How Does Ambient Temperature Affect Chiller Performance?

An air-cooled recirculating chiller removes heat from the process fluid and rejects that heat into the surrounding air through its condenser.

As the ambient air temperature increases, it becomes more difficult for the refrigeration system to reject heat. This can reduce the cooling capacity available from the chiller, particularly when operating towards the upper end of its permitted ambient temperature range.

For this reason, cooling capacity should always be considered at the required process fluid temperature and expected ambient conditions, rather than selecting a chiller based on nominal cooling capacity alone.

When specifying a chiller, consider the conditions at the location where the unit will actually be installed.

The temperature immediately surrounding a chiller can be higher than the general room temperature, particularly where:

• Several pieces of heat-generating equipment are installed nearby
• The chiller is located in a small or poorly ventilated room
• Airflow around the chiller is restricted
• Hot discharge air is able to recirculate back towards the chiller’s air inlet

Air-cooled chillers also reject the heat removed from the process into the surrounding room. This should be taken into account when considering the ventilation or environmental control required for the installation.

For applications where higher ambient temperatures are expected, a High Ambient configuration is available on compatible ATC chiller models.

The High Ambient configuration uses high-speed fans in place of the standard fans to support operation in higher ambient conditions.

Availability depends on the chiller model, so the expected maximum ambient temperature should be provided when discussing your application with ATC.

Low ambient conditions can also need consideration.

For compatible models, the Low Temperature Option Pack (OP00001) can be offered for standard fluid temperature setpoints where the chiller itself will be operating in a low ambient environment.

The pack includes internal insulation to minimise heat transfer and help prevent condensation forming internally, together with an adjusted hot gas bypass setting.

Compatibility an operating limits should be confirmed for the specific chiller model.

Where a suitably facility chilled water system is available, a Water-Cooled configuration may be appropriate for some applications.

Instead of rejecting heat into the surrounding air, a water-cooled configuration uses water for heat rejection. This can provide more stable operation in high ambient conditions while also reducing heat rejection into the room and operating noise.

Water-Cooled configurations are only available on compatible models and require a suitable facility chilled water supply.

Correct siting is an important part of chiller installation.

Ensure that the chiller is installed indoors within its specified operating conditions and that there is adequate airflow around the unit. Air inlets and outlets should not be obstructed, and the installation should avoid arrangements that allow warm discharge air to be drawn back into the chiller.

The room itself should also be capable of managing the heat rejected by the chiller.

When specifying a chiller, tell us about the expected conditions at the installation location, particularly if the environment will be unusually warm or cold.

Alongside the ambient conditions, we will normally need to understand:

• What is being cooled
• Required heat load (kW)
• Required process fluid temperature
• Required flow rate
• Coolant type
• Any stated pressure requirement

Together this information allows us to assess the cooling requirement and identify an appropriate standard chiller and configuration.

If your operating environment falls outside the standard capabilities of our product range, the requirement can be referred to our Engineering team for assessment as a non-standard requirement.