Syed Taqi Hussain, while giving tips to improve the quality of controlled air, says that Variable Air Volume box is a smarter way to control indoor space temperature.

The major function of an air distribution system is to provide comfort to building occupants. This article seeks to help specifying and design engineers create better zone comfort.

People are thermally comfortable when their body heat loss equals their heat production, without them sensing any changes in the temperature.

ASHRAE defines comfort as:

• Maintaining a temperature of 22.7°C (73°F) – 25°C (77°F)
• Relative humidity of 25% to 60%
• Maximum velocity in the occupied zone is 50 FPM

HOW DOES AN ENGINEER DETERMINE CFM?

The cooling or heating load (BTU/Hr) in any space determines the quantity of air (CFM) that the space requires to satisfy the heat gain or loss. ∆T (Delta T) is the difference between the supply of air temperature and the room temperature, and is called the temperature differential. As the load changes and goes either up or down, CFM demand too changes. Thus, the need to change the CFM to match the load changes in a given space.

The devices most commonly used to control the load or air volume to a zone are called Air Terminals – Variable Air Volume (VAV).

VAV boxes and their controllers are the most essential components of an HVAC system to achieve indoor comfort. Their proper selection and operation is, therefore, essential for optimum temperature control.

At present, bypass VAV, pressure independent VAV and CAV are the most commonly used types in the market. Apart from the standard types, other types include, parallel fan-powered induction, dual-duct air terminal units.

Bypass terminal units:

These units are designed to achieve variable air volume delivery of conditioned air to a room through a single duct. These are constant volume air distribution systems. Variable air volume control is achieved by directing the airflow either to a room or to a bypass port in direct response to signals from the room thermostat, and is the modulating type.

Pressure independent VAV:

Here, the temperature in the room is controlled by varying the amount of supply of air introduced into the space.

Pressure independent CAV:

Here, the temperature in the room is controlled by varying the temperature of the supply air introduced into the space, keeping the amount of air supplied as constant.

In a pressure independent system, the most important factor for the best performance of VAV is the selection of an accurate flow sensor. In multi-point averaging flow sensor with flow sampling of both velocity pressure and flow, the differential pressure provides precise air flow calculations.

As conditioned air enters the terminal unit, the sensor calculates velocity pressure in W.C (Pv) and converts its value to CFM. A signal is sent to the actuator, which then adjusts the damper shaft to open or close to reach the desired CFM (Min/Max/Constant).

While selecting air terminal units, the information provided on a schedule is critical. Without complete information, you will be forced to make assumptions which will probably lead to product performance problems at the job site.

An improper pressure drop assumption could lead you to believe that you are not able to meet the consultant specification. Apparent NC levels, therefore, may seem to be unattainable.

The most important information which an engineer needs while selecting a VAV unit include:

• Maximum CFM
• Minimum CFM
• Fan CFM (Fan-powered terminals)
• Primary supply pressure
• Sound performance criteria
• Heating requirements

UNDERSTANDING PRESSURES

Primary supply pressure is the system pressure provided by the central air handling equipment to the terminal unit inlet damper.

Minimum pressure is the minimum primary supply pressure required to deliver a given CFM at a given pressure.

Downstream static pressure is the pressure that is measured or specified downstream of the terminal unit, as it is demonstrated in figure 2:

Noise criteria (NC) and values:

The NC value of a terminal unit at a specific flow is absolutely dependent upon the primary supply pressure. If you do not know the primary supply pressure, you cannot estimate the NC. Given below is a list that could be helpful:

• General offices: NC 30 to NC 35
• Open-plan-office areas: NC 40
• Conference rooms: NC 30
• Auditoriums: NC 30
• Lobbies and corridors: NC 40
• Executive offices: NC 25 to NC 30
• Computer/equipment rooms: NC 40 to NC 45
• Classrooms: NC 25 to NC 30

HEATING CALCULATIONS

In order to obtain the desired temperatures in any occupied space and to provide the needed heating capacity, duct heaters are used in line with the VAV boxes. The heater capacity is selected as per the details provided below:

• kW = Power in kW
• CFM: Air volume in cubic feet per minute
• T°2: Temperature of air leaving heater
• T°1: Temperature of air entering heater

Duct heaters can be selected for the best performance as per the criteria given above:

CONTROLS AND CALIBRATION

The majority of controls installed in HVAC systems today are Direct Digital Controls (DDC). The controls can be DDC or application-specific controllers (VAV controllers). It is recommended to have controls supplied by the VAV manufacturer with complete calibration and testing from the factory. This procedure benefits the MEP contractors during testing and commissioning. The boxes are calibrated for min/max/constant flow as per the required schedule. And if used for a BMS project, the MAC address/device number is factory-set with a proper tag on each VAV unit.

