Microchannel coils in free cooling applications

Air-based free cooling uses low-temperature ambient air as a cooling medium for chilled water systems, thus providing significant opportunities to generate energy savings. The more time the chilled water system can operate in the free cooling mode, the higher the energy savings it can deliver.

Air-to-water (single-phase) microchannel heat exchangers are remarkable by closer approach temperature, thus giving additional opportunities for free cooling in applications.

In addition to the increase of free cooling time, being all conditions equal, microchannel water coils offer numerous other advantages over finned tube designs, including:

• Lower fan energy consumption (and lower fan sound emissions) due to lower air resistance of the coils, or
• Increased airflow and consequentially increased free cooling capacity, or
• Lower system cost and smaller footprint caused by decreased coil size and number of fans used
• Lower tubeside pressure drop reduces pump energy consumption
• Precise free cooling capacity control

A good example of the above advantages is Kaltra’s latest free cooling chillers, where we employed microchannel free cooling coils. During field tests, Lightstream Freecool chiller (will be available for orders in Q4 2016) achieved 100% cooling capacity in free cooling mode at 4K higher ambient – compared to the same model equipped with finned tube heat exchangers. Such an increase in free cooling time translates to power savings of about 250,000kWh per 1000kW of cooling per year – for Central Europe.

Microchannel coils much less prone to clogging and easier to clean, and this has made it possible to equip Lightstream Freecool chillers with an automatic coil cleaning system. The system determines the need for cleaning by reading from air differential pressure transmitters and initiate cleaning when the pressure difference rises above a set point.

Lightstream Freecool range is based on inverter-driven screw compressors, one per refrigeration circuit, and delivers infinite capacity control in applications. Chillers are available charged with either R134a or lower GWP refrigerant R1234ze, in cooling capacity ranging from 450 to 1200kW.

Introduced this quarter, Lightstream Freecool chillers will be available for orders in Q4 2016.