Bitzer-Covent-copyNORWAY: A three-year search for the optimal compressor with capacity control by Norwegian AHU manufacturer Covent has ended with the selection of a Bitzer Ecoline compressor and CRII capacity control.

As the leading producer of ventilation units with and without cooling in Norway, Covent has been looking for suitable capacity control since 2012. The company has over 40 years of experience in the production of ventilation units. In Bjerkreim, a small community in the southwest of Norway, 60km south of Stavanger, 100 Covent employees produce around 1,200 ventilation units each year.

Since August 2015, the latest Covent line has now been equipped with Ecoline reciprocating compressors and CRII capacity control from Bitzer.

“Many of our units have variable ventilation volumes, so we need a cooling system that works reliably with both high and low air streams and can be flexibly adjusted by capacity control,” said Jostein Jensen, technical manager at Covent. “The decisive improvement for us is that we no longer have three-step capacity control for two compressors as we did previously – but rather, each individual Ecoline reciprocating compressor is variably controllable. That increases system efficiency and reduces installation costs.”

High standards

The Norwegian company’s requirements were demanding: they wanted a solution with a capacity regulator for a broad area of application and with very high system efficiency. The units also had to be easy to operate and reliable. Bitzer tailored the capacity control to its tried-and-tested Ecoline reciprocating compressors. The compressor with the CRII system is almost infinitely variable depending on the operating conditions and refrigerant thanks to a specially adjusted control algorithm. 

At the very beginning of the project, Covent and Bitzer also got the Swedish controls company Regin involved. Regin specially adjusted its controllers to the system requirements of CRII so that both work together optimally.

Flexible capacity control

With the help of CRII, the Ecoline compressors reach a very broad range of control of between 10% and and 100% in the two-, four- and six-cylinder versions. Tandem compressors can even operate with a part load of just 5%. The CRII control features a newly constructed control piston with a hollow structure which allows a higher switching frequency, ensuring lower variations in controlled values, temperature and pressure. Combined with the increased range of control, this provides improved system efficiency.