The obvious lesson is that hot air is buoyant and the hotter it is the more buoyant it becomes. When prepping for launch the crews use their direct fired burners to blast hot air into the balloon causing it to fill and lift. Once the balloon is vertical the crew fires the burners at full heat to get the balloon off the ground and on its way upward. While in the air you can hear the burners firing whenever the balloon starts to drop below the altitude the pilot is looking for. Short blasts produce little heat and balloon either stays stable or starts to slowly descend. Long blasts produce more heat and the balloon rises.
So...what does this have to do with eCommerce and warehouses? While the HVAC equipment cannot produce air that is hot enough to lift the building off the ground it can produce air that is hot enough to rise rapidly and stay near the top of the space. In an eCommerce fulfillment building with dozens of humans occupying the bottom 6 feet of the building that hot air can be a problem.
There are some HVAC companies that propose using very high temperature air to heat the entire space. This becomes a real challenge as the hotter the air the more it wants to stay up near the ceiling. There are a couple of ways to deal with this but both ways impact electrical operating costs.
One method is to install several large fans that are intended to pull air from the ceiling space and force it down to the floor level. In addition to the electric power required to spin the fans this solution can also make it difficult to achieve the rack heights that are desired in the building. There may also be structural cost implications depending upon the weight of the fan/motor assemblies.
The other method is to use the HVAC equipment fans themselves to force the hot air to the floor area. This also requires electrical energy to overcome the buoyancy of the air. A secondary characteristic of this method is that the velocity of the air from the HVAC unit must be pretty high in order to force the air downward. The result is a column of air moving at pretty high speed that reaches the floor in a relatively small area that can cause worker discomfort or stir up paperwork or products that are in the airstream.
Mestex has been producing a product concept for decades that overcomes these problems. The concept is called "air turnover" and many companies have since copied the idea under different names. The idea is simple....push warm (not hot) air into the space just above the worker level and pull it back across the floor where the workers benefit from the relatively slow moving warm air flow. Not only does this method produce even temperatures where it is needed it also avoids wasting heat energy that collects near the ceiling with the hot air methods.
Deciding how to design an air turnover system can be challenging since the system sends air into the occupied space that also includes equipment, bottoms of racks, conveyor systems and such. Another Mestex first is the use of Computational Fluid Dynamic ("CFD") modeling of the space to refine and optimize these designs. CFD modeling originated in the defense industry to model aircraft performance and later was adopted by the process industry to evaluate things such as the impact of ocean currents on offshore oil rigs. Since air is a fluid Mestex started using CFD modeling 20 years ago to assure owners that temperature critical products would be kept at the proper condition. Mestex' use of CFD has expanded over the years to optimizing more mundane warehouse applications as well as more sophisticated applications such as data centers. This expertise is available exclusively for Mestex customers.
So the next time you see a hot air balloon rising into the air you can appreciate the challenges of heating a warehouse or eCommerce building.
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