Before I begin this article I would like to thank the many owners, architects, engineers, and contractors who have embraced Variable Refrigerant Flow (VRF) technology for whole-building air conditioning and heating. VRF has found its way into almost every conceivable building type across south Alabama, south Mississippi, and the Panhandle of Florida. As long as VRF is properly applied and designed, I challenge you to find a better HVAC system in terms of first cost, lifecycle cost, maintenance cost, design flexibility, footprint, reliability, and most importantly, energy-efficiency.
From High Schools to Souvenir Shops to Prisons to Military Bases, VRF (and particularly the LG Electronics Multi-V line we represent) has found its way into your design toolbox in a big way. Growing up my father taught me the importance of properly maintaining my tools, so I want to take a little time today to sharpen your VRF knowledge by quickly reviewing Best Practices When Designing Variable Refrigerant Flow Systems.
A word of caution before we begin: while most of what I discuss below can be applied to any VRF design, there are significant differences between LG’s Multi-V VRF system and those of its competitors in terms of capabilities and capacities. If you want to learn more about why LG Multi-V might be a good choice on your next VRF project, please contact us.
STEP 1: Due Diligence
The first key to a great VRF design is making sure that this equipment is a good fit for the project. Things such as energy-efficiency, life-cycle cost, building diversity/use, and project timeline plays a big role in determining if VRF is a good fit. Below are some questions and comments to get you started thinking:
- Is energy efficiency a consideration, and if so, to what degree (Energy Star, LEED, etc)? VRF’s main selling point is its outstanding energy efficiency versus other commercial HVAC systems. Consider using tools such as LG’s free LEEP Energy Estimator or EnergySoft’s EnergyPro software to determine energy savings and lifecycle costs.
- How quickly is the equipment needed? LG maintains an expansive inventory of VRF equipment in warehouses across the United Sates. Readily-availably equipment works out well for compressed construction deadlines or for quick turn around HVAC retrofits.
- Will VRF be a cost-effective choice? McNellage & Associates provides a full-range of HVAC equipment, including package units, complete VAV systems, water-source heat pumps, complete VRF systems, and complete chiller systems. We can quickly provide budget numbers based on a wide range of potential equipment selections to help you make the right choice. To get a good understanding of VRF’s operating costs versus other systems please see the last page of this PDF.
- Does this building lend itself to VRF? Not every facility is a perfect fit for VRF equipment. In order to understand if this equipment is a good fit you need to understand the building’s diversity by analyzing its use, occupancy patterns, and solar load profiles. You also need to have a thorough understanding of how to properly apply VRF equipment to best make this determination. Please contact us if you have questions or need training on LG’s Multi-V Variable Refrigerant Flow equipment.
- Does the project team understand VRF technology? Variable Refrigerant Flow systems have many benefits, but are often incorrectly perceived as finicky, complex, and difficult to understand HVAC systems. It is important that the entire project team (from the owner to the design engineer to the installing contractor) understand how VRF works. LG has developed an industry-leading education and oversight program that makes sure expectations are met and exceeded throughout every step of the process
- Is reliability important? Want to know why there are less failures of VRF systems than any other type of HVAC equipment? The answer is attention to detail. LG understands that the only way their Multi-V equipment will be widely specified and installed is to ensure that each job is the best that it can be. Unlike other VRF manufacturers, LG requires rep involvement during the design, installation, and commission process of each VRF job and requires refrigerant piping & modeling information be submitted for engineering review prior to equipment release. This careful attention to detail also extends to installing contractors, who are required to attend VRF installation at one of LG’s many training facilities across the United States before they are allowed to take possession of equipment.
STEP 2: VRF Equipment Selection
Now that we have determined that LG’s Multi-V VRF equipment is a good fit for your project we need to step back and review the project requirements and figure out how to best apply it. The first step is to develop the building’s heating and cooling load requirements on a zone by zone basis. Zones are spaces that are served by individual VRF air handlers (large zones can be served by groups of air handlers). Below are some questions and comments to get you thinking about proper VRF equipment selection:
- Heat Recovery or Heat Pump? VRF Heat Pump systems are analogous to 2-Pipe CW/HW systems in that the network of VRF air handlers all have to be heating OR cooling. VRF Heat Recovery Systems, which reuse waste refrigerant and as a result are extremely energy efficient, are analogous to 4-Pipe CW/HW systems in that they allow the network of VRF air handlers to cool or heat independent of each other while operating off the same condensing unit.
