Assessing the thermal performance of phase change materials in composite hot humid/hot dry climates: an examination of office buildings in Abuja-Nigeria

Abstract

The aim of this study is to investigate the possibility of using Phase Change Materials (PCM) in improving indoor thermal comfort while conserving electricity in office buildings in the composite Hot Humid/Hot Dry climate of Abuja, Nigeria. The first stage is a quantitative investigation of electricity consumption in 15 Nigerian office Buildings. Purpose-built mechanically cooled office buildings are selectively chosen across major Nigerian cities and climates. The surveyed data is analysed and used to construct a hypothetical office building as a base case. Scientifically validated software DesignBuilder v3 and EnergyPlus V6 and V7 are used for the parametric analysis of simulation results. The building simulations are used in two stages, firstly to test passive and climatically responsive scenarios to reduce electricity consumption then secondly to study the potential benefit of incorporating PCM in the building fabric and its effect on thermal comfort and electricity conservation. Results show that cooling, lighting, and appliance loads account for approximately 40%, 12% and 48% respectively of electricity consumption in the buildings audited. Power outages are frequently experienced necessitating alternative power usage. A data collection method is presented for energy auditors in locations where alternative back-up power is essential. Simulation results indicate that the magnitude of energy saving can be achieved by optimizing the passive and climate sensitive design aspects of the building and an electricity saving of 26% is predicted. Analysis indicates that it is difficult to achieve thermal comfort in office buildings in Abuja without mechanical cooling. Adding such a PCM to the building fabric of a cyclically cooled mechanical building may alleviate indoor discomfort for about 2 hours in case of power outage and is predicted to save 7% of cooling load. Cyclic cooling is the cooling of the interiors long enough to maintain comfort for a maximum duration within the working hours. The use of lightweight partitions instead of the heavyweight ones common in Nigeria is shown to a 2-fold improvement in consumption. Adding a PCM to light-weight partition walls with transition temperature of 24°C, conductivity of 0.5W/m K, and a thickness of 10mm gives the best predicted energy savings.