Hall ventilation: design perfection for manufacturing and production halls

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State-of-the-art ventilation and air-conditioning systems ensure that the air quality in manufacturing and production halls complies with the legal requirements for places of work. If ventilation systems are to be efficient and economical, it is important to consider the indoor air flow and the supply air flow at great length.

Manufacturing and production halls differ greatly from one another in their construction and use. And the requirements for room temperature and air humidity are never the same either. There simply isn’t a one-size-fits-all ventilation and air-conditioning solution – hall buildings and ventilation system designs vary too much. When it comes to creating tailored, efficient ventilation systems, it is important to distribute the supply air flow by controlling the flow of air in the room so that heat, humidity and pollutant loads can be effectively collected and discharged with the extract air. Choosing the indoor air flow wisely is absolutely crucial here. Depending on the load profile in question, mixed and stratification flow ventilation concepts tend to be the most popular choices in manufacturing and production halls.

Custom hall ventilation: thermal streams as a dimensioning parameter

 

                    
As a general rule, mixed flow is used for smaller heat and substance loads, whilst stratification flow is used for larger loads.

With mixed flow ventilation, a state required solely in the work area is created in the whole hall. This is why the principle is restricted to smaller heat and substance loads. When concentrations of pollutants are relatively high, additional collection devices (extraction systems) are required at the points of release. The required supply air flow is calculated separately on the basis of heat and substance loads and then whichever value is higher is taken as the basis for the design.

The principle of mixed ventilation_Hoval
Schematic representation of mixed flow ventilation in a production hall

Large heat and substance loads linked to a specific point, i.e. released within thermal flows, can be handled efficiently with stratification flow ventilation. It should be noted that discharges from thermal flows and weak sources emitting pollutants (e.g. workpieces for temporary storage or shavings) may occur in the surrounding area. It all comes down to the calculations of the substance load (extract air) and supply air through the relevant thermal flows. In order for the “layer boundary” effect to occur, the air flows that are moved up and guided down must be equal.

If stratification flow ventilation is selected for the air flow, it is important to ensure that appropriate air supply lines can be conducted into the work area and that there are no lateral flows.

Supply air entering close to the floor in the working area_Hoval
Schematic representation of stratification flow ventilation in a production hall

Impact of collection devices

Collection devices have a major impact on the quality of ventilation solutions. They ensure that released substances are collected at the very point at which they are released so they can then be discharged. (If substances end up in the work area due to the collection process being incomplete, a lot of additional work is required to discharge them with additional ventilation measures.)


The aim is to achieve maximum efficiency whilst keeping collected air flows to a minimum. The devices therefore need to be designed with precision, especially since the operating costs and initial investment (e.g. air duct, filter and fan) increase as the collected air flow increases.

If collection devices are planned or already in place, the (known) collected air flow needs to be added to the calculated supply air flow in the case of both mixed and stratification flow.

In order to avoid polluted air flowing back into the work area, it is also important to ensure that the extract air is not just all collected air.

The air flow in the upper area of a hall can be guaranteed as required by taking two measures:

  • Positioning the air outlets at the highest (possible) point in the hall
  • Calculating the magnitude of the extract air flow using m& AB   ≥ 0.3 ⋅ m& ZU. In the case of stratification flow, at least 20% of the extract air flow should be discharged at the highest point.

Impact of clean air return

Clean air return involves polluted air being removed from the work area, cleaned and returned to the room. In the case of:

  • mixed flow ventilation, there is no change to the supply air flow.
  • When it comes to stratification flow ventilation with return into the lower layer, there is no change to the supply air flow. In the case of return into the upper layer, the return air flow is added to the supply air flow.

Impact of decentralised machine coolers

Decentralised machine coolers are designed as split units (indoor and outdoor unit). The cooling air required is removed from the work area. The air heated up during the cooling process in then returned to the work area. In the case of mixed flow, there is no change to the supply air flow here. With stratification flow, cooler extract air flows are directed up and added to the thermal flows.

Schematic description of a production hall design:

 

 

 

 

 

Loads

  • Small head load
  • Substance load
  • Small heat load + substance load
  • Large heat load
  • Large heat load + substance load, released in thermal flow

Air flow

Mixing

Stratifying

Prerequisite

 

  • Air line possible in the work area
  • No lateral flow

Colletion from the work area

  • Add collection air flow to the supply air flow
  • Check the extract air flow: mAB  ³ 0,3× mZU

 

  • Add collection air flow to the supply air flow
  • Check the extract air flow: m& AB  ³ 0,3× mZU
  • Lead 0,2 × mAB to highest point

 

Clean air recirculation

  • No impact on the supply air flow

 

  • Within the lower layer:
  • No Impact on the supply air flow
  • From the lower into the upper layer:
  • Add clean air flow to the supply air flow

Decentralised machine cooling

  • No impact on the supply air flow
  • Direct cooler extract air flows upwards
  • Add cooler extract air flows to the supply air flow

 

Target values in the work area

Temperature

Substance concentration

Temperature

Substance concentration

Supply air flow from

Heat load

Substance load

Total of thermal flows

Substance load calculation

Heat load with substance load

Maximum value is

supply air flow in design

Maximum value is

supply air flow in design

Further blogs

 

We recommend that you check out these other blogs if you are interested in finding out more about the information covered in this article:

  • Mixed and stratification flow ventilation in production halls
  • Pollution in the working area – what you need to know
  • Load calculation – what you need to know
Author
Tobias Brugger
 
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