There is nothing as energy efficient as a power draw that is turned off - and that is the "secret" behind Multistack and Airstack modular chillers.
Normally, a building's cooling system is handled by a massive water chiller capable of producing several hundred tons of cooling capacity. When running at full capacity, it is highly efficient, but that is also the problem with its design. Most facilities only hit maximum demand a few days a year, which leaves approximately 360 days at less than full demand. That means all of the power required to run a huge compressor is wasted - which brings things back to the thought: nothing is more efficient than off.
Sparta, Wis.-based Multistack builds modular chillers with multiple smaller compressors that are connected to offer the same overall capacity as a large chiller. Multiple compressors offer two benefits. The first is the ability to turn off the compressors - power draws - when they are not needed, allowing for maximum efficiency. The second is redundancy. In the event of a compressor failure, the multiple connected units provide a backup system. In order to have a backup system with a more traditional large chiller system, there needs to be a second large chiller system, which can add significant cost.
Multistack further increased efficiency by adding MagLev technology to its Airstack and Multistack lines. MagLev, short for magnetic levitation, means what it suggests: something floating in a magnetic field. In this case, it is a two-stage impeller spinning inside the chiller compressor. Traditional chiller compressors use bearings that encapsulate the impeller shaft, making full contact, and use grease and oil as a lubricant between the bearings and the shaft. The floating impeller eliminates the conventional bearings and lubrication, so at compressor startup, there is no mechanical resistance to overcome and the amount of draw is reduced. Additionally, the compressor can run at varied speeds to provide the best partial-load performance.
Other benefits of a modular chiller system include:
- Simplified installation. Individual modules fit through doors and in freight elevators.
- Simplified expansion. Modules can be added as needed.
- Minimal refrigerant charge.
- Quieter operation than a full-sized chiller.
- Oil-free refrigerant system, so oil cannot foul heat transfer surfaces to degenerate the system's efficiency.
- Lower required electrical startup current. A modular compressor such as the MagLev requires as little as 2 A. A full-size compressor requires 500 to 600 A.