In the July 2021 issue of Climate Control Middle East, empanelled columnist, Dan Mizesko, in his article, ‘Don’t believe the hype about VRF systems’, asserted that chilled water systems are more efficient than VRF (variable refrigerant flow) systems, adding that the data proves the claim. (The article is available at www.climatecontrolme.com.) Here, two manufacturers of VRF systems and an MEP contractor present their side of the argument…
Consulting Sales Director,
Daikin Middle East and Africa:
Dan Mizesko’s article was, indeed, an interesting one, but I would like to clear the air on behalf of all VRF/VRV industry professionals. At Daikin, we take pride in having introduced VRV systems, in 1982, and are equally happy to chronicle the addition of numerous innovations that have ensured high performance characteristics. If you have not read Dan’s article, here is an executive summary:
- The author believes that only a chilled water system can provide better efficiency – no matter what type of project it is applied to.
- He contends that R410A entering the system could pose the threat of asphyxiation but also accepts that ASHRAE Standard 15 can be used to check if this could be a problem.
- The author points out that the global warming potential (GWP) for R410A (VRV) is 2,088, whereas the GWP for R134A (chiller) is 1,430.
- The author points to other issues, such as a dedicated fresh-air-handling unit (FAHU), long piping and joints, a fan-coil unit (FCU) in each room, long drain piping, quick heat-up of fresh air and the maximum allowable refrigerant concentration. He further says that in case of a leak, the new refrigerant needs to be replaced in full.
- Later in the article, the author accepts that VRV systems are suitable for small buildings but questions the pipe length, temperature and maximum load, which can decrease the efficiency of VRV systems.
- He says that the cost of a chilled water system is lower than that of a VRV system. He says that actual efficiency claims of VRV systems are difficult to verify in the absence of data and that a variable-pump chilled water system is better.
Further to Dan’s words, I would like to offer my perspective on VRV systems vis-à-vis chilled water systems… Chilled water systems are right up there in terms of technological prowess, but there are certain factors that dictate their performance:
- For example, chilled water systems are deemed to be practical for a minimum capacity of 100 TR, and only on availability of a stand-by chiller. VRV systems, on the other hand, constitute multiple modules of 6-20 HP, which make up the total building load; such an arrangement provides great flexibility for designers and end-users.
- A chilled water system requires a dedicated fixed plant room space for the chiller and pump room. And did you know that a space f 1,500-1,800mm is recommended between two chillers? VRV systems, on the other hand, can be accommodated in a flexible space around the building, freeing up usable floor space.
- Diversity of load is a hallmark with chilled water systems. It is equally a noteworthy feature in the case of VRF systems, which can boast of a combination of 50-130%.
- In the case of a large community – comprising groups of buildings that may come up in different phases or, once ready, may have different loads – providing a central chilled water plant will require an underground piping network to be installed as infrastructure, along with a continuously working pumping system and a heat exchanger at each building, with a lower supply water temperature of 4.5 degrees C, which makes the cost of a chilled water system higher for tenants, in addition to the grave threat of Low Delta T Syndrome. By the way, laying the piping network is an additional cost. In sharp contrast, a VRV system can be installed without having to meet the requirement of costly underground piping or continuous pumping circuit. In the case of VRV, it is just one system for each building or zone, which translates to providing flexible and practical solutions.
- A Direct Expansion system like VRV, in which the cooling effect takes place directly in the fan-coil unit (FCU), is able to respond quickly to small load changes. Indeed, the compressor can unload faster, which results in superior part-load efficiency. In the case of a chiller, it takes 30-60 minutes for it to load 100%.
- Many chillers are made with a 10-year-old legacy design of twin-screw compressors with little technological advancement. Over and above that, the manufacturers cannot provide on-site compressor service; indeed, the equipment has to be shipped for factory-only repairs, due to close tolerances. That said, some manufacturers of single-screw compressor chillers can provide on-site service without expensive and delayed factory repairs. VRV systems feature asymmetric scroll with inverter technology. They come with one or more compressors per module, which makes them more reliable and easier to maintain.
