Development of EnergyPlus Simulation Models for Displacement Ventilation and Natural Ventilation

Goal Statement:
The aim of this project is to enhance the capabilities of EnergyPlus by a series of modeling studies to provide accurate estimates of building energy use. This effort focuses on modeling occupied spaces cooled by non-conventional ventilation strategies, such as wind-driven or stack-driven natural ventilation or displacement ventilation.

A major limitation of the current version of EnergyPlus is that it treats every space within a building as though it contains air of uniform temperature. Different spaces may have different temperatures, but there is no allowance for the possibility of stratification within an individual space. Consequently when stratification occurs, calculations such as the heat transfer from walls will be in error.

The assumption of "well-mixed" spaces is the simplest approximation that can be made; although it captures the first-order effects of airflow and heat transfer, significant errors can occur when stratification or other spatial variability is present.

Results:
Research has concentrated on four areas:

• The effects of cross ventilation; This ventilation is usually wind driven but may also be mechanically imposed.
• Transient ventilation between two connected spaces
• Natural displacement ventilation of a building space
• Assessment and debugging of the COMIS interface in EnergyPlus

Progress has been made in the following areas:

• A draft implementation of the natural ventilation model, particularly wind-driven cross ventilation
• The addition of a Flow Decision Maker (FDM) to determine the most likely airflow pattern (mixed, displacement or cross/ventilation flow)
• Laying out of the basis for simulation of user-controlled openings
• Production of a documented model for wind-driven cross-ventilation (Natural Ventilation)

Details on the model development.

Downloads and Links:

• "Simplified Models for Heat Transfer in Rooms", Carrilho da Graça, G., University of California, San Diego. (3.13 MB, 265 pp)
   
• "Simplified Modeling Of Cross Ventilation Airflow", Carrilho da Graça, G., P.F. Linden, ASHRAE Transactions V109 Pt.1, Atlanta, USA. (1.1 MB, 32 pp)

Contact: Philip Haves, Lawrence Berkeley National Laboratory (LBNL), (510) 486-6512 or Paul Linden, University of California, San Diego, (858) 822-2274