Seeing heat and cooling operate together is a reason to understand the sequence. It is not enough, by itself, to declare waste or to switch one function off.
Literature summary: cooling followed by reheat can serve a moisture-control purpose. Other overlap can arise from excessive cooling, control settings or leaking valves. Different zones may also legitimately have different demands.
Commissioning compares intended operation with physical response. A displayed valve percentage does not prove water flow, and a satisfied zone temperature does not show whether the system achieved it efficiently.
Decision example — If a heating command is zero while air warms across a coil, check sensor boundaries, other heat sources and valve operation with a qualified provider. The observation is a fault hypothesis; it is not a measured energy-saving opportunity until the cause and baseline are verified.
Field method
What to record and compare
Record place, time, weather, occupancy, instrument and operating state. Keep observations separate from explanations.
01
GCT field method 1 — Identify the intended sequence, zone served, moisture requirement, occupied schedule and current temporary overrides.
02
GCT field method 2 — Align timestamps for heating/cooling commands, supply and zone conditions, fan mode and relevant feedback. Label missing or substituted points.
03
GCT field method 3 — Have qualified personnel compare commanded state with actual equipment response using safe access and defined measurement locations.
04
GCT field method 4 — Declare an acceptance target before an authorized correction. Test relevant operating modes, not only the easiest weather condition.
05
GCT field method 5 — Retest, remove temporary overrides and keep the issue record. Quantify savings only with an appropriate baseline, measurements and stated adjustments.
New source links and claims reviewed November 4, 2026. A source explains the stated mechanism; it does not diagnose a particular building or endorse ICY.
Pacific Northwest National Laboratory
Guides to Re-Tuning Measures
Economizer suitability depends on conditions and controls; damper command is not outdoor-air fraction; Some reheat serves dehumidification; excessive simultaneous heating and cooling needs sequence-based investigation
Do not bypass freeze protection, dehumidification, ventilation, combustion safeguards or electrical interlocks. Control changes and valve tests require authorization and the responsible qualified provider.
