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A Guide To Destratification Heating

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01 September 2014

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The Carbon Trust estimates that the use of destratification fans in industrial buildings with high ceilings, operating a warm air heating system, can reduce energy consumption by 20%. Maximising the savings depends on the right design and using the most appropriate product. Wasting energy by not preventing stratification. This blog post gives you a guide to destratification heating and explores the considerations and benefits of installing a destratification system in your building.

Every building will experience some degree of thermal stratification, a natural process that causes warm air rises to the ceiling or roof space and displaces cooler air, pushing it downwards into the occupied space. In most workspaces, irrespective of the height of the ceiling, the occupied space where people need to be kept warm is up to around 2m from the floor. Any energy used to heat the air above this point is therefore generally wasteful. For example, in a typical pitched roof building with an average height of 5-7m, the temperature difference between the working zone and the roof space will be around 5°C. This is a clear indication of significant energy wastage, as much of the energy consumed by the heating plant is being used to heat unoccupied areas of the building – namely the roof space!

 A simple but highly effective solution is to use destratification fans working in harmony with a warm air heating system to return the warm air from the roof space back to the occupied space.

How does destratification heating work?

Increased Fabric Heat Losses

The higher temperature air in the roof space also has implications for how quickly the building loses heat. For example, the set-point temperature for the working zone may be 19°C. On a cold day with an outdoor temperature of -1°C this would provide a temperature difference between the working zone and the outside of 20°C. However, as noted above, the air in the roof space will be at a temperature of around 24°C, creating a temperature difference between the roof space and the outside air of 25°C. This is significant because the rate of heat loss is influenced by the temperature gradient. This means that the higher temperature difference between the air in the roof space and the outside air will increase the rate of heat loss through the roof membrane. Reducing the temperature of the air in the roof space will reduce the rate of heat loss through the roof membrane.

Infiltration Losses

Another issue to consider is the effect of temperature gradients on the natural rate of ventilation, whereby air enters and leaves the building through leakage points in the building fabric. It is well established that some of the warm buoyant air rising into the roof space will leave the building through high-level leakage points. This will create a small negative pressure that will have the effect of drawing more cold outside air into the building through lower level leakage points. This cold air entering the building at low level therefore reduces the temperature in the working zone so that the heating system needs to consume more energy to restore the required set-point temperature. Fabric heat losses and air infiltration are particularly significant issues in older buildings that have poor thermal insulation and many leakage points.

The Benefits Of Destratification Heating

A well-designed destratification system addresses all of these issues by ensuring effective distribution of heat throughout the space so that stratification is minimised and there is only a very small temperature gradient between the working zone and the roof space. The ability of the destratification system to reduce the temperature of the air in the roof space also reduces the rate of heat loss through the roof. For example, if the roof space temperature were reduced from 24°C to 20.5°C this would result in around a 14% reduction in the heat loss through the roof membrane. In many cases improving the distribution of warm air with destratification will make it possible to maintain the required temperature in the working zone with fewer warm air heaters, thereby reducing both capital and running costs. In industrial buildings, the destratification fans will also recirculate the heat from machinery, so that less energy is consumed by the heating system.

Furthermore, improved air distribution helps to eliminate hot and cold spots in the working zone to improve comfort levels. Destratification fans can also be used to provide cooling draughts of air during the summer.

What is Destratification Heating

Design Considerations For Destratificaton Heating

Destratification systems, whether being installed in new premises or retrofitted in an existing building, should always be designed by experienced professionals. In this way, the system will deliver optimum performance with a fast return on investment.

Key design considerations include:

  • Most suitable type of fan (see below).
  • Mounting height to prevent draughts.
  • Number of fans required.
  • Positioning for optimum air distribution.
  • Access for maintenance.
  • Noise levels.
  • Direction of air flow where mezzanine floors are present.

Types Of Destratification Fans

There are essentially two types of commonly used destratification fan:

  • Low velocity blade or propeller fan– These work by churning the air and are most appropriate for ceiling heights between 5m and 10m.
  • High velocity axial fan – These send a significant amount of air at high speed towards the floor and are best for heights of 10m to 20m.

Both types of fan can be thermostatically controlled and there are several control options available:

  • Fans only come on when heating is on.
  • Fans are controlled independently of the heating.
  • Fan operation is linked to air temperature at ceiling height.
  • Speed control to prevent draughts.
  • Summer option for cooling.

Summary Of The Benefits Of Destratification Heating

  • Improved heat distribution throughout the space.
  • Reduced heat losses through roof fabric.
  • Reduced cooling effects of air infiltration.
  • Increased energy efficiency.
  • Lower energy costs.
  • Improved comfort for workforce.
  • Potentially fewer heaters required.
  • Can be used for cooling in the summer.

What is Destratification Heating

What’s next?

To find out more about how destratification heating can reduce your energy bills, contact Powrmatic on 01460 53535 or [email protected] Or contact your local Powrmatic-approved destratification installer

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