Hot Water Supply Temperature setpoint reset control is poor

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