Modelling an air handling unit, building and occupant, regarding energy, moisture and frost protection

• Main Author: Daugela, Marius
• Format: Other/Unknown Material
• Language: English
• Published: Lunds universitet/Avdelningen för Energi och byggnadsdesign 2022
• Subjects: Technology and Engineering; Kiruna
• Online Access: http://lup.lub.lu.se/student-papers/record/9103591

Frost formation in heat exchangers is an often accruing issue in cold climates. The aim of the project is to calculate the risk of frost formation in different Swedish cities by modeling vapor and frost behavior in heat exchangers. Objectives of this paper are firstly, to analyze selected indoor and outdoor climate conditions, secondly, to propose a reasonable simulation model, thirdly, to analyze risk of frost formation and discuss different frost protection strategies. Using psychometrics. ASHRAE heat exchanger calculation. condensation and frost calculation methods, heat plate exchanger and enthalpy wheel were simulated using Python programming language. Calculations were done using two methods. The first method was to take the heat exchanger as a whole. using efficiency as a static number for simplification purposes. The heat exchanger was assumed to be a dimensionless unit. Using this type of approach. the performances of the crossflow plate heat exchanger and enthalpy wheel were simulated for every hour of the year. The second method was to simulate the crossflow plate heat exchanger in more detail. A two dimensional model was subdivided into small squares. Subdivision of the heat exchanger module allowed to simulate the exchanger in greater detail to see where the condensation and frost happened and if it blocked exhaust airstreams. The calculation of the heat exchanger module was done in the following steps: The first step was to divide the U value according to the subdivision of the heat exchanger. Then, estimated flow rates were subdivided accordingly. Then, each subdivision was considered as a ’’small’’ independent exchanger, while the whole module was considered as a chain of many small exchangers. Putting the values into matrixes made it possible to analyze data for every hour of the year. It was concluded that the risk of frost in heat exchangers was highest in Kiruna and Ostersund due low outdoor air temperatures during the winter, however heat recovery systems in Copenhagen and Gothenburg still ...