Withair® Air-cooled Chillers with Free Cooling System (Integrated Water-side Economizer)

Withair® Free Cooling System / Integrated Water-side Economizer Solutions

The Free Cooling System option (sometimes referred to as “integrated water-side economizer” in the industry) adds a fluid-to-air heat exchanger coil in series with the chiller refrigerant condenser coil. The heat rejection airflow moves across both coils, allowing heat rejection and chilled fluid cooling without the need for vapor compression when outdoor air temperatures are lower than the cooling fluid temperature. Withair’s Free Cooling System solution that combines the benefits of an integrated water-side economizer with Variable Frequency Drive (VFD) compression technology and total unit configurability, using a VFD to meet partial load demands and varying outdoor ambient conditions at optimized efficiency levels, offering solutions fully tailored to the application requirement.

For building load profiles where there is a cooling demand and ambient temperatures are below the design chilled fluid temperature, Free Cooling System allows that demand to be met using much less power than normal vapor compression mechanical cooling. This can offer substantial cost of operation benefits to the building owner. Having the coils integrated into the chiller instead of using a separate dry cooler allows for economizing without the need for additional footprint and uses the same fans and fan motors already on the chiller, saving cost and space. It also reduces the number of electrical and piping connections needed, lowering install cost. Having the mechanical portion and controls portion bundled into one piece of equipment helps ensure plug-and-play operation, reduces the chance of field control issues, and allows the chiller to optimize efficiency and first cost.

Operating Modes

Mechanical Cooling Only – This mode operates like a normal chiller with compressors and refrigerant used to remove the heat from the building. Mechanical cooling is used where ambient temperature is above the loop water temperature. 2-way valves bypass the water/glycol mixture around the Free Cooling coils so that they are not in the loop and do not contribute to the pressure drop of the system.

Hybrid – In this mode, both mechanical and cooling are engaged. The 2-way valves direct the water/glycol mixture through the Free Cooling coils first, allowing the cool ambient air to remove some of the heat from the loop. The water/glycol mixture then flows through the evaporator where the remaining heat load is removed. Hybrid mode allows you to get some benefit from the Free Cooling coils even when it isn’t cold enough to achieve removal of 100% of the load with the Free Cooling coils only.

Free Cooling System Only – When ambient temperature is lower than the water/glycol temperature, the chiller will disengage the compressors and all of the load will be rejected by the Free Cooling coils. The water/glycol mixture continues to flow through both the Free Cooling coils and the evaporator so that if the load can no longer be met by just the Free Cooling coils, the compressors will be enabled and switch back into hybrid mode. The colder the ambient temperature, the greater the amount of heat a given coil can reject. During Free Cooling mode, the only power draw is from the operation of the condenser fans and water pump.