Monitoring optimises energy use
Extracting, treating and pumping water uses a huge amount of energy. Accurate monitoring can identify leakage and reduce energy consumption, says Tony Hoyle, ABB's flow products managerPumping accounts for more than 80% of the electricity used in drinking water systems. Given that water supply systems are responsible for 2% to 3% of the world's electricity consumption, it is vital that the energy used in pumping is accurately measured, and efforts made to reduce it. Even with the UK's many gravity-fed systems, water has been pumped extensively by the time it reaches our taps.
The first step to energy management is to assess energy performance. This can only be done through accurate measurement of flow rates, leakage levels and pumping efficiency. Mechanical meters, electromagnetic meters or insertion probes can all help manage networks, and identify areas for cost savings.
Monitoring without disruption
South East Water (SEW) wanted reusable flow meters it could tap into its trunk mains without interrupting the water supply. This would have been impossible with conventional, full-bore flow meters.
AquaProbes from ABB were chosen because they feature an electromagnetic sensor head suspended on a support rod that passes through the pipe wall. This enables metering without disrupting the water supply.
SEW's distribution network has expanded over many decades. In some areas, this means that it is not always clear whether the company's assets are optimised.
"We might have several inlets to a reservoir, for example, but we wouldn't necessarily know precisely how much water is entering the site from each one," says northern leakage manager Richard Moss.
Much of SEW's network runs under relatively flat areas, which means the water must be actively pumped rather than being moved under gravity. "We need to make sure that we're using our assets efficiently and moving water in the most cost-effective way. Domestic power bills have risen by 30% to 40% in recent months and it's the same for industry. We need to reduce pumping costs for the benefit of our customers," he says.
ABB has delivered an initial consignment of 20 AquaProbe units. According to Moss, this looks set to be followed by further orders in the coming months as the programme expands.
One method growing in importance is defining district metered areas. This is an area of the network that can be isolated by boundary valves, and for which the quantities of water entering and leaving can be metered.
The subsequent analysis of flow and pressure, especially at night when water useage drops dramatically, enables specialists to calculate the level of leakage in the district. This can determine whether leak reduction work should be carried out, and helps target maintenance in those areas where it will have the greatest impact.
Every day in the UK, more than 3,600Ml of water leak from in excess of 330,000km of water mains. Identifying leakage is therefore crucial to minimising energy waste, because every drop of water lost has been abstracted, treated and pumped, and will have to be processed again after it has returned to the water table.
ABB says that, given the energy savings that can be made from improved leak
detection, many water companies are upgrading to electromagnetic metering. The technology offers improved accuracy over a wider range of flows. For example, ABB's AquaMaster meters offer +/-0.5% uncertainty and a dynamic turndown range of 1000:1. The company says these meters can even detect a toilet flushing.
As well as offering a lower accuracy than electromagnetic meters when new, mechanical meters also suffer from poor long-term reliability, as wear causes progressive deterioration in performance. Accuracy at low flows is essential for capturing leakage data for effective leakage management.
The power of data
Analysis of the treatment and distribution system allows the identification of electricity cost savings through better procurement tariffs, potential changes to pumping regimes and pump replacement programmes. Typical energy efficiency measures for water companies are the replacement old motors for higher efficiency ones, installation of variable speed drives to control pump speed and flow, refurbishment of pumps and the coating of internal pump components.
Possibly the biggest potential for energy savings comes from the drives that control pumping operations. Typically, reducing the speed of a pump from 100% to 80% can cut energy consumption by up to 50%. Also, many of today's working drives were installed 15 years ago. A modern variable-speed drive will cause substantially lower energy losses than an older unit, so the whole system needs to be considered.
Variable-speed drives also give a significant added smoothness to starting and
stopping. This reduces pressure surges and pipe hammer, thus eliminating one of the causes of leakage.
Monitoring and targeting is a powerful weapon against inefficient processes. By identifying wasteful areas, water companies can plan equipment improvements such as drives and motors, which can make a big difference to the bottom line.
Given the amount of energy used to pump water around, pumping efficiency
is a good place to start for an energy efficiency drive.