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26 Chilled Beams The energy study


The EDSL Tas Energy study released in the summer of 2013 was the source of much debate in the industry. Here, Andrew Jackson, chairman of the CBCA comments on the study’s results.


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THE LATEST STUDY by the CBCA (Chilled Beam and Ceiling Association) reveals critical considerations for energy savings in commercial buildings. This is timely for the industry as a whole to examine the options for cooling technology in order to assess the most energy efficient options. This new EDSL Tas Energy Study has simulated the dynamic thermal performance of four differently-sized office buildings, and compared the energy


consumption, CO2 emissions and the running costs of different HVAC systems within these office buildings.


Systems


The three systems analysed were: VAV fan coil units with EC motors, passive chilled beams (95% convective/5% radiant) and active chilled beams. The building models have Part L2 notional constructions and glazing percentages. The models have been zoned as specified in the NCM (National Calculation Methodology) Guide and incorporates 6m perimeter zones which enable the different solar gains to be analysed. Each HVAC system included a high efficiency chiller which supplies chilled water to the terminal units being analysed. An air source heat pump supplies heating and cooling to the DX coils in the AHU which includes heat recovery; the AHU for all systems is sized to provide the minimum fresh air requirements in accordance with NCM methodology for an internal office environment. All systems included a boiler with an efficiency of 90% and DFX performance was taken from typical Mitsubishi VRF heat recovery unit.


Results


The annual plant energy running costs savings achieved


using chilled beams can be seen in the annual plant energy cost comparison chart which is split for each particular building and shows the available annual running cost saving expressed as a percentage against the VAV fan coil system benchmark (100%).


The results are important for the industry as a whole as the Annual Plant Energy Cost Comparison revealed that there are potential energy and cost savings that can be made using products that are already available on the market. These energy cost savings were shown to amount annually to approximately 17% for the passive chilled beam system and approximately 22% on average for the active chilled beam system over the VAV fan coil system modelled.


The passive chilled beam system’s energy consumption was slightly higher than the active beam system, primarily because the passive beam’s displacement ventilation system requires a higher fresh air supply temperature in order to meet occupant comfort than that of the active chilled beam system – both systems had the same fixed AHU SFPs.


The increased air supply temperature on the modelled displacement ventilation system results in increased energy usage on the fresh air re-heat DX circuit, and also results in less airside cooling being available. Therefore during certain times of the year where outside conditions effectively allow the active beams to have a higher level of ‘free’ airside cooling than a passive system, which will have to make up any shortfall or airside cooling through waterside cooling which results in a slight increase in the chiller energy consultation. Additional energy savings can be achieved by increasing the chilled water flow and


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