Energy & Power
Energy & Power
Power is the rate of energy transfer.
Power, usually measured in Watt (W), is an instantaneous measure. It measures how fast the energy is transferred at a given moment.
Energy is usually measured in Watt Hours (Wh). Energy can be delivered in many forms, the most common being electricity. Gas and heat (usually carried by hot water) are also ways of delivering energy to a facility. The ezeio system can be used to monitor any type of energy and power when connected to the appropriate sensor/meter.
Below is a summary of the most common Power and Energy monitoring applications. Please click to read more.
An electricity meter or energy meter is a device that measures the amount of electric energy transferred.
In the simplest case, the electrical power is calculated by multiplying the voltage with the current. Energy is calculated by monitoring power over time.
In an AC circuit the situation is a bit more complex, as the voltage and current alternates and may be out of phase depending on the load. This is why a dedicated meter is required that continuously monitors both voltage and current and calculates the power hundreds or thousands times per second.
To accurately monitor power and energy, both current and voltage has to be monitored at the same time.
The simplest form of energy meter has a pulse output. Each pulse will mean a certain amount of energy has flowed through the meter. For example, the meter may be marked “500 p/kWh”, which simply means that when we count 500 pulses, that’s 1kWh. So each pulse is 1kWh/500 = 2Wh. Common types of pulse outputs are “S0” and “KYZ”. These types of outputs can be directly connected to the ezeio input terminals. Up to four (4) pulse meters can be connected to the ezeio.
Some meters have a digital output. The ezeio supports Modbus directly, and through the Modbus communication the meter can communicate more information than the pulse output can convey. A Modbus meter may provide information about both power and energy for each phase, voltage, current, power factor and many other parameters. The ezeio supports up to 20 Modbus meters at the same time.
For small installations, an in-line meter with built-in sensors can be used. Typically in-line meters are rated for loads smaller than 100A. For larger loads, external Current Transformers are typically required.
The current through an AC wire can be monitored using a Current Transformer (CT). There are several types of CT’s to choose from.
Solid Core vs Split Core
Split core transformers can be opened. That way they can be clamped around the monitored wire without interfering with the circuit – sometimes even without switching the power off. While convenient, split core CT’s usually costs a little more than solid core CT’s, and sometimes suffer from lower accuracy.
The simplest form of CT outputs a current that is relative to the current flowing through the eye of the CT. An unconnected CT output may carry a dangerous voltage, so safety may be an issue with this type of CT. The most common type is rated 5A at full scale, so for example a 5/400A CT would output 5A when 400A flows through the eye, and 2.5A when 200A flows through it.
Some CT’s have a calibrated resistor built in that makes the output from the CT a voltage rather than a current. These CT’s are safe to work with even when they are not connected to the meter. A common rating is 1/3V (0.333V) at full scale.
Some CT’s have a DC output. This type of CT cannot be used with an energy meter, but may be convenient if only a current reading is required, for example to monitor run time. Note that monitoring only current will not be satisfactory to calculate energy/power in an AC circuit. Many of the “home energy monitors” only monitor current, and thus will not be very accurate.
Rogowski coil (a.k.a Rope CT)
Rogowski Coils are very convenient for monitoring large diameter, or oddly shaped conductors, and since they are flexible they offer many mounting options. Rogowski coils are suitable for very high loads (1000A ++), but are usually less accurate than regular CT’s at lower currents. They require a separately powered integrator circuit to work with most meters.
Selecting the right CT
These questions must be answered in order to select an appropriate CT:
- What is the diameter of the cables? How large must the eye of the CT be?
- Are there any space constraints where the CT’s are to be mounted?
- What is the max current that will flow through the circuit? If this can’t be determined, what is the fuse rating on the measured circuit?
- What types of CTs does the meter support (5A/0.333V/other?)
- What accuracy is required for the application?
To measure the amount of energy transported through a gas line, the type of gas needs to be known, and a flow meter is needed.
Gas flow meters typically have a pulse output. Each pulse will correspond to a certain volume of gas. The ezeio can directly monitor the pulse output from a gas meter.
Selecting a gas meter require specific knowledge about the installation requirements, local regulations and the properties of the measured medium. eze System does not carry or specify these meters. Please contact your local utility or contractor to work out the specifics.
Water is commonly used to transport thermal energy to or from a facility, sometimes called District Heating (or cooling). Pool heaters are also examples of heat transport systems where the water is heated up by the sun, moved through hoses and tubes with a pump, and leaves off that energy to the pool water.
To calculate the energy transfer in such a system, the following must be known:
- The type of fluid (usually water)
- The temperature of the fluid entering the consumer.
- The temperature of the fluid returning from the consumer.
- The rate of flow.
Two temperature probes and a flow meter will provide the data needed to calculate the energy transfer. There are special integrators designed to do the calculation and conversion to kWh or BTU and keeping track of the energy transfer. The ezeio is also capable of acting as an integrator, reading the flow and temperatures directly from the sensors.