The delta between EWT and LWT is the single most important number in a chiller plant walk-around, and it needs to be logged with a timestamp and an operator name — not recalled from memory at the end of a shift.
The Cost of Casual Monitoring Rounds
Industrial HVAC technicians who run their rounds from memory and paper logs share a predictable failure pattern. The EWT and LWT readings from the morning walk get written on a log sheet that lives in a binder near the plant room door. When refrigerant charge starts dropping and approach temperatures begin creeping over the next three weeks, no one sees the trend because no one has the data in a form that can be trended. The chiller trips on high discharge pressure on a Thursday afternoon, and the post-mortem conversation reveals that the LWT had been climbing 0.3°C per week for a month.
Two-phase industrial cooling plants compound this problem. When you have dual chillers, dual compressor banks, and three pumps, the interaction effects matter. Chiller 1 running on Compressor A with LWT at 9.8°C means something different when Pump 2 is carrying the full building loop than when Pumps 1 and 3 are sharing it. Paper logs almost never capture enough of this context to support a meaningful failure analysis.
What a Structured Round Log Captures
Every entry in this template timestamps to a specific datetime and tags the technician who performed the round. That combination — timestamp plus person — is the minimum viable audit trail for an SLA-governed facility. The Pump field and Chiller Running field are multichoice checkboxes, so the operating configuration is logged in two taps rather than a written note that might say "both running" without specifying which pumps.
The thermal telemetry fields — EWT and LWT for each chiller — are the core diagnostic data. Chiller 1 EWT and Chiller 1 LWT give you the entering and leaving water temperatures across the evaporator barrel. The difference between them, the delta-T, is your load indicator. A chiller sized for a 5°C delta-T running at 2.5°C delta is either under-loaded or has a hydronic flow problem. A chiller hitting 7°C delta under design conditions has a refrigerant charge issue or fouled heat exchange surfaces that will show up on the compressor discharge pressure before it shows up anywhere visible. The setpoint field anchors the data — a Chiller 1 LWT of 9.2°C against a setpoint of 8.0°C tells a different story than 8.4°C against an 8.0°C setpoint.
The fan count per chiller — Chiller 1 Fans, Chiller 2 Fans — is the condensing side context. On an air-cooled chiller, fan count tells you ambient load and condenser approach. If the fan count is maxed and the LWT is still elevated, you're looking at condenser fouling or high ambient. If fans are running at partial load and approach is still clean, the machine is healthy. Logging it as an integer each round catches the slow degradation of condenser fin fouling that nobody notices until kW/TR starts climbing.
Six Months of Round Data and What It Shows
At a hundred round entries across two shifts over six months, the EWT and LWT fields produce trend lines. A Memento filter sorted by datetime with Chiller 1 LWT charted over time shows you the seasonal load profile, the impact of maintenance interventions, and any anomalous excursions that preceded unplanned downtime. The technician name field lets you audit consistency — whether different operators log comparable readings under comparable conditions, which is relevant for any facility where round quality varies by shift.
The PH-2 section mirrors the structure for a second plant area, with its own chiller running states, compressor selections, and thermal telemetry. That duplication is the template doing exactly what multi-plant monitoring requires: parallel data capture with no ambiguity about which plant generated which reading.