ABX: Natural Ventilation Design

I recently presented a talk titled Natural Ventilation Design at the 2013 ArchitectureBoston Expo.

It is not uncommon to find buildings where the natural ventilation system does not perform as planned (or at all). Designing a natural ventilation strategy, even for a single office, can be more complex than is usually thought. It requires making sure that all of the elements in the flow path are carefully accounted for and modeled, and overlooking simple things such as the presence of an insect screen can lead to occupant discomfort and a more extensive use of air conditioning than was originally planned.

The goal of this talk was to address five of the most common mistakes encountered in the design of natural ventilation systems, and how to avoid repeating them. The following five useful tips were provided to improve the design practice:

• Do not confuse “weather analysis” with “natural ventilation potential.” The fact that the climate is benevolent to natural ventilation does not guarantee that a natural ventilation system will be successful.
   
• Make sure to account for all pressure losses in the flow path. Not accounting for a simple flow restriction, such as an insect screen, can lead to overestimating the flowrate by 28% (or under-sizing the operable window area by that same amount).

• Account for “unlikely” wind conditions. The fact that the wind comes from the North 50% of the time still leaves wind coming from other directions the other 50%! Studying the behavior of the airflow from all wind directions is very important as it ensures that the system always works as planned. 

• Model the internal temperature distribution in a typical floor. Most energy modeling software predicts a single temperature for each building zone. In reality, the air stratifies and creates both hot and cold spots. Running a Computational Fluid Dynamics (CFD) simulation is essential to ensure that air flows through the space as planned.
   
• Consider fan-assisted ventilation. This type of ventilation can significantly increase the amount of time one can get “free cooling”. The energy consumed by a fan is extremely small compared to that of an air conditioner.

To view a larger version of the graph, click here.

Related:
ABX: Reduction by Ventilation
Natural Ventilation Design
A Practical Approach to Natural Ventilation