Computer modelling microclimate performance assessment by cmb14063


									             Computer modelling: microclimate performance assessment

                                                             Decisions taken by a design team can have a significant
                                                             impact on energy consumption, indoor climate perfor-
                                                             mance, occupant health and productivity. To get things
                                                             right and avoid expensive post occupancy remedial
                                                             treatment, designers need to be able to predict air
                                                             movement, temperature distribution and concentra-
                                                             tions of airborne pollutants and smoke.

                                                             Using well proven computational techniques such as CFD
                                                             (computational fluid dynamics) and dynamic thermal
                                                             energy modelling, BRE experts are able to provide
                                                             solutions in all aspects of building and environmental
                                                             engineering design including:
                                                             • temperature distribution
                                                             • ventilation effectiveness
                                                             • thermal comfort
                                                             • air quality
                                                             • electric lighting and day lighting
                                                             • fire and smoke movement
                                                             • occupant evacuation

                                                             For some designs, we may recommend physical modelling
                                                             tests in BRE’s Environmental Chamber. Here within a
                                                             controlled but versatile area, performance is simulated and
                                                             monitored in real life conditions.

                                                             ‘Virtual’ wind tunnel modelling
                                                             In certain circumstances, CFD modelling can be used as an
                                                             alternative to wind tunnel testing. When this is the case,
                                                             our experts design a programme of work that will predict
                                                             airflow and highlight the impact of the wind on building
                                                             performance and pedestrian comfort. If a design needs to
                                                             be changed, we work closely with the client to develop a
                                                             sound and commercially viable solution.

                                                             For more information about our CFD services
                                                             please contact:
                                                             T +44 (0)1923 664300

             BRE, Garston, Watford         BRE Scotland
             Hertfordshire WD25 9XX        Kelvin Road
                                           East Kilbride

             T 01923 664000
             F 01923 664010                Glasgow G75 0RZ
             E-mail:   T 01355 576200
                    F 01355 576210
Case studies

A major shopping centre                                        A major retail development
Here the design team were concerned about the influence        The main concern on this project was to predict the
of a complex roof structure on the mechanical exhaust          microclimate conditions in and around the development
systems.                                                       and the effect it would have on pedestrian comfort.
                                                               ‘Virtual’ wind tunnel modelling based on CFD techniques
The geometrical complexity of the atrium space and roof
                                                               was used to simulate the external airflow pattern, wind
structure meant that the preliminary zone model calcu-
                                                               speed and pressure distribution in and around the
lations could provide only an approximate assessment of
the required smoke exhaust capacity. JASMINE* computer
simulations were performed to study the smoke hazard           Although some localised ‘higher than desirable’ air speeds
associated with a fire in a ground floor shop unit, and to     were predicted with rather severe specified wind condi-
determine the exhaust capacity of the smoke control            tions, these were not in the locality of the main core of the
system required to allow people to evacuate the building       development and pedestrian walkways. BRE worked
safely.                                                        closely with the architects to develop appropriate, safe
A range of smoke exhaust configurations were modelled
to find the optimum arrangement for the distribution of
fans so as to minimise the amount of ducting and cabling.      And at home...BRE’s Environmental Building
                                                               The design brief for this project required a strong emphasis
An international airport                                       on energy-efficient and environmentally friendly building
                                                               service systems. At the design stage we were able to
Coupling a study of smoke and heat transport with
                                                               predict the annual energy and microclimate performance.
predictions of human behaviour, we were able to provide
                                                               This involved dynamic thermal energy and CFD modelling.
the client with a complete integrated smoke movement
and evacuation analysis. This was used to inform the design    Dynamic thermal energy modelling was used to study the
of the smoke extraction system.                                overall energy and environmental performance of the
                                                               building, followed by detailed microclimate simulations.
The main issue here was whether the proposed open plan
                                                               CFD simulations were undertaken to examine the
design for the arrival/departure area and the retail atrium
                                                               operation of the natural ventilation concept, in particular
space would be safe in the event of an accepted fire
                                                               in respect of the five ventilation shafts. These had been
scenario. It was proposed to use minimal compartmenta-
                                                               designed to assist the cross-ventilation flow of air in the
tion and structural fire protection, and to leave the HVAC
                                                               event of low atmospheric wind conditions. The study
system running in 100% replacement mode.
                                                               confirmed that the ventilation shafts were of benefit in
The design fire used for the modelling studies was based       conditions of moderate external temperature and low
on a luggage fire test undertaken at BRE. Using this data as   external wind, with particular benefit for the night-cooling
the source term in JASMINE* computer simulations, we           cycle where it is important to maximise the flow of
were able to demonstrate that the smoke layer in the           external air across the exposed thermal slab inside the
departure/arrival area and retail atrium space would not       office space.
cause a problem to the evacuating people, and that the
structural elements would not be damaged by the heat.

The integrated smoke movement and egress simulations
confirmed the original design concept.

* JASMINE is a fire special-purpose computational fluid
  dynamics (CFD) code developed by FRS/BRE

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