INTRODUCTION

The Rickard Variable Volume 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 air conditioning ductwork 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.

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 volume 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 24 V AC electric actuator which drives the vanes in response to a signal received from the temperature controller (wall mounted thermostat). 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.

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 significant labor and can be carried out with minimal disruption to room occupants.

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. Thereafter the following should be considered:

THROW

This is the distance from the diffuser at which the air velocity has reduced to 50 FPM, measured with vertical vanes at 0 deg.& 45deg.

NOISE LEVEL REQUIREMENTS

This must be checked to ensure compliance with project specifications.

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 in. WG.

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.