Implementation of a simplified model for natural ventilation in BE15
Authors
Chittenden, Francine Thérèse ; Vladimirova, Evelina Emilova
Term
4. Term
Education
Publication year
2018
Submitted on
2018-01-10
Pages
81
Abstract
This thesis examines whether the simplified airflow calculation method in prEN 16798-7:2015 can be implemented in Denmark’s energy compliance tool BE15 to provide a calculated, rather than user-defined, contribution from natural night cooling. The approach compares airflows computed using prEN 16798-7 (integrated in BE15) against BSim simulations under identical boundary conditions from a single case study with four window options and safety-limited openings. The focus is residential night cooling during the cooling season, varying window opening area, wind speed, indoor/outdoor temperatures, wind pressure coefficients and wind speed correction factors. Two natural ventilation principles are assessed: single-sided and cross ventilation. Findings show that for single-sided ventilation prEN 16798-7 generally underestimates airflow relative to BSim, and larger free openings lead to more buoyancy-driven flows. For direct cross ventilation, input values are critical; when parameters are aligned, calculated airflows are mostly comparable to or lower than BSim (only 6 of 128 cases were higher). Against SBi 213 guidance, large discrepancies appear: SBi can substantially under- or overestimate airflows depending on effective opening area, indicating that BE15 would benefit from a calculation-based method. Based on the analyses, the authors recommend adjustments to the BE15 weather file and software changes to compute night airflows for the Family-type building parameter. Overall, the results suggest prEN 16798-7 offers a promising basis for calculating natural night cooling in BE15.
Denne afhandling undersøger, om den forenklede beregningsmetode for naturlig ventilation i prEN 16798-7:2015 kan implementeres i Danmarks energiberegningsprogram BE15 som et beregnet natkølingsbidrag i stedet for brugerdefinerede værdier. Metoden testes ved at beregne luftskifte gennem vinduer ud fra de samme randbetingelser i ét casestudie (fire vinduesløsninger, sikkerhedsbegrænsede åbninger) og sammenligne resultaterne fra prEN 16798-7 (integreret i BE15) med simuleringer i BSim. Fokus er natkøling i boliger i kølesæsonen, og der varieres i åbningsareal, vindhastighed, indendørs/udendørs temperaturer, vindtrykskoefficienter og hastighedskorrektionsfaktorer. To ventilationsprincipper vurderes: enkelt-sidet og krydsventilation. Resultaterne viser, at prEN 16798-7 generelt undervurderer luftstrømmen for enkelt-sidet ventilation sammenlignet med BSim, og at større frie åbningsarealer øger opdriftsdominansen. For direkte krydsventilation er inputparametre afgørende; når de holdes konsistente, er de beregnede luftstrømme overvejende på niveau med eller lavere end BSim (kun 6 af 128 tilfælde var højere). Sammenlignet med SBi 213’s anbefalinger ses betydelige afvigelser: SBi kan både under- og overvurdere luftstrømme markant afhængigt af åbningsarealet, hvilket peger på, at BE15 vil have fordel af en beregningsbaseret tilgang. På baggrund af analyserne anbefales justeringer af BE15’s vejrdatafil og en omskrivning, så natlig luftstrøm beregnes for familietype-bygninger. Samlet set indikerer resultaterne, at prEN 16798-7 kan levere et lovende grundlag for at beregne naturlig natkøling i BE15.
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Keywords