By Benjamin Brits
Variable refrigerant flow (VRF) has been around for a long time, as with most HVAC technology, and continues to evolve.
Today’s technology in this category needs to address so many elements in meeting client demands and so all manufacturers continually invest significant amounts of money in research and development to bring to market their latest ideas in addressing those various needs.
The VRF concept, pioneered by Daikin in the 80s (patented as VRV), initiated the simultaneous ability of cooling and heating functions – whereas in the past either one or the other mode could be delivered at a time to individual indoor units. Each brand today is referenced by a particular model name while their branch controllers would follow a similar convention and are the ‘junctions’ where heat recovery control takes place and essentially enables dual mode function. All the brands currently work on a three-pipe system, with the exception of Mitsubishi, who uses their exclusive patented two-pipe system.
“In simple terms, VRF systems, through the use of MCU (Mode Change Units), allow users on a single circuit to individually change between heating and cooling mode. The system is able to adjust the speed of the inverter compressor to meet the required capacity need of the system,” says Tinus du Plessis, project engineer at Fourways Air South Africa.
System performance, energy efficiency, reliability and capacity will be the words you read on any supplier’s marketing sheets as these elements are the talking points around the world. For the most part, we see a significant mindset shift in end users’ awareness of environmental impacts. These factors also open more doors to participate in the now highly competitive business environment.
This, for example, can be linked to a commercial office space where significant savings can be achieved through reduced HVAC operating costs, addressing limited plant room space offering more ‘lettable area’, a retrofitted building’s structural capacity not needing to be reviewed, meeting an aesthetic requirement, or overall lifespan-operational-costs.
So, from monitoring and control technology, to new smaller chassis, to increased horsepower and the latest compressor capacities, each of the brands available in South Africa, have their own benefits and sometimes niche sectors that they are able to be best utilised in.
VRF function today enables an assortment of flexible solutions that can incorporate all indoor units – wall units, ducted units, cassette units, fan-coil units, and standing units. Systems can also be linked into air handlers, and packaged units. Further, any mix of units is also possible.
“Every generation of VRF that is released will be improved by addressing limitations of the previous versions, but also specific to what markets require. This is achieved as new technology and methods evolve and can be anything from the improvement of the communication and control system to the incorporation of region-specific safety measures.
“An example of this is that South Africa is notorious for erratic power supply and load shedding, and so electronic components within our VRF range have been developed to address protection to minimising damage to units without any additional costs to the client. Another example is if an indoor unit is faulty, to limit the number of units that this affects – you obviously want to avoid a whole office sitting without their ACs working, or critical areas for that matter. Gree has implemented technology called CAN Communications Technology – where if an indoor or outdoor problem occurs, the technology automatically isolates the affected unit while the rest of the VRF system continues to operate without the building experiencing any interruptions. When it comes to heat recovery boxes, Gree has a range of 1 port, 2 ports, 4 ports and 8 ports. Our 4 port is driven by 2 PC boards, each driving two indoor units; while our 8-port box is driven by 4 PC boards, each driving 2 indoor units. Such a design ensures minimal disruption to users within a building. We have also introduced a dual solar/grid VRF system – essentially meaning that you can run a system on whatever portion of solar PV energy you chose supplemented by grid power or on 100% solar power,” says Sibusiso Ndelu, Business Development Manager at Gree South Africa.
The pipelines on VRF systems are also astronomical elements. If you look at the total piping on a project, although there are limitations per system, they can reach kilometres. Suppliers today are also working on improving this capacity per system. Also being improved is the vertical differential between outdoor and indoor units.
“Toshiba has just released their latest SMMS-u VRF system to the local market (featured in this issue) that has been recognised for a number of its features, most notably the improvements of the chassis design which is smaller but has increased capacity to 24HP through the implementation of a three-sided condenser design, and improved twin and world-first triple rotary compressor technology that further enables a diverse range of outputs and is customisable to exactly what clients need. Rotary compressors are known to provide better efficiency for part load operation. This is of particular value in today’s environment where many unique applications and the sensible heat load of buildings have also changed with the improvement and energy efficiency of other electronics and electrical appliances such as lighting.
“We have also increased the compressor capacity to 120cc allowing longer pipe runs (1200m) and increased vertical height differentials between indoor and outdoor units (110m). We are also able to now offer the lowest capacity of 0.3 horsepower (0.84 kilowatts) with this new system catering to smaller offices or meeting rooms. Also on the list of highlights is our intelligent control system that allows for variable operation and load distribution between indoor units thus increasing efficiency and user comfortability,” says Beswent Bester, specifying engineer at AHI Carrier Toshiba SA.
