According to §16, section 3 of the German energy saving regulations (Energieeinsparverordnung EnEV), all non-residential buildings over 1,000 m² (including museums, libraries and archives) must have an energy performance certificate. The certificate states the calculated energy demand of the building. This depends firstly on the structural thermal protection and secondly on the type of building services plant used. The energy performance certificate must also include recommendations on how to improve energy performance. For smaller buildings it is still advisable to get an energy performance certificate in order to obtain information about potential energy savings. In addition to the figures for area and volume for all the heat-conducting building elements, the present thermal protection values and the relevant figures for the building services plant used must be known. If they are not known, it is necessary to consult the paperwork or visually inspect the relevant building elements in order to determine the figures, and calculate areas and volumes as well if necessary. The types of professionals legally entitled to issue energy performance certificates can vary from state to state. Consult the Chamber of Architects (Landesarchitektenkammer) or Chamber of Engineers (Landesingenieurkammer) in your particular state.

Chambers of Architects in Germany

Chambers of Engineers in Germany

The better the thermal protection, the higher the interior surface temperature will be, and consequently the lower the risk of mold growth and moisture condensation on the interior surfaces of the building elements. The relative humidity threshold resulting from the thermal protection or the calculated relative humidity threshold are key values for designing the indoor climate and protecting the cultural property. You can obtain information about this from a Chamber of Architects, Chamber of Engineers or Chamber of Commerce and Industry.

Chambers of Engineers in Germany

Chambers of Architects in Germany

Chambers of Commerce and Industry in Germany

Condensation on the inside of window panes is a sign that the indoor relative humidity is too high in relation to the thermal protection provided by the glazing. As a result, mold can form in the area of window jambs or other interior surfaces of exterior building elements (e.g. thermal bridges such as at exterior wall corners).
The table at the link below provides an overview of the thresholds for indoor relative humidity above which condensation can be expected on the interior surfaces of glazing given a room air temperature of 20 °C and an outdoor temperature of 15 °C. It should also be noted that, particularly in the case of windows with insulated glass units, condensation can form much earlier in the area of edge seals as these create a thermal bridge. In the case of secondary glazing and double windows, however, condensation can also form on the inside of the outer glass panes. This may be because the air trapped in the gap between the panes, or between the inner and outer windows in the case of double windows, is cooled when the outdoor temperature drops, and consequently moisture condenses on the inside surface of the outer panes. Alternatively, it may also be due to warm moist air flowing into the gap between the panes or between the inner and outer window through loose joints between the interior casement and the interior window frame and too tight joints between the outer casement and the exterior window frame. This air then cools down and condensation forms on the surface of the glazing. The latter case in particular presents a serious condensation issue. To minimize this effect, it is possible to make the interior casements close tightly and to insert a ventilation slit in the frame for the exterior casements.

Table: Relative humidity threshold and U-value of glazing

Mold is a natural constituent of "aeroplankton", that is to say varying amounts of mold spores can be carried in the air depending on the time of year. A certain moisture potential conducive to mold growth on the surface of building elements must exist. This may be present as a result of the interaction between the indoor climate and the interior surfaces of exterior building elements. This is because the interior surface temperatures of the exterior building elements may in some cases be significantly lower than the temperature of the indoor air during periods when the building is heated. This causes the air passing along the interior surfaces of building elements to cool down. Elevated levels of moisture in building materials as a result of sorption and capillary condensation can then occur on the surface of the building elements, which is conducive to mold growth. As the thermal protection values of the building elements have a decisive influence on the interior surface temperatures of exterior building elements, the lower the thermal protection is, the greater the risk that mold will form on the interior surfaces. However, mold can also form as a result of other issues, such as inadequate weatherproofing or leaks from pipes carrying water. If mold is present, it is essential to investigate what is causing it.

If you have items in your collection that are sensitive to damp, such as paper, fabrics, organic materials and paintings, it is highly advisable to continuously measure and monitor the indoor environmental conditions. The measurements should preferably be taken in the vicinity of the holdings to be protected. The measurement data should be used to monitor and control any ventilation and air conditioning systems installed. The measurements should preferably be recorded electronically, and the measurement data forwarded to a central monitoring system. Measurements with hygrothermographs (combined device that measures and records both the air temperature and the relative humidity) are however more problematic, firstly because monitoring hygrothermographs is labor-intensive, and secondly because measurement inaccuracies can occur if they are not regularly calibrated.

