VRV Basics

This tech tip was written by experienced tech and VRV specialist Ryan Findley. Thanks, Ryan.


This is a quick overview, not a substitute for taking proper manufacturer training.

 

This tech tip is geared towards the mechanic who is fairly new to VRV systems. As with anything, before we harness the ability to install or service anything, we first must understand the fundamentals. Even though some VRV systems might feel overwhelming, they still function like standard heat pumps.

Note: VRV refers specifically to Daikin, and this tech tip is written primarily from a Daikin point of view

Let’s start at the beginning. There are two product lines in VRV: heat pump and heat recovery. The heat pump is simply the same setup as your residential heat pump running two pipes from the indoor units to the outdoor units. Heat recovery is running three pipes from the outdoor units to the indoor units, giving the machine the ability to run heat and cooling simultaneously. Daikin heat pump model numbers are RXYQ, where heat recovery will be REMQ or REYQ.

 

First, let’s identify some components. In a VRV system, we have outdoor units, which are also commonly referred to as modules.  Modules come in various sizes ranging from 6-12 ton in heat pump and 6-10 ton in heat recovery in the VRV 3 line. VRV 4 ranges from 6-14 tons. Modules can be combined in tandem up to a total of three outdoor modules.

 

Indoor units

Indoor units (or fan coils) come in many different types, but the most common ones used are the ceiling cassette and the ducted units.

Refnets

Refnets are a Y-type fitting designed to provide equal flow to both the main piping continuing on and also the branch piping that is taking off of the main. Refnet installation is critical.  Follow manufacturers' recommended install practices of keeping the angle of the refnet below 15 degrees for outdoor unit piping and 30 degrees for indoor piping. To see the adverse effects of improper installation, see this video.

Branch selector boxes

Branch selector boxes, or BS boxes for short, are only used in heat recovery applications. BS boxes will have the three pipes coming from the outdoor units piped directly to them. They are made up of solenoids and EEVS. The fan coils determine the mode of operation, but the actual change of operation mode occurs in the BS box.

 

Communication wiring

VRV systems are basically one giant communicating residential variable speed heat pump. Information is shared from the fan coils to the outdoor units across a daisy chain of communication wiring. The wire should be 18/2 non-shielded stranded. The system should also be wired, as shown in your submittal documents from your sales engineer.

 

PVE Oil

Polyvinyl ether oil is used in the VRV product line. It’s used because of its outstanding miscibility at low refrigerant velocities. It’s noteworthy that PVE is more hygroscopic than POE oil is. The big difference between the two is that PVE can be dehydrated by pulling a vacuum on it, whereas POE will not. Another difference is when PVE interacts with moisture, it doesn’t produce acids via hydrolysis. If PVE is exposed to moisture, it turns the oil into sludge.

 

Heat pump vs. Heat Recovery

A heat pump system operates with only two pipes running between the outdoor and indoor units. One line is always a liquid line, whereas the other line is either hot gas or suction gas. The mode of operation is determined by a master stat (designated at startup). The master stat is the only one in the system who has the ability to change the mode of operation. There’s a more complicated way to control these if you have an iTouch Manager, which we will discuss later. Heat recovery uses a three-pipe setup and BS boxes. The three pipes consist of a liquid line, a suction line, and a dual high pressure/low-pressure line. When the machine is in full heating mode, the dual gas line will have discharge gas going down it. The liquid line remains the liquid line, and the suction pipe is not being used. In full cooling mode, the dual gas line turns into an additional suction line. The suction line and liquid line act as they would in a standard A/C. Parallel operation is when there is a demand for heating and cooling at the same time. In this mode, the dual gas line will be in heating mode.

 

Differences between VRV 3 and VRV 4

There are a few big differences between the two product lines. The first is that VRV 3 uses a crossover line that runs between all modules if there is more than one. VRV 4 does not have that. VRV 3 has one inverter compressor and one standard compressor (in modules that have more than one compressor). VRV 4 has two inverter compressors, again, if it’s a module that has more than one compressor. Both product lines have different inverter boards and different cabinets. VRV 4 also has a split outdoor heat exchanger that allows half of the coil to be in one mode of operation while the other half could be in another mode of operation. VRV 4 inverter boards are cooled by subcooled refrigerant that runs on the back of the heat sink. VRV 3 inverter boards are air-cooled from the inside of the cabinet near the outdoor fan motor.

 

Filter Driers

Filter driers are not used unless there is burnout of a compressor. If a burnout cleanup is required, follow the manufacturer's recommended clean-up procedure.

—Ryan

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