Pipe Surface Water Temperature

Understand how to measure Pipe Surface Water Temperature. Learn which tools and meter specifications you need to capture valid temperature readings. Follow a clear, step-by-step procedure to take multiple spot measurements and record your data for analysis and use in calculations.

Used to measure:

Measurement Overview

What:Hourly measurements of water temperature (°F).

Why:Used to determine the cooling load and heat rejected by a cooling plant, the heat load delivered by a heating plant, and the heat recovered by an economizer.

Duration:Best practice is to collect the data for a minimum of six weeks at one-hour intervals.

When:Measurements should be taken when the system of interest is operating under normal conditions.

Type of Measurement:Proxy.

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This technique uses a 4-channel analog logger with a thermocouple sensor to record long-term water temperature (°F) measurements at one-hour intervals. It measures fluid temperature from the surface of a pipe rather than directly in the water stream. The collected data can be used to determine the cooling load and heat rejected by a cooling plant, the heat load delivered by a heating plant, and the heat recovered by an economizer. For more details on how collected data is used for calculations, refer to the calculation methodology of the system being measured.

Measurements should be taken at one-hour intervals rather than as instantaneous values. When recording hourly measurements, the logger captures multiple temperature readings throughout the hour and stores the average value. Since temperature can fluctuate within an hour, an instantaneous reading may not accurately reflect these variations.

The duration of the long-term measurement should be a minimum of six weeks. Measurements should be taken when the system of interest is operating under normal conditions.

info Types of Measurements

Direct: Specifies a quantity of the exact item being measured.
Proxy: Provides an indication of the system operation but does not directly measure the quantity in question.

Measurement Tools

The measurement tool needed for this procedure is a 4-channel analog logger that is compatible with thermocouple sensors. Thermocouple sensors are specially designed to measure very high temperatures, such as as those within the flue stack of a boiler, and very low temperatures, such as those on the surface of water pipes for a chiller system. Different thermocouple sensors are used to measure hot or cold pipes.

NYC agency personnel can borrow measurement data loggers, meters, or sensors from our tool library, by selecting tools based on the required measurement duration. See recommended tools found in our library:

HOBO Four Channel Analog Data Logger Onset UX120-006M

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Standalone data logger that monitors up to four external sensors like thermocouple sensors.

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Thermocouple Sensor Onset TC6-T

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Beaded thermocouple probe, Teflon-insulated and responsive over a range of -200 to 100℃ (-328 to 212℉).

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info Logger Setup

Please note that loggers will require setup with a computer or phone using the manufacturer’s proprietary software prior to installation and measurement logging and that older loggers will require the use of a cable to connect to a computer. Refer to the measurement equipment’s user manual for a detailed description of setup requirements.

Measurement Steps

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Prepare Tools

Use the manufacturer’s software to set up and launch the logger(s). Refer to the equipment’s user manual for detailed instructions on how to set up the logger.

Logging interval: 1-hour4
Date and time to start logging
Date and time to stop logging
Value(s) to measure: Temperature (oF)
Activate input channels on the logger
Type of thermocouple sensor (K-type or T-type)
Sampling interval: 1-second

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Install Tools

Connect the sensors to the data logger.
Place the data logger near the pipes. Avoid adhering the logger to the pipe itself.
Clean the surface of the pipe where the sensor will be placed, removing any dust.
Place the sensor on the clean surface and apply thermal tape to fully cover the sensor.

Close up of the four channel data logger and two thermocouple sensors installed on a chiller. — Data logger placed on a chiller with two thermocouple sensors connected to it.

Close up of a thermocouple sensor taped to a pipe surface. — Thermocouple sensor taped to the pipe surface of a chilled water return line.

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Verify Data Acquisition

Wait 24-48 hours to verify data collection. Return to the location of the measured equipment and use a laptop or a phone with the manufacturer’s proprietary software installed to do the following:

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Do not remove the logger or sensors. If you remove the logger, you may need to start over with the setup and installation process.

If necessary, connect the logger to a laptop or phone via USB cable. Otherwise, use the software to connect with the data logger via Bluetooth.
Analyze the data with a plot graph. This can be done with the proprietary software or Microsoft Excel after exporting the dataset as a .csv file.
Determine whether measured results align with the expected operation of the system or component.

How to check data of bluetooth loggers using HOBOware (9 min).

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Retrieve Tools and Data

After verifying that the logger is collecting data, do the following:

Allow the logger to collect data for the remainder of the measurement period.
After the measurement period has concluded, remove the logger from the panel.
If necessary, connect the logger to a laptop or phone via USB cable. Otherwise, use the software to connect with the data logger via Bluetooth.
Use the proprietary software to stop the logger and end data collection.
Download all data from the logger and save the file in the .csv file format for analysis.

How to extract data from the logger and convert to csv on HOBOware (5 min).

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Select Calculator(s)

These calculators will output estimated annual energy consumption or heat transfer for relevant components using measured data. Download the calculator for your specific component’s measurement strategy and add your measurement data.

Heat Exchangers

Liquid-to-Liquid Heat Transfer (Plate and Frame Heat Exchanger) Calculator

Estimates the annual heat transfer during the heating and cooling season of two fluids in a plate and frame heat exchanger.