Communication technology for some VRF brands has improved so that if something does go wrong, the fault can be isolated, and the system can continue to run. This is applicable to both indoor and outdoor units, as well as condenser banks that are typically installed with a master/slave configuration.
“Even if anything happens to your master condenser’s compressor in your set, this will be isolated, and your system will still continue to operate with an instantaneous switchover to the slave. Because an under capacity now occurs, an alert via SMS or email can be set up to notify the facility manager or technician that something is wrong. So, communication and control has seen defined improvement in IoT and AI methodology for new VRF models such as our sixth-generation unit called GMV6. VRF has reached the point where the biggest improvements are now in electronic technology. One particular challenge for installations in this system type is at the commissioning stage when addressing the units or allocating an address to each unit is done. This can be executed in a manual way, however Gree has developed advanced technology to achieve this electronically with the intention of saving time where many units are installed in a building. We are able to simply plug in a laptop into any of the connected units and run the self-addressing programme to fulfil this function. All of the data is then saved in the cloud,” Ndelu adds.
Marco Ferdinandi, marketing director at Mitsubishi Electric Airconditioning SA expresses a different view on unit addressing, “Yes, one of the challenges in a VRF system is the addressing. In our view though, the manual addressing function is the better option. All the components have a relationship with each other and communicate needs or status via this address. (Physical addressing is the process of going to each unit and setting the address via a group of dip switches). Although there is the functionality to do this electronically, the SA power supply as mentioned by Sibusiso being what it is, shuts down at various times and at varying frequencies. What does occur with electronic devices is that they often go out of sync so to speak, and when power is restored, the units start up and the process to get all these units to identify themselves again must be completed. We all know about ‘technology gremlins’ that change things in the system because of timing delays, and so can lead to the system not receiving the correct data by for example the swopping of units. This cannot happen with manual addressing and is the reason it is a preference for us.”
Another consideration that makes VRF attractive is that no high-capacity dedicated power supply is required, which can be extremely costly in a project. The technology can be installed using electricity supply that is already part of a building, while consumption is determined by variable load. It is also unlikely that all units will operate simultaneously.
“The number of indoor units that can be linked to a single system depends on supplier to supplier, but generally speaking most manufacturers can connect 64 indoor units on one system. You could control eight systems from one controller and linking systems you can connect up to 256 indoor units in a building and taking that further to an internet-based system program, you can link up to 4 096 indoor units across different buildings. Samsung also incorporates wind-free technology that is unique by maintaining room temperature once the set point has been reached and does not start and switch off like other units. You can imagine with the number of possible units in a building the power savings this can achieve,” adds du Plessis.
Older systems can also be retrofitted by adding VRF components to them without the need to remove the whole old system. This is particularly useful for example in air handlers where a coil unit can be installed within the AHU and connected as a specific unit to the VRF system. Secondary coils can also be fitted to older systems that cannot function on generator power when there is a power outage due to electrical capacity needs of the older system, while VRF requires significantly lower power and could keep the HVAC system operational in those conditions – this application could include older hospitals or clinics.
VRF has also become a popular choice because of the fact that legislation has limited the amount of refrigerant allowed per system. This is particularly relevant to occupied spaces so commercial building like hotels can be fitted with several individual systems that serve certain areas or floors to meet the requirement. The limitation you do have, however, is that in cases of a lot of indoor units, you have the equivalent requirement for leak detection, and in very large installations this sometimes becomes impractical from a feasibility aspect.
“The push to implement our two-pipe system has been a unique offering for Mitsubishi Electric Airconditioners. All other suppliers implement a varied configuration around a three-pipe system to achieve the heating or cooling required. Our further incorporating of water through our hybrid chilled water VRF solution is a great step. We have been able to take all the best elements of chilled water and VRF technology and combine these into one system and we believe this has changed the VRF landscape. While water is known to be an excellent absorber of heat, the further advantage of this technology is that it reduces the amount of copper pipe work by using Pex PVC piping between the BC controller and the indoors, reducing potential copper theft. Leaks are also easy to find and a major benefit is the limiting and elimination of sensors that are now required through the EN 378 standard for occupied spaces,” adds Ferdinandi.
The EN378 standard: Refrigerating systems and heat pumps: safety and environmental requirements relates to the amount of allowed refrigerant within a confined occupied space. VRF systems, carrying significant amounts of refrigerant, fall within the limit values of the standard.
