INTRODUCTION

The RICKARD VARIABLE VOLUME Linear Diffuser (VLN)

The Rickard Variable Volume VAV Linear Diffuser (VLN) provides an effective means of distributing conditioned air into the perimeter zones of a building, where the temperature control requirements are the most demanding. The slim and attractive shape of the diffuser extrusions ensures that the unit blends into any ceiling design and meets most architectural requirements. At the same time the superior aerodynamic design ensures that the air diffusion is draftless, quiet and efficient.

SPECIAL FEATURES

The VLN boasts features not generally found on other similar products. The air pattern is adjustable from below to change from two-way blow to one-way blow in either direction or even to blow vertically downward.

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 aerodynamically designed, extruded aluminum vanes by means of an electric, thermal or pneumatic actuator, so as to vary the aperture through which the air passes at the point of exit from the diffuser. This results in the variable volume concept, which effectively maintains air discharge velocities throughout the range of volume control, from 100% down to approximately 30%. The standard VLN has two slots and is available in lengths of 24", 36" and 48". Other lengths are available upon request. The extrusions have been engineered for butting together lengths with hairline precision so that an unlimited length of continuous diffuser is possible without sacrificing the attractive appearance. In this case the volume control modules may be placed anywhere along the length of the continuous diffuser. The center core is easily removable. The volume control section is constructed using corrosion resistant galvanized steel. The extruded aluminum diffuser sections ship with standard white finish.

AIRFLOW DIRECTION

Another useful feature of the Rickard VLN is the ease with which the direction of the airflow may be changed. Although the airflow direction is not normally changed once the system is operating, it does simplify the ordering and installation procedure. All units are identical and the choice of one-way or two-way blow is easily implemented on site by simply flipping the flow-directing vanes to the preferred side. One way blow to the left or to the right may similarly be selected. The supply air volume is not affected by the selection of blow direction. For high ceilings it is possible to direct the air downwards for better room penetration.

MAINTENANCE

As with all Rickard Air Diffusion products, the VLN requires no routine preventative maintenance.

DIFFUSER SELECTION

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 the branch ducts should be in the range 650-120ft/min. Thereafter the following parameters should be considered:

THROW

This is the distance from the diffuser at which the velocity has reduced to 50ft/min when measured 1 in. below the ceiling (or from the wall) with the diffuser in the fully open position. Throw remains essentially constant throughout the range of volume control, a feature of the variable volume diffuser.

NOISE LEVEL REQUIREMENTS

Each project will have a different noise level requirement and the VLN selection procedure must take this into account.

DUCT STATIC PRESSURE

Diffuser performance has been established using diffuser neck TOTAL pressure, although what is normally known and controlled is branch duct STATIC pressure. What happens to the static pressure between the branch duct and the diffuser depends on the length and type of duct used. For simplicity, it may be assumed that branch duct static pressure approximates diffuser neck total pressure. This would be a valid assumption where the flexible duct length (if used) is not excessive and does not have tight radius bends. Although the selection table gives diffuser performance for a neck total pressure ranging from 0.08 - 0.40 in w.g., caution should be exercised when selecting diffusers outside the range of 0.16 - 0.32 in w.g . At lower pressures room air movement and induction may be insufficient and at higher pressures drafts and excessive noise may result. Best results are obtained when diffusers are selected at branch duct static pressures in the range 0.02 - 0.30 in w.g. Note that all diffusers on a particular branch duct will operate at the same static pressure because this is the basis on which the system has been designed. Diffusers which are able to supply more air than required will automatically throttle back to the required amount in response to the temperature controller signal, resulting in a self-balancing system.

HEATING

It is possible to fit the VLN with an integral electric re-heater and the necessary controls to provide proportional heating. The heater element would be of the black heat incoloy stainless steel sheathed type with a heating density of 20W/inČ. Overheat safeties are also provided.

TEMPERATURE CONTROLS

GENERAL DESCRIPTION

The Rickard VLN can be supplied complete with a choice of electronic temperature controls which will give accurate and reliable proportional-integral temperature control to maintain the desired setpoint temperature throughout the day.