Solar System

Calculating the position of the sun as it moves across the South West London sky is among the more complex routines performed by a Trend building management system in the Natural History Museum’s Darwin Centre (Phase One). Supplied and engineered by Energy Efficient Controls (EEC) Ltd, the system uses its solar tracking measurements to reduce the building’s energy consumption by automatically adjusting louvres on the south-facing glass façade. Inside the centre it maintains a closely controlled environment for staff, visitors and 22 million specimens from the museum’s collections.

The Darwin Centre is the most significant new development at the Natural History Museum’s South Kensington site since the latter opened over 120 years ago. It provides unprecedented visitor access to the museum’s vast and priceless life science collections, over 99% of which are currently hidden from the public’s gaze. In addition to guided tours, there are ‘meet-the-scientist’ sessions, when those who study the collections explain their research work. The £27million first phase of the centre houses the zoological specimens, some of which are centuries old. A second and final phase takes the entomology and botany collections.

Temperature and humidity control

Phase One of the centre comprises a 7-storey air conditioned building with a central atrium, to one side of which are the specimen storage facilities and to the other offices and laboratories. Each side is served by a pair of air handling units, with fan coil units in the offices and labs. The heating circuits are supplied by LTHW calorifiers that connect to the museum’s main boilers. The building has its own roof-mounted chillers. All the HVAC plant is controlled and monitored by Trend IQ controllers, each of the 96 fan coil units is fitted with an IQ212.

The majority of specimens now being moved into the building are preserved in methyl alcohol. To prevent this evaporating the storage areas must be kept at a fairly low temperature. At the same time humidity must not be too high as this would cause the labels on the specimen containers to peel off. The Trend system controls the air handling plant cooling and heater batteries to achieve a temperature set point of 13oC and a relative humidity of 55% (+/-5%). By applying enthalpy control it always uses the most energy efficient balance of fresh and re-circulated air.

Minimising heat gains and losses

The stores occupy the north side of the building. The offices/labs are on the south side, which features a double-skinned façade that is designed to maximise natural day lighting while minimising heat gains and losses. Between the outer glass screen wall and the building’s main skin is a 1m wide air space, which acts as a natural chimney for venting hot air. Behind the outer glass is a series of perforated steel louvres.

Using current time and date information, the Trend system computes the sun’s height in the sky. From this continually changing altitude measurement it angles the louvres to either reflect or let in the sun’s rays, depending on whether the office and laboratory areas require cooling or heating. Readings taken from a solar glare sensor tell it if the sun is obscured by cloud, which makes solar shading unnecessary and thus allow the louvres to be opened when there is demand for cooling.

If the air temperature in the gap between the two skins exceeds a preset maximum, the system vents the heat by operating high level dampers. At night it closes both the louvres and dampers, and the air space then acts as a layer of insulation that greatly reduces building heat loss.

Another of the Trend system’s functions is to monitor every fire damper in the building and generate an alarm should any of these inadvertently close. It also interfaces with gas detection equipment that monitors the level of alcohol in the air in the storage areas. Were this to exceed a preset value, the system would increase the ventilation rate.

The controllers are arranged on two local area networks; on one are the IQ250s and 241s that control the main plant, and on the other the fan coil units’ IQ212s. The LANs have been linked together via the building’s Ethernet IT network (using Trend EINC routers). Also connected to this is the system’s main operator interface – a Trend 962 supervisor in the museum’s estates office. ‘Client’ 962s (comprising nothing more than Internet Explorer) will provide system access inside the Darwin Centre.

Trend for twenty years

Trend building controls are not new to the Natural History Museum. The first were installed nearly two decades ago and the system that has subsequently developed now covers most of the site. EEC Ltd carried out several phases of the expansion. The site’s Ethernet network integrates the latest controls with the existing installation.

The main contractor on Phase One of the Darwin Centre was Shepherd Construction, with Shepherd Engineering Services acting as the M&E contractor. Buro Happold was the building services consultant. The building was designed by HOK.