Open-access content Thursday 21st February 2013 — updated 3.30pm, Tuesday 26th May 2020
Graham Mills, managing director of Drumbeat Energy Management explains the process of 'thermal destratification', and outlines some of the equipment options.
22 February 2013
The ongoing trend towards higher energy prices has had several knock-on effects.
One of which has been to stimulate research into finding cost-effective ways to reduce energy consumption in the buildings where people live, work and play. However,
this can be a complicated and costly procedure.
A process called 'thermal destratification' can be used to significantly reduce energy consumption in buildings.
The fact that hot air rises and cool air falls is a basic element of physics. The reason behind this is that cooler air is denser and heavier than warm air.
This causes it to fall, and in turn, push warmer air upwards. A loft or attic living space is often far warmer than the room below; mezzanine offices can suffer from uncomfortably high temperatures in comparison to the cool factory floor below.
A major energy waste
So perhaps a more accurate statement is that 'cool air falls and heat rises'. Either way, when this process takes place indoors, it causes the coolest temperatures to gather at the floor, while warmest temperatures collect at the ceiling or roof. This layering of rising temperatures, from cool to hot or vice versa is called 'thermal stratification' and is deemed by many as the biggest waste of energy in buildings today.
The pursuit of managing and maintaining a building's internal environment and comfort levels can be a costly endeavour. The biggest cost is usually heating and cooling, normally accounting for over half of a building's total energy usage. From offices to aircraft hangars, attempts to provide ideal conditions for staff, customers and/or stock can consume vast amounts of energy, producing large volumes of carbon dioxide and resulting in expensive utility bills.
Heat accumulates at the ceiling until set temperature is reached at the thermostat, usually located at floor level. When cooling, the cool air sinks, pooling at low points. It is difficult to distribute cooled air within densely occupied buildings, such as call centres, where cubicles and workstations prevent thorough circulation, resulting in unbalanced hot and cold spots.
In both instances conventional heating and cooling systems may be over-delivering to maintain desired conditions, and this is where vast quantities of energy can be wasted.
Thermal destratification is the process of eliminating a building's temperature variations to create a uniform temperature from floor to ceiling.
This is achieved by circulating or mixing the internal air until the temperature has been equalised through the use of thermal destratification fans. This equalisation of air temperature makes the very best use of heating and cooling supplied, thus reducing energy consumption.
There are various types of fan available, some more efficient than others. Those mentioned below are the main players in the industry. All operate on the principle of keeping air constantly on the move so that temperatures do not accumulate.
The 'blade' or propeller fan
The cheapest variety, works by 'churning' the air. However, not all the air is directed downward and certainly complete destratification is not achieved. Savings in the region of 5-10 per cent have been reported
The wall-mounted box fan
These are fixed to the wall at head height and angled upwards. They work by sending air in the direction of the ceiling to push warm air gathered there to floor level. This requires very high levels of air movement. The airflow not only has to travel to the ceiling and back down to the floor, but has to do this with sufficient force to overcome the natural tendency of warm air to rise again before reaching floor level.
This type of fan has shown better results than the blade fan, but is normally restricted to industrial buildings where noise and excessive airflow are not a problem. Savings in the region of 10-20 per cent are often recorded.
The ceiling-mounted box fan
These units are fixed to the ceiling and send a significant volume of air at high speed towards the floor. Depending on the height of these fans, the impact at floor level can cover a diameter of anything between 2-7 metres. Often, this impact is not important and savings in the region of 15-20 per cent can be achieved.
The ceiling-mounted jet fan
These are installed at ceiling height and send the air through a nozzle to the floor in a slow-moving column. This latest generation of fan uses very low levels of power, due to the fact that it pushes air through only a very small space: the column. As the airflow doesn't spread out, it doesn't lose momentum. Once it reaches floor level, the airflow blankets out in all directions before rising and being re-circulated through the fan.
These fans operate at a very low decibel level, which, when combined with minimal air movement, makes them ideal for sensitive environments that would not be able to accept the other types of destratification fans. Savings of between 20-35 per cent can result, although higher levels have been recorded.
The original blade fan has been used for over 100 years. Box fans were introduced in the late 1960s and the jet fan has been available since 2005. Today, there is a type of destratification fan to fit every type of building.
If thermal comfort or temperature regulation is an issue - from car showrooms to warehouses - destratification fans are a simple, efficient and cost-effective solution.