03 Indoor Climate
Introduction
It is the atmosphere of a living space. It captures and displays the essence of a home. It fills the outer form with life. It creates harmony (or disharmony), which affects the entire human condition – mind, soul, and body.
Figure: The hearth as the center of warmth. Healthy indoor climate due to a radiant heating system and natural building materials such as wood and clay. Photo: Dirk Dittmar, Building Biology Consulting Office IBN
The selection of building materials and the type of construction influence the quality of the indoor climate, which very much defines both the quality of living in a given building as well as its biological effect. We should always keep this in mind with almost any building project, be it small or big. The following discussion not only applies to residential buildings but also to schools, hospitals, nursing homes, and especially to the large number of office spaces and workshops.
Today there is so much talk about a positive work "climate" and a people-friendly work environment that the health and human factor aspects of indoor climate are often overlooked.
Even in places where performance is a priority such as educational institutions and workplaces, a healthy indoor climate is just as important as organization, efficiency, and optimum indoor furnishings and technologies. In addition to the quantitative performance, an appropriate indoor climate promotes human health (low sick leave rates, reaching old age), contentment, well-being, and generally a positive work or 1 learning environment. And as has been repeatedly demonstrated, it also has a positive impact on work performance.
The connection between human health and the built environment has now been recognized the world over. The term "sick building syndrome" (SBS) has been established. It basically refers to those factors of a building that may cause illness in occupants even though the symptoms cannot be traced to specific pollutants or sources within the building. In contrast, the term "building-related illness" (BRI) is used when symptoms of a diagnosable illness are identified and can be attributed directly to airborne building contaminants.
How important the impact of microclimate factors is has now also been recognized by the legislators; among others, this is documented in the minimum safety and health requirements of the Council Directive of the European Communities as well as the German Workplace Ordinance of the Federal Ministry of Labor and Social Affairs.
Climate factors
Definitions
• Climate: The sum total of all meteorological variables for a given region within a larger time frame. The determining factors of these "weather conditions" include: incoming solar radiation, solar radiation reflected back from the Earth, water vapor content of the air, wind, air pressure, dust and CO2 level of the air. • Air conditioning: A process in which the air temperature, supply air, and air humidity are monitored and controlled by air-conditioning equipment. • Bioclimatology: A branch of knowledge concerned with the impact of climate on biological systems (in this context, especially on human beings). • Bioclimatology or how to create a healthy indoor climate is one of the most difficult branches of science because it is extremely complex. Those who are responsible for the indoor climate quality such as architects, building services engineers, energy advisors, and construction companies must, therefore, have a vast knowledge in this field.
The factors that affect indoor climate are shown in the Figure below. Air, temperature, humidity, and electroclimate with their many variables mutually influence each other to a lesser or greater degree, which, in turn, are shaped by the building materials, the construction type, installations, furnishings, and the type of neighborhood.
By applying the existing knowledge of building-related climate factors, it is possible to create a comfortable and healthy indoor climate.
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The climate inside buildings is also heavily influenced from the outside. The climate on Earth has been the foundation of the development and maintenance of living beings (plants, animals, humans) for billions of years. Solar radiation or sunlight play a particularly important role (see also course module "Light and Lighting"): All life processes, especially photosynthesis and molecular motions, depend on it—but also diseases.
The natural balance of our climate is often—independent of global warming—seriously disturbed. The level of air pollution in urban centers, traffic corridors, and industrial areas is higher than in rural areas: less natural daylight and cosmic radiation exposure, less oxygen-rich and ion-rich fresh air, rather low air humidity but quite high air temperatures
("urban stone desert). The CO2 level is also above the normal threshold value. And last but not least, the constant exposure to the various forms of electromagnetic pollution is very alarming.
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Bioclimate and health
Which positive and which negative effects the bioclimate can have on human health are listed in the table below:
Bioclimate describes the physical and mental influences that are caused by climate factors, which act either singly or in combination.
How strongly humans, as well as animals and plants, are affected by a given climate depends on their state of health. According to experiments carried out by Sir Jagadish Chandra Bose, healthy plants would die only at temperatures around 60 degrees Celsius (140°F), whereas less robust plants from a greenhouse would already die at temperatures around 30 degrees Celsius (86°F). With regard to bioclimatology and a healthy indoor climate, this finding should also be very important.
On the one hand, the human body must constantly defend itself against climate and other stressors and suffers, therefore, from stress symptoms. Sooner or later this may lead to the development of chronic diseases. On the other hand, climate has the potential to contribute to everything that allows people to be happy and content: well- being and health, harmony and joy of living. Unfortunately, the negative effects of climate factors are more prevalent today. It is rare to find a home with a healthy indoor climate. As with so many other areas of building, the fundamental laws of nature and biological considerations have been seriously neglected in this regard.
4 About the development of buildings
In the animal kingdom, we can find examples of simple ways to build. Here we can study how climate factors are the driving force behind the building of nests, caves, dwellings, etc. Animals, for example, pick materials with a high insulation value that are porous and loosely packed. They also make use of the great insulating quality of still air. Animals can find the required building materials in their immediate natural environment such as twigs, wood, clay, hay, leaves, feathers, and wool. The various layers are arranged in such a manner that the insulation increases from the outside toward the inside.
The nests of blackbirds and swallows, the tree hallows of woodpeckers, or the burrows of hamsters are all great examples. Even such ground breeders as the pewits use the insulating quality of twigs and rocks—in the case of sandpipers seashells—which they arrange so expertly that the still air pockets found in-between those layers can protect their fragile eggs and young birds from the moist, cold underground.
Ancient dwellings of human origin are rather similar to those of animals. Even today there are still regions where huts, tree houses, caves, yurts, and tents are built from wood, bamboo, clay, rocks, reed, straw, millet straw, leaves, cotton, wool, or bark.
Figure: Building with bamboo in Indonesia
Locally available building materials, the prevalent climate conditions, and the types of construction are closely related to each other. Simplicity and functionality are the hallmarks of such dwellings.
5 Even in steppes and desert zones that face extreme changes in daily weather conditions, these dwellings have been serving the needs of the local people for thousands of years. Moreover, this type of weather protection is completely free of charge; it only requires the labor of the homeowner and maybe that of his or her neighbor. And also in more sophisticated buildings with added structural strength and home decor, time-tested and locally available building materials are used, following traditional building methods. Stone and brick structures, primarily air-dried clay bricks, played a greater role in the development of cities in warmer regions such as Egypt, Greece, Rome, and Iraq; the scarcity of wood due to forest clearing had promoted this way of building.
In Europe, about 60-70% mineral-based building materials (bricks, clay, lime, etc.) and about 30-40% plant-based building materials (wood, cork, straw, reed) were used until the beginning, and in some regions until the middle, of the 20th century. In only a very short time, this ratio has radically changed. Today, only 10-20% mineral-based and 1- 5% plant-based building materials are used; the large majority of the remaining 80-90% of the building materials consists of highly processed and synthetic materials (concrete, steel, glass, plastics, etc.). This is especially true for a large portion of new construction. This change—also in combination with modern heating systems and electrical wiring systems—has led to a myriad of unsolved problems, especially with regard to indoor climate. Climate considerations for livestock barns
Prof. Hinrich Bielenberg from the Braunschweig University of Technology in Germany carried out much research in this area. After having studied several thousand livestock barns, he arrived at the following conclusions: ”Bad” livestock barns shorten the animals' life-span, cause sterility and many diseases (infectious diseases, rheumatism, and others), reduce performance (weight gain, milk output), and increase feed consumption. In the case of pigs, the feed consumption almost doubles compared to ”healthy” livestock barns.
These negative effects are primarily mediated by climate factors such as the temperature of air, walls, and flooring; air humidity and building material moisture content, air and vapor exchange (ventilation, diffusion, condensation); fresh air supply; air ionization and indoor electromagnetic quality; water vapor sorption capacity of building materials (moisture exchange, odor, uptake of toxins); drafts; thermal insulation or conduction.
Based on his research, Bielenberg is convinced that the air quality in a wrongly built livestock barn cannot be saved with the installation of a ventilation system later on. Hard building materials such as concrete and natural stone, he considers to be unsuitable. The composition of a given barn ceiling is especially important for the air quality of a livestock barn because it acts as a buffer zone. Ideally, the ceiling is made of e.g. wooden boards that are covered with straw or a straw-clay mixture.
