This tech tip is written by experienced tech and VRF / VRV specialist Ryan Findley. Thanks Ryan! (Note: Ryan refers to VRV rather than VRF because he specializes in Daikin and these articles are written from a Daikin VRV perspective)


In this tech tip, I’ll be going over a few things related to the install of VRV systems.  

THIS IS NOT MEANT TO TAKE THE PLACE OF A FACTORY PROVIDED INSTALLATION CLASS

 

Any questions should be directed to your rep sales engineer or the manufacturers specific instructions. It’s better to ask and double check than have to do something twice.

The install is the most critical part of a successful system, without a quality install you will not get desirable results.  There are many issues that can come arise from install issues, but here are a few of the most common ones.

Leaks and Tightness Test 

Flares…..I know, everyone hates them but a properly made and installed flare is an effective mechanical joint.  Be sure to ream (deburr) the tubing, use your flare sizing guide tool to assure the flare is a good flare. I have made my fair share of flares that looked good but didn’t pass the test with the gauge.  If you don’t have one, you need one. The link to the one I use will be at the bottom. Also, be sure to use a torque wrench and torque all flares to the appropriate torque specs. I have come across a lot of them that leak after the change of season with the corresponding expansion and contraction.  Often, they’ll last 3-6 months before they start to leak.

Be sure to complete the tightness test in accordance with the install procedure, finishing pressure being 550 psi (450 for the FXTQ) for 24 hours or more. Be sure to record your test pressure and temperature at the beginning and end and compensate for pressure change based on changes in ambient temperature 

Notes from Bryan: The HVAC School app is free and has a nitrogen pressure change calculator. Also, In my contracting business, we find that using a good, quality, modern flaring tool with a depth gauge and clutch as well as some assembly lubricant such a refrigerant oil or Nylog can really help make a great, tight-fitting flare with less galling. 

Refnets

Be sure to mount your refnets within the allowable angle which is 15 degrees for outdoor refnets and 30 degrees for indoor refnets.  If you’re interested in why this matters, see this video.

Finishing Vacuum

Be sure to get below 500 microns and hold.  A new and tight system should easily be able to get down under 300 and hold there, if not then you want to investigate further.  

Pipe Insulation

Make sure you use insulation with the outside diameter of at least ¾”.  If line sets run through an attic or unconditioned space, this is especially important.  Be sure to seal the joints with appropriate glues or tapes designed for the purpose. 

Purge & Flow Nitrogen

It’s very important that you displace all air with nitrogen by purging first, then flow nitrogen at a very low rate anytime you are brazing.  There are filters/strainers everywhere in the system that are fine mesh that can be clogged up very easily.  See pictures below.

Moisture

Moisture can be a major issue with the use of PVE oil.  PVE is more hygroscopic than POE is but rather than hydrolysis occurring it changes into a sludge.  This sludge can gum up mechanical components in the refrigeration system which can cause premature failures. Be sure to complete a decay test after you have reached your finishing vacuum, it’ll tell the tale if there’s moisture in the system or not.   

Communication wiring

Be sure to daisy chain your wiring.  Also, make sure to use non-shielded 18/2 stranded wire (or whatever your particular product requires) and install it according to the submittals from your sales engineer.  

Setting The Units

Verify that the units are set in the proper order, the largest unit goes closest to the indoor units on down to the smallest unit (VRV 4).  VRV 3 has a cross over line that goes between the modules so this is not a concern.

20/40 Rule

To reduce refrigerant noise, it’s recommended to keep the first elbow after a refnet at least 20” away and 40” away for branch boxes.

Line Length Measurements

Please, please, please keep track of and measure the lineset!

Send it to your sales engineer so that the correct additional charge can be calculated. These are critical charge machines so every pound matters.

Oil Traps

Only inverted traps are allowed in the VRV piping.  Oil traps are a major concern for these machines as they aren’t able to overcome them in oil return mode. The more oil that gets trapped out in the system, eventually you’ll start losing bearings in the compressors.  I have changed many compressors that have nearly no oil left in them. Be mindful of keeping piping on the same level. There are specific rules about oil traps in your install class.

Expansion Joints

Install expansion joints per your sales engineer requirements.  This is important because of the possibility of a large change in temperature that the pipe is under and needs to be allowed to expand and contract.  If not, there’s a possibility of blowing out the end of a fitting.

Pipe Clamps

Do NOT tighten your pipe clamps down with your impact driver. The pipe needs the ability to move, otherwise there’s a chance you can blow out a fitting.

Unit Placement

Be sure to have the units mounted on stands above the highest average snowfall.  Having snow pile up or water from defrost freeze in the pans or on the bottom of the coils can be very problematic.  Be sure the bottom of the units are clean as that can cause the water not to drain out of the pan also.

— Ryan

PS- Here is a good Flare Gauge available from TruTech Tools 

This tech tip is 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, the ability to install or service anything we first must understand the basic fundamentals.  Even though some VRV systems might feel like a bit of overwhelming, but they still function the same as a standard heat pump.

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 2 pipes from the indoor units to the outdoor units.  Heat recovery is running 3 pipes from the outdoor units to the indoor units allowing the machine the ability to run heat and cooling simultaneously. Daikin Heat pump model #’s are RXYQ where heat recovery will be REMQ or REYQ.

 

First, let’s identify some components.  In a VRV system we have the 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 3 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 visually show what 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 3 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 the mode of operation 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

Polyvinylether 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 to sludge.

 

Heat pump vs Heat Recovery

A heat pump system operates with only 2 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.  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 3 pipe setup and bs boxes.  The 3 pipes consist of a liquid line, 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 it 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.  First is VRV 3 uses a crossover line that runs between all of the modules, if there are more than one.  VRV 4 does not have that.  VRV 3 has 1 inverter compressor and 1 standard compressor (in modules that have more than 1 compressor).  VRV 4 has 2 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 ½ of the coil to be in one mode of operation while the other ½ could be in another mode of operation.  VRV  4 inverter boards are cooled by subcooled refrigerant that runs on the back of the heat sync.  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 manufacturers recommended clean up procedure.

–Ryan

 

 

 

 

 

 

 

Scroll to top
Translate »

Daily Tech Tip

Get the (near) daily Tech Tip email right in your inbox!
Email address
Name