Current Filter: CAD>>>>>Case Study>

   

Morgan Sindall Professional Services Ltd. (MSPS), the multi-disciplinary design consultancy, was employed in the detailed design stages of Birmingham's new £189 million public library, which celebrated its position as Europe's largest library in a launch opening in September 2013. Capable of holding up to 3,000 people, the Library of Birmingham is home to books, computers, theatres and an exhibition gallery. A key feature of the building is its use of natural ventilation, designed to operate between 16-22°C.

Capita were the project building services designers that engaged MSPS in the detailed design stage, contracting them to deliver a comprehensive computational fluid dynamics (CFD) analysis, used to test and validate the performance of the building's proposed natural ventilation system and identify any potential design issues.

There were two main elements to the proposed CFD analysis, the first looking at the buildings energy and cost efficiency, predicting the building's temperatures, natural ventilation air velocities, pressure differentials and design issues. Using CFD, MSPS was able to analyse occupant comfort and demonstrate that the natural ventilation system could provide an efficient ventilation solution, reducing the mechanical heating and cooling systems' hours of operation and overall building energy consumption.

The second was to look at the user's or occupant's experience. The CFD analysis helped to model, and therefore create, comfortable and suitable environments throughout the year. Occupant comfort was analysed and measured using Predicted Mean Vote of Comfort (PMV) and Percentage of People Dissatisfied (PPD). Both PMV and PPD take into account users' activity levels, what they would be wearing at different times of the year and how the building's temperatures fluctuate throughout the day. In addition, airflow velocities required analysis in the many different areas of the vast library to understand the air movement across doorways.

THE SOLUTION
MSPS investigated key design performance issues during system peak design conditions (16 and 22°C) that required analysis, including: air movement patterns from the natural ventilation intake air boxes, through the atrium and within workspaces; the temperature profiles throughout the different floors; the air velocity through intake air boxes, at occupant level and through the atrium and areas with a high concentration of people with dissatisfied comfort.

Not limited to just air movement, MSPS' CFD modelling took into account light transmission, refraction, radiant effects, emissivity and conductance of the building's glazing; and the density, heat conductivity and emissivity of ceiling and floor materials. Other aspects included the complex natural ventilation system incorporating inlet air boxes around the perimeter of each floor, an open grid ceiling, the atrium and roof mounted louvres. Heat gains within the space considered lighting, localised occupants, equipment, the radient effect and solar heat gains.

Using these factors, the model data helped determine what temperatures could be expected at different times of the year and throughout the day. Each air box was modeled separately and consisted of louvers, dampers, insect mesh and attenuator.

A transient modelling and analysis system was chosen because the library's natural ventilation system volume flow rates are dependent on the stack effect temperature and pressure differentials, determined by both internal and external conditions that vary from floor to floor and throughout the day. Transient modelling produced a more realistic prediction of a varied and changing environment. (This was used instead of steady state modelling, which is useful for balanced systems like mechanical ventilation systems.)

Transient modelling also included a sub solar calculation that allowed the use of solar positioning within the modelling system, used to demonstrate the solar radiant effect of the sun on working spaces and allowing analysis of parts of the building, which would increase in temperature at certain times, due to solar gain.

MSPS measured occupant comfort using a combination of two indices. The first, PMV predicts the mean response of a large group of people on a scale of three to minus three, with three being hot and minus three being cold. The PMV calculation takes into account predicted metabolic rates, activity levels and clothing, as well as all associated environmental conditions.

The other index, PPD uses the PMV to determine the percentage of people that are likely to feel too hot or too cold in any given environment. Using these indices, MSPS' transient CFD modelling approach was able to assess each floor and ascertain what percentage of people the temperature and air velocities would dissatisfy.

Page   1  2