Armed with the above information, an engineer or the contracting company in-charge of providing quality indoor space conditions, can serve the clients and end-users better. After all, in the final analysis, the aim of MEP contractors and consultants is to strive to provide perfect indoor space conditions through their products, services and expertise.

The writer is Product Manager, VAV & Controls Energy Industrial Company, Representative – Metalaire, USA. He can be contacted at: taqi@energyind.ae

Prakash Krishnamoorthy, Sales Manager (Middle East Area) at Carrier Transicold Europe – Gulf Office, was a presenter on Day 2 of Food Chain UAE. Here, in Part 3 of our continuing coverage of the seminar, we bring to you excerpts from his presentation from a transport refrigeration perspective on cold chain management, in which he addressed critical issues of concern …

A chain is only as strong as its weakest link. Any interruption to the cold chain constitutes a hazard to the health of the consumer, because it ought to be remembered that cold does not kill microbes, it just slows their development. Hence, a robust cold chain is not just essential but critical.

Prakash Krishnamoorthy

So what are the general risks associated with refrigerated transportation in the event of an interruption to the cold chain? There are three types – microbial, chemical and physical.

In the case of microbial risk, a cursory glance at the temperatures of the principal pathogens where multiplications stops, does tell quite a story. For the toxicogenesis of staphylococci and Clostridium botulinum A and B, the temperature is +10°C. It is -12°C for all bacterial multiplication and -18°C for microbial multiplication. In short, owing to the clear danger from microbes, any interruptions in the cold chain, even for a short period of time, are hazards for consumer health.

Chemical risks are owing to accidental contact with a non-food substance, such as lubricating oil spilt on the floor or on cooling units. Also, presence of residues from cleaning products or disinfectants can lead to chemical risks.

Physical risks are caused by solid particles of various types and sizes. Air-borne dust circulated by a unit’s fans, or introduced via the air vent or when the vehicle doors are opened, is one such situation. Also, dirt from vehicle floors, refrigerating chambers and handling areas can lead to contamination. As far as physical risks are concerned, the moral of the story is: the vehicles must be clean and the packaging adequate.

At this juncture, it is worth looking at ATP (Agreement on International Transport of Perishables Foodstuff), which is regarded as a key regulating body of the transport refrigeration industry. ATP is basically the agreement on the international carriage of perishable foodstuffs and on the special equipment to be used. The first ATP regulation was defined as far back as 1971. Seven countries signed the regulation. From 1975 onwards, there have been progressive agreements among 35 additional countries, including the United States, and belonging to the European Union, Eastern Europe and Northern Africa.

ATP’s mission is simple: Ensure the minimum equipment specifications for international transport and ensure the quality of perishable foodstuffs during their transportation.

ATP’s regulations, revised each year by a UN working group, are applicable to all national and international transport activities.

ATP stakeholders include box manufacturers, unit manufacturers, installers and transporters.

In the case of box manufacturers, ATP stipulates that in the case of isothermic devices, the coefficient of heat transfer (k) must be certified by a test in a tunnel by a certified laboratory. And in the case of carriers, the refrigeration capacities must be certified for each model by an authorised laboratory; the test results are valid for six years.

In the case of an assembler of a refrigerated vehicle, which basically constitutes the box and the refrigerated unit, the refrigeration unit should have a safety coefficient > 1.75, which corresponds to a pull down time of six hours to reach -20°C with a 30°C ambient. A higher safety coefficient is considered when chilled produce are involved, as many are extremely temperature sensitive.

And in the case of a transporter, the refrigerated vehicle must have an ATP certificate delivered by an institution with a governmental agreement (TUV in Germany, Cemafroid in France and CRT in the United Kingdom).

The transportation temperature of the products, according to their nature, must be specified.

• Class A: set point from 12°C to 0°C
• Class B: set point from 12°C to -10°C
• Class C: set point from 12°C to -20°C

A key element in transport refrigeration is a set of loading practices for goods. We need to keep in mind that transport refrigeration is designed to only maintain temperatures and not to cool the product. Poor air distribution is one of the primary causes of product deterioration.

