Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/851629
6 | august 2017 | WWt | www.wwtonline.co.uk Ben PiPer technical Director atkins Planning for extreme weather events The challenge of climate change resilience means that the conventional deterministic approach to drought planning is no longer appropriate W ith the unusually hot weather in June, with temperatures exceeding 30 degrees in the UK combined with a prolonged period of less than average rainfall, the debate about extreme weather continues. One issue to be addressed is where the responsibility lies for ensuring our resources are future-proofed to cope with this stress. But to what extent has the water industry taken a role in helping to future-proof its infrastructure from weather extremes so it can demonstrate that resilience is part of its long-term planning? To start with, the priority of the UK water industry is clear – to provide a safe, reliable supply for customers across the UK. And to achieve this, there has been an increasing need to ensure that the water industry as a whole plans for the long term. Put simply, there is more need than ever before for it to consider its role in protecting the UK against the growing risk of drought. So what has happened to date? Since the privatisation of the water industry in 1989, the approaches and methodologies for water resource planning in the UK have developed into a set of guidelines that all water companies must adhere to in their Water Resource Management Plans (WRMP) and Drought Plans. In addition to the general development of methodologies to capture more robust data and to employ new analytical techniques, there have also been a number of extreme weather events - such as the 1995 drought that particularly impacted the north east, the 2007 summer floods, the dry winter of 2011- 2012, and in parts of the UK, the dry winter of 2016-2017 continuing into 2017. These factors combined have not just changed conventional methodologies, but they have also changed legislation and regulation too. For example, the 1997 Water Summit led to the production of a 10-point plan on improving water management including the setting of mandatory leakage targets. The traditional approach to water resource planning has been to assess how a water resource system would respond to high-levels of demand together with water resource availability under certain design conditions. Within the UK, the accepted practice has been to forecast 'dry year' demands (based on the pattern and magnitude of water into supply that have been experienced) and to use data from historic drought records. However, weather in recent years has thrown the credibility of this approach into doubt – take the dry winter of 2011- 2012 where there was concern that there would be restrictions during the 2012 London Olympic and Paralympic Games - this was quickly followed in April 2012 with the highest ever recorded rainfall totals in many places. With the threat that climate change is likely to increase the frequency and magnitude of extreme weather events, it's safe to say that as experts in the water industry, the conventional deterministic approach to supply-demand balance Armed with this information in advance, utilities planning new sites can avoid future energy use disappointment. But what about existing systems? The good news is that certain components can be fine-tuned, replaced or adjusted to improve the overall efficiency. Additional energy savings can be achieved by ensuring the individual components of a pump's electrical system are optimised. For example, selecting the most efficient motor for the duty could increase efficiency by up to five percent. However, the greatest savings are achieved by reducing the speed of the pump. A 2 Hz reduction in speed is a 12 percent energy saving typically on a pump system. One method is to change the control philosophy of the VSD driving the pump motor to pump slower for longer. This is particularly effective when used to switch operation of pumps to periods when tariff costs are lower. This simple change can reduce energy costs by thousands of pounds a year, putting utility providers well on the way to achieving their 20 percent energy reduction target. SPOnSOreD BY stuart Foster, uk Water Manager (Drives) aBB The new approach to energy efficiency Many pump systems are far less energy efficient than they appear to be, and optimising electrical systems is the key T he increasingly competitive nature of the water industry is prompting water and wastewater service suppliers to adopt ever more progressive ways to reduce energy use. These suppliers tell us that in order to remain competitive they must reduce their energy use by a staggering 20 percent on average, and with absolutely no reduction in the volume or quality of services provided. It is a huge challenge. Installing energy-saving technology, for example variable speed drives (VSDs) and high efficiency motors, is proven to reduce energy use – but many water facilities already have those in place and yet must still achieve a 20 percent energy reduction. So where can they find those savings? In many cases, greater efficiency can be achieved by optimising the electrical system driving pumps. An electrical system typically comprises a transformer, VSD, electric motor, switchgear and cabling. The savings can be great – between five and 10 percent typically. It's just a case of knowing where to look. The fact is many pump systems are far less efficient than they may appear to be. O£en when specifying such a system, designers simply multiply the catalogue efficiencies for each component to get overall system efficiency. For example, if each component is listed as 98% efficient, there may be an assumption that the entire system will also be 98% efficient. However, in reality the actual overall system efficiency could be far lower. This is for two reasons. Firstly, catalogue efficiencies are based on manufacturers' best efficiency figures based on laboratory rather than actual conditions. Secondly, simply connecting components together overlooks some fundamental lessons of physics which causes the components to react with each other in unexpected ways that may have a negative impact on overall pump system efficiency. The Talk: opinion "the accepted practice has been to forecast dry year demands and use data from historic drought records… this approach has now been thrown into doubt."