Estimating Natural Ventilation Using Weibull Distribution

From eSociety, November 2018

In the article “Statistical Analysis of Wind Data Using Weibull Distribution for Natural Ventilation Estimation” that appears in the October edition of Science and Technology for the Built Environment, researchers used the Weibull distribution in a current study to represent high-resolution historical wind data, statistically, for a  one-year period to find out more about wind variability and its effect on airflow rate estimation.

The research proposed a method that could be used to characterize wind speed variances, especially with small time-step wind data. The method enables building designers to do a statistical airflow analysis, according to the paper’s abstract.

The researchers Sheng Wang, Student Member ASHRAE; Yun Zhang, Student Member ASHRAE; Michael Waring, Ph.D.; and L. James Lo, Ph.D., Associate Member ASHRAE, discuss the significance and challenges of their research. The researchers are associated with Drexel University in Philadelphia, Pa.

1. What is the significance of this research?

This is one of the first attempts to assess the natural ventilation flow rate in terms of statistical variations instead of a single averaged value from the prevailing wind. This method could allow designers and researchers to take the variable wind interaction with buildings into consideration in their work.

2. Why is it important to explore this topic now?

As natural ventilation is becoming an important strategy for low-energy building designs, engineers often find determining the wind effect on building's envelope and HVAC system is difficult due to the wind speed and rapid direction changes.

Traditionally, this fast variation is too difficult to assess and often ignored, but such omittance creates significant uncertainties in the operational conditions of the system design, especially when natural ventilation is involved (without a fan to enforce a flow rate).

3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?

While the results presented in this research are exploratory in nature, the potential impact is that eventually, engineers will have the confidence in the probability of a certain wind effect acting on the building system for a given location and climate.

Also, the fact that some of the investigation strategies were borrowed from wind power engineering shows the importance of understanding the availability of applicable research across multiple disciplines and industries.

4. How can this research further the industry's knowledge on this topic?

By introducing the temporal variance in both ventilation and comfort designs, the result is a more robust design process that can predict the system performance with greater confidence. This confidence will translate into more comfort with higher energy efficiency by leveraging natural ventilation in a more predictable and applicable manner.

5. Were there any surprises or unforeseen challenges for you when preparing this research?

There are always unforeseen challenges in research.

In this case, the human intuition of seasonal impact of wind direction and speed changes is less impactful than originally believed in some climates. This means any rule of thumb-based design cannot be applied uniformly across all climates. Also, the complexity of determining the best design strategy for a corresponding location is one of the biggest challenges.

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