Storage Systems: how to choose - Mecalux.com

Choosing between the various storage systems for each customer's needs is a process that includes numerous aspects. In this article it analyses some basic criteria, since by understanding how these affect a final decision will make it easier to later analyse other more complex criteria.

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There are four basic issues:

• The capacity to be obtained.
• The speed to be reached.
• The variety and type of products to be stored
• The general cost of the solution.

The following is an explanation of how each of these will condition the planning of the facility.

Installation with a combined storage system.

Capacity to be obtained

The "Pallet racking systems" section, which discussed storing pallets on racking units, highlighted the potential capacity to be achieved with each of the possible systems. There, it showed that compact systems offer greater storage capacity or, in other words, the same available surface area can house a larger number of goods.

At this point it is important to remember the issue discussed in the  "A comparison of pallet rack capacity" article concerning physical and effective capacities, since with high-density systems there can be significant differences between the two, owing to the large number of empty spaces that can exist in a normal workflow.

Pallet racking units, in contrast, offer lower physical capacity than their compact counterparts. Yet as long as the right management system is used this physical capacity is very similar to effective capacity, since there are almost no empty spaces in the standard workflow.

Maximum effective capacity in a pallet warehouse is obtained by using a system that combines the best features of these two options, namely selective pallet racks on mobile bases. With this system, as long as a competent management system is employed then high physical capacity is achieved, similar to that reached with compact solutions, plus effective capacity that is very close to physical capacity.

Warehouse of a company selling floor and wall tiles.

In addition to making the most of the warehouse’s available surface area, the solution must also take into account the available vertical space. To this end, as long as the regulations so allow, it is helpful to use systems that make use of the full height of the facility or to build tall automated warehouses (as illustrated in the image above)..

Desired speed

Often, it is essential to minimise the time spent performing operations in the warehouse, particularly if the installation is medium or large in size. The number of operators required is directly related to this factor and, as a result, so is the added cost for each operation performed.

To measure the time taken to perform each task, one must calculate the time spent covering the distance between the initial point and the point where the goods are stored and add this to the time taken to return to the starting point. The exception is a combined movement (taking advantage of the journey to collect some goods to leave other goods, or vice versa); in which case, these times are measured separately.

When analysing the different operations, for goods on pallets the slowest and least dynamic system is the drive-in racking system, followed by push-back racks. The fastest option is gravity-flow racking, followed by a system based on pallet racks. Between these two extremes are the mobile base and Pallet Shuttle solutions, but the results of these depends on the number of consecutive operations carried out in each lane.

Automated warehouse installations, for their part, are quick if tasks are properly programmed.

Product variety and type

With this factor, the suitability of the chosen solution depends on the range of SKUs, the number of pallets or boxes per product, and the time the goods will spend in the warehouse.

If the goods are on pallets, there is a wide range of SKUs, and there are few pallets of each of these, the ideal system is static pallet racking units. However, another very good option is to install these on mobile bases.

In the opposite situation, where there are few SKUs and lots of pallets of each of these, any compact system is optimal. If, in addition, the goods are going to spend a great deal of time without being moved, drive-in racking is also ideal.

When the goods to be stored are handled in boxes or loose items in specific positions, individual storage and loose product solutions can be used, except when the products are of an irregular shape.

In addition to these considerations, another factor that determines the system to be used is rotation. Thus, any storage system can be used for rotation A products (high consumption) on pallets, but high-density systems are particularly appropriate. It is common to use these systems with such products; however, one must not forget the greater time required to perform maneuvers.

In terms of B products (medium consumption), the ideal options are those that use pallet racks, push-back racks, and shallow live racking units.

General cost

The fourth factor to be considered when choosing a storage option is its set-up and operating costs. Its ultimate purpose is to help generate company business. For the company to be competitive, operational costs must be as low as possible.

It is also important to estimate the period required to generate a return on investment (ROI), which must also be as short as possible. Some companies have a policy of not undertaking investments which have a ROI of more than three years.

As a result, in most cases the solution chosen will be that which offers the most competitive price and the shortest period required to obtain a return on the investment. In addition, the customer must be capable of financing the chosen solution.

While the choice of the appropriate storage system, adequate flows, operating method, warehouse location, etc. all have significant repercussions on the financial performance of the warehouse, the factor that will have the biggest impact on this performance is the solution chosen for the picking or preparation of orders (the operating methods of which are explained below).

The tables below show a comparison of the different pallet racking solutions, although it only includes the factors with the greatest influence. The final score is merely intended as a measure of the scale of the advantages and disadvantages of the different systems; it does not imply that the system with the highest score is always the best. In each case, one system will be better suited than another. In formulating this comparison, no consideration has been given to picking operations, only an assessment of the storage of pallets, accessibility, and capacity.

