Can you provide some basic information about variable refrigerant flow (VRF)? Is it an appropriate technology in the mild Pacific Northwest climate?
Variable Refrigerant Flow (VRF) heating and cooling systems were introduced in Japan over 20 years ago and now condition over 50% of Japanese medium-sized (less than 70,000 square foot) commercial buildings and about 35% of larger buildings. They quickly became popular in Asia, Australia and Europe, and were introduced in the U.S. in the early 2000s. Applications include offices, retail spaces, hotels, luxury apartments, light industrial buildings and data centers, including both new and existing buildings.
What is VRF?
VRF systems (also known as variable refrigerant volume, VRV) are heating, ventilating and air conditioning (HVAC) systems similar to ductless heat pumps used in residences and spot cooling in commercial buildings. VRF systems are typically larger, installed in commercial buildings, and include more indoor units per outdoor unit than ductless heat pumps, as illustrated in Table 1.
Table 1: General Comparisons
Ductless Heat pump
VRF heating or cooling
VRF with/simultaneous heating and cooling
|Maximum size (tons)
|Number of indoor zones per outdoor condensing unit
||Up to 50
||Up to 50
While the efficiencies of ductless heat pumps and VRF systems are similar, VRF systems with simultaneous heating and cooling will use less energy due to their ability to transfer heat among zones. VRF indoor air handlers are available in many styles to accommodate existing architecture. Compared to ducted systems that cool by airflow, VRF systems provide heating and cooling using refrigerant, thereby eliminating duct losses.
There are four components that are modulated to control temperatures and optimize energy use: the condenser fan, the indoor fan coil, the compressor, and the expansion valve. The controls for VRF are somewhat more complicated than ductless heat pumps but no more complicated than a chiller and boiler plant type system. Features vary from one manufacturer to another (ease of retrofit, first cost, etc), but energy savings claims are similar.
Factors to Consider for Simultaneous Heating and Cooling
Some VRF systems can provide simultaneous heating and cooling capability. These systems have better part-load efficiencies and potentially higher energy savings and incentives (compared to VRF systems without simultaneous heating and cooling).
Good applications include buildings in which different zones may require heating and cooling at the same time. For example, the VRF can transfer heat removed from an area requiring cooling (such as an interior data center) to another area that is in heating mode (such as an external office zone), rather than simply rejecting the heat from the warmer zone to the outside.
Some of the benefits of VRF systems are:
- Potential operating cost savings due to better part-load efficiencies and duct loss minimization, when compared to standard air-to-air heat pumps
- Smaller mechanical space requirements – both interior and exterior
- Design flexibility with the variety of indoor air handler options
- Easier retrofits where running ductwork is an issue, such as an older building currently lacking ductwork
- Greater rentable space due to smaller mechanical rooms and less space required between floors for ductwork
- Relatively lighter weight, minimizing structural requirements
- Potentially lower electrical retrofit costs; always check electrical requirements for the replacement system
Due to its mild climate, the Pacific Northwest benefits greatly from a technology that offers internal/external heat recovery. VRF offers this. For comparison, the Integrated Part Load Value (IPLV) for non-inverter driven technologies (for example, a 12-ton packaged heat pump) is 9.9, while the IPLV for VRF 18.6. In the mild Pacific Northwest climate, where HVAC systems often run at part load, IPLV is very relevant.
If the Pacific Northwest market reacts to this technology as markets in some other countries have, this could have a high market penetration. In countries where this technology has been present for a decade or more, it is installed in 50% of buildings up to 70,000 square feet and one-third of the commercial buildings more than 70,000 square feet according to the article “Variable Refrigerant Flow Systems,” American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Journal, April 2007.
Non Energy Benefits
- According to the manufacturers, VRF provides less temperature fluctuations due to the variable frequency drive (VFD) fan, inverter compressors, and throttling expansion valve.
- VRF takes up less space due to minimal, if any, space-consuming ductwork. This is a great feature for both new and renovation projects. This allows for more rentable space and reduces the cost of new construction.
- VRF is less noisy than water source heat pumps because the compressors are not located in the conditioned space.
- Often these systems are supplied with few or no ducts. Systems with fewer ducts tend to deliver better indoor air quality, since mold growth and dust accumulation often occurs in ducts.
- VRF is available in geothermal applications, providing for even higher efficiencies.
- VRF is lighter weight than variable air volume (VAV) systems, so structural concerns are less.
- Though these units are relatively new to the U.S., the expectation is that VRF has a long life relative to most other technologies due to the soft start of the inverter-driven compressors (as provided by historical data from ASHRAE).
- Maintenance is minimized with the self diagnostics available locally or remotely.
- The VRF system is an efficient technology for many buildings with multiple zones, such as offices, residential, mercantile and education occupancies.
- From the ASHRAE: Service Life and Maintenance Cost Database
you can see that this technology has among the highest expected lives of large HVAC systems (about 20 years).
- Hot water can be generated using a desuperheater connected to the VRF system, reducing the cost of hot water by about 50%.
There are some concerns about refrigerant safety, with so much refrigerant volume that could potentially spill into an occupied space. This concern needs to be addressed by the system design engineer, as it should be with any technology.
O & M Costs
Per a price quote from two design/build HVAC contractors in the Northwest, the following would be what they would charge on a project:
- Annual maintenance on the VAV system would be $9,000 per year.
- Annual maintenance on the VRF system would be $5,800 per year.
This is roughly a 36% saving in maintenance. The VRF maintenance would consist of cleaning the outdoor coils and replacing the indoor filters. Maintenance of other technologies would include chiller-boiler system, cooling tower maintenance, or big air handling unit (AHU) maintenance.
Initial pre-assessment information to make estimates of longevity and operations and maintenance costs can be obtained from the ASHRAE: Service Life and Maintenance Cost Database.