6 Physiological considerations
The human body maintains a constant core body temperature (internal organs) of ca. 37°C or 98.6°F; only a few tenths of a degree higher are already regarded as a fever. Across individual body areas, temperatures range from 22°C or 71.6°F for the nose and ears to 40°C or 104°F for the liver. The skin temperature falls within 30-35°C or 86-95°F, on average at 32°C or 89.6°F.
Body heat is constantly generated by the body's metabolic activity. The energy turnover is especially dependent on body movement and during vigorous exercise it can increase by 30%. The balance of body heat is constantly maintained by regulating skin blood circulation, skin pore size, perspiration rate, and breathing volume.
The human body either gives off heat—under normal conditions on average 100 W/h— or, depending on the external climate conditions, picks up heat.
The amount of heat transfer is dependent on indoor air temperature, surface temperature, air humidity, air movement, and thermal conduction of contact materials such as clothing (see also course modules "Environmental Building Materials Assessment / Building Science" and "Energy-efficient Building Design").
7 Thermal conduction and surface temperature
The heat transfer of the human body is to a great extent affected by the surface temperature of the surrounding surface areas as well as furnishings, especially with regard to thermal conduction and thermal radiation. Not only the surface temperatures of flooring, walls, and windows are of concern but also those of furniture (especially tabletops), equipment and machine parts, as well as clothing (especially footwear).
Figure: Comparison of heat transfer rates of various body parts (20°C / 68°F ambient indoor temperature) Source: W. Frank, Gesundheits-Ingenieur 2, 1969
According to the above Figure, the primary cause of thermal perception is the thermal energy that is either gained or lost by the body's surface through thermal radiation, convection, and conduction. The comparison of the heat transfer rates of various body parts shows that those areas that lose the most heat such as head, hands, and feet comprise only about 12% of the total body surface area. Feet lose heat primarily via thermal conduction through the soles of footwear, whereas head, hands, and trunk exchange heat mainly through thermal radiation and convection. Despite their rather small surfaces areas, head, hands, and feet serve as special indicators of thermal comfort.
8 At this point of our discussion, the following observation can be made: For a healthy indoor climate, sufficiently high surface temperatures and especially flooring that is warm to the feet (including appropriate footwear) are very important. A building material is considered to be warm to the feet when its thermal conductivity is ca. 0.20 W/mK.
A comparison of flooring materials:
Carpeting 0.06 W/mK
Cork tiles 0.07 W/mK
Softwood (e.g. spruce flooring) 0.13 W/mK
Linoleum 0.17 W/mK
Hardwood (e.g. oak parquet) 0.18 W/mK
Ceramic tiles 1.30 W/mK
Cement floor 1.40 W/mK
Marble 3.50 W/mK
The difference in thermal conductivity between a carpet and a marble floor, for example, is 1 : 58.
Experiments with an artificial foot of 30°C or 86°F confirm the importance of flooring that is warm to the feet. After 5 1/2 minutes of contact with a selected flooring material, the foot temperature was reduced to:
Cement screed ca. 24°C ca. 75°F
24 mm / 1-inch wood flooring ca. 28°C ca. 82°F
8 mm / 1/3-inch cork parquet ca. 29°C ca. 84°F
These surface temperature patterns can have a great impact on our well-being and health (common cold, rheumatism, circulatory disorders, disorders of internal organs). This holds especially true for children, who play on the floor, and those people who adhere to a sedentary lifestyle.
9 The thermal properties of building materials, especially thermal conduction and heat storage capacity, also determine the speed with which a given surface temperature can be reached when heating a space.
In an experiment, the indoor air temperature of a given room was raised from 5°C to 20°C (41°F to 68°F) after one hour of heating. The respective surface areas gained heat as follows:
• Cement floor went up to 7°C or 45°F • Wood floor went up to 12°C or 54°F • Cork floor went up to 16°C or 61°F
Figure: Correlation between mean indoor air temperature and wall surface temperature (thermal comfort zone in blue) Source: Wilhelm Ledwina, Angewandte Bioklimatologie mit modernen naturnahen Heilmethoden [Applied bioclimatology with modern natural healing methods], 1981
The Figure above reveals the following correlations: If the mean wall surface temperature (including windows) falls 5°C or 9°F below the indoor air temperature of about 20°C or 68°F, the latter has to be raised by about 2-3°C or 3.6-5.4°F in order to ensure that human temperature perception is within the thermal comfort zone.
An increase in indoor air temperature by about 1°C or 1.8°F will result in an increase in heating costs by ca. 5-6%. So if the indoor air temperature is raised, for example, from 21°C to 23°C or 69.8°F to 73.4°F, the heating costs will increase by ca. 10-12%.
Therefore, walls and floors of living spaces should ideally be at the most 2°C or 3.6 °F lower or at the most 5°C or 9°F higher (e.g. in-wall or in-floor heating) than the indoor air, measured at 10 cm distance. 10 When the temperature falls below the dew point, condensation may occur on cold surfaces. This is another reason why sufficiently high surface temperatures are so important because the damage both to the building as well as the occupants' health can be avoided. Moisture accumulation, corrosion, cracking plaster, peeling paint and wallpaper, lowered thermal insulation, mold and fungal contamination, just to name a few, may, for example, result in allergies, asthma, and rheumatism (see also course module "Air and Pollutants").
The thermal insulation of exterior building components such as exterior walls should be chosen in such a way that the dew point is moved to the outside of the wall system and the thermal transfer coefficient (U-value) or thermal resistance (R-value) meets local building codes. In Germany, with a mainly moderate to cold climate zone, the IBN recommends to keep the heat transfer coefficient or U-value below 0.5 W/m2K, which is equivalent to an R-value of about R-20 (see also course module "Environmental Building Materials Assessment / Building Science"). Moisture accumulation, inappropriate dimensions, or thermal bridges (e.g. foundation walls, exterior corners, or cantilever balcony slabs) often lead to surface temperatures on the inside of exterior walls, especially in older buildings, that are well below the optimal temperature of ca. 20°C or 68°F. It is best not to place beds against such cold walls. At least the thermally sensitive head should not be placed in their immediate vicinity; this also applies to areas right below windows.
Large pieces of furniture and built-in cabinets including their contents are also at risk when placed against such cold walls. Since those furnishings reduce or even prevent much-needed air circulation, the furniture itself as well as its contents (clothing, books) are prone to moisture damage, musty odor, and mold growth. From a building science point of view, they are nothing more than interior insulation that moves the dew point farther inside and increases the incidence of condensation.
11 Windows and indoor climate
In the context of indoor surface and air temperatures, window areas play an important part, especially in modern glass architecture with a preference for large window areas that often can take up more than 40% of the total floor area. In these types of rooms, the heat loss through windows can be substantial ("heat leaks").
Type of window Ug-value* Surface temperature Surface temperature W/m2K at 0°C / 32°F at -10°C / 14°F Single glazing 5.8 4.9°C /40.8°F -2.6°C / 27.3°F Laminated glass 3.4 11.2°C /52.2°F 6.7°C / 44.0°F Insulating double glazing 2.8 12.7°C / 54.9°F 9.1°C / 48.3°F Insulating triple glazing 2.3 14.0°C / 57.2°F 11.0°C / 51.8°F Casement window (1 + 2) 2.0 14.8°C / 58.6°F 12.2°C / 54.0°F Casement window (2 + 2) 1.4 16.4°C / 61.2°F 14.5°C / 58.1°F High-solar-gain low-E double 1.1 18.1°C / 64.6°F 16.7°C / 62.1°F glazing High-solar-gain low-E triple 0.6 19.4°C / 66.9°F 18.7°C / 65.7°F glazing For comparison: Exterior wall 0.4 19.0°C / 66.2°F 18.4°C / 65.1°F *U-value = heat transfer coefficient Ug-value = U-value of glazing, see also "Envrionmental Building Materials Assessment / Building Science"
Table: U-factor and temperature of interior window surfaces at an indoor temperature of 21°C / 70°F
According to this table, the differences between the indoor air temperature of 21°C or 69.8°F and the temperatures at the windows are as follows: 16.1°C to 23.6°C or 61°F to 74.5°F for single glazing and 8.3°C to 11.9°C or 46.9°F to 53.4°F for insulating double glazing. This not only leads to drafts and thermal discomfort but also to an enormously high heat loss.
Due to passive solar gain, indoor temperatures may easily exceed the desired level which is why ventilation strategies must be implemented. Providing ventilation through open windows and doors will only be truly effective when it is done during the cool morning, evening, or night hours so that the entire building structure can release stored heat. However, because of outdoor noise levels, windows often cannot be opened sufficiently; in those instances, mechanical ventilation systems may make sense.
