Civil Engineering Reference
In-Depth Information
coil (only if the main cooling is not suffi cient) in the chilled beam and then enters
the room to offset the room sensible load.
The chilled beam system provides excellent thermal comfort, energy conserva-
tion and effi cient use of space due to high heat capacity of water used as heat trans-
fer medium (Virta et al.
2003
).
The sources of energy consumption in this type of systems are the air handling
unit supply fan motor input power, return fan motor input power (if it is required),
electric preheat strip (if it is used for freeze protection instead of hot water coil) in
air handling unit and electric baseboard reheat unit (if it is used for dehumidifi cation
or heating instead of hot water coil).
Duct air leakage, heat transfer from ducts connecting air handling unit to the
chilled beams, and effi ciency loss in water coils are other sources that can indirectly
increase the energy consumption of the system. The small energy consumed by low
voltage power provided for control valves and dampers, and the power input to the
variable frequency drives for supply and return fans that can be factored in supply
and return fan consumption itself are the other sources of energy consumption.
8.13.9
Hybrid Ventilation
A hybrid ventilation system is a system that it is designed and has the potential to be
switched between the mechanical and natural ventilation modes. Before going any
further, it should be comprehended that the effectiveness of a hybrid system has
close dependency on the outdoor climate surrounding the building. Therefore
selecting the proper locations for installing a hybrid ventilation system is one of the
most important prerequisites of a successful project.
The obvious difference between a mechanical ventilation system and a natural
ventilation system is the use of a mechanically operating device (usually a fan) that
facilitates the fl ow of the required outdoor air into and out of the building in case of
the mechanical ventilation system. In case of the natural ventilation system, build-
ing relies solely on means of directing the outdoor air into and out of the building,
such as operable windows.
The important point to remember is that in a hybrid system as a support to the
shortfalls of the natural ventilation system a mechanical ventilation system can be
supplemented any time during or after the original design was done. To the contrary
it is not simply possible to enhance an existing mechanically ventilated building
with natural ventilation supporting system. A successful natural ventilation system
demands utilization of envelope elements such as openings and construction masses
which are part of the structure of the building that are not simply reconfi gurable
after the original design is completed. Therefore to design a successful hybrid ven-
tilated system it is crucial to design the (hybrid) ventilation system as part of the
original building design itself.
In general, natural ventilation systems can be categorized into two types of wind-
driven and buoyancy-driven systems. As it appears from the names of these two
