Identification of Energy Saving Potential of Different Thermal Insulation Through Mathematical Modelling

Abstract

A country's economic development is proportionate to its energy consumption. The consumption of energy in India is distributed among four main sectors: industrial, building (residential/ commercial), transportation and agricultural areas. Among this, the building sector has a high energy consumption share. Energy consumption rate has gradually increased due to population growth, urbanization and industrial growth. The heat gain in buildings generally occurs through walls, ceiling, floor, windows and air infiltration. To reduce load (heat gain in building) on air conditioning system and thereby power consumption, one of the ways is to thermally insulate the building on all sides. In the present work, a mathematical model is developed to demonstrate energy saving potential of a thermally insulated, air conditioned room and identify the best insulation. Solar radiation (heat flux addition) and cooling capacity of air conditioner are applied as boundary conditions at different walls of the room. No-slip boundary condition is taken at the boundary of the room i.e. velocities at the boundary are taken as zero. The room is discretised using Finite Volume Method and governing equations are solved simultaneously to obtain temperature at different nodes inside the room. A code is developed to calculate the mean temperature inside the room and AC working (on) time. Simulations have been carried out for four different conductivities and seven different thicknesses of insulations namely Polyurethane Foam, Extruded Polystyrene Foam, Fiberglass and Rockwool. AC on-off (time step) cycle for different insulations (conductivities) and thicknesses, 2-D temperature contour variations and velocity profiles at mid-planes are generated as outcome of the code which are important tools and parameters for determining the energy saving potential of different thermal insulations at different thicknesses and calculation of optimum thickness. The amount of energy (electricity) consumed and saved is calculated on the basis of how long the AC works and the duration for which the AC on-off cycle is computed. A graph is plotted for Cost of electrical energy saved/day vs Thickness of insulated wall for different insulation and optimum thickness of insulated wall is obtained from it. Energy saved is directly proportional to the thickness of insulation used and inversely proportional to the conductivity of the insulation. Optimum thicknesses for Polyurethane Foam (PUF), Extruded Polystyrene Foam (XPS), Fiberglass and Rockwool come out to be 0.15 m, 0.2 m 0.2 m and 0.225 m respectively. Saving in cost of electricity is maximum for Polyurethane Foam insulation with conductivity, k = 0.021 W/mK at insulated wall thickness of 0.275 m and minimum for Rockwool insulation with conductivity, k = 0.045 W/mK at insulated wall thickness of 0.125 m.