A variable refrigerant flow (VRF) system provides flexible installation and energy-saving cooling and heating comfort. These systems are widely considered as an alternative to traditional systems for applications where zoning or part load operation is considered necessary. Variable refrigerant flow is a system for heating and cooling spaces that is quickly gaining worldwide acceptance and popularity. Although VRF, which uses refrigerant for heating and cool spaces in either a subcooled liquid or superheated vapor state, was invented in Japan in 1982, it was only introduced to the US in the 2000s.
This "new" technology is spreading rapidly across several large markets and is now a viable heating and cooling option in nearly any application. Modern variable refrigerant flow (VRF) systems offer some major benefits, like zoning, individual temperature control, minimized ductwork, excluding the need for secondary fluids (chilled-water or hot-water distribution), and related costs. This all-electrical system consists of a single outdoor condensing unit, multiple indoor units serving various areas, branch selector refrigerant piping, and related controls.
What are variable refrigerant flow systems?
The VRF definition is a very simple, and literal, expansion of the tried and tested process of refrigeration. It should be clarified first by contrasting it to a conventional chiller system: instead of the evaporator being a heat exchanger where the refrigerant cools down water to be circulated through terminal units to cool a vacuum, the refrigerant flows through coils inside a "indoor unit" that blasts air from the conditioned room over the coils (which act as the evaporator), cooling the air and cooling the coils.
The refrigerant goes back to the "Outdoor Unit" to be pressurized by the compressor and to reject heat in the coils of the outdoor unit to the atmosphere (this takes the place of a condenser in a conventional system). This subcooled liquid refrigerant travels back to the coils to refresh the space further. The process is simply reversed when heating. The coils receive superheated, vaporized refrigerant, which is cooled by the air in the space served by the indoor unit, and then delivered to the outdoor unit for vaporization (by absorbing ambient heat from the atmosphere) and returned by the newly pressurized compressor system.
Types of variable refrigerant flow systems:
Heat pump systems
A heat pump is an electric system that extracts and transfers heat from one location to another. The heat pump is no new technology; it has been used for decades in Canada and around the world. Both refrigerators and air-conditioners are common examples of this technology.
Heat pumps transfer heat into a process of evaporation and condensation, by circulating a product called a refrigerant. The refrigerant is pumped between two heat exchanger coils by a compressor. The refrigerant is evaporated at low pressure in one coil, and it absorbs heat from its environment. On the way to the other coil, the refrigerant is then compressed, where it condenses at high pressure. At this point in the cycle, it releases the heat that it absorbed earlier.
Heat recovery systems
Heat recovery systems are whole-house ventilation systems that supply dry rooms with fresh air, and remove stagnant air from wet spaces. Two fans duct and move all air flows: one on the supply side and one on the extract side. It uses a heat exchanger to transfer heat from the fresh air to the warm exhaust.
Buildings are much more insulated and airtight nowadays, so it is important that an adequate ventilation system is in place. Installing a heat recovery unit is becoming more a necessity than a choice with the current building regulations. It is important that you have adequate supply of air from bathrooms and kitchens to all the rooms and extraction. Insufficient ventilation can result in growth of the mold, damage to the condensation and unhealthy living conditions.
3 reasons why variable refrigerant flow systems are a preferred choice among end users:
Cost effective installation
The installation of a VRF system may be a cost-effective alternative to conventional systems involving ductwork or large pipe sizes, and in the case of chilled water systems, pumps and boilers depending on application.
Outdoor units are light in weight with a small footprint. This means they will fit into a service elevator, so no crane is necessary to lift to a rooftop installation. In some situations, savings can be achieved on the total construction cost because the lightweight unit ensures that no additional support system is needed in the roof.
Control means comfort
The key to providing comfort is to provide heating or cooling without swings in room temperature, when and where it is required. The compressor is either on or off in conventional systems so even spaces that have individual controls experience fluctuations in room temperature as the compressor stops and then begins to maintain thermostat setting again.
In a VRF system, as the compressor speed will differ, the compressor does not turn on and off, but will run continuously for longer periods. The refrigerant flow required is supplied to the indoor fan coil and, once the set level is reached, the refrigerant flow is adjusted to keep the room temperature smooth without any fluctuations. The indoor unit fan speeds and louver locations can be adjusted in addition to providing distinct setpoints to provide additional comfort in space.
It uses a heat recovery system to heat residential or industrial complexes. It works by extracting most and stagnating air from wet rooms, recovering the heat that would otherwise be lost. Most of these systems are equipped with filters which filter out and replace toxic pollutants with fresh air. Heat recovery systems, HRV or MVHR, work through a ventilation machine that is usually installed in a building's attic, plant space, or elsewhere in the roof. These systems are equipped with filters which are used to filter out the extracted air from outside with the one coming in. A set of pipes run throughout your home, and for both filtered and incoming air, there are two separate lines of pipes.
These two never mix, and the separate airflows never have a chance of cross-contamination. The entire system is connected to air valves which move through a carefully designed network of ducts into each room. HRV protects you because it makes your house airtight, ensuring that no hot or cold air can ever escape because of factors such as poor insulation, poor windows, etc. This system extracts moist, stale air from all damp rooms and replaces it with new , clean, filtered, fresh, warm air without allowing any of it to escape. HRV devices will now completely ventilate almost 95 percent of the heat that would usually go to waste by fleeing into the atmosphere and then negatively impact it.
To sum up
Variable refrigerant flow (VRF) has increasingly become the top HVAC option in facilities since its first state-side implementation. What started out as an idealized and imported next-gen approach for HVAC is now finding a base. It really started out as a niche product, looking at buildings that didn’t have enough space or a lot of ductwork, but now we’re seeing that this can be applied to basically any building. When properly incorporated into a house, VRF can provide FMs with greater control and efficiency of HVAC.
There is no doubt that the VRF systems which are out today will be improved as the popularity of this system continues to increase and there is competition between manufacturers to produce the best product. Meanwhile, it's best to study the operating principles of what's currently out there in order to maximize the efficiency of these integrated systems through proper design, installation and commissioning.