Typically, the sources of heat ingress are conduction (from the product), convection (through open doors) and radiation (through the trailer floor, sides and roof). Hence, a simple action like trying to park the vehicle in the shade, when not in use, helps remove the heat that has entered the body from the sun.

The loading should be done after pre-cooling the box to the desired temperature. Care should be taken to ensure that products are always loaded at the correct temperature and that they are loaded from a refrigerated bay. This is extremely critical to maintain the cold chain.

The benefit is as much in the details. For instance, care should be taken to ensure that fresh produce are not wrapped in plastic, as doing so prevents air circulation from reaching the load.

It must be ensured that the evaporator is not obstructed with the loaded goods and that air circulation is not impeded at all times. Equally important, it is essential to defrost 30 minutes after loading for fresh products and to stop the unit at the time of opening the doors.

Correct pallet use is also part of transport refrigeration best practices, wherever used. For instance, orientation should allow airflow to the head of the body. Pallets should allow airflow through and under the load. Airflow down the side of the load (minimum 25mm airflow around the sides of load, and preferably 50) is important. Airflow from the rear door (minimum 100mm from the rear door) is equally important. A word of caution: loading to the ceiling will cause short cycling.

Correct loading

Generally speaking, correct loading means not mixing refrigerated and dry goods in the same compartment. Speaking of which, in the event of a second compartment, it should not be cooled by a fan from the first compartment for good hygiene and to maintain better temperature control.

Speaking of hygiene, transport refrigeration is as much about the personnel involved. They should be trained to uphold hygiene rules, cleanliness, cold chain and products temperature. Personnel health should be controlled regularly, and this includes the wearing of clean clothes.

The loading personnel must control:

• The cleanliness of the inner sides (walls, roof and floor)
• Product temperature before loading
• Proper product packaging
• Separation between non-packaged food and packaged food
• Separation of incompatible products

Refrigerated transport is a very important link in the cold chain. Higher risks of cold chain failures occur during transportation, as the environment – in the forms of speed and external temperature, to name two – changes continuously.

Risks of cold chains failures can be minimised by following ATP standards and by respecting good loading and hygiene practices. Doing so will lead to improved quality of transported products and consumer health protection.

Company signals an intent to paint pharaoh-land green

Jotun Paints has announced that it is looking towards strengthening its market presence in Egypt with the introduction of its revolutionary ‘Green Single Source Solution’ concept across the country’s increasing number of construction and development projects. The company said the move reflects its commitment towards supporting the call for more sustainable buildings and infrastructure projects in the country. The ‘Green Single Source Solution’ is part of Jotun’s strategic initiative to provide a holistic approach to high quality and cost-effective paints and coatings solutions that are energy efficient and have low Volatile Organic Compounds (VOCs), to ensure less impact towards people’s health and the environment, the company said.

According to Jotun senior executives, the increasing number of construction and development projects in Egypt is accompanied with the call to implement more green building policies and guidelines. The company believes that paints and coatings to be used in these current and future crops of projects should leave less of a carbon footprint and offer key advantages like durability, high performance, energy efficiency, and a strong capacity to minimise impact on air quality and add more aesthetic value to a project. In line with this, the manufacturer is launching the ‘Jotun Green Paint System’, which includes paints that qualify for many Green Building Rating Systems that are widely being followed across the globe. The launch follows the company’s recent participation as one of the main sponsors of the ‘Cost-Effective Sustainable Design and Construction Exhibition’, which was held for the first time in Egypt.

“Egypt is currently experiencing rapid growth and development in its construction sector, with investments expected to grow to around US$ 7.3 billion by 2015, said Tor Hatlo-Johansen, General Manager, El-Mohandes Jotun Egypt.” He added: “The anticipated entry of strategic infrastructure projects over the next five years comes with the growing demand for buildings and other development projects to be more ‘green’ compliant. Developers are now hiring architects and consultants with local experience and knowledge of designing and constructing energy-efficient and sustainable projects. The three things at the top of everyone’s agenda are sustainability, efficiency and cost. To meet this demand, Jotun is introducing the use of its ‘Green Single Source Solution’ as an effective measure that adds more ‘green’ value to these current line of projects.”

Company extends Toolbocks facility for BlackBerry, Android

After introducing Toolbocks, a refrigeration app for the iPhone, GEA Bock has offered it now also for Blackberry Smartphones and phones with the operating system, Android, the company recently announced.

Apps, as the small programs for smartphones are called, are growing in popularity and offer applications and compact information about various topics. Whether it is sports, news, routes or calculations, the information that is sent to the mobile device can be accessed directly, no matter where the user is located, and quickly ensure the latest news or advice.