Low-E glazing is coated with a microscopically thin film of silver or gold (metal coating thickness 0.011 µm), which reflects back the long-wave infrared radiation from indoors. During winter the metal coating contributes to substantial energy savings, but it also prevents cooling during summer, which would have to be compensated for with increased ventilation. Once all advantages and disadvantages are considered, low-E
12 windows certainly have their place in the building industry (see also course modules "Energy-efficient Building Design" and "Light and Lighting").
Metal-coated solar-control glazing, which is mainly used in office buildings, reflects both some infrared (heat) as well as optical radiation (light). It does so not only in summer but also on cold days at which time solar heat would be desirable, among other things, to save energy. As an alternative, solar protection systems would be better or electrically conductive glazing, which offers on-demand shading (not yet commercially available).
Even more important than installing the appropriate glazing is the effort to regularly spend time outdoors. It is only out in the open air that humans are immersed in the radiation environment of the atmosphere and the Earth without any barriers; it is only here that humans are exposed to sufficient UV radiation and the entire spectrum of natural daylight. This is especially important for sick people who are no longer able to go outside on their own. Therefore, each and every apartment and home should have a wind-protected area (SE to SW) with barrier-free access to the open air (e.g. patio, porch, balcony).
Solar shading devices (louvers, blinds, etc.) do decrease heat gain, but they also diminish visible light transmittance and a clear view to the outside. Thus they are not ideal. Provided that roof and balcony overhangs are properly dimensioned, it is often possible to do without solar shading devices in moderate climate zones. Solar radiation is best controlled with deciduous trees (including shrubs, perennials, or pergolas with climbing plants). During summer their leaves reduce the solar radiation. During winter, when the trees have shed their leaves, the solar energy can then be used for heating the indoors.
There are many factors that need to be properly balanced while considering the building materials for the entire structure to achieve optimal thermal, air, and light conditions during each season: the size and positioning of windows, the shading due to trees and plants, drapes, porches, roof overhangs, balconies, railings, etc. This type of "natural climate control" not only provides a comfortable indoor climate, but in many locations it also makes air-conditioning systems unnecessary and, in combination with other strategies, reduces heating costs.
These issues concerning thermal comfort are very important and should be considered right from the start of the planning process based on a design of natural and structural climate control. Building Biology Energy Advisors IBN are especially well qualified for this task.
13 Optimum indoor air temperature
The following criteria affect human thermal comfort, singly and in combination: air temperature, surface temperature, type of heating source, air movement as result of unbalanced thermal conditions, drafts, and temperature-related air humidity.
Our temperature perception averages between air and surface temperatures of a given space, but it is limited to differences of ±2 to 3°C or ±3.6 to 5.4°F between these two sources of heat. Individual surface areas, mostly windows or thermal bridges, cause thermal discomfort when they exceed the above-mentioned temperature difference. The physiological impact is based on the uneven heat loss of the human body as well as convective drafts (see Figure Correlation between mean indoor air temperature and wall surface temperature ).
Thermal perception varies greatly among different individuals, especially with regard to clothing, physical activity, food consumption, age, health status, gender, adaptation, type of heating, air humidity, season, light and color conditions. Air temperatures between 20-24°C or 68-75°F are considered normal. However, 22°C or 68°F are considered warm in winter but cool in summer. A warm color such as orange, for example, increases the subjective perception of temperature by 1-2°C or 1.8-3.6°F (see also course module "Natural Colors and Finishes"). The thermal comfort zone of "comfortably warm" falls between 17°C and 27°C or 63°F and 81°F. It should go without saying then to show tolerance to those people with a different temperature perception. In occupational settings, it would be very useful to establish workspaces with different temperature zones.
Indoor air temperature recommendations
Living room and office 18 - 22°C 64 - 72°F Bedroom 15 - 17°C 59 - 63°F Bathroom 20 - 23°C 68 - 73°F Staircase 10 - 14°C 50 - 57°F Kitchen and during light physical activity 18 - 20°C 64 - 68°F Workshops and during heavy physical activity 15 - 17°C 59 - 63°F
Habituation plays an important part in the physiological sensitivity to temperature, e.g. to high indoor air temperatures. For health and environmental reasons, it would be desirable to regularly check if the indoor air temperature could be slightly lowered. Wearing warmer clothing at home and at work should also not be a taboo topic.
14
clo = clothing unit = insulation value of clothing 1 clo is equivalent to the thermal resistance 160 m2K/kW
Figure: Impact of relative air humidity, clothing, and activity level on thermal comfort temperature Source: Wegner, J. „Luftqualität in Innenräumen [Indoor air quality]“, G. Fischer Verlag, 1982
The temperature range of thermal comfort is very broad from about 0°C to 30°C or 32°F to 86°F, especially when considering extreme values of such factors as air humidity, activity level, and clothing (clo) (see also Figures).
Figure: Relationship between clothing and its insulation value Source: Klaus Fiedler, Alles über gesundes Wohnen [Everything about healthy living], Wohnmedizin im Alltag, 1997
For energy and health reasons, it is not desirable to maintain the same high temperature throughout an entire building.
15 Even in nature large differences can be found within a small space (sunshine/shadow, with or without wind, on stone or wood floor). Stimulation caused by changes in temperature levels can refresh and strengthen the human body. Similar temperatures across the rooms of a building with low energy consumption, however, cannot be avoided. It is recommended that in particular occupants of those buildings spend more time out of doors.
As could be shown in a series of tests at schools and workplaces, excessively high temperatures—whose perception varies greatly among individuals and can be easily reached with a few degrees Celsius during physically demanding work—lead to a poorer ability to concentrate, a lower performance, more mistakes, an increased pulse rate and skin moisture/temperature, as well as to tiredness and discomfort.
During intense mental activities, the air temperature should not rise above 18°C or 64.4°F. Provided that the surface temperatures, especially those of the floor, are sufficiently high, an air temperature of only 16°C or 61°F has been shown to work best ("Keep your head cool and your feet warm."). Appropriately low temperatures promote deep breathing, which is especially important for regeneration during sleep. This positive effect may also be mediated through the increasing level of oxygen found in air when its temperature decreases.
Feeling too cold, however, also diminishes the ability to concentrate during mental activities and causes restlessness, a desire to move, decreased body heat, and discomfort.
Within the thermal comfort zone, air humidity does not have any substantial effect on temperature perception.
The base temperature level experienced as comfortable increases with increasing air movement. This is especially true of drafts along the floor. A difference of only 2°C or 3.6°F between surface and air temperatures will cause an air speed of 20 cm/s or 40 ft/min (fpm), which is about the threshold level of draft sensations. In living and work spaces, the air speed should not exceed 15 cm/s or 30 ft/min (fpm) during sedentary activities.
Minimal air movement is especially important during sedentary activities and rest. Drafts are perceived as uncomfortable. They cause massive heat loss in localized areas and especially sensitive people may develop colds, conjunctivitis, as well as neuralgic (intense, typically intermittent pain along the course of certain nerves) and rheumatoid disorders. Draft is one of the most frequent causes of occupational diseases (source: Hauptverband der gewerblichen Berufsgenossenschaften, today called "German Social Accident Insurance").
During strenuous physical activities, an air speed of 50 cm/s or 98 ft/m (fpm) can also be tolerated or even enjoyed. Totally still air, however, is undesirable since it impairs breathing and leads to heat stress, perspiration, and tiredness. It also diminishes the fresh air supply and causes heat and moisture to accumulate in certain areas of a given space. 16 In occupational health and safety regulations, special attention is given to favorable temperature conditions: quotes from the German Workplace Ordinance (ArbStättV) (2004/Germany), Thermal Environmental Conditions for Human Occupancy (ASHRAE Standard 55-2010/USA), Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings (ASHRAE Standard 62-2013/USA), Office Ergonomics (CSA Standard CAN/CSA Z412-00 R2011/Canada), Thermal Comfort Guidance (2012/Australia), The Workplace (Health, Safety and Welfare) Regulations (1992/UK), Directive Concerning the Minimum Safety and Health Requirements for the Workplace (1989/European Council).
Summary of indoor air temperature
Optimum indoor air temperature depends on:
• Surface temperature of all surrounding surface areas • Individual perception • Clothing • Type of activity • Air movement (draft) Indoor air temperatures that are too high or too low will cause thermal discomfort and lead to health problems in the long run.
For energy and health reasons, it is not desirable to maintain the same temperature throughout an entire building.
It is important to be able to quickly adjust the indoor thermal environment.
