REDUCING REFRIGERATION ENERGY CONSUMPTION
August 2008

When J Sainsbury’s looked to reduce its energy consumption by 15%, it enlisted the help of Parasense to implement solutions within the refrigeration infrastructure of selected sites.

Parasense are no strangers when it comes to cutting energy usage in the retail industry – throughout their 20 year history they have been manufacturing control solutions specifically designed to improve efficiency of operation and reduce consumption in existing equipment.

Key Account Manager, Steve McMahon, explains; ‘it’s a well documented fact that the largest energy consumer in a food retail environment is the refrigeration system – this can consume as much as 70% of a store’s total energy, so we felt it was very important to come up with a product that would target this equipment and maximise the efficient running throughout the year.

‘Our team of refrigeration and electrical engineers designed a condenser control system that would work the condenser coil much more effectively than a conventional control unit. This enables the refrigeration compressor pack to run far more efficiently and thus make large energy savings.’

The solution to the application takes the form of our VSDM Controller. This system utilises a Hitachi X200 VSD per pair of fans coupled to our CDM (Condenser Control Board). The system is then controlled around local temperature and pressure set-points to give precise floating head pressure control. The implementation of this system is made feasible using Hitachi’s high efficiency VSD technology to achieve accurate speed control.

Steve takes up the story: ‘we knew that the traditional reasons for using inverters (ie, reducing the direct energy consumption of the motor being controlled to match load requirement) was not going to be the prime mover for us when we started the design process for the VSDM control system. What the X200 inverters allowed us to do was control the discharge pressure of the refrigerant fluid through the condenser very accurately, which in turn meant that the optimum condensing conditions were maintained within very tight bands; a lot of control systems will overshoot a pre-determined set point, then overcompensate and so on – this creates a see-saw effect and massively increases energy consumption of the whole refrigeration system as it works overtime to keep up with the control logic (or, rather, the lack of it). We felt that the X200 inverter was by far the best option for our control system to maintain fluid pressure and condensing temperature within the optimum operating conditions.’

The results surprised even Steve: ‘when we initially began the design process for the VSDM condenser controller we projected annual energy savings in the region of 8-10% of the total refrigeration system energy consumption. However, once we began seeing the energy consumption figures from the installations we carried out, we soon realised that we had been very conservative; we have seen daily savings of over 30% on some of the systems, which equates to over 20% annual energy savings.’

Another very pleasing by-product of using the X200 inverters was the power factor correction that inherently comes from using a variable speed drive on a motor application, thus improving the fans’ efficiency even further.

The last word comes from Steve, who is understandably pleased with how the X200 has performed within the VSDM condenser control system: ‘We are very proud of the results that we have seen from installations over the last year and the phenomenal energy savings that we have achieved could not have been done without the X200 doing its job so well. We are looking forward to saving energy for many more of our retail clients with the X200 inverter as an essential component of our VSDM condenser control system.’