Missed tricks

Posted on 7 May 2008 by The Manufacturer

There has been much hype about turning off lights at the end of the day, but other highly effective ways for reducing energy costs are being overlooked. Debbie Giggle explores some of these frequently missed opportunities

Many manufacturers want to cut energy costs, but are we looking in all the right places?
David Lewis of npower Business said: “In our experience, the key processes in manufacturing sites are generally very energy efficient, particularly where commercial margins are tight. Time and effort focused on OEE often improves energy efficiency as well as production performance. But, away from the key processes, around the site, it is common to see the same manufacturer missing opportunity after opportunity.”
So where should we be focusing attention? Experts believe that certain traditional practices within manufacturing, if rethought, could significantly improve energy efficiency performance. Some of these follow.
Many energy using devices are seen by manufacturers as commodity purchases. This can mean that the purchasing priority is lowest cost rather than energy efficiency. Time is seldom invested to analyse the actual cost of ownership of that component throughout its lifetime in terms of energy consumption. A rethink here, though, could be a big money-saver.
Martin Brown of the Siemens Drives Technology Division explained: “Motors and drives have long lives, which is great, but a new one is often ordered in a rush because an existing unit has reached the end of the road. The temptation then is to specify a ‘like-for-like’ replacement to get everything back up and running as soon as possible. There isn’t time to compare more energy efficient alternatives.
“I’m not advising anyone to replace equipment that is in perfect working order, but with today’s specification software it’s very simple to make these comparisons.”
The Siemens software programme Sinasave assists customers to assess payback periods for different models. It compares fixed and variable speed motors, with and without drives, across a range of different scenarios. As well as comparing upfront cost it calculates energy consumption throughout the product’s life. Similar software is available free for other energy-using devices such as pumps. But does energy efficiency come at a premium price?
“There may be a slightly higher upfront cost, perhaps five or 10 per cent,” Brown said, “but typical payback periods are rapid, months rather than years, and the unit is then actively reducing consumption throughout its life. The statistic is that something like 30 per cent of industrial energy is consumed by motors. So that’s a big opportunity to improve energy efficiency by just phasing in better technology over time.”
Perhaps regular technology reviews using software like Sinasave could be used to predetermine migration paths for production equipment, so that incremental improvements in energy efficiency will automatically be achieved as energy-consuming devices are routinely replaced.
Lewis said: “Manufacturers often apply different approaches depending on whether equipment is process critical or utility-based. Building services equipment is often located elsewhere, or someone else’s responsibility. It’s understandable that more attention is given to process critical kit. Breaks in production have serious repercussions. But utilities equipment, when overlooked, can become a major contributor of waste.”
From an energy efficiency point of view, we can’t afford to differentiate. A pump is using energy whether it is providing hot water for washrooms or cooling a process. But the bad news is that the one serving the washrooms might be far less efficient.
Building services equipment for factories and offices is often not specified by the company that ends up paying the bills. It might pre-date the manufacturer’s arrival on site or have been installed by a property management company leasing the site. In reality, energy efficiency and long-term cost of ownership were probably well down the list of priorities for this original specifier,
who would almost certainly have focused on lowest upfront cost.
But the manufacturer, who ends up paying the bills, is restricted by energy efficiency levels fixed for the life of the equipment by the original specifier.
Only by site-occupier ‘pull through’ is this situation likely to change.
Peter Wolff of Armstrong, a manufacturer of heating ventilation and air conditioning (HVAC) equipment said: “HVAC equipment has a long life, and a production engineer might turn his or her nose up at some of the older, less efficient components found in the typical boiler room. If energy costs are low these components may not be a problem, but when energy costs soar, they can become a liability.
“Belt and pulley driven pumps are one example. Historically they were preferred over direct drive alternatives, and a large population is still installed in commercial premises for heating and chilled water. In good condition, the belt drive should only absorb a small figure percentage of the pump’s absorbed power. Over time, however, performance falls very short as power loss from the belt drive rises dramatically, leading to wasted energy. In addition, belt drives were often used during commissioning to account for system resistance that came in well under the estimate. Rather than de-speed the pump with a new pulley, the commissioning set would be used to adjust the resistance back up to design and get the flow rate throttled back to 100 per cent of design. In cases like this a pump will significantly underperform – in energy efficiency terms – throughout its lifetime.
“It makes sense to review your existing building services provision to check that you’re not operating a system which is inherently inefficient.
Are your pumps suitable for the duty? What would the payback period be if you substituted alternative system components within the same piping? There are numerous solutions, ranging from a simple replacement pump of the right duty, right through to substitution with a variable drive pump with built-in sensor, which will deliver immediate energy reductions. It just needs someone to ask the right questions.”
Over-sizing is a common problem and appears to apply across many energy-using devices. “Over-sizing of motors is widespread,” commented Brown. “Motors are at their most efficient at full load, so running a motor throughout its life at lower loads significantly reduces efficiency even with the most energy efficient models. And when the motor is over-sized, the rest is too: the fusing, the cabling and the drive.”
The same applies to building services. “Pumps are often deliberately over-sized at design stage to ‘err on the side of caution’,” added Wolff.
“Frequently, pump motors are also over-sized to allow for future duty increases that, often, never materialise.”
If equipment manufacturers advocate accurate selection of equipment for the required duty rather than trying to sell us bigger, more expensive devices, then surely we need to think whether ‘building in room for error’ is an outdated design approach that is being perpetuated without good technical foundation.
This problem occurs where control philosophies lag behind advances in energy efficient technology. Condensing boilers are one example.
Steve Cooper, managing director of Armstrong Integrated Systems (a specialist in plant room construction and integration) explained: “The vast majority of condensing boilers installed will never provide the energy savings or CO2 reductions they should. This is because their system design temperatures, control philosophies and hydraulic design have been based on earlier, less efficient technologies.
“With regard to system design temperatures, for example, the UK has traditionally favoured the tried and tested 82°C supply, 71°C return, but this is far from ideal in condensing applications. Condensing mode requires a return temperature of 54°C or below. So maximum system temperatures of 70°C supply and 50°C return arepreferable or, to condense continuously, 50 supply and 30 return.
“In addition, conventional boiler sequencing ignites each boiler in series until the load is met. This was fine in the days when boilers were at their most efficient at full load. Modern condensing boilers, however, are at their most efficient at low load. So by sequencing them in the conventional way we are in fact switching them at their least efficient point.
“Lastly, most current system designs incorporate a constant flow primary circuit. While this ensures that boilers are never starved of water, it wastes energy by mixing flow and return circuits, and reducing delta T in part load conditions.”
Equipment manufacturers urge system designers to consider the complete system when installing new technology to optimise on the latest features.
Lastly, Lewis points out the importance of establishing and maintaining energy efficiency practices. “Sub-metering is an important tool in reducing energy consumption, but sometimes a system of metering is installed and then left to fall into disrepair. If the system is maintained, the data will retain its credibility. Energy suppliers can do a lot through sub-metering and usage analysis to help identify waste.
“Also, make sure that employees understand what energy efficiency practices you want them to follow. Employees won’t generally take decisions like switching off equipment or lights without a clear steer from management.”
Many other issues arose during these discussions,such as the importance of lighting systems which optimise on natural lighting, and more effective drying technologies that slash energy consumption. It’s a huge subject, but the practices outlined above might perhaps stimulate some energy saving ideas.