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Is your economiser doing anything?
Free cooling only saves money while the damper moves, the sensor reads and the controls agree. Three questions will tell you which of those to look at first.
The check
Answer from what you have seen, not from the drawings. This points at the likely state of the equipment — it does not replace opening the unit up, which is a ten-minute job on most roofs. It runs in your browser and nothing is sent anywhere.
Likely state
A damper that moves with the call for cooling, on a sensor somebody has checked, is doing what it was fitted to do.
- Keep it in the maintenance schedule — linkages seize, actuators fail and sensors drift, usually without symptoms.
- Ask for the changeover setting to be recorded, so the next technician does not reset it to a guess.
- Worth verifying once with measurements rather than by eye.
A damper that never opens means the compressor runs on mild days when outdoor air would have done the work. Nothing breaks, the building still cools, and the cost goes unnoticed.
- Common causes: a failed actuator, a seized linkage, a disconnected sensor, or someone disabling it years ago after a complaint.
- It is usually a repair rather than a replacement, and it is one of the few genuinely quick paybacks in this trade.
- Ask for the actuator to be tested rather than just looked at.
A damper that is open all the time brings outdoor air in when it should not: humid and dusty in summer, freezing in winter. It is the version of this fault people do notice, because comfort suffers.
- In cold weather a stuck damper can freeze a coil, which turns an inexpensive repair into an expensive one.
- Check the actuator and the minimum position setting — the minimum is often set far higher than the building needs.
- Minimum outdoor air still has to meet the building's ventilation requirement; closing it entirely is not the fix.
Where the damper moves but the sensing is missing or unchecked, the unit is deciding when to use outdoor air on information it may not have. That is where the odd behaviour comes from.
- Sensors drift. An enthalpy or temperature sensor that has not been checked in years is not a control, it is a guess.
- Changeover settings get left at factory defaults that suit a different climate.
- This is an hour with a meter, not a capital project.
Most buildings do not know the answer, which is itself the answer: nobody has checked. On a roof with several units it is a short inspection and it is where a lot of quiet waste is found.
- We will open each unit, operate the damper, test the actuator and check the sensor.
- You get the state of each economiser recorded in the asset register rather than as a verbal note.
- Where one is disabled, we will tell you why it probably was — often a complaint that had a different cause.
One limit worth stating: economisers are a saving, not a ventilation strategy. An occupied building has a minimum outdoor air requirement, and that comes first — we will not set a damper below it to save energy.
A valley climate suits free cooling
- Big daily swingsDry air and cool mornings mean many hours each year when outdoor air is genuinely cooler than return air.
- Long shoulder seasonsSpring and autumn are where most of the saving sits, and they are exactly when nobody is thinking about the roof.
- Dust and smokeBoth argue for sensible minimums and clean filters, not for disabling the economiser altogether.
- It fails silentlyThe building still gets cold, so nothing prompts a call. That is why it belongs on a schedule.
