Case Study: NBM blows moulding costs out of the (chilled) water

UK processor Northumbria Blow Mouldings (NBM) says it is on target to save over £80,000 a year on cooling costs thanks to an energy-saving cooling system from IsoCool. Involving replacement of the plant’s existing beside-the-machine chillers with centralised chilled water and adiabatic cooling systems, the project is designed to optimise efficiency through the exploitation of direct air cooling and a heat exchanger. The system has a return on investment schedule of less than two years.

NBM Ltd., a part of the DNR Ltd. group of companies, specialises in the design and manufacture of extrusion blow-moulded containers for the packaging of food, personal care, household toiletries and industrial products.

NBM Managing Director Brian Wiper asked IsoCool to review the incumbent cooling system responsible for supporting the plant’s 16 blow moulding machines. Comprised of several beside-the-machine chillers with a total cooling capacity of 705kW and installed electrical power of 275kW, the system delivered chilled water to the moulds and hydraulics at 10˚C.

IsoCool provided a proposal for improving the system, including the separation of the hydraulic cooling system from the chillers, with a predicted payback schedule of 23 months.

“From the outset of the project the expertise in assessing exactly what we required was excellent, involving complex mathematical equations and investigations into what we had and what was needed to move forward. The decision to go ahead was simplified by the projected energy-saving figures, added to the fact that the North East enjoys typically cooler weather throughout the year,” said Brian.

To increase the energy efficiency of the system, IsoCool replaced the existing beside the machine chillers with a centralised chiller system for the moulds (utilising two of the existing chillers which were suitable for centralisation), plus a Eurochiller AX-A water chiller, and an IsoCool pump and tank group. For the hydraulics, IsoCool installed an ADCOOLER adiabatic cooler, employing an existing pump and tank group. IsoCool Managing Director, Nigel Hallett, explained the reasoning behind separating the two systems:

“The requirement for cooling water for the hydraulic circuit is of a significantly higher temperature than the mould circuit, so it doesn’t make sense to run this on energy-intensive chillers. Our adiabatic cooler, on the other hand, automatically functions as an air blast cooler when the ambient is three degrees below the return water temperature from the moulds. By bridging the two circuits with an IsoFC heat exchanger, we are able to maximise the efficiency of the system as a whole. Due to the cooler climatic conditions in the area, the system should benefit from up to 100% direct air cooling for much of the year.”

The IsoFC energy-saving device works by connecting the mould and hydraulic cooling circuits through a high efficiency packaged heat exchanger unit with intelligent software, facilitating energy transfer between the systems without them mixing. During low ambient conditions, the IsoFC uses surplus capacity from the adiabatic cooler to pre-cool water returning from the mould circuits before it reaches the refrigeration plant. Both circuits continue to fulfill their primary functions, but with the benefits of having the life span of the components of the chiller plant extended by the reduced utilisation.  

“This solution not only maximises energy efficiency for the hydraulic cooling system, but also allows NBM to take advantage of the adiabatic cooling system during low ambient conditions to further energy savings,” explained Nigel. “Overall, we have calculated that the system will run on partial free cooling for approximately one third of the year, and up to 100% direct air cooling – i.e. with the chillers switched off completely - for over 2,000 hours every year.”