The Evolution of Chilled Beams
European design engineers discovered that if they lowered chilled beams below a ceiling, each individual panel’s convection-cooling component could be increased. This satisfied the need for increased cooling loads caused by the expanded use of computers within the space. In addition, higher cooling capacities were needed for exterior zones to deliver better overall comfort. By lowering the panels, chilled panel capacity could be increased to approximately 120 to 150 Btuh per square foot of the beam or beam coil area. Also known as a passive chilled beam, this configuration resembles a beam when mounted below a ceiling and is passive because natural convection is the convective-cooling component.
The high cooling capacity of a passive chilled beam can help satisfy increased equipment loads in interior spaces and solar loads in exterior spaces. To further boost a passive chilled beam’s cooling capacity, conditioned ventilation air from a DOAS can be used to flow air through a chilled coil, further increasing the beam’s convective component. This configuration is known as an active chilled beam. Ventilation air is introduced to a chilled beam through a venturi, generating a higher velocity and, subsequently, a lower pressure region inside the chilled beam. This low-pressure region induces room air to flow up through the chilled coil and mix with primary air from the DOAS. The airflow over the chilled coil is reversed for an active chilled beam, and the induced room air flows up through the coil.
Active chilled beams sometimes are referred to as “induction diffusers.” Air from an active chilled beam is introduced into a space through a slot diffuser, creating a Coanda Effect. Inducing warm room air to blow through a chilled coil substantially increases chilled beam capacity. Active chilled beam capacities range from 350 to 600 Btuh per sq. ft. of beam or beam-coil area. Depending on the temperature and quantity of primary air supply from a DOAS, this can add up to 300 Btuh per sq. ft. of beam or beam-coil area. An active chilled beam can deliver from 500 to 900 Btuh per beam or beam-coil area between the chilled coil and primary air.
One thing radiant and chilled beam systems have in common is lower air volumes (1 to 2 ACH vs. 7 to 10 ACH). Lower horsepower and fewer materials are needed to achieve the same or better levels of comfort than with air systems, such as variable-air-volume (VAV), rooftop, variable-volume-and-temperature, and constant-air-volume systems.
The total peak power demand of radiant cooling system, including transport and generation systems, is almost 25% less than that of an all-air system. This decrease – which includes a 50% reduction in transport energy – is caused by the reduction of air quantities needed to cool the building. However, a radiant cooling system requires approximately twice as much chilled water flow as a conventional system, causing an increase in pump horsepower.
Next up…Lowering peak power demand.
Filed under: Radiant Cooling & Chilled Beams