- A chilled water system is designed by expert consultants, who put together the chillers, pumps, hydronic design and controls. The assembly is on-site by contractors, and the commissioning is by third-party experts following all the applicable codes. At the end of the day, though, a properly designed chilled water system has the same sophistication of a VRV system; only, it is more expensive than a VRV system. A properly designed chilled water system makes sense in the case of large projects, but in smalland medium-sized projects, which outnumber large projects, the design is not of the same standard, which results in poorer performance. This is evident from the large number of experts in the market who work purely to increase the efficiency of existing buildings.
- A chilled water system with the newest technology requires collaboration among various experts specialising in chillers, pumps, valves, water treatment and controls, to name a few. And if there is a problem in the system, the owner needs to identify the particular equipment at fault, which is a formidable task. In the case of a VRV system, there is only one expert that the owner needs to reach out to – the manufacturer.
- Water-cooled chillers offer better efficiency, but so do water-cooled VRV systems. Case-in point, the 4,000 TR water-cooled system at a hotel in Qatar (G+40 building); the owner opted for a water-cooled VRV system in place of a chilled water system.
- All air systems, comprising AHU and VAV, do not represent a practical solution for every application, and that’s the reason we have a large number of chilled water FCUs. VRV systems can work with AHUs as well as with FCUs. In fact, the sheer variety of VRV FCUs is common knowledge; and they boast highly practical features, such as auto ESP and auto-filter cleaning, amongst others.
As for claims relating to energy efficiency, data is available in abundance – I am happy to point to the many buildings with Daikin Cloud, providing live and continuous energy-usage data on dashboards.
The design of VRV systems requires considering actual piping, which is easy with VRVCAD; and the software provides actual capacity, along with easy pipe sizing. A typical VRV system features refnet connections for easy installation, and thermostat and central controls, as well.
As for concentration of refrigerant, ASHRAE Standard 15, ASHRAE Standard 34 and EN375 provide the direction, with which it is possible to very well manage any building without the need of an extensive leak-detection system.
In summary, VRV systems represent a great option for providing energy-efficient solutions, when we have situations like:
- Small zone loads 1.5-15 kW each
- Individual control
- Different type of FCU requirements
- Phased start-up requirements
- Separate billing
- Centralised system for
Managing Director, Lexzander:
I read with interest Dan Mizesko’s article, ‘Don’t believe the hype about VRF systems’, in the July 2021 issue of Climate Control Middle East. While the article is informative, its contents are questionable, as certain observations are inaccurate or exaggerated.
I feel Dan needs to take a second look and give each of the systems – chilled water (CHW) and VRF – its due before drawing what I can only characterise as arbitrary conclusions. To start with, the efficiency of a system goes beyond how each key element – that is, product and process – is designed.
The engineering, installation, commissioning and, most importantly, the maintenance have a huge role to play in arriving at the system’s flexibility and operational efficiency; and the related costs – capital and operational – have a say in the long run. We cannot overlook the flexibility the VRF system gives to the end-user; more on that, later.
Let me touch base on some of the points that Dan raised that need a second look:
a) Dedicated ventilation system: While I concur with Dan’s analogy on the popular refrigerant in use for VRFs, R-410A, his observation that thousands of feet of running with this refrigerant could be a health hazard, is totally inaccurate and incorrect. Much like a CHW system, a very small percentage of VRF piping runs in occupied areas. It is mainly limited to air wells or shafts. Of course, this will vary from one application to the next, but still, the piping in occupied areas is limited in most cases. Also, whatever could be the leaks, due to various reasons, gets diluted in the air. So the need for a dedicated ventilation system does not arise.
b) Long refrigerant lines and large number of branch connections, resulting in chances of refrigerant leakage: Any system is as good as it is installed. So leakage – or the absence of it – depends on the workmanship. For some applications, a dedicated VRF system is preferable to a CHW system. So the application decides the system, rather than otherwise
c) The need for condensate drain lines for each VRF indoor unit: CHW fan-coil units (FCUs) also need condensate drain lines, so I don’t see what the issue is.