Different people have different needs for thermal comfort.
Indoor humidity and health
For a long time, low indoor humidity levels were seen as the cause of numerous health symptoms. Today we know that the actual cause of these mostly respiratory and skin- related symptoms is not dry air but the increased dust level and static electricity associated with it, beside other possible causes.
The most common measure of air humidity is relative air humidity. Among experts, however, the preferred measure is absolute air humidity because this measure reflects the actual amount of water vapor in a given volume of air. It allows you to calculate how much condensate may be formed at maximum or how much water must be evaporated in order to reach a desirable level of air humidity. 17 Humans breathe ca. 23,000 times per day, thereby moving about 12 m3 or 424 ft3 of air and, under normal conditions, exhaling 60 g or 2 oz of water vapor per hour. At high humidity levels, however, this amount of water vapor is substantially reduced, e.g. 30 g or 1 oz per hour at 70% relative air humidity and 20°C or 68°F. During high physical activity, it can increase up to 150 g or 5 1/3 oz per hour in dry, warm air. Exhaled air is saturated with water vapor and kept at body temperature. In other words, it contains 43.92 g or 1 1/2 oz of water per 1 m3 or 35 ft3 of air at a body temperature of 37°C or 98.6°F. The humidification is achieved by the large inner surface area of the lung, which measures 100-120 m2 or 1076-1292 ft2. The cooler and drier the inhaled air is, the more water vapor can be passed on during breathing. At 0°C or 32°F, the inhaled air contains a maximum of 4.84 g water/m3 so that humans can exhale 39.08 g/m3.
Along with the water vapor, toxic metabolic products are also exhaled.
Air temperature Relative Waster content Amount of body air humidity (%) of air (g/m3) moisture given off per m3 of breathing air 0°C / 32°F - 100 4.84 39.08 Snowfall 0°C / 32°F - Nice 50 2.42 41.50 winter day 4°C / 39°F - Nice 100 6.40 37.52 fall day 18°C / 64°F - Good 45 6.93 36.99 indoor climate 20°C / 68°F - Good 50 8.65 35.27 indoor climate 20°C / 68°F - Dry 25 4.33 39.59 indoor climate 20°C / 68°F - Humid 70 12.11 31.81 indoor climate 30°C / 86°F - Nice 10 3.03 40.89 summer day 30°C / 86°F - Humid 40 12.12 31.80 summer day 30°C / 86°F - 100 30.30 13.62 Tropical climate Table: Impact of air temperature and air humidity on the amount of body moisture given off per m3 of breathing air
18 The question we face is which level is more desirable and which is the optimum level? Experience tells us that we feel especially well in cool, dry air during winter sports activities and that winter vacations tend to be more refreshing than summer vacations. This type of climate promotes deep breathing. The same also applies to dry air during warm summer days. At 30°C or 86°F and 10% relative air humidity, people feel quite comfortable. However, at 30°C or 86°F and 40% relative air humidity, the weather will already be considered to be muggy. Dry or cold air, respectively, allows large amounts of moisture to be excreted through breathing, including metabolic waste products and heat generated by the body's metabolic activity.
In contrast, breathing is more difficult during humid weather conditions or in spaces with high air humidity. Humid air makes one tired, leads to heat stress, autointoxication, and fatigue. Except for viruses, high humidity levels increase the level of disease- causing microorganisms. Odor nuisance is also greater than in dry air. In this context, associated building damage, increased energy consumption, and mold contamination along with the resulting diseases also need to be taken into account. An indoor climate of 20°C or 68°F will promote such conditions especially from 60% relative air humidity, but not when the air is cooler. This comparison makes clear that it is the absolute air humidity that is crucial for physiological considerations.
From a medical perspective, relative air humidity levels of about 45-50% are often considered to be optimal at common indoor air temperatures; these levels should neither fall below 30% nor exceed 60% relative air humidity. During winter, however, relative air humidity levels in our living spaces, workplaces, and classrooms often range between 20% and 35%, and even 15% is not rare, especially during cold, dry days and when ventilation as well as air-conditioning is used in spaces with higher room temperatures.
Occupants of such rooms often complain about "bad air" and such symptoms as colds, dry throat, dry eyes, dry skin, as well as fatigue, headaches, and a decline in performance. According to available studies, however, we need to be more specific (sources: Das Luftfeuchte-Buch [The air humidity handbook] by Dipl.-Ing. Jens Bellmer and a literature review by the Berufsgenossenschaftlichen Institut für Arbeitsschutz BGIA [today called Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA)], 2007):
• Dry throat There is this notion that very dry air would dry out the mucous membranes of the airways, which would lower their resistance against bacteria and viruses and, as a result, would also increase a person's susceptibility to colds and the flu. It is a fact, however, that the humidity level of the inhaled air on its way to the lungs is regulated. Healthy airways are capable of humidifying the inhaled air to compensate for its dryness, even for extended periods of time. This statement applies to low-dust air only. In addition, these statements also do not apply to people suffering from respiratory diseases such as asthma.
19 • Colds and the Flu Most studies come to the conclusion that the lower the relative air humidity is, the more likely it will be that a person comes down with the flu. Presumably, the cause is that the survival rate of flu viruses is much higher at lower levels of relative air humidity than at higher levels. In addition, low relative air humidity supports the development of dust and also keeps those dust particles and the attached microorganisms airborne longer.
• Dry eyes By increasing the relative air humidity, the incidence of dry eye symptoms can be reduced. The cause is assumed to be a decreased rate of evaporation of the tear fluid as well as a lower dust level as the humidity rises.
• Skin problems In many people low air humidity causes dry skin. The causes are still unclear. It is assumed that, among other things, a low relative air humidity causes an increase in static electricity (see further below) that, in turn, also causes an increase in the level of fine dust, which settles on the skin, extracts moisture from the skin, and thus may trigger skin problems.
As a general rule, dry air is not the actual cause of the described symptoms but of the following factors (source, among others: Gassel R. P., “Innenraumbehaglichkeit [Indoor thermal comfort]”, journal “Wohnmedizin” No. 41, 2003):
• Drafts • Air pollutants • Increased dust level, e.g. when dust particles are burnt due to heating systems with a high surface temperature • Static electricity • Preexisting diseases, especially of the respiratory tract and skin Low relative air humidity supports the development of dust and also keeps those dust particles and the attached microorganisms airborne longer.
In addition, low air humidity promotes an increase in electrostatic charges, for example, across synthetic carpeting or high-gloss finished surfaces and an increase in associated phenomena such as electrostatic discharge sparks on door handles, fly- away hair, crackling when taking off a piece of clothing, accumulation of dust particles as well as dust clusters. It also causes indoor air ionization to become predominantly positively or negatively charged. The airways are lined with mucous membranes whose epithelium features tiny hairs (cilia) that beat back and forth. This natural movement is slowed down when exposed to positively charged, dusty air. As a result, crusts form, its self-cleaning action regarding dust and bacteria is impaired, and disease may set in.
20 Therefore, the adverse health effects of low relative air humidity are mostly indirect. This statement certainly has practical implications because a desired water vapor content of the air would have to be adjusted with costly air-conditioning or with often insufficiently effective humidification units, which may even pose a health risk as a breeding ground of microorganisms. In contrast, it is often sufficient to reduce the dust accumulation with suitable strategies (vacuuming with HEPA filter, damp mopping, etc.).
What affects indoor humidity?
Indoor air humidity depends on:
• Indoor air and surface temperatures (when indoor air temperature rises, the relative air humidity drops) • Type of heating system (especially with regard to radiant and convective heat) • Intensity of ventilation • Type of building materials and furnishings (hygroscopicity, diffusion; see also course module "Environmental Building Materials Assessment / Building Science") • Number of occupants in a given room (or room size per person) • Activity level of occupants • Outside climate
Provided that many of the materials of a given space are hygroscopic or capable of taking up moisture, the humidity fluctuations of the air will be reduced and less water vapor will escape through natural ventilation, and thus the humidity level will on average be somewhat higher. The building materials that at the same time are open to water vapor diffusion prevent the occurrence of condensation, so this is another reason why the indoor air would lose less humidity.
Moreover, the room size per person and the activity level of the occupants are also important factors. As mentioned earlier, the amount of water vapor generated through breathing and perspiration is not negligible. This is especially important to consider in high-occupancy spaces, e.g. meeting rooms and classrooms.
The amount of water vapor in a normal residence, however, is also not negligible. In a 3- person household, about 6 liters or 1.4 gallons are generated daily. This amount must be taken into account in order to avoid mold and moisture damage.
