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A major reason for pushing to implement the chilled / hot water hybdrid VRF system in the hotel area was because the technology has a significantly lower refrigerant requirement but also is a solution that is very environmentally-friendly . Secondly , you don ’ t want to run a refrigerant through any room where an occupant sleeps because if there is a leak in the pipe work , even a slow leak , it can be extremely dangerous .
Leaks are a reality in any AC system no matter what technology you choose . With the hybrid system the refrigerant runs outside of the rooms in the passageways between the hybrid box connector ( HBC ) controller and the outdoor units , all of the internal reticulation to the hideaway units in the rooms only contain water supplied via PEX piping which has no harmful aspects if a leak does occur .
Why this is important is because the EN378 standard : Refrigerating systems and heat pumps : safety and environmental requirements has now come to the fore and relates to the amount of allowed refrigerant within a confined occupied space . VRF system can carry up to 60kg of refrigerant , so they fall within this limit value immediately . If a leak occurs , you can land up with 60kg of refrigerant being dumped into a space . This would remove the oxygen because refrigerant is heavier , and the person in the room could suffocate and die .
EN378 further specifies that if the amount of refrigerant exceeds the limit-value , refrigerant sensors must be installed in the space . These sensors need to be calibrated , tested and further connected to the building management system ( BMS ) that will then in turn connect to a separate alarm system installed in every room , or facility . This naturally carries a lot more costs in the actual products required , but installation too .
The VRF solution comes with the BC controllers that are the ‘ unique piece of the system ’. Effectively how they work is that when one system is rejecting its by-product – for example a hot gas – the BC controller will capture that hot gas and then divert it to an evaporator that is looking for a heating function . Mitsubishi Electric took this design further realising the potential to make it water-based and went through years of development to get right . The only refrigerant in the system now is between the BC controller and the condenser . Everything between the BC controller and the evaporator , now commonly referred to as the fan coil , is either chilled water or hot water , importantly only using two pipes irrespective of the mode .
The BC controller can send chilled water at 5 ° C or hot water at 60 ° C , offering a wide range of operating conditions . The new hybrid technology has further eliminated two thirds of the refrigerant requirement in a VFR system , replacing this with water . The result is that the parameters and restrictions of EN375 can be bypassed ,
RACA Journal
1 . Various push fans are located in the basement to control smoke flow towards the inlets .
2 . One of the box connector controllers on the lower office levels . 3 . The fresh air inlet located in the mid-building plant room .
4 . The mid-building plant room was purpose fitted with air bricks to allow fresh air to the system feeding the various floors .
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RACA Journal I February 2021 www . hvacronline . co . za