Low energy domestic buildings: the impact of mechanical ventilation and heat recovery (MVHR) systems

To date the majority of studies using low energy buildings for experimental measurements have looked at the buildings energy conservation and the reduction of energy use. Due to the stipulated and required airtightness levels within Approved Documents for the design and construction of low energy domestic buildings (LEDB), buildings with low ventilation will experience problems of moisture, and the indoor environmental quality (IEQ) of the building and its indicators (VOCs, CO2 (dilution ventilation), CO, RH, temperature) as well as introducing overheating during summer months. This study aims to focus on the impact of Mechanical ventilation with heat recovery (MVHR) on the indoor environment of LEDBs and how IEQ indicators and other indoor variables would impact on the functionality of the building and hence the comfort of occupants.

The principal aim of this proposed research is to advance the current understanding of, and improve the performance of domestic buildings through more efficient ventilation. It is hoped that an increase in low energy domestic buildings will improve energy conservation to meet government targets while avoiding adverse impacts on the indoor environment due to the required levels of airtightness. This project involves a detailed study of existing LEDB and new builds, investigating the ventilation, heating systems and other parameters – in relation to the impact of moisture transfer (e.g. mould growth), temperature and relative humidity (RH) patterns.

However, low energy homes/refurbished present a different challenge. In cases where new /refurbished buildings are designed with high levels of airtightness, adequate ventilation is increasingly relied on to ensure satisfactory indoor environmental quality (IEQ) and the removal of pollutants generated within a building, while minimising energy demand. It is therefore expected that mechanical ventilation with heat recovery (MVHR) would be applied.

Aim
The aim of this research is to determine how the interaction between occupants (householders) and MVHR systems could impact the IEQ and consequently developing a robust data set that will improve future interventions.

Objectives
The key objectives are as follows:
1) To investigate the extent to which MVHR systems influence the indoor environment of low energy domestic buildings.
2) To determine the performance of MVHR systems in the control of condensation formation risks and the removal of indoor pollutants.
3) To establish the design parameters of LEDBs that affects the relationship between the internal and external environments.
4) To improve the general understanding of the building performance through modelling, giving consideration to different climatic conditions. The model will be validated by experimental results to be obtained by monitoring at different locations within a LEDB.

METHODS
Experimental measurements will be carried out in occupied new/refurbished low energy domestic buildings. IES/TRNSYS simulation package is will be used to assess the performance of the building mechanical ventilation and heat recovery systems in this study. With this modelling software, the detailed analysis of the performance of LEDBs in relation to flow rates, indoor temperatures and possible humidity levels with respect to the climates across UK will be modelled and simulated. This is of immense importance to researchers and the building industry due to the lack of experimental data which would otherwise not be possible to obtain. In addition, the predicted mean vote (PMV) and the Predicted Percentage Dissatisfied (PPD), of the indoor environment can be modelled and predicted.