Building electric power load assessment
This chapter provides an introduction to simple methods of load assessment for electric power systems in buildings. The need for load assessment as part of the design development process has been outlined in Chapter 2. It is also a necessary step in the selection of an energy strategy to minimise carbon emissions, as outlined in Chapter 3. A brief overview provides the context for some of the key issues for power system infrastructure design related to selection of equipment locations in buildings. The specific requirements for load assessment are outlined, together with a review of the nature of load patterns and profiles for electricity in buildings. The main methods for load assessment are described, including guidance on applying diversity factors. In practice, early estimation is usually based on load per unit area, or unit of accommodation. Typical load densities are provided for a range of systems and types of functional spaces in buildings. In commercial or public buildings, the electric power load is usually dominated by the main items of mechanical plant in the heating, ventilation and air-conditioning (HVAC) systems. Simple methods of early stage load assessment are described for the main items of mechanical plant, together with methods for some of the more problematic electrical loads, such as process loads. An introduction is provided for the more complex data processing loads and those supported by uninterruptible power supply (UPS) systems. The relevance of day, night, summer and winter load variations is outlined. A sample tabulation method is provided to illustrate a simple initial load assessment. Most electrical systems have a considerable proportion of non-linear load that gives rise to harmonics. This chapter concludes with a brief discussion on the impact of harmonics on equipment sizing and capacities.