21 Sources of moisture in residential buildings
Person at rest ca. 40 g/h Person performing light activities ca. 90 g/h Houseplant (medium size) ca. 5 g/h Cooking and wet cleaning ca. 600 g/h Washer ca. 300g/load Dishwasher ca. 200g/load Shower ca. 1700 g/bathroom Bath ca. 1100 g/bathroom Open water surfaces ca. 40-200 g/h and m2 or 10.8 ft2
Accumulation of moisture in a 3-person household
Persons (at home for 17 h) 2550 g/day 15 houseplants (different sizes) 1000 g/day Kitchen 800 g/day Bathroom 800 g/day Miscellaneous 700 g/day Total 5850 g/day
Tables: Various sources; among others, German Federal Office for Building and Regional Planning (BBR)
22 How are air humidity, thermal insulation, wall moisture, and mold contamination connected?
The negative consequences of wall moisture and mold are very complex:
• Poor indoor climate • Toxic mold spores • Cold walls • Increase in heating requirements due to evaporation cooling and lower insulation value (higher U-value, lower R-value). The U-value of damp building components is usually considerably higher and the R-value considerably lower than the laboratory values provided by the manufacturer. • Unpleasant odor • Favorable conditions for insects, bacteria, and mites • Destruction of the building structure (efflorescent salts, corrosion, frost, fungal growth) but also furniture, clothing, etc.
What are the causes of moisture problems with mold?
In common lawsuits, not only tenants and landlords, building owners and building contractors or architects fight over these problems but also building experts, building scientists, as well as lawyers. We will not discuss building defects that are due to construction errors such as a leaky roof or the lack of barrier layers as the cause of moisture problems.
On the one hand, occupants are accused of incorrect behavior. The most common accusations are:
• Insufficient or incorrect ventilation • Insufficient heating • Insufficient spacing between furniture and exterior walls • Excessive moisture accumulation due to cooking and washing (without exhaust fan) or because of too many indoor plants
On the other hand, the phenomenon can also be explained by building science; the most frequent causes are:
• Poor insulation values (dew point too far on the inside) • Thermal bridges, e.g. cantilever balcony • Missing or faulty vapor barrier/retarder • Leaks (cracks, joints, etc.) 23 • Insufficient vapor diffusion capacity • Use of nonhygroscopic building materials (and furniture) • Windows too airtight
Building experts usually suggest the following strategies to solve moisture problems:
• Additional insulation of exterior walls • Installation of vapor barriers • Controlled air supply and air exhaust • Modification of user behavior of occupants
Building biology environmental consultants strive for a natural solution to these problems. The experience with natural building materials as well as the respect for the laws of building science form the basis. In new or retrofit buildings that were properly built according to building biology and building science principles, there will be no condensation problems under normal occupancy conditions.
When natural building materials open to diffusion such as wood, brick, clay, and lime plaster are used, these materials absorb moisture and wick it away through capillary action (buffer effect). As far as building science is concerned, this is an important property that is blocked or at least dramatically reduced through vapor barriers, dense coatings, wood products with a high adhesive content (e.g. OSB boards, particle boards), synthetic resin plasters, or synthetic insulation materials.
How to best remedy a damp building with mold growth? (see also PDF "Schimmel - Ursachen, Folgen und Sanierung" and course module "Air and Pollutants")
As a first step, it is important to discern the causes of the moisture. Not every building can be transformed into a perfect eco-home, meeting all building biology requirements. However, the quality of living can always be noticeably improved.
As a general rule, the moisture content of the exterior walls shall be measured on the surface and at mid-wall with a wall and wood moisture meter. If any of those areas check out to be too damp, possibly the plaster, acrylic latex finishes (exterior and interior), airtight wallpapers, or the like must be removed. Masonry or concrete walls should be left to dry out for several months before they are refinished with materials open to diffusion, or before an exterior insulation is installed.
Often, however, it may not be possible or desirable to carry out such costly and complex remediation efforts. In those cases, it is recommended to take one remediation step at a time. Only if the one step taken does not deliver long-lasting results will the next step be taken. Often, however, only the combination of several steps will provide the desirable result:
24 1. Remove surface mold in a manner that is both safe and professional (caution: mold spores can be highly toxic!, see also course module "Air and Pollutants")
2. Change occupants' behavior: ventilation, heating, reduce moisture sources
3. Monitor air humidity with hygrometer
4. Carry out remediation measures: remove building defects due to construction and/or building science errors, possibly install exterior insulation (see also course module "Environmental Building Materials Assessment / Building Science" and others)
5. Install self-adjusting trickle vents in the windows and/or install a mechanical ventilation system
6. Possibly add baseboard, floor, or wall heating (see also course module "Heating and Ventilation")
Figure: Maximum water vapor content of air in relation to temperature The warmer the air is, the more moisture it can absorb: 0°C or 32°F = 5 g/m³, 20°C or 68°F= 18 g/m³. When cold outside air is heated up, the moisture from building materials and furniture is absorbed. The colder and drier the outside air is, the shorter the ventilation periods can be. Ideally, occupants cross-ventilate by completely opening windows (and doors!) on opposite sides of a room several times a day. In contrast, ventilating a basement in summer usually is counterproductive because warm outside air cools down and the excessive moisture may condense.
At night, at least one window should be slightly open in the bedroom or an appropriate ventilation system should be installed. Bedrooms must not be heated with the warm, stale, and damp air from the living room or even the kitchen or bathroom. Bedrooms often are not heated as much and the surface temperatures of their walls tend to be lower. As a result, condensation may occur when the relatively damp air from the bathroom or kitchen cools down. Bedding and mattresses would also absorb this moisture and then provide a breeding ground for mites, mold, and bacteria.
25 Kitchens as well as bathrooms, especially bathrooms without windows, should be equipped with an air exhaust fan. Furniture should be kept 5-10 cm or 2-4 in from exterior walls; large pictures are best not hung on exterior walls.
In Germany, social housing from the postwar period and numerous others from the 50s and 70s have been renovated since the 90s. Since then, many apartments have developed moisture damage and mold. What happened?
• Single masonry heaters were replaced with central heating systems. Thus the chimney stack effect is missing, which creates negative pressure in the rooms so that cold outside air is sucked into the building through leaks in the building envelope.
• Leaky windows were replaced with airtight windows.
• Insulating glazing replaces single and double glazing. As a result, the dew point of window glazing (fogged-up windows, window frost) moves toward window jambs, room corners, etc.
• New bathrooms, which are used more often for showering and bathing, were added and thus more moisture is added, too.
• Interior insulation was installed. As a result, the dew point moves closer to the inside and condensation occurs (see also course module "Environmental Building Materials Assessment / Building Science").
All of these installations caused considerable problems, which often required a second remediation effort only a few years later: repair of the new damage and installation of exterior insulation.
26 Summary of indoor air humidity
Air humidity is closely linked to:
• Temperature (including outdoor temperature) • Dust level and microbial count • Gases and airborne particulates • Ions and static electricity
Major factors that affect relative air humidity:
• Indoor air temperature • Type of heating • Level of ventilation • Building materials • Number of occupants • Number of persons in a given room • Moisture sources (plants, cooking, shower, etc.)
Disadvantages of warm-dry air caused by heating:
• Especially due to a higher dust level, mucous membranes of the respiratory tract become dry and irritated; colds, dry eyes, skin problems, tiredness, and headaches occur more frequently • Increase in static electricity • Decrease in negative ions
Disadvantages of too humid air:
• Breathing becomes difficult • Tiredness • Leads to autointoxication over time • Building damage • Mold contamination
Recommendations for healthy humidity levels:
• Average relative air humidity from about 40% to 60 %: If air humidity falls below this range for a few days, this is usually not a problem and there is no need to artificially humidify the indoor air. Where appropriate, the indoor air temperature can be lowered, whereby relative air humidity will increase. Then the air is often perceived as more comfortable.
• Avoid air that is too humid (>60% r.h.): This is much more important than to avoid dry air. Humid air is perceived as tiring, often leads to odor pollution, and 27 promotes the development of pests and microorganisms harmful to health such as mold, fungi, and bacteria, which eventually can also lead to building damage.
• Keep dust level low: Use materials that do not generate and/or attract dust (e.g. avoid wall-to-wall carpeting). Use a vacuum cleaner with HEPA filter, prefer damp mopping, clean heating elements, etc.
