Objective/ Method/Outcome
Objective: Determines if the hot water supply temperature setpoint reset is controlling poorly.
Method: The Desired Supply Water Temperature is determined based on Outdoor Air Temperature and ASHRAE Standards, then it’s compared with the Supply Water Temperature and Supply Water Temperature Setpoint Deadband. An insight is generated if a mismatch occurs for longer than the defined Threshold for Faulty Hours Per Day.
Outcome: This rule generates an insight.
Description
Reference: ASHRAE Standard 90.1-6.5.4.4 /ASHRAE Guideline 36-5.21.4. This rule determines whether the hot 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 hot water supply temperatures by outdoor air temperature.
Message
Supply water temperature is not modulating with relation to the changes of outdoor air temperature.
Rule Template
Insight Type: Energy
Trigger Type: Active High
Logic
Inputs
| Input | Unit | Tags | Description |
| Outdoor Air Temperature | ° | Outdoor Air Temperature | The recorded outdoor air temperature |
| Threshold for Faulty Hours Per Day | Hours | The minimum hours of fault that can trigger an insight | |
| Supply Water Temperature Setpoint Deadband | ° | The acceptable supply water temperature deviation from setpoint that is considered normal | |
| Supply Water Temperature | ° | Hot Water Supply Temperature | The recorded hot water supply temperature |
| Sensible Heat Gain | BTU/h | The calculated sensible heat gain | |
| Natural Gas Rate | $/mmBTU | The cost of natural gas per mmBTU | |
| Hot Water System Status | Boiler Command, Hot Water System Enabled, Boiler Status | The recorded HWS status | |
| Weeks Of Operation | The annual weeks of operation |
Notes
1. The hot water temperature reset equation was obtained by analyzing data from ASHRAE Standard 90.1-G3.1.3.4. Hot water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 82°C at –7°C and below, 66°C at 10°C and above, and ramped linearly between 82°C and 66°C at temperatures between –7°C and 10°C.
2. Expected values for “Hot Water System Status” inputs are “0” or “1”.
Default Values:
Const. – Threshold for Faulty Hours Per Day [hrs]: 2
Const. – Supply Water Temperature Setpoint Deadband [°C]: 2
Const. – Natural Gas Rate [$/mmBTU]: 3
Const. – Weeks of Operation: 26
