacity and control to the size and thermal characteristics of UK dwellings. Implementation of these findings by heat pump manufacturers and installers could promote a more rapid transition to renewable heat both in the UK and internationally wherever similar housing stocks and climates exist.

Long-term monitoring and performance of ground source heat pumps. A. Stafford: Buildings Research and Information, Vol 39, Issue 6, pp566-573, 2011.
Abstract:
The results of a full annual cycle of detailed monitoring of ten domestic GSHP systems installed in similar properties are presented. The monitoring scheme used was designed to allow full characterisation of the system, including monitoring of the heat supplied by the pump to both space heating and domestic hot water (DHW), and also monitoring of the energy consumption of the various heat pump constituents. This approach is contrasted with a more commonly adopted approach where SPF values are obtained without invading the heat pump enclosure. A number of issues are discussed which can lead to significant inconsistencies in the latter approach. Quantitative differences in the SPF obtained by the two methods are calculated or estimated for the monitored systems. Generally, the simpler approach leads to underestimation of the SPF by an amount which is variable and dependent on factors such as DHW usage, pump settings and precise meter locations.

Predicting In-situ Heat Pump Performance: An Investigation into a Single Ground-Source Heat Pump system in the context of 10 similar systems. A. Stafford and D. Lilley. Energy and Buildings
Abstract:
Ten similar ground-source heat pump systems installed in small rural social housing bungalows in the UK have been monitored in detail over a period of more than one year. The purpose of the present work was to take one system at random, and study its performance characteristics in the context of the group, in order to explore the potential for predicting performance from a few readily obtainable parameters. The chosen system performed relatively well in summer and relatively poorly in winter (despite an average temperature lift for space-heating). This was found to be readily explicable in terms of domestic hot water set-point temperature, and compressor cycling behaviour. The latter may be affected by building fabric issues, or by user behaviour (e.g. window-opening). The study suggests that where sizeable groups of similar systems are installed in similar buildings (e.g. by social housing providers), an appropriate monitoring strategy may be to monitor a sample of installations in detail, and  to predict the performance of the remainder based on  limited but more easily obtained data. However, the limited dataset may need to include internal and ground-loop fluid temperatures, heat pump electricity consumption, and some detailed knowledge of building fabric and occupier practices.

The Effects of Weather Conditions on Domestic Ground-Source Heat Pump Performance in the UK. A Stafford. Accepted for SEB12 International Conference, September 2012, Stockholm, and to be published as a book chapter.
Abstract:
Unpredictable and variable weather is often cited as one of the factors which may contribute to the underperformance of heat pumps in the UK, compared with other European countries. In this study, 10 similar ground-source heat pump systems, installed in existing social housing in North Yorkshire, were monitored intensively over a period of almost two years. A weather station, closely co-located with six of the ten dwellings, was also established giving data on local external temperatures and other parameters. Differences in the performance characteristics of the heat pump systems over 2010 and 2011 are assessed with particular reference to differences in local weather conditions.

Article title: Production Efficiency of Hot Water for Domestic Use,Reference:: ENB3797 Journal title: Energy & Buildings. P. Boait, D. Dixon, D.Fan and A.Stafford. Accepted manuscript (unedited version) available online: 23-JUL-2012
DOI: http://dx.doi.org/10.1016/j.enbuild.2012.07.011