Inkludering av mikroklima i simuleringsmodeller for bygninger | Introducing microclimate into simulation models for buildings

Bærekraftig utvikling krever høyytelsesbygninger. Smarte løsninger i prosjektering av nye bygg og rehabilitering av eldre bygg kan bidra til å redusere energiforbruk og klimagassutslipp, samt å øke holdbarhet og levetid for bygningsmaterialer. Bygningssimulering (Building Performace Simulation, BPS) er et viktig verktøy for å tilrettelegge for både god prosjektering av nye bygg og rehabilitering av eldre bygg. Optimalisering av simuleringsmodeller for bygninger kan effektivisere beslutningsprosessene og bidra til bærekraftig utvikling. Klimabelastninger er viktige variabler i BPS. Opptredende klimabelastning på en bygning påvirkes av omkringliggende mikroklima. Bygninger med lik oppbygning og identisk geometrisk utforming kan være utsatt for ulike klimabelastninger innenfor samme bygrense, på grunn av ulik omkringliggende topologi. Ved å ta hensyn til mikroklima kan man oppnå mer nøyaktige data på klimabelastninger, som resulterer i mer nøyaktige bygningssimuleringer. Dette PhD forskningsprosjektet sikter på å forbedre aspekter ved bygningssimuleringer ved å ta hensyn til mikroklima. Klimabelastningene fra vind, slagregn og solstråling som opptrer på bygninger defineres med hensyn til mikroklima, og det er undersøkt hvordan man kan inkludere dem i bygningssimuleringsmodeller.

English. The contemporary sustainability imperativeness requires high performancebuildings. Smart solutions during the design or retrofitting phase cansignificantly contribute towards decreasing the energy consumption and gasemissions, as well as increasing the durability and life cycle of buildingmaterials. An invaluable tool that can facilitate both the design and retrofittingprocess is the building performance simulation. The optimization of buildingsimulation models can lead towards better decision-making, and subsequentlytowards sustainability.Climatic loads are one of the key variables in the building performancesimulation. However, the climatic loads acting on buildings are determined bythe micro scale climate. Buildings with the exact same geometry andconstruction can be subjected to different climatic loads depending on the localdistrict morphology they belong to, even within the borders of the same city.Increasing the accuracy of climatic loads by taking into consideration themicroclimate, will automatically increase the prediction accuracy of thebuilding performance simulation.This PhD research project aims on improving aspects of the buildingperformance simulation by accounting for the microclimate. The climatedriven loads of wind, wind-driven rain and solar radiation acting on buildingsare defined with respect to the microclimate, and some methods to introducethem in simulation models for buildings are investigated.A simple hygrothermal model that can predict how the surface temperatureand moisture content vary spatially along building façades is developed. Themodel is developed upon the basic principles of heat and moisture transportwithin the context of building physics. The developed model takes intoconsideration the microclimatic loads of wind-driven rain and solar radiation,which are determined by the surroundings and the building’s geometry. Inaddition, the building’s spatial architectural details are considered, thusrevealing areas of high-exposure or shelter from rain and solar radiation. As aresult, the climate-driven loads acting on the building façade investigated aremore accurately defined. In contrast to most of the contemporary simulationmodels that treat façades uniformly, the developed model is able to predict thespatial variations of surface temperature and moisture content along thebuilding façades. On-site surface temperature and moisture measurements intwo different façades verify the spatial accuracy of the model presented.Furthermore, the micro-scale wind effects on buildings are researched. Thewind-induced pressurization of the building envelope is one of the drivingmechanisms of air infiltration, and air infiltration is crucial to the buildingenergy consumption. As a result, predicting with high accuracy the windinduced pressures acting on buildings can significantly improve the calculationof air infiltration and consequently of building energy demands.Full-scale measurements on two reference buildings reveal high spatialpressure variations along the building façades. The measurements reveal thatthe wind-induced pressure variations are essentially determined by thebuilding’s surroundings and geometry. A common method to express the windinduced pressure acting on a body is by means of wind pressure coefficients(Cp). Therefore, the use of building-specific wind pressure coefficients asappropriate boundary conditions that can introduce the microclimate intobuilding energy simulation is researched.Building-specific wind pressure coefficients are calculated through full-scalemeasurements and computational fluid dynamics (CFD) simulations. Theresults show that building-specific wind pressure coefficients are able tocapture the microclimatic effect. The use of building-specific Cp values onbuilding energy simulations for the calculation of air infiltration is validatedagainst tracer gas measurements for a reference building. In contrast to theconventional methods used for the air infiltration calculation, building-specificwind pressure coefficients manage to account for the microclimate. The resultsindicate that the prediction accuracy of calculated air infiltration rates usingbuilding-specific Cp values is significantly higher than the rest of the methods.Furthermore, the use of fluctuating building-specific Cp values is evaluated. TheMonte Carlo method is employed, and the probability distribution function(pdf) of building-specific Cp values is combined with the wind speed pdf. Crossvalidation with on-site measurements suggests that the statistical method canimprove even further the accuracy of the air infiltration calculation.