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Guide to DDC

Chapter 2

Input Devices and Sensors

Energy Measurements

The measurement of energy is a very important aspect of the DDC system. Savings due to operational procedures and equipment performance can be directly determined through this measurement. A variety of devices and methods are currently available.

Types of Energy Measurement Devices

The three most common energy measurements used for DDC systems are airside, waterside and electrical energy measurements. Airside energy measurements are typically calculated in the DDC system using air temperature and flow rate measurements. Waterside energy can be calculated in the DDC system or with energy measuring devices called BTU meters. Electrical energy measurements can be calculated in the DDC system or with Power Monitoring Devices.

BTU Metering Devices

BTU meters are used to determine energy flows in hydronic systems within a facility for accounting or control purposes. Determination of heat flow requires measuring the heat transfer medium flow and the difference in temperature between the supply and return to the metered load or producer.

With suitable software, this can be accomplished using the DDC system. This may also be accomplished external to the DDC system using a microprocessor-based computer with flow and temperature inputs, and analog output to the DDC system representing totalized energy consumption in BTU or ton-hours, or energy flow in BTU per hour, tons, or similar units. Many manufacturers of flow measurement devices offer this type of system.

Power Monitoring Devices

Power monitoring devices can be used to monitor electrical energy usage. They can either directly measure the energy usage by providing pulses that represent kW per hour, or can provide an analog signal that measures power which can be used in an energy calculation (over time) in the DDC system. For more details please refer to the previous section on Power Monitoring Devices.

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