By Eamonn Ryan
VRF refers to a variable refrigerant flow air-conditioning system consisting of outdoor units connected with refrigerant piping to numerous indoor units.
A VRF system provides precise capacity control in order to meet each zone’s demand. The control of the correct refrigerant amount and refrigerant temperature ensure the system operates at the optimum capacity for user comfort and energy saving.
Beswent Bester, Toshiba specifying engineer & head of Technical at AHI Carriers explains how it works: “Each indoor unit has an array of thermistors for monitoring the refrigerant temperature and return air temperature. A modulating expansion device is also fitted to each indoor unit for modulating the flow and temperature of the refrigerant. The information accumulated from each indoor unit provides the outdoor unit with sufficient information in order to optimise the refrigerant flow and refrigerant temperature, satisfying the demand and efficiency requirements of the total building.
“Not only can the outdoor unit provide capacity control, but the indoor units can also control capacity by implementing variable evaporating or condensing temperature control, avoiding frequent on/off switching of the indoor units and maintaining a more precise space temperature.
“The outdoor units incorporate variable heat exchangers, such as a main HEX and sub HEX, which allows the outdoor unit to control the flow of refrigerant through the heat exchangers, to best match the local ambient condition and indoor demand. A VRF system relies heavily on the inverter technology incorporated in the equipment for compressor speed control, and fan motor speed control on both
the indoor units and outdoor units. Older VRF equipment incorporated a fixed speed compressor and an inverter compressor. However, more and more suppliers moved to all inverter compressors.”
There are two main types of VRF systems:
- Heat Pump systems, which are also referred to as two-pipe systems.
- Heat Recovery systems, which are also referred to as three-pipe systems.
Bester explains two VRF sub-categories:
- Mini VRF, which could be heat pump or heat recovery, and these systems normally cover a capacity range from 8kW to 35kW. These smaller capacities are generally used for light commercial and residential applications but are not limited to these applications.
- Air to water VRF is also an option and utilises a cooling tower and water flow for heat exchange on the outdoor unit. This type of system has a lower demand worldwide and not all suppliers can offer this option.
He describes the benefits as they apply to four different categories:
- The building owner
- End user/employees
- Installers/maintenance contractors
“From a building owner’s perspective there is an initial customer saving compared to a chiller plant, with architectural flexibility relating to the partitioning inside which can change at any stage and the air conditioning equipment can be adapted to it. It utilises space efficiently, with no construction or space requirements.
“There is a saving on operating cost, improved energy efficiency and ‘green’ certificate rating. Where there are multiple tenants they can each be individually billed and it permits remote operation and monitoring. The building owner can monitor the operation of the system and get email notifications of errors.
“For the operator, there are various control solutions which integrate with a BMS system enabling control of off-peak electricity usage, whereby the VRF can be cut back on usage during those times.
“For the occupants or users, there is individual control for each room or zone, operating for holiday and overtime work or temperature and humidity control according to occupants’ comfort and it is an easy control function.
“For the installer, on the maintenance side there’s less installation cost if you compare it to a chilled water design, equal compressor operation meaning that the running hours on the compressors can be equalised if you’ve got multiple compressors. It offers flexible piping installation, easier access for status check and option settings, less maintenance costs and easy maintenance, as well as precise detection of refrigerant leakage,” says Bester.
A majority of VRF systems in the market utilise refrigerant as the heat transfer medium which has better heat transfer properties compared to water. “Compared to chilled water systems, there are many pros and cons, depending on the application and site conditions, however I strongly agree that there is a market for both types of equipment.”
He lists the pros:
- Individual control for every indoor unit
- Individual electrical power consumption billing for tenants
- No equipment room required, and low ceiling heights are not a concern. Service shafts can be much smaller
- Easy maintenance and support from one supplier/contact point
- Maintenance costs are lower
- Low noise levels for indoor units and outdoor units
- Avoid up to 20% energy losses due to large ducting such as for AHU systems
- Smaller piping and ducting compared to chilled water systems with the same capacity
- Light weight and compact equipment. VRF installation is approximately 40% less expensive compared to a chilled water plant. These savings include rigging of chillers, cooling towers and AHU/FAUs
- Space saving is a major factor
- Heat recovery is easily achieved when utilising a heat recovery VRF system and the heat recovery is further enhanced with hot water modules for domestic water and air to air heat exchangers for fresh air treatment
- Backup operation available in the event of a compressor or inverter PCB failure
“In respect of inverter compressors, the scroll compressor has been the most popular for VRF equipment. However, some manufacturers use twin rotary compressors and Toshiba launched the world’s first triple rotary compressor incorporated in the latest heat pump VRF. In general, rotary compressors offer a better part load efficiency than scroll compressors and scroll compressors have a better full load efficiency. The scroll compressor has seen improvements in the last decade. The inverter technology allows compressor frequency changes of 0.1Hz to 1Hz, depending on the manufacturer, and this contributes to precise capacity control resulting in end-user comfort and increased energy efficiency. Minimum compressor frequency of 15Hz to a maximum frequency of 115Hz but this is manufacturing depended.
