FLEXSYS SYSTEM – SUMMER/WINTER
OPERATION COMPARISON

SUMMER - FLEXSYS COOLING
Conditioned air leaves the Variable Air Volume (VAV) air handling unit at 15°C. The main fan inverter control is the same as that used for any VAV system.

There is a temperature pickup through the low to medium velocity main duct of approximately 0.5°C so air enters the raised access floor plenum at approximately 15.5°C.

Air enters the floor plenum through specially designed Fire dampers (FD) and Pressure Control Dampers (PCD’s). The PCD’s are controlled by a Modular Integrated Terminal- Intelligent floor box (MIT-I) which holds the grille pressure constant to make the system pressure independent. One MIT-I is used for each pressurised plenum. Note that on all jobs to date the use of conventional fire barriers has been eliminated.

To compensate for temperature pickup across the floor plenum, ‘Rifle ducts’ are used to distribute the air evenly around the floor plenum and run out between the floor pedestals in 525mm x 225mm uninsulated ducts that sit on the floor slab. Rifle ducts ensure the supply air temperature rise to the furthest Modular Integrated Terminals (MIT) is limited to 1.5°C.

Air enters the space via the MIT floor terminals. For cooling only applications these are designated MIT-C. The amount of air supplied to the space is controlled by the actuator and damper arrangement in each terminal. Groups of up to 14 MIT’s are controlled by a York Flexcool zone controller and a room sensor set at 1500mm above finished floor level (FFL) to monitor the room temperature.

All the FlexSys components are connected using York’s Plug ‘N’ Play cable technology. Using local small power supplies ( provided by others) the controller transforms down to a 24 volt control circuit which connects all the MIT’s and the Sensor to the controller. A LAN circuit is normally installed at the same time.

All MIT terminals are fitted with a minimum fresh air stop which can be easily altered if the occupancy level changes.

York installs the MIT boxes into pre-cut floor tiles, provided by others, along with all the underfloor controls and cables.

The return air leaves the space normally though return air light fittings and then back to the Air handling Unit.

WINTER – FLEXSYS HEATING
FlexSys can also be used to satisfy the heating requirements in the building. This will be for the perimeter zones, internal meeting rooms and possibly around certain types of Atria.

MIT-G floor terminals are used for heating. These look the same as the MIT-C unit from the occupied space, but have a duct spigot added to the plenum box below floor level. One or more MIT-G terminals are connected to each side of a Modular Fan terminal heating unit (MFT) using insulated flexible duct.

The number of MIT terminals required and resultant layout is normally dictated by the cooling load and the MFT boxes are positioned on the floor slab between the MIT-G’s.

As the system changes from cooling to heating the cooling load is at a minimum and the MIT dampers are shut down to minimum fresh air. If the space temperature continues to drop the controls will energise the heating circuit and the MFT fan will run (it does not run in cooling mode). Air is sucked from the room via MIT-G’s at approximately 22°C, passing through the attached MFT’ and is redistributed into the space via MIT-G’s. As the space temperature continues to fall the MFT heater will be activated and raise the supply air temperature to the space to satisfy the heat losses.

In most buildings, and in particular Part L new build, electric heaters controlled by current valves are used. For applications requiring high heating loads hot water coils are used. There is a range of MFT’s available to satisfy varying zone requirements.

The MFT units and associated ductwork are designed to have a very low pressure drop.

The cooling/heating zones are controlled by York Flexheat zone controllers and all components in the zone are connected using Plug ‘N’ Play cable technology as described above.

As for FlexSys cooling above, all items are installed by York using quick release snap connectors.