Abstract: The HVAC condition based maintenance system and method provides for a system to reduce operating costs by replacing existing time based scheduled maintenance with an on-condition based maintenance system and method for continuous monitoring and acquiring condition based data from an operating HVAC system, transmitting data to a remote server for storage, analysis and trending, recognizing operational performance reductions based on the comparison of current trending to historical data, and for triggering notification of failures and corrective action based on routine, impending and immediate problem recognition. Additionally, the acquired data is used to derive actual heat load characteristic of the building, identify HVAC system deficiencies, building deficiencies and installation issues and load imbalance of multi-unit systems providing direction for system improvements.

Abstract: A differential pressure indicator includes a housing having first and second pressure ports for fluid and a bore communicating with the pressure ports. A piston is movable in the bore between an actuated and an unactuated position in response to a pressure differential between the first and second pressure ports. A sensor senses movement of the piston between the actuated and the unactuated positions. A fluid control mechanism varies the effective surface area of the piston communicating with the first pressure port when the piston is in the unactuated position in accordance with variations in temperature of fluid at one of the pressure ports. The indicator is thereby prevented from actuating at low temperatures at which the fluid has a high viscosity.