By Benjamin Brits
For some time now in the market there has been fierce discussion, reasoning, and rationale for each of these solutions, but which is the right choice for your application?
The “battle for supremacy” of these systems has in fact been ongoing for years accompanied with some strong opinions and statements that surface. I remember vividly that one of my first interactions in the HVAC&R industry was an article presented by an experienced engineer around making unsubstantiated comments around this very subject matter – and here we are more than two years down the line already.
VRF systems require small plantroom spaces and can easily be hidden behind facades, within service levels or on small platforms. Image credit: Chillers are more efficient at high-capacity loads such as what is required at a hospital with 24hr operation. Image credit: © RACA Journal | Benjamin Brits
It is quite clear from our dealings in the local market since then, that there is a definite preference for one solution over the other when considering different role players’ views, and the installations we get to visit. But, for the record, the same is true from examples all around the world – thus indicating that there is strong ongoing support for each respective solution. When you go and research the differences between these system-types further, you will find comments that go far beyond two years.
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Taking on these sorts of topics in reality involves some quite complex decisions that can’t always be covered to the fullest degree that they deserve, and by no means does this Journal advocate for, or intend to imply, that one technology is better than the other. This article aims to offer information based on research, industry engagement and a glimpse of future trends that may influence the way in which equipment is selected. The information also aims to offer an alternative perspective on factors that could impact such choices that may not be knowledge to all. To answer the simplest question, yes, both of these system-types are here to stay.
It has been suggested that one of the trickiest tasks for a facility owner, consultant, or contractor (whoever is ultimately responsible for the decision) is in selection of the best equipment for providing the best outcome. Now taking that a step further, the “best outcome” can also mean different things to different people. While some are only concerned about capital investment, others may prioritise operational aspects, and still others may demand reliability at all costs, or the latest technology and functionality. There are obviously several thought processes involved in choosing either of these systems as the correct one for your commercial or industrial HVAC system proposal.
Chillers are more efficient at high-capacity loads such as what is required at a hospital with 24hr operation. Image credit: © RACA Journal | Benjamin Brits
Suited applications for each solution
As with nearly all technology, including the HVAC&R industry, it’s about understanding the particular application – which is multi-layered in itself. Today certain industries, such as this one, also have to apply forethought around how choices or recommendations will play out in time related to trends, new design methodology, legislation and training requirements for an increasingly changing world.
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So, it’s not only about all of the regular tick boxes: base heat load, capacity, operating conditions and related factors etc – there are now energy demand issues and a growing responsibility from the client’s perspective around operational costs, sustainability and environmental ratings to name a few. What also needs to be factored nowadays are the need for maintenance and the availability of technical expertise. This is relevant locally where you may want to get in the absolute latest technology, but without the correct support structure the costs of service will escalate.
Many facilities today make use of both chillers and VRF systems to meet various demands (including air handling units and cooling towers). Image credit: © RACA Journal | Benjamin Brits
Both chiller and VRF systems may be suited well to several applications respectively while each will have their benefits based on what the system is required to achieve. Driven on the demand for each type, major manufacturers and suppliers have developed their line-ups to accommodate both systems for different applications and designs they will cater to.
When you consider a chiller, it is common that association is made for these systems towards industrial scale or process cooling, while VRF has been associated mostly with comfort conditions. This is not quite an accurate association anymore given the development of these systems that have also been used in hybrid techniques (making use of various technology/systems together). Again, depending on the scale of the application, these systems may very well be relevant to either – based on technology advancements, for example a VRF system could be the correct choice for a small-scale industrial cooling application that makes a limited amount of specialised stock units and operates two hours a day.
Some of the benefits to consider of each system-type in a quick view could include:
Chillers |
VRF |
| Suited for larger capacity projects and large common areas. | Beneficial for individual office temperature control. |
| Most industrial/process cooling uses this system type. | Various indoor units are available to suit the application – including hot water modules, fresh air units and air-air HR units. |
| Has the benefit of free-cooling options – particularly useful during seasonal temperature fluctuations. | Ease of power distribution and individual power consumption billing. |
| Benefit of ease of humidity control and incorporating humidification on existing AHU and FAUs. | No plant room required, and low ceiling void space required. Studies indicate a 300mm reduction in duct size and 30% space saving due to no vertical ducting required. |
| Plant rooms and central systems allow for maintenance without interrupting tenants. | Less general maintenance is required. |
| Chillers have a long life expectancy. Up to 30 years. | Air-conditioning to critical areas on back-up electrical power is easier to control and avoid increased costs and capacity on generators or solar power. |
| Individual components can be replaced easily. | Simultaneous heating and cooling is possible. |
| Tried and tested technology and well-known HVAC solution. | Benefits from new technology and control methodology. |
This table is by no means a full list of information and with each suggestion may come one, or many facts, to add relevance.
