EN 16798 et al: humidity in European regulations


There are a number of international regulations for HVAC systems in residential and non-residential areas. From the point of view of the building, the most important is the EN 16798 series of standards. Their main focus is always on the air quality in rooms and air hygiene. In the meantime, energy-efficient operation has also become increasingly important. The requirements of regulations, standards or directives concern testing and measuring procedures for the handover, execution and operation, hygiene, hygiene inspections or maintenance and service of the systems.

But what is the actual significance of indoor humidity in international standards and legislation, and what is the current situation? Let us look at an example: Since 1 January 2018, new minimum heat recovery figures have been applicable in Europe for non-residential ventilation systems.

For closed loop systems this is 68 percent, for rotary and plate heat exchangers 73 percent. This is stipulated by the Ecodesign Directive, or more precisely its implementation by EU Regulation 1253/2014 “Ecodesign requirements for ventilation units”. The European industry associations Eurovent and EVIA are currently working on incorporating moisture recovery into the EU Regulation along with efficiency-enhancing measures for non-residential ventilation systems for heat and moisture recovery. This means the associated energy for dehumidification (cooling) as well as all the humidification and frost protection required. It therefore seems to be of importance.

Fig. 1: EU Directive 2018/844 – official title “Energy Performance of Buildings Directive” (EPBD)

The building itself

When looking through European regulations, attention is first drawn to the Energy Performance of Buildings Directive 2018/844 (EPBD). It was amended and published by the European Parliament in May 2018. As part of the ongoing process, the EPBD continues to address new requirements to further improve the energy efficiency of buildings, to contribute to the reduction of greenhouse gas emissions by 2050 and to decarbonise the building stock, which, according to the Commission, accounted for around 36 percent of all CO2 emissions in the Union in 2018. At the same time, however, it is essential to ensure comfort levels and air quality. On closer inspection, it becomes apparent that what is meant by “indoor climate” is defined by all possible parameters – but without any statements about indoor air humidity. Here are three examples:

  • In item 13, it refers to the World Health Organization guidelines of 2009. This states: “concerning indoor air quality, better performing buildings provide higher comfort levels and wellbeing for their occupants and improve health. Thermal bridges, inadequate insulation and unplanned air pathways can result in surface temperatures below the dewpoint of the air and in dampness. It is therefore essential to ensure a complete and homogeneous insulation of the building including balconies, fenestrations, roofs, walls, doors and floors, and particular attention should be paid to preventing the temperature on any inner surface of the building from dropping below the dewpoint temperature.”
  • Item 21 then discusses the monitoring of indoor climate in these words: “The installation of self-regulating devices in existing buildings for the separate regulation of the temperature in each room or, where justified, in a designated heated zone of the building unit should be considered where economically feasible, for example where the cost is less than 10% of the total costs of the replaced heat generators.”
  • Furthermore, the EPBD also remains vague on the monitoring obligation in item 36 regarding air humidity in rooms: “When carrying out inspections and in order to achieve the intended building energy performance improvements in practice, the aim should be to improve the actual energy performance of heating systems, air-conditioning systems and ventilation systems under real-life use conditions. The actual performance of such systems is governed by the energy used under dynamically varying typical or average operating conditions …”

Details are provided by the new EN 16798

The Energy Performance of Buildings Directive therefore sets the guidelines, but does not go into the details of systems engineering. For this, the specialist planner needs another European regulation: EN 16798 “Energy performance of buildings”. This is regarded as the implementation standard of the EPBD and has become the central work for ventilation and air-conditioning technology in Europe.

Standard / TR Previous number Content
EN 16798-1
TR 16798-2
EN 15251 Indoor climate conditions and usage profiles
EN 16798-3
TR 16798-4
EN 13779 Performance requirements for ventilation and air conditioning systems and room cooling systems
EN 16798-5
TR 16798-6
EN 15241 Energy calculations for ventilation systems
EN 16798-7
TR 16798-8
EN 15242 Calculation methods for the determination of air flow rates in buildings
EN 16798-9
TR 16798-10
EN 15243
Calculation methods for energy requirements of cooling systems
EN 16798-11
TR 16798-12
EN 15243
Load calculations
EN 16798-13
TR 16798-14
EN 15243
Calculation methods for refrigeration systems
EN 16798-15
TR 16798-16
EN 15243
Calculation methods for energy requirements of cooling systems - Storage
EN 16798-17
TR 16798-18
EN 15239
EN 15240
Guidelines for inspection of ventilation systems

Fig. 2: The EN 16798 series of standards deals with the overall energy performance of buildings in nine parts plus nine technical reports. With the publication of the white papers many previous standards became invalid.

This series of standards, planned in 18 parts, was launched in July 2015 with Part 1 on “Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics”. In fact, Part 1 only appeared after the second approval procedure of the member states in May 2019. It is a restructured continuation of EN 15251 “Indoor environmental input parameters”, which, at the same time, became invalid. This differentiated room comfort with active humidification and dehumidification into three categories with minimum and maximum temperatures for winter and summer. With the new Part 1, Category IV has been incorporated into EN 16798. In addition, relative indoor air humidity also appears for all four categories. Minimum and maximum values of between 20 and 70 % are defined for each category, depending on weather, room temperature and type of use. Furthermore, EN 16798 Part 1 recommends an absolute indoor air humidity of less than 12 g/kg at all times.

