The potential for energy saving in existing solid wall dwellings through mechanical ventilation and heat recovery

Panel: 6. Innovations in buildings and appliances

This is a peer-reviewed paper.

Authors:
Phillip Banfill, Heriot-Watt University, United Kingdom
Sophie Simpson, School of the Built Environment, Heriot-Watt University, United Kingdom
Mark Gillott, School of Architecture and Built Environment, University of Nottingham, United Kingdom
Jennifer White, School of Architecture and Built Environment, University of Nottingham, United Kingdom

Abstract

Mechanical ventilation with heat recovery (MVHR) is increasingly being promoted in the UK as a means of reducing the CO2 emissions from dwellings and installers report growing activity in the retrofit market. The behaviour of a whole-house MVHR system installed in an experimental house, purpose built to typical 1930s standards, has been simulated, at a series of air permeability values corresponding to those achieved in the retrofit upgrading process. There is a critical value below which the air permeability, as measured in a 50 Pa pressurisation test, must fall before MVHR makes an overall energy saving. In the house considered this is 3 – 5 m3/m2.h (4 – 6.5 ach-1), although more significant savings of 9-12% are achieved when the air tightness is improved to Passivhaus standards of 0.63 m3/m2.h (0.6 ach-1). When the CO2 emissions are considered, the air permeability needs to approach Passivhaus standards to ensure an overall reduction, because the electricity needed to run the MVHR system has a CO2 intensity almost three times that of the gas used to heat the house. Airtightness is a critical factor in achieving energy and CO2 reductions and it is easy for designers to over-estimate the potential savings.

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