Site parameters
Some of the other considerations to take into account may be for example, looking at a project from the design concept stage and evaluating what you have to work with in terms of plant room space – is the building big enough to accommodate a centralised plant room and the associated equipment such as pumps and cooling towers, or, if pipe runs are easy or difficult, how will ducting affect the design, how long or high is the building, what sort of temperature control is required, how much of the building or facility contains common areas, and of those common areas, how large is the void, and so on.
The questions for a retrofit or replacement project may consider different points too that will determine the choices of equipment to be made. Here for instance changing of an entire system may be needed for other reasons than meets the eye – a structure may not be able to accommodate any additional load or electricity supply may be limited or capped.
Technical expertise
The available technical skills within a region may also be a factor when choosing the appropriate system, particularly when technology changes dramatically or there is a fundamental shift in sector labour demand and supply. This could be very relevant from a client’s perspective – as they will be the ones responsible for servicing and repairs. While a suitably certified plumber (that generally comes with a lesser rate) could perform certain system tasks on a chilled water system, other components or choices with VRF may require specialists (that come at higher rates).
Selection of each system type must therefore involve cognisance of different skill sets based on difficulty – pipework is far simpler than understanding a controller or the comprehension of error codes. The same applies for fault finding – the more complex a system becomes with pipe runs, no matter if chilled/hot water or refrigerant, the more time may need to be spent on site. Refrigerant leaks may prove to be more difficult to find while water leaks are easily visible. Here too the acknowledgement of various building and industry specific standards and legislation becomes important for technical teams. Standards require the limiting of refrigerant leaks into an occupied space and the use of detection alarms with VRF systems, however with chilled water loops this does not feature.
The same principle applies for servicing and repair (or replacement) of components, ease of access of the system and the amount of service points. This factor is extended the more pipes a system needs to include where pipe runs may reach kilometres in a single facility.
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Capacity and system operation
Designs need to take into account intermediate months where you have varying proportion temperature requirements (Eg 10% cooling, 40% heating). What becomes a challenge to negotiate in a system selection is when there is a requirement under these conditions to distribute full volumes throughout the system to have on-demand heating or cooling. If using a chiller system, in part load it may become energy-consuming with an example such as this to have the necessary availability in pipe loops, while a VRF system can supply hot or cold gas immediately as and when required. Essentially one would need to take into account what is happening with each system in “standby-mode”. For facilities that have high demands and operate long hours, the efficiency of each system type also features.
Capacity of either heating or cooling will also be a determining factor in system selection and if your proportion for cooling only or heating only is at 80% 24hours a day, it would be probable that a chiller would be more suitable. On the converse, if you have an office block or 20 different tenants that will demand different temperatures for only a few hours a day, it makes sense to rather select a VRF system.
Some chillers can use free cooling with seasonal conditions – such as during winter times when ambient temperatures are naturally lower. Image credit: AHI Carrier
Development of each system
Today both chillers and VRF systems incorporate inverter technology which is what has shaped these systems over time. However, when you consider larger capacity chillers and related components such as boilers, compressors with magnetic bearings, and so on, these sorts of developments are not feasible to adopt in VRF systems owing to scale. On the other hand, VRF systems with smaller capacity components are enabled to more easily develop and implement technological changes and therefore after being trialled and tested – the technology that can make chillers better can be transferred.
Currently, components-wise each system contains similar technology such as compressors that can step up and down as demand requires, but when you get to screw type chillers on the largest scale, there is not much of a comparison in technology. The same applies for centrifugal compressors and oil free compressors for chillers.
VRF systems are something which are better suited to applications where you have several smaller applications, many hotel rooms and the like where engineers need to accommodate many people with different demands, and which gives the occupant the ideal setting for their individual requirement. Chilled water systems are better suited to larger space cooling where individual control is not of critical importance to comfort.
