engineering

Nonintrusive load monitoring

Nonintrusive load monitoring is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nonintrusive load monitoring rather than just read about it. In short: Nonintrusive load monitoring (NILM), nonintrusive appliance load monitoring (NIALM), or energy disaggregation is a process for analyzing changes in the voltage and current going into a house and deducing what appliances are used in the house as well as their individual energy consumption. Electric meters with NILM technology are used by utility companies to survey the specific uses of electric power in different hom…

Key takeaways

Nonintrusive load monitoring belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nonintrusive load monitoring to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nonintrusive load monitoring from memory before moving on to harder problems.

Reference excerpt

Nonintrusive load monitoring (NILM), nonintrusive appliance load monitoring (NIALM), or energy disaggregation is a process for analyzing changes in the voltage and current going into a house and deducing what appliances are used in the house as well as their individual energy consumption. Electric meters with NILM technology are used by utility companies to survey the specific uses of electric power in different homes. NILM is considered a low-cost alternative to attaching individual monitors on each appliance. It does, however, present privacy concerns.

Background and theory Nonintrusive load monitoring was invented by George W. Hart, Ed Kern and Fred Schweppe of MIT in the early 1980s with funding from the Electric Power Research Institute.

The basic process is described in U.S. patent 4,858,141. As shown in figure 1 from the patent, a digital AC monitor is attached to the single-phase power going into a residence. Changes in the voltage and current are measured (i.e. admittance measurement unit), normalized (scaler) and recorded (net change detector unit). A cluster analysis is then performed to identify when different appliances are turned on and off. If a 60-watt bulb is turned on, for example, followed by a 100-watt bulb being turned on, followed by the 60-watt bulb being turned off followed by the 100-watt bulb being turned off, the NIALM unit will match the on and off signals from the 60-watt bulb and the on and off signals from the 100-watt bulb to determine how much power was used by each bulb and when. The system is sufficiently sensitive that individual 60-watt bulbs can be discriminated due to the normal variations in actual power draw of bulbs with the same nominal rating (e.g. one bulb might draw 61 watts, another 62 watts).

The system can measure both reactive power and real power. Hence two appliances with the same total power draw can be distinguished by differences in their complex impedance. As shown in figure 8 from the patent, for example, a refrigerator electric motor and a pure resistive heater can be distinguished in part because the electric motor has significant changes in reactive power when it turns on and off, whereas the heater has almost none. NILM systems can also identify appliances with a series of individual changes in power draw. These appliances are modeled as finite-state machines. A dishwasher, for example, has heaters and motors that turn on and off during a typical dishwashing cycle. These will be identified as clusters, and power draw for the entire cluster will be recorded. Hence “dishwasher” power draw can be identified as opposed to “resistor heating unit” and “electric motor”.

Applications "Extremely cost-effective" load identification Cheap detection of startup transients, line or equipment faults, etc. Perform surveys of both residential and commercial energy consumption. Demand response system for use on the smart grid. Monitor systems on-board ships for safe systems operation with fewer sensors.

Privacy concerns NILM can detect what types of appliances people have and their behavioral patterns. Patterns of energy use may indicate behavior patterns, such as routine times that nobody is at home, or embarrassing or illegal behavior of residents. It could, for example, reveal when the occupants of a house are using the shower, or when individual lights are turned on and off. If the NILM is running remotely at a utility or by a third party, the homeowner may not know that their behavior is being monitored and recorded. A stand-alone in-home system, under the control of the user, can provide feedback about energy use, without revealing information to others. Drawing links between their behavior and energy consumption may help reduce energy consumption, improve efficiency, flatten peak loads, save money, or balance appliance use with green energy availability. However the use of a stand-alone system does not protect one from remote monitoring. The accuracy and capability of this technology is still developing and is not 100% reliable in near-real-time, such that complete information is accumulated and analyzed over periods ranging from minutes to hours.

Software A framework for non-intrusive load monitoring and diagnostics (M. Eng. thesis) contains code listings for an implementation Non-Intrusive Load Monitoring Toolkit (NILMTK) - An open source project written in Python

See also Energy monitoring and targeting Google PowerMeter Home energy monitor Smart meter

References

Illustrations

Worked examples

Example 1 — a first encounter with Nonintrusive load monitoring

Start with the simplest possible case. Write down what Nonintrusive load monitoring claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nonintrusive load monitoring before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nonintrusive load monitoring ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nonintrusive load monitoring

In research: Nonintrusive load monitoring appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nonintrusive load monitoring in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nonintrusive load monitoring is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrical engineering, Electricity meters, Surveillance, so understanding it makes those chapters shorter.
In everyday life: Look for Nonintrusive load monitoring outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Nonintrusive load monitoring in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nonintrusive load monitoring means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nonintrusive load monitoring out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nonintrusive load monitoring in simple terms?

Why does Nonintrusive load monitoring matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nonintrusive load monitoring?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nonintrusive load monitoring.