Energy is expensive — especially when it comes to cooling. Regardless of what part of the country a processing facility is in, it is likely the owner/operator is actively looking for ways to lower energy costs while creating a comfortable place for employees to work. High volume, low speed (HVLS) fans were developed to be an efficient solution that can help reduce energy costs. When traditional HVACs system are supplemented with an HVLS fan, the fan may help a processing facility improve energy efficiency, regulate temperature in the manufacturing environment and reduce HVAC costs. Additional benefits include:
• Lower carbon footprint in the manufacturing process.
• Reduced space cooling component size and cost.
• The ability to meet space cooling guidelines such as ASHRAE, EnergyStar and LEED.
How HVLS Fans Work
People have been using fans to cool themselves long before the advent of the electric motor. At some point however, engineers became so focused on using speed to increase fan displacement — the cubic feet of air per minute (cfm) moved through a fan — that some important physics-based issues were overlooked.
First, high velocity air movement is both unpleasant and disruptive. Second, air speed beyond four or five miles per hour usually offers little if any additional cooling benefit. Instead, very slow moving air cools best in hot, highly humid conditions.
Small high-speed box fans are popular and create a pressure differential that is essential for many applications; however, where gentle air movement is the objective, pressure differential is not important. Therefore, displacement — the amount of air that actually moves through the fan — is of no real significance. It is the downstream effects that are important.
A turbulent, high velocity air jet dissipates very quickly. A large column of air, however, “travels” farther than a small one. The friction between moving air and stationary air occurs at the periphery of the moving column. The perimeter of a column varies directly with column diameter. While the cross-sectional area varies with the square of the diameter, the large column has proportionately fewer peripheries and therefore less drag. The air column from a 3-foot diameter fan has more than six times as much friction interface per cubic foot than the air column from a 20-foot fan. This is why a large, slow moving fan actually cools better and more efficiently than a small, high speed fan.
When the down column of air from an HVLS fan reaches the floor, the air turns in the horizontal direction away from the column in all directions. The air flowing outward is called the horizontal floor jet. Because the height of the floor jet is determined by the diameter of the column of air, a larger diameter fan naturally produces a larger air column and, thus, a higher floor jet. Smaller high-speed fans of equivalent displacement are incapable of producing the same effect.
The power to drive a fan increases roughly with the cube of the average air speed through the fan. A small, high speed commercial fan that moves air at 20 miles per hour requires about 64 times as much power as a large-sized fan moving air at 5 miles per hour. Air speed, combined with fan effectiveness, means that when the objective is to cool people or products, very large, low-speed fans are more efficient and effective than small, high speed fans.
One HVLS fan consumes about the same amount of electricity as one high speed fan while moving more than 12 times the amount of air.
How HVLS Fans Help Regulate Temperatures
Air quality is important in every facility. Indoor air, when it is not continuously mixed with fresh air, becomes stuffy and smelly, and temperatures can increase quickly if not checked. Indoor air quality and temperature can affect employee comfort and ultimately productivity. Workplaces also are in constant flux due to production, and stock movement and distribution face ongoing temperature battles. Large-size HVLS fans can help regulate temperatures due to a principle of thermodynamics on which the technology was developed: latent heat.
When considering adding an HVLS fan to supplement the HVAC system for equipment and space cooling, there are several items to consider. Prospective users should compare HVLS fans and manufacturers to ensure they are getting the best performance for the application and need.
• Performance Needs. Take a good look at the facility space and existing cooling systems to see which HVLS fan best meets the needs. Can you take advantage of natural ventilation, or do you need to supplement a forced-air system?
• Installation. Building parameters, support beams or structures, clearance requirements and built-in control features will all affect installation and, ultimately, a fan’s performance. To maintain continuous air exchange, installing one HVLS fan per 20,000 ft2 of space is recommended.
• Customer Service and Warranties. The HVLS fan manufacturer selected should be just as available as the representative group selling you the fan, and the manufacturer should help you have a good understanding of the warranty coverage.
Supplementing traditional space cooling systems with HVLS fans provides an efficient solution to help reduce energy costs, increase energy efficiency and keep indoor temperatures balanced and regulated within any industrial application.
Cooling Terms Defined
To fully understand how latent heat makes high-volume, low-speed (HVLS) fans an alternative to traditional cooling systems, one must first understand how heat can be exchanged through objects — even humans — in work environments.
Sensible heat is heat exchanged when the temperature changes, for example, in a room. When an object is heated, its temperature rises. The increase in heat, which causes the temperature to rise, is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat that is removed also is called sensible heat.
For example, it takes 1 BTU to heat 1 lb of water by 1°F. Traditional systems like air-conditioning systems have what is called a sensible cooling load to overcome as it works to cool a room. To be effective, these systems must battle glass doors and windows, sunlight through skylights, area partitions, ceiling heights, roofs, air infiltration, and heat from humans in order to lower the temperature in the room.
Latent heat is the exchange of heat that occurs with a change of a state of matter. All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor), but changes such as these require the addition or removal of heat. The heat released when water vapor condenses to water (changes state) is about 1,060 BTU (British thermal unit measurement), a thousand times greater than the 1 BTU of sensible heat example.
Evaporation and Air Movement
Latent heat of vaporization cannot happen if the moisture is not allowed to evaporate. Stagnant, humid air on moist skin hinders evaporation and therefore reduces the latent heat absorbed.
Consider the fact that moisture on your skin is potential energy (heat) waiting to be used to help cool your body. The introduction of moving air, through HVLS fans, removes the stagnant, humid air from moist skin, allowing evaporation to take place, thus increasing the latent heat absorbed (in this way, the potential energy is released). The old air near our bodies is replaced by drier air that can continue to absorb evaporating sweat.
By assisting air conditioning units to continuously mix incoming fresh air with stale air, HVLS fans minimize the total amount of ventilation required to achieve adequate air quality, and use less energy, which helps lower HVAC costs.
HVLS fan technology helps products and machinery balanced and controlled at the correct temperatures and keep employees comfortable, safe and productive.
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