For a site with hundreds of window-opening motors and actuators, the system has proved robust. However, in Pavilion A, virtually every window motor has been replaced since 2001. The new motors have software that only drives the motors for a certain period. This prevents the motors trying to push the actuators beyond the point of maximum window opening. For the earlier motors, a pressure sensor would sense that the window was fully open. When those sensors failed, the motors would continue to drive the actuators, forcing gears to slip over the chains.
The lighting throughout the site is under the control of a Philips ECS system. Absence detection was employed in Phase 1 to cover for occupants failing to turn off lights when they left work. As most occupants of the (largely cellular) offices do turn off their lights, it was decided not to extend the absence detection system into the Phase 2 pavilions. In any case, absence detection proved to be a mild irritation to seated occupants working for longer than 20 minutes, as the system turns off the lights.
Lighting has significant out-of-hours use, due to long working hours. When a person enters a pavilion at night, all access routes stay lit for security reasons. In Phase 2 pavilions (which have no passive infrared detection) the lighting can stay on all night.
Pavilions F, G and H were subjected to an energy assessment to stage 2 of the CIBSE TM22 Energy Analysis Reporting Method.
Pavilion F is home to a COSMOS supercomputer that runs 24 h/day. The maximum load of the computer and its accessories is around 36 kW, but there is no sub-metering to verify its consumption. Pavilion G houses boilers and pump sets.
Occupants' computers are left running overnight in all pavilions as a matter of IT policy, primarily to perform campus-wide mathematical calculations (that would otherwise mean a much larger server) but also to enable out-of-hours software upgrades and maintenance.
Treated floor areas were estimated using guidance from Energy Consumption Guide 19.
The averaged electricity consumption for each of the three pavilions is estimated at 106 kWh/m2/y. As there are no established energy benchmarks for the CMS type of building, Chris Parkin created a set of bespoke benchmarks based on the proportions of the pavilions that were either naturally ventilated or air-conditioned (the latter estimated at 20 percent). Adjustments were also made for longer operating hours, but at a reduced 2300 degree-days per year.
As a consequence, electricity use comes in between the bespoke good practice benchmark of 74 kWh/m2/y, and a typical benchmark of 126 kWh/m2/y.
It was not possible to dis-aggregate the gas consumption of the three pavilions from that of an adjacent Ambient Flow Facility building (AFF), as there is no sub-metering on the gas supplies or heat meters. The gas consumption figure is therefore based on the sum of the treated floor areas of the pavilions and the AFF (5007 m2).
Correcting for degree days, the (estimated average) gas consumption for each pavilion is 155 kWh/m2/y - considerably higher than the bespoke good practice benchmark of 86 kWh/m2/y but below the typical benchmark of 163 kWh/m2/y.
Occupant survey results
In 2001, an occupant satisfaction survey was carried out in Pavilion B - plus smaller studies of Pavilions C and D. This revealed that the occupants regarded the buildings as comfortable. The responses were in the top decile for overall comfort and air quality in winter, lighting overall, comfort overall and needs. Relatively low scores were for temperature in summer, space at desks and health perception.
In July 2006, an identical survey was carried out in the three Phase 2 pavilions. As in 2002, the Pavilions returned very good scores for all criteria except air temperature and air quality in summer. The aggregated scores may be adversely affected by the large proportion of Pavilion B that has a high south-facing component, and the well-known problems with user controls and window opening. July was also the warmest month since records began in 1659. The maximum temperature measured in Cambridge University Botanical Gardens was 35.6 C on the 19 July. This compares with the dry bulb design condition of 28 C.
The CMS site is an extremely agreeable place to work, and the site plan fosters a strong sense of community. The buildings have aged well, a consequence of a good choice of building materials and high levels of building services maintenance.
The building highlights the virtues of good user controls and the importance of proper operating and maintenance manuals in order for the buildings to be operated in line with the design intention. The lack of heating and chilled water sub-metering, absence of energy monitoring software, and inability by the facilities staff to spend any time on energy saving activities militates against improvements in the site's energy efficiency. Despite these shortcomings, the estimated energy consumption has bettered what might be considered typical for buildings of this kind. It would be interesting to see how the site would improve given sufficient time, effort and metering technology.
For more information contact Roderic Bunn at BSRIA:
T: 01344 465516