Customer Brief: Morson

For more than 25 years, Morson Projects, headquartered in Manchester, UK has been providing multi-disciplined engineering, design and project management services to international clients from a wide range of industries, from automotive to nuclear design to utilities. A key sector of the company’s business is ventilation and HVAC analysis for all types of process, commercial and residential buildings.

One of the company’s most recent challenges involved conducting a design study of a proposed car park (parking garage) for Granary Wharf, a shopping and tourist area in the UK. Although it encompassed only a single floor with 90 spaces and three exits/entrances, ventilation requirements for the parking area were complex.

Simulating Normal and Fiery Conditions

Morson Projects was asked to produce an analysis of the car park to show that the mechanical ventilation system would work as designed, adhering to the British Standard for safety. That means providing a minimum of six air changes per hour with fans running at half speed and 10 air changes per hour with fans running at full speed.

The client also asked Morson to do what is known as an eight-megawatt fire analysis – the equivalent of the energy given off by two cars on fire. This analysis is designed to show that the ventilation system will clear smoke adequately enough within 60 seconds to allow people to escape the car park safely. Two months after doing the 60-second fire analysis, the client came back to Morson and asked to see the effects of smoke after 180 seconds.

Better Results in Less Time

CFdesign air flow analysis of the car park under normal circumstances. Different layout arrangements of the jet fans were tested to optimize air flow and extraction rates in the car park to prevent carbon monoxide build-up. The simulations showed that the car park was being supplied with sufficient fresh air from the outside to relieve the small areas of low air speed. General circulation of the air was good with no dead spots. Modeling and analysis took about a week.

The fire simulation required something the set up a transient analysis with time steps that saved results at certain points to show smoke movement without any mechanical ventilation from the impulse fans. These results – first for 60-second intervals and later for 180-second intervals – were then used for the full eight-megawatt analysis showing what would happen when the impulse fans were turned on to remove the smoke.

Positions of the fans and the fires were changed to optimize smoke removal and to improve areas where the LMA was too high. Additional complexity was added when blocks used to represent cars were introduced to see how air and smoke movement would change with the car park at 80-percent capacity. Because the car park has a high roof, the presence of cars did not have a significant effect on smoke movement. The final ventilation configuration showed good air circulation, with only small areas of recirculation and no dead spots.

The 60-second and 180-second smoke analyses took about two weeks to complete, since the model had already been created for the original analysis. CFdesign’s ability to output features, plots and animations showing transient conditions added a richness to the company’s reports.

“CFdesign has shortened the solution time of analyses by almost two-thirds,” said Chris Roach, CFD specialist for Morson Projects.

Customer Input Helps Drive CFdesign’s Evolution

A CFdesign feature that has been critical to Morson Projects is something called local mean age of air (LMA), which Blue Ridge Numerics added by Roach’s request.

“LMA is the period of time a quantity of air is circulated around the same area or building,” says Roach. “When you select ‘residence time’ within CFdesign, it automatically shows results on a plot or isosurface. This is one of the most important features we use for CFD analysis.”