Study on Discomfort Degree Hours of Building Treated with Different Thermal Insulating Materials by Computer Software

Introduction

The most common application of degree day is the analysis of energy consumption in existing buildings. Since energy demand for space conditioning (heating or cooling) has a linear relationship with temperature difference, which follows that there should be a linear relationship between energy consumed and discomfort degree hours in a year. By using this theoretical1 approach, monthly or annually energy estimate can be calculated for heating and cooling. Degree day provides a simple estimation of annual load of a building for a location based on tabulated discomfort degree hour value. This method2 may be used with accuracy where a building use, HVAC equipment efficiency, indoor temperature and internal gains are relatively constant. The energy analysis method3 is called a bin method and is often used where equipments have efficiency as a function of outdoor air temperature. Amongst two main uses of discomfort degree hours in building, one is to estimate energy consumption4 due to space conditioning for new building and major refurbishment for ongoing energy monitoring and analysis of existing buildings. Degree days are essentially the summation of temperature difference over time and hence they capture both extremity and duration of indoor temperatures. The temperature differences are between a reference temperature or threshold temperature and the indoor air temperature. Cooling or heating discomfort degree hours are calculated from temperatures below or above the threshold winter or threshold summer temperatures respectively. The heating or cooling energy (KWh) demand is equal to the product of overall heat loss or gain coefficient and respective degree hours.

Thermal insulation materials have properties to resist heat flow. Amongst various thermal insulation materials used in buildings, some of them are Expanded Polystyrene (EPS), Neopor, Peripor, Styropor, Elastospray, Elastopor etc. These materials are easier to install as these are lightweight and are available in desired size and thickness. The insulating properties (K, R and U-values) of a thermal insulation material depend upon thickness, density and the constituent materials. The new construction practice requires more cautiousness in design for providing acceptable indoor environment quality otherwise building will not function well under extreme climate conditions and over heating or cooling problem may result. Performance of different insulating materials in buildings are needed to be evaluated quantitatively for their thermal behaviors as if they are applied to actual building for a whole year covering most of the weather condition that the building may face. In this study, a computer simulation method5 has been used to determine building discomfort degree hours. The computer software used for energy simulation in building is described here.