Taking control of air conditioning

Published:  16 July, 2006

CONTROLS
Today’s sophisticated air-conditioning equipment and systems require precise control of internal components such as inverter drives and electronic expansion valves and conditions in the air-conditioned spaces to deliver their full potential.

FRASER HYMAS discusses the importance of electronic controls to enable air-conditioning to perform to its best potential — and even generate invoices for air-conditioning services.

Controlling electrical components in an air-conditioning system is vital to ensure correct and efficient operation. It has become even more important to increase energy savings. It is also an essential expectation of customers that they have the opportunity to ‘control’ their working environment and, theoretically at least, the functioning of their air-conditioning systems.

Two types of control are involved — the functioning of the equipment electronically and the manipulation of the conditions within the occupied space.

Reliable electronics

Since the advent of cheaper and highly reliable electronics, today’s air-conditioning systems rely internally more and more on complex electronic control rather than the electro-mechanical control of old. Externally, a wide variety of systems are provided to enable air-conditioning equipment to interface with users.

In recent years, many controls have been developed and introduced to reduce the energy consumption of the components. One of the most important of these is the electronic inverter for driving the compressor and, even, the fan motors.

The technology behind an inverter is relatively complex, but the net result is very straightforward — energy savings of more than 40% over non-inverter controlled equipment. An inverter controls the compressor according to the load and reduces the compressor speed as the room temperature set point is reached. This is much more efficient than a compressor with direct-online starting.

A directly driven compressor operates at fixed speed and does not compensate for the reduction in load as the set point is reached, resulting in constant stop/start operation.

The inverter, through its electronics, reduces the starting current required. This is achieved by the inverter controlling the power delivered to the motor at start-up and just after. This is of great benefit when the power supply is restricted. A useful benefit this is that a single-phase, rather than 3-phase, supply can be used for much commercial air conditioning.

Fan motors inside air-conditioning equipment are critical to the function. The transfer of heat away from the coil is vital. The outdoor fan is required to run at different speeds for different modes of operation under different outdoor conditions to maintain efficient system operation. The indoor fan is also important, as it delivers the heating or cooling the user requires.

In the past, such fans were mostly controlled via taps for the different speeds. This approach was very effective, but the speed change was sometimes audible for the customer. The degree of control was also limited to the amount of taps or relays that could be fitted to the control PCB.

New technology now allows DC fan motors to be used in these applications. This type of fan motor and control are more efficient, once again through the use of electronics. The advantage to the end user is that the motors are much quieter. These DC motors generally have a speed transducer to give accurate speed control of the motor, also assisting further in improving the system efficiency.

Other components in the air-conditioning system have benefited from advances in electronics. In many systems refrigerant expansion was, and still is, managed via mechanical expansion valves and capillaries. However, some systems now use electronic expansion valves. These produce greater efficiency, as the degree of opening can be controlled via sensors in the unit and predetermined control algorithms in the software on the micro-controller.

Profound effect

Such components have become very important in air-conditioning systems to increase energy-efficiency ratios and coefficients of performance. No single individual component makes a massive difference but the combination has a profound net effect.

With regard to external or room control, electronics is once again to the fore, with central control of several separate systems being popular. Remote Internet control, energy-monitoring data and innovations such as touch screens or keyable pads are the latest attractions to the end-user. Infra-red remote room control has become commonplace in the last few years.

Open protocols

Interfaces with building-management systems are commonly offered by manufacturers like Toshiba, but open-protocol technology is also offered by companies which have recognised it as the future of customer control technology.

To provide centralised control, Toshiba, for example, uses a wide range of controllers that can be adapted to complex control scenarios — from relatively simple central controllers with limited connectivity to systems for on/off control and basic reporting of faults.

When more complex control solutions are required, Toshiba has developed a large toolbox of software solutions that are easily implemented and fully tried and tested — allowing fully functional seamless links to all major BMS manufacturers.

Hand in hand with the ability to interface with BMS choices, Toshiba can also provide complex control solutions with specific dedicated graphics for standard air-conditioner types and a fully customisable graphics package to suit any building. This software acts as a fully-functional supervisor which can interface with other items of building plant via the digital input/output modules.

This type of software also provides reportable alarm management, with dedicated reporting to a wide range of other sources. There are many generic versions available, with dedicated diagnostic software routines and many functions that allow programming related to specific equipment functions.

A good example is the input from a fire alarm to stop and restart the whole office building or, perhaps, large retail store.

Hotels

Another would be a hotel where specific operating conditions are required for the various states of occupancy. This type of application would use a digital input module or read an occupancy status sent to it by an indoor unit that has been inactive for a pre-set length of time.

Some hotels use the programmes to enable room occupants to set their comfort preferences. These can be maintained and repeated on re-occupancy in the short or long term.

As recording energy consumption becomes increasingly vital in all commercial buildings, the latest versions of controls software from leading air-conditioning manufacturers is even being designed to generate invoices for air conditioning or, indeed, many other building services via the appropriate energy meters and a dedicated report generating electronic module. The future is here!

Fraser Hymas is UK controls specialist with Toshiba Air Conditioning, United Technologies House, Guildford Road, Leatherhead, Surrey KT22 9UT.



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