500 Bed Hotel - Mechanical Ventilation

Introduction

This 500 bed hotel to the north-west of London is designed around a central atrium, which is planned to contain the reception area and two cafes/restaurants.

The large glazed frontage, shown to the left is east-facing, and consquently any over-heating due to solar gain is likely to occur in the early morning. To mitigate against this, shading is provided by a roof overhang (shown to the left) and several walkways (see CFD section below).

The plan is to cool the space using strategically placed displacement terminals delivering air at 18 degrees. Flow Analysis were commissioned to determine how many terminals would be required to ensure that the air temperature in the atrium does not exceed 21 degrees.

Dynamic Thermal Simulation

The dynamic thermal simulation model was built from the architect's drawings, details of building materials and heat gains determined from a complex schedule of occupancy. A south-east of England weather file was used to drive the simulation.

As expected, the simulations predicted peak temperatures to occur in the morning (around 9am) during the summer months (see the graphs to the right).

The thermal properties of the glass were found to be of over-riding importance to the predicted temperatures in the atrium. Two types of glass were tested in the model, which resulted in the predicted air temperatures differing by about 1 degree. However, this extra 1 degree required 63% more displacement air - a massive increase, in order to maintain the temperature below the strict 21 degrees design criterion.

The ground level of the atrium was divided into six zones which enabled the optimum placement of the extra displacement terminals to be determined.

Computational Fluid Dynamics

The CFD approach allows for much more detail to be added to the model. The figure to the left shows the bridges at four levels and the raised cafeteria platform with individual displacement terminals and the central 'wine-tower'.

The results shown below are a 'snapshot' at 9am, July 8th, chosen due to the particularly severe solar gains.

With the lower specification glazing, the sun causes significant heating of the floor near to the east-facing glazing, which leads to the predicted severe air movement shown in the velocity vector figure to the right.

Elsewhere, the air speed is predicted to be comfortable, at less than 0.3m/s. In most of the occupied zone, the temperatures are predicted to be comfortable, the exception being in a speciality restaurant area (top left) where there appears to be too much cooling.

Conclusions

The properties of the glazing were found to be of paramount importance to the predicted environment. It is recommended that high specification glazing is used.

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