By now, there exist additional smartphone platforms apart from the iPhone with its system software IOS that are increasingly used – in the business area mainly the BlackBerry devices by the company Research in Motion and the Google operating system, Android. GEA Bock also has recognised this trend and, thus, has offered its customers and all experts the possibility, to access the refrigeration App Toolbocks via the BlackBerry App World and the Android Market, the company said.

Clearly structured and easily understandable the Toolbocks helps with the conversion of the most common units and is, therefore, a helpful tool for all work around the compressor, the company said.

Hybrid sealant, advocates claim, seals, eliminates moisture threat and highlights larger leak holes for repair

Most HVAC&R service techs that are refrigeration leak sealant advocates, say they’d rather fight than switch from the practice of sealing microscopic system leaks with conventional sealants.

However the next generation of sealants – those with a combination sealant, drying agent and dye – are quickly converting even the staunchest regulars of the original sealants.

North American HVAC&R wholesalers on the front lines of the trend say service techs are buying more combination sealants than sealant-only leak applications. “We see a major trend in leak repair where HVAC&R service techs are switching from just sealants to the newer all-in-one sealant applications that also have a drying agent and a dye in it,” said Larry Baker, Branch Manager, of the Baton Rouge (in the US state of Louisiana) branch of Appliance Parts Inc, an HVAC&R distributor with eight locations throughout Louisiana.

Patrick O’Donnell, President of HVAC&R contractor, LoneStar Heating & Cooling, in Houston, Texas, has used conventional sealants since they were invented in 2002. Although he has had hundreds of successful applications of the original sealants in the field, O’Donnell immediately jumped on board when manufacturers began combining sealants with drying agents and dyes in 2009. O’Donnell, whose business is 70% commercial with a specialty in foodservice and restaurants, has used the hybrid sealants in everything from  rooftop package units, split air conditioning systems, walk-in coolers, reach-in refrigerators, prep stations and other refrigeration units.

“It’s a no brainer,” said O’Donnell, who has switched to the new type of sealant. “You seal the system and the drying agent removes any moisture to protect against waxing and acid formulation. Then, if the system develops a different leak sometime in the future, the residual sealant in the system’s refrigerant and oil seals it immediately when it leaks out with the refrigerant. If a future leak is larger than 300 microns (the size of a dot made by a ballpoint pen), the advanced flash dye in the system highlights the leak area for detection when using an ultraviolet light and expedites the time-consuming task of finding refrigerant leaks.”

O’Donnell had a couple of clogged metering devices in the past with the original sealants, but he attributes that to previous service companies he suspects exposed the system to moisture that reacted with the sealant inside the system. Today, with over 50 applications of the new sealant, by Cliplight, O’Donnell said he hasn’t had any moisture issues, nor has he had to perform the time-consuming triple evacuations recommended with the original sealants, even on R-410A systems. “You never know who was on a job previously and if they used poor installation practices, so one reason we switched to Super Seal Total was it eliminated the system moisture,” said O’Donnell. “And if you need dye in a system, there’s no mess. Just connect the vacuum-packed can to the low side and contents mix with the refrigerant and oil. You never touch or see the dye unless the system leaks someday.”

Strengthens its engineering team in Jordan

Victaulic, manufacturer of mechanical pipe joining systems, headquartered in Pennsylvania, has announced the appointment of Anas Ghaith to expand its engineering team in the Middle East market. Ghaith joins Victaulic from a major mechanical engineering company, where he was a project engineer, the announcement said, and added that Ghaith, who holds a BSc in Mechatronics Engineering, brings with him a raft of relevant professional experience in technical support, project management, design, inspection and sales.

In his new role as Sales Engineer, Ghaith will be responsible for expanding the already growing market for mechanical piping technology throughout Jordan and delivering increased technical support on projects, said Victaulic.

Commenting on his appointment, Ghaith said, “I am settling into my new role with Victaulic and very much enjoying using my experience and knowledge to grow market share for a very interesting and innovative range of products.”

Trane has announced that it has acquired the services of a distributor for Qatar. The distributor, Doha-based Qatar Electromechanical Solutions (QEMS), came on board in June 2011 and will look after the Residential and Light Commercial range of the business, the company said. Trane’s Doha office will look after the Applied side of the company’s business.

Saudi Arabia-based Super Cool KSA has reiterated its status as dealer and distributor of specialised products onto the Middle Eastern market.

