This multi‐year project developed EnergyPlus/UFAD, a version the publicly available wholebuilding energy simulation program EnergyPlus that adds the capability for modeling underfloor air distribution systems. The project also developed a practical design tool for determining the cooling airflow quantity for underfloor air distribution systems. EnergyPlus/UFAD and the cooling airflow design tool are the first validated underfloor air distribution system tools of their kind. As such, they represent a significant advance in the state of the art of the design and energy analysis of such systems. This highly collaborative effort involved experts and facilities from four organizations, including the Center for the Built Environment at University of California, Berkeley; University of California, San Diego; Lawrence Berkeley National Laboratory; and York International.

This final report and seven appendices present experimental testing and analytical and computational fluid dynamics modeling on room air stratification and underfloor plenum distribution—critical efforts that informed the development of models for EnergyPlus. Also discussed are new implementations of heating, ventilation, and air conditioning systems to support underfloor air distribution system modeling in EnergyPlus and the development of a practical design tool for such systems.

The design for the new Federal Building for San Francisco includes an office tower that is to be naturally ventilated. Each floor is designed to be cross-ventilated, through upper windows that are controlled by the building management system (BMS). Users have control over lower windows, which can be as much as 50 percent of the total openable area. There are significant differences in the performance and the control of the windward and leeward sides of the building, and separate monitoring and control strategies are determined for each side. The performance and control of the building has been designed and tested using a modified version of EnergyPlus. Results from studies with EnergyPlus and CFD are used in designing the control strategy. EnergyPlus was extended to model a simplified version of the airflow pattern determined using CFD. Wind-driven cross-ventilation produces a main jet through the upper openings of the building, across the ceiling from the windward to the leeward side. Below this jet, the occupied regions are subject to a recirculating air flow. Results show that temperatures within the building are predicted to be satisfactory, provided a suitable control strategy is implemented uses night cooling in periods of hot weather. The control strategy has 10 window opening modes. EnergyPlus was extended to simulate the effects of these modes, and to assess the effects of different forms of user behavior. The results show how user behavior can significantly influence the building performance.

This research program investigated the potential energy savings to be gained by retrofitting non-domestic buildings in California with natural ventilation for cooling. The simplest and most cost effective retrofit is to open windows on the façade and turn off any mechanical ventilation. To make the problem tractable attention was restricted to wind-driven natural ventilation. Stack-driven ventilation is likely to also be present in practice, and usually improves the cooling potential.

The program was split into three major projects. Project 1 assessed the potential of and the barriers to the implementation of natural ventilation. Project 2 examined induced air movement and the possible ingress of outdoor pollutants. Project 3 produced new tools for predicting the energy performance of naturally ventilated buildings, and provided training in their use.

The major barriers to the introduction are the lack of specific design guidance and a lack to easy-to-use modeling tools. These are compounded by a lack of design experience and case studies and the mandatory requirements for the amount and location of openable area specified in Title 24.

Research on wind-driven natural ventilation using computational fluid dynamics and wind tunnel tests provided new algorithms for cross ventilation, single-sided ventilation and corner ventilation, accounting for opening size, location and number, and the effects of sheltering by neighboring buildings. These algorithms were implemented in EnergyPlus, and the new version of the code was used in three training sessions to provide the design and engineering community with some familiarity in the new modules that calculate natural ventilation.

The overall outcome of this program is a comprehensive study of the current issues concerning retrofitting commercial buildings in California and an assessment of the potential risks and benefits. It has also significantly extended the capabilities for modeling, design, and operation of naturally ventilated buildings in California.