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THERMO-DISC
VARIABLE VOLUME CEILING DIFFUSER
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APPLICATIONS
ADVANTAGES
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1 INTRODUCTION The RICKARD VARIABLE GEOMETRY THERMO-DISC Ceiling Diffuser is a thermally powered VAV diffuser which contains its own temperature sensing and volume control mechanism. In appearance and construction the Thermo-Disc is similar to the popular electronically controlled vari-disc diffuser but has the advantage that it requires no external wiring or power supply. The Thermo-Disc is available in two basic options. The 5 series is a cooling only VAV diffuser while the 4 series will provide full VAV temperature control in both cooling and heating modes. The change-over between control modes is automatic and is carried out by means of a unique patented change-over mechanism. Supply air is discharged horizontally in a uniform 360 degree radial pattern while the Variable Geometry feature ensures that adequate room air movement is maintained throughout the full range of volume variation. All diffusers are manufactured from electro-galvanised sheet steel and are finished in a chip-resistant baked epoxy powder coating which is available in a wide range of colours 2 OPERATION GENERAL DESCRIPTION Room temperature is controlled by varying the supply air volume in accordance with demand. No other system is more energy efficient, since the volume of air is controlled to match exactly the requirements of the space served by the unit, no more or less. Volume control is achieved by moving a disc, known as the control disc, vertically up and down in the diffuser 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 approximately 30%. The position of the control disc is varied by means of a wax filled thermal element which responds to changes in sensed temperature. The wax contained in the thermal element melts at the formulated temperatures to expand or contract. With a rise in sensed temperature the expanding wax extends the plunger, causing the amplifying lever-arm mechanism to move the control disc such that the supply air volume is changed to the extent that is required to maintain constant room temperature. When the wax cools down the plunger retracts under the action of the return spring, causing the control disc to move in the opposite direction to counter the change in sensed temperature. The room temperature sensing element is located on the appearance panel, otherwise known as the trim-plate. This is the ideal position to sense room temperature owing to the high rate of induction of room air across the trim-plate. Adjustment of the room temperature setpoint is achieved by rotating the adjustment knob on the changeover mechanism. To access this knob, unscrew the two support pins which hold the trim plate in position and allow the entire disc mechanism assembly to hinge down on the third support post. The adjustment knob has calibrated markings and the setpoint may be adjusted to suit individual requirements. It is advisable that no changes are made to the factory setpoint of 720 celsius until the space is occupied. This will give realistic operating conditions, after which individual units may be adjusted to suit individual requirements. HEATING/COOLING THERMO-DISC The Series 4 heating/cooling Thermo-Disc is identical in appearance and performance to the cooling only version, the only difference being the addition of a change-over mechanism which automatically changes the action of the diffuser when in the heating mode. This allows full VAV control of room temperature when warm air is supplied to the diffuser. The change-over mechanism is operated by means of a thermal element identical to the one used for sensing room temperature. The mechanism consists of a return spring and lever arm and is rigidly attached to the controlling mechanism of the cooling only Thermo-Disc. When the supply air temperature exceeds 72 degrees fahrenheight the changeover is initiated and at 79 degrees fahrenheight the change-over to heating mode is completed. Now the diffuser will open as sensed room temperature decreases, and vice verse. Change-over back to cooling mode is completed when supply air temperature drops to 66 degrees fahrenheight. For best results the supply air temperature should be maintained above or below the change-over temperature range although operation within this range is feasible and does not create any problems. For a full description of VAV systems go to Section 1 of this catalogue. 3 DIMENSIONS AND MOUNTING METHODS The basic THERMO-DISC ceiling diffuser concept supports a wide range of diffusion unit styles. The basic diffuser usually drops into a square opening between ceiling tees, although ceiling openings need not be square and in fact, in the case of plastered ceilings, are often circular 4 ADVANTAGES OF THE THERMO-DISC Personalized comfort The Thermo-Disc controls its own VAV zone, with each diffuser being adjusted individually between temperatures of 66 degrees fahrenheight - 77 degrees fahrenheight. The Thermo-Disc will sense and control the temperature within 3 degrees fahrenheight of set temperature. (Factory setting 72 degrees fahrenheight). There is no need for thermostats, which are often situated incorrectly i.e. in incorrect room. This is because it is right in the diffuser itself, which is the best position for sensing the average room temperature. Capital & operating cost savings The Thermo-Disc is a self powered system, which requires no other power source i.e. electrical or pneumatic. There are numerous savings on cabling/piping, thermostats and other electrical/mechanical equipment which are no longer required. Low maintenance The Thermo-Disc is reliable and requires no routine preventative maintenance. The absence of electrical or pneumatic equipment and accessories also means less maintenance and fewer potential problems. All moving components are easily accessible from below the ceiling. The entire control mechanisms may in fact be removed from below within a matter of seconds. The only items ever likely to need attention are the thermal elements and these may easily be replaced, should the need ever arise. Rickard offers a 3-year warranty on the thermal element itself. Flexibility The Thermo-Disc can be relocated with ease, without having to move electrical cables/pneumatic tubes and other related equipment. If additional units are required, these are fitted with minimal disruptions to the overall air handling system. 5 TEN YEAR WARRANTY Rickard warrants that its Thermo-Disc diffusers, exclusive of any options or accessories (whether factory or field installed) shall be free from defects in material or workmanship for a period of ten (10) years from the date of shipment and agrees to repair or replace, at its option, any parts that fail during said period due to any such defects which would not have occurred had reasonable care been taken,provided that such parts have been inspected by Rickard and found defective and provided the diffusers have been given normal and proper usage and all parts and controls remain unaltered. Rickard makes no warranty of merchantability of products or of their fitness for any purpose or any other express or implied warranty which extends beyond the limited warranty above. RickardŐs liability for any and all losses and damages resulting from defects shall in no event exceed the cost of repair or replacement of parts found defective upon examination by Rickard. In no event shall Rickard be liable for incidental, indirect or consequential damages or damages or injury to persons or property. Rickard shall not be responsible for freight to or from its premises in connection with the inspection, repair or replacement or parts under the terms of this limited warranty nor for the cost of removal or installation.
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