Modelling an air handling unit, building and occupant variation regarding energy, moisture and frost protection based on measurements of an air handling unit and occupants’ moisture supply

Abstract

AbstractObjectives of this paper are to propose a reasonable simulation model that can handle condensation and frost formation in heat exchangers dependent on moisture concentration and outdoor climate conditions, and to analyze risk of frost formation and discuss different frost protection strategies. Using psychometrics, American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) heat exchanger calculation, condensation and frost calculation methods, simulations models for heat recovery ventilation and energy recovery ventilation are developed. It is concluded that the risk of frost in heat exchangers is higher in northern Sweden than in southern Sweden and Denmark due to low outdoor air temperatures during the winter, however heat recovery systems in Copenhagen and Gothenburg still has a risk of frost formation even though these cities has relatively warm weather conditions. Out of several simulation models that are created during the study, the detailed model that takes condensation effect into consideration, is proven to be worthy to be used in further investigations, due to results that more accurately represent real word conditions. Risk of frost formation becomes significantly lower in every city when heat recovery ventilation is changed into energy recovery ventilation. Even though heat recovery ventilation is simulated only with the simplified model, it is safe to assume that it will still be effective in reality. Although bypass strategies were effective at eliminating the risk of frost in heat recovery units, they are not as efficient from an energy perspective. The more air is by-passed through the cross-flow plate heat exchanger, the fewer opportunities there are to recover energy from exhaust air, which leads to lower supply air temperatures and higher energy need for heating a living space.