VDI 2035

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The VDI 2035 series of guidelines describes the state of the art for the water quality of hot water heating systems and is intended to help minimize damage from corrosion and stone formation in these systems. Sheet 3 also deals with the exhaust gas-side corrosion of metallic materials in hot water heating systems, directly heated water heating systems and the associated exhaust systems. The series of guidelines VDI 2035 was first published in 1979 and has been one of the most important technical rules in the field of heating / heating technology ever since.

Structure of the series of guidelines

Surname Issue date
VDI 2035 sheet 1 Avoidance of damage in hot water heating systems - stone formation in drinking water heating and hot water heating systems 2005-12
VDI 2035 sheet 1 Correction avoidance of damage in hot water heating systems - stone formation in drinking water heating and hot water heating systems - correction to guideline VDI 2035 sheet 1: 2005-12 2006-12
VDI 2035 sheet 2 Avoidance of damage in hot water heating systems - corrosion on the water side 2009-08
VDI 2035 sheet 3 Avoiding damage in hot water heating systems - corrosion on the exhaust gas side 2014-07

Basics

Fresh water is problematic in heating systems: it brings in alkaline earths as hardness constituents and oxygen. The hardness builders can lead to deposits and stone formation, oxygen to corrosion damage. Modern systems are not only more energy efficient than old ones, they are often also very compact and thin-walled. This makes them significantly more prone to the above problems.

The VDI 2035 series of guidelines therefore specifies requirements for the fill and top-up water in heating systems. For small systems like those in single-family houses, the fill and top-up water does not have to be treated. In larger systems, however, requirements for the pH value , conductivity (salt content) and alkaline earth content (hardness) must be met.

For the maintenance of the heating system, it is recommended that the water only be drained from those parts of the system for which this is essential, and that only the missing amount of water be refilled. If the heating water has to be supplemented or replaced, softened water should be used for this. As an empirical value, VDI 2035 Part 1 assumes that all the water in a well-maintained heating system should not be replaced more than three times over its service life.

For reasons of hygiene, drinking water installations must not be connected to non-drinking water installations without a safety device. The hose connected for convenience and left connected after refilling the heater between the tap and heater is illegal because it can become a breeding ground for germs that can endanger the hygiene of the entire drinking water installation despite the valve being closed.

Areas of application

Sheet 1 - stone formation

The guideline VDI 2035 Part 1 applies to drinking water heating systems according to DIN 4753 and for hot water heating systems according to DIN EN 12828 within a building if the flow temperature does not exceed 100 ° C as intended. This guideline also applies to heat contracting systems in which building complexes are supplied if it is ensured that the supplementary water volume is no more than twice the filling water volume during the service life of the system. Otherwise, as for industrial and district heating systems, the AGFW worksheet FW 510 or the VdTÜV information sheet TCh 1466 must be taken into account.

Sheet 2 - Waterside corrosion

The guideline VDI 2035 Part 2 applies to hot water heating systems in accordance with EN 12828 within a building if the flow temperature does not exceed 100 ° C as intended. In addition, this guideline applies to heat contracting systems in which building complexes are supplied if it is ensured that the make-up water volume is no more than twice the filling water volume during the service life of the system. Otherwise, as for industrial and district heating systems, the AGFW FW 510 worksheet or the VdTÜV MB TECH 1466 instruction sheet must be observed. This guideline provides information and in individual cases formulates requirements to reduce the likelihood of corrosion on the heating water side in hot water heating systems.

Sheet 3 - Corrosion on the exhaust gas side

This guideline deals with the exhaust-gas side corrosion of metallic materials from directly heated water heating systems in hot water heating systems and from the associated exhaust systems. The application of the guideline enables the probability of component failure or functional impairment to be minimized through proper planning, execution and operation. This guideline is aimed at manufacturers, planners, specialist companies and system operators. Corrosion in the high temperature range, such as scaling, is not the subject of this guideline.

Pressure maintenance, venting and degassing

The subjects of pressure maintenance, venting and degassing are dealt with in detail in the VDI 4708 series of guidelines. This guideline applies to fluid circuits in heating systems for which an interruption in heating or circulation (e.g. in summer or for night reduction) is a regular operation. It is used to design pressure maintenance systems and to check them in the event of operation and maintenance. Pressure protection and safety equipment are not part of this guideline. The guideline supplements the present guidelines for the design, manufacture and testing of the pressure maintenance, ventilation and degassing systems or their system components with regard to the thermohydraulic integration into the fluid circuits through recommendations and design guidelines.

Training

Due to the increasing complexity of modern hot water heating systems, compliance with the stipulations in the series of guidelines VDI 2035 and VDI 4708 must be guaranteed to ensure functionality and the requirements for energy efficiency and service life. The VDI 4704 guideline addresses these important issues and offers a training concept that is aimed at all specialists involved in the planning, construction, operation and maintenance of hot water heating systems. Training categories for different target groups with entry requirements, learning content and the framework conditions are presented. Through further training in the areas of water quality, stone formation, water-side corrosion, pressure maintenance, ventilation and degassing, the likelihood of damage to system components as well as malfunctions should be reduced.

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