Variable Speed Drives

The installation of VSDs to fan and pump motors in their various applications in building services equipment provides a closer match between the motor speed and the output requirements, thereby reducing electricity consumption.

Estimates for the costs and savings associated with this technology were derived from data given in the NHS Energy Efficiency Fund (Final Report February 2015) and also data from EEVS’ database of energy efficiency projects in the NHS.

The cost and carbon savings associated with expected reductions in kWh consumption were extrapolated over time using the cost and carbon intensity projections provided by the DECC/HM Treasury Green Book guidance on valuing energy use and greenhouse gas emissions.

The resulting figures were sense checked by stakeholders with experience of building energy efficiency interventions.

Case study sources

NHS Energy Efficiency Fund Report

Green Book supplementary guidance: valuation of energy use and greenhouse gas emissions for appraisal

Financial Calculations


Energy savings were normalised using the energy spend of the NHS trust from which the various data sources were taken. This gave an average saving of £50,000 annually per trust based on the gas costs in 2015. Values were extrapolated over time using costs from the Treasury Green Book guidance.


Average capital costs per NHS trust normalised by energy spend were taken as £155,000.

Carbon Calculations

Average carbon savings per trust were calculated using carbon intensity projections from the DECC/HM Treasury Green Book guidance. In 2015, the carbon savings derived from the expected kWh savings were 300 tCO2 per annum for NHS Trusts.


Building energy efficiency interventions will have a wide variation in their scope, likely costs and savings, depending on factors such as the existing technologies and the funding sources used for the project. The results are therefore indicative rather than definitive, and are intended to give a sense of scale for the potential savings.