Engineers at Fläkt Woods R&D centre in Jönköping, Sweden, have created a world first; an air-handling unit with twin wheels. It uses approximately 50% less energy on the cooling coil without the requirement for a re-heater battery in the summer cycle.
Chilled beam systems offer exceptional comfort and indoor air quality (IAQ), however to avoid the issue of condensation on cold surfaces the dew point temperature of the air needs to be controlled at a level below that of the cold surface in question. The dew point temperature of outdoor air in the summer can often be well above the surface temperature of the coil in a chilled beam. This means that we must remove moisture before supplying it to the room. The traditional method is to use a cooling coil to condense out the water and then a re-heater to warm the air to a suitable supply-air temperature. This method demands a large cooling plant and is costly to run.
Explains Mike Beeton, Chilled Beams Product Manager at the Company, Using our knowledge of twin wheel technology and active chilled beam systems, engineers have created a more efficient method of providing dehumidification to the primary fresh air in order to avoid problems with condensation.
This technology is being utilised in London on one of the largest chilled beam projects in the Capital, where Fläkt Woods is supplying in excess of 2,300 chilled beams together with the AHUs VAV boxes and Displacement terminals, on Peninsula Central office development, part of the Terry Farrells giant Greenwich Peninsula master plan.
Prior to installation, both M&E consultants, Hilson Moran and the M&E contractor, Skanska, visited the Flakt Woods facilities Centre at in Jönköping in Sweden, where they witnessed a successful purpose built mock-up of the system simulating both summer and winter conditions
The first two office buildings comprise two separate buildings with a central pedestrian route between them, and it is here that employees of Transport for London, who has pre-let the first building, will be able to experience the new system when they move in later this year. The second building comprising 115,000 sq ft will be ready for occupation at the end of 2009.
As the name implies, the system uses two thermal wheels (rotary heat exchangers).
In winter, the heat of the exhaust air is absorbed by an aluminium rotor, which then delivers the heat to the supply air; and vice versa, in summer. Rotary heat exchangers are used when the supply and exhaust air ducts converge at one point. Low velocities through the rotor can ensure optimum heat exchange efficiencies typically between 70 -85% and pressure loss of 60 Pa. Whats more, owing to the reheat wheel, a separate re-heater is no longer required. This is ideal for a chilled beam installation that avoids any moisture problems.
In winter operation, the benefits are substantial as well. Not only do you get high levels of heat recovery but also most of the humidification load is supplied by the hygroscopic wheel further reducing the energy demand.