Mitsubishi Electric claims its new unit uses less refrigerant than traditional VRF systems and provides simultaneous heating and cooling in a simplified two-pipe design. RAC reports - simply regsiter to view
Mitsubishi believes its new Hybrid-VRF (HVRF) system is set to challenge traditional chillers, thanks to its ability to use water to replace refrigerant in occupied spaces.
The company claims the system, which provides simultaneous heating and cooling through a simplified two-pipe design, removes the need for leak detection equipment and allows more properties to take advantage of manageable phased installation through the system’s modular design.
At the heart of the new system is a hybrid branch controller (HBC) box, which is connected to the outdoor unit via traditional refrigerant piping.
Between the HBC and indoor fan coils, the system uses plastic or copper water piping but still offers high sensible cooling and stable room temperatures for maximum comfort.
“Many buildings have been traditionally cooled and heated through chiller technology and boilers, but with increasing legislation on energy efficiency and the rising cost of fuel, we now need a low-carbon, cost-effective alternative,” explains Mitsubishi Electric’s Mark Grayston. “We have developed this new approach to answer the need for energy efficiency and internal comfort.”
The company has produced detailed modelling that demonstrates a 49 per cent reduction in annual run costs compared with a traditional four-pipe system and a 43 per cent reduction in emissions.
According to the company, savings are even greater when heat recovery is taken into account, with a 60 per cent run cost saving and a reduction of CO2 emissions of 75 per cent. Design and installation costs are reduced by 24 per cent when comparing two 70 kW chiller units working with a 50 kW boiler, next to five 20 kW HVRF units, both systems providing 104 kW peak cooling and 63 kW peak heating loads.
Having no refrigerant in occupied spaces, while delivering simultaneous heating and cooling via quiet fan coils, means HVRF is particularly suited to applications such as hotels.
Current legislation restricts the use of refrigerants in buildings, with EN378 in particular intended to minimise possible hazards to persons, property and the environment from refrigerating systems and refrigerants.
As such, leak detection must be provided if, in the case of R410A, a concentration of 0.44 kg/m3 refrigerant could be exceeded if the entire refrigerant from a system were to leak into a single room.
Generally, this limits systems to about 20 kg of R410A for hotels, or forces the addition of leak detection systems. The only other option is to break larger systems down into smaller ones. Either way, an increase in cost and complexity cannot be avoided. Until now.
The outdoor unit behaves in much the same way as a two-pipe heat recovery VRF system with two refrigerant pipes connecting a the HBC. Instead of two refrigerant pipes sending refrigerant for cooling or heating to the indoor units, hot or cold water is sent instead.
Efficiency is further improved from the heat-recovery defrost, enabling short defrost times with immediate return to heating.
HVRF provides the function of a four-pipe fan coil system and the efficiency of VRF in one system. Load capacity control is achieved through the use of inverter driven pumps and flow control valves which are all built into the HBC. Phased installation also reduces building down-time and room sizes can be reduced while still providing a high end heating and cooling system.
Hybrid-VRF case study
Working Environments provided a range of mechanical and electrical services to amalgamate three south coast locations into one – at Monza House in Southampton. The aim was for a modern, comfortable environment for staff and customers and turn the interior of the building into a “Centre of Excellence”.
The company is a business solutions provider for Mitsubishi Electric, and when special projects director Mike Jenkins heard of Mitsubishi’s new air conditioning system, he wanted to be one of the first to check its capabilities.
The 15-week refurbishment work was split into several phases. First, an existing warehouse was redeveloped into a new office area, seating 58 engineering and surveying staff, eight meeting rooms, an IT training suite and a staff breakout area. A new plant room, print room and 80-seat auditorium were also created.
Next, the ground floor offices and corridors were modified to provide access to the new office area. These areas are served by a single air handling unit providing fresh air along with two traditional City Multi VRF systems with both ducted and ceiling cassettes.
The existing first floor offices were then modernised and this is where the HVRF system was installed, which allows Working Environments to compare the two systems.
“We have also installed monitoring equipment to allow us to see how well the system is working for us and the feedback from staff has been fantastic,” explains Working Environments’ special projects director Mike Jenkins. “Everyone has noticed how fresher and more balanced the internal temperatures have been and we’ve also noticed fewer drafts.”