d) Compliance with maximum allowable refrigerant quantities within a given volume: In relative terms, it does not matter, as both are closed systems. e) Effect on capacity from choice of piping length: For particular applications, this is a non-issue, as proper sizing of piping will minimise capacity losses.
f) Capital, installation, operational and maintenance costs: From a capital cost/TR perspective, a VRF system is any time cheaper than a CHW system. And installation-wise, a VRF system is less complicated than a CHW system, given that there are fewer number of systems involved, which means lesser demand for expertise.
From an operational costs perspective, the costs associated with VRF systems are compatible with, or lesser than, CHW systems. Also, the operational costs of CHW systems are heavily dependent on design, installation and, most importantly, the expertise to commission and maintain the plant. And as for maintenance costs, a VRF system wins hands down.
The application decides the type of system – that is, VRF or CHW – and its effectiveness. In my view, Dan misses the point by generalising and, most importantly, leaning more towards CHW system without considering the application it is meant for.
Sales Director (UAE, Oman, Qatar), Qingdao Hisense HVAC Equipment Company Middle East and North Africa (MENA):
Exactly, there is much hype about VRF systems – that they can be used for all applications. That is what I felt after reading Dan Mizesko’s in-depth analysis. Indeed, VRF systems are not suitable for high-rise developments above 14 floors, mega shopping malls and five-star hotels. However, there are some applications where I see an obvious migration from chilled water systems to VRFs.
These applications include – but are not limited to – low- and mid-rise residential buildings up to 15 floors, standalone supermarkets, schools, villas and three-star hotels. I can say this with a great measure of confidence, for I have witnessed the migration through working closely in the air conditioning industry and in the Middle East region for the past two decades.
In 2002, when I first landed in Dubai, chiller systems were the common features in residential buildings and schools; the market share for VRF systems was negligible. In fact, many stakeholders were unaware of the benefits of VRF systems at that point in time. That was the era when they were experiencing some pain with chiller systems over high electrical consumption costs, higher AMCs and expensive spare parts.
Let me clarify here that a higher electrical bill was not purely owing to inefficiency of the chiller system; more so, it was from the thought pattern that since chiller electrical consumption is already included in the rent or has a fixed service charge – advertised as free AC – the end-user was overusing it, leading to wastage of energy.
Instances abounded of tenants going on vacation and smugly leaving the fan-coil units running for weeks and even months, knowing very well they did not have to face the consequences of having to pay for the electricity used to keep them running 24×7. And sadly enough, the building owners took the hit for this. Later, BTU meters came to the rescue, but it is an entirely different story that very few buildings with standalone chillers use BTU meters, as the building owner is averse to taking on the additional headache of having to bill and recover the consumption fee from the tenants.
Another reason for high electrical consumption from running chiller systems is that since the chiller is connected to the building owner’s DB, it will always fall in the topmost slab of electrical tariff – 44 fils per kW – whereas the standalone air conditioner in every apartment, which is connected to the apartment’s DB, will mostly fall in the first or second slab. So, the tenant has to pay almost double the tariff for the same kW consumption, if opting for a chiller. I have experienced the above issues during numerous discussions with various small- and medium-size developers.
In such circumstances, VRFs came to the rescue as a pain killer. Indeed, the circumstances triggered a favourable consideration of VRF systems and led to a sharp increase in uptake in the coming years. Other driving factors emerged, as the market plunged into an in-depth scrutiny and realised the advantage of opting for VRF systems.
