Chiller Maintenance Checklist

Approach temperature earns its place at the top of this document because it is the only reading on a chiller service sheet that is simultaneously a condition measurement and a cost measurement. The physics is simple enough: heat has to cross a tube wall, and approach is the temperature difference required to push it across. A clean tube needs very little difference. As scale, biofilm or debris builds on the water side, the same heat transfer needs a bigger gap, so the refrigerant has to run colder on the evaporator or hotter on the condenser, and the compressor has to work harder to maintain it. Every tenth of a degree of widening is energy, continuously, for as long as the machine runs. What makes it useful rather than merely interesting is that it moves long before anything else does. The chiller still makes its setpoint. Nothing alarms. Occupants are comfortable. The only other symptom is an electricity bill that rises gradually in a building where a dozen other things also changed, which is why fouling is so often diagnosed a season late or not at all. A condenser approach carried forward across services, with the commissioned figure beside it and an action threshold attached, converts that into a decision: at 1.8 against a commissioned 0.8 and a threshold of 2.0, the tubes get cleaned at the next convenient window rather than after a summer of paying for them. The second thing worth copying is downloading the fault history, for a related reason: auto-resetting trips leave no physical trace at all, and a machine that has protected itself four times since the last visit is describing a developing problem that an inspection cannot see.

Nothing about this chiller is broken, and the most important line on the sheet is a number that has moved by one degree over several years. The machine makes its setpoint, no protection device has operated, the oil analysis came back normal and there is no refrigerant loss. On a conventional service sheet this is a clean visit. The approach row says something different: 0.8 when the machine was commissioned, 1.1 at the last service, 1.8 now. That is not a fault, it is fouling, and the shape of it matters as much as the value, because the step from 1.1 to 1.8 is larger than the step from 0.8 to 1.1, which suggests the rate is increasing rather than holding. The action threshold of 2.0 is what turns the observation into a decision with a date: clean the condenser tubes before the season rather than after it. Catch it here and the cost is a planned tube clean in a convenient window. Miss it and the machine runs all summer at a widening approach, the compressor works harder every hour it runs, and the cost arrives as consumption that will be attributed to the weather, occupancy or tariff long before anybody looks at a maintenance record from May.

One thing this document deliberately does not carry is a water treatment table, and that absence is a design decision rather than an oversight. The chiller condenser and the cooling tower are a single circuit of the same water. Keeping a set of test results on the chiller sheet and another on the tower sheet produces two records of one system, taken at different times by different people against possibly different targets, and the predictable outcome is a tower that passes its own tests while the chiller it serves quietly fouls. Section 7 of this template therefore records which tower serves this machine, where the water record is held, and what the tubes actually looked like, and then asks the one question worth asking: does the tube condition agree with the water test record. If approach is widening while the tests read clean, one of the two is wrong, and that is a far more useful finding than a second set of numbers. The water regime itself, including dosing, biocide and the legionella controls, belongs to the cooling tower maintenance checklist. The heating side of the same plant room is the boiler maintenance checklist.