Since the indoor climate depends on air exchange with the outdoor air, and also extreme solar radiation can be expected in buildings above ground in the summer during heatwaves for example, if rooms are not air conditioned, the indoor air can reach temperatures that are significantly higher than the outdoor temperature.

Summer condensation

In Germany, heating systems are dimensioned for a certain outdoor temperature which varies from region to region (design temperature, DIN EN 12831). This means that the room air temperature for which the heating system was designed can be guaranteed up to this defined temperature. If the outdoor temperature drops below this for a prolonged period, the room air temperature will also fall. To determine the impact of such a situation on the use of the building and extrapolate measures for its operation, the heating system as well as the thermal and moisture protection limits of the building envelope must be known.

The negative impact of extreme humidity on the building and collections along with measures for recognizing and rectifying unfavorable conditions are set out in the introduction to the Climate section.

Different indoor environmental conditions may be advisable to protect and preserve various types of holdings. While stone sculptures are relatively insensitive to the indoor climate, in the case of sculptures made of ferrous metals it may be expedient to keep the relative humidity below 55 % in order to prevent corrosion processes starting. With wood, canvas and paper on the other hand, because dampness causes them to deform it is important to keep any fluctuations in relative humidity to a minimum. The ideal level of indoor relative humidity greatly depends on the particular material concerned. The AMEV guidelines (Arbeitskreis Maschinen- und Elektrotechnik staatlicher und kommunaler Verwaltungen - mechanical and electrical engineering working group for government agencies and municipal authorities) provide a good starting point for determining what indoor environmental conditions are suitable in each case. Irrespective of these, however, it is always advisable to seek the advice of a specialist conservator.

AMEV guidelines

How heavily rooms are used greatly influences the relative humidity as people's bodies continually give off moisture as a result of metabolic processes. Visitors can also bring more moisture into rooms on damp clothing. Particularly in the case of rooms without air conditioning, this moisture load can lead to large fluctuations in the indoor relative humidity or cause it to become too high. With this in mind, it may be advisable to record and control the number of visitors as part of an indoor climate measurement and monitoring regimen, especially in institutions without air conditioning. Jackets, coats, large bags and umbrellas should always be deposited before visiting any exhibition galleries or user rooms.

Rooms are sometimes also used for hosting celebrations and special events (e.g. Museum Nights, concerts, state visits etc.). Large gatherings of people, and also the associated catering, increase the moisture load in the rooms. This can have an impermissible impact on collections, and in historic buildings it could cause structural damage to the interior surfaces of the building elements. It is vital to be aware of the impact of such special events on the indoor climate and to develop a strategy for countering the resulting higher moisture loads (e.g. with portable dehumidifiers).

Hygrothermal building simulation

Items held in collections are constantly interacting with the ambient climate so these climate values and any fluctuations in them play an important role. This applies not only to libraries, archives and rooms in which objects are exhibited or stored, but also to items during transport. The lender and the exhibitor should therefore define and agree the limit values that will apply to exhibition and storage as well as seamlessly during transportation. For the borrowing institution, it is essential to continuously monitor and log the ambient climate conditions, both while an object is in storage and on display as well as during transportation, in order to defend against any subsequent claims for compensation. This can be done for example with data loggers that continuously record both the temperature and ambient relative humidity during the transport process. Depending on the nature of the artifact, it may be necessary to transport it in special climate-controlled containers. The individual requirements to be met must be agreed between the lender and the borrower on the basis of conservatorial principles.

Together with efflorescence, powdery or peeling paint is often caused by the action of moisture and salt deposition. Moisture infiltration may be the result of inadequate weatherproofing, rising damp, damaged vertical damp-proofing, or leaks from pipes carrying water. Any moisture that penetrates the building usually also brings harmful salts with it. These salts then crystallize on the evaporative surface of the moisture and cause damage to the surface of building elements.

