27-Danfoss Ltd Invertor Drives Controls Motors News 010708

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Danfoss Ltd - Radisson SAS hotel achieves 70% energy savings on air handling units

The 4 star deluxe Radisson SAS Hotel Manchester Airport has set itself the target of achieving 5% reductions in energy and water usage year-on-year. As a first step toward this target, Tim Biss, the hotel’s Chief Engineer, looked at the air conditioning systems which represent a major part of the hotel’s energy consumption and how the energy usage of the air handling units (AHUs) and constant temperature (CT) pumps could be reduced by variable speed control of the fans and pumps.

The building, containing 31 function suites and 360 bedrooms, is controlled as a number of zones including the east and west wings, the kitchen, restaurant, public areas and the ballroom, as the major elements of the system. The whole building environment is controlled by an IMServ Europe BAS 2800+ building energy management system (BEMS)

IMServ Europe, formerly Satchwell and now part of the Invensys Group, have an ongoing Support and Energy Partnership with Radisson, as part of which they hold regular energy management meetings. IMServ called upon Danfoss, with whom they work regularly, to conduct a survey of the hotel’s climate control system and advise on the retrofitting of variable speed controls to the AHUs and pumps.

The east and west wings of the hotel are served by AHUs 4 & 8, each comprising an 11kW forced draught fan and a 7.5kW extract fan, running on average 20 hours per day. Running costs for each of the systems were measured at £5478 per annum. Danfoss VLT 6000 variable speed drives were fitted to these fans and linked into the IMServ BEMS.

Previously started direct on line, and run at constant speed, the drives are now commanded on / off via a time schedule (digital output) on the BEMS. Once enabled, the drives can then be initiated to run at a speed, controlled via a 0-10v analogue signal from the BEMS,
varied dependant upon a pressure transducer located in the supply duct, reporting to the BEMS and maintaining duct static pressure at a set value.

Costs were also curtailed by selecting IP54 VLT 6000 series drives which are specifically designed for this type of application. The drives were mounted on steel racks adjacent to the motors in the plant rooms and this made for a quick and easy low cost 3-wire in /3-wire out retrofit exercise. After the installation of the drives, energy costs were measured at £1634 per annum, a saving for each system of £3844 per annum – a huge reduction of 70%. Despite the relatively small ratings involved, the payback period was calculated to be only 10 months.

This simple low cost exercise and the significant savings achieved, prompted the addition of variable speed control to the 37kW constant temperature pumps. Again a Danfoss VLT 6000 unit was fitted adjacent to the duty and standby pumps and linked into the BEMS. The CT pumps run 23 hours per day, supplying cooling water to the air handling units, and prior to modification, were operating at 23kW absorbed power, costing £8244 per annum. Running on variable speed control, annual energy costs were down to £4670, a saving of 45% with a payback period of 1 year 5 months.

Subsequently, VLT 6000 drives have also been fitted to the 15kW motors powering the air handling units for the ballroom and public areas and the restaurant and kitchens are now also being fitted with 15kW drives, with a projected payback period of 15 months. A further 6 drive systems will be fitted over the coming months and the Radisson SAS Manchester Airport Hotel now hopes a major portion of the costs imposed by the Climate Change Levy will be offset simply by the adoption of variable speed control on their fans and pumps.

Email: uk.drives.sales@danfoss.com