Why do high-pressure alerts appear on DX systems in the summer?

Environmental conditions have changed

Many DX cooling systems still in operation today were designed years ago, when the outdoor temperature used for summer sizing was typically 32–35 °C. Nowadays, however, heatwaves of 38–40 °C are becoming increasingly common, placing a significantly greater load on outdoor condensers. The cooling system itself has not changed – but the environmental conditions have.

What happens in such cases?

The role of the outdoor condenser in a DX system is to extract heat from the refrigerant and release it into the outside air. As the outdoor temperature rises, the temperature difference between the condenser and the ambient air becomes smaller. As a result, heat dissipation efficiency decreases, condensing pressure increases, the compressor operates under greater strain, and may eventually reach the high-pressure protection threshold. A high-pressure shutdown is not a system fault, but a built-in safety feature that protects the compressor from excessive pressure, high discharge gas temperatures and the resulting mechanical damage.

Why is this a problem in a data centre?

The greatest risk is that a breakdown will occur precisely when cooling capacity is most needed.
Recurring high-pressure faults can result in:
• reduced availability;
• increased strain on the compressors;
• more frequent breakdowns;
• accelerated wear and tear on components;
• increased operational risk.
If the same issue recurs every summer, it is likely that we are not dealing with a one-off fault, but rather a lack of design margin.

How can the cooling margin be increased again?

There is no single solution that applies equally to all sites. The appropriate technical intervention depends, amongst other things, on:
• the design of the condenser;
• the refrigerant used;
• the pipework;
• the available space;
• the availability of water supply;
• the redundancy configuration;
• and future cooling requirements.

In practice, two tried-and-tested solutions can be applied.

1. Adiabatic pre-cooling using existing condensers

In many cases, there is no need to replace the entire outdoor unit. Adiabatic pre-cooling reduces the temperature of the air entering the condenser, thereby improving heat dissipation efficiency even on the hottest summer days. As a result, condensing pressure is reduced, the load on the compressor is eased, and the likelihood of high-pressure faults occurring is significantly reduced. This solution is particularly advantageous at sites where a suitable water supply is available and a rapid, cost-effective upgrade is required.

2. Resizing the outdoor condenser

If adiabatic pre-cooling is not applicable or undesirable, it is worth reviewing the selection of the condenser. Many existing systems were designed based on older sizing criteria. Given today’s climatic conditions, it may be advisable to use an outdoor unit that has been sized for an outdoor temperature of 45 °C. In the long term, this can ensure greater operational reliability, lower compressor load and greater cooling reserve.

We don’t just deal with the alarm; we address the root cause as well.

If high-pressure faults recur every summer, it is worth inspecting the entire system, rather than simply clearing the fault code. Experience shows that a proper technical inspection can often identify in advance the areas likely to cause problems during peak summer loads. As the Hungarian representative of STULZ, we assist with the inspection of existing DX cooling systems, the verification of the sizing of outdoor condensers, and the selection of the most suitable technical solution – whether this involves adiabatic pre-cooling, condenser replacement or complete system optimisation.