My statement about an increase in uptake is not my hypothesis; rather, it is backed by the increase in sales figures – and as the saying goes, “Figures don’t lie.” In 2002, the share of VRF systems out of the total DX commercial air conditioner market was almost zero per cent; by 2020, it had increased to almost 60%, with a year-on-year growth of 10-15%. Now, the question arises – whose market is VRF eating into? The answer is obvious – it is taking large chunks out of the air-cooled chiller market, owing to the aforementioned reasons and owing to the following factors…
Lower capex and opex: With numerous VRF players available in the market, the price of VRF equipment has become highly competitive. The total capex – the sum of the cost of equipment, installation and piping – of VRF systems is 15-20% lower than that of chilled water systems, even after considering the additional electrical cost of power cabling to multiple VRF outdoor units. The AMC cost of VRF systems is lower than that of chilled water systems, as the cost of spare parts of chilled water systems is higher and involves co-ordination with multiple vendors. Indeed, the cost of chilled water systems includes chillers, pumps, valve kit and chemical dosing, to name a few.
Lower connected electrical load: A VRF system offers lower connected electrical load (1.2 kW/TR) against 1.6-1.7 kW/TR, including pumps, in a chilled water system. Even with deration, owing to long piping, the connected load of a VRF system does not exceed 1.4 kW/TR for an outdoor unit, which still is lower than that of a chilled water system. This 20-25% increase in the connected load leads to increase in the connection fee for the developer. With an average connection fee of AED 1,500/kW, you are talking of a substantially high cost for the building owner. Indeed, in the case of a building with 1,000 TR of air conditioning, this extra cost would translate to anywhere between AED 300,000 and AED 450,000.
Faster procurement and installation… lower chances of human error: A VRF system has fewer number of components, namely indoor and outdoor units, Y branches, remote controller, copper piping, insulation and refrigerant charge. In the case of a chilled water system, you have to contend with chillers, primary and secondary pumps, valve kits, pressurisation tank, chemical dosing system, two-way valves with actuators, BMS controls, MS piping and insulation.
The greater number of components means a longer procurement time, co-ordination with multiple vendors, and perfect functioning of multiple components to get the optimal performance. Indeed, the proper selection of chillers, pumps, controls and two-way valves coming from multiple vendors is key for the designed performance.
There is a higher chance of design errors, unless there is a proper system of tight verification by consultants and contractors in place. Indeed, the complexity places a weightier burden on consultants to evaluate the submittal of multiple components in a chilled water system. In the case of VRF systems, the challenge is less formidable, as the responsibility of proper design rests with the VRF vendor. Also, the design is software-driven, which means lower chances of human error.
Also, the contractor is in a position to save time involved in techno-commercial negotiations, considering the fact that they have fewer components (2-3) to contend with, compared to 8-10 components in chilled water systems. Redundancy: VRF systems offer higher redundancy through multiple compressors in each module, and multiple modules in each system. Also, the capacity of each compressor is a maximum of 10 TR, which means the cooling impact is only 10 TR, in case of failure of one compressor.
However, in the case of chillers, the impacted area will be bigger – often about 100 TR. This threat necessitates a standby chiller and pump, especially for critical applications, which in turn, drives the cost up and increases the requirement for space. Better control options: VRF systems offer diverse cost-effective control options, like central controllers, IoT interfaces, home automation interface and APP-based cloud controls. In the case of chilled water systems, the cost of implementation of controls is expensive.
VRF systems offer benefit to all stakeholders, be they developers, consultants, contractors or FM companies; little wonder that I have seen many building owners changing from chilled water systems to VRF systems for their upcoming buildings, as a reaction to learning from the experience of working on earlier projects that involved chilled water systems; I have hardly seen the reverse migration phenomenon happening.
There are some issues of concern surrounding VRF systems, as well, but hey, nothing is perfect in this world! That said, addressing the concerns relating to ASHRAE 34 (Addendum L) regarding the “Refrigerant concentration level” can be taken care during the design stage by avoiding connection of the smaller room Indoor to the bigger outdoor unit.
The impact can also be reduced by providing a door undercut in the smaller room and having an adjacent ventilated room, like a toilet. VRF systems have been in operations for 15 years in the GCC region and, through that, have validated the afore-mentioned benefits during one complete lifecycle. I rest my case!