Measurements Required:

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Calculation Methodology

This methodology works with hourly data only and each measurement is taken at the start of the hour. If the system operates seasonally, measurements should be taken for the duration of the season at one-hour intervals. If the system is not weather dependent, then a minimum of six (6) weeks of hourly data is required for this methodology to work.

The following equations are used to calculate the sensible heat transferred by the heat exchanger for a full year. All data used in this section should be measured with data loggers per the measurements techniques above.

Table 2. Hourly measured data to calculate heat transfer.
Hourly Measured Values
$$T_1, T_2, T_3, T_4$$	Fluid Temperatures (F)
$$Q_1$$	Fluid 1: Water flow rate (GPM)
$$Q_2$$	Fluid 2: Water flow rate (GPM)

Calculate the mass flow rate of fluid 1 and fluid 2 leaving the heat exchanger for each hour interval.

\begin{equation} \dot{m_1} = Q_1 * 0.13368 * d \end{equation}

Where,

$\dot{m_1} =$ hourly mass flow rate of fluid 1 leaving the heat exchanger ($lb_m$/min)

$Q_1 =$ hourly flow rate of fluid 1 leaving the heat exchanger (GPM)

$d =$ density of water, 62 $(lb/ft^3)$

$0.13368 =$ unit conversion, GPM to $(ft^3/min)$

\begin{equation} \dot{m_2} = Q_2 * 0.13368 * d \end{equation}

Where,

$\dot{m_2} =$ hourly mass flow rate of fluid 2 leaving the heat exchanger ($lb_m$/min)

$Q_2 =$ hourly flow rate of fluid 2 leaving the heat exchanger (GPM)

$d =$ density of water, 62 $(lb/ft^3)$

$0.13368 =$ unit conversion, GPM to $(ft^3/min)$

Heat transfer should be calculated only when the heat exchanger is operating. This can be determined by checking the temperature difference across the recovery system in both the supply side and waste heat stream side. Another condition is that water flow should exist across the heat exchanger.

\begin{equation} \text{If} \hspace{2mm} \begin{cases} T_1 - T_2 > 1 & \text{if heat transfer occurs}\\ T_1 - T_2 < -1 & \text{if heat transfer occurs} \\ -1 < T_1 - T_2 < 1 & \text{if no heat transfer occurs} \end{cases} \end{equation}

Where,

$T_1 =$ meausured hourly temperature of fluid 1 entering the heat exchanger (F)

$T_2 =$ meausured hourly temperature of fluid 1 leaving the heat exchanger (F)

\begin{equation} \text{If} \hspace{2mm} \begin{cases} T_3 - T_4 > 1 & \text{if heat transfer occurs}\\ T_3 - T_4 < -1 & \text{if heat transfer occurs} \\ -1 < T_3 - T_4 < 1 & \text{if no heat transfer occurs} \end{cases} \end{equation}

Where,

$T_3 =$ meausured hourly temperature of fluid 1 entering the heat exchanger (F)

$T_4 =$ meausured hourly temperature of fluid 1 leaving the heat exchanger (F)

\begin{equation} \text{If} \hspace{2mm} \begin{cases} Q_1 > 0 & \text{if heat transfer occurs}\\ Q_1 < 0 & \text{if no heat transfer occurs} \end{cases} \end{equation}

Where,

$Q_1 =$ hourly flow rate of fluid 1 leaving the heat exchanger (GPM)

Calculate the sensible heat transferred by the heat exchanger for each hour interval.

\begin{equation} q_{s1} = \dot{m_1} * 60 * (T_1 - T_2) \end{equation}

Where,

$q_{s1} =$ sensible heat transferred by the heat exchanger every hour for fluid 1(Btu/h)

$60 =$ unit conversion, (min/hour)

$\dot{m_1} =$ hourly mass flow rate of fluid 1 leaving the heat exchanger ($lb_m$\min)

$T_1 =$ hourly fluid 1 entering the heat exchanger temperature (F)

$T_2 =$ hourly fluid 1 leaving the heat exchanger temperature (F)

\begin{equation} q_{s2} = \dot{m_2} * 60 * (T_3 - T_4) \end{equation}

Where,

$q_{s2} =$ sensible heat transferred by the heat exchanger every hour for fluid 2(Btu/h)

$60 =$ unit conversion, (min/hour)

$\dot{m_2} =$ hourly mass flow rate of fluid 2 leaving the heat exchanger ($lb_m$\min)

$T_3 =$ hourly fluid 2 entering the heat exchanger temperature (F)

$T_4 =$ hourly fluid 2 leaving the heat exchanger temperature (F)

Calculate the total heat transfer by the heat exchanger for a whole year.

\begin{equation} Q_s = \sum_{t=0}^{8760} q_s \end{equation}

Where,

$Q_s =$ total sensible heat transfer for a whole year (Btu/h)

$q_s =$ sensible heat transferred by the heat exchanger every hour (Btu/h)

$t =$ hours

Troubleshooting

This section provides some troubleshooting tips for the most common issues with tool installation.

Verify that the logger is calibrated. Re-calibrate the tool if necessary. Clean the surface of the pipe with a damp cloth to wipe off any dirt and grime. Ensure the sensor is covered with thermal tape to prevent measurement of the ambient air around the pipe.