Cost Estimating of Typical Bhutanese Residential Apartment Including Energy Performance using BIM and Energy Simulator

Abstract

Bhutan is in the Himalayan Mountain between India and China. Most of the districts experience cold weather from September to February month and moderate with humid temperatures in summer. Due to cold weather, people use simple heating systems such as electrical heating systems and kerosene heating systems to heat space. However, these heating devices consume a lot of energy thereby hampering the economy of the nation. Building designers and engineers use simple drawing programs like 2D AutoCAD and Google SketchUp for drawing, quantity takeout, and visualization. The application of the BIM concept in the construction sector is extremely limited due to a lack of resources. So, in this study, the BIM is applied in analyzing the energy performance of typical Bhutanese residential buildings. The typical Bhutanese residential building uses traditional plastered brick walls and concrete block walls without insulation, resulting in greater heat loss from the structure. The heat loss from the building has a direct impact on the energy consumption of the building. Moreover, the choice of construction materials is based on its ease and availability and there was no comprehensive study done on exploring building attributes which can minimize the construction cost and energy consumption. The purpose of this study was to cost estimate of building alternatives and perform energy performance of building using BIM and to provide better alternatives that can improve the comfort for occupants. So, the model has been constructed using software called ‘Open Building Designer’. The model was first created in Open Building Designer and exported to ‘Energy Simulator’ with help of an energy analysis tool. The simulation was carried out on the six building alternatives which were classified based on the floors and walls attributes. The simulation was carried out and a comparison was drawn between building scenarios based on annual electricity consumption, heat loss, and heat gain. The simulation result revealed that the typical two storied Bhutanese residential building can consume energy of 15301.43 kWh per year amounting to Nu. 37488. The results showed that brick and concrete block walls lose more heat than stone walls, whereas stone walls can retain the most heat. It was discovered that walls with better insulation can retain the most heat and lose the least amount of heat. The CIBSE heat gain tool was used to calculate the heat gain in building models. The heat gain result revealed that the building obtains heat from solar, fabric, casual, convective, and latent sources. The building constructed with traditional materials (timber, stone wall) will cost minimum construction cost of Nu. 2399006 while building constructed with modern materials (cement, concrete, reinforcement etc.) will cost maximum of Nu. 5931026. It was found that the cost of constructing increases as better insulated materials is employed, but that the energy performance of insulated walls is far superior to that of uninsulated walls. The result shows that a large portion of a residential building's budget is spent on building construction and good amount in operational energy use. The specific amount of money is also spent for operational water use and demolition. If the building owner does not take a bank loan, a 20-year return period is sufficient to fully repay the initial investment. However, if the owner takes out a complete construction loan, it will take at least 30 years for the owner to pay off the interest and the initial expenditure. (Nu: Ngultrum; Bhutanese currency; 1 US $≅45 Nu).

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