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Energy


in wasted money, shortened equipment lifecycles and unnecessary carbon emissions. Replacing fixed speed plant with variable speed equipment (which is more efficient at part load) can be the key to significant energy and cost savings. For example, replacing constant water


volume, fixed speed pumps on three port control, with variable speed, variable volume pumps with two port operation can reduce running costs considerably. Typically, no pipe changes are needed to achieve this. Keep the existing body casing with the inlet-outlet connections in place but remove the rest of the pump set. Replace it with a close coupled pump with integrated frequency inverter converting from three port control valves to two port operation. The by-passes become redundant. With “sensorless” software built into the drive, the motor will automatically sense when the two port valves are opening or closing and adjust the speed, and hence the output, of the pump to suit. Advice from your pump manufacturer will help to ensure that the system design is correct to optimise the variable speed capabilities of the pump.


Control technology If your building already has variable speed capability, improved operation could be possible through more advanced control technology. The majority of chiller plants use technology based on independent control loops with PID feedback control. PID feedback loops are able to control a single device effectively, controlling a single variable such as pressure or temperature that is on a single control loop. Any process that has changing conditions would be too complex for PID control, however, and as part of a network communicating and controlling a number of varying devices, it does not have the flexibility to continuously adapt to varying loads that are encountered in HVAC applications. It is an analogue era technology trying to cope in a digital age. The resulting annual average system COP (between 3.2 and 2.2) is insufficient to meet today’s carbon reduction targets. These shortcomings in control strategy explain why so many chilled water systems are underperforming – even those that have been installed over the last few years incorporating sophisticated BMS and variable speed capability.


A fully-integrated chilled water plant package


A solution is to utilise digital relational control technology which is capable of treating the entire system ‘holistically’, rather than as individual sub-systems. This provides a number of benefits. Firstly it will sequence variable speed components such as pumps and chillers to operate at their “sweet point” – the position on their Natural Curve at which they are most efficient given the current building load. Secondly, these relational control methodologies have the ability to calculate and determine the best power relationship between the chiller, condenser pump and tower fan, balancing the load between devices to achieve the same net “tonnage” for a lower kW input. So instead of running devices at full speed, and sequencing them on or off to match varying demand, the system components are operated at their peak efficiency at all times, both individually and collectively. This achieves a COP of greater than 7.0 compared to previous averages of between 3.2 and 2.2.


New builds and retrofit When installing new chilled water systems, a solution is to specify, from the outset, an offsite manufactured, fully- integrated chilled water plant package which incorporates relational control technology. Alternatively a chilled water integrated plant control system, can be integrated into the design. Another option might be a retrofit relational control solution. Technology of this type is ideal for retrofit in buildings with chiller plant less than five years old, with greater than 3 million ton-hrs of operation per year (1,000 tons at 3,000 run hours per year). Each solution optimises the chilled water system automatically and continuously, bridging the gap between theoretical and actual energy savings.


Author information


Steve Cooper is Director of Sustainable Design at Armstrong Fluid Technology. With more than 1,000 employees worldwide, operating seven manufacturing facilities on three continents, Armstrong Fluid Technology is known around the world as a leader and innovator in design, engineering and manufacturing of integrated solutions within the building oriented fluid-flow equipment industry. Armstrong products are internationally recognised for design innovation, quality, long service life, and superior operating economy. In 2014 Armstrong Fluid Technology celebrated its 80th year in business and 10th year of operation in the UK. The company serves customers through a network of sales offices, supplying solutions and services to homes and businesses in more than 50 countries. In the UK, Armstrong Fluid Technology has manufacturing facilities in Manchester and Halesowen, West Midlands, and a sales office in London. For more information contact: Tel: 08444 145 145 Fax: 08444 145 146 Email: marketing@ armstrongfluidtechnology.com Website: www.armstrongfluidtechnology.com Address: Wolverton Street, Manchester M11 2ET


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