USE OF SIMPLIFIED SYSTEM MODELS TO MEASURE RETROFIT ENERGY SAVINGS

The retrofit of dual-duct constant volume systems (DDCV) with energy-e fficient variable air volume systems (VAV) has become common in recent years. In general, the energy savings from such retrofits are estimat ed by developing a temperature-dependent regression model using whole building preretrofit energy consumption data. Model predictions are th en compared with measured post retrofit consumption, to determine the savings. In cases where the preretrofit energy consumption is not avai lable such a method cannot be implemented. This paper describes a meth od that can be used to calculate savings in such cases. The method is based on use of simplified calibrated system models. A VAV model was d eveloped based on the ASHRAE TC 4. 7 Simplified Energy Analysis Proced ure (SEAP) (Knebel, 1983) and calibrated with the postretrofit energy consumption of a large engineering center in Central Texas. The loads from the calibrated VAV model were then used with the DDCV model to es timate the preretrofit energy use, also based on TC 4.7 SEAP, and appa rent savings were determined as the difference between the DDCV predic ted consumption and measured energy consumption for the postretrofit V AV system. The simulated hourly cooling energy consumption from the VA V model was within +/-1GJ (+/-20 percent) of the measured consumption. The simulated daily consumption (the sum of 24 hours of consumption) compared better with the measured daily consumption (within +/-7 perce nt). The apparent saving from the retrofit of the DDCV system with VA V was about 684 GJ in cooling energy and 324 GJ in heating energy for a three-week period June-July 1991.