- Capacity, Voltage and Phase? LG’s Multi-V condensing units cover the range from 3 to 38.2 tons and are available in 208-230/1/60, 208-230/3/60, and 460/3/60. Unlike its competition, all of LG’s VRF air handlers are 208-230/1/60. To explore more LG Multi-V project data please click here.
- What is your condensate plan? Much like the fan coils of a chilled water system, VRF air handlers require condensate drain line connections. LG’s Multi-V VRF system only requires condensate drain line connections at the air handlers for both their Heat Pump and Heat Recovery Systems. This is not the case with all VRF manufacturers – some require additional condensate drain connections for Heat Recovery equipment.
- What is your plan for large, open spaces? Buildings such as schools often have large open spaces with high ceilings (think gyms, cafeterias, etc). These spaces typically have predictable use patterns and uniform cooling/heating requirements. While LG manufactures single phase ducted high static air handlers up to 8 tons that could serve these areas, a cost-to-benefit calculation might be helpful to see if these areas might be better served by larger unitary package equipment.
- What is your plan for outside air? In about 99.5% of all instances, outside air should not be handled by any VRF system and no outside air should be introduced into any VRF air handlers. This is probably the most asked question in regards to VRF. Don’t do it – your client and your liability insurance will thank you. For more information on this please contact us.
STEP 3: Refrigerant Piping & Modeling
Refrigerant Piping & Modeling is ABSOLUTELY THE MOST IMPORTANT STEP IN THIS ENTIRE PROCESS. If you skip, neglect, ignore, or don’t pay enough attention to your refrigerant piping plan there will be problems, most likely very large ones that will take lots of time and money to fix. Run like hell from any VRF Manufacturer who doesn’t require a detailed refrigerant pipe model along with the equipment Purchase Order.
That being said, it is actually very easy to develop a detailed refrigerant model as long as you work with a Manufacturers’ Representative who knows what they are doing and has lots of experience with VRF systems. Each VRF manufacturer approaches refrigerant piping differently, so it is strongly suggested to work in tandem with a VRF sales engineer from the very beginning of the project. VRF sales engineers do this stuff every day and can prevent you from unnecessarily banging your head against the wall.
Once you have selected your VRF equipment and its location you need to develop a refrigerant piping plan to ensure that the system will function correctly. As with all things in life, Variable Refrigerant Flow systems have pages and pages of rules regarding where you can locate equipment, how far it can from other equipment, what size the connecting pipes should be, etc. To reduce the inherent complexity of doing all this by hand, LG makes available a refrigerant piping program that easily and quickly facilitates variable refrigerant system modeling. This program uses a drag and drop interface and is very easy to understand and use (see below for a screenshot). Please contact us for training or assistance with this free program.
STEP 4: Specification
Specifying VRF systems is really not much different that specifying other HVAC systems. You publish a schedule, plans, and specifications. The key to a good VRF specification is making it as easy as possible for all trades involved in the project to understand how the system is assembled from a group of components and installed as a system. Below are some suggestions to ensure a great VRF spec:
- Use McNellage & Associate’s Microsoft Excel VRF system template for your schedule. Our template shows the system layout in an extremely logical fashion. Please contact us for this template.
- Don’t use the generic LG Multi-V spec. Work with your LG Rep to ensure that you have a concise specification that covers this exact project and provides a pathway for approved equals.
- Publish the LG Refrigerant Piping Model on the plans as a general guide for the installing contractor. To protect yourself against unknown job site piping obstructions, make a note placing the installing contractor ultimately responsible for proper estimation, coordination, and installation of VRF refrigerant piping. Ensure that the contractor is aware that they are also responsible for updating the piping model if he deviates at all from the lengths you have listed on the plans.
- Draw refrigerant lines directly on your plans. The benefit of publishing refrigerant lines is that you aren’t leaving the coordination up to the contractor or project manager, who might choose to run refrigerant piping in places you might now prefer. Not all engineers are in favor of this and may choose to only publish the piping model.