Standardised the right way: What's new about DIN 1988-500:2021-05?

What exactly is regulated by DIN 1988-500?

Clean drinking water is one of our most precious and important goods. For all of us to be able to rely on truly clean water coming out of the tap, hardly any application is as stringently regulated and controlled as that of drinking water valves, including the corresponding technical infrastructure.

For drinking water installations in Germany the "Codes of practice for drinking water installations" set the standard. They comprise the European standard DIN EN 1717, the DIN EN 806 series of standards and the national DIN 1988 standard. The latter standard is subdivided into the following parts:

• Part 100: Protection of drinking water, drinking water quality control; DVGW code of practice (DVGW: German Technical and Scientific Association for Gas and Water)
• Part 200: Installation Type A (closed system) - Planning, components, apparatus, materials; DVGW code of practice
• Part 300: Pipe sizing; DVGW code of practice
• Part 500: Pressure boosting stations with RPM-regulated pumps
• Part 600: Drinking water installations in connection with fire fighting and fire protection installations

The codes of practice for drinking water installations have been updated continuously for several years – with the objective of creating a set of comprehensive regulations valid in all of Europe (EN 806 series and EN 1717) in the medium term. The required supplementary national standards (such as DIN 1988) are already being checked to be sure they are up to date and match the European developments.

Criteria for the design of pressure booster systems

DIN standard 1988-500 defines the criteria for planning and designing pressure booster systems. Such pressure booster systems are required whenever the drinking water pressure is insufficient for reaching all levels of a high-rise building. Commonly, the pressure in the connecting line (SPLN 2 - 3.5 bar, which is the minimum supply pressure of the water utilities) only manages to supply sufficient water to the valves of buildings that are no more than four storeys high. The technical challenge is to use systems with variable speed pumps to provide all storeys with a constant supply pressure – at all times, also at fluctuating volume demand.

In May 2021 the DIN 1988-500:2021-05 standard for pressure booster systems with variable speed pumps replaced the previous, more than 10-year-old DIN 1988-500:2011-02. The standard's requirements on planning and design respond to the increased requirements on convenience, hygiene and energy efficiency of pressure booster systems. This type of system generally maintains a constant pressure within the characteristic curve range without the need for accumulators.

Details of what's new about the DIN 1988-500:2021-05 standard

What exactly has changed in version DIN 1988-500:2021-05 compared to the previous version 2011-02? The changes cover at least six different points:

• Aspects of drinking water hygiene added
• Section on materials added
• Schematics revised showing pressure zones with a differentiated evaluation for cold drinking water and hot drinking water installations
• Requirements on place of installation added
• Section on flow rate revised
• Requirements on indirect connection specified in detail

1. Aspects of drinking water hygiene added

According to the new standard, a system is only considered ready for operation when the requirements on transport, storage, installation and commissioning are met. In particular, this refers to the measures taken to maintain absolutely hygienic drinking water conditions in pressure booster systems. 

The owner or the owner's representative must report the pressure booster system's readiness for operation to the responsible authorities (e.g. the water utility company). And what's really important: Prior to commissioning, the consultant has to complete specific documentation as evidence that the approved connection specifications and the requirements of the German drinking water regulation have been met.

2. Section on materials added

A new feature is that the Umweltbundesamt (German Environment Agency) regularly publishes a list of all materials approved for drinking water applications – and these materials that will come into contact with the fluid handled are the only materials that may be used for pressure booster systems. This regulation was not part of the previous version of the standard, which specified suitability for drinking water but not an approval by the German Environment Agency.

This means specifically: In accordance with §17 of the German drinking water regulation (TrinkwV), the material-specific evaluation criteria and guidelines stipulated by the German Environment Agency apply to all materials in contact with drinking water: Metal materials and coatings that will come into contact with drinking water have to meet the evaluation criteria for metal materials in contact with drinking water (metal evaluation criteria). Organic materials have to meet the German Environment Agency's material-specific evaluation criteria and guidelines for the hygienic evaluation of materials in contact with drinking water.

3. Schematics revised showing pressure zones with a differentiated evaluation for cold drinking water and hot drinking water installations

The previous standard described four pressure zones for cold water, which have now been supplemented by the pressure zones for hot water (drinking water heating systems). This results in several combinations of pressure zone arrangements in the planning phase.

