Building Technology Systems (BTS), an independent control system expert with wide experience of energy optimisation, has selected variable speed ac drives from Vacon for use in an important energy efficiency project at one of Europe’s largest and most prestigious conference hotels – the four-star London Hilton Metropole, located on Edgware Road.
A total of 26 Vacon NXL drives, with ratings from 5.5kW to 30kW, and two NXS drives rated at 45kW have been installed at the hotel, where they are controlling the pumps used in the building’s extensive chilled water and LTHW (low-temperature hot water) systems. All of the drives used on the project were supplied by Vacon technical partner Park Electrical Services of Wrexham.
The drives replace fixed speed starters that had been in use on the chilled water and LTHW systems since they were first installed. While these starters were operationally satisfactory, and were standard equipment at the time of installation, they mean that the pumps always operate at full speed even when demand is low.
By replacing them with variable speed ac drives, it is now possible to match the speed of the pumps to the instantaneous demand on the systems, which means that the pumps run at reduced speed almost all of the time. This leads to big energy savings – as the energy requirements of pumps of the type in use at the Metropole Hotel vary as the cube of the running speed, if the speed is reduced by just 30%, the energy needed to drive it is reduced by almost two thirds.
“Vacon drives were particularly well suited for this application as they are compact, they offer PID control facilities as standard, and they have integrated EMC filters,” said Dean Brookes, a director of BTS. “We could, therefore, install them in any convenient location, without having to worry about mounting additional components. A further benefit is that they have an IP54 rating, so for indoor applications they don’t need to be mounted within an enclosure – they can simply be fixed directly to the wall.”
The BTS engineers also found that the NXL and NXS drives, which feature a time-saving start-up wizard that automatically determines the best operating parameters for the application, were fast and easy to set up. The very competitive pricing of the units was another important benefit, both for BTS and for the end user.
Taking full advantage of the communications options offered by Vacon drives and working closely with Les Cordery, Facilities Manager at the London Metropole, the BTS engineer linked the drives to the hotel’s building management system (BMS). The engineers also added pressure sensors to some of the cold water and LTHW circuits, allowing modification of the variable volume systems so that the pump speeds are modulated to accurately match the actual load of the building at all times.
“The installation work was carried out with a minimum of disruption to the hotel’s operations, and the new drives have proved very satisfactory,” said Dean Brookes. “They operate fully automatically, they require no routine maintenance, and they are providing the hotel with very significant energy savings. The cost of purchasing and installing them will be recouped very quickly and, of course, the hotel’s carbon footprint has been dramatically improved, something that is of particular concern to the Hilton Hotel Group.”