68 International Journal of Green Technology, 2019, 5, 68-75 E-ISSN: 2414-2077/19 © 2019 International Journal of Green Technology Post Occupancy Energy Efficiency and Indoor Environment Performance in Selected Commercial Buildings in Nairobi, Kenya David Nzioka Mulei 1,* , Paul Mwangi Njogu 1 and David Wafula Wekesa 2 1 Institute of Energy and Environmental Technology, JKUAT, 62000, Nairobi, Kenya 2 Department of Physics, Multimedia University of Kenya, 15653, Nairobi, Kenya Abstract: The cost of electricity and health of occupants inside buildings has led to an increased need for sustainable green buildings. The construction industry has come up with designs, construction and occupancy guided on sustainable principles. In Kenya, a few buildings have been built with such guidelines. It is imperative to conduct post-occupancy studies to ascertain that the green buildings are sustainable. This study sought to evaluate energy efficiency and indoor environment performance in green buildings. A total of four buildings, two green and two non-green, were considered in this study. Energy efficiency were determined using electricity bills provided by Kenya Power while indoor and outdoor carbon dioxide (CO2), relative humidity and temperature were measured using Carbon dioxide meters’ model HT-2000. The study found that energy consumption in green buildings was significantly different from that of non-green buildings (p_=_1.18E-12), but consumption for non-green buildings was not significantly different (p=0.7). Average mean CO2 concentrations in green buildings were 534 ppm and 608 ppm and 689 ppm to 695 ppm in non-green buildings. Mean temperature levels in green buildings were 21 0 C and 25 0 C and 23 0 C and 26 0 C in non-green buildings. Mean relative humidity in green buildings were 53% and 55% and 58% to 60% in non-green buildings. Mean airflow rates (ventilation rate) for green buildings were 0.06h -1 and 0.03h -1 while non-green buildings were 0.006h -1 and 0.003h -1 . Keywords: Green building, Carbon dioxide, Relative humidity, occupants, temperature, correlation. 1. INTRODUCTION Energy efficiency in buildings has become a major consideration in the built-sector due to increasing consumptions, 60% of total energy consumed by buildings in USA and 40% in European Union, contributing to about 36% greenhouse gas emissions [1]. Green buildings quantify energy use during design through modeling and simulation, which may deviate during occupation by about 25% [2-6]. Globally 30-40% of energy is consumed in buildings (18,19). In Kenya, Benchmark and Baseline consumption were established in 2012, but no research has been undertaken to inform how efficient green buildings are during occupation. Ventilation systems allow fresh air inside the buildings and removes humid and contaminated air out of the building while impacting energy losses in the building and comfort [7]. Air change rate in naturally ventilated buildings depend on geographical location, weather conditions, building characteristics and occupant behaviors [8]. Simulation and modelling are used to determine ventilation rates at design stage [910]. Natural air ventilation and indoor air quality in buildings is influenced by the tightness of the buildings [11]. Experimentally, adequacy of ventilation and air change (Mechanical, natural or infiltration) can be Address correspondence to this article at the Institute of Energy and Environmental Technology, JKUAT, 62000, Nairobi, Kenya; Tel: +254714095930; E-mail: Nzioka.mulei34@gmail.com calculated using the tracer gas method and applying the mixed mass balance model. The method can either utilize metabolically generated CO 2 (as used in this study) or use CO 2 introduced mechanically and the evolution of the tracer gas concentration with time analyzed mathematically to determine the flow rates in the building envelop [7,8,12-14]. Although green buildings should have demand controlled ventilation, designing for natural ventilation require great considerations for the airflows in the buildings. Studying ventilation rates in the buildings is important to inform whether the buildings are performing optimally. Classifying green buildings as green during occupation is equally important as classifying them as green at design and construction stages [17]. Relying on simulated and modelled energy consumption and airflow rates does not always give the actual performance of the buildings. Therefore, the study focuses on determining energy and indoor quality performance of green buildings in Nairobi Kenya. 2. FEATURES OF GREEN BUILDINGS Several characteristics distinguish green buildings from conventional buildings; first, site selection should consider ecological sensitive areas such as public green areas, flood-prone areas and cultural areas. Secondly, green buildings should re-use, recycle and use locally available raw materials to reduce embodied energy and reduce greenhouse gas emission. Third,