For example, a vertical temperature gradient should be aimed for to keep heat loss to a minimum by keeping temperature rises as low as possible, especially in the upper hall area. One way of making this possible is to maintain maximum air circulation down the aisles. The flow conditions will be optimised, for example, by using gridded shelving systems that are permeable and have a generous gap between them and the floor.
The specific flow properties of torsion air distributors – including the patented Air-Injector from Hoval – ensure that the air inside logistics halls is distributed exactly as required.
In order for the flow to pass efficiently to the next shelves, a space of 0.2 to 0.3 metres (m) should be left between the floor and the shelving. The improved air distribution makes it possible to optimise the flow of up to three aisles with a series of air passages. (Refer to Fig. 1: Air flow through aisles.)
Rows of shelves restrict the rotationally symmetrical flow of torsion air distributors. The fronts of the rows of shelves act as walls as far as air flow is concerned, causing wall jets to form (Coanda Effect). These have a wider reach than open jets (Regenscheit’s Formulation) and a greater mounting height than is the case with free flow distribution. The extent can stretch as far as 1.5 m.
The individual ventilation units are then operated with the heat output resulting from the maximum possible temperature difference with the fixed mounting height and volumetric current. An on-off control system is all that it takes to maintain a frost-free room temperature and only a few units need to be installed.
This is where torsion air distributors come in, as they boost the temperature range and heat output. In heating mode, the air flow is highly concentrated and there is no need to apply supply air directly to the top shelves. Consequently, the supply air can be blown in at a temperature of around three Kelvin (K) higher than the upper temperature limit. The heat output required can then be achieved with fewer units, which cuts back on the initial investment and ongoing operating costs. Not to mention that it’s good news for the environment too.
During the summer months, the set temperature limits can be followed using recirculated or outdoor air units. Air from the outside can be used for direct and/or
indirect cooling. Automated system control comes highly recommended in order to follow those temperature limits to the letter.
If a lower and upper temperature limit need to be followed, the vertical temperature gradient is crucial. Say, for example, that goods need to be stored at between 18 degrees Celsius and 21 degrees Celsius (3 K) – the height of the hall cannot exceed 12 m with a gradient of 0.25 K/m.
Centralised vs. decentralised supply of media
The supply of heating and cooling media can be centralised or decentralised for recirculated and outdoor air units. As far as logistics halls are concerned, decentralised solutions are the best option. Their implementation with recirculated and/or outdoor air units, equipped with reversible heat pumps, is a lot less elaborate than a centralised supply consisting of a boiler system, water chiller and the relevant hydraulic system. Decentralised systems don’t take up any precious storage space with heating facilities either. Another advantage of decentralised heating and ventilation systems is that, structurally speaking, relatively small individual point loads are easier to integrate into a hall setting than large single loads.
Modern electric forklifts are powered by lithium-ion batteries. No hydrogen is released when they are being charged, which puts them at an advantage over standard lead-acid batteries. This also means that their charging stations don’t need to comply with the ATEX Directive for explosion protection and prevention and no further ventilation measures need to be taken.
If shelf conveying systems are in use, the heat released by the systems needs to be taken into account when calculating the cooling load.