• Use materials with humidity-buffering properties, which do not become easily charged: Most of the materials recommended in building biology such as wood, natural fibers, as well as clay and lime products belong here. Please note that these materials should not be covered/painted with varnishes or varnish-like coatings (e.g. acrylic latex paints).
• Choose a radiant heating system: In the case of a radiant heating system, lower indoor air temperatures (see above) are usually perceived as more comfortable compared to a convective heating system.
• Optimize ventilation: In winter, windows may be opened too often or the outdoor air intake setting of the ventilation system may be too high. This causes relative air humidity levels to fall. Ventilation, therefore, should be optimized according to the fresh air supply actually required—also for reasons of energy efficiency.
• Avoid humidifiers whenever possible because they are associated with a high risk of microbial contamination as well as high electricity costs, unpleasant noise, and electromagnetic fields. If a humidifier cannot be avoided, it should have a hygrometer that turns the unit off when a certain level of relative air humidity is exceeded. In addition, such units need to be regularly maintained and cleaned. Indoor plants are better than a technical device, but the potential presence of mold and bacteria in the potting soil must also be taken into consideration.
28
Heating climate
It is well known that the heating system is an important factor of indoor climate, and in central Europe it determines indoor air quality 60% of the year. It is less often considered that the occupants' health and well-being is also dependent on the performance of the heating system. In this area as well, technical and economic considerations are the predominant factors.
The term "heating climate" not only refers to indoor air temperature as commonly thought, but it also includes surface temperature, the type of heat, horizontal and vertical temperature differences across a given room, air humidity, air and dust circulation, dust and gas formation, odors, air ionization including electrostatic charges, and many other things such as electromagnetic field exposures and noise.
Requirements of a heating system optimized for health (See also course module "Heating and Ventilation.")
• High percentage of radiant heat with relatively cool, pleasant breathing air • Low surface temperature of heating elements, up to ca. 70°C or 158°F • Low temperature difference between surface and air temperature, max. difference about 2°C or 3.6°F • Low air and dust circulation • No thermal monotony • Adjustable to accommodate different individual needs • No buildup of electrostatic charges, field distortion, and unipolar air ionization (see also course module "Electromagnetic Radiation") • No electromagnetic field emissions (see also course module "Electromagnetic Radiation") • Easy to regulate while maintaining a constant temperature and easy to clean (no dust traps) • No odor pollution • No noise pollution • Climate-aware design and orientation of the entire building structure • Drying out of building, especially the exterior walls The ideal heating system, which would meet all of the above requirements, does not exist. To evaluate the optimal heating climate, it is well worth studying outdoor climate conditions during fair weather and sunshine. The sun emits radiant heat, which can heat our body even when there is frost. Temperatures between head and foot area vary only slightly. In general, this climate is perceived as comfortable by humans.
The German grundofen, a "true" masonry heater, and an in-wall heating system come the closest to the ideal heating system. They create a comfortable indoor atmosphere. Each occupant can choose the heating zone of his or her preference, since the radiant heat decreases as the inverse square of the distance. 29 Many people have rediscovered this original source of heat with its comfortable radiant heat so that it got back in style. One large masonry heater or grundofen in the center of the building is often sufficient to heat several rooms or even a smaller, well-insulated single-family home. Modern masonry heaters are equipped with exterior air supply and automatic controls. With the addition of a water storage tank, they can be transformed into a central heating system.
The other types of heating deviate more or less from the ideal conditions. This holds especially true for single space heaters, which, due to their very hot surface temperatures, give rise to air and dust circulation, as well as burnt dust particles. In this process, ammonia and organic acids are formed that cause odor pollution and may lead to irritations. Moreover, larger dust particles can disintegrate into fine particulate matter that is harmful to human health (source: Dr. med. Walter Conzelmann, Urbach).
Ventilation and health
The air we breath is often polluted. Pollutants include carbon dioxide, carbon monoxide, sulfur dioxide, nitric oxides, hydrocarbons, dust particles, etc. Especially in major urban areas, heavy traffic, and industrial areas, polluted air causes major health problems including acute and chronic diseases, lowered immune response, higher susceptibility to infectious diseases, lower life expectancy, as well as mental disorders.
This is the context in which we need to see the impact of the often heavily polluted outdoor air on the indoor air quality. Outdoor and indoor air must be considered together, especially when air-conditioning and ventilation systems are discussed.
With regard to quantity and quality, the supply of fresh air must be ensured for the following reasons: a) Lack of oxygen and excess of carbon dioxide
In enclosed spaces, breathing causes carbon dioxide levels to increase and oxygen levels to decrease. Fresh air contains about 21% oxygen and 0.04% carbon dioxide. At rest (0.5 m3/h), the exhaled air contains about 16% oxygen and 4% carbon dioxide. Sensitive brain cells are the first to be adversely affected by a lack of oxygen and an excess of carbon dioxide. Already at a level of 20% oxygen and 0.07% carbon dioxide, the first ill effects include tiredness, poor performance, headaches, and an increased breathing rate. Then labored breathing sets in. In the end, suffocation occurs at 15% oxygen and 5.4% carbon dioxide.
A carbon dioxide level of 0.07% (700 ppm or parts per million) should not be exceeded on a permanent basis.In the context of indoor air ventilation, note that the carbon dioxide level in outdoor air is often considerably higher in urban areas than in 30 rural areas. In urban areas, it may prove difficult to keep carbon dioxide levels of the indoor air below 700 ppm on a permanent basis.
We urgently warn against supplying humans with used air (see also the PDF Effects of CO2 levels on humans").
Time CO2 Number of persons 8:00 a.m. 575 - 9:00 a.m. 709 1 10:00 a.m. 678* 1 11:00 a.m. 1173 2 12:00 noon 1023 1 * Reduced levels due to frequent opening of doors
Table: Measurement of carbon dioxide levels in an office (old building) with ca. 15 m² or 161 ft2 ground floor and ca. 40 m³ or 1413 ft3 volume without ventilation with different occupancy rates (measurements by IBN)
b) Other air pollutants
Ill health, intolerable discomfort, and decreased physical performance also occur due to outdoor air pollution such as carbon monoxide, sulfur dioxide, nitrogen dioxide, aldehyde, hydrocarbons, and particulate matter (e.g. from combustion and industrial facilities, traffic, farming of animals, smoking). c) Odor pollution
The accumulation of odorous substances in indoor spaces—especially in workplaces, meeting rooms, and classrooms— often leads to intolerable odor pollution associated with discomfort and aversion. It is well known that not only ventilation and solar exposure will quickly help dissipate bad odors but absorbent building materials, as well. d) Regulation of air humidity through ventilation
Set the minimum air exchange rate in such a way that, even at the lowest anticipated indoor surface temperature, the indoor air humidity is also reduced to a level that prevents condensation from forming on any surface (see also PDF "Mold - Causes, consequence, and remediation").
Rule of thumb: When airing a space, the outdoor temperature should be at least 5°C or 9°F below the indoor air temperature to lower the moisture level in the air and materials, which is especially important for damp basements in summer.
31 e) Microorganisms harmful to health
Under normal conditions and relatively clean air, the microbial count of indoor as well as outdoor air is 100-200 colony forming units per cubic meter or CFU/m3. After water damage, the microbial count (bacteria, viruses, molds, yeasts) of indoor air often exceeds 2000 CFU/m3. Through sufficient natural ventilation and solar exposure, disease-causing microorganisms will be killed and thus reduced. If in doubt or if a high microbial count is suspected, however, an analysis and appropriate remediation are in order. f) Supply of negatively charged oxygen
The supply of ionized fresh air, that is, negatively charged oxygen is essential. Due to electron exchange, the air and especially the oxygen it contains is neutralized during breathing, which is particularly important for the regulation of the entire body such as cell charges, blood pressure, metabolism, cilia movement of mucous membranes, and growth. By the sea, the level of negatively charged small air ions can be above 2000 negative ions per cubic centimeters, whereas in apartments with cigarette smoke, this level drops to only 200 ions per cubic centimeters or less in combination with an accumulation of positively charged air pollutants. The ion counter monitoring of small air ion levels in a classroom revealed that the number of positively charged ions remained constant over one hour, whereas almost all of the negatively charged ions had been used up within the same time. Therefore, a constant air exchange is also necessary to supply negatively charged oxygen.
Heating systems also have a profound impact on air ionization. Through air movement (e.g. convective heating system), atoms and molecules are discharged while radiant heat (e.g. masonry heater) promotes the formation of negatively charged air ions.
