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.

Do We Need More Engineers?

The Engineer Debate:
Quantity vs. Quality

According to the Bureau of Labor Statistics, the number of science and engineering jobs in the U.S. is expected to grow more than 1 million between 2010 to 2020. What's more, it is expected that the nation will need 1.3 million of these professionals to replace workers who are exiting the field.

Despite these statistics, engineering ranks number 6 on the hardest jobs to fill in the U.S. As many firms struggle to find competent employees to hire.  The question is why, when there seems to be so many engineers looking for employment and so many eager firms looking to hire?

It is this question the PE Magazine attempts to dissect in their October issue.  So who is right? Does the U.S. need more engineers or fewer engineers? And does the problem stem from the lack of preparation of our graduates or does responsibility rest on the unrealistic expectations of firms who are hiring?  

Perhaps both are to blame.  Here is a breakdown of some of the noticeable deficiencies of graduates with engineering degrees along with the firms seeking to hire:  

The Graduates 

• The large majority of graduates lack  field experience, which means firms must invest a substantial amount of time training recent graduates. 
• There is no universal software used by every firm. Often graduates aren't familiar with the software utilized by the firm they are applying to because often what they use in their classes is not always the same. 
• Lastly, graduates lack initiative on the job, which if a sought after quality by most firms. 

The Employers 

• One of the major problems with employers is that they desire something unavailable in the market place. As experienced engineers with the technical skills they require often have secure positions and/or expect substantial wages for their expertise. 
• Likewise, employers have unrealistic expectations for their new hires.  
• Lastly, many employers don't want to pay what it may take to secure talent. 

What's the Solution?  

There isn't a perfect solution, but clearly the academic and professional world must work together to overcome these difficulties.

Engineering curriculum should require students to partake in an internship for a semester, which is common for degrees like education.  Likewise, engineering firms must recognize that perfection does not exist. Instead, new hires must be viewed as the investment that they are.  It may take years for the new hire to reach its full productivity comparable to the employee's salary. 

Tell us what you think?
Should companies be concerned about the potential lack of engineers or is it simply a result of inefficient preparation of graduates or unrealistic expectation?

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" 

HVAC Commissioning--Why You Need it

HVAC commissioning can enhance the lifespan
 of your mechanical equipment. 

What is HVAC Commissioning?  

HVAC commissioning is a thorough and comprehensive testing of a mechanical system's performance.  Many owner's are less than eager to spend more money, when they are already spending money to the contractor or engineer to fix the problem.   What most owner's don't realize is that commissioning can extend the life of equipment, while reducing operating costs and increasing the comfort of occupancy.

While the equipment should be properly installed in theory, there is not always sufficient evidence that the system is operating as optimally as it was design.  Varying operating conditions can certainly affect the equipment's ability to function properly.  It is usefully after the installation that the user discovers problems, and many times will attempt to fix the problem with patch and it makes it impossible to go back to the original intent of system.

Commissioning Process

Typically the commissioning contractor is the original contractor who installed the work, while the commissioning agent is the engineer who designed the project or was involved with the design process. The agent will stimulate a variety of operation conditions and work with the contractor to determine if the system is responding properly.

If discrepancies are noted, they will be diagnosed and resolved during the commissioning process.  Once, this is completed, the equipment is turned back over to the owner in perfect condition and in mechanical systems should be commissioned.

Any project with an automatic control of mechanical systems should be commissioned including:

• air conditioning unit 
• heating or cooling plant upgrades 
• project involving replacement or installation of automatic valves or dampers
• any installation or replacement fans, heating and ventilating units and duct heaters 

Looking for a competent engineering firm to commission your mechanical system?  RGD Consulting Engineers has 35 years of experience and can make sure your facility is operating effectively and efficiently.  

Autodesk to Acquire Structural Fabrication & Detailing Technology from Graitec

Autodesk, Inc. has signed an agreement with Graitec shareholders in order to acquire certain technologies, including Graitec's Advanced Steel and Advanced Concrete product lines and employees.  This addition to Autodesk will further enhance their product offers for structural engineering along with their portfolio of technology for Building Information Modeling (BIM) for structural fabrication and detailing.

According to Amar Hanspal, Autodesk senior vice president of Information Modeling and Platform Products, Autodesk is committed to offering its users the most comprehensive engineering tools.  The acquisition of Graitec technology "will provide our customers with a more seamless structural engineering workflow from design to fabrication and to construction, with enhanced offerings for structural steel and concrete detailing." 

Graitec, a company based out of France,  provides CAD and engineering software for structural engineering, civil engineering and building construction globally. Its products support BIM-based steel and reinforced concrete workflows.  The company will continue to produce  BIM software and services to complement Autodesk, so that the industry can continue to pursue maximum efficiency and performance. 

The acquisition is likely to occur at the close of the 4th quarter of the fiscal year 2014. 

This article was derived from the press release titled "Autodesk Signs Agreement to Acquire Structural Fabrication and Detailing Technology from Graitec, published on October 2, 2013 in Market Watch. 

Solar Powered Systems Give Hope for Developing Countries

Solar Powered Sterilization System developed
by researchers at Rice University. 

For developing countries, the basic amenities are a rarity often taken for granted by those who are privileged enough to use them on a daily basis.

However, technological advancements, such as solar power systems, are giving hope that one day developing countries may have access to electricity, sewage treatment and other services.

Researchers from The Rice University Laboratory for Nanophotonics in Houston, have developed a solar-powered sterilization system that uses nanometerials to create steam from water.  This system has the ability to convert as much as 80% of sunlight's energy to heat that is capable of killing germs. Researchers are optimistic that this system could help countries that lack sanitation.

In a report published by the Proceedings of the National Academy of Sciences, when the system is used in conjunction with a specially designed autoclave, it is capable of sterilizing medical instruments and sanitizing human waste.  The setup can reportedly handle the waste of a family of 4 with two treatments a week.

According to Naomi Halas, one of the team leaders, a professor and fellow nanophotonics researcher at Rice, the ability of the solar system to efficiency convert sunlight into steam, opens the door for sterilization systems that are independent of electricity.

The efficiency of the system originates from the use of light-harvested nanoparticles. These particles heat up so quickly that they instantaneously vaporize the water and create steam, all before the water even boils.

This system is more than 24% energy efficient. This is even more remarkable when compared to the photovoltaic solar panels, which have an energy efficiency of around 15%.

The heat and pressure created by the steam also sufficiently kills microbes as well as spores and viruses.

This article was derived from the headline "Focused Attention," which appeared in the October 2013 edition of Mechanical Engineering.