CHILLERS
At the time of writing there does not appear to be a non-flammable, low GWP refrigerant suitable for use in VRF/V air conditioning that can be used to replace outgoing R410A. There are no currently available HFO alternatives that are seen as suitable candidates. As a result, a question mark hangs over the future of VRF/V air conditioning, at least in the form in which we know it. In response, some manufacturers have
developed a so-called hybrid technology approach to VRF/V, which keeps most of the DX refrigerant section outside the building, while using a heat exchanger to transfer heating and cooling to a non-DX (typically chilled water) coolant circuit within the building.
This approach can reduce the refrigerant charge and overcome the risk of releasing refrigerant into the occupied space. However, a potential downside is loss of efficiency, as a result of adding an additional heat exchange stage to the process, and the additional pumping requirements of the secondary circuit.
The heat exchangers in these hybrid modules are also relatively small and may be prone to blockage, so water quality and treatment are paramount. There remain pipework length issues with these units, unlike with chilled or hot water,
and future flexibility is not as straightforward as with a hot and cold ‘ring main’.
The stakes for manufacturers are high. Huge effort and investment is being devoted to developing alternative solutions, based either on hitherto unknown low GWP refrigerants operating on current or adapted technology, or systems using existing refrigerants and novel approaches. The problems facing the VRF/V market open up opportunities for alternative technologies and approaches. Chiller-based systems have developed very significantly in recent years; by coupling modern chillers and heat pumps with high performance inverter-controlled pumps and motors, the energy efficiency of these systems has been transformed. With improved controls and excellent part-load performance, the best of today’s high efficiency chillers offer an attractive alternative solution.
One of the major forms of VRF/V applicable in the UK climate, the three-pipe heat recovery option is now being replicated with air-source hybrid heat pumps, using a so-called ‘polyvalent’ approach to deliver ‘free’ low temperature hot water or chilled water around buildings as the byproduct of cooling or heating elsewhere in the system.
Due to its efficiency and flexibility, which in many instances are a match for VRF/V, this approach also shows great promise for the future. As well as breathtaking reductions in energy consumption, the mainstream adoption of Turbocor-type oil-less compressor-based systems has added savings in ongoing servicing and maintenance costs, low power draw on start-up, low noise operation and reduced size and weight.
Additionally, and now that the technology has been adopted by so many manufacturers, the sharp price premium once attached to Turbocor- based systems has reduced – and the gap is closing.
Of course, no one should rule out the emergence of a new technology to replace conventional VRF/V given the deep pockets and engineering expertise of the companies involved. However, unless the uncertainty over VRF/V is resolved soon, the industry may need to turn to a lternative approaches.
Ironically, the demise of VRF/V may also mark a return to modern versions of conventional chiller and heat pump technology, which for so long has suffered in the face of VRF/V’s seeming inexorable advance.
Petra
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