Understanding Variable Refrigerant Flows

Common in Europe and Asia, VRF systems have recently become more popular in North America.  Its  ability to respond to fluctuation in space load conditions, means it can reduce energy costs significantly.

There are two basic systems--water-cooled and air-cooled.  A simple VRF system consists of an outdoor condensing unit and multiple indoor evaporators. The condenser and evaporators are connected by a complex set of oil and refrigerant pipes and governed by individual thermostat controls.

Installation 

While VRFs can help save on energy costs,  it is not suitable for all facilities.  Before installing an HVAC system, you should have a professional engineer determine if a VRF system is appropriate for your building.

If the engineer recommends the use of a VRF, the next decision is to determining whether you will need a water-cooled system or an air-cooled system. As the requirements for these two systems can vary and may impact architectural elements.

Air Cooled VRF

For air-cooled systems, an exterior space is required for the installation of a condenser. The space selected for the installation must be away from windows, accessible to maintenance and support weight of the units.  These units, can be unsightly and may need to be hidden from view with an architectural enclosure.

Water Cooled VRF 

For water cooled system is used, a small closet is often required to house the required water source units that compromise units.

In addition, for both air cooled and water cooled systems, a feasible path to route the refrigerant pipes is required.

Another challenge for specifying VRF systems is the provision of a separate outside air supply to each indoor unit to comply with ASHARE Standard 62.1 and building codes.  This requires larger facilities to have a separate outside air fan and control system, and in humid climates providing outside air to each indoor unit helps ensure good indoor air quality.

Negatives of VRF systems

Due to the limitation on the indoor coil maximum and minimum dry and wet bulb temperatures, the units are unsuitable for 100% air applications, particularly in hot and humid climates.   Another concern, is that the cooling capacity available to an indoor section is reduced when there are lower outdoor temperatures, which limits the use of the system in a cold climate to serve rooms that require year-round cooling, such as a server room.

That being said, VRF systems offer benefits beyond energy savings. Its ability to heat and cool separate space at the same time in the same building,  vary compressor speed to meet load condition, and its quieter operations are also other reasons why a VRF system should be considered.

The Benefits of Displacement Ventilation

One of the most common forms of air distribution for HVAC system is overhead mixing, which is why you will often see air distribution devices--diffusers--blowing tempered air on commercial facilities such as offices, schools and hospitals. 

Diffusers use high pressure to throw the tempered air into a room, mix with the room air and subsequently heat or cool the space.

• Less energy because the space is condition only when occupied

• Less energy from reduced fan power by blowing that air at a slower pace

• Increased comfort of occupants because less air movement 

• Decreased contaminant risks, because there is no mixing of air.  

This technology has its flaws, as the mixed air can be subjected to airborne contamination and consequently lead to poor indoor air quality. Another concern with mixing ventilation is the location of the diffuers. It is common for diffusers to be placed 8-12 ft above the floor. This means that energy is wasted heating and cooling unoccupied space.  

For these reasons, an increasing number of energy and HVAC engineers are turning to alternative designs  in order to temper the space in more effective, efficient and clean ways. 

A popular alternative to this traditional mixing ventilation is a method referred to as displacement ventilation.  Displacement ventilation  is an air distribution technology that introduces cool air to a space at a low velocity through larger diffusers usually located near floor level.  

By utilizing buoyancy forces in a room, generated by heat sources such as people, lighting, computers, electrical equipment, exc., this system is able to remove contaminants and heat from the occupied space.  The conditioned air is then able to migrate naturally to the heat sources of occupants throughout the room. This is due to the fact that heat drives air movement, and since our bodies naturally give off a thermal plume of consistent heat, the conditioned air finds its way to us and cools us off. 

As air conditioned air enters the space, it displaces the room air through natural buoyancy and exhausts through a high point in the room.  Because the the air is not mixed contaminant particles can be removed. 

Displacement Air Ventilation is Recommended

Displacement ventilation is a recommended ventilation system for a variety of facilities because of the above mentioned benefits.  The ASHARE has passed Addendum G to standard 170-2008 "Ventilation of Healthcare Facilities" and recognizes the use of displacement ventilation in healthcare facilities, likewise The Collaborative for High Performance Schools recommends displacement ventilation as the preferred distribution method in education facilities.

Sources: 

Erway, Joel. Engineering.com " Rethinking Air Distribution with HVAC Systems" 15 October 2013. 

Engineering Guide-Displacement Ventilation Guide" 

What’s so special about Clubhouses?

Ballen Isle Country Club
West Palm Beach, Florida

The Complexities of Designing HVAC Systems for Clubhouses  

Clubhouses are unique among buildings. They house restaurants, community centers, banquet halls, entertainment complexes, retail spaces, fitness and spa centers and even offices all wrapped up into one facility! 

Dripping Diffusers

The clubhouses' unique nature is one of the major reasons why faulty HVAC systems are common; especially in humid climates such as Florida.

Perhaps, one of the most frequent issues that engineers uncover during a due diligence survey is a facility operating under a severely negative air pressure condition.

Common Symptoms of Negative Air Pressurization  

•  A lack of fresh or clean air, instead a musty smell or other bad odors lingering in the air
• Condensation on the Diffusers
• Visible Mold or Mildew Growth along with Moisture on the Walls 
• Sticky or Damp Furnishings
• Varying Temperatures Throughout the Facility 
• Stagnant, Stale or Heavy Air that causes Humidity or Condensation 
• A Rush of Air or Draft when Opening an Exterior Door 

According to Bob Davenport, RGD Consulting Engineers' Principal Engineer, who has over 35 years of experience designing HVAC systems, "Operating a clubhouse with severely negative pressure can result in serious indoor air quality problems over time." 

Solutions

 If not caught before the start of microbial growth, negatively pressurized facility can be a costly issue to rectify. This is why having the proper HVAC equipment and a good maintenance program is important to preventing issues such as negative air pressure from occurring. 

Ensuring that the clubhouse building is equipped with 100% outside air pre-conditioner, runs continuously and supplies a constant and equal volume of dehumidified outside air to the building is key to maintaining the air pressure. 

There are a variety of methods for achieving this goal, and the most effective HVAC design system can be determined by a professional engineer after completing a thorough survey of the facility's systems. However, even the best designed HVAC systems can fail when they are not maintained. 

Just as important as working closely with an engineer for the design of your facility's HVAC system, is the creation of an aggressive maintenance program.   With these two factors planned well, your facility's HVAC system will stay balanced and healthy for years to come. 

This article is adapted from "Is Your Clubhouse Stuffy" written by Robert Davenport, PE, LEED AP + BC. 

Thermostat Wars: HVAC vs. Home Security Industries

The HVAC industry is battling with homeowners, home security and home automation companies to determine who has the authority to install thermostats as a part of "smart home systems." 

The issues has taken on new heights with several HVAC industry organizations pushing for legislation to prevent home security and other non HVAC companies from replacing thermostats with products that communicate with security and home control systems. 

HVAC companies claim that HVAC systems use exclusive protocols and special communicating thermostats to control equipment that don't follow standard thermostat configurations, protocols or wiring. 

According to Dominick Guarino, the CEO of the National Comfort Institute, this approach to this issue has little substantiation, as many home security and home automation companies have their employees complete extensive education to be able to install this technology. However,  the issue that should be at the forefront of this battle, is who is responsible if the technology is incorrectly installed.  

Guarino recommends that instead of fighting this issue on a government level,  HVAC companies should fight this battle in the marketplace through education.  Let your customers know that having a third party install an intelligent thermostat could have negative consequences.

To learn more about this issue, visit the original article here.