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Feature
PIPE AND VALVE SELECTION FOR A COOLING SYSTEM
Complied by Eamonn Ryan
Each component of valves , pipes and controls throughout a cooling system is critical to the overall efficiency and effectiveness .
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When designing a cooling system , it is crucial to choose the right pipes and valves . It ’ s important to understand the options available and the possible outcomes associated with each selection . Many factors can impact the effectiveness , longevity and quality of the overall cooling system , and each of these factors should be examined when choosing the best pipes and valves for the application . In most cases , valves , piping and sensors are all key factors to a cooling system ’ s effectiveness and overall quality .
PRESSURE INDEPENDENT CONTROL VALVES Automated Control Solutions ( ACS ) supplies several brands of control and balancing valves . Today , ACS primarily distributes Danfoss , iSMA Controlli , Genebre and Honeywell valves and Actuators , particularly for chilled water application . ACS services HVAC system integrators and mechanical contractors with high end quality international products . Adrian Hofmann , technical sales and support at ACS , says : “ when it comes to the big tenders for large buildings and shopping malls , engineers like good quality valves and Danfoss and iSMA Controlli valves fit the bill nicely . There are two different sets of valves we do from Danfoss and iSMA Controlli : conventional two- and three-way control valves with manual balancing . This is the traditional way that people still use valves – up to about 150mm in two-way , and in three-way up to 300mm for chiller plant managing . We also do Danfoss ’ AB-QM 4.0 range , which is their Pressure Independent Control Valve ( PICV ) solution from 10mm up to 250mm , which are massive pressure independent control valves combined with automatic balancing valves . In particular , data centres like those valves because they require less commissioning and have far better control with up to 100 % valve authority . PICV are combo two-way control valves with built-in automatic balancing valves which also save space on the valve arrangement , as there is now only one valve installed instead of two – this makes for a very neat installation .” iSMA Controlli valves and actuators are an alternative to Danfoss , they have some highly specialised stainless-steel options with actuators suitable for outdoor installations with IP65 enclosures – unique products with competitive pricing .
Conventional valves have been around a long time and Hofmann explains that one can either have on-off control or
RACA Journal I January 2024 modulating control . “ Modulating control is not new and gives superior control of the water flow . You ' d have a controller like an ‘ iSMA AAC20 ’ on an AHU unit giving a 0-to-10-volt signal to the actuator , which would be open or closed or anywhere in between the whole time , depending on the demand through the building ,” says Hofman .
In the past , there were constant flow systems with threeway valves . There could be a set of pumps running full blast all day long regardless of the load , with the only thing changing being that the valve opens and closes , and water either goes through the coil or bypasses back to the chiller – a highly energyinefficient system . “ Now , with the design of the PICV , it ' s a control valve and an automatic balancing valve all in one piece . There is no running up and down for weeks balancing the system – the valves are pre-set on installation , and they will take care of the rest . There ' s no bypass at the coils , which means variable speed drives ( VSD ) can now control the pumps to maximum efficiency , in the morning and evening , when the load is low , the VSDs run slowly , and entire plant runs more energy efficiently . As a result , those PICVs have grown in popularity – even though they ' re more expensive than conventional valves , they provide a good return on investment on energy saving alone , never mind the savings on installation and commissioning ,” says Hofmann .
BALANCING THE SYSTEM He says the PICV is pre-set according to the flow requirement during installation , the valve taking care of the rest . The manual balancing valve can only be set once the water is pumping through the whole system at full load . Only at that point can the commissioning engineers start adjusting each valve , whether it be for fan coil units , AHUs , the branches or the risers – on big systems there are typically hundreds of these valves . What happens is , as one starts throttling these manual balancing valves to let the required amount of flow through , pressure starts increasing in the rest of the system , with the result the commissioning engineers must return to the previous valves to balance them again , this could take approximately two to three attempts ‘ per valve ’ to balance the system . “ PICVs always let just the required amount through the coil , regardless of changing system pressures , so the pump is running at the right speed , and the whole system is more efficient – for a
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