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| SECTION
7 - SIDEWALL VARIABLE VOLUME OUTLET |
1
INTRODUCTION
The RICKARD VARIABLE GEOMETRY Wall/Bulkhead Diffuser (WBD) is normally used in areas where restricted ceiling voids exist or where fully-covered ceilings are not available. The WBD, as its name implies, is intended to discharge supply air into the conditioned space from either a sidewall or bulkhead. Frequently office areas have dividing passageways with ceiling heights lower than those within the offices. In this situation the airconditioning ducting may be run in the void between the hall ceiling and the slab above, with the WBD units regulating the air flow from the duct into the offices. In many instances, this ceiling void may also act as a return air plenum. The RICKARD WBD has an excellent ability to distribute air across deep offices, reflected by the throw figures in the selection table. There will be instances where these throws are actually too great for an area. In this case it is only necessary to change the angle of the double deflection grille blades to reduce throws to the desired level. When installed, the grille is the only visible part of the RICKARD WBD diffuser. It is usually supplied in natural anodized aluminum but may alternatively be epoxy powder coated in a wide range of colors to suit architectural requirements.
2 OPERATION
GENERAL DESCRIPTION
Room temperature is controlled by varying the supply air volume
in accordance with demand. Volume control is achieved by opening
or closing a set of airfoil shaped aluminum vanes so as to vary
the aperture through which air passes. This results in the "VARIABLE
GEOMETRY" concept which effectively maintains constant
air movement in the room throughout the range of control, from
100% down to as low as 30%.
The position of the vanes is varied by means of a pneumatic
or 24 V AC electric actuator which drives the vanes in response
to a signal received from the temperature controller. When used
with the RICKARD controller, the WBD will control room temperature
on a proportional-integral basis. Maximum and minimum air volumes
may be adjusted to suit the particular design conditions. For
a detailed description of VAV systems refer to Section 1 of
this catalogue.
MAINTENANCE
Although the WBD requires no routine preventative maintenance,
the RICKARD controller is accessible from the room. As a result
of the "modular" design of the WBD, changing faulty
components does not require highly skilled labor and can be
carried out with minimal disruption to room occupants.
3 SELECTING THE WBD
GENERAL
The first consideration when designing a system is to calculate
the required air volume and temperature to satisfy room conditions
at maximum heat loads. It is recommended that ducting is sized
using the static-regain method. Velocities in branch ducts should
be in the range 650-1200 FPM (3.5-6m/s). Thereafter the following
should be considered:
THROW
TThis is the distance from the diffuser at which the air velocity has reduced to (0,25m/s), 50 FPM, measured with vertical vanes at 0 deg.& 45deg. (0deg.& 45deg.).
NOISE LEVEL REQUIREMENTS
This must be checked to ensure compliance with project specifications. The NC levels given in the selection Table are taken at a distance of (2m) 6ft from the diffuser in a normal office environment. These represent only the noise regenerated by the diffuser and do not take into account any duct-borne noise. (To obtain approximate dBA readings, add 5 dB to the NC levels).
DUCT DESIGN
Use the static regain method of duct sizing to ensure that static
pressure remains the same throughout a particular duct run.
Best results are obtained when diffusers are selected in the
range 0.12 - 0.16'WG (30-40Pa)
4 CONTROLS
GENERAL DESCRIPTION
The WBD diffuser can be supplied complete with electronic controls
to give accurate and reliable proportional-integral cooling
control to maintain a constant room temperature.
REVERSING CHANGE-OVER
The REVERSING CHANGE-OVER facility is a plug-in conversion to
our standard temperature controller that changes the actuator
from direct to reverse acting. Normally, as the sensed temperature
rises, the air volume from the terminal increases, while in
the reverse mode, the air volume from the terminal will increase
as the room temperature decreases. Practically, this means varying
the volume of cold air to cool in summer and varying the
volume of warm air to heat in winter.
The REVERSING CHANGE-OVER sensor is placed in the primary air
stream supplying the air terminal. Care must be taken to ensure
that, if the diffuser has a heater fitted, this sensor is installed
in such a way that it is not affected by radiant heat from the
heater. Whenever the primary air temperature exceeds the sensed
room temperature, the change-over feature is invoked. Normal
operation is resumed when the primary air temperature drops
below the room temperature.
SLAVING FACILITY
It is possible to control up to six diffusers from one controller.
POWER SUPPLY
The controller requires a 24V AC power supply for operation. Diffusers may however have a 110V or 230V/24V power pack which will be fitted to one of the diffusers. The power pack has a built in conditioning curent that supplies a clean 24V, unaffected by electrical spikes & noise.
THE VARIABLE GEOMETRY SIDEWALL VAV
UNIT PERFORMANCE
The performance data quoted below is first for standard WBD
units fitted with electric actuator. Secondly, performance data
is given for WBD units fitted with pneumatic actuators. In the
case of the WBD with electric actuator and integral controls,
the overall unit width includes provision for a control panel.
HOW
THE WBD PERFORMANCE DATA WAS ESTABLISHED
The WBD units were tested in our laboratory to establish their
respective performance ratings. To achieve this each unit
was installed in a bulkhead of a laboratory and tested for
volume using a calibrated orifice in a length of straight
ducting. Throw was checked using a hot wire anemometer. Noise
tests were performed separately in a reverberation chamber.Throw
is the distance from the face of the grille to the point at
which the air velocity is 50 FPM (o.25m/s)measured with vertical
vanes at 0 degrees and 45 degrees. Noise levels are for a
standard office measured 6ft (2m) from the unit. Rickard Air
Diffusion Pty. Ltd. reserves the right to change specifications
and data without prior notice.
Rickard air diffusion Pty. Ltd. reserves the right to change
specifications and data without prior notice.
UNITED
STATES OFFICE
Rickard Air Diffusion, 1401 N. Plano Road, Richardson, TX. 75081
TEL: (972) 744 9090, FAX: (972) 238 0641
HEAD OFFICE RICKARD AIR DIFFUSION (PTY) LTD,
P.O. BOX 103 OTTERY 7808,
Tel : ++27 (021) 704 1533 Fax: ++27 (021) 704 1004
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