Energy-led retrofitting of solid wall dwellings: technical and user perspectives on airtightness

Purpose – 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. However, the airtightness of a dwelling is a crucially important factor governing the achievement of CO2 reductions, and the purpose of this paper is to understand the technical implications of airtightness levels in an experimental dwelling, purpose built to typical 1930s standards, at the same time as gaining the users’ perspectives on airtightness and ventilation in their homes. Design/methodology/approach – In-depth interviews were carried out with 20 households to collect information on their retrofit and improvement strategies, attitudes to energy saving and their living practices as they impinge on ventilation. The experimental house was sealed in a series of interventions, leading to successive reductions in the air permeability as measured by a 50?Pa pressurisation test. The behaviour of a whole-house MVHR system installed in the experimental house, was simulated using IES Virtual Environment, using a range of air permeability values corresponding to those achieved in the retrofit upgrading process. Findings – In the house considered, air permeability must be reduced below 5?m3/m2h for MVHR to make an overall energy and CO2 saving. However, to achieve this required a level of disruption that, on the basis of the views expressed, would be unlikely to be tolerated by owners of solid wall dwellings. Originality/value – The paper is the first to combine results from a user-centred approach to exploring the existing practices of householders with a simulation of the energy and CO2 performance at different levels of airtightness of an experimental house in which MVHR has been installed

Energy-led retrofitting of solid wall dwellings - technical and user perspectives on airtightness

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. In parallel with a survey of householder preferences and practices, the behaviour of a whole-house MVHR system installed in an experimental house, purpose built to typical 1930s standards, has been simulated. The range of air permeability values corresponded to those achieved in a retrofit upgrading process carried out on the house. In the house considered, air permeability, as measured in a 50 Pa pressurisation test, must be reduced below 5 m3/m2.h for MVHR to make an overall energy and CO2 saving. This required a level of disruption that would be unlikely to be tolerated by owners of solid wall dwellings

Energy-led domestic retrofit: impact of the intervention sequence

Interviews conducted with householders reveal that energy efficiency is often a lesser motivation than other factors for undertaking home improvement work. Homeowners' approach to refurbishment is typically staged over several years, not as a whole house retrofit. As the operational performance of an individual emission-reducing technology typically depends on what other measures are already in place, the retrofit intervention sequence can potentially affect the overall performance of the dwelling. The impact of the intervention sequence on a semi-detached 1930s house is investigated with dynamic thermal modelling, using five sequences based on different homeowner personas developed from qualitative interviews. The results show that, whilst a whole house retrofit would reduce cumulative CO2 emissions over 25 years by 54%, the sequences actually implemented by the individual households result in significantly smaller reductions of between 42% and 24%. This variation in operational performance due to the intervention sequence means that there is a variable return on the investment for a particular technology and, significantly, that different sequences will yield different cumulative emission reductions. This has significant consequences for policies providing financial incentives for energy-led retrofit, particularly to include the intervention sequence and timing