These include Solar Gard and Armorcoat products, first launched in the Kingdom in 2003.

According to the company, Solar Gard architectural films are famous for their high-quality manufacturing, heat-reflection capabilities and professional installation, which contribute to energy conservation.

Armorcoat safety film is “a proven cost-effective glass retrofit to counter terrorism, vandalism or even smash & grab thefts, thus increasing the life of the glass and protecting investment,” the company claims.

Company says flex ducts meet higher thermal requirements

ATCO Rubber Products, manufacturer of flexible ducts used for HVAC systems for residential and commercial applications, has stated in a communiqué that governments, local jurisdictions and utility companies are increasingly putting a premium on thermal performance, and demand higher thermal performance ratings on all duct insulation products. In the light of this, the manufacturer has said that it has developed products with industry standards, and supplies flex ducts that have varying R-values to meet higher thermal requirements.

The company has further stated that its insulated flex ducts are labelled with R-values classified by Underwriters Laboratories and the Air Diffusion Council (ADC) Seal of Certification. With 13 shipping locations coast-to-coast, ATCO claimed that it can deliver flex ducts with the necessary thermal ratings to a wide area.

The company claimed that in the region, the manufacturing plant, ATCO ME, located in Sharjah, made all its flexible ducts as per the UL certification. It said that it produced the inner cores and outer vapour barriers as per the guidelines of the UL listing, while the UL-recognised fibreglass insulation, made especially for flexible air ducts by Owens Corning, is shipped from the United States to comply with the requirements. The finished air duct is assembled in the Sharjah plant, with UL guidelines being followed at every step to maintain the UL listing as a Class 1 air duct.

Apart from this, the company said that its rubber and polyester core duct products have received the Greenguard school indoor air quality product certification, which states that ATCO’s products are designed to be “low emitting” in regard to volatile organic compounds, including but not limited to formaldehyde. The wide variety of flexible ducts that it offers meet stringent requirements of different countries, said ATCO.

Company says the new feature will lower inlet air temperature by up to 20ºC, and will enhance efficiency even in high-ambient conditions

Cooling systems operating outside design parameters typically run an increased risk of breakdowns, higher energy costs and lower operational efficiency. In view of this, Trane recently announced the introduction of an adiabatic cooling feature to help building owners and facility managers achieve optimal operating performance and energy savings.

Trane Adiabatic Cooling, the company claimed, improves HVAC system reliability and efficiency by decreasing the temperature of the air entering the coil. The air temperature reduction generated by adiabatic cooling can reach up to 20ºC. A mere 10ºC temperature drop generates an average of 13% reduction in power consumption, delivering immediate cost savings and environmental benefits, Trane said.

The adiabatic cooling concept uses the cooling properties of water by intermittently evaporating water on a large mesh in front of the coils, while preventing the water from actually reaching the coil. As a result, the air temperature drops before it reaches the condenser. Adiabatic cooling directly contributes to HVAC efficiency, helping the system maintain full load even during peak season. Occupant comfort increases, as the system operates at full capacity at all times, regardless of the ambient conditions, Trane said.

Implementing adiabatic cooling ensures reduced discharge temperature, as well as lower oil and motor winding temperature, Trane said, adding that these factors contribute to compressor and overall system reliability.

“Trane Adiabatic Cooling helps customers address the operational challenges that prevent a facility from reaching maximum efficiency, reliability and comfort,” said Jose Laloggia, service and parts leader for the Trane commercial business in Europe, Middle East, India and Africa. “Adiabatic cooling is designed to be flexible, simple to install and economical with very limited maintenance required so HVAC system performance can reach optimal levels.”

Adiabatic cooling provides the greatest energy relief to building owners and facility managers with systems operating in adverse conditions, the company added. Examples include environments with extremely high ambient temperatures, regular sand or dust storms, or a limited power supply. Locations dealing with air recirculation as a result of undersized installation clearances between units will also benefit, Trane added. Other applications include systems retrofitted with the high-pressure refrigerant R404a, which limits ambient air temperatures.

The mesh provides shading to the coils, thus avoiding the solar radiation effect. It also acts as a self-cleaning filter protecting the coils. The sectional mesh design allows adiabatic cooling to be installed in a wide range of air-cooled HVAC systems, from mini-splits to chilled water systems, Trane said.

The water spray system works with normal main pressures; a water pump or water treatment are not required, Trane said, adding that a dedicated controller ensures minimal water consumption.