Cool comfort

Business clients are increasingly aware of the effect of indoor climate on productivity and well being of their staff. Those involved in the design and construction stage now look to prove beforehand that the systems and products will meet the necessary specifications in order to fulfil the client's aspirations.

Laboratory-based modelling successfully predicts real life situations and makes it possible to achieve the correct results first time.

BSRIA has recently undertaken laboratory tests, at the instruction of Hoare Lea for BP International, on chilled ceiling and beam combinations with a displacement ventilation system.

The tests were undertaken on a full-scale mock-up of a typical perimeter office arrangement proposed for phase two of BP's 60 000 m² redevelopment project at Sunbury-on-Thames. The purpose of the tests was to establish the indoor climate and cooling performance of the system when subject to solar and internal heat loads.

The BP Sunbury mock-up was unusual in the way that the chilled beam was arranged above a sloping ceiling and approximately 1m away from the facade.

While similar tests had been carried out on the earlier phase one project, they were undertaken after contracts had been let for the different elements of the system at a time with critical programme implications. The aim of these tests was to validate a range of products beforehand so that tenderers would have wide procurement choices open to them.

Test programme
Six room air movement surveys, were carried out by BSRIA to assess the resulting indoor climate utilising four different chilled beam products put forward by manufacturers to meet Hoare Lea's performance criteria.

To assess the indoor microclimate performance of the proposed design, it was necessary to obtain values of air velocities and air temperatures within a typical modular space of the enclosure. This was achieved by physical modelling techniques, which involved the actual measurements of air velocities and temperatures in a laboratory based full size mock-up. The purpose of the measurements was to assess the performance of the combination of chilled beam and chilled ceiling and to assess the resulting indoor environment conditions.

A twin skin test room with internal dimensions of 3·2 m wide by 5·1 m deep by 3·2 m in height was constructed within a BSRIA environmental test chamber at its Crowthorne site.

A ventilation plant supplied fresh air at the specified temperature and flowrate using a centrifugal fan chiller and expansion coil, an electric heater battery and an airflow temperature feedback controller. Sophisticated monitoring equipment was used to record the supply and extract flowrates. The air was supplied via floor mounted displacement diffusers. Extract was through a plenum situated above the ceiling of the test rig.

The thermal loads in the test facility were set up according to Hoare Lea's specification and were simulated by the use of electrical heating to represent the solar gain, small power equipment, occupancy, and lighting. Each of the electrical heat loads was adjusted in turn using a single-phase electricity meter to measure the power drawn.

The conditions for each test were established using the thermal gains and system settings specified. When steady state was reached, the following parameters were measured:

• supply and extract air temperatures
• supply and return water temperatures and flow rates
• surface temperatures of internal and external walls
• room air temperatures and air velocities
• globe temperature
• electrical consumption

For the room air movement surveys, temperature and velocity measurements were taken on a regular 5 by 11 grid, starting 0.5m from each wall. Air temperatures and air velocities were measured in the mock-up in six heights: 0·1 m, 0·5 m, 0·9 m, 1·2 m, 1·5 m and 1·8 m. The height for the globe temperature bulb was attached to the pole and measured at 1·1 m.

Once stable conditions had been reached, the room was scanned with an instrumented anemometer pole. The pole was moved sequentially through the grid positions in the space. Readings were taken over a period of 120 seconds at each position. On completion of each set of readings, the data were recorded automatically and an engineer moved the pole to the next grid position. This process was continued until all measurement grid locations have been visited. Following full testing of each chilled beam, smoke visualisation tests were undertaken.

As the object of all hvac systems is to provide the proper combination of temperature, humidity and air movement within the occupied zone, it is essential to have indicators to define the performance of the system used.

The measured physical parameters were analysed along with key indicators of indoor environment performance. This included predicted mean vote which characterises the thermal sensation of the human body.

Conclusion
The series of laboratory-based tests on the mock-up of BP Sunbury has been carried out for a combination of beams with louvred and 50% perforated ceiling tiles. In each case a detailed set of data has been obtained covering indoor climate parameters and the overall performance of the chilled beams, with the predicted mean vote and percentage people dissatisfied calculated using a clothing level of 1 met. The tests have shown that all the chilled beams tested deal effectively with the perimeter heat gains (1·3 kW), within a zone that extends about 2-2.5 m into the room (except the 50% perforated tile test which extended the zone further into the room). The ability to capture and deal with solar heat gains at the perimeter is an important feature of this kind of system as it releases the full potential of the inboard chilled ceilings to deal with internal heat gain sources.

All chilled beam/ceiling combinations tested provided the required thermal performance to meet the design cooling duties. The tests also indicated that the chilled beams respond very effectively to changes in the solar convection load.