Please note: Drinking water heating and the corresponding pressure changes (causing a thermal expansion of the fluid) are now taken into account. In the case of different pressure zones, central drinking water heating systems have to provide Potable Water Cold (PWC), Potable Water Hot (PWH) and Potable Water Hot Circulation (PWH-C) matching the corresponding joint pressure zone.

4. Requirements on place of installation added

The new standard requires pressure booster systems to be installed without sound transmission to the building structure. Like in the previous standard, the system and its components have to be arranged in a frost-proof, well-ventilated and lockable room. What's new: The room must be free from any negative influences on the drinking water (e.g. thermal loads or other chemical or physical influences). The stagnation periods must be observed, bearing in mind that the cold drinking water must not heat up to a temperature exceeding 25 °C. Heat sources and room temperatures in the technical facilities are to be taken into account.

Like before, the installation room has to feature a sufficiently dimensioned drain connection. This drain connection has to be able to drain the maximum possible flow rate without any backflow in accordance with DIN 1986-100 and the DIN EN 12056 series of standards. The maximum possible flow rate has to be calculated comprising, for example, the inlet-side flow rate in the event of a pipe rupture and the volume of the inlet tank of the pressure booster systems.

The pressure booster system also has to be freely accessible for maintenance inspections, maintenance and repair. The place of installation must not be in the immediate vicinity of sleeping and living quarters. If this is not an option, technical measures have to be taken to prevent loud noise emissions.

5. Section on flow rate revised

The required flow rate (peak flow rate QD) still has to be calculated to DIN 1988-300 (pipe sizing). The maximum flow velocity in the connection line and inlet line of the pressure booster system must not exceed 2 m/s for noise protection reasons. Reducing the inlet-side pressure by half was an option according to the previous standard. These days, however, if a variable speed pressure booster system is operated as intended, starting up and stopping a pump will not cause any significant changes in flow velocity in the connection line that would lead to pressure surges.

If one or several pumps of a variable speed pressure booster system are stopped improperly (e.g. in the event of a power failure), the maximum pressure difference between the actual pressure in the connection line and the static pressure must not exceed 0.1 MPa. This is ensured by observing the above-mentioned maximum flow velocity of 2 m/s in the inlet line already in the planning phase.

6. Requirements on indirect connection specified in detail

For an indirect connection an open inlet tank "open to atmosphere" with air gap still has to be fitted upstream of the pressure booster system. What's new is that the water quality has to be monitored regularly. And: The scope and frequency of monitoring measures has to be defined for the planning, implementation and operating phases as part of the drinking water hygiene risk evaluation. 

For an indirect connection, drinking water hygiene – especially with regards to microbiological requirements – has to be monitored during operation. 

With a free air gap in contact with the atmosphere, the energy of the supply pressure can no longer be harvested. A downstream pump draws water out of the inlet tank and adjusts its pressure to the set outlet pressure. An indirect connection may be necessary when the water utility specifies it as a requirement, for example, or when a minimum supply pressure SPLN < 0.1 MPa has to be met, when consumption is higher for a short time (storage) or if system separation is needed, for instance to prevent any hazards at extraction points where a liquid of category 5 could be created and the extraction point has to be supplied with food-grade water (see DIN 1988-100).

The requirements on the inlet tank design have not changed, except: An open inlet valve must not cause the pressure to fall under the minimum permissible supply pressure SPLN (3.1) and the inlet tank should (but does not have to) be fitted with a water level gauge.

Perfectly prepared: KSB's pressure booster systems of the KSB Delta series

With its pressure booster systems of the comprehensive KSB Delta product family, KSB offers the right solution for every application. Whether pressure booster systems are needed for residential or office buildings, hotels, department stores or hospitals, commercial or industrial plants: KSB's offer comprises the most diverse variants of its KSB Delta pressure booster systems as standard, matching the specific requirements:

• Maximum flow rate between 9 and 960 m³/h
• Maximum head between 55 and 154 metres of water
• Maximum motor rating between 1.5 and 30 kW
• Up to 6 pumps per system
• Various control options (parameters can also be set per app)
• Modbus connection to a building management system as standard, further bus connections optional
• Fluid temperature monitoring (optional)

A dependable and economical operation is characteristic of all our reliable and energy-efficient pumps. The systems are impressively easy to install and commission. And all models of the KSB Delta family meet the increased requirements of the DIN 1988-500:2021-05 standard.