EN378 further specifies that if the amount of refrigerant exceeds the limit-value, refrigerant sensors must be installed in the space as indicated. 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, not only in the actual products required, but installation cost too.
“Something to note, specifically if we take a look at energy efficiencies and new technology, is that we have a lot of solutions in the market, but the problem is everybody is ‘pushing for maximum energy efficiency. But at the end of the day, there is always the cost factor that clients are not willing to pay for. Yes, energy efficiency will be included in proposals but at the final stages will get dropped due to costs. Energy efficiency is important, but the local market does not seem to have the required appetite, which is actually essential these days,” says Bester.
Douglas Scott, mechanical engineer at HCM Contractors says, “The pro points in VRF are definitely that it’s great for applications with varying loads, especially systems with full fresh air. Manufacturers, as has already been mentioned, spend a lot of money on R&D and by using their VRF systems, you gain access to this technology.”
According to a statement from Daikin South Africa: “Daikin follows an application-based strategy and from an environmental point of view we always look mainly towards the Total Equivalent Warming Impact (TEWI), which covers both the potential CO₂ emissions in case of leaks and the guaranteed CO₂ emissions from electricity consumption. It is furthermore not just GWP that dictates the impact of a refrigerant on the environment as each refrigerant has different characteristics and charge (amount of kilograms needed to reach a certain capacity), efficiency, cost of components, technical requirements and complexity of handling can be totally different. Therefore, we have assessed various refrigerants (R32, blends, natural refrigerants and HFOs) based on four criteria (overall environmental impact, energy efficiency, safety and cost-effectiveness), and have utilised many of these refrigerants in selected applications. After examining the key properties, Daikin has concluded that R32 is today, for a large part of the direct expansion type cooling and heating equipment – including single package products, the best option.”
Installation and maintenance
“You always have to consider what the cost of maintenance is, and the cheapest solutions are never the right choice and educating the end users in this regard is so important. The consultant and installation team may offer a 12- or 18-month warranty, but after that when maintenance is in the hands of the owner and things go wrong, they need availability of support from suppliers and not to have to replace their entire HVAC system. One thing all suppliers need to consider is that once a warranty period is over, it doesn’t matter who was involved in the process – the only thing the end user will see is the name of the brand on the unit in their office not working,” says Ndelu.
Manufacturers spend a lot of time during development with installation and maintenance in mind. The easier the installation the quicker it is, and the less parts involved in a system means fewer replacement components too. Time means money – and the less time required on site means profitability for the contractor, as well as savings for the client. A simple example is the ability to reduce the amount of electronics that are typically the costly elements. If something does go wrong for the client, it makes sense that replacement of one component rather than two is more cost-effective.
VRF, as a flexible solution, can meet any realistic budget and because of its modular nature, is easy to roll out in portions which allows for installing particular sections at pre-planned times. This is a useful benefit, especially in today’s time where owners are squeezed, by allowing them to build according to their finances.
That being said, VRF systems can be complicated and are in fact delicate systems that require contractors that have had sufficient training, as every supplier will tell you. Each VRF system will have many pipe runs and this can get extremely confusing. Obviously, systems won’t work correctly if pipes are connected incorrectly and a further complication is that these problems would typically only be discovered at the commissioning stage.
Scott notes some of the cons in VRF systems that should be taken under consideration in his view,” Technician’s must be properly trained to install and diagnose VRF systems and thus training needs to be manufacturer-specific. In theory, the level of technician that works on these system-types should be at a higher level, but the reality is, your average property owner can’t tell the difference between a capable technician and an incapable one. Skill availability is particularly worse in remote or outlying areas. Technology has also advanced so rapidly in recent times, we find our VRF systems may soon contain obsolete technology. Most of the major players have good support, but it’s a concern that spares may not be available when you need them in future. Further, as large amounts of electronics are used, they can be susceptible to power spikes as has been mentioned, while this is true for all electrical equipment.”
All suppliers have the strategy of regular site visits in support of the installation teams to ensure the system is installed correctly. Not all suppliers perform the actual commissioning themselves and leave it up to their contractor base. The installation in VRF systems requires many Ref-Net joins and if these joins are not levelled correctly they will create ‘dead legs’ in the system and cause functionality issues which is one element we have seen a number of times in the installation process. The ease of the installation really all comes down to the technical expertise of the technicians and can also be perceived as a negative for this solution because we have unfortunately seen some terrible work out in the field, and this damages the overall reputation of VRF as a solution,” notes Ferdinandi.
