Abstract

Realisation of Zero Energy Buildings (ZEB) for residential use cannot succeed without: minimising leakages, increasing thermal insulation and using reliable and energy efficient system solutions. However, very airtight houses may have a negative impact on thermal comfort and indoor air quality. Focussing on ventilation systems then becomes a requirement.

In cold climates, temperature differences between indoor and outdoor air often exceed 40 °C during winter. State-of-the-art heat recovery systems may not be able to handle these differences while providing proper air quality and preventing excessively dry indoor air.

The present study of energy recovery systems focuses on apartment buildings located in cold climates countries using central air handling units. Heat exchangers recovering sensible heat are compared with energy exchangers with recovery of both sensible and latent heat. For the latter, both adjacent and non-adjacent solutions are considered.

A specific net energy savings factor is developed taking into account the energy recovered, but also the pressure drops and the variation on the effectiveness of the fan given the installation of the heat/energy recovery.

Heat exchangers are efficient and reliable. Recuperative heat exchangers normally imply no air quality problems, but have severe freezing problems. Regenerative heat exchangers encounter small freezing problems, but do not prevent transfer of odours from extract air to supply air. Regenerative energy exchangers provide an efficient heat and moisture exchange between exhaust and supply air flows, diminishing ice formation and the humidification requirement for indoor air.

Realisation of Net Zero Energy Buildings (NZEB) for residential use depends on, among many other things, minimizing air leakages. However, very airtight houses will have an increased risk for problems regarding indoor humidity, thermal comfort and indoor air quality. Focusing on ventilation systems becomes a requirement in this situation. For cold climates, mechanical ventilation systems are the state of the art solution and in order to achieve a further reduction in energy use, the focus must be on efficient energy recovery. This paper focuses on a quasi-counter flow membrane-based heat and moisture recovery system for cold climates such as the Norwegian climate. The membrane separates the two air streams and allows both heat and moisture transfer. Its effectiveness is crucially depending on the heat and mass transfer resistance of the membrane that separates the two air streams and therefore the characteristics of membranes have to be deeply analysed. To analyse the membrane, this study starts with a detailed theoretical study of the forces governing transfer through membranes. A literature review of available measurements for membrane resistance is performed. Following this, heat and mass transfer in selected types of membranes will be measured in order to validate the results of the theoretical analyse. The conclusion to be taken from this study is the selection of the characteristics of the most suitable membrane for a residential heat and moisture exchanger in cold climates.