SCVH VAV COOLING/HEATING

COANDA EFFECT SUPPLY
AIR ENTRAINMENT

Coanda Effect: The velocity of the supply air stream, as it passes along the ceiling surface, creates a low pressure area along surface. Maintaining the discharge velocity as the supply air volume is reduced provides a maximum Coanda Effect and eliminates the possible effect of vertical drop of colder and heavier supply air.

Entrainment: The incorporation of surrounding room air into the main supply air path. Maintaining the discharge velocity as supply air volume is reduced provides maximum entrainment. Maximum entrainment provides the shortest path required to change supply air temperature to the average room temperature, thus absorbing the heat generated within the space.

HOW IT WORKS

The SCVH is a thermally powered VAV diffuser which is completely self-contained and self-powered. The mechanism is operated by four thermostatic actuators. The actuators provide VAV room temperature control in heating and cooling. The simple design is based on fewer moving parts to hinder the actuator’s response. A cone shaped diffusion damper creating less turbulence allows complete and even air distribution. 1/8" foam padding for quiet operation.

OPERATION

Change over between heating and cooling modes is determined by supply air temperature. When heating cycle is initiated, actuator #1 will react first, lowering damper to full open position (full heating).

Then actuator #2, the heating slave, reacts at 78 degrees or greater, positioning the heating u-arm to engage actuator #3, the room thermostat for heating control.

As the room warms, actuator #3 begins to sense room temperature to vary the heating supply volume to achieve and sustain the desired room temperature. The factory set point of 74 degrees is adjustable between 72 - 78 degrees. For less heating, turn actuator #3 clockwise. For more heating turn actuator #3 counter-clockwise. Each full turn will equal plus or minus 2 degrees. A drop in room temperature and unit will respond by opening to increase heating volume until the room temperature reaches the desired set point.

VAV cooling control is initiated when supply air is below 68 degrees.

In cooling mode actuators #1 & #2, do not react. This engages the cooling control actuator #4 which will vary the supply air when cooling. A rise in room temperature and unit will respond by allowing cool air into the space until the room temperature reaches the desired set point. All units are factory set at 74 degrees, and are adjustable between 72 and 78 degrees.

For a cooler room temperature turn actuator #4 clockwise. For a warmer room temperature turn actuator #4 counter-clockwise.

Determine room temperature set point by aligning the end of the actuator with the indicators on the temperature scale. Each full turn or indicator will equal plus or minus 2 degrees.

INDUCTION

Room air is induced across actuators #3 and #4 by use of a simple induction wing. This diverts a small amount of supply air which induces a room air sample through an induction trough located on the back side of the appearance panel.

Face Panel Removal

The solid face panel is held in place by four spring clips. To remove the face panel for room temperature adjustments, approach panel from the induction trough side (the rectangle opening) reach above the panel on both sides with your forefingers until you are able to place your forefingers behind the spring clips. Using your thumbs on the front edge of the panel push the panel back or away from you while pulling the spring clip spring clips forward or toward you with your forefingers. Lower the panel and pull forward to disconnect the panel from the rear spring clips. When reattaching face panel the induction trough must be positioned directly opposite of induction wing.

Temperature Adjustment
Cooling Adjustment

All “Smart“ diffusers feature an easy to read room temperature set-point scale. Room temperature adjustments are made by simply turning the VAV room temperature control thermostatic actuator #4 clockwise for a cooler room temperature and counter clockwise for a warmer room temperature. Determine room temperature set-point by aligning the end of the actuator with the indicators on the temperature scale. Each full rotation or each indicator on the temperature scale will equal plus or minus two degrees. For factory set-point of 74 degrees, turn actuator clockwise to stop, then turn counter clockwise three full turns.

Heating Adjustment

The room temperature set point is controlled by the red actuator #3. For a cooler room temperature turn actuator #3 clockwise. For a warmer room temperature turn actuator #3 counter-clockwise. Each full turn equals plus or minus 2 degrees

Smart diffusers utilize significant spring pressure to accurately control the thermal actuators sensitivity to temperature change and reduce inherent hysteresis.

Note: When actuators are warm they may be slightly difficult to adjust.