Rickard VSW 150 Manual

FEATURES
FORM FACTOR
RICKARD diffusers are fitted with electric re-heaters that are either
housed in a modular sleeve (VCD1, VSD1, CCD3, CSD3, VSW1 &
CSW3's) or fitted directly to the unit (WBD, VLN). The heaters are
energised when additional heating is required in a room.
VAV PLATE DIFFUSER FITTED WITH MODULAR HEATER SPIGOT
WBD WITH DEDICATED HEATER FITTED
Electric heating can be considered to save energy when they are
used to heat isolated offices that wouldn't be efficiently heated by
raising the central plants temperature. The most efficient scenario in
heating is for the central plant to supply sufficient heated air to allow
most of the zones to be in control when the diffusers damper is
close to minimum position. Zones that are colder are controlled by
the diffuser opening further. Zones that cannot be satisfied by the
diffuser supplying warm air at full volume are toped up with supple-
mentary heating.
The most efficient scenario in cooling is for the central plant to sup-
ply sufficient cool air to allow most of the zones to be in control
when the diffuser dampers are close to minimum position. Zones
that are warmer can be controlled by the diffuser opening further.
Zones that cannot be warmed sufficiently by reducing the cold air
supply can be controlled by heating this reduced volume of air.
If the room temperature were to fall by 0.5°C below set point, the
Triac Controller will commence energizing the heater proportionally
and will fully energize the heater when the room temperature is ap-
proximately 1.5°C below set point.
To ensure a building is efficiently heated it is necessary to integrate
the Rickard VAV diffuser system with the central plant BMS. This is
possible by using Rickard's MLM BMS Compatible Controls.
PROPORTIONAL HEATING
For accurate control of room temperature, the electric re-heater is
controlled on a step-less, proportional basis. In addition to having a
proportional output signal for cooling control, the temperature con-
troller also has a proportional output signal for heating.
This is done by means of a triac switching set (current valve) which
varies the heater output capacity by cycling the power supply to the
heater on and off – Pulse Width Modulation (PWM). This switching
takes place over a cycle of approximately 2 seconds and always oc-
curs at zero voltage to avoid radio frequency interference and volt-
age spikes. The "on" and "off" periods are varied in proportion to
the amount of heating required, i.e. a required heating capacity of
75% will result in an "on" period of 1.5 seconds and an "off" period
of 0.5 seconds.
CONTROLS
In a situation where multiple diffusers are controlled from a single
controller, each diffuser will be fitted with its own triac that will re-
ceive a heating signal from the Primary controller. From the table
"Maximum Recommended Heater Output (Watts)" at the end of this
section, notice that for each neck total pressure there is a specific
heater output quoted. For each diffuser size a standard heater capac-
ity is referenced e.g. in the case of a VCD 250 diffuser, the re-heater
sleeve would be factory fitted with a 1500 watt heater. By utilizing
the RICKARD MLM or MLM Interoperable BMS Compatible Controls,
the heater can be electronically set for an output from 100 to 1500W
to match the design engineer's requirements. If the diffuser neck
total pressure were to be set to 50Pa and the minimum desired air
flow was 30% of maximum with a 17°C temperature rise, the heater
output for a VCD 250 should be set to 1350 watts. Please refer to
the MLM software help section for setup information.
IMPORTANT ELECTRICAL INFORMATION: Electrical reticulation
should be designed to manage the heaters full capacity i.e. when a
heater is set to 50%, the heater element draws the same current as it
would when set to 100% but only draws it for 50% of the time.