When it comes to the planning, design and energy-efficient operation of buildings, Part 3 of EN 16798 applies. It covers the design of ventilation and air-conditioning systems as well as room cooling systems in non-residential buildings intended for human occupancy – however, without applications for industry and process engineering. Part 3 adopts much of the contents of the revised EN 13779 “Ventilation for non-residential buildings - Performance requirements for ventilation and room-conditioning systems”. However, it also contains new requirements for equipment and system technology for air filters, heat recovery and the quality of supply air. The remaining content then specifically states that HVAC, air conditioning and room cooling systems can influence the thermal indoor climate, the indoor air quality, the indoor air humidity and the acoustics in the room and that humidity control on the supply air side is mandatory in order to exclude the possibility of condensation forming. This establishes a connection to Part 1 as to how the proposed indoor air humidity or air quality is to be ensured.

The following Parts 5 to 15 of EN 16798 address various calculation methods related to mechanical ventilation systems, including heating, cooling and distribution. Consideration is given to the moisture content of the supply air recommended in Part 1 to ensure the indoor air humidity and the auxiliary energy required for humidification and dehumidification. It replaces the previous EU standards 15241, 15242 and 15253, which also specified all calculation methods.

Last but not least is Part 17 of EN 16798 concerning the “Inspection of ventilation and air conditioning systems”. It replaces the previous EN 15239 “Guidelines for inspection of ventilation systems” and EN 15240 “Guidelines for inspection of air conditioning systems”. As far as humidity is concerned, it is primarily concerned with the prevention of condensation and hygienic aspects. To this end, not only humidity, but also other various parameters and properties of the moving air and the ventilation system must be recorded, tested and evaluated during inspections. For the procedure, reference is made to EN 12599 “Test procedures and measurement methods to hand over air conditioning and ventilation systems”. This specifies tests, test procedures and measuring instruments, such as the new testo 400, for determining the serviceability of installed systems at handover; these measures are carried out before, during and after handover. The great user benefit offered by Testo's universal measuring instrument lies in the standard-compliant measuring procedure and complete documentation including photos and comments. As the main purpose of an inspection, part 17 of EN 16798 describes how operators and owners of buildings are advised by the inspection report on how to reduce the energy consumption of systems while maintaining acceptable indoor climate conditions.

From “can” to “must”

The European EN 16798 series of standards thus provides a series of specifications for air humidity in rooms, in ventilation systems and in buildings. However, none of them is mandatory or to be understood as a legal requirement. Rather, they are intended as recommendations for maintaining the relative humidity in indoor air in relation to the temperature in the room and the season. Furthermore, it is only when an air conditioning or ventilation unit with a technical device humidifies or dehumidifies the supply or exhaust air that the above-mentioned parts 1 to 17 apply in terms of humidity. This is often the case when moisture-sensitive goods and storage facilities, production processes or health care facilities set humidity specifications for other reasons or when there is a risk of icing up in commercial cooling systems due to excessive humidity at temperatures below zero. It must then be ensured that the auxiliary energy required to regulate the humidity in the room is used as efficiently as possible and that condensate does not cause any hygienic problems in the ventilation unit, the supply lines or the recooling unit. Regular inspections are consequently part of the operation of air conditioning and ventilation systems.

The European industry associations Eurovent and EVIA are currently pursuing a different approach. With their position paper on the EU Regulation 1253/2014 on “Ecodesign requirements for ventilation units”, the upcoming revision procedure in 2020 is intended to introduce system parameter “c” that takes into account the technical recovery of air humidity by means of a sorption rotor, removable storage tank or membrane heat exchanger. With reference to the four categories of Part 1 of EN 16798 mentioned above and the types of building use specified in its annex, simulation calculations were carried out for the cities of Milan, Valencia, Oslo and Munich – with promising results. Based on this, even under the most unfavourable environmental conditions, the factor c=0.08 could be added to the calculation of the heat recovery coefficient already required by law today.

Fig. 3: Extract from the position paper submitted to the EU Commission regarding the revision of EU Regulation 1253/2014 on “Ecodesign requirements for ventilation units” and the consideration of a system parameter for the recovery of moisture.

This is because indoor air humidity, which is recovered, does not have to be generated at all using auxiliary energy. Therefore, dehumidification is of great benefit in summer, as exhaust air is drier than outside air. As such, dehumidification becomes the most essential component of cooling, which means that, depending on the location in Europe, a mechanical refrigeration system can be considerably smaller. Furthermore, drying the exhaust air in winter prevents the heat exchanger from icing up, which is why no further auxiliary power measures are required to prevent ice from forming.

The final table (Fig. 4) from Eurovent shows the calculated figures in red for the operating case “5 days a week from 7 a.m. to 6 p.m. throughout the year”. This corresponds, for example, to the usage patterns of countless office or administration buildings.

If Eurovent and EVIA are successful with their entries, then soon ventilation systems in non-residential buildings will be able to include not only heat recovery, but also recovered moisture in the indoor air in the building assessment – which, incidentally, is actually required by the Energy Performance of Buildings Directive mentioned at the beginning of this article. After all, as stated there under item 7:

“The 2015 Paris Agreement on climate change following the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21) boosts the Union’s efforts to decarbonise its building stock. Taking into account that almost 50% of Union’s final energy consumption is used for heating and cooling, of which 80% is used in buildings, the achievement of the Union’s energy and climate goals is linked to the Union’s efforts to renovate its building stock by giving priority to energy efficiency, making use of the ‘energy efficiency first’ principle as well as considering deployment of renewables.”


Fig. 4: Simulation calculations for system parameter “c” for moisture recovery in European cities. The calculated figures in red represent the operating case “5 days a week from 7 a.m. to 6 p.m. throughout the year”.

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