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TREND Terminal Unit Controllers Maximise Energy & Time Savings

Air conditioning terminal units can be operated with unparalleled energy efficiency when fitted with controllers from Trend Control System Ltd’s new IQeco range. Moreover, features such as soft addressing and bar code identification make for faster controller set-up and commissioning, which can save days on larger projects. The four models that make up the range together meet the control requirements of virtually all fan coil and VAV units, with one even able to provide full room control, including light switching and dimming. All the controllers are available in fixed-function form – with a wide choice of standard strategies - or as fully-programmable versions, though it is very simple to convert the former to the latter to accommodate future control needs.

IQeco controllers use the BACnet data communications protocol and are designed to connect to an MS/TP field bus. Their functionality has been independently tested and certified by WSP Lab in Stuttgart, an accredited testing laboratory for BACnet devices.

Three of the controllers – the IQeco 31, 35 and 38 – are for fan coil unit control. They have a flexible mix of inputs and outputs and have point counts of 4i/6o, 7i/9o and 9i/11o respectively. All have a minimum of one analogue output and one universal input. The latter – of which there are four on the IQeco 38 – can be set to serve a variety of functions, such as the input for a CO2 sensor or a fan speed selector. The other model in the range is the IQeco VAV, which is for control of variable air volume units and has an integral pressure transducer and optional damper actuator.

The inclusion of at least one analogue output on the fan coil controllers is important from an energy saving perspective as it allows stepless control of fan speed on FCUs with electronically commutated (brushless) motors. A standard strategy can be provided that will run the fan at a minimum speed and only increase it when demand cannot be met through control of the heating/cooling valves alone. This can easily halve power consumption.

All three models have inputs for both a space and a discharge air temperature sensor, enabling additional economies to be made through closer control. They also possess a self-reset facility that automatically returns the space temperature setpoint to its original value one hour after it has been locally adjusted – which would typically be done through a wall-mounted keypad/display. Another standard feature is virtual heat metering, which calculates energy usage based on valve position.

Even the controllers themselves are designed to use a minimum of energy. They are available in 24V and mains (230V) versions, the latter having a switched-mode power supply. This makes it up to 80% more power efficient than a conventional fan coil controller incorporating a transformer.

The IQeco 38 has the i/o capacity to control not only room air conditioning but also lighting and blinds. Use of natural lighting can be maximised by switching/dimming of the lights and/or blind positioning in response to photocell sensor measurements. Operation of the fan coil unit can be geared to the readings from a PIR presence detector, preventing it from running when the room is unoccupied, while the input from a CO2 sensor can help determine when the fan runs and at what speed. The 31, 35 and 38 all have a window contact input to allow automatic shut-down should a window be opened. They can also interact with Trend window controls used for natural ventilation.

Those opting for the fixed-function controllers can select from 40 different control strategies, which cater for the majority of applications. Almost any user need can be met by the programmable versions, a big advantage of which is their ability to allow last minute design changes. For an additional cost, even the fixed-function variety can have their control strategies reconfigured by ‘unlocking’ their inherent programmability – this being done in the field.

Unlike competitors’ products the IQeco controllers do not incorporate DIP switches for setting their network addresses. Instead, addresses are assigned via the network using Trend’s standard engineering tool (SET). This is less time consuming and avoids having to return to a controller – which being fitted to the FCU is located above the ceiling and thus not easily accessible – if the address has been wrongly entered or not set up first time around.

The process can be simplified further by combining ‘soft’ addressing with barcode identification. One way this can be done is by scanning an identifying label on the controller, which results in SET automatically assigning the correct address. Alternatively, where the FCU’s manufacturer has attached a larger (Trend supplied) bar code label to the unit itself, this could be scanned instead – but from floor level. Another option involves taking a second (tear-off) label from each controller, attaching it to a drawing such as a network diagram and then reading each one in turn. IQeco also has a service PIN button that can be used to broadcast the controller’s network position to SET.

SET comes with a monitoring tool that aids IQeco commissioning by allowing rapid checking of controller set-up, communications, etc. Time savings may also result because the universal inputs are configured for their specific roles via the controller’s software, rather than being a hardware adjustment. The controller’s service PIN button will also activate various modes of operation – including hydraulic balancing of the fan coils.

The use of IQeco and SET can yield appreciable time savings on installation and commissioning. In a building with hundreds of fan coil units the job could take several days less, which given the tight deadlines on most projects would usually prove significant.

IQeco controllers can be seamlessly integrated within a Trend building energy management system and can fully interact with other IQ controllers (such as those on the main air handling plant) and be adjusted and monitored through the BEMS’s main operator interface – normally a Trend ‘963’ supervisor – or an IQView touch-screen display. Local viewing and adjustment of temperature can be via a Trend RD (room display unit).

Up to 64 IQecos can be connected to a single MS/TP bus, with each bus being linked to the BEMS’s TCP/IP network via a Trend BINC router. This can also perform functions such as setting the start/stop times for groups of fan coil units. Other MS/TP devices can operate on the same bus.