Tag: ductless

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

 

 

 

 

 

 

 

I hear many techs complain about the finicky and ineffective nature of electronic leak detection. So much so that some claim that is is a waste of time altogether. we recently located a leak inside the fins of a ductless evaporator coil, pinpointed to an exact spot using an electronic leak detector. For demonstration purposes, we took that coil and performed a definitive test to locate it in the video below.

A leak detector can be tricky to use so here are some of our top tips –

  • Know your detector. Know it’s limitations, it’s sensitivity and what can cause false positives. For example, some leak detectors will sound off on certain cleaners or even soap bubbles. My detector sounds off when jostled or when the tip is blocked.
  • Keep a reference bottle so you can check your detector every time before you use it.
  • Maintain your detector and replace the sensor as required. Most heated diode detectors require sensor replacement every 100 hrs or so.
  • Keep it out of moisture. Most detectors will be damaged by almost any amount of moisture.
  • Move slowly and steadily. Don’t jump around or get impatient.
  • Most refrigerant is heavier than air which means that starting from the top and working down is usually a more effective way to pinpoint.
  • Go back to the same point again and again to confirm a leak. Don’t condemn a component based on one “hit”
  • Find the leak WITH BUBBLES whenever remotely possible, even after pinpointing with a detector.

— Bryan

First off we need to clarify that very few unitary manufacturers use flares anymore. You will most often find flares on ductless and VRF / VRV systems and in refrigeration. A flare uses a flared female cone formed into tubing (usually copper) that is pressed onto a male cone (usually brass) by a threaded flare nut. A flare shouldn’t be confused with a chatleff fitting that uses a threaded nut and seals with teflon or nylon seal.

This is not a full lesson on how to make a flare, this will give you some best practices to make a flare that doesn’t leak.

  • Use proper depth, the old school method is to bring the copper up a dimes width above the block but modern flaring blocks usually have built in gauges that work well.
  • Don’t trust factory flares. In many cases factory line-set flares are made poorly, often it’s better to just cut them off and start over
  • Ream the copper before flaring to remove the burr but don’t OVEREAM and thin out the copper edge.
  • Use a good, modern flaring tool designed for refrigeration. This is a great one
  • When making the flare use a bit of refrigerant oil, or even a better a bit of Nylog. You only need a drop or two, one drop on the flare while making it to prevent binding and create a smoother flare surface with a bit on the back of the flare as well to allow the nut to slide easily. I also like one small drop on the threads and spread to the mating surfaces. Some manufacturers disagree with this due to the effect it has on torque specs so always follow their recommendations when in doubt. In my experience a bit of assembly lubricant really helps.
  • Use a flare wrench instead of an adjustable wrench and tighten with a torque wrench.  I understand that very few techs do this… but it is a great practice if you want to get it right the first time with no leaks and no damage. This can be done easily be done with a set of SAE crowsfoot flare nut wrenches and a 3/8″ torque wrench. As always use manufacturers torque specs if available. If not you may use the chart below. Make sure to keep the crowsfoot at 90 degrees to the wrench (perpendicular) and place your hand on the end grip of the wrench. If you have lubricant on the threads stay on the low side of the torque rating.

Some things NOT to do that I’ve seen –

  • Don’t use leak lock or teflon tape on flares
  • Don’t Over Tighten flares to try and get them to stop leaking. If they are properly torqued and still leak they are made wrong
  • Don’t use too much oil or nylog, a drop or two will do
  • Don’t try and jam a teflon seal from a chatleff on a flare

Using these practices we have VERY FEW leaks on flare fittings.

Some other things to note –

There is a company called Spin that uses a flaring tool that goes on a drill. Their tool actually heats and anneals the copper. They claim they don’t need to get the flare to 45 degrees because the annealing makes the copper soft enough that the nut itself with finish the flare. We have used it a few times with good results.

There are now companies that make nylon / teflon (I’m actually not sure what they are made of) gasket inserts that go into a flare. Some techs swear by them, I really don’t see the necessity but I don’t have any experience with them.

Finally, make sure when your system has flares to pressure test to the rated test pressure and bubble test the joints. Then perform a vacuum to below 500 microns and decay test. This will help ensure that you got it right. If it leaks, cut it off and remake it.

  • Use a good tool
  • Get depth correct
  • Ream properly
  • Use a good assembly lubricant
  • Torque properly
  • Pressure test to 300+ PSIG (in most cases) and bubble test carefully

— Bryan

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