HVAC basics: VRF and VAV systems

HVAC basics: VRF and VAV systems

Not all HVAC systems are created equal and each system is tailored to meet different needs. From simple air conditioning set-ups for home use to complex industrial cooling systems, HVAC technology is extremely diverse. In our current series on HVAC basics, we are yet to explain two very common systems: Variable Refrigerant Flow (VRF) and Variable Air Volume (VAV).

Most traditional HVAC systems, like those you’d find in a domestic space, employ Constant Air Volume (CAV). These systems don’t provide much flexibility for users that seek to achieve specific temperatures in different sections of their buildings, particularly large ones. VRF and VAV, on the other hand, provide more flexibility. Let’s look closer.

How do VRF and VAV systems work?

VRF systems are actually a fairly recent development in HVAC technology. VRF is efficient and effective for large-scale heating and cooling because they can be programmed to operate at specific temperatures during specific times of the day in different zones of a building. Unlike CAV, which is a constantly running system with limited temperature control, VRF is more efficient in terms of cost and energy usage.

VRF doesn’t rely on fans and water coolers but instead on liquid refrigerants as the principal medium to regulate temperature. A VRF system uses a series of adjustable motor units to regulate refrigerant flow across different building zones, which are then used to pump out cool or warm air. These motors can be set up across as many areas of a building as needed, making it easier to control the temperatures of the respective zones. Energy efficiency in VRF is key because by manually controlling air flow, motors can operate “as-needed”, rather than be constantly switched on. This is not possible when employing CAV systems, which are on constantly, thus wasting a great deal of energy.

Meanwhile, Variable Air Volume (VAV) systems work more like CAV systems in that they maintain a constant air flow but of a specific set temperature. This means that if you want to maintain a precise ambient temperature throughout a whole building like a shopping mall or an office block, VAV is the perfect solution. That’s not to say temperature can’t be adjusted in smaller areas; to achieve this air boxes can be fitted across rooms to modify airflow levels, effectively moderating temperature to fit their comfort needs.

Which one is right for me?

Every structure is unique and individual needs and building size all come into play when deciding on the perfect HVAC solution. VRF and VAV both have their uses, but the specific features and requirements of a structure and its users should be considered before deciding which one is right for you.

An experienced MEP consultant will be able to provide the guidance and support you need to equip you with your ideal HVAC system. By carefully considering how each system would work in conjunction with other building features (light, insulation, ventilation, etc.), an MEP engineer will be able to advise which system will be the most sustainable, affordable and effective.



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