The building sector is the largest consumer of the primary sources of energy worldwide. The most commonly used primary sources of energy to generate electricity are oil, coal, peat, shale, natural gas, nuclear, hydro, renewables, biofuels, and waste. The energy demand by the building sector is about 40% of the world's energy production.Net Zero Energy Buildings (NZEBs) is the best solution recommended by the energy experts to reduce substantial pressure on primary sources of energy contributed by the building sector. There is a marginal gap between estimates made during the design stage and actual energy performance of residential buildings, primarily due to a lack of understanding of the factors affecting energy use and whole building simulations software limitations. The purpose of this research work was to conduct a comparative analysis of a predicted versus actual energy consumption of prototype Net Zero Energy Building (NZEB) constructed at Higher College of Technology, Muscat. Hourly Analysis Program (HAP V4.2) was used to predict energy demand of NZEB at HCT and same size regular house in Muscat. PVWatts calculator was used to determining possible power generation by the PV system installed on the roof in the form of a canopy. The constructed house was tested for one month to perform multiple tasks as per competition requirements in which one of the major tasks was to produce onsite energy production by PV panel's equivalent to the energy consumed by the house. The actual energy consumption results were compared with the simulated result and observed that actual energy demand of house was approximately 20% lower than that predicted by the simulation tool. The comparison of simulation results between NZEB and regular house indicated 61.24 % less energy demand of NZEB, mainly due to less HVAC load. The simulation result for BEI of NZEB showed 87.20 kWh/m 2 /year as compare to 225.1 kWh/m 2 /year for same size regular house. The simulated result obtained from PVWatts calculator for competition period and actual production of an installed PV system at the top roof showed a minor deviation of 0.73% only. It is also observed from the results during the competition period house exported 1221 kWh energy to the grid.

The Building sector is the largest consumer of energy worldwide. Net Zero Energy Residential Building (NZERB) is one of the prudent approaches to reduce pressure on primary sources of energy. The main objective of this study is to use Taguchi simulation based on orthogonal arrays approach to optimize thermal envelope of a building, SEER value of HVAC system, lighting power density, and ventilation level to reduce the Building Energy Intensity (BEI) 50% lower than the base case building according to International Energy Conservation Codes 2015. In this study whole building energy simulation was performed by Hourly Analysis Energy Program and PVWatts calculator was used to estimate the size of the PV system for balancing the energy demand of the house. The results of Taguchi simulation approach show that by decreasing the U value of wall, windows, roof, floor to 0.1, 0.8, 0.1, 0.2 W/m2. °K respectively and ventilation rate 0.15 l/s-m2, lights of 110 lm/W and SEER of the HVAC system 4 (W/W option) reduce BEI from 147.78 kWh/m2/year for base case building to 67.085 kWh/m2/year for optimal design case. PV system size estimation was performed with PVWatts calculator. PV Watts recommended the size of 13kW DC rating system (open rack type) of 15% efficiency for the weather of Johor Bahru to meet the annual energy demand of the proposed optimal building design.