15.9 MEASURING ENERGY USE IN EXISTING BUILDING HVAC SYSTEMS
Before individual energy conservation can be decided upon, an analysis of the energy consumption of the system should be carried out. In existing buildings, this is best done by an actual hourly measurement of energy used throughout the system for the whole year. This is often not fully possible because of the lack of suitable instrumentation. It is recommended that this procedure be carried out.
The most complete procedure in analyzing energy use in existing building includes measuring energy consumption of each piece of equipment, flow rates, temperatures, and pressures and noting types of systems, controls, and their operations. Other interrelated system operations would also be analyzed (e.g ,lighting). The physical conditions of the building would be noted. The results will suggest what conservation steps should be implemented.
The amount of detail to which the analysis is carried out largely depends on how much conservation gain is expected and the cost of the analysis itself. It is not possible to describe one single energy analysis procedure, because each case will be different. A list of some energy conserving measures that may result from studies will be listed later.
If it is not possible to measure the actual energy consumption in an existing building, a reasonably accurate estimate can be made by an energy simulation of the system operation, as is done in the design stages of new buildings. This will be explained in the next section.
If the cost of a detailed energy analysis is prohibitive, a “walk – through” survey and recommendations by an experienced energy consultant may suffice, but are not usually as effective.