Drives and Controls Magazine
VSD-controlled chillers cut energy use by up to 70%
Published:  15 June, 2017

Rittal has developed a variable-speed system for chilling machine tool cooling liquids which, it says, marks “a huge leap in energy efficiency”, achieving energy savings of up to 70% compared to chillers that use hot gas bypass control systems.

Cooling accounts for up to 15% of the power consumption of a machine tool because the temperature of the cooling medium has to be controlled extremely precisely – with a maximum hysteresis of just 0.5K. Larger fluctuations could result in thermal expansion, leading to inaccuracies in workpieces.

Conventional control systems operate the cooling compressor at full capacity, “destroying” much of the cooling power, according to Rittal. The ratio of the cooling capacity to the electrical power consumed – known as the Energy Efficiency Ratio, or EER – for such systems is typically around 1. The new Blue e+ chiller system uses inverter-controlled DC synchronous motors to provide the precise amount of cooling needed, resulting in an EER of 3.

The DC motors are more efficient than conventional AC asynchronous motors in most areas of operation. Using an inverter in conjunction with DC radial fans and an electronic expansion valve allows the speed of the DC motors to be controlled precisely, so that the chillers always operate at optimum speed. Hysteresis is minimised, without having to waste cooling power unnecessarily.

And, because the motors are rarely turned on or off, the components are said to have longer operating lives.

Rittal's Blue e+ chiller system provides the precise amount of cooling needed for machine-tool liquids

Another innovation in the new chillers is the use of microchannels in the heat exchangers. These increase the surface area for exchanging heat between the refrigerant and the cooling water, reducing the amount of refrigerant needed by 55%.

The chillers will be available in three performance classes and cooling outputs of 2.5, 4 and 6kW, adjustable from 20–100%. They can be used in ambient temperatures from –5°C to +50°C.

The chillers can communicate wirelessly using NFC technology with Rittal’s Blue e+ app running on a mobile device. This link can be used to transmit data and to configure the chillers. They can also communicate via a USB wired connection with Rittal’s RiDiag III parametrisation and diagnostic software.