COOLING CHILLED BEAMS
kWh/yr 12,000
Geothermal Cooling with typical chillers 9,000
Cooling with geothermal energy Energy and CO2 reduction CO2 reduction over baseline
kWh/year 11,350 2,200 -9,150
kgCO2 4,800 900
-3,900 -6.7%
Chilled beam comparison between open loop geothermal generator (8.9 kWe/kWth) and air cooled chiller (2.5kWe/kWth)
6,000
(Part L compliance calculations in accordance with the National Calculation Methodology, and using dynamic simulation with accredited software, IESve V6.0.2)
3,000
The 950 sq m area served by the chilled beams was modelled using commercial accredited software. When considering the yearly operational benefits of a chilled beam connected to an open loop geothermal system, compared with a chilled beam connected to a traditional air-cooled chiller with a seasonal efficiency of 2.5, the expectation for this system is clear – as shown here.
0
/year
Cooling with typical chillers
Cooling with geothermal energy
air pressure drop and the potential for noise due to higher air velocities in beams closest to the main distribution. The planning required for incorporating
The geothermal cooling system is ‘demand-led’ being controlled directly by measured occupancy levels
chilled beams into a building design should not be underestimated, particularly when, as in this case, they are being used in conjunction with an exposed soffit; interconnecting pipework and ductwork are fully exposed and the units themselves will shield some of the beneficial thermal mass from the occupants below. Additionally the height – usually a minimum of 2.7 metres from the floor – and the relationship to occupants needs consideration in terms of maintaining appropriate comfort, and, of reducing the potential for close exposure to low temperatures above occupants heads. Relative to a distributed system such
as fan coils, the maintenance of a chilled beam system is less as it has fewer filters. However, water flow rates are usually low, which can result in dirt particles gravitating out and depositing in water coils, so the use of filters or particle separation with appropriate maintenance and flushing is essential. Chilled beams can typically operate at
a chilled water flow temperature of 15C, which in itself can achieve significant energy savings over a traditional system that requires refrigeration to supply water temperatures below 10C; but when connected to the open loop geothermal system, with a generator efficiency of 8.9 kWe/kWth, the benefits in terms of reduced CO2 emissions have been modelled as significant.
50 CIBSE Journal November 2011 The geothermal cooling system is
‘demand-led’ being controlled directly by measured occupancy levels. The floor templates are zoned into 14 occupied areas, six of which are cellularised offices and the remaining eight are open-plan spaces. Each zone is capable of independently controlling temperature and air flow through variable volume dampers and a two port valve cassette system. Occupant sensing is achieved through passive infra red sensors located throughout floor templates, which monitor occupancy levels and report, via a building management system, to variable volume secondary pumps. These react by increasing or reducing air and water volumes as required – thus optimising the energy consumed by the pump. Photovoltaic cells incorporated into
glazed modules act as solar shades to minimize solar gain to the building whilst generating electricity. Each module was specifically designed to create a glazed atrium forming the roof, spanning the existing and new building. The technology was completed in 2010
as part of the two-year refurbishment project, and is in the process of having the monitoring system re-commissioned. Some initial test data is available, but further system commissioning is currently in process and further data will be made available during the operational period of the building.
l Paul Downie is founder of Downie Consulting Engineers
www.downieconsult.com
www.cibsejournal.com
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