“Outdoor units with multiple compressors and inverter circuits can operate with only one compressor at minimum frequency which increases efficiency even further and allows for backup operation during a compressor mechanical failure or inverter PCB failure,” he suggests.
Retrofitting buildings with VRF: benefits and considerations
As the demand for energy-efficient and sustainable building solutions continues to rise, retrofitting buildings with Variable Refrigerant Flow (VRF) air-conditioning systems has become a popular option.
VRF systems provide an alternative to traditional chilled water and DX systems, with many benefits for building owners and occupants. Byron Taylor, sales engineer of Service First Group, distributor of Trane systems, spoke to RACA Journal about the benefits of VRF systems and the considerations that need to be taken into account when retrofitting buildings with them.
“In my opinion, there’s been something of a market shift from the traditional VRF systems of the past to a growing demand to convert or retrofit buildings from either a chilled water system or DX system to an air handling unit (AHU) hybrid VRF system. The primary reasons are, number one, the overall building efficiency can be improved with VRF; and number two, the payback period is usually shorter should you decide to go for a VRF hybrid system as opposed to a chilled water or DX system. Especially with a client looking for a Green Star rating, we are finding that the TVR Hybrids are typically a better solution for those clients. There are obviously exceptions where chilled water systems are essential.
“It’s not a quick fix, but a cost-effective way to upgrade your HVAC system where, perhaps, you may have old air handling units (AHUs) that still comply in good condition, that can be converted, refurbished and connected to a VRF condenser to create an AHU Hybrid system. That’s an attractive option because it reduces lead times and can be done in stages rather than shutting down the entire building. That means there’s no downtime in the building which is better for employees. On the efficiency side, if you get the correct control systems in place, the power consumption reduces dramatically.
“With multiple VRF Hybrid systems, you are able to provide heating and cooling to different areas of a building at the same time, with each area controlled individually. This helps reduce energy consumption as only the areas that require heating or cooling are targeted. VRF systems also have inverter technology, which allows them to adjust their output to match the required heating or cooling demand. This ensures that the system is not wasting energy by running at a constant high capacity when it is not needed,” says Taylor.
“The improved energy efficiency of VRF systems translates into cost savings for building owners. The lower energy consumption of VRF systems means that electricity bills are lower, which can lead to significant savings over the lifetime of the system. In addition, the payback period for a VRF system is generally shorter than for a traditional chilled water or DX system. This is due to the lower installation costs in some cases, as well as the lower ongoing maintenance costs associated with VRF systems,” he explains.
VRF systems are designed to be flexible, which makes them ideal for retrofitting into existing buildings. Taylor explains that the individual AHUs can be installed in various locations, such as the roof or plant room, and ducting can be installed throughout the building to provide heating and cooling to different areas. This means that the VRF system can be tailored to meet the specific needs of the building, without requiring major changes to the existing structure.
“VRF systems provide a comfortable environment for building occupants, as each area can be individually controlled. This means that temperature can be adjusted to suit the needs of the occupants, which can have a positive impact on their health and wellbeing. In addition, VRF systems operate quietly, which makes them ideal for use in areas where noise levels need to be kept to a minimum.”
When retrofitting a building with a VRF system, it is important to consider the system design, says Taylor. “The size and layout of the building will need to be taken into account, as well as the number of AHUs that will be required. The VRF system will also need to be designed to ensure that it is compatible with the existing electrical and mechanical systems in the building.
“The installation of a VRF system can be complex, and it is important to work with a qualified and experienced installer. The installation process may involve making changes to the existing structure, such as installing ducting or upgrading electrical systems. It is important to ensure that the installation is carried out safely and that all relevant regulations and standards are followed,” he says.
Like any air-conditioning system, VRF systems require ongoing maintenance to ensure that they continue to operate efficiently and effectively. It is important to schedule regular maintenance checks to identify and address any issues before they become major problems. This can help to extend the lifespan of the system and ensure that it continues to provide optimal heating and cooling to the building.
Trane is a Eurovent compliant system wherein R22 has been phased out. “Trane International is spending huge funds on research and development to find new, greener and better refrigerants which will in time be introduced here in South Africa. While in Europe they are introducing new refrigerants as we speak, locally it may take some years still to go completely ‘green’ with regard to gas refrigerants.”
