Hot Water System – Hot water return temperature is too high for condensing to occur

Objective/ Method/Outcome

Objective: Determines if return water heat can be recovered for condensing boilers.

Method: Compares the hot water return temperature to the defined boiler condensing temperature threshold and temperature sensor error threshold. An insight is generated when the hot water return temperature exceeds these thresholds for greater than the defined daily threshold.

Outcome: This rule generates an insight.

Description

Reference: ASHRAE Guideline 36-5.21.11 This rule is applied to condensing boiler only. It determines if heat from return water can be recovered properly. This rule is part of the CopperTree Standard rule-set.

Default Priority

Medium

Diagnosis

1. Hot water supply temperature setpoint is too high.

2. Hot water load is too low. High bypass flow is raising the entering water temperature.

3. Hot water coils are not designed for condensing at current loads.

Message

Hot water return temperature is too high for condensing to occur.

Rule Template

Insight Type: Fault Detection

Trigger Type: Active High

Inputs

Input	Units	Tags	Description
Hot Water Return Temperature	°	Hot Water Return Temperature
Threshold – Boiler condensing temperature	°
Threshold – Temperature error for hot water temperature sensor	°
Threshold – Daily Hours of Faulty Operation	Hours		The minimum hours of fault that can trigger an insight
Hot Water System Status		Boiler Command, Hot Water System Enabled, Boiler Status

Notes

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

Default Values:

Const. – Threshold – Daily Hours of Faulty Operation [Hours]: : 2

Const. – Threshold – Temperature error for hot water temperature sensors[*C]: 3

Const. – Threshold – Boiler condensing temperature[*C]: 57