STORAGE SYSTEM COMPARISON TABLE Direct access storage systems

Pallet racks

Pallet racking on Mobile bases Double-deep pallet racks VNA pallet racks Automated pallet racking Automated double-deep  pallet racking

Use of surface area

2 5 3 3 3 4

Use of volume

2 4 3 3 3 3 Access to any pallet 5 5 2 5 5 4(A) Speed of
access/agility
(movements
per hour) 4 3 2(B) 3 5(C) 4(A) Stock rotation 4(D) 4(D) 2(B) 4(D) 5 4(A) FIFO FIFO FIFO (relative) FIFO FIFO FIFO (relative) Height of top level (m) 2 2 1 3 5 4 <10 <10 <8 <14 <45 <40 Aisle width (m) 3 2 3 4 5 5 2.20/3.50 (E) 3.00/3.50 (E) 3.00 (E) 1.55/1.80 (F) 1.55 1.55 Initial investment 4 (low) 3 (medium) 4 (low) 3 (medium) 2 (high) 2 (high) Handling equipment (forklift)

·Stacker
·Reach truck
·Counterbalanced forklift

·Reach truck
·Counterbalanced forklift

·Custom reach truck

·Trilateral VNA

·Bilateral VNA

·Stacker crane ·Stacker crane Advantages (average score)* 3.25 3.50 2.50 3.50 4.12 3.75 HIGH-DENSITY STORAGE SYSTEMS Compact storage systems

Drive-in pallet racks

Push-back with trolleys Push-back with rollers Pallet Shuttle Live racks with rollers

Automated Pallet Shuttle

UNISTAR supply professional and honest service.

Automated live racks with rollers Use of surface area 5 4 4 5 5 5 5

Use of volume

5 4 4 4 4 4 4 Access to any pallet 1 2 2 1 2 2 2 Speed of access/agility (movements per hour) 2 3 3 3 4 4 5 Stock rotation 1 2 2 2 5 2 5 LIFO LIFO LIFO LIFO FIFO LIFO FIFO Height of top level (m) 2 1 1 2 3 3 4 <10 <7.5 <7.5 <10 (E) <14 (E) <40 <40 (G) Aisle width (m) 2 2 2 2 3 4 4 3.00/3.50 (H) 3.00/3.50 (H) 3.00/3.50 (H) 3.00/3.50 (H) 1.80/3.50 (H) 1.55 1.55 Initial investment 4 (low) 3 (medium) 3 (medium) 3 (medium) 2 (high) 2 (high) 1 (very high) Handling equipment (forklift)

·Reach truck
·Counterbalanced forklift

·Reach truck
·Counterbalanced forklift

·Reach truck
·Counterbalanced forklift

·Reach truck
·Counterbalanced forklift
·Trilateral VNA

·Reach truck
·Counterbalanced forklift
·Trilateral VNA

·Stacker crane ·Stacker crane Advantages (average score)* 2.75 2.62 2.62 2.75 3.50 3.40 3.75

SCORE: 1 (low) to 6 (very high). For “initial investment”, the values are reversed. 
* Average obtained from the eight numerical variables.

(A) With WMS and relocation bay
(B) With WMS and A-B-C management can be greater
(C) Programmed operation
(D) With suitable WMS
(E) Depends on the forklift
(F) Depends on whether it is bilateral or trilateral
(G) It is vital to ensure the pallets are of good quality
(H) Depends on the forklift and simultaneity in an aisle

Combination of factors

It is common to find installations where a number of the factors described above have been taken into account. It is also normal to use several storage systems, each for a specific type of product. We have already seen some examples, such as in the "Combined storage systems " article, in which pallet racking units are combined with racking units on mobile bases, drive-in pallet racking units, flow rack systems and, in addition, roller conveyors to reduce maneuvering times.

The combination of factors and storage solutions allows unique facilities to be created that are best adapted to the specific needs of the companies that operate them.

Optimisation of the factors in automated warehouses

The tables above show that automated warehouses combine the optimisation of basic criteria. The only problem here is their higher initial cost. However, they provide significant advantages, such as their large storage capacity, greater construction height, perfect control and management, high performance at points of entry and exit (these are totally automated), a minimal requirement for personnel, greater accessibility to products, easier rotation, etc.

Warehouse of a cosmetics distribution company.

Automated systems can be used just to position goods, for internal transportation, or both. The latter is most common, since it considerably increases the number of movements that can be carried out and, in addition, operators only have to load and unload the trucks or containers.

Fully automated warehouse solutions have suitable conveyors installed in the dock areas. In general, these conveyors are configured to operate with stacker cranes. This system is used in both exit and entry areas, but for entry areas gauge and pallet control elements must be fitted to guarantee the smooth running of the automated machines and devices.

Checkpoint entrance in an automated warehouse.

The warehouse is far more than just a simple space to store goods. Good (or bad) management of all operations in the warehouse (receipt and dispatch of goods, preparation of orders, maintenance, storage...) will directly impact the performance of a company or business.

