An active chilled beam cooling system is to play a key role in delivering an expected 20 per cent reduction in cooling and ventilation energy consumption at the new Genomic Science Building at the University of North Carolina.
The Genomic Science Building has been designed to obtain a Silver certification rating under the Leadership in Energy & Environmental Design (LEED) programme from the United States Green Building Council.

The active chilled beam cooling system was developed by Affiliated Engineers, Inc. (AEI), Chapel Hill, North Carolina in collaboration with the project architect, Skidmore, Owings, and Merrill LLP (SOM). AEI engineers used Flovent computational fluid dynamics (CFD) software from the Mentor Graphics Corporation Mechanical Analysis Division to maximise the energy savings.
The Genomic Science Building is a $125 million research laboratory which will complement the eight-storey Medical Bio-molecular Research Building on the UNC School of Medicine Campus.

The new building will provide approximately 210,000 ft² of classrooms, laboratories and offices including nine wet labs, four bio-informatics labs, a 250-seat lecture hall, a 450-seat lecture hall, an 80-seat classroom, and four 30-seat seminar rooms. The construction start date was February 2009 and the projected completion date is February 2011.

LEED rating systems

UNC set the goal for the Genomic Science Building to exceed the requirements necessary to be certified at the Silver Level of the LEED rating systems.


The LEED Green Building Rating System was created by the US Green Building Council (USGBC) to establish a common standard. Affiliated Engineers had to provide an energy efficient mechanical design for the Genomic Science Building. Energy savings constitute the largest of five categories from which points can be obtained towards LEED certification.

'AEI was looking at ways to improve energy efficiency for the building,' said Bill Talbert, an AEI engineer, 'and chilled beams can be very promising in laboratories with equipment-driven loads'.

Cooling with chilled beams differs from conventional overhead supply air distribution in that they minimise the need for forced air supply by using natural convection or induced convection for cooling.

Passive chilled beams consist of an exposed chilled water coil suspended from the ceiling. Chilled water flows through the coil and convection induces warm air from the space across the coil which falls back into the space creating a natural air flow.

Active chilled beams use supply air distribution nozzles which magnify the effect of natural induction by creating a negative pressure zone on one side of the beam. Air systems are used to supply the minimum ventilation requirements for the lab while the chilled beams are used to meet the cooling loads that aren't met by the ventilation air. A key benefit of chilled beams comes from their ability to reduce the amount of energy used by the ventilation system.

Accomplishing cooling with pumped water instead of forced air is more efficient since water has a volumetric heat capacity 3,500 times that of air. In addition, the reduction in duct size can help lower floor-to-floor heights, which cuts construction costs.

Benefits from the use of chilled beams can be significantly greater in laboratories. Ventilation requirements in laboratories are often very high so the capital investment and energy savings provided by chilled beams can be large.

To evaluate the viability of this approach, AEI engineers needed to determine the type and size of chilled beams that would be needed and then estimate the amount of energy it would consume. CFD can calculate and graphically illustrate complex airflow patterns and space temperatures. The user may change the layout of the building or the operating conditions, and observe the effect of the changes on the airflow patterns and temperature distribution, and how they impact the cooling performance. Engineers are able to evaluate the performance of alternative equipment configurations.

AEI engineers used Flovent CFD software to simulate the operation of the HVAC system.

In lieu of modelling a whole laboratory, a representative laboratory bench module was selected to reduce input and simulation time. Flovent's built-in editor was used to generate the geometry of the laboratory and the major pieces of equipment in the room. Laboratory equipment heat dissipation was based on equipment manufacturer data provided by the laboratory planner, Research Facilities Design. Interior lighting and occupant loads were included.

Typical laboratory

The model consisted of a typical laboratory in the new building. An active beam cooling system was modelled which has two airflows, the airflow which is forced through the beam nozzles and the airflow induced by the lower temperature and negative pressure in the beam. The engineers defined the geometry of an active beam cooling system, the heat transfer between the air and the beam, the supply air temperature to the beam and the induced air volume through the beam. A steady state analysis of the chilled beams operating was simulated. The CFD simulation provided the temperatures, airflows and pressures at all areas. This made it possible to determine the cooling performance of the design and provided information that helped understand why.

AEI engineers used the results to work out the mechanical system requirements. A variety of active beam scenarios were analysed and a design was identified. The final design consists of three eight-foot TROX active chilled beam units above each bench aisle, each with 130 ft³ per minute (CFM) of primary flow at 55ºF and a 310 CFM-induced flow rate. The laboratories also have a dedicated air terminal unit which distributes air at the curtain wall to provide perimeter conditioning.

AEI engineers then used the resulting chilled beam capacities and ventilation requirements to work out an annual energy consumption simulation for the laboratory space. In addition to the chilled beam and ventilation system descriptions, the energy simulation includes annual operational schedules, internal loads, and weather data. TRNSYS, a Fortran programme used to simulate the transient performance of thermal energy systems was used to simulate energy use.

The energy analysis predicted the energy consumption of the laboratory conditioning systems will be about 20 per cent lower than conventional designs based on ASHRAE Standard 90.1-2004. These improvements played a key role in the energy efficient design of the building which is expected to help it achieve a Silver Level rating under LEED when it is completed.

For more information about Flovent, visit www.mentor.com/mechanical or
contact: 020 8487 3000