Chilled Water System – Chilled Water Supply Temperature setpoint reset control

Objective/ Method/Outcome

Objective: Determines if chilled water system is modulating when outdoor air temperature changes.

Method: The chilled water temperature reset schedule and the output dry-bulb temperature were used to determine if the Chilled Water System complies with ASHRAE Standard 90.1-G3.1.3.9.

Outcome: When a mismatch occurs, an insight is triggered.

Description

Reference: ASHRAE Standard 90.1-6.5.4.4/ASHRAE Guideline 36-5.20.5

This rule determines whether the chilled water system is operating efficiently in accordance with variance in outdoor dry-bulb temperature.

This rule is part of the CopperTree Standard rule-set.

Default Priority

Medium

Diagnosis

  1. Reset chilled water supply temperatures by outdoor air temperature.

Message

Supply water temperature not modulating with relation to the changes of outdoor air temperature.

Rule Template

Insight Type: Energy

Trigger Type: Active High

Inputs

InputUnitsTagsDescription
Outdoor Air Temperature°Outdoor Air TemperatureThe recorded outdoor air temperature.
Threshold for Faulty Hours Per Day  The minimum hour of fault that can trigger an insight. Set to 10 hours a day.
Chilled Water System Status Chiller Command, Chilled Water System Enabled, Chiller StatusThe recorded status of the chilled water system.
Energy Rate$/kWh The set energy rate for the site. Set to 0.1 by default.
Weeks of Operation  Number of weeks a year the unit is expected to be operational. Set to 26 by default.
Supply Water Temperature°Chilled Water Supply TemperatureRecorded supply water temperature.
Baseline Chiller COP  The baseline chiller efficiency. Set to 6 by default.
Sensible Heat GainBTU/h The sensible heat gain determined using ASHRAE guidelines. Set to 1000000 BTU/hr by default.
Supply Water Temperature Setpoint Deadband° The tolerated difference between supply water temperature and setpoint. Set to 2°C

Notes

1. The chilled water temperature reset schedule was obtained by analyzing data from ASHRAE Standard 90.1-G3.1.3.9. Chilled-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 7°C at 27°C and above, 12°C at 16°C and below, and ramped linearly between 7°C and 12°C at temperatures between 27°C and 16°C.

2. Expected values for “Chilled Water System Status” inputs are “0” or “1”.

Default Values:

Const. – Threshold for Faulty Hours Per Week [hours]: 10

Const. – Supply Water Temperature Setpoint Deadband [°]: 2

Const. – Energy Rate [$/kWh]: 0.1

Const. – Weeks of Operation: 26 Const. – Baseline Chiller COP: 6