VRF systems also demand flushing with nitrogen during installation welding, and taking short cuts in this particular function were noted by several companies that can cause system failures and must be avoided. “We have seen that this step was left out on only the last two welds of the last pipe run of an installation, but resulted in one of the control boxes needing to be replaced – therefore stressing the need to follow best practices,” says Ndelu.
“With regards to the installation training for our VRF technology, we don’t schedule training sessions for numerous contractors, we do contract-specific training at their premises. The reason for this is we have noticed that this method offers a better outcome because sometimes you will find technicians won’t participate with other companies being involved (for various reasons) thus not giving them the answers they need to suitably understand installation requirements. Naturally, this is more time consuming at the end of the day because we do the same training over and over for numerous contractors, but the results prove beneficial for our approach. We have also included near field communication (NFC) on all our outdoor units. This allows the technician to connect to these units with an Android phone, giving access to all the operating data on the system that can be analysed for performance and troubleshooting. Reports can be shared directly with our technical team via email and so we can also see exactly what the system is currently doing while the contractors are on site to provide further guidance,” adds Bester.
Looking to the future
As technology transitions to more environmentally friendly refrigerants, the shift is going to require significant training initiatives, and in South Africa this will be a particular challenge to regulate as many of the lower GWP refrigerants are mildly flammable and thus perceived hazardous. The reality is that we don’t have the same enforced regulatory or environmental compliance like for example the US or Europe, while even these leading economies have shown that training for new low GWP refrigerants is lacking.
“The future will definitely include technology-driven aspects. Today we already have apps and digital means to monitor, diagnose and control systems and this can be done on your smart phone. Further, the future really depends on refrigerant demand factors which is an interesting situation for equipment manufacturers. Every time a new refrigerant is released, in terms of a manufacturing perspective, you have to adjust your whole production processes because not all refrigerants have the same properties. This naturally causes price implications that need to be considered,” says Ndelu.
The transition to R32 refrigerant is where each supplier is going to end up either way. Mostly they already have these systems available but haven’t introduced them as yet to the local market for a number of reasons, one being resistance. This is the same scenario when R410a was introduced many years ago and everyone dug their heels in. The same resistance can be expected because right now R32 is more expensive and runs at higher pressures, and so it’s getting considered in the same way. Overseas, R32 systems are already being installed as the norm and factories are ready for the shift.
“One of the biggest plus points where I think the Korean companies like Samsung will be strong, is their digital and control technology. They are continuously developing and changing these aspects to make everything more effortless. The controllers already include great features and have moved to a touch screen function which allows the user to navigate it as easily as they would their own Samsung cell phone. Samsung’s strategy is to keep things simple and easy to use,” notes du Plessis.
“VRF is so flexible and efficient, and these systems are getting more and more intelligent. In fact, they are getting to a point now where, as Tinus has mentioned, wireless communication is coming in and all you will have to do in future is provide power to the units. IoT is a big reality for the world and with all the available technology we may expect to see incorporation of a different level via all the smart devices we possess. Our phones, watches and cars already have intelligence, and it would not be unreasonable to think that all these technologies can be linked, so, when you are feeling too hot or too cold, for example, your watch will identify this from your body temperature and automatically communicate this to the AC system to adjust the temperature when you walk into your office. We already have extremely intelligent scientists that are doing amazing things, and this is where Mitsubishi is pushing in the right direction,” says Ferdinandi.
“In our opinion, we are all trying to cut down on the amount of refrigerant moving through a building, but the time will come where this aspect will become very strict to mandatory in South Africa, so depending on the type of refrigerant used (in terms of GWP and OD), the companies like Toshiba that are focusing on different technology to solve this will be a step ahead. We have already started cutting back on the amount of refrigerant and have removed the liquid receiver in our outdoor units to be able to operate our systems with less refrigerant. Safety aspects will also become more regulated going forward and the requirements for leak detection systems and system shut-offs we believe will become critical,” adds Bester.
“Change is indeed inevitable and Daikin kickstarted the transition by pioneering the introduction of R32 into South Africa. We see this as a vital part of being a sustainable manufacturer/brand. We expect going forward that we will continue taking the lead on this. We cannot comment on other suppliers on how soon they will make the shift or what has made them decide to wait. We can only comment that based on what we see happening in other markets that alternatives are available for most brands offered in South Africa, and we believe this is a missed opportunity for the South African market which we obviously regret. Daikin will continue to challenge itself in the technical development of new technologies that will support the global goal of CO₂ emission reductions,” concludes Daikin.
Content sources and opinions:
AHI Carrier Toshiba
Mitsubishi Electric Airconditioning