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
- 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
| Input | Units | Tags | Description |
|---|---|---|---|
| Outdoor Air Temperature | ° | Outdoor Air Temperature | The 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 Status | The recorded status of the chilled water system. | |
| Energy Rate | $/kWh | The set energy rate for the site. Set to 0.1 by default. | |
| Weeks of Operation | Number of weeks a year the unit is expected to be operational. Set to 26 by default. | ||
| Supply Water Temperature | ° | Chilled Water Supply Temperature | Recorded supply water temperature. |
| Baseline Chiller COP | The baseline chiller efficiency. Set to 6 by default. | ||
| Sensible Heat Gain | BTU/h | The sensible heat gain determined using ASHRAE guidelines. Set to 1000000 BTU/hr by default. | |
| Supply Water Temperature Setpoint Deadband | ° | The tolerated difference between supply water temperature and setpoint. Set to 2°C |
Notes
1. The chilled water temperature reset schedule was obtained by analyzing data from ASHRAE Standard 90.1-G3.1.3.9. Chilled-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 7°C at 27°C and above, 12°C at 16°C and below, and ramped linearly between 7°C and 12°C at temperatures between 27°C and 16°C.
2. Expected values for “Chilled Water System Status” inputs are “0” or “1”.
Default Values:
Const. – Threshold for Faulty Hours Per Week [hours]: 10
Const. – Supply Water Temperature Setpoint Deadband [°]: 2
Const. – Energy Rate [$/kWh]: 0.1
Const. – Weeks of Operation: 26 Const. – Baseline Chiller COP: 6