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You are here: Home / Archives for VRF

May 08 2018

The VRF Checklist

RMH VRF
By Kevin Angle, PE

If you’re anything like me, you are constantly making lists, whether it be a grocery list, materials list, or to-do list to make sure everything gets done. In my opinion, lists are one of those “necessary evils.” They can seem aggravating at times because, let’s face it, the entire list rarely gets checked off!

As VRF systems are continuing to grow in the marketplace across the globe, as well as here in the United States, it is perhaps time to create a checklist for VRF systems. These systems are being installed in numerous buildings throughout the country. In many cases, manufacturers are directly designing these systems for contractors to install. While this may be an effective approach for some projects, there are significant benefits to having an engineer, working with the manufacturer, to review the design criteria, design the system, and develop sealed and signed construction documents in accordance with the building codes.

A Checklist for VRF Systems

By no means is this list inclusive, but it can be viewed as a baseline to incorporate the fundamental elements required for your VRF system to meet those baseline expectations, and you can “check the boxes.”

■ Ventilation

Couple VRF system with a ventilation system, whether it be natural or mechanical. Natural ventilation would typically include operable windows in accordance with building code requirements. Mechanical ventilation can be accomplished through various methods, including direct mechanical ventilation to the space or common ventilation ducted to each air handler or fan coil unit.

■ Refrigerant Piping Location

Do not locate refrigerant piping in an elevator, enclosed public stairway, stair landing, or means of egress. Install refrigerant piping a minimum of 7.25 feet above the finished floor.

■ ASHRAE Compliance

Comply with ASHRAE 15 and ASHRAE 34, as both standards are referenced in the International Mechanical Code. If you are utilizing a VRF system and are not aware of these standards, you should get up to speed quickly. ASHRAE 15 was put in place around 1930, while VRF systems were first installed around 1980. Therefore, some of the information within ASHRAE 15 does not specifically address VRF systems. In future updates, however, I predict this standard will address VRF systems. Until then we must comply with the current standard.

The ASHRAE standard considers the ability of people to respond to potential exposure to refrigerants, which are classified within ASHRAE 34 with an RCL (Refrigeration Concentration Limit) designation. The standard relates to a leak of refrigerant and its ability to displace oxygen and affect the personal safety of occupants. A leak may occur in any space, and the entire amount of refrigerant within the system or circuit should be considered. An example would be R-410A, which has a maximum RCL of 26 lbs. per 1000 ft3 of room volume for occupied spaces. Most manufacturers calculate the pounds of refrigerant based on the line lengths of refrigerant piping. Smaller rooms with refrigerant-based evaporators may pose issues when considering RCL; therefore, each space volume should be evaluated to make sure the refrigerant concentration limit is not exceeded.

There are some strategies to yield refrigeration concentrations below the limits, like utilizing door undercuts or transfer grilles to increase the volume of rooms. In my opinion, these approaches tend to be ineffective and should not be used, as most refrigerants are heavier than air, and transferred air will not be effective in dispersing the refrigerant.

Many hotel brand standards and medical facility standards require that designers subtract the bed and other furniture in the rooms from the total volume, as the refrigerant will disperse around the bed. Certain school districts do not allow designers to utilize the full height of a room, as the student breathing zones are lower than full height. These items must be considered by designers, who in turn must utilize their engineering judgement to protect the occupants.

■ System Selection

Select the appropriate system type. There are multiple types of VRF systems in the marketplace, including the following air-cooled outdoor units:

  • Heat pumps
  • Heat pumps with heat recovery
  • Heat pumps with auxiliary heating or hyper-heat

Heat pump systems are traditionally rated at 47° F and heating capacity is reduced below 47° F. Most manufacturers’ heat pump VRF systems can only supply 60% of heating capacity at 5° F. In climate zones with winter design temps below 47° F, the hyper-heat option or auxiliary heating methods should be implemented to provide adequate heating capacity. Heat recovery options provide the system the ability to simultaneously heat and cool for temperature controls zones that have differing needs.

■ Line Lengths

Verify that line lengths of refrigerant are within manufacturers’ requirements. Limitations of the refrigerant line lengths vary among manufacturers.

■ Qualifications

Engage a qualified engineer and contractor with the experience and certification to design and install VRF systems.

In summary, VRF systems have many advantages over traditional HVAC systems in certain applications, and I predict they will continue to increase their market share within the HVAC industry. However, using proper precaution when designing and installing VRF systems is critical to providing a system that is both code-compliant and highly effective.

