Window Design and Natural Ventilation Relationship in Terms of Reducing Carbon Dioxide and Improving Thermal Comfort

Natural ventilation (NV) through window openings is an inexpensive and effective solution to bring fresh air into internal spaces and improve indoor environmental conditions. This study attempts to address the “indoor air quality – thermal comfort” dilemma of naturally ventilated office buildings through the effective use of early window design. This study proposes a method of early window design for an optimised natural ventilation potential, by reducing the level of indoor carbon dioxide (CO2) concentration and improving thermal comfort, and consequently minimising supplementary heating/cooling loads. The model consists of various stages: (1) Knowledge acquisition, (2) establishing a relationship between window design and natural ventilation, (3) identifying performance criteria and design of experiments (DOE), (4) conducting performance-based dynamic simulations, (5) evaluation of findings, and (6) making informed design decisions. The study also proposed an evaluation method by which the assessments of indoor CO2 concentration and adaptive thermal comfort were performed using the threshold suggested by the World Health Organisation (WHO) and the acceptability categories of the British/European standard EN 15251:2007. The measurement criteria are: carbon dioxide levels, airflow rate, air conditioning (AC) loads, and thermal comfort. The relevant indicator was the time (hours) during which pertinent performance criteria were met in the occupancy period, as well as the AC loads during that time. As suggested by the EN 15251:2007 standard, the hourly dynamic simulation method was employed using EDSL Tas Engineering. The proposed model was applied using different hypothetical scenarios of different types of office spaces, NV strategies, and window design possibilities. The findings show that the developed model of performance-based window design enables the handling of various window design variables along with different performance criteria to determine the near-optimal window design alternatives for effective NV and mixed mode (MM) offices. This model can guide architects towards making knowledge based and informed-decisions in the early stages of office window design. Keywords: window design, natural ventilation, indoor air quality, carbon dioxide (CO2) concentration, adaptive thermal comfort, office building, Performance-based design.