32 Fresh air requirements of indoor spaces
A rule of thumb says that—during normal outdoor conditions—one liter (quart) of exhaled carbon dioxide requires about 1 cubic meter or 35 cubic feet of fresh air, which translates into 30-60 cubic meter of fresh air per person per hour (m3/h) or 18-35 cubic feet per person per minute (CFM).
At rest or while performing light work, a minimum air exchange rate of 50 m3/h or 30 CFM per person is considered necessary according to the German standard DIN 1946-0. In North America, the minimum ventilation requirements of the ASHRAE standard 62.1-2010 for commercial and high-rise residential buildings recommends only 26-34 m3/h or 15-20 CFM per person, a level at which complaints usually increase. In 2013 the ASHRAE standard for low-rise residential buildings 62.2-2013 increased the mechanical ventilation rate to 7.5 CFM per person plus 3 CFM (formerly 1 CFM) per 100 ft2.
While performing medium work (kitchen, workshop), the fresh air requirement will double (see Figure).
In rooms with an open fire such as a fireplace or stove or in rooms with cigarette smoke, the required amount of fresh air is several times higher. In commercial settings, the required air exchange rates are sometimes lower, 10-25 m3/h or 5.9-14.7 CFM (see German standard DIN 1946).
33 In general, the air exchange rate is a good indicator of the overall indoor air quality. According to investigations of new buildings without controlled ventilation and closed windows, the air exchange rate was mostly between 0.2 and 0.5 m3/h or 0.1 and 0.3 CFM.
In a 50 m3 or 1766 ft3 room with three occupants, the carbon dioxide level of the air increased within four hours to
7. 0.30 % (3000 ppm) at 0.3 air change per hour (ACH) 8. 0.15 % (1500 ppm) at 1.0 air change per hour (ACH) 9. 0.09 % (900 ppm) at 2.0 air changes per hour (ACH) It is desirable to keep carbon dioxide levels below 0.07% or 700 ppm.
The concentration of other air pollutants such as formaldehyde and radon is also strongly related to the air exchange rate.
A low air exchange rate can also be the cause of an increase in air humidity and, in turn, an increase in molds, bacteria, viruses, mites, and pests.
Summary of fresh air requirements
At rest or light activity levels, an air change of 50 m3/h or 30 cfm per person is recommended.
The supply of fresh air must be ensured for the following reasons:
• To provide sufficient oxygen (in normal outdoor air, the O2 level is 21%), • To avoid increased levels of carbon dioxide and other air pollutants, • To regulate indoor air humidity, • To avoid odor pollution, • To reduce microorganisms, • To supply negative ions.
The required air exchange rate may have to be increased for the following reasons:
• The number of persons in a given room increases. • There is a fireplace in the room that is dependent on indoor air for its air supply (open- hearth fireplace, gas stove, etc.). • Someone smokes cigarettes. • Occupants have a high activity level. • The level of air pollutants such as formaldehyde or radon increases.
34 Types of ventilation
Sufficient ventilation is a prerequisite for healthy indoor air, especially in mostly airtight buildings. Since rooms are often aired either too little or also too much (waste of energy), self-adjusting trickle vents or controlled ventilation systems provide a sensible alternative (see also course module "Heating and Ventilation"). For reasons of preventive health care and building preservation, the knowledge regarding appropriate manual or automatic ventilation is very important with regard to moisture and mold.
Natural ventilation
Temperature difference and wind pressure are the natural forces that provide the air exchange. We differentiate between the following types of natural ventilation: a) Natural air infiltration b) Manual window ventilation
c) Automatic window ventilation d) Ventilation with trickle vents e) Stack ventilation
a) Natural air infiltration
The contribution of natural air infiltration to the overall ventilation of a building can be substantial in certain building types (e.g. porous walls made from lightweight wood wool boards), which are no longer allowed today, or in older, leaky buildings. Depending on the strength of the wind, rates can range from 1 to 2 air changes per hour. In modern buildings, however, those rates often drop to only 0.2 to 0.5 air changes per hour. In order to save energy, building biology design also aims at this level of air exchange rate. The required ventilation can be provided by the following options: b) Manual window ventilation
We distinguish between
• Air leakage (AL) through window cracks and joints between window sash and frame, and • Ventilation through open windows
35 On average, the air leakage rate of windows, French doors, and exterior doors (in m3 of air per meter linear joint length at a pressure differential of 1 kPa/m2 per hour = AL rate for windows) is as follows:
• 1.0-3.0 m3/h per meter without window sealing • 0.2-1.0 m3/h per meter with window sealing
Because of the heat loss during ventilation, air leakage should not be higher than necessary. In North America, the air leakage rate of ENERGY STAR®-certified windows and sliding glass doors must be below ≤1.65 m3/h per meter of product opening or ≤1.5 L/s per square meter of product area. Moreover, draft conditions must be taken into account.
It says in the German Energy Conservation Ordinance (EnEV):
"New buildings must be constructed in such a way that the building envelope that transfers heat including cracks is permanently sealed airtight according to the generally accepted rules of technology."
and:
"New buildings must be constructed in such a way that the required minimum air exchange rate is provided to ensure the health of the occupants and the safe functioning of the heating system.”
Today the combined ventilation of air leakage through windows and natural air infiltration is not sufficient in new as well as renovated old buildings to meet the requirements of an adequate air exchange. Therefore, ventilation through open windows or other ventilation strategies as described below are required.
Crack ventilation means that a window or French door is opened a crack in either tilt or turn position; in winter, one complete air change takes ca. 30-75 minutes. The opening of a ventilation damper or ventilation slider is also included here. In most windows, crack ventilation cannot be controlled too much. In experiments at the Vienna University of Technology (Austria), the tilt of a window could be adjusted in 12 increments with a maximum tilt angle of 14 cm (5.5 in), thereby allowing for an air exchange rate between 20 and 200 m3/h or 11.8 and 118 CFM. Accessories for such air latches, for example, are available from hardware stores.
Intermittent ventilation means that all windows of a given room are briefly opened to allow for a complete air change; in winter, one complete air change takes ca. 4-6 minutes.
Cross ventilation means that opposite windows or at least windows from walls at right angles, which can also be located in different rooms, are opened at the same time. If windows from different rooms are separated by a door, the latter also needs to be open or a screen door needs to be installed. The above figure clearly shows that cross 36 ventilation is the most effective type of window ventilation.
During the cold season, a fast air exchange is desirable. In order to keep the heat loss low (the lower the heat loss, the faster the heating) and to avoid mold growth (in window areas with permanent ventilation of tilted windows due to a drop below the dew point), cross ventilation with wide open windows and doors for a limited period of time is always preferable to a continuous ventilation through, for example, tilted windows. However, an adequate air exchange rate must be provided in any case. It may become necessary to cross-ventilate every hour. If this sounds impractical, there are power modules for tilting windows automatically, self-adjusting trickle vents, or simple mechanical ventilation units.
The required air exchange rate depends on the outside temperatures. The lower the temperature difference between the inside and the outside air, the longer the ventilation period must be.
Low temperature difference = low air pressure gradient = slow air change (typical under summer conditions)
High temperature difference = high air pressure gradient = fast air change (typical under winter conditions)
In the case of wide open windows, for example, one complete air change takes on average (see also PDF Approximate duration of one complete air change): in spring and autumn 8 - 15 min. in summer 25 - 30 min. in winter 4 - 6 min.
When windows open to the outside as is traditionally common in Northern Germany and Scandinavian countries, opening windows is made easier. There is no flower pot in the way when opening a window.
It is not recommended to open windows near high-traffic roads during rush hour because of the air pollution and noise level—at least not the windows facing the road. For those situations, there are windows available with integrated air vents or sliders complete with filter medium, or windows with integrated trickle vents. A ventilation system can also be an acceptable solution.
In the classroom of a school, the IBN carried out carbon dioxide measurements. The results provided in the table CO2 measurements at a school (PDF) confirm that only regular cross-ventilation with wide open windows ensures a sufficient supply of oxygen during winter when permanently tilted windows are not an option for reasons of energy efficiency and draft effects. As long as there are no draft effects or noise from the outside, it is also sufficient to open all windows on a regular basis.
37 c) Automatic window ventilation
These motorized modules have originally been developed for difficult to reach windows (skylights), for people with physical disabilities, or for centralized window control in commercial settings, but they can also be used quite well in conventional settings. And with an appropriate layout, they can be a great and energy-efficient alternative to ventilation systems.
