by Katie Daniel | May 18, 2016 3:18 pm
By Andy Olson
Canada’s warehouses, manufacturing plants, and other large, open industrial facilities face unique environmental control challenges. During the country’s famously frigid winters, inhabitants often shiver at floor-level, while heated air rises into the rafters. However, in the summer, these spaces can become uncomfortably hot and sticky. They also face indoor air quality (IAQ) issues and—because of their sheer size—potential difficulties with zone-specific management.
While HVAC and building management systems (BMS) can address these problems to some extent, facilities managers now have another weapon in their arsenal: networked systems of high-volume, low-speed (HVLS) fans. By mixing heat-stratified layers of air, HVLS fans make HVAC systems more efficient, significantly improving employee comfort and health 365 days a year. They also help reduce energy consumption, combat IAQ concerns, and can even be integrated into fire prevention systems.
Spreading the warmth in winter
While most people equate fan usage with warm summer weather, their benefits in winter may be even more pronounced. Although HVAC systems do an efficient job of providing heated or cooled air to specified areas of a building, they do not optimize airflow—and, as every grade-schooler knows, warm air rises. Thus, in tall warehouses there may be an 8 to 10 C (14 to 18 F) difference between the floor-level workspace and the ceiling during the heating season as a result of warm, light air rising and cold, heavy air settling. As such, a heating system must work hard for extended periods to maintain the temperature near the floor, or at the thermostat setpoint, wasting precious energy and dollars (Figure 1).
HVLS ceiling fans mitigate the rising heat effect by gently moving the warm air near the ceiling back down toward the floor where it is needed. The air reaches the floor below the fan, where it then moves horizontally a metre or so above the floor. The air eventually rises to the ceiling where it is cycled downward again. This mixing effect, known as destratification, creates a much more uniform air temperature with perhaps a single degree of difference from floor to ceiling. Facilities equipped with HVLS fans lower the burden on the heating system, reduce energy consumption, and save money.
Conventional high-speed ceiling fans do not have this effect. Although they have been used to help circulate air for many years, they are ineffective in moving the warm air from ceiling-to-floor. By quickly spreading airflow away from the fan, little of that air reaches people working at the ground level. Thus, in facilities with traditional high-speed ceiling fans, the full benefits of the HVAC system are rarely realized.
Heat stress protection
Much of urbanized Canada experiences hot and humid weather in the summer months—presenting problems for industrial facilities. Heat stroke, heat exhaustion, and other temperature-related medical issues can also directly affect an organization’s bottom line, causing insurance and regulatory headaches—not to mention lowering employee productivity and morale. With online commerce driving an ever-faster pace of shipping and receiving, and average monthly temperatures on the rise, it is more important than ever for facility managers to take precautions to guard against heat-related problems.
While adding air-conditioning to a plant or distribution centre is the best-case scenario, it is not always practical due to cost considerations and building configurations. With or without air-conditioning, most heat-stress-prone warehouses can benefit immensely from HVLS fans.
Although smaller, floor-mounted fans can be helpful in limited areas, their high-wind speed can cause problems while their noisy operation introduces other stress-inducing factors. They also use a relatively high amount of electricity. HVLS fans, on the other hand, use relatively little energy and provide a gentle, quiet breeze that is very comforting to workers. Various studies have estimated a 3.2 to 4.8-km/h (1.9 to 2.9-mph) air speed creates a cooling sensation of up to 6 C (10 F). Air moving faster than 8 km/h (5 mph) can be disruptive and provides little, if any, added cooling benefit.
The advantage of HVLS fans is their ability to move large volumes of air and create a steady, light breeze. When the breeze reaches people during the warm months, it creates an evaporative cooling effect and reduces the effective temperature by 5 to 6 C (9 to 10 F). To put this in perspective, the effective temperature of a 29-C (84-C) warehouse environment can be dropped to 23-C (73-C) by adding a fan moving air at 5 km/h (3 mph). (For more information, see NASA’s CR-1205-1 report). This 6-C (11-F) cooling sensation can make workers up to 35 per cent more productive.
Technically advanced HVLS fans can move large volumes of air over an area up to 2044 m2 (22,000 sf). A single HVLS fan can replace as many as 10 to 20 floor fans, reducing clutter on the ground and lowering the chances of an accident. By mixing air, HVLS fans also help air-conditioning systems work more efficiently, allowing them to be operated at a lower setpoint. The breeze from an HVLS fan typically allows up to a 2 to 3 C (3 to 5 F) increase in the air-conditioning system’s thermostat setting without affecting employee comfort.
Helping fight two common air quality issues
In addition to temperature moderation, HVLS fans are also helpful in combatting two commonly experienced air-related health/safety issues:
Sweating slab syndrome occurs when moisture intermittently develops on the surface of an interior concrete slab, such as a warehouse floor. The phenomenon can increase the slipperiness of the concrete surface and pose a serious risk to the safety of workers and material handling operations. Dewpoint condensation is a common cause of this moisture accumulation. This happens when warm, humid air enters the structure through open doorways, windows, and vents. As warm air diffuses throughout the structure, it will condense on any surface at or below dewpoint temperature—which is often the floor surface. When this balmy air enters, it takes far less time to change the interior air temperature than it does the temperature of the slab. With such a rapid change in conditions, the slab temperature can easily be found at or below dewpoint.
Many large facilities provide little air movement and may exhaust interior air through roof vents, creating negative pressure in the building. Negative pressure within a structure quickly allows exterior air and other conditions to enter the building when loading dock doors are open. HVLS ceiling fans can help reduce or eliminate slab sweating by minimizing ceiling-to-floor temperature differentials and increasing the surface evaporation rate. Additionally, commercial dehumidification units can alter the interior building environment and help reduce or eliminate ‘slab sweating.’
