What is a VRF system?

Variable Refrigerant Flow (VRF) systems are typically installed with an air conditioner inverter which adds a DC inverter to the compressor to support variable motor speed. By operating at varying speeds, VRF units work only at the needed rate allowing for substantial energy savings at part load conditions. Heat recovery VRF technology allows individual units to heat or cool as required, while the compressor load benefits from the internal heat recovery. 

The two main system types of VRF's are two pipe and three pipe systems. In two pipe VRF system all of the zones should be in cooling or heating. And in case of three pipe system with heat recovery, it is possible to heat certain zones while cooling others. While the VRF systems have greater initial cost, it allows for better zonal thermal control and overall greater efficiencies.

VRV / VRF HVAC connectivity diagram

VRF Performance

When considering the efficiency and effectiveness of an air-source VRF system, the coefficient of performance (COP) is typically the best metric – the higher the COP, the better the performance – and it's dependent on modulation level and outdoor temperature; the colder it is outside, the less efficient the system is at extracting heat from the air while operating at maximum capacity.

Heat pump VRF systems are famous for having some of the highest COPs in the market and have demonstrated radically-improved heating performance under low-temperature conditions (near or below 5°F), while continuing to offer highly efficient cooling at high temperatures. In order to address the myth that these systems do not work properly in colder climates, Northeast Efficiency Coop has created an ASHP product list with COP and other data about the performance of many heat pumps at lower temperatures. The lowest-performing system on the list has a COP of 1.75 at maximum capacity when the outdoor temp is 5°F. At warmer outside temperatures the heating COP can be as high as 4, however to ensure simulation results are conservative, a default of 1.75 is used on the platform.

DOAS and VRF system

Dedicated Outdoor Air Systems (DOAS) complement VRF systems to meet building comfort demands and provide complete, high-performance HVAC solutions.


Pairing both these systems provide:

• Simplified system design

• Increased efficiencies

Thus, each VRF system in cove.tool operates with DOAS.

VRF systems cove.tool supports

Cove.tool supports the following VRF systems:
a. DOAS with VRF

b. DOAS w/ VRF, with Electric Boiler and Cooling Tower
c. DOAS w/ VRF, with Gas Boiler and Cooling Tower

d. DOAS w/ VRF, with Ground Source

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