Typical use of VRF applications in commercial buildings
Hong Cheng of LG Electronics says that Variable Refrigerant Flow (VRF) is an energy-efficient HVAC system with sophisticated controls and sensors integrated together. It can effectively control the indoor temperature to create micro-climate zones to suit each individual according to each occupant’s specific needs, in different zones of a building.
The drive to combat global warming, reduce carbon emissions and achieve net zero by 2050 sees the benefits of VRF systems in high-performance modern buildings in greater demand as they offer a more sustainable built environment, which has become more and more pronounced. Compared with traditional HVAC systems, VRF systems are a renewable and more environmentally friendly energy solution that can greatly reduce carbon emissions from commercial buildings. They also have characteristics of low operational noise, compact size, advanced comfort control, design flexibility, as well as high energy efficiency. As one of the best low carbon heating options available in the current market, together with these superior advantages, the VRF market in the UK construction industry will inevitably continue to grow in decades to come.
Depending on the energy source, a VRF unit can be classified as an air source or water source system. While the former takes energy from the outside air, the latter extracts energy from a large body of water.
The large water source could be a pond, lake, river, stream, seawater, or even underground water such as in old mine workings. These systems can also utilise energy sources that would otherwise be wasted, such as industrial cooling towers, and computer/server rooms, and turn otherwise wasted energy into useful energy to heat buildings. The energy absorbed by the outdoor unit is transferred to the indoor space for heating or cooling in buildings.
In comparison, air source VRF systems are far more commonly used in the UK construction industry, but water source VRF generally has higher efficiency than air source systems as heat transfers better in water. The water sourced outdoor unit is typically installed indoors and requires a large water source for operation. While the air sourced outdoor unit is installed outside.
Furthermore, the water source VRF system does not need to defrost operation and generally has low operational noise as there are no fans in the ODU. Unlike the air sourced unit where the outdoor air temperature is influenced by external weather conditions and can vary significantly throughout the year, the temperature of the water source is not affected by external conditions as much.
VRF comes in two formats
Regardless of the energy source type, VRF comes in two formats: a two-pipe heat pump and a three-pipe heat recovery system.
With a heat pump system, all indoor units connected to the system operate in the same mode, either cooling or heating but not both at the same time. A schematic diagram of a typical heat pump VRF system is shown in Figure 1.
With a heat recovery system, the indoor units can heat in certain areas whilst simultaneously cooling in others. The energy recovered from the indoor units operating in cooling mode, can be transferred to other units operating in heating mode, and vice versa. This setup requires a heat recovery box, which is an internally piped, intermediate refrigerant control device, between the outdoor and indoor units.
In comparison, the heat recovery system has more potential for energy saving during operation. A schematic diagram of a typical heat recovery VRF system is shown in Figure 2.
Typically a VRF system consists of at least one outdoor unit with multiple indoor units, a network of refrigerant piping, system controls, a communication network, and heat recovery boxes where applicable. The inverter compressor of the VRF system is able to adjust the refrigerant rate in the system and deliver what is required by each indoor unit.
VRF systems are based on the refrigerant flow between the outdoor unit and multiple indoor units. The refrigerant flow to each indoor unit can be controlled and adjusted depending on the specific thermal needs in different building zones.
In conjunction with different indoor units, the energy taken by outdoor units from either an external air source or water source can be used to provide the following indoor solutions:
• Space conditioning i.e. heating or cooling via a regular air conditioning indoor unit, it can also work with underfloor heating or radiators via a hydro kit.
• In conjunction with a hydro kit, VRF can produce Domestic Hot Water (DHW) for building occupants.
There is a wide range of different types of indoor units for the design consultant to select for projects.
For different design styles, regular VRF indoor units (i.e. refrigerant based) have Ceiling Mounted Cassettes, Ceiling Concealed Ducted units, Floor Standing Units, Ceiling & Floor Convertible Units, Ceiling Suspended Units, or wall Mounted Units. However, the most commonly used IDUs in UK’s commercial buildings are cassettes and ducted units.
Using a hydro kit as an indoor unit, VRF can also provide hot water that may be used for underfloor heating systems radiators or for domestic water supply.
In special applications, VRF systems can also be used to serve the DX coils of a Recovery Ventilator (ERV-DX) or Air Handling Unit (AHU) to heat or cool incoming outdoor air for building ventilation.
Figure 1 and 2 have illustrated some of the indoor units.
In addition, having recognised the importance of indoor air quality to the health and well-being of the building occupants, a number of air purification measures, such as fine dust filter, UV germicidal irradiation, dust electrification plus PM1.0 filter, deodorisation filter and so on, have been developed as accessories such as the air purification kit for LG’s dual vane 4-way cassette and UVnano Filter Box for ducted units, or built into the indoor unit such as the Micro Dust Filtering system for LG’s wall mounted unit. This enables airborne pollutants to be removed while indoor air is being conditioned.
A Building Management System (BMS) is a computer-based control system that is often used for facility management to control and monitor the mechanical and electrical services installed in commercial buildings. This includes services such as HVAC, lighting, fire detection, lifts, security systems and the like. BMS is most commonly found in large construction projects with extensive building services.
BMS uses data communication protocols to integrate the different elements of building services into the building’s automatic control network. However, the building management systems available in the current market support different types of protocols. The main ones that are most commonly used in the construction industry are BACnet, Modbus and LonWorks.
VRF systems often come with centralised controllers to monitor and control the outdoor and indoor units in the systems. Some of them, have built-in BACnet and Modbus connections and can interface with BMS that supports these protocols directly. Some of them may need gateways to be able to connect to BMS. In general, there are options for the design consultants to choose from to effectively control the VRF systems.
Of course, there are wired or wireless remote controllers for the user to control the indoor units.
Heat pumps, one of the very best low carbon options, require a small amount of electricity to run, but are typically 4 times more energy efficient than the conventional fossil fuel heating systems they replace. If the small power supply required comes from renewable sources, such as solar PV panels, the system itself will become totally carbon neutral.
To decarbonise the construction sector, heat pump technology will play a vital role to help to achieve the UK’s target of net zero by 2050. When future-proofing new buildings for efficiency, resiliency, sustainability and a superior comfort experience, VRF systems will logically become the obvious choices for future HVAC systems. Its market to replace conventional fossil fuel heating systems in existing buildings is expected to grow hugely in the foreseeable future.
