comfort advantages as well as the potential to save energy, which makes them
attractive to the high-performance building
and sustainable design professionals.
Chilled beams have been a hot
item for the past 15 or so years
in Europe and Australia and are
also becoming more frequently
used and investigated in the U.S.
How Do They Save Energy?
The green aspects of CBs are attractive
to building owners and design professionals
due to the simple fact that water is a more
efficient means of conveying cooling energy
than air is (volumetric heat capacity or specific heat) and thus reduces the fan energy
required. While primary air is still delivered
to the CBs, the majority of the space cooling
is handled with pipes and pumps, not ducts
and fans. For example, a 1-inch pipe can
carry amounts of thermal energy similar to
an 18-inch-by-18-inch duct.
As stated earlier, chilled beams can only
remove the sensible heat in the space;
therefore, the latent heat load is typically
handled by a dedicated outside air system
(DOAS), which wrings most of the moisture out of the primary air stream. Since
the DOAS only handles about twice the
ventilation air required for occupancy, they
are inherently smaller than traditional air-handling units by 25 percent to 35 percent.
Not only are the DOAS air-handling
units smaller in physical size, but so are the
associated primary air ductwork and fan
motors. These size reductions translate not
only to the air-side cost savings but also
fan energy savings. The energy savings of
CBs help consulting engineers as well as
building owners meet future energy codes
that are requiring a reduction in building
energy usage by 30 percent over standard
ASHRAE 90.1-compliant buildings.
To illustrate the energy-saving potential
of chilled-beam technology, it can be helpful
to compare the energy usage of traditional
HVAC systems to systems using CBs. Figure 1,
created using the DOE-2-driven energy
modeling software eQuest®, shows that CBs
do use less overall energy when compared
to the following systems: fan-powered
variable air volume (VAV), under-floor air
distribution (UFAD) and ceiling-mounted fan
coil units (FCU).
Note that chilled beams require less
energy for space cooling (fan and latent
cooling energy) as well as for pumps and
auxiliary equipment. Furthermore, energy is
saved because warmer chilled water must
be used to prevent condensation from
forming on the chilled-beam heat transfer
surfaces and dripping (raining) on the
occupants. The success of the CB requires
that the space humidity be controlled; hence
the chilled-water entering temperature
must be 3-4 degrees F above the room
design dew point, which results in supply
temperatures of 55-60 F.
The use of warmer chilled water also
saves a great deal of energy since many
times chilled-water return from the DOAS
cooling coils can be used as CB supply water.
(This is referred to as a chilled-water cascade
effect). For example, if the chilled-water
entering temperature for the DOAS unit is
44 F, with a 16 F delta T, then the 60 F
leaving water can be run to the chilled-beam water system and potentially returned
back to the source at 67 F using standard
temperature drops – a 23 F delta T. That is
just far out! This enables a larger delta T
for the chilled-water system, which we all
know uses smaller pipes and pumps. This
also has a beneficial effect back at the
central plant or the energy transfer station.
Where Can Chilled
Beams Be Used?
Can chilled beams be used everywhere? Not really. We still haven’t found
the perfect HVAC system yet. That is why
there are consultants! CBs are mostly used
in commercial office buildings and K- 12
schools, and they are also being used in
laboratories with high sensible loads. But
due to the warmer chilled-water supply
temperature requirement, CBs cannot be
used in spaces with high latent loads,
spaces exposed to humid conditions or
large quantities of unconditioned outside
air, such as lobbies, vestibules, atriums,
theaters, restaurants, kitchens, pools,
gyms and airport jet ways. Spaces that
have high ceilings (higher than 14 ft) are
also not appropriate, since the characteristics
of induced room air flow are lost.
Since chilled beams are not the panacea
for the HVAC world, their advantages must
be weighed against their disadvantages.
The key points are summarized in table 1.
As with any technology used correctly
– and like Scotty you don’t try to change
the laws of physics – chilled beams can be
an extremely effective cooling solution and
offer a reduced energy footprint to your
building. So whether you enjoy Star Trek