Smart Metering (AMI/AMR) in the Water Industry
Advanced Metering Infrastructure (AMI) and Automatic Meter Reading (AMR), sometimes referred to as 'Smart Metering', has become a 'hot topic' in the last few years. Much of the interest has focussed on the energy sector, but installations are happening in the water sector. There has been a lot of discussion about the advantages, both to customers and suppliers, of having consumption data readily available, but there seems to have been very limited focus on the practicalities of the technologies. In order to objectively consider the most effective way to obtain and manage consumption data, it is important to understand the technologies available, in terms of the advantages and disadvantages (this makes it a long blog, so I appologise!).
Water meters have two key parts, one to measure the flow, and one to record it. In a simple mechanical meter this consists of a water vane on which a jet of water is directed, turning the vane: such units are termed velocity or speed meters. Volumetric or displacement meters measure a volume of flow for each turn of a piston are generally more accurate than speed meters and are now often used for measuring domestic flows. There are newer types of water meters, based on ultrasonic and electromagnetic technologies. These are generally very accurate, and have no moving parts, however at present they are relatively expensive, so only used for larger meters. The article in Wikipedia on water meters gives quite a good overview, if you would like to know more about them.
The measurement of the flow must be transmitted to the recording unit, generally referred to as a register. In very simple meters this is a direct drive to a series of dials, with appropriate gearing. As however direct drive requires a good mechanical seal on the drive shaft, most modern mechanical meters use a contact-less transmission system. This used to be a magnetic unit, but now inductive coils or optical sensors are more common, as they are less prone to outside interference (e.g. a magnet placed by the meter to reduce readings!). The register itself can either be a mechanical or electronic unit. Domestic meters generally only record the volume of water supplied, and not the instantaneous flow. Extra sensors can be added, such as pressure transducers, but these add to the unit cost (and maintenance issues). All modern units produce a pulse that can be read and transmitted.
Transmitters are the core of any Automated Meter Reading (AMR) system. Systems can just transmit flow, but most now have in-built memory so they can record and transmit other data, e.g. leak, meter blocked, magnetic fraud, overflow, underflow, AMR unclipped or back flow. Some AMR units have processing built into them, so analysis can be undertaken. Systems can either be uni-directional, that just transmits data, or bi-directional, which allows the meter to be queried or re-programmed. Transmission by the unit can be local (collected by walk-by or drive-by), via mobile networks (GPRS or similar), or fixed networks. As such there are a lot of similarities with electricity AMR systems. Note that transmission frequencies and protocols are a very complex area, and not one I intend to cover in this blog!
However water meters are installed in diverse locations, often in the ground, far from any power supply. Because they can be installed in locations where there is a risk of explosive gases, all forms of power supply and circuitry must be sealed. Thus most water meter AMRs (and electronic water meters) run off batteries, in sealed units, and generally it is not possible to change the battery. The unit is therefore redundant once the battery has expired. The life of uni-directional unit is about 15+ years whereas for a bi-directional unit it is often much less (depending on the number of requests made to the unit, each of these requests draining battery power). Additional sensors (e.g. pressure transducers) further reduce battery life. AMR equipped meters are circa $50, and installation typically about $80, therefore installing bi-directional units can increase the cost of ownership.
All of these points lead to questions about the shape of any Advanced Metering Infrastructure (AMI). In some areas the water industry has taken a 'wait and learn' stance, hoping that the energy sector will resolve most of the issues, although in some regions AMR is quite well established (i.e. the United States, where circa 35% of supply sites have AMR fitted). In all cases there is a drive for making meters 'smarter', but is this the best option?
Let us consider how data from a water meter can be used. Unless we record flows at intervals of about 10 seconds, sudden peak demands (e.g. toilet flushes) will be missed: note that current meters generally record at 1 hour intervals or less. Recording flow at 10 second intervals will lead to excessive amounts of data, and is actually of very limited use, as we already know how much water a toilet uses, and the amount of times a toilet is flushed is related to other matters! If flow data were recorded every 15 minutes this would allow overall usage to be tracked over time, and anomalies such as sudden increases or no flow to be identified.
As discussed, more functionality in the meter requires more power. As power in most water meters is finite, I believe that we should actually be aiming to reduce the requirements of the meter, thus increasing its useful life. If meters are limited to recording flows at 15 minute intervals, and transmitting the data at intervals suitable for collection (say every 5 minutes), the battery life can be similar to the meter (at least 15 years). Intelligence can then be added by external systems.
External systems can then be used for both storing the data long term, and analysing, as well of course for billing purposes. Analysis of such data is not complex, and thus could be accomplished by many systems. Some have developed specialist units, either for the consumer or the utility, but considering the type of processing required, this could be accomplished on PCs, smartphones or web engines, based on meter data management packages. The water utility could thus offer their customers the tools to be able to track, and reduce, their water usage over time, identifying high consumption.
Let us consider a possible scenario. A water utility installs water meters with uni-directional AMR systems, transmitting both by allowable frequencies and via a widely used domestic protocol, such as WiFi (with suitable security). To reduce costs with telecoms suppliers, it does not use mobile or fixed networks, rather makes a commercial arrangement with a municipal service, such as refuse collection, to host receivers on their vehicles. The municipal service downloads the data to the water utility on return to base at the end of each shift. Data is thus collected from all customers every one or two weeks, depending on the frequency of collection. The water utility then uploads the data, using it internally for billing purposes and to check for anomalies (e.g. sudden increased usage, possible leakage). It also makes the data available to customers via a secure Smart Customer Portal, who can then use the various Portal tools to analyse their usage. By entering a few details in the Portal (i.e. number of people at the address, typical water uses, etc.) the system makes suggestions as to how the customer can make water savings. If the customer gives other details, such as phone number, the system sends automated alerts flagging abnormal use. The water utility also offers its customers smartphone and PC apps, giving the same functionality as the Smart Customer Portal, but with the added benefit of viewing usage in real time using WiFi. In this scenario, not only does the water utility reduce the cost of new AMR meters (as the life of the units will be maximised), and minimise telecoms charges, but also enhances its reputation with customers, and reduces consumption.
All of the technologies in the scenario above are available now.
