The energy consumption of data centres is increasing over and over. However, there are few decision support systems introduced for data centre practitioners to use it for their daily operations, including simulating their new server installation and forecasting power consumption for the target periods. We propose a simulation model based on CloudSim, which is widely used for data centre research. Our simulation model will be tested with datasets, including IT work-loads, cooling performance, and power consumption of servers and cooling devices. In the final stage, we provide a decision support system to monitor, forecast, and optimise the power consumption of a data centre easily on the web.