ABB’s Carl Turbi explores some of the underused features and funcons hidden inside modern variable speed drives (VSDs) which could save you space, me and money

How to unleash your variable speed drive’s true potential

he variable speed drive (VSD) has been in commercial usage for some 50 years, and has been a mainstay of HVAC systems for several decades. There’s simply no other technology on the market that matches a VSD in its core competency of providing precise and energy efficient control of motor speed. However, to view a drive merely for starting and stopping motors is to miss the huge cost saving potential hidden under a modern VSD’s bonnet. By utilising the advanced functions within the drive, consultants, OEMs and panel builders can eliminate potential redundant components and save space, as well as reducing panel component and installation costs by as much as 50 percent. Typically, a cabinet in a HVAC system will include thermostats used for controlling cabinet fans to save standby losses, timer relays, contactors and door-mounted HMIs. It may have an ammeter indicating amps or volts or true process values such as ambient temperature. And it might include a mini PLC for decision-making or for controlling the system to behave differently depending on the time of day, or to monitor variables in the field to inform how the equipment operates.

T Hidden talents

Yet the duties of all these components, and others in addition, can actually be carried out by the VSD. If we take the cabinet described earlier, the thermostat (costing upwards of £200) can immediately be removed as the drive will monitor the temperature and signal the fan within the drive to run when cooling is required but can also be linked to the thermostat on the enclosure fan and engage automatically when required. Timer relays (upwards of £100) are no longer needed either as the drive’s real-time clock can be used to set timers to either start or stop an application running depending on operating conditions. For HVAC systems this can take into account seasonal, weekly, daily or even hourly variations. The safety contactor can be removed as the drive has built-in safe torque off (STO). This is an SIL 3 PL e stop function which is in fact safer than a contactor would be, as when activated it cannot be circumvented, nor will it fail over time. Using the drive’s fieldbus (Modbus or BACnet which is native to the product) means that unused drive I/O can be utilised to gather telemetry onto the fieldbus system without having to purchase additional remote I/O stations. Integral safety functions enable distribution of functional safety throughout a facility, making more cost-effective wiring installations and simpler system design. This is because the drive contains pre-certified safety functions that can simply be programmed to meet the needs of risk assessments. The VSD’s capability also reduces the need cut into the doors of cabinets to accommodate external HMI displays. In ABB’s range of HVAC VSDs for instance, the drive offers 21 variables, displayed via graphs, charts and meter readings that can speak the language of a given application and the engineers who operate it. There is no need for any analogue meters as the keypad has a view that performs the same task as an analogue moving iron meter, scaled and labelled in the appropriate units. The keypad negates the need for cabinet furniture such as start/stop buttons, as these can be programmed into the keypad. However, if visibility of certain values is imperative then ABB offer a remote keypad mounting kit (DPMP-04) with Weatherproof conditioning.

Freedom to customise

Text editing means that information from the drive can be translated into language that operators


and maintenance personnel can understand. For instance, rather than displaying the motor speed in rpm, and the user having to then translate this into airflow, the drive can be customised to make these calculations itself, and present the information as you need it. When it comes to diagnosing errors, rather than having to check the manual to decipher a particular fault condition, the drive can be programmed to tell you in plain English what the problem is, where it is, and even how to fix it.

This eliminates the need to connect an HMI to Modbus, saving substantial costs. As well as making life easier for the customer, it actually makes life easier for technical support too. Faults can be easily described, helping everyone to quickly get onto the same page to help make a quick and accurate diagnosis of the problem, and an action plan to resolve it. An OEM using this aspect of drive functionality can be sure that such a package is truly customer-friendly. A VSD also includes energy management tools, which can remove the need for an external energy meter (costing upwards of £200), while specific maintenance intervals can also be programmed into the drive, for instance after a certain number of weeks, or a certain number of motor revolutions, whichever comes first. In this regard, the drive is not dissimilar to service alerts on the dashboard of your car.

Adapt to thrive

One of the most impressive, yet little known tricks that the VSD holds up its sleeve is a function known as “adaptive programming”. A typical VSD is built with pre-set parameters that allow you to control how the drive operates. These are designed to cater for all but the most extreme scenarios and make programming of drives easier. However, parameterisation by its very nature can limit what you are able to tell the drive to do. Adaptive programming allows you to break free of these limits, and fully customise the control function. For instance, if you wanted the drive to delay its activation until a particular valve is open, normally this would be achieved using relays, timers or PLCs. Adaptive programming allows you to do all this within the drive, once again saving on component cost, installation time and cabinet space.

Adaptive programming is ideal for retrospectively engineering your way out of technical challenges. New equipment can

uSome of the features built into a drive which could save up to 50 percent of the cost of cabinet components

sometimes cause unforeseen issues. For instance, a newly installed fan might be particularly noisy when powering up compared to the fan it replaced. You could install a mini-PLC to inhibit the fan’s start, however this would require rewiring the cabinet and additional project time. Adaptive programming allows you to achieve the same result using only the drive.

In a HVAC context, adaptive programming means that dampers can be controlled, CO2 can be monitored and measured, while blocked filters can be readily identified using the drive’s user load curves. This negates the need for expensive external I/O points connected to the BMS. Components like AHU filters are typically cleaned in accordance with the user manual, but this prescriptive approach does not take into account whether the filters actually need cleaning at a given interval. Using a drive to tell you exactly when filters need cleaning can save time and money in the long run by eliminating unnecessary maintenance.

In conclusion

The VSD has already reinvented itself several times over the years. When first introduced commercially they were originally associated with precision control. Later on it became abundantly clear that they could have a drastic impact on motor energy efficiency. Now the VSD is reinventing itself again as a master of versatility. It allows more functionality to be packed into smaller spaces, in less time and at a lower cost. With a VSD, you truly can have it all. ABB (ABBN: SIX Swiss Ex) is a pioneering technology leader with a comprehensive offering for digital industries. With a history of innovation spanning more than 130 years, ABB is today a leader in digital industries with four customer- focused, globally leading businesses: Electrification, Industrial Automation, Motion, and Robotics & Discrete Automation, supported by its common ABB Ability™ digital platform. ABB’s market leading Power Grids business will be divested to Hitachi in 2020. ABB operates in more than 100 countries with about 147,000 employees.

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