Current status in SA between systems
For certain sectors of the market there is definitely big competition between selecting chillers and VRF systems. What has been noted is that based on historical factors of what works for companies that have been in the industry for much longer and have great knowledge of chillers, their function, and design – this is their preferred system no matter what the application is because it’s simple to replicate. Here there is also a great show of support for this type of system because of the known fact that a chilled water system also comes with a longer lifespan than a VRF system. This attraction to chiller solutions further involves the fact that even though chiller technology may change, they are easy to work on and replaceability of individual components is seamless compared to the technology involved in VRF systems where if a PC board fails an entire section of a facility may be offline or communication between components can be broken. VRF technology when it changes can also mean an outcome of replacement of an entire system while a chiller can be replaced totally from where it stands, and the system can continue (perhaps with a few modifications at most). Chillers can also operate on manual controls where this is not possible for VRF systems, and chillers can also utilise free cooling options.
Selection of a VRF system then for the other parties is preferred because it provides exceptional energy consumption values and offers the ability to bill clients individually. It incorporates the latest exceptional technology, installation is easy and doesn’t require any special additional electricity supply points. VRF systems also have the great benefit of being modular and can thus be added on as demand changes and central plant rooms are not required. Their footprint is far lower so saving space is a plus and then from a sensitive environmental aspect the use of a precious resource, water, is limited. VRF systems are also supported from suppliers with the benefit of “included calculations and drawings” making it a simple choice for clients to make use of. Selecting VRF systems is also known to just be easier from a holistic design point of view.
From an environmental perspective, both systems do have arguments for them related to resources and also refrigerants.
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Looking at building and global trends
From an ownership point of view, system selection has also seen influence of late depending on who has the buying power. Is this the building owner or the developer? If the owners of the building, a great deal of importance falls around how long they plan to own the building before offloading it, this may be a five-year period and therefore they will have concerns over investment returns but in the case of owning a building for its lifespan, operational costs are far more important. If a developer of properties, generally speaking what matters is the lowest capital costs irrespective. The commonly referred to statement here has become “whose problem is this system going to be?”.
Plant equipment is also in the transitioning phase as harmful refrigerants are being phased out and what this means is that one has to consider what is going to happen in the short, medium and long term. This is particularly important because when refrigerants change you do get those replacements with similar characteristics, but this is not always the case where one would have to replace all of the refrigerant piping, oils would be different, and operating pressures become a factor. The use of sub-cooling circuits will also be a factor where applicable.
Given the habitual nature of people and sticking to “what they know” it becomes easy to fall into the trap of not doing the necessary research around what new technology is out there and what has become important in terms of design methodology. Moving forward, it can’t continue to simply be around meeting a tight budget. Dynamics of the world have changed and with that the way in which systems need to operate too and how designers need to negotiate various scenarios and comply with regulations. This requires strong and supported views of sustainability, not only for the clients, but industry at large.
Globally, and in South Africa, trends for quite some time now have been moving away from the situation where 100 people each have their own offices to more of an open-plan setting. So, historically people were able to access and control their individual spaces as they required, but with the shift in operation, individual control is far less of a trend today. Coupled to that is the fact that many businesses are shifting to alternative arrangements for their employees through the amount of time people spend at the office versus out on the road or at home. This then means that other than boardrooms and a few key personnel offices that deal with sensitive work functions or documents (or they are the boss), that control has become less of a requirement for new facilities.
Offices of the future will be around having more general zones, a few meeting rooms and what is termed today as “hot desks” – a desk that you use as an employee, but the desk is not your permanent workstation (tomorrow that space may have a different owner). This trend has been the driving factor for some suppliers to have already developed solutions to cater to such needs. These factors all dramatically change the way a building’s HVAC system will need to work and be specified. The incorporation of more ventilation, filtration and efficiency has been growing ever since the onset of the pandemic and the end user, or building occupant, has become more aware of air quality and general health.
Chiller and VRF capacities
Chiller rated capacities generally range from 8kW to 10.5MW whereas a single VRF system may provide rated capacities from 11.2kW up to 336kW.
Local suppliers have much in terms of specifications, product details and ranges, and case studies demonstrating the working, benefits and best suited applications for each system that are available to industry.
Sources:
- AHI Carrier Toshiba
- Daikin
- Engineering Forum (international)
- General industry engagement
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