Sick building syndrome refers to situations where building occupants experience acute health and comfort effects that appear to be linked to time spent indoors, even though specific causes cannot be identified. In contrast, the term ‘building related illness’ (BRI) is used when symptoms of a diagnosable illness are identified and can be attributed directly to airborne building contaminants. Though the causes of SBS may be unknown, most affected building occupants have clinically identifiable symptoms (e.g. headache, dizziness, and nausea), which are typically relieved soon after leaving the building.
There are various causes of SBS, which are primarily related to stagnant or dead air. These include poor building design, maintenance, and/or operation of the structure’s ventilation system.
The ventilation system in particular is often found to be problematic, and can be a source of irritants. Additionally, a poor ventilation system can result in a buildup of pollutants within the building—causing the indoor environment to have an air quality much lower than the outdoor air. Humidity may also be a factor. While high relative humility (RH) may contribute to biological pollutant problems, an unusually low level may worsen the effects of mucosal irritants and may even prove irritating itself.
Although slab sweating and SBS have different causes, they have similar solutions—at least to some degree. Increasing ventilation rates and air distribution can often be a cost-effective means of reducing indoor pollutant levels and providing relief. HVAC systems should be designed to meet ventilation standards in local building codes, but many do not. Fortunately, HVLS fans can dramatically increase their effectiveness. For example, by minimizing ceiling-to-floor temperature differentials and increasing the surface evaporation rate, they help reduce or eliminate slab sweating. For sick building syndrome, the increased air movement HVLS fans provide helps dissipate humidity and disperse concentrations of airborne contaminants such as chemical fumes, pollens, bioaerosols, or other volatile organic compounds (VOCs).
Although high-speed ceiling or floor fans can help increase air movement, HVLS fans move larger volumes of air while using less energy, and produce a less-disruptive wind speed. Additionally, having multiple floor fans can increase clutter and the chance of accidents involving equipment and electrical cords. High-volume, high-speed (HVHS) fans can be used to complement HVLS fans in smaller areas or areas where direct ‘blasts’ of air are needed for short periods, such as down rack aisles, under mezzanines, or in other spaces where it might be impossible to install an HVLS fan.
Although HVLS fans impact up to 2044 m2, many large facilities employ multiple fans to enhance environmental control. In facilities with ambient sunlight or temperature-affecting operations (i.e. loading docks) in one part of the building but not another, the fan speed, timing, and other settings may need to vary by location—creating a maintenance challenge. Fortunately, the most advanced HVLS fans can be linked into networks of up to 18, depending on the manufacturer, and run off of a single controller. This allows for independent speed adjustments, scheduled start/stop times and the ability to start/stop based on preset temperature settings—a feature that can be very important in operations such as:
An optional Ethernet port allows the system to be accessed through a remote device such as a smartphone or other mobile device. Additionally, the fans can be programmed into a building management system and connected to other infrastructure equipment such as exhaust fans. A ‘fire stop’ option is also available, in which the BMS automatically turns off the HVLS fans and activates sprinklers in the event of a fire.
The use of HVLS fans has gained increased attention as a practical and affordable solution to improve air movement, reduce heat stress, and create overall better environmental control. These types of fans are now recognized as a valuable supplement to help facility designers and engineers control energy costs and improve employee comfort and productivity. However, capitalizing on the advantages of HVLS fans does require careful analysis of each application, as well as each HVLS fan design.
Creating a more comfortable, healthier workplace clearly signals that a company’s management is willing to invest in employees and is serious about their safety, and the integrity of the products it manufactures or handles. All these factors can have a direct and significant impact on the organization’s bottom line.
|TYPES OF HEAT STRESS|
Heat stress can manifest itself in a variety of forms. While some cases are less severe than others, all are potentially dangerous. The mildest form is heat fatigue—workers begin to lose concentration and perform erratically—and heat rash—sweat ducts get plugged and skin becomes agitated and painful. People who have had previous heat rash or extreme sunburns can become more prone to this. Heat stress may also cause heat cramps, typically in the larger muscles used during work such as the back, arms, legs, and abdomen. Dehydration and electrolyte imbalance caused by prolonged sweating are typically its causes.
Heat exhaustion, heat syncope (fainting), and heat stroke are among the most serious types of heat stress disorders. Heat syncope usually happens because of a pooling of blood in the lower extremities and dilated vessels of the skin, leading to low blood pressure and sudden unconsciousness. Heat exhaustion can occur on its own or as a prelude to fainting. Common symptoms are similar to heat fatigue, but are more severe, including diarrhea, nausea, and disorientation.
Heat stroke is the most serious heat stress disorder and can be life-threatening. It occurs when the body’s temperature regulation systems fail and its temperature rises to critical levels. It can be marked by an absence of sweating, confusion, fainting, and/or convulsions. Hospitalization is critical for anyone who suffers a heat stroke.
Certain types of people are more prone to heat stress than others, including those who may be older, smaller, or exceed standard weight by 15 per cent or more.* Interestingly, men tend fare better than women in hot, dry heat, but women fare better in extreme humidity. In all cases, fitness is a benefit, while drug and alcohol abuse, high blood pressure, and chronic heart problems or other chronic diseases are a disadvantage. The pace of work is a factor across all categories as well. The more energy a worker expends, the higher the risk of a heat stress-related episode.
* See www.mayoclinic.org/diseases-conditions/heat-exhaustion/basics/risk-factors/con-20033366 for more information.
Andy Olson is a marketing manager at Rite Hite. He can be reached via e-mail at firstname.lastname@example.org.
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