Rotork actuators improve air conditioning performance at the National Portrait Gallery

"The installation of Rotork IQ electric valve actuators on the air conditioning plant has enabled us to operate the system with improved efficiency and economy". Says Allan Tyrrell, Engineering Manager at the National Portrait Gallery in Central London.

In combination with sophisticated lighting control equipment, the advanced air conditioning plant helps to look after the well-being of a priceless collection of 10,000 portraits - the oldest dating from 1505 - together with a photographic collection, archives, a library and visiting exhibitions. Gallery temperatures are maintained at 21?C, with 50% relative humidity, under the control of an Allen Bradley building management system (BMS) with only very small margins for error throughout the changing seasons of the year.

Allan Tyrrell recognised how a valve automation upgrade would improve the performance of the air conditioning system. He explains: "Two new Carrier chillers were installed on the roof in 2000, each served by a 30kW pump. Experience showed that running both chillers at once was not always necessary and during these periods operating both pumps and trying to balance the chiller settings to achieve the desired coolant temperature of 6?C proved to be an uneconomical and inefficient way of operating the system.

However, shutting down a chiller circuit involved switching off the appropriate pump and laboriously closing one of two 150mm isolating gate valves, both inconveniently sited on the roof. By motorising these isolating valves and linking their operation to the pumps, these actions could be brought under the automatic control of the BMS, enabling the system to run much more responsively and therefore more efficiently."

Allan contacted Rotork as he had successfully used Rotork electric actuators at other sites and been impressed with their high reliability and low maintenance requirements. Rotork's specialist Site Services Department offered a complete package for the National Portrait Gallery project, encompassing a survey of the existing valves, actuator sizing, design and fabrication of valve adaptation, actuation installation, wiring up and commissioning.

Meanwhile, software company Davenport Controls worked with Carriers to develop the programme that would enable the IQ actuators to be controlled by the BMS, using signals from temperature and flow rate sensors in the pipework.

Allan concludes: "Operating experience has vindicated the decision to upgrade, with the plant running more efficiently and without the need for human intervention. The Rotork actuators are normally running fully automatically, but they still give us the ability to operate the valves locally if there is a problem with the control system, or even manually in the unlikely event of a loss of power."