Design Example

The capabilities of the displacement and cross ventilation models in EnergyPlus are illustrated here in the analysis of a simple design example. We will analyze a single zone office building with 40m² of floor area (W=8m, D=5m, H=4m) and two levels of internal gains.

For an office building in a warm climate (California) the largest portion of HVAC energy usage is for cooling. A single zone office building will be analyzed will the goal of reducing cooling energy demand. The building will be cooled using different systems and ventilation strategies. We will begin by analyzing naturally cooled configurations, using ventilation air (cases labeled NAT). The next step will be to analyze the effect of the addition of a limited amount of radiative cooling (cases labeled HYB). Finally two possibilities for mechanical cooling will be analyzed: a variable air volume system with displacement or mixing ventilation (cases labeled MEC).

We would like to achieve an average flow rate of 15 l/s per occupant and minimize the number of warm hours. Thermal comfort will be evaluated with two levels of complexity: simple (using the average between room air and mean radiant temperatures) and detailed (using the Fanger model). The analysis will be done using three typical climate weeks (spring, summer and the hottest week of the year) for each of three locations used (San Diego, Los Angeles inland, and San Francisco).

Sequence of cases analyzed

The analysis begins with two cases with no mechanical cooling, in two different ventilation geometries (cross and displacement ventilation).

In the third and fourth cases (HYB) radiative cooling is added, operating in conjunction with the natural ventilation system. In order to maintain the thermal stratification even when the vertically averaged indoor temperature is lower than the outdoor dry bulb a solar chimney is added in the second of the hybrid cases (label SC).

Finally, two mechanically cooled cases are analyzed, using displacement and mixing ventilation.

Files used in the analysis

All files used in the analysis (IDF and Result Files) are available for individual download below.

If you prefer a single downlaod including all files use this link.