Chilled beams are gaining popularity in North America, so engineers are establishing better models and methods for their performance. Terminal unit
geometry of active chilled beams is one area
where researchers are improving efficiency.
As chilled beam systems continue to take
root in facilities vying for greater energy
efficiency, scientists are learning more about
how valuable they are and how to best optimize them. Two recent studies identify the
performance of each type of system – passive and active chilled beams.
A MODEL FOR PASSIVE
A study from the Ray W. Herrick
Laboratories at Purdue University’s School
of Mechanical Engineering sought to evaluate the performance of passive chilled beam
systems compared to conventional systems.
While passive chilled beam systems can
reduce cooling requirements, improve comfort, increase energy efficiency and reduce
ductwork, this evaluation has been difficult in
ENERGY EFFICIENCY MODELS
“Passive chilled beam modeling is challenging because they have a complex geometry
and the primary heat transfer mechanisms of
radiation and natural convection are strongly
coupled to the space characteristics and thermal conditions,” explain the researchers.
One way the Purdue team has developed
modeling is to “consider both the chilled
beam and its surroundings, since the perfor-
mance of passive chilled beams are strongly
coupled to the specific characteristics and
conditions within the spaces.”
Using the model, the research team found
that radiation cooling of a passive chilled
beam system provided total energy savings
of 10-21%, depending on the system config-
uration. These results were found using the
weather conditions of the Indiana-based lab.
The researchers established four key conclusions from the model, including:
■ Energy savings of up to 12% are possible
using a passive chilled beam system under
Midwest weather conditions compared to
a traditional air system only controlling air
■ A separate chiller with a higher chiller
water operating temperature can provide
an additional 11% in energy savings.
■ Thermal comfort improvement with passive chilled beams can be achieved with a
reduced relative air speed rather than the
increased radiation cooling effect.
■ Radiation cooling was calculated as 5-7%
of the cooling capacity for the configuration in this study, which is essentially
inconsequential in terms of thermal comfort estimation.
CHILLED BEAM SYSTEMS
An article in Applied Thermal Engineering
examines configurations of active chilled
beams to find which unit geometries provided the most efficiency.
One of the key metrics for this study is the
entrainment ratio (ER), which is “the ratio
of the mass flow rate of room air induced to
the mass flow rate of primary air supplied,”
according to the study. As an index for
active chilled beam systems, it identifies the
efficiency of the terminal unit, as well as the
overall energy performance.
Using this index, the researchers were
able to confirm that terminal unit geometry
increases entrainment performance.
“Induction can be enhanced by locating
the nozzles as well as the induction kernel
closer to the center of the terminal unit,”
write the researchers. “This modification
makes the space inside the terminal unit
more effectively used for air mixing and
Furthermore, the researchers studied
mixing chamber nozzles, finding that the
optimal nozzle length is between 60 and
80mm. With a 70mm nozzle, they were able
to increase the ER by 30%, proving that the
nozzle can dictate other geometric charac-
teristics of the terminal unit.
Radiation cooling of a passive chilled beam
system provided total energy savings of 10-21%,
depending on the system configuration.