Commercial Chiller Maintenance: What Building Managers Should Monitor

Why chiller monitoring matters

In a chilled water building, one or two chillers supply cooling to every air handling unit and fan coil. When a chiller fails, the whole building feels it. Chiller faults rarely appear without warning: they show up first as changes in temperatures, pressures, alarms and run patterns. If someone is watching those trends, problems can be fixed in planned time rather than during a heatwave.

Readings building managers can watch

You do not need to be a refrigeration engineer to spot a developing problem. Most chiller controllers and BMS systems show these values:

A low delta T is one of the most common chilled water problems. When return water comes back barely warmer than flow water, chillers run more machines than needed, pumps use more energy, and spaces at the end of the system can still be warm.

What engineers check

A planned chiller maintenance visit typically covers:

• refrigerant pressures, superheat and subcooling compared with expected values
• evaporator and condenser approach temperatures, which rise as heat exchangers foul
• compressor oil level, oil condition and, where specified, oil analysis
• electrical connections, contactors, starters and drives, including thermal imaging where specified
• condenser coil cleaning and fan operation on air-cooled machines
• flow switches, safety devices and interlocks
• controls, setpoints, sequencing and BMS integration
• statutory F-gas leak checks at the interval set by the refrigerant charge
• water treatment and strainers on the chilled water side

Air-cooled condensers

Many chillers serving London commercial buildings are air-cooled and sit on roofs. Their condenser coils collect dust, pollen, leaves and pigeon debris. Dirty coils raise condensing pressure, increase energy use and cause high-pressure trips on the hottest afternoons, which is exactly when cooling is needed most. Pre-summer coil cleaning and a check that no plant, screens or stored items restrict airflow make a noticeable difference.

Water treatment

The chilled water circuit needs treating to control corrosion, scale and microbiological growth. Poor water quality fouls heat exchangers and control valves and can cause strainer blockages and pump failures. Regular sampling and dosing should be part of the maintenance arrangement for the whole circuit, not just the chiller.

Water-cooled chillers that reject heat through cooling towers or evaporative condensers are a legionella risk. These must be notified to the local authority and managed under HSE’s ACOP L8.

Compliance points

• F gas: chillers often hold large refrigerant charges, which puts many into the 6-monthly leak check band or the band where automatic leak detection is mandatory. See our F-gas leak check guide.
• Pressure systems: refrigeration systems can fall within the Pressure Systems Safety Regulations 2000. Whether a written scheme of examination is required depends on the system. Confirm with a competent person or your insurer.
• TM44: chilled water systems are air conditioning systems under the energy performance regulations and need a TM44 inspection at least every five years.

Using trend data

If your BMS logs chiller data, a monthly look at a few trends will catch most developing problems early:

1. Chilled water flow temperature against setpoint.
2. Delta T across the plant.
3. Compressor starts and run hours.
4. Alarm counts by type.

Changes in these are worth raising with your maintenance contractor before they become breakdowns. See HVAC controls and BMS.

When to call for help

Call an engineer for repeated trips, a chiller that will not restart, loss of cooling to critical areas, refrigerant alarms or visible oil and refrigerant leaks. For an urgent loss of cooling, use our 24/7 contact line on 020 7998 9005. For planned work, see chiller services.