Ventilation and air conditioning systems are used to supply certain areas with air. The air may be conditioned constantly or variably depending on the requirements for the level of purity (reduce pollutants), temperature, humidity, air volume, air velocity and air exchange rate, and depending on the capacity and quality of the ventilation and air conditioning systems installed.

Types of mechanical ventilation

Definition of ventilation system/air conditioning system

With age, the performance and control parameters (volumetric flows, temperatures, relative humidity, etc.) on technical equipment usually change, for example as a result of wear on drive elements or measurement drift on measurement and control systems. It is therefore advisable to regularly check the relevant nominal and performance data.

AMEV guidelines on ventilation and air conditioning systems in public buildings

In order to provide optimal protection for collections and operate mechanical room air handling systems economically, it is essential to have a detailed knowledge of the properties of materials in the collection, as well as a knowledge of any factors related to the surroundings which have an impact on the collection and which could cause their condition to change or even trigger harmful interactions. In order to assess whether the design and capacity of existing mechanical room air handling systems are still able to meet the requirements, it is essential to know the following fundamental data:
- Nature of the artifacts (type of material and its sensitivity to humidity, light, temperature and dust)
- Building (location, position, neighborhood influences, structural parameters such as heat loss, uncontrolled infiltration of outdoor air)
- Performance data of building services plant (air volumes, hygienic air exchange, control zones for humidification and dehumidification, room and system temperatures, quality of filter stages, etc.)
- Usage (occupancy, operating hours, etc.).

The servicing and maintenance of ventilation and air conditioning systems has a major impact on their operation and their cost-effectiveness. Regular servicing and maintenance preserves the value of collections as well as the systems themselves, and also ensures safe operation with respect to fire safety, hygiene aspects and health protection. As a rule, the following elements should be included in the servicing and maintenance regimen:
- Air flow
- Ventilators
- Air filters
- Air heaters, air coolers and heat recovery systems along with their primary systems
- Refrigeration units, cooling and dehumidification equipment
- Kitchen extractor fans and cooker hoods
- Disposal (filter residues, coolants, used oil etc.)
- Security systems and fire safety equipment
- Measurement and control systems plus building automation systems.
The requirements for servicing and maintenance of ventilation and air conditioning systems are specified in some cases in statutory building regulations, e.g. state building regulations (with respect to fire safety and plant safety), energy saving regulations, the regulations for protecting the climate from changes due to certain fluorinated greenhouse gases (Chemicals Climate Protection Regulation (Chemikalien-Klimaschutzverordnung - ChemKlimaschutzV)), and in some cases in the relevant technology standards, especially VDI 6022 Part 1-4: Hygiene Requirements for Ventilation and Air Conditioning Systems and Units, as well as the manufacturer's/supplier's servicing and maintenance instructions. An important prerequisite for ensuring the all-round effectiveness of servicing and maintenance work is the availability of comprehensive and up-to-date system documentation (function diagrams, floor and central plans, system and function descriptions including a list of the key system parameters and data, device lists detailing the key device data, list of safety-relevant components for repeat tests, such as fire safety flaps, mechanical smoke extractors etc., with their inspection dates). Only expert staff or external specialist firms should be tasked with carrying out servicing and maintenance work, preferably ones certified to VDI 6022: Hygiene Requirements for Ventilation and Air Conditioning Systems. The statutory requirements for servicing and maintenance are set out in section 3 of the energy saving regulations (existing buildings and systems); see §11 of the regulations (maintaining energy efficiency), in particular paragraphs (1), (2) and (3).

Energy saving regulations, Federal Ministry of Economic Affairs and Energy (BMWi)

Maintenance building technology working group (AIG) of the German Engineering Federation (VDMA)

Based on the Energy Performance of Buildings Directive 2002/91/EC of the European Parliament and Council issued on December 16, 2002, the requirement for energy performance inspections of air conditioning systems was incorporated in §12 of the German energy saving regulations (Energieeinsparverordnung EnEV). See the link below for detailed specifications as to when an air conditioning system (applicable to full or partial systems with or without a ventilation function provided they have an effective rated output of more than 12 kW per building) is subject to the EnEV inspection requirements.

Inspection of air conditioning systems

Website of German Building Climate Association (Fachverband Gebäude-Klima FGK)