September 2, 2016 by JS Rancourt
One of the sometimes overlooked advantages of VRV systems are their integral controls. Many VRV systems operate without any 3rd party building automation system, and simply operate using their local or central plug-and-play controllers. However, as the VRV plug-and-play controllers become more advanced and more customizable to accommodate different applications, some building owners and operators are sometimes left helpless with a seemingly faulty VRV system, often due to improper programming and training.
The majority of properly commissioned VRV systems make it through their warranty period (warranty periods now extend up to 10 years for some manufacturers) with little to no failures. Therefore, if a VRV system is not acting as predicted, or is not delivering the comfort level desired, the first aspects to look into are the controls and programming. This is where a very experienced VRV technician can come very handy; one who understands the programming of these systems inside and out. Service contractors should seek more training on the service and controls side of VRV systems, and should engage the VRV manufacturer when necessary. As little as one site visit by a very experienced VRV service technician could save you hours of headaches and complaints.
One of the first control aspects that our technicians evaluate is the setup of the Mode changeover of each fan coil and of the system in general (for 2-pipe heat pump systems). Are the thermostats responsible for switching the fan coil between heating and cooling mode? If so, what are the primary and secondary deadbands, and what is the guard timer? Or, if the changeover is being done centrally, is it being done properly?
At an even more basic level, our service technicians will often start by asking the facility manager and the end users if they understand how their system is being switched between heating and cooling. Simply understanding the sequence in place often helps reduce the number of complaints, and empowers the facility managers and end users to take better advantage of their VRV system.
The second control aspect that often generates complaints revolves around the fan speed control of the fan coils. During active cooling and active heating, the end user can select the desired fan speed from the local controller. However, the latest VRV systems (by Daikin) also have an automatic fan speed option, which automatically increases or decreases the fan speed depending on how far from set point a space is. This contributes to energy savings as well as user comfort. However, if an end user does not understand that their VRV unit is in automatic fan mode, feeling the fan speed go up and down can be frustrating.
VRV fan coils are also programmed to set the speed of the fan when the units are in Thermo-Off. This term refers to a fan coil not actively cooling or actively heating, which occurs when the room temperature is within approximately 0.5C from set point. In other words, this is when the unit is at rest. During these periods, the fans can be programmed to remain running at the user selected speed, or the they can be programmed to go to a very low speed, or to simply be turned off. Different applications can benefit from these different settings, but end users who do not understand these settings can easily get frustrated with their unit, and think that it has a mind of its own.
These are just a few examples of VRV control settings commonly misunderstood and misapplied, which can result in building owners and operators thinking that their VRV system is not functional, even though it could be operating exactly as instructed. As new VRV technology and new controllers emerge, the list of programmable option increases. From self-cleaning cassettes with programmable options to the sensitivity setting of motion sensors that determine human presence to prevent drafts, the list goes on.
Is your VRV system defective? The answer is, it could be, but chances are, it is not. Most real issues with VRV systems are self-diagnosed and immediately communicated at the local thermostat and/or central controller or BAS. This is similar to your check engine light in your car, except the actual error code is directly shown on all thermostats and central controllers, and details on the code and troubleshooting steps are available online and on multiple free mobile Apps.
Ensuring that your VRV system is properly programmed, and continuously ensuring that the programming is optimized year over year not only helps with user comfort and satisfaction, but also ensures that your system is running as efficiently as possible. VRV systems consuming more energy than predicted are often found with improper Mode changeover sequences causing fan coils and systems to flip flop between heating and cooling and to fight with each other.
Contact your service contractor and encourage them to review the programming and controls of your VRV system, or ask your manufacturer to come do a review of your system.
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