Air movement can have a significant influence on human thermal comfort.
- Wind chill in cold conditions is considered detrimental.
- Air movement in neutral to warm environments is considered beneficial.
This is because normally under conditions with air temperatures above 23C, the body needs to lose heat in order to maintain a constant internal temperature.
“Unlike air conditioners,
which cool rooms,
HVLS cool people.”
Synthesis fans increase air speed at the occupant level, which facilitates more efficient heat rejection, cooling the occupant, rather than the space. Elevated air speed increases the rate of convective and evaporative heat loss from the body, thus making the occupant feel cooler without changing the dry bulb temperature of the air.
In Winter, hot air is less dense than cold air, which causes hot air to naturally rise to the ceiling level through a process called convection.
Where there is still air, layers of constant temperature is formed – the coldest at the bottom and the warmest at the top. This is called stratification.
The most efficient and effective way of mixing air in a stratified space is to push the hot air down to the occupant level. This allows for complete mixing of the air in the space while decreasing both heat loss through the buildings’ walls and roof and building energy consumption.
Large diameter fans can move more air than smaller fans at the same speed and the air from the large fan will travel a lot farther then the air coming from the smaller fan because; a turbulent, high velocity air jet dissipates very quickly while a large column of air travels farther than a small one due to the friction between moving air and stationary air, which occurs at the periphery of the moving column.
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”.
Since 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.
Synthesis Fans can also help in combating two common air-related health/safety issues: sweating slab syndrome and sick building syndrome.
Sweating slab syndrome (SSS) is a phenomenon that occurs when moisture intermittently develops on the surface of an interior concrete slab. It can increase the slipperiness of the floor and increase safety risk for workers. Dew point 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 that warm air diffuses throughout the structure, it will condense on any surface that is at or below dew point temperature—which is often the floor surface.
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.
Sick building syndrome (SBS) refers to situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building.
There are a variety of causes for SBS, 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 at the heart of the problem and can itself be a source of irritants. In addition, a poor ventilation system can result in a buildup of pollutants within the building, in which case the indoor environment can often have air quality much lower than the outdoor air. Humidity may also be a factor. While high relative humility may contribute to biological pollutant problems, an unusually low level may worsen the effects of mucosal irritants and may even prove irritating itself.