VRF

Overview

A Variable refrigerant flow, or VRF system, is an HVAC system where refrigerant is the only coolant material. VRF uses refrigerant as the cooling and heating catalyst. This refrigerant is conditioned by one or more outdoor units and is circulated within the building to indoor units.

Types of VRF systems

There are three basic types of VRF systems:

• vrf-coolingOnly-system: Cooling only VRF systems can only cool; heating is not available
• vrf-heatPump-system: Heat pump VRF system can reverse the direction of the refrigerant flow to provide heating or cooling to the indoor space. All indoor units connected to a heat pump system can use individual control and set points, but they operate in the same mode of either heating or cooling at any given time.
• vrf-heatRecovery-system: Heat recovery units are heat pump systems that can provide simultaneous heating and cooling. All indoor units connected to a heat recovery system not only can use individual control and set points, but they can also individually operate in heating or cooling mode at any given time.

VRF Equipment

VRF system consists of the following equipment:

• Outdoor Units: Outdoor unit has one or more compressors. As each indoor unit sends a demand to the outdoor unit, outdoor unit delivers the amount of refrigerant needed to meet the individual requirements of each indoor unit.
• Refrigerant Plant: Multiple outdoor units can be connected, and the refrigerant plant covers all the connected outdoor units.
• Branch Selectors : Branch selectors are used for heat recovery VRF system as control devices directing the liquid refrigerant or gas refrigerant to zones requiring cooling or heating
• Indoor Units: Indoor units operate to satisfy a heating or cooling load in a zone based on a zone thermostat temperature set point

Outdoor Units

Outdoor units are modeled with the vrf-outdoorUnit tags. They can be water or air cooled. An outdoor unit contains a compressor, circuit board and a heat exchange coil. In case of air cooled units they also have a propeller fan. These units are typically situated outside the condtitioned space, and pump refrigerant to and from its companion indoor units.

Indoor Units

Indoor units are modeled with the vrf-indoorUnit tags. Indoor units are located inside the conditioned space and provide conditioned air to the spacs. This unit generallycontains a heat exchange coil, filters, remote signal receiver, and fan.

Branch Selector

Branch selectors are modeled with the branchSelector tag. Branch selectors are used for heat recovery VRF system as control devices directing the liquid refrigerant or gas refrigerant to zones requiring cooling or heating.

Refrigerant Plant

Refrigerant plants are modeled with the vrf-refrig-plant tags. They model a group of outdoor units as a single black box. If one VRF system has multiple outdoor units, refrigerant plants work as heat-source side for the entire VRF systems, combining multiple outdoor units. These plants are composed of outdoor units as sub-equipment.