Closed-Loop Dry Cooler

In a closed loop, as soon as ambient sits far enough below the required supply temperature, the dry cooler can reject the full load on its own and mechanical cooling can stop. System draw is then fan power alone, an order away from compressor operation. The changeover point is set jointly by the required supply temperature, the margin carried in the selection and local climate — it is not a fixed number. The higher the acceptable supply temperature and the larger the selection margin, the more hours per year the chillers stay off. Deciding whether a project should be built around free cooling means running hourly local weather data against the supply temperature, not applying a rule of thumb.

A dry cooler is bounded by ambient dry-bulb temperature, which makes the summer extreme the controlling condition for selection. Adiabatic pre-cooling adds water to the entering air, pulling intake temperature from dry-bulb toward wet-bulb and buying capacity during hot hours — which avoids sizing the whole machine one step up for a few hundred hours a year. The pad method produces no droplets; the spray method is simpler in construction but stricter on water quality. Both need self-drain: pipework and pad face drain down when the system is off for winter, to avoid freezing. Water consumption is calculated against the hours actually run, and is normally far below the year-round make-up of evaporative equipment.

On hot sites the controlling condition is the summer extreme, and where the selection point is set decides both machine size and whether adiabatic pre-cooling is needed. At altitude, lower air density reduces mass flow at a given speed, so heat rejection must be corrected for actual altitude and fan motors derated or specified for high altitude. On severe cold sites the priority is freeze protection: glycol concentration is set against the lowest ambient with the effect of low-temperature viscosity on pressure drop checked, drain points are provided on sections that can be emptied, and sections that cannot be drained are trace heated. Dusty sites need wider fin spacing and provision for washing, since fouling degrades heat transfer faster than corrosion does.

The controller modulates fan speed against outlet fluid temperature, with set point, dead band and alarm thresholds tuned to the project duty during commissioning. Upper and lower fan speed limits prevent prolonged low-speed running from starving the motor of cooling; speed faults and high or low outlet temperature alarm separately, with a delay available to ride through transients. If the control signal is lost the unit enters continuous cooling rather than stopping, so heat still leaves the loop during a fault. Running state, alarms and speed can be pushed to a third-party monitoring platform through a data interface; protocol and point list scope are agreed when the control scheme is confirmed.

Overall dimensions decide the transport method: units inside the standard box envelope ship complete in a container, oversized units go by flatbed or ship in sections for site assembly. Lifting lugs are fitted, and lifting attitude and sling angles are given on the general arrangement drawing to avoid twisting the frame on an angled lift. After placement, leg positions and foundation inserts are checked against the drawing, and level is controlled — vent and drain points work by elevation, and a tilted unit will not vent cleanly. Relative elevations of the low-point drain and high-point vent are verified before site pipework is connected. Work at site reduces to pipe, cable and commissioning.