There’s no doubt that heating or cooling a building can take up a large chunk of your fuel bills, and put a dent in your green credentials. In the European Union for example, around 50% of a building’s energy consumption goes on heating and air conditioning. Finding an energy efficient heating, ventilating and air conditioning (HVAC) system that can deliver on all your thermal comfort requirements, while keeping running costs down, may seem like a pipe dream. But fear not, systems do exist and at the top of the list sits Variable Refrigerant Flow (VRF). Eurovent Certita Certification (ECC) explains all you need to know…
When it comes to HVAC energy use, Variable Refrigerant Flow systems are one of the most efficient solutions available. Depending on the system installed, VRF can be used for cooling only, or cooling and heating, and crucially can offer different temperatures in different rooms or zones. VRF systems distribute refrigerant directly to individual indoor units (fan coils etc), in a ‘common’ refrigeration piping system, rather than using large ductwork, or a chilled water loop.
VRF systems use variable motor speed to produce variable refrigerant flow (hence the name). The compressor calculates what is needed to meet the indoor temperature required, and will produce an output that circulates the minimum amount of refrigerant needed to cool or heat room(s).
VRF typically comes in two-pipe heat pump systems that allow either heating or cooling, or three-pipe heat recovery systems, which can provide heating and cooling to different areas simultaneously. As they are ductless, VRF systems do not provide ventilation. There will be at least one condensing unit, which can either be air-cooled or water-cooled. Some ranges of VRF systems will allow a single VRF condenser to connect to up to 64 indoor units.
Traditional HVAC units operate as an on / off system. It’s all or nothing when it comes to the energy used to drive the compressor. The compressor is the heart of the system and uses the highest amount of energy of all the components. VRF systems adapt refrigerant flow depending on end user demand, so it only ever uses the exact amount of energy required. As temperature demands change throughout the day, so does the workload of the compressor. This clever way of modulating compressor output to meet demand, means there is no waste, and so it delivers higher energy and fuel savings compared to other systems.
There are two main types of VRF systems, heat pump VRF or heat recovery VRF. Heat pump systems are very efficient in their own right. However, heat recovery VRF systems can reuse waste heat. Instead of releasing unwanted heat to the atmosphere, it is sent to other areas of the building that require heating. This saves even more energy and reduces waste further.
Eurovent Certita Certification certify a number of VRF systems. The three types of systems certified under the Eurovent Certified Performance VRF programme are:
These types of units gain their name from the fact they use air to release heat to the outside atmosphere via a condenser coil. Air-cooled VRF condenser units are predominantly installed outside, and use ambient air. They require a large surface area to exchange heat, meaning that a single commercial VRF outdoor unit can be around the size of a large fridge freezer, while residential systems can be half the size. A bank is composed of multiple commercial VRF outdoor units and can occupy a large part of a roof, on a skyscraper per example.
Water-cooled VRF units use water to release heat to the outside atmosphere and will require a separate cooling tower or dry cooler. The units are usually installed indoors and are much smaller than their air-cooled counterparts.
High ambient VRF systems are designed for use in:
It’s often stated that VRF systems can offer efficiencies a third higher than conventional systems. There have been a number of studies over the years, with an Evaluation of energy savings potential of variable refrigerant flow (VRF) from variable air volume (VAV) in the U.S. climate locations, finding that heat pump VRF models had around 14%–39% annual HVAC site energy savings potential, over rooftop variable air volume systems (RTU-VAV) in 16 US climate locations. Results of simulations also showed that the VRF systems would save around 15–42% and 18–33% for HVAC site and source energy uses compared to the RTU-VAV systems.
When it comes to your energy bills that is a substantial saving. While VRF may have more up-front installation costs compared to some HVAC systems, the whole life cycle costs are considerably lower. VRF can offer a much quicker return on investment compared to other HVAC systems.
When it comes to certification, the energy performance of VRF systems is measured by SEER (seasonal energy efficiency ratio for cooling mode) or ηsc, and SCOP (seasonal coefficient of performance for heating mode) or ηsh. The higher this performance, the more efficient the VRF will be. Some of the aspects we test for include:
Performance at standard conditions
Seasonal performance in cold mode
Seasonal performance in hot mode
The best way to choose an energy efficient VRF system is to compare products objectively to make an informed decision.
View and compare the energy efficiency of certified VRF products in our certified product directory. The easy to use search facility lets you view products by family, type, brand, model name and certificate number.