Number one for Energy Efficiency
The energy required to heat, cool, ventilate and light Cellnet's new Service Provision Division HQ at No1 Leeds City Office Park is only 25% of that needed by a typical prestige office building - and this despite it being fully air conditioned.
A Trend building management system has made a vital contribution to this high level of energy efficiency. As well as controlling all the HVAC services - which include chilled ceilings - it has enabled remote monitoring of their performance, and this has led to problems being quickly identified and put right. Most of the system was supplied, engineered and commissioned by AES Control Systems of Northampton - to Oscar Faber's detailed design and specification.
No 1 Leeds Office Park was developed by British Gas Properties and provides 6500m2 of office space. The subject of an EU grant (under the Thermie scheme), it is one of eight 'Energy Comfort 2000' projects, whose purpose has been to develop concepts for commercial and public building which significantly reduce energy consumption.
The building combines a range of features designed to limit energy usage, such as high thermal mass, high levels of insulation, high utilisation of natural light and solar shading. Originally, it was intended that the offices would be cooled partly by natural ventilation and partly by a low velocity mechanical system, with occasional use of forced night ventilation in the summer. However, when the premises were let to mobile phone operator Cellnet, it became immediately apparent that this would not meet their needs - largely because the building was to be used 24hours a day. Some form of air conditioning was unavoidable.
Oscar Faber developed a novel solution based on an initial concept devised by Sonofoss Design Services Ltd; it involved the installation of large chilled ceiling panels throughout most of the three-storey building. It was also necessary to upgrade the existing H&V plant.
This included installing an extra boiler and adding cooling and humidification to the main air-handling unit, which delivers air, at floor level, to the whole building. Yet, though the services have been substantially uprated, energy consumption is in fact slightly less than the level originally predicted for the building.
Because they have a large surface area and the 'coolth' they provide is over 50% radiant, the ceiling panels can be supplied with water at relatively high temperature (14-18°C). This is primarily supplied (via a heat exchanger, secondary circuit and zone valves), by a cooling tower circuit. Should this be unable to maintain the temperature setpoint then chilled water is directly injected into the secondary, the source being a pair of 200kW chillers (with heat recovery) whose main function is to serve computer room air conditioning plant. In practice the cooling tower circuit copes unaided virtually all of the time. Indeed, the chilled water valve has gone months without opening at all.
All of the cooling/chilled water plant is automatically controlled and monitored by the Trend BMS, as is the air handling plant, boilers and heating/hot water circuits. Many of the strategies it implements are designed to save energy by avoiding unnecessary plant operation.
For instance, on the cooling tower circuit it closely regulates pump and tower fan speeds (via inverter drives) in strict accordance with demand.
In operating the main AHU, it constantly monitors air quality throughout the space and controls the recirculation damper and fan speeds accordingly, one effect of which is to prevent energy wastage when building occupancy levels fall. Among its many other tasks, the BMS also controls the AHU's heat recovery system to achieve maximum savings. The BMS comprises nine Trend IQ intelligent controllers of various sizes. Two were installed when the original plant went in and AES has had to modify and expand the control strategies these implement. The system's main operator interface is a graphics-based Trend 945 supervisor, which is used by the building's facilities manager and maintenance team.
The system has also been monitoring the site's gas and electricity consumption and the figures have been used in a report on the building produced by consultants ECD. Data collected during a four-month monitoring period showed a total energy usage equating to carbon dioxide emissions of just 37kg/m2/yr.
Though excellent energy efficiency has already been achieved there is still scope for further savings through measures such as fine tuning of certain control settings and modifying some aspects of how plant is operated.
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