Chilled Water System – Bypass Valve is Open while Pump Speed is High

Objective/ Method/Outcome

Objective: Determines if the chiller bypass valve is open while pump speed is higher than a defined threshold.

Method: Determines if the pump speed is greater than the defined speed threshold while the bypass valve is open and generates an insight when this fault occurs for greater than the defined daily threshold. Avoidable Cost and Potential Savings are determined by calculating unnecessary pump energy consumption.

Outcome: This rule generates an insight.

Description

Reference: ASHRAE Guideline 36-5.20.8 This rule is applied for variable primary chilled water system. A bypass valve is required to ensure minimum flow through the chillers, especially in situations where the system is demanding little or no flow. If pump speed is still high while the bypass valve is opening, cooling could be insufficient as chilled water is circling via bypass loop. This rule is part of the CopperTree Standard rule-set.

Default Priority

Medium

Diagnosis

1. Check if bypass valve is leaking or manually overridden.

2. Check if speed is manually overridden.

3. Review control sequence.

Message

Bypass valve is open while the pump is running at a high speed.

Rule Template

Insight Type: Fault Detection

Trigger Type: Active High

Notes

1. Expected values for “Pump Speed” inputs are “100” if they are constant speed pumps or not available.

Default Values:

Const. – Chilled Water Pump VFD Speed Threshold [%]: 30

Const. – Threshold – Weekly Hours of Faulty Operation [hrs]: 4

Const. – Energy Rate [$/kWh]: 0.1

Const. – Pumps Power Rating [HP]: 10

Const. – Weeks of Operation: 26