Destratification Fans Explained | HeatingSave

Why do I need to know?

In a building with a large open space, such as a warehouse, hall or auditorium with a roof height of four metres or more, the air will stratify (unless you have an Air Handling Unit), which means all the hot air will get stuck in the roof space.

Heating this space without using destratification fans will mean your heating bills are much higher than they should be. Installing these bucket-like, variable speed destratification fans strategically in large open spaces will mix the air to provide a constant temperature and air quality.

How does destratification work?

Stratification can occur

naturally, through solar radiation entering windows or solar gain through poorly insulated roves and wall panels
via heating systems using radiators or ground level heating such as electric radiant fires
with the use of overhead gas radiant heaters such as black bulb types

The top diagram shows an example of a warehouse where air has stratified.

Modern destratification fans work by pushing the hot air stuck in the roof space down to ground level, as shown on the bottom diagram.

Each fan has a temperature sensor attached to the fan air intake so that the temperature of the air passing into the fan can be measured. Another sensor, or group of sensors, is installed at ground level.

BEMS control

It's important that a Building Energy Management System (BEMS) is used to control and monitor the destratification process. Choose a BEMS system that provides minute by minute recording of temperatures so that you can use the software to visualise the destratification process.

This will enable you to trim the settings to achieve full destratification whilst at the same time blowing as little air around the building as possible, to avoid complaints from employees regarding draughts and the noise of the fan (to pre-empt this it is best to buy low dB fans in the first place).

The typical setup and control of destratification fans using a BEMS is shown below. The system will measure the temperature difference ("DeltaT") between the fan and the ground level temperature, and then varies the fan speed depending upon DeltaT.

This screenshot shows a typical fan setup on a BEMS system (HeatingSave used in this example). The BEMS system needs to know the temperature sensor associated with the fan and the BEMS relay that controls the fan.

The BEMS system will then create a destratification zone for each fan or set of fans and assign the fan and sensors to this zone, as shown above.

The BMS then allows you the trim the settings with slider bars for DeltaT and a compensation for use in hot weather to provide a minimum fan speed to cool everyone.

Typically fans have EC motors with a 0-10 volts DC control, where 0 volts turns off the fan and 10 volts is full speed (typically between 1,200 and 1,800 revolutions per minute). Fan speeds faster than this can be noisy and create an excessive downdraft. EC motors are much quieter, so always choose these in preference.

Use-case example:

The Coplow Centre in Leicestershire is a large village hall/community centre with a six-metre-high hall with a vaulted roof, heated with gas black bulb heaters. Installing two destratification fans linked to a BEMS system (HeatingSave) cut the time to heat the hall and the energy costs by a staggering 90%. This was in part due to the building fabric which is concrete and steel and leaks heat like a sieve.

The Coplow Centre's HeatingSave system produces temperature and energy usage data for each minute and has visualisation software so that this can be graphed.

The graphs below show the hall apex temperatures before and after the HeatingSave system was installed. Note the air high temperatures in the roof space in the before graph. See how the difference in the roof space and the ground levels are better balanced. However, due to the poor insulation within the fabric of the building, there is still a significant difference, but this has been minimised.

If you are interested in installing HeatingSave and destratification fans in your business, get in touch with us today.