New research from the University of Liverpool’s Engineering Department has discovered that heating power savings of over 40% can be achieved in a heated warehouse with the use of high-volume, low-speed (HVLS) fans.
HVLS fans are a new generation of very large, ceiling mounted multibladed de-stratification fans, of up to 7.3 metres in diameter, that move slowly, using minimal power.
Researchers from the university modelled the airflow and heat transfer in a heated warehouse building to investigate the levels of de-stratification offered by high-volume, low-speed (HVLS) fans, and reported that for “an outside temperature of 4°C, the analysis has indicated heating power savings of between 40 and 45% when the HVLS fan is deployed.”
The researchers report that “thermal stratification occurs in heated buildings due to the natural buoyancy of warm air, causing heated air to rise and gather at the ceiling.” Roughly speaking, this results in temperatures increasing by 0.5°C to 1°C each metre from the floor to the ceiling. The effect causes energy wastage due to the fact that most of the room (above the height of the thermostat) is heated to a higher temperature than the thermostat set-point, located much lower in the building.
Effectively, power is being wasted heating the roof space to between 7 and 15°C higher than the working area in a 15 metre high warehouse.
However the study shows that HVLS fans can successfully reduce this wastage. HVLS fans are typically located close to the roof and provide thermal de-stratification by pushing the warm air down towards the ground. This creates convection currents and also encourages mixing between the warm and cold air, leading to a more uniform temperature distribution and less energy wastage.
The researchers found that there was very little difference in temperature between the working level and the upper levels of the warehouse when a HVLS is installed. This means that in order to achieve a comfortable working temperature, the roof space does not have to be heated to a much higher level.
The authors state, “Anecdotal evidence from existing HVLS users has indicated that, following the installation of the fans, substantial energy savings have been made through the winter months, leading to a reduction in heating bills. Although the way in which these fans work is fairly well understood, very little in the way of scientific research has been carried out to corroborate these in-situ findings. As a first step towards gaining a better understanding of the physical mechanisms at work, this report provides details of a computational study of heat and fluid flow within a generic warehouse building with a single heater and HVLS fan installed.”
“The absolute power savings double when the temperature falls from 4°C to -4°C. This corresponds to a saving of between 1 and 1.5kW per degree the temperature falls below 4°C.”
“For the cases studied, energy savings offered by the HVLS fans for an outside temperature of 4°C were seen to peak at between 40% and 45%. Additional savings were observed as outside temperature was reduced. It was found that maximum benefit from the fans could be gained for warehouse heights above 15.0m, although even at a height of 12.5m the level of energy saving was approximately 32%.”
“The model has demonstrated that the HVLS fan is effective due to convective mass and heat transfer, shifting large volumes of air from the upper part of the warehouse to the ground. This sets up air currents which also encourage mixing, leading to complete de-stratification of the warehouse.”
A major supermarket is already using this new technology successfully at one of its key warehouses and has made substantial energy savings as a result.
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