The warehouse must be in a planned and structured place. The first thing to do, after the acquisition of the land and the building, is to prepare an appropriate warehouse design or layout for the business, taking into account the main storage areas. At the heart of everything naturally are the storage systems where the goods are stored. Storage can be at floor level (without any type of installation and support) or on industrial racking, with this being the best option for most loads. However, there are several types of industrial racking for heavy loads, whose characteristics meet different and specific needs.

But… how to choose the most appropriate industrial racking? And how do you know which logistics solution to install in the warehouse or distribution centre?

There is no single and clear answer, but certain criteria should be considered in the adaptation or optimisation process of a warehouse with industrial racking. These are as follows:

Characteristics of the warehouse premises or building:

The dimensions of the warehouse are a determining factor when choosing one storage system or another. That is, the height of the warehouse and surface area should undoubtedly be the first factor to consider.

For example, for a warehouse that is more than 12 metres high, the appropriate storage solution to fully optimise that verticality, and hence the investment, may be a warehouse with racking that not only supports the load but also the external enclosures and that allows the integration of stacker crane type automated systems, as in clad-rack warehouses.

However, for a warehouse with a reduced horizontal surface the priority may be high-density storage to store the maximum number of unit loads rather than direct access to the goods. In such cases, the appropriate storage system would be a compact solution such as Drive In / Drive Through Racking Systems, Live Pallet Racking (FIFO) or Push-Back Racking (LIFO), or Pallet Shuttle Systems.

Type of goods or product to store:

It is assumed that a business organisation thoroughly knows its product and everything related to its marketing. Not all loads can be stored in any industrial racking.

When it comes to size, loads can be small or medium, large or very large. In other words, if the unit loads are cartons that can be handled manually by a person, it is very likely that the racking that best adapts to that load will be longspan shelving or carton flow rack systems. There is also the option of installing adjustable pallet racking systems with galvanised trays or chipboard panels to store individual cartons.

However, if the unit loads are large pallet loads, the various industrial pallet racking options should be considered.

The load may also be very voluminous or long. In this case, cantilever racking is most appropriate for storing these types of goods that may be tubes, beams, etc., very common in outdoor warehouses. In short, knowing the type of load and its commercial management are criteria and factors to include when configuring a storage solution in a logistics centre.

Flow of goods and rotation:

Another criterion to consider when classifying goods, which can determine the subsequent choice and installation of the industrial racking, is stock rotation, since some storage systems favour a faster rotation than others. For example, perishable products or fashion accessories have a very fast rotation, as they need to be despatched in a short period of time so that they do not deteriorate or become obsolete.

FIFO live pallet racking, which has an incline so that the goods can move within the structure, are designed for whoever needs a fast stock rotation and wants to optimise as much space as possible. The same is true with drive through compact racking or pallet shuttle racking systems. All share a key differentiating characteristic: they work according to the FIFO management method, i.e., the first product in is the first one out. There is therefore immediate access to the product to be unloaded.

This does not mean fast rotation is always ideal for all companies or is the objective of the warehouse. Direct access to goods or having industrial racking with greater margin for adaptation in the future may be another option.

Special requirements:

Many goods can be stored in a dry environment in normal environmental conditions, but certain products need the environment in which they are stored to meet very specific conditions so that they do not deteriorate and therefore cause losses. For example, certain items from the food sector, which require a refrigerated or freezing environment or vaccines for COVID-19 and many other pharmaceutical products.

In warehouses with cold stores or freezing chambers, it is very common to find storage systems that enable a temperature uniformity and the circulation of cold air. These warehouses also generally have high density and compact storage solutions to exploit every cubic metre and the energy cost is fully optimised. Further options include mobile racking, drive in racking systems and pallet shuttle racking systems. Adjustable pallet racking is more frequent in refrigerated environments but less so in freezing ones.

The need may also arise to store delicate or hazardous products. For example, when installing industrial racking where chemicals are to be stored, it is important to know especially the chemical compatibility of products. This will indicate the extent to which a chemical can have contact with another without causing corrosion or negative exchanges in their characteristics.

Human and mechanical resources:

Whether we are talking about a new warehouse or a redesign is being considered, the professional profile of people who work in the warehouse and the mechanical and technological resources they will have at their disposal must be taken into account: forklifts, stacker cranes, etc. Firstly, for the simple matter of operational planning and, secondly, because they are factors that require a certain investment.

For example, the initial investment will not be the same in a conventional warehouse or an automated warehouse (whether for pallets or for cartons as in the miniload system) where the flow of goods will depend 100% on automated machinery.

It will also be necessary to implement staff safety measures and measures for the maintenance and prevention of industrial racking and mechanical resources, to help avoid any accident and also extend the useful life of the storage systems.

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