It has been estimated that some 82% of all current energy saving projects is in the area of heating, ventilation and air conditioning (HVAC). Clearly, this activity is well under way in the West, where the concept of the ‘intelligent building’ has become the norm in any new-build situation, but energy saving is also an issue in countries such as China, where the potential market for energy saving equipment and ancillaries is enormous. The HVAC market is growing at the rate of 6% per year, so it is a serious business area for drives - perhaps the key energy saving product in this particular market segment, dominated as it is by motor driven pumps and fans.
Gaining market positions in the HVAC sector has been the subject of feverish activity among the majors in recent years. Most of them pay rather more than lip service to it, with specialist divisions set up and products developed to serve the needs of the sector. Among them, Danfoss claims to have the number one position globally and number two in the Americas. The company has around a hundred people dedicated to HVAC drives sales and reveals sales growth almost twice that of the global rate. Not surprising then, that the company recently launched a drive in its established VLT range, purpose built for the sector.
The new VLT HVAC drive is based on Danfoss’ VLT 6000 platform and introduces a lot of innovative features for the industry. First and foremost, it is an energy efficient product in its own right, broaching the 98% efficiency barrier for the first time. The reduction in internal losses - mainly in the form of heat - is highly significant in terms of the thousands of kilowatt-hours saved over the drive’s lifetime, the corresponding reduction in carbon emissions and also in reduced payback times.
A 150kW drive, for example, based upon continuous operation in an air conditioning application, will yield a benefit of over 25,000kWhrs and over ten tonnes of carbon emission savings per year. Moreover, the improvement in the payback period is equivalent to that yielded by the Enhanced Capital Allowance tax break. The heat loss reduction, along with a 50oC ambient operating specification, also enables the drives to be protected to IP66 environmental rating or installed in more compact enclosures.
The VLT HVAC drive also improves motor efficiency, thanks to an automatic energy optimisation feature that continuously monitors flux levels and varies the drive output to maintain optimum motor magnetisation commensurate with load conditions. Danfoss says this feature can improve motor efficiency by between 5 and 15% at partial load - the most common operating conditions for fans, pumps and compressors. An added bonus is a reduction in noise. Automatic motor adaptation is also available, which ‘tunes’ the inverter to the motor, giving the user freedom of choice when it comes to motor selection, particularly when retrofitting high-efficiency motors. The energy efficiency gains arising from this feature alone are sufficient to justify the replacement of older, less efficient inverters.
Applying the drive in the field has been simplified by the development of software suites and features dedicated to fan, pump and compressor operation. The drive’s Local Control Panel gives access to a quick set-up menu, which, in turn, lets the user into an HVAC application menu and an HVAC function menu. There is also a ‘personal’ menu for more experienced users that can be fully customised. Dual-layer password protection keeps the OEM equipment set-up and end-user local set-up routines completely separate.
The drive has four independent auto-tune PID controllers for air handling functions such as fan volume, and the control of valves and dampers, which can be used to reduce the burden on building management systems (BMS). Indeed, the drive’s I/O is available as a remote I/O facility for the BMS; room temperature sensors, for example, can be connected directly to the drive to achieve a decentralised control function, effectively extending the capacity of the BMS. The drive can be programmed to take account of work day and weekend load conditions, and carry out local control functions like flow balancing between fresh and exhaust air.
The drive’s ability to detect changes in current relative to speed is also put to good use for maintenance purposes. The feature enables the detection of belt failure, the onset of which can be signalled to the BMS without having to rely on air flow monitors. An integral ‘alarm clock’ can also be programmed to alert maintenance staff to a range of timed actions.
The drives in action
Some 28 Danfoss VLT6000 HVAC drives have been retrofitted on an air handling complex at Belfast Airport to control 28 fans serving 40% of the airport’s climate control system. Despite hot summer conditions, during which the air conditioning system functioned satisfactorily with the fans at 80% speed, the actual savings exceeded expectations and the energy bill was down by over £15,000 for the initial three month trial period. Based on this, the airport technical supervisor calculates that the investment will pay back in less than eight months, a result that will probably see the drives installed across the entire climate control system. Once this is achieved, it is estimated that the airport will save in excess of £60,000 annually on its electricity costs - equivalent to a reduction in carbon emissions of over 500 tonnes per year.