Cost effectiveness of thermal mitigation based on the long term thermal analysis of a large office building

Multi-storey steel-and-glass office buildings suffer from a strong thermal load during the summertime, particularly in Mediterranean countries, and thermal discomfort is a very likely occurrence, even when a massive air conditioning centralized system is operated. Significant departures from thermal comfort conditions have been proven to result in decreased performance for office workers, which translates into a additional costs for the employer.  In this work we initially use the results of an extensive measurement campaign to characterize the overall summer comfort, using long term descriptors which also integrate a method to select the appropriate thermal quality class for each environment. We then simulate the change in the thermal environment produced by the use of solar control films, a very simple and low cost thermal mitigation action, and calculate the associated thermal-induced increase in performance. Finally, we estimate the costs and benefits so that the cost-effectiveness of such an action is calculated. Results show that the fractional discomfort time (PMV outside the -0.5 to 0.5 range) is 15 – 20% at best and can grow up to 70 – 80% in specific rooms. Performance improvements up to 1.5% can be achieved. Although this figure may look unimpressive, the implied cost to benefit ratio is nonetheless very small (1/8 to 1/3 – that is benefits exceed costs by a factor 3 to 8). Considerations based on economics as well as general well being of employees strongly recommend the adoption of solar control films or similar technical improvements.