Development and Analysis of Model Based Economizer Strategies

Abstract

Two new model based economizer strategies were developed and implemented in the EnergyPlus simulation program. Model performance was verified by comparing EnergyPlus results with previously developed models. Results agreed within 25%. Both detailed and bypass coil models were evaluated for potential use in the model based economizer strategies. Energy and peak load analyses were performed for three benchmark buildings using five economizer strategies for 15 US climatic conditions. The impact of sensor errors on energy savings and coil design was also discussed. For office type buildings, it was found that model based economizer strategies do have energy savings potential as long as sensors are well maintained. However, if sensors are poorly maintained, differential dry bulb was found to be the best strategy. For Hospitals and Hotels with high minimum outside air requirements due to high occupancy, the economizer strategies resulted in lower energy savings. The bypass coil model was found to be in agreement with results obtained for detailed coil model based strategies. Using different simulation methods to size the cooling coil can change the coil size by up to 100%. Accounting for sensor error in simulation based coil design, tends to decrease the difference between the design day and annual peak cooling coil loads. Based on the results of the study, it was recommended that simulation capabilities should be modified to account for user specified sensor errors and ASHRAE standards should be modified to characterize economizer use based on building use and qualities of sensors.