Why Use Electricity Monitors?
Monitoring energy usage is essential for managing energy costs and consumption on the farm. Utility bills provide one way to track total electricity use over time (see Understanding On-Farm Utility Costs & Billing). However, since electricity costs are dependent on timing of demand as well as quantity used, additional information – beyond total electricity use – is required to manage costs.
As tools to monitor electricity have become more versatile, available, and less expensive, their use on farms to identify short and long term trends and patterns is increasingly practical.
Most commercial electricity customers pay a charge for peak rate of use (peak or maximum demand) during a billing period. Monitoring tools can identify the periods of high energy use and identify equipment that contributes to large demands. They pinpoint inefficiencies, waste, and phantom losses. Electricity monitors give feedback allowing for specific cost cutting changes in the way you use electricity, such as:
- staggering times of high demand equipment usage to lower peak rate charge;
- avoiding equipment use during peak demand periods when energy is most expensive;
- use of variable frequency drive devices to better match needs;
- and determining if the purchase of more energy already own makes sense for your operation.
Electricity Monitor Types
As seen in Table 1, the various types of electrical monitoring devices are designed for different applications and uses. To get a handle on electricity costs, your farm may use different types of monitors depending on the type of electric service (two or three phase), how deeply you want to look into your electric usage (for example, do you want separate information from cooling units and fans), and how you want to record the data for analysis. Electricity Monitor types include:
- Point of use monitors – Relatively inexpensive devices that measure electrical use for a single receptacle or a single piece of equipment. The simplest of these plug into existing receptacles (typically 120 volts) and provide a readout of real-time electricity use & total consumption over time. They also monitor and display voltage and current. More sophisticated instruments can provide recording of data for later review and analysis. These monitors may need to be wired into the electrical circuit that supplies the equipment, but can be used at higher voltages and currents.
- Meter monitors – These attach to the electric meter providing instantaneous information (rather than monthly like a utility bill) about total electricity use. These devices provide some mechanism for transmitting the data for display or data recording.
- Single phase electric panel monitors – Intended to provide monitoring of an entire building, system or sub-panel, the simplest of this type monitors the total electrical use in a single panel; others provide the capability to monitor individual circuits as well. They typically include data recording and storage capability, and may also provide an interface to connect to computer networks. This interface can be used to transfer data to computing equipment for analysis and review, and in some cases can be used to provide online access to the monitoring equipment and stored data. Typically these require that an electrician install at least part of the system.
- Larger installations and three phase power monitors – A variety of devices designed to provide sub-metering capability. Tend to be more expensive than single phase or point of use monitors and typically require an electrician for some aspects of the installation.
Monitoring System Components
Electrical monitoring equipment typically includes a variety of components, including a display, some form of input device, a processor, software, and sensors. These may be in a single enclosure or several discrete components.
- Display – Text and graphics that display electrical use (in watts or kilowatts), voltage, current (in amps), total use (in watt-hours or kilowatt hours) and other parameters of interest. May be customizable to provide additional information such as actual electricity cost. May require connection to a computer or network to provide access to this information.
- Input device – equipment or switch between different items on the display.
- Processing unit – Manages the various components of the systems. Includes the electronics to convert analog information from sensors into digital data, controllers for displays, input devices, and memory for data storage as well as managing the interfaces for network or computer connections.
- Software – Often a combination of programs within the equipment and software that runs on a personal computer or online. May provide options for information display (graphic or text) as well as options for reading and recoding information, transferring data to spreadsheets and other software, and establishing time intervals for reading or recording.
- Sensors – Many monitors include external current transducers (CTs) to measure current through individual wires. These are typically donut shaped devices connected to a pair of wires that connect to the processing unit or terminals on an analog to digital converter. The wires that carry the electrical power being measured pass through the center of the sensor. The CT may have a hinged section that allows the sensor to slip around the wire without disconnecting any of the wiring. Smaller CTs generally require that the wire be disconnected so that it can pass through the sensor.
Selecting Monitoring Equipment
Consider the following features when selecting and purchasing equipment to monitor electrical use:
- Cost (including installation costs)
- Online data access
- Expandable capabilities via additional sensors
- User friendly display and data evaluation
- Wireless connection capability vs hard wiring
- Hinged jaw current transducer sensors vs electrical wiring disconnection for insertion into the current transducer.
- Data recording capacity and recording intervals
Electricity Monitoring Example
The role of electricity monitoring on your farm is complex and more easily understood by working through examples. Dairy and greenhouse operations have intensive electrical energy needs and in particular benefit from monitoring, but significant savings on all farms are possible.
Electricity Monitoring on a Diversified Farm – Case study by T.Manning, Bioresource Engineer