Static shelving systems "person-to-goods" principle (PzW)

Definition: Static shelving systems based on the "person-to-goods" (PzW) principle

The term static shelving systems refers to storage solutions in which the shelving units themselves are mounted in a fixed position. Unlike dynamic systems (such as mobile or carousel racking), the storage unit does not move.

The "person-to-goods" principle (PzW), often referred to as "man-to-goods", describes the method of picking. In this case, the warehouse employee (order picker) physically moves to the storage location of the goods – whether on foot, with a picking trolley or by means of an industrial truck (FFZ) – in order to pick (pick) the items for an order.

The combination of static racking and the PzW principle is the world's most widespread and classic form of warehousing and order picking. It is in direct contrast to the "goods-to-person" principle (WzP), in which automated systems (e.g. an automated small parts warehouse, AS/RS) bring the goods to the stationary employee.

Functionality and typical rack types in PzW operation

In PzW operations, the order picker is the central player. The process, controlled by a warehouse management system (WMS) or by means of a pick list, typically includes the following steps:

1. Start of the order: The order picker receives the order (e.g. via MDE device, pick-by-voice or pick-by-light).
2. Path to storage location: The employee moves to the first storage bin (shelf compartment).
3. Pick: The item is removed in the specified quantity.
4. Acknowledgment: The pick is confirmed in the system.
5. Transport: The employee drives or walks to the next pick location or to the goods issue/consolidation station.

The dominant factor in the efficiency of this system is the travel time, which often accounts for 50% to 70% of the total picking time.

The most common static shelving systems optimized for PzW:

• Shelving racks: The classic shelving system for the manual picking of small parts (SKUs) that can be gripped by hand. Common in e-commerce warehouses or for C-parts management.
• Pallet racking (wide or narrow aisle): The standard rack for storing Euro pallets or lattice boxes. The PzW process usually takes place "man-high" (for opening cartons) or by means of FFZ (e.g. high-rack forklifts, narrow-aisle forklifts), with the driver (the person) driving to the goods (pallet).
• Cantilever racks: Static systems for the storage of long goods (pipes, panels, wood), in which the employee also drives to the rack to remove the material.

PzW from the perspective of contract logistics (3PL)

For contract logistics service providers (3PL), the PzW principle is often the strategic choice in static racks, even if automated WzP systems promise higher picking performance. The reasons lie in the specific requirements of the 3PL business:

1. Maximum flexibility: 3PLs often manage heterogeneous customers (clients) with vastly different item structures (SKUs), volume fluctuations, and seasonality. Static PzW systems can be quickly adapted to new product ranges. A shelving unit is easier to reconfigure than an AS/RS.
2. Scalability (personnel): With PzW, performance is directly linked to personnel deployment. Order peaks (e.g. Black Friday) can be absorbed by the short-term increase in the number of employees (often through temporary work). Automated systems have a fixed upper limit (the "bottleneck" of mechanics).
3. Low investment costs (CAPEX): The initial investment in racks and standard FFZs is significantly lower than in complex automation. This is crucial for 3- to 5-year logistics contracts, as the investment (ROI) must pay for itself during this period. Costs are shifted to variable operating costs (OPEX), primarily staff.

In contract logistics, the efficiency of PzW is therefore controlled less by mechanics than by excellent WMS (e.g. multi-order picking, route-optimised forklift guidance systems) and good personnel management.

Requirements for the logistics property and hall planning

The decision for a static PzW system has a direct and fundamental impact on the specifications of the logistics property (hall):

• Bottom plate: This is often the most critical point. While shelving racks have low requirements, pallet racks – especially high racks or narrow-aisle warehouses – require extremely flat floors (according to DIN 18202 or VDMA guidelines) and a high point load capability to accommodate the setting of the shelf feet and the dynamic loads of the FFZs.
• Hall height (UKB): The usable height (lower edge of the truss, UKB) defines the storage capacity. Modern logistics properties are often planned with 10 m to 12.5 m UKB in order to enable 5–7 pallet levels in PzW operation (by means of reach or high-bay forklifts).
• Aisle widths: The choice of the FFZ dictates the aisle width and thus the space efficiency.
• Wide aisle warehouse (approx. 3.00 m – 4.50 m): Minimal use of space, but high flexibility (standard forklift).
• Narrow-aisle warehouse (VNA) (approx. 1.70 m – 2.10 m): High use of space and space, but requires special (and expensive) narrow-aisle forklifts (often inductive or rail-guided) and places the highest demands on floor evenness.
• Technical building equipment (TGA): PzW systems require continuous, low-shadow lighting within the corridors. Narrow-aisle warehouses or high racks often require special fire detection and sprinkler technology (e.g. ESFR or in-rack sprinklers), which affects real estate costs.

Cost-effectiveness and limits of the PzW principle

The profitability of PzW systems depends heavily on the handling and the variety of articles .

Advantages (cost-effectiveness):

• Low capital expenditure (CAPEX).
• High flexibility for assortment and volume changes.
• Robustness and low susceptibility to technical failures (failure of a forklift does not stop the warehouse).
• Well suited for bulky, heavy or "unwieldy" items that are difficult to automate.

Challenges and limitations (costs):

• High operating costs (OPEX): Personnel costs are the dominant factor. Rising wages and staff shortages worsen profitability compared to automation.
• Low picking performance: A manual picker achieves about 80 to 150 picks per hour in the PzW system (depending on optimization). Automated WzP systems achieve 600 to 1,000 picks/hour at the picking station.
• Ergonomics: PzW is physically demanding (long walks, bending, lifting). This potentially leads to higher sick leave and requires ergonomic design (e.g. avoidance of floor or overhead storage areas for fast-moving items).
• Space requirement: Due to the necessary traffic routes (aisles), the space efficiency (storage area vs. traffic area) is often lower than with high-density automated systems.

Questions and Answers (Q&A) on Static PzW Systems

Question: Isn't the "person-to-goods" principle outdated? Answer: No. Although automation (WzP) is increasing, PzW remains the most flexible and for many applications (e.g. low/medium turnover, high article variety, volatile demand, contract logistics) the most economical method. Modern bearings are often hybrids that combine PzW for slow-moving vehicles and WzP for fast-moving vehicles.

Question: How can the efficiency of a PzW bearing be increased? Answer: Primarily through software and process optimization, not through the shelves themselves. Key factors are: (1) A good WMS for route optimisation (e.g. "serpentine line" through the aisles), (2) batch picking (multi-order picking), (3) use of pick-by-scan or pick-by-voice to reduce search and control times and (4) a well-thought-out ABC analysis during storage (fast-moving at the front).

Question: What role does the logistics property play in the conversion from wide aisle to narrow aisle (both PzW)? Answer: A decisive one. Retrofitting is often not trivial. The floor must meet the extremely high flatness requirements for narrow-aisle forklifts (regrinding is expensive). A guide wire induction guide may have to be embedded in the ground. The lighting and sprinkler system may need to be adjusted as the shelves are higher and denser.

Conclusion: The continued dominance of static PzW systems

Static racking systems in PzW operations are the foundation of physical warehouse logistics. While they reach their performance limits at very high, standardized throughput, they remain indispensable due to their unbeatable flexibility, scalability and low investment costs . Especially in contract logistics, which thrives on changing customer requirements, and in e-commerce with its volatile peaks, the PzW principle ensures the operational ability to act. However, the success of this system depends largely on the intelligent control by the WMS and the ergonomic design of the processes and the logistics property.