Technical
An asymmetric plate heat exchanger design will reduce internal volume on the refrigerant side and the amount of refrigerant in the system , without an adverse impact on waterside pressure . As a side benefit , this will result in improved heat transfer performance .
• Considering the system architecture Traditional flooded evaporators require a large pool of refrigerant to work . In falling film evaporators however , refrigerant is sprayed on the tube bundle and only a small portion of the tubes are submerged in refrigerant , resulting in significant charge reductions .
In direct expansion ( DX ) systems , the refrigerant flows inside the tubes using flow boiling and condensation processes . DX systems will typically have less refrigerant charge than flooded systems but will also be less efficient .
New DX heat exchanger technologies , such as micro plate heat exchangers , work with a very small temperature difference , and offer a similar performance to flooded and falling film systems . In some applications though , it isn ’ t feasible to have a packaged solution . The evaporator and condenser sections can only be connected by long refrigerant lines and require a significant charge .
Alternatively , a water-cooled condenser and a brine loop can be used to carry the heat from the condenser to a remote cooler , which eliminates long refrigerant pipes and will significantly reduce system charge .
• Taking advantage of newer compressor technology A system design engineer has few tools to meet everincreasing efficiency requirements . One method could be to use a larger heat exchanger with a smaller temperature difference . However , while this is a reliable way to increase system efficiency , it uses more refrigerant .
High efficiency compressors can improve efficiency not just in full-load situations or applications , but also in part-loads . This is particularly true for variable speed compressors , and those which use an intermediate discharge valve to prevent over compression in part-load conditions . Using an oil-free centrifugal compressor with variable speed functionality can significantly increase compressor efficiency .
By taking advantage of newer compressor technologies , it ’ s possible to meet efficiency requirements without increasing charge .
• Deploying smart control systems Taking better control of system conditions can give an immediate refrigerant saving . Using an electronic expansion valve ( EEV ) to replace a thermal expansion valve ( TXV ) results in better control of superheat and more effective use of heat exchangers , especially in partload conditions .
For example , using variable speed fan control to control head pressure , instead of a mechanical valve to flood a heat exchanger , may mean that the size of the receiver can be eliminated or , at least , reduced .
And a variable speed drive for the condenser fan motor means it can adapt to any condition and power consumption can be decreased . This is a far better way to increase part-load efficiency rather than using larger heat exchangers that use more refrigerant .
• Match the solution to your specific requirements Clearly , there is no one right answer covering all applications . But as refrigerant prices continue to play an important role in system design decisions , and as safety continues to be an increasing concern for those using flammable refrigerants , it ’ s likely that engineers will use a combination of methods to improve cost , efficiency , and competitiveness . RACA
Energy efficient cooling and humidification
For more than 60 years , Munters has continued to innovate in the climate control technologies . Our cooling products are based on a low energy solution harnessing nature ’ s own way to cool and humidify . No chemicals are used in this modern method of adiabatic cooling . The systems just needs water and air . It ’ s as simple as that .
• Data centre cooling / humidification
• Industrial applications ; automotive , electronics , plastic industries , etc .
• Human comfort
Welcome to contact us and we will tell you more about our sustainable solutions for humidification and cooling .
Munters ( Pty ) Ltd info @ munters . co . za / www . munters . co . za
www . hvacronline . co . za RACA Journal I June 2022 65