We’ve seen an increased interest in Variable Refrigerant Flow (VRF) (aka Variable Refrigerant Volume or VRV) systems. Many view them as a panacea for a building’s HVAC needs. For building owners or managers with no prior experience with VRF/VRV units, we recommend considering the following tips for project success to avoid issues during the installation or operation of a VRF/VRV system.
Advantages of VRF/VRV Systems
Building owners and managers have various motivations to go with VRF/VRV units, some of which include:
- Space constraints on the roof or ground, limiting installation of large air handling units or packaged units
- Perceived lower first cost
- Simplicity of operation
- Perceived to be technologically advanced and new
- Energy efficiency
Tips for a Successfully VRF/VRVs Project
1. Size Accurately.
Be sure unit sizing meets the conditioning needs of your space.
VRF fan coil units (aka indoor units) cannot maintain setpoints if they lack the capacity to meet the loads of the space. If the fan coil units are intended to only provide incremental conditioning, they may only re-circulate air in the zone. Capacity might not be a major issue for spaces that don’t require ventilation. But for spaces that need ventilation, you will need a separate make-up air unit (MAU) with cooling and heating coils to temper outdoor air and supply it to the individual fan coil units.
For example, we worked on a medium sized office building in Mountain View that needed to do morning warm-up. The VRF units installed as a part of C&S did not have that capacity. The building had to install a MAU during TI. They currently use the MAU for morning warm-up and ventilation during occupancy.
2. Account for Additional Space and Costs.
Delivering fresh air requires additional ductwork and terminal boxes and possibly a building management system.
Outside air that is tempered by the MAU’s needs to be delivered to individual fan coil units in the zones. You need to account for space as well as cost associated with installing VAV boxes that deliver tempered air to the fan coil units. In addition, you may also need a BMS to operate the MAU and the terminal boxes in conjunction with the VRF/VRV units.
3. Consider Ventilation Needs.
If the zone that is being conditioned using a VRF/VRV unit needs to be ventilated – you need to provide access to operable windows or account for a MAU to tackle ASHRAE Standard 62.1 ventilation requirements.
Designing a space with operable windows isn’t always a viable option. In that case, you need to account for a MAU that will deliver tempered outdoor air to the fan coil units in the zone. Ensure your property has enough room to accommodate a MAU in addition to all the VRF/VRV condensing units.
4. Ensure Your BMS Can Communicate.
If you plan on integrating proprietary VRF/VRV unit with a BACnet enabled BMS, order your VRF/VRV unit with an adapter that will enable communication between the two. Without this adapter the building maintenance staff will have to manage two separate front ends to run the building HVAC system.
5. Plan for Frequent Maintenance.
Conducting regular maintenance checks will be a necessity (six month or one-year interval depending on your systems complexity).
Your building will have long lines of refrigerants running from the condensers to the fan coil units and vice versa. Locating and detecting refrigerant leaks is important and can be very difficult – as the refrigerant piping might run into inaccessible locations. If leaks occur in the indoor fan coil unit, it needs to be disassembled. Refrigerant leaks can cause asphyxiation if a leak occurs in a confined space, or with inadequate ventilation.
6. Be aware of refrigerant availability with HFC Phase out.
As discussed in a prior post, California and other states are regulating the phase out of hydrofluorocarbons (HFC) refrigerants which will impact the availability of refrigerants currently used by most VRF/VRV systems.
The California Air Resources Board has initiated a plan to prohibit any refrigerant with a Global Warming Potential (or GWP) higher than 750 starting in 2023. That would phase out the use of R-410a, the refrigerant used in most of today’s VRF systems. Although there are some refrigerants that fall under the GWP < 750 threshold, their use in VRF/VRV systems is not yet clear. So, you could have a new system full of an obsolete refrigerant if you’re not careful, and maintenance or conversion to a new refrigerant could get costly.
Planning for Successful VRF/VRV Installation
If you think a VRF unit is a good fit for your building, you should consider these tips early in the project (i.e., design phase) to avoid costly changes later. In addition, if you plan to apply for LEED credits, meet ASHRAE Standard 62.1 ventilation requirements by designing operable windows or by using a MAU, it is even more critical to address these concerns early on. If you would like to discuss your VRF/VRV project or other ways to make your building more energy efficient, contact us anytime.
This post was originally published on the kW Engineering blog.