Considering VRF as an option on your next project? Interested in our AIA CES program on VRF applications? Contact:

Kevin G. Angle, PE
Mechanical Engineer
717.434.1562

Thomas E. Leary, PE
Executive Vice President
717.434.1555

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When do Variant Refrigerant Flow (VRF) Systems Make Sense? 

Written by Scott Butcher · Categorized: HVAC Posts, VRF · Tagged: Variable Refrigerant Flow, VRF

Feb 28 2018

VRF Infographic

JDB Engineering just published a new infographic about Variable Refrigerant Flow (VRF) systems: overview, applications, sustainability, ideal building types, advantages, and disadvantages.

Check it out:

VRF Infographic

Interested to learn more about VRF Systems? Contact Timothy A. Warren, PE, LEED AP, president of JDB Engineering, Inc.

Also check out Kevin Angle’s blogs, When Do Variable Refrigerant Flow (VRF) Systems Make Sense? and The VRF Checklist as well as our AIA LU/HSW-approved training program, Real-World Applications for VRF Systems.

Written by Scott Butcher · Categorized: HVAC Posts, VRF · Tagged: Variable Refrigerant Flow, VRF

Feb 29 2016

When Do Variable Refrigerant Flow (VRF) Systems Make Sense?

VRF

by Kevin G. Angle, PE, LEED Green Assoc.

Having three young children at home, I hear all kinds of music in the car and in the house. Lately, my kids have become excited when Meghan Trainor’s “All About the Bass” comes on the radio – I regularly listen to all three of them in the backseat of the car screaming the lyrics. While writing this post, I was tempted to title it “VRF – It’s All About the Application.” VRF, which is also called VRV, has gained popularity as a newer technology in the United States. This type of air conditioning system utilizes Variable Refrigerant Flow (or Volume).

VRF systems are often viewed as an enhanced version of ductless split systems, which have been successfully installed for many decades.  The term “variable refrigerant flow” refers to changing the flow of refrigerant to each indoor unit. The Variable Refrigerant Flow enhancement comes with multiple indoor unit evaporators or condensers, up to 16 with various manufacturers, utilized with a single outdoor condensing unit or heat pump. Due to the advanced use of variable speed compressors, drives, and inverter-driven fans, many manufacturers of these systems are capable of providing simultaneous heating and cooling through their indoor units. Most manufacturers refer to these as heat recovery systems, and they have various methods of recovering the heat through either a two-pipe or three-pipe system.

Now that we know the capabilities of a VRF system, when does it make sense to use it? It’s all about the application (queue the music!).  On the renovation of a relatively small government housing project (5,000 sq. ft.), we were tasked within the design criteria to provide a central HVAC system that also provided individual temperature control within each dormitory room. In addition, we had to meet the design requirements of a LEED-certified building, which requires energy savings of 30% compared to the baseline system. Those two criteria limited our options and led us in the direction of VRF. In the end, VRF and geothermal systems were the only two systems able to meet the energy savings.

So we know that the application of VRF works for a smaller building, but is it an option for larger buildings? I would say yes – but again, it’s about finding the right application. VRF systems are good for potential high-rise buildings, which have varying exposures and varying loads throughout the building. VRF heat recovery systems will perform well where one space may need heating, while the adjacent space may need cooling. VRF systems are expensive in terms of first cost – in many cases 2 to 2.5 times compared to a traditional packaged DX system. However, our energy models are indicating that in some cases, as much as 50% energy savings may be achieved when compared to baseline systems. Also, it is important to note that VRF systems do require a dedicated outdoor air system to meet ventilation codes, which in many cases adds to the first cost. Buildings with operable windows or natural ventilation are prime candidates for VRF. VRF also makes sense for historic renovation projects, where it is easier and less invasive to install refrigerant piping than larger hot or chilled water piping, along with associated ductwork.

VRF systems have been used with some success for larger assembly spaces; however, indoor units are typically limited in capacity to approximately 3-5 tons of cooling. As a result, VRF systems may not be the best solution for this application or for any type of industrial or manufacturing building. Albeit a newer technology with many uncertainties surrounding the reliability of energy models, actual savings in labor, and first cost, VRF systems have proven to have a spot in the marketplace with the right application. VRF systems are not new to Europe, and have been successfully used there for more than twenty years, which must say something.

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Written by Scott Butcher · Categorized: HVAC Posts, VRF · Tagged: HVAC, Kevin Angle, VRF

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