02-01-2013, 02:33 PM
NON-INTRUSIVE LOAD MONITORING
[attachment=46185]
Introduction
Residential buildings account for as much as 37% of the total electricity use in the United States (Energy Information Administration [EIA] 2008),Hence , Conservation opportunities have the most impact may seem obvious.
There are many opportunities for reducing electricity consumption in buildings, but identifying and quantifying them is often perceived to be too time-consuming or too expensive to justify, particularly in single-family homes.
Energy audits are one way to obtain accurate and objective assessments of how to achieve savings.
An Energy audit is a process by which a building is inspected and analyzed by an experienced technician to determine how energy is used in it, with the goal of identifying opportunities for reducing the amount needed to operate the building while maintaining comfort levels.
WHY ?
Traditional load-monitoring instrumentation systems employ meters/sensors for each load to be monitored because they tend to be comprehensive, systematic, and convenient. Hence these are intrusive methods.
These meters may incur significant time and costs to install and maintain. Furthermore, increasing numbers of meters may influence system reliability. Some research also indicate that the utility of load-monitoring systems have been questioned by load-monitoring system practitioners.
Hence future studies of load-monitoring systems focuses more significant issues, such as strategies for minimizing the number of instruments using non-intrusive load monitoring (NILM) system.
TYPES OF NALM
There are 2 NALM types based on degrees of non-intrusiveness The second, less intrusive one is more ambitious technically, but has greater advantages:
(MS) “Manual-Setup”: A MS-NALM is a nonintrusive appliance behaviour tracker which requires a onetime intrusive period for setup. During the intrusive setup period, signatures are observed and named as appliances are manually turned on and off. It is distinguished from conventional intrusive instrumentation in that no hardware ever enters the premises being monitored.
(AS) “Automatic-Setup”: An AS-NALM sets itself up as it measures the load, using a prior information about the characteristics of possible appliances. It must determine the important signatures, and the appliances with which they are associated, without the benefit of any entry or appliance survey.
SIGNATURE
Load signature is defined as the electrical behavior of an individual appliance/equipment when its in operation(like heartbeat of human)
It is recorded as template for each device. It is unique due to which it plays a crucial role in deciding the appliance
The NALM monitors the total load , checking for certain “signatures” which provide information about the activity of the appliances which constitute the load. For example, if the residence contains a refrigerator which consumes 250 W and 200 VAR, then a step increase of that characteristic size indicates that the refrigerator turned on, and a decrease of that size indicates the turn-off events.
NORMALIZATION
The essence of the NALM is that changes detected-in the total load should give information about events within the load Hence, admittance is preferable to power and current as a signature. It is a voltage-independent property Since it is somewhat unfamiliar and one lacks engineering intuition about the values to expect and their units ( siemens ).
ADVANTAGES
Complex hardware is prone to many types of failure. In comparisons with the NALM, field tests showed examples where conventional instrumentation suffered losses.
The AS-NALM automatically adjusts to changes in the appliance inventory and unreported appliances. This overcomes a common problem with intrusive instrumentation in which appliances which the utility is unaware of remain unmonitored.
Lower cost, finer resolution, and ease of installation, removal, and maintenance (without requiring an appointment with the residents to gain entry) are very valuable features from the utility perspective
DISADVANTAGES
The method has not yet been fully specified for multistate appliances such as dishwashers, washing machines, and heat pumps. It has not been specified at all for continuously variable appliances.
The NALM may have a greater potential for undetected error. As the total load is disaggregated in software rather than the hardware of separate sensors and communication channels, there is a greater potential for the reported data to contain significant errors. An unusual appliance, not encountered in field tests, might have properties which confuse the software. This is clearly a matter to be concerned about, which we can only address with more extensive field tests.