The passive house (PH) standard is seen as the future minimal requirement for buildings in Norway, where a specific definition has been developed (NS 3700). Nevertheless, the relation between this standard and air heating (AH) is not clear while both concepts are often associated. The present contribution investigates challenges for AH in terms of thermal dynamics (e.g. temperature distribution and control) as well as the feasibility of the AH concept. This is done using detailed dynamic simulations on a typical detached house typology. Results show some limitations of the AH concept in Nordic countries, as well as provide guidelines for the design procedure.
Freeze protection in ventilation systems is important to avoid freeze damages and increase in maintenance costs. Freezing in a ventilation system can appear in construction and operation phase. The aim of this study was to test a new method for freeze protection in ventilation system. This method implies use of an additional heat exchanger. The method used two hydronic circuits: the first one with water on energy supply side, and second one with mixture of glycol and water at the secondary side. The mixture transfers heat from the energy source via an additional heat exchanger to the coil in the air handling unit (AHU). AHU with freeze protection from a manufacturer was tested in the laboratory. Since it was not possible to obtain a supply air temperature of -20 oC in the laboratory conditions, a model was developed on the MATLAB\Simulink platform. Several operation scenarios were tested on the Simulink model and they included use of three types of energy sources: boiler, heat pump, and district heating with outdoor temperature compensation. Results showed that even new method with mixture of glycol and water could tolerate low air temperature, the AHU would require known sequence control for freezing protection, where the circulation pump between energy source and heat exchanger starts first. This sequence control is necessary regardless of energy source. Finally, the article gave recommendations on how to define sequence control to avoid freezing in AHU.
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.