This paper summarizes the initial findings of the research that was done for the ASHRAE Task Group on Dynamic Response. The project ASHRAE RP-321 was entitled "HVAC System Dynamics and Energy Use in Existing Buildings." The overall objective of the project was to determine operating strategies for HVAC systems which incorporate system dynamics and interactions and which will potentially reduce energy use.

The computer algorithms that were developed for the modeling of HVAC equipment (cooling tower, water chiller, air handling unit, etc.) are described. TRNSYS (a computer code developed by the Solar Energy Laboratory at the University of Wisconsin-Madison) was used to link the individual component models together in order to simulate the HVAC system of a building. Comparison between measured data and the model predictions are given.

Short term tests of equipment dynamics were conducted to determine the significant dynamic effects. The results showed that the significant transient effects were:

• the cooling tower response to fan speed changes;
• the "flush time" of the chilled water through the system;
• the effects of the building structure due to capacitance.

The transient effects that were not significant (due to their very short time duration) were:

• the chiller response to set point (supply water) change;
• the air handling unit response to set point (supply air) changes.

The end results of this project are the identification and investigation of potential energy saving HVAC operating strategies and the availability of "reliable" equipment models. The final results on dynamic control will be the subject of a following paper. The groups that could benefit the most from these models are building operators, HVAC controls persons, and future researchers.