In small applications, VRF may be more efficient as well as easier to install and to control. “Although the initial capex might be higher, the payback period is usually within three years to four years depending. On the other hand, if the building is located along the coastline, where it’s exposed to harsher elements, a water-cooled chiller might be a more logical choice for the greater longevity of the equipment. Each application has its unique needs and requires careful consideration before deciding on the type of cooling system to use,” says Byron.
“Moreover, we have found that there are some skills required to install VRF systems which are still lacking in the industry. Many contractors treat it like a straightforward DX application, compromising on commissioning integrity, which can result in compressor failures and callbacks. Therefore, upskilling installers and strict commissioning protocols are necessary to ensure proper installations.
“The HVAC industry is highly competitive, especially for small business owners, as they compete against household names like Samsung and LG. The industry is in many cases price-driven on the DX and VRF side, and having the right stock at the right time is crucial for success,” he says.
In conclusion, Byron summarises that VRF technology offers many benefits, including energy efficiency, flexibility and ease of control. However, it is essential to consider the specific needs of each application before deciding on the type of HVAC system to use. It is also crucial to upskill installers and have strict commissioning protocols to ensure proper installations.
VRF heat pump retrofits: A cost-effective solution for multi-use buildings
VRF systems are an excellent choice for retrofitting older buildings with outdated HVAC systems, particularly those with multi-use applications.
The modular design, individual temperature control, and energy efficiency of VRF systems make them an increasingly popular choice for projects around the world. However, as with any HVAC system, there are pros and cons to consider, depending on the specific needs of the building and its tenants.
One example of a VRF retrofit is a new hotel project in Johannesburg, where an existing six-story lawyer’s office building was converted into a 459-room hotel.
Barry Wallett, RPM Engineering Group managing director, explains that in a typical VRF system, a single outdoor unit is connected to multiple indoor units, which can be adjusted to provide cooling or heating as required. “The VRF heat pump system is particularly effective, where large seasonal temperature variations can be accommodated, particularly in Johannesburg South Africa, where summers can be very hot and winters very cold. However, the system has also been adapted to work effectively in smaller, multi-occupancy spaces, such as individual rooms, meeting rooms etc, where it allows individual occupants to adjust the temperature of their workspace to suit their own needs.”
The challenge in the hotel project was to install a VRF system that met all the necessary acoustic requirements and that would accommodate the various temperature preferences of the hotel’s guests, while meeting the necessary budgetary requirements. “VRF systems are a good choice for such projects because they are efficient, modular, and offer individual temperature control for each room or space.”
The hotel project involved the installation of 34 individual VRF systems, with one centralised controller governing the building’s heating and cooling mode. The building manager determined when the changeover from summer to winter would occur for each system, based on the specific temperature zone needed for guest comfort. The system has proven to be successful, with high energy efficiency and individualised temperature control for each room.
However, Wallett points out that while VRF systems are an effective solution for retrofitting multi-use buildings they are not always the practical choice for every situation. “For example, chilled water generators are still a popular choice for larger buildings that have a large cooling demand. VRF systems are often chosen for their cost-effectiveness, ease of installation, and energy efficiency. Moreover, the system’s modular design makes it easy to repurpose as necessary, depending on the building’s changing needs,” says Wallett.
Aside from the hotel project, there are several other notable VRF heat pump retrofit projects around the world. Wallett describes one such example as being the Asia New Bull project in China, where an existing 36 -story building was converted into a hotel. The project was challenging due to the densely populated space and the need to accommodate individual temperature preferences for each guest. However, the VRF heat pump system was able to meet these requirements while maintaining high energy efficiency and cost-effectiveness.
He notes that VRF systems are also being used for retrofitting existing package plants, where traditional systems have lower efficiency ratings. “By replacing the traditional condensers with VRF condensers, the package units can achieve efficiency ratings of up to 4 to 5 COP (coefficient of performance), compared to the traditional 2.5 to 3 COP. This energy efficiency comes at an up-front cost, of course, but the payback period is well within what financial experts consider to be suitable use of the system,” he says.
The VRF system is also being used increasingly in other applications, such as hospitals and manufacturing processes. By replacing traditional condenser fans with variable-speed fans, VRF technology can significantly increase the efficiency of these systems, resulting in energy savings and reduced running costs. This technology has been particularly effective in the packaging industry, where energy efficiency is a key concern.
Wallett adds that a reason for the popularity of VRF technology is its ability to be customised to suit specific building requirements. “For example, in multi-tenant buildings, the VRF system can be used to accurately measure individual energy consumption, allowing for more accurate billing. Additionally, the system can be used in conjunction with other technologies, such as solar panels or geothermal systems, to further increase energy efficiency and reduce costs.
“With continued development and innovation, it is likely that VRF technology will continue to play an increasingly important role in the design and construction of buildings in the future,” says Wallett.