Feature people still use valves – up to about 150mm in two-way , and in three-way up to 300mm for chiller plant managing . And we do Danfoss ’ AB-QM 4.0 range , which is their pressure independent control valve ( PICV ) 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 .
“ We also do some iSMA Controlli valves and actuators as an alternative to Danfoss , they have some very specialised stainlesssteel options with actuators suitable for outdoor installations with IP65 enclosures ,” says Hofmann .
Conventional valves have been around a long time , and Hofmann explains that one can either have on-off control or modulating control . “ Modulating control has been around for ages on AHUs . You ' d have a controller 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 .”
In the past , there were constant flow systems with three-way 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 very energy inefficient 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 preset , 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 expensive , they provide a good return on investment on energy saving alone , never mind the savings on installation and commissioning ,” says Hofmann .
The PICV is pre-set according to the flow requirement during installation , and 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 being typically hundreds of these valves . What happens is , as one starts throttling these valves to let the required amount of flow through , pressure starts increasing on the rest of the line with the result the engineers must return to the previous valves to throttle them and back to the first valve of all . This is because the pressure has increased in the system and they need to balance that valve again . This has to be repeated around three times to get a properly balanced 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
ACS © Eamonn Ryan | RACA Journal
A DN150 Danfoss AB-QM PICV valve and Danfoss NovoCon BACnet actuator also installed at a data centre in Johannesburg on a bypass line .
WIKA Marketing Manager : Greg Rusznyak and Lloyd Townsend , product manager at WIKA .
www . refrigerationandaircon . co . za RACA Journal I April 2023 29