ESP-r Simulation Results
Simulations of the telecoms base shelter model were undertaken using ESP-r software in order to estimate the possibility of reducing the total amount of energy used by the cooling system. Studies show that a huge percentage of overall electrical energy is used for cooling the base shelter, especially in the tropics. In order to minimise the demand for cooling, a free-cooling system was incorporated in the model which functions when the ambient temperature falls below 25 degrees Celsius.
Changing the air infiltration rate from 0 to 20 AC/hour in steps of 2AC/h, the practical air infiltration value that gives maximum energy savings on the air conditioning system was obtained. This means that at this air change rate, the energy load by the air conditioner and dehumidifier is minimal. The results of this simulation are shown at the Table 1.
From Graph 1 it was observed that with an increment in the rate of air change from 0 to 10 the annual energy load decreased rapidly. Further increase of air change rate did not exhibit any significant improvement. So taking into account the area of the shelter, the infiltration of 180 m3/hour (10AC/hour) is the best free-cooling option adoptable. Graph 2 shows the annual temperature distribution.
In the winter season due to free cooling, the dry bulb temperature of the shelter was below 25 degrees especially at night time when the ambient temperature is low. During this period the air conditioner is switched OFF while cool natural air is streamed through the shelter.(Graph 3, Graph 4).
This saves 851 kWh of electricity per year. During the summer season, the air conditioner is always operational. The maximum power consumption of the air conditioner is 1200W.
The other experiment was done using varying insulation thickness. Insulation helps reduce heat transfer from external environment to the shelter. Currently, many companies offer shelters with an insulation range between 60 and 120 mm. So in a series of simulations, the influence of insulation thickness on cooling load was investigated.
In Graph 5 it was observed that by varying of insulation thickness between 60-120mm gave a reduction in cooling demands. It was therefore determined that an insulation thickness of 100 - 120mm polyurethane foam is best suited for use in the tropics.
