University College - London

Significantly, it is the first anywhere to feature passive downdraught cooling. A Trend BMS supplied and engineered by Lincoln Green BMS Ltd ensures that the SSEES’s cleverly designed new premises operate exactly as intended by architects Short & Associates and building services consultants Environmental Design Partnership. The advanced, Ethernet-based system features the recently developed Trend OPC server, which allows it to individually control the opening and closing of 150 windows.

 

Hemmed in on three sides by other UCL premises, the new 7-storey building serves both as a library for SSEES’s rare collection of books and as office accommodation. The building’s lower floors are largely library areas, while the upper ones are a mix of open plan areas and individual offices. From ground level up, all floors surround a large central lightwell, which is a key element of the ventilation and cooling system. It is through windows in the lightwell that air enters the floors; it exits via an outer set of high-level windows to a stairwell or risers and is exhausted through 14 stacks, being drawn out naturally by the thermal effect these induce. The only windows in the building that actually open to the outside world are at the head of the lightwell.

 

The fact that nighttime temperatures in central London can be 6oC higher than in rural areas posed a particular challenge, since it limits the opportunity for night cooling of the building fabric during peak summer conditions. It has thus been necessary to provide additional cooling during the day. Environmental Design Partnership, in conjunction with the Institute of Energy and Sustainable Development, devised a unique, low-energy solution. It takes the form of a ring of cooling coils situated next to the windows in the lightwell head. When the windows are opened, the air is chilled and a passive downdraught effect thus created – ie, cool air is drawn down the lightwell and on to the floors.

 

There is only one fan in the entire building, this being needed to assist ventilation of the lower ground floor, which does not connect to the lightwell.

 

The higher temperatures in the capital could also have made it difficult to maintain the thermal stack effect that is necessary for natural ventilation. The problem has been innovatively avoided by having the chiller condenser water circuits pass through the stacks; the heat from the condenser water warms up the surrounding air, thereby encouraging its upward movement.

 

Virtually all areas are heated by radiator circuits, the primary heat source for which is a district heating scheme. Fresh air normally enters the building through ground floor dampers, and is then heated to 20oC before rising up the lightwell. As well as providing (displacement) ventilation of the floors, the flow of air is also used to cool any area that is showing signs of overheating. It is only in hot weather that the cooling coils are activated and the airflow in the lightwell reversed. When ambient conditions make night cooling feasible, all the windows and dampers in the building are fully opened.

 

The Trend BMS provides close, coordinated control of every element of the heating, cooling and ventilation system – continually modulating window and stack and inlet damper positions to ensure that desired conditions are maintained without unnecessary use of energy. It constantly monitors readings from numerous temperature and air quality sensors, as well as from a roof-mounted weather station that measures wind speed and direction and whether it is raining – data that affects its control of the top lightwell windows.

 

Lincoln Green has installed 12 Trend IQ3xcite controllers to perform the various control and monitoring functions. The Ethernet network to which these link also connects to the Trend OPC server. OPC is a standard interface that allows interoperability between control applications – in this case between the BMS controllers and a WindowMaster window actuating system. By means of the interface the former are able to signal the latter and tell it by how much to open or close any one of the 150 windows. The BMS also poles every window once a minute; if it finds one open that should be closed it raises an alarm.

 

The availability of the Trend OPC server obviated the need either to develop a custom designed interface or to hardwire the BMS to every one of the numerous WindowMaster controllers. The latter option would have proved very difficult anyway owing to the limited space in which to run cable, there only being a depth of 65mm within the floor void.

 

In the open plan areas the inlet windows are opened/closed in sequence to match ventilation and/or cooling demand. The outlet windows in each area are moved by a corresponding amount. The degree of opening of the stack dampers is also matched to the position of the windows, thereby achieving stable airflow. When air quality and temperature requirements in a zone are satisfied, all windows are fully closed, which avoids having to treat fresh air unnecessarily and thus reduces energy consumption.

 

Lincoln Green has had to create a control strategy of some complexity. A measure of this can be gained from looking at the effect of a single office temperature sensor registering an increase. This could lead to the opening of an inlet and an outlet window and the movement of a supply and stack damper. Since one IQ3 positions the stack dampers and there is another on each floor controlling the windows, there is a high level of inter-controller communications. Considerable comms traffic is also generated due to the interface with the WindowMaster system.

 

Owing to the IQ3xcites’ highly flexible firmware structure, the need for a large number of controller comms modules did not present a problem. In addition, the controllers’ use of an Ethernet network has meant that the unusually large amount of data traffic could easily be accommodated. However, probably the main advantage of using a high-speed network such as Ethernet is that it will make it much easier for Lincoln Green to remotely interrogate the system. As part of its contract, the company will monitor the building for a year.

 

There are Trend controls elsewhere on the UCL estate and FM staff will be able to manage and monitor the new system, via the university Intranet, from an existing Trend ‘963’ supervisor. There is also a ‘963’ within the SSEES building.

 

Lincoln Green BMS Ltd can be contacted on 0115 955 5770.