The Virtual Moveable End Cap II modular chiller from Multistack.

Consider the chiller. One of the most basic definitions is “a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.”

But these days a lot more terminology is attached to the equipment. Consider such terms as “simultaneous heating and cooling,” “single refrigerant lift and counter-flow,” “dual-independent compressors,” and “virtual moveable end cap.”

Such are some newer chillers. In this case, all of those terms have been attached to the Virtual Moveable End Cap II (VMEII) modular chiller developed by Multistack.

Howard Kelly, marketing director for the company, called it “the ultimate solution to simultaneous heating and cooling needs.”

The approach uses a combination of 10-, 15-, 20-, 30-, 50-, 70-, and 85-ton dedicated heat recovery chillers (DHRC) to create systems from 20 to 600 tons to provide full heating and cooling requirements for the building - with simultaneous mode being the first stage. With the use of a geothermal field, VME II can accommodate uneven heating and cooling loads.

“No reversing valves are used in the modules and the engineering design is based on a single refrigerant lift and counterflow in the heat exchangers to allow for maximum energy efficiencies,” said Kelly.

The modules use dual-independent compressors for redundancy. VME II is based on DHRC units that allow the production of hot and cold water simultaneously while tying into closed or ground loop water sources - without requiring the use of geothermal water as a buffer.


Some of the aspects of the concept as described by the manufacturer:

• Single point electrical connection for valves and modules;

• Disconnecting circuit breaker for each module;

• A modulating valve for built-in head control and water temperature;

• VME valves not required between constant simultaneous load modules;

• Compressor run time equalization;

• Built in heat recovery for simultaneous efficiency; and

• Single refrigeration lift for more efficiency.

Said Kelly, “This design dramatically reduces piping and electrical costs as well as reducing the footprint needed to meet architectural limitations.”

The valve units are factory wired and assembled and are powered by Multistack’s buss bar system.

Kelly noted that since the system is modular, it can be expanded to meet additional building needs in the future. “This eliminates the waste of discarding an undersized system as a company grows.”

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Sidebar: Pre-Approval

Multistack has announced California Office of Statewide Health Planning and Development (OSHPD) Pre-Approval Certification for Multistack MS modular chillers. Units that have passed the testing procedure include the MS10X, MS15X, MS20X, MS30X, MS50X, MS70X, MS105X, MS135X, MS145X, MS165X, and the MS80T.

According to a statement from the company, “By achieving this certification, Multistack MS Modular water-cooled chillers are in compliance with ASCE 7-05 Chapter 13, assuring safety and security for patients and employees. The testing involved in meeting these standards is considered to be the most rigorous in the United States, and is viewed by many as the default standard for products used in health care, educational, and civic institutions.”

Publication date:05/09/2011