Figure: Power modules for automatically tilting windows
At the IBN, we tested the power modules for automatically tilting windows (manufacturer: WindowMaster GmbH, 32549 Bad Oeynhausen, www.windowmaster.de) in combination with the following sensors (www.sauter-cumulus.de):
• Timer
• CO2 meter • Humidity meter
All sensors functioned properly. Our tests have shown that in many cases the power modules for automatically tilting windows provide a great alternative to manual ventilation or controlled ventilation systems. The following aspects, however, also need to be taken into consideration:
• Sufficient and energy-efficient air exchange rates can only be achieved with cross- ventilation. This means that windows on opposite walls or at least windows on walls at right angles to each other need to be both fitted with power modules to be able to tilt the windows at the same time. If windows from different rooms are separated by a door, the latter also needs to be open or a screen door needs to be installed.
• The power modules for automatically tilting windows are relatively loud (ca. 60 dB(A)) and therefore are less suitable for sound-sensitive rooms such as bedrooms.
38 • The windows of a given room will be opened based on the programmed times as well as the measured carbon dioxide and humidity levels. The opening of the windows will occur regardless of whether a disturbing noise or objectionable odor will enter the room at that time.
• Timers do not register an increase in carbon dioxide levels when the number of occupants increases.
Therefore, it is recommended that sensors are combined with manual switches, which can be used to manually open or close the windows independent of the sensors at any time. For instance, it is important to open a window whenever the exhaust fan is turned on in the kitchen. d) Ventilation with trickle vents
Trickle vents are usually installed in the upper window frame. It is also possible to integrate such elements into already installed windows. There are also self-adjusting and sound-insulated trickle vents available, which automatically limit the air transfer during strong winds. Every common room should at least have one air trickle vent. Air trickle vents are available from e.g. Aldes GmbH, Aereco GmbH, or D+H Mechatronic AG.
Figure: Humidity-controlled trickle vent above wood window (length/height/depth = ca. 420/27/45 mm), source: Aereco GmbH
In general, these types of trickle vents are not sufficient to meet all ventilation needs, but they provide at least a minimum air exchange rate. Especially in airtight new buildings or renovated old buildings, such trickle vents are important to replace air where indoor air- dependent open fireplaces or exhaust fans in bathrooms and kitchens are used. When trickle vents are combined with a simple air exhaust unit, this setup can meet all ventilation needs if dimensioned properly.
39 e) Stack ventilation
In this case, exhaust air escapes through a vent pipe or stack that like a chimney is usually extended above the roof. Since air pressure decreases with increasing height, a slight negative pressure is created that makes fresh air flow into the rooms through openings and cracks, and exhaust air escape through the stack. If the stack height is low—and especially during high-pressure weather conditions—this type of ventilation, however, is not sufficient—and in some cases the air flow may even become reversed. The quantitative and qualitative performance of stack ventilation can be improved by using fans and particulate filters.
Sample calculations of ventilation requirements
Based on the following sample calculations, the fresh air requirements for living spaces or workplaces can be estimated with a reasonable degree of accuracy:
Assumptions: In a living room with a surface area of 5 x 5 m or 16 x 16 ft and a height of 2.5 m or 8 ft, there are 3 occupants (nonsmokers).
• Recommended fresh air requirement: 3 x 50 m3 = 150 m3/h or 3 x 29.5 ft3 = 88.5 CFM • Air volume of the living room: 5 x 5 x 2.5 m = 62.5 m3, minus furniture = ca. 60 m3 or 16 x 16 x 8 ft = 2048 ft3, minus furniture = ca. 1960 ft3 • It follows that the air should be changed (= air exchange rate) ca. 2.5 times per hour (150 m3/h : 60 m3 or (88.5 CFM : 1960 ft3) x 60 min).
Case I:
The room is located in a newly built masonry building. The properly sealed windows and doors are closed. Including the air infiltration rate, an air exchange rate of ca. 0.2 per hour is assumed.
With dedicated window ventilation, an additional air exchange rate of 2.3 per hour (2.5 - 0.2) should be targeted. When the occupants are at rest, an air exchange rate of ca. 2 per hour would be sufficient. When the occupants carry out light activities such as ironing laundry, playing games, or making crafts, an air exchange rate of ca. 3 per hour should be targeted. For the situations listed below, an air exchange rate of ca. 2 per hour is assumed.
According to the Approximate duration of a complete air change (PDF), the following 40 recommendations regarding ventilation can be made:
• Cross ventilation and wide open windows or French doors: – In winter, air 2 times per hour for 2-4 minutes:– In spring/fall, air 2 times per hour for 4-10 minutes– In summer, air 2 times per hour for 12-20 minutes
• Cross ventilation and tilted windows or French doors, or wide open windows without cross ventilation:– In winter, air 2 times per hour for 4-6 minutes– In spring/fall, air 2 times per hour for 8-15 minutes– In summer, air 2 times per hour for 25-30 minutes (= continuous ventilation!)
• Tilted window without cross ventilation: Even in winter, the occupants would have to air 2 times per hour for 30-75 minutes. This means that, even with continuous ventilation, the recommended air exchange rate would only be achieved under optimal conditions. During the other seasons, it is not possible to provide sufficient ventilation through a tilted window only.
The duration of opening windows and to optimize energy loss can be shortened by opening two or more windows and/or doors to other rooms. As an alternative solution, a simple exhaust air unit or a controlled ventilation system makes sense. To make the building envelope less airtight would not make sense. The latter would cause a loss of control over the air exchange and thus over the energy loss and the condensation risk in building components. As a result, noise protection would also be lowered.
Case II:
The same assumptions of Case I also apply to Case II. But the room is located in an older, relatively leaky masonry building where windows have no seals, the attic is uninsulated, etc. The properly sealed windows and doors are closed. Including the air infiltration rate, an air exchange rate of ca. 2.0 per hour is assumed. Due to the high air exchange rate, we do not differentiate between rest and light activities. With dedicated window ventilation, an additional air exchange rate of 0.5 per hour (2.5 - 2.0) should be targeted.
As a result, the following recommendations regarding ventilation can be made:
• Cross ventilation and wide open windows or French doors: – In winter, air every 2 hours for 2-4 minutes – In spring/fall, air every 2 hours for 4-10 minutes – In summer, air every 2 hours for 12-20 minutes
• Cross ventilation and tilted windows or French doors, or wide open windows without cross ventilation: – In winter, air every 2 hours for 4-6 minutes – In spring/fall, air every 2 hours for 8-15 minutes
41 – In summer, air every 2 hours for 25-30 minutes
• Tilted window without cross ventilation: – In winter, air every 2 hours for 30-75 minutes – In spring/fall, air every 2 hours for 1-3 hours (= continuous ventilation!). – During summer, it is not possible to provide sufficient ventilation through a tilted window only.
The duration of opening windows can be shortened by opening two or more windows and/or doors to other rooms. In most cases, it is possible to open the windows more frequently but for a shorter time. It does not makes sense to install a ventilation system in a leaky building. Should the building become better sealed later on to save energy, the ventilation strategy must be adjusted to the new conditions in order to prevent condensation.
Controlled ventilation
Ventilation systems (see also course module "Heating and Ventilation") use fans or air handling units that promote air circulation and supply fresh air either by negative pressure in the room (negative pressure mechanical ventilation system) or positive pressure in the room (positive pressure mechanical ventilation system). Balanced systems have also been developed; they are suitable for heat recovery.
In comparison to natural types of ventilation, they have the following advantages:
• Controlled supply of fresh air and/or exhaust of air pollutants based on actual requirements (air quality, air humidity, air temperature) • Optimization of heating energy consumption • Filtration of outside air (fine particulate matter, pollen, etc.) • Improved comfort (occupants must not open any windows themselves) • Ventilation possible even when there is outside noise
Due to design and/or installation mistakes as well as poor maintenance, the following defects may occur:
• Too high or too low air change • Hygienic problems because of poor filter quality and/or poor filter maintenance or a missing condensate drain in geothermal heat exchangers • Noise problems (monotonous white noise, noise transmission, etc.) • Poor matching with fireplaces or exhaust fans • Drafts
42 Ventilation systems that are properly designed, installed, and adjusted, as well as maintained on a regular basis are rarely a cause of concern; this was also the result of a survey by the IBN (IBN journal Wohnung +Gesundheit No. 114).
As a minimum, airtight buildings must at least have a simple exhaust air unit with air supply openings in each room or alternatively an automatic window ventilation. By taking building biology and energy-saving considerations into account, so-called decentralized ventilation systems with heat recovery should be chosen more frequently.
43 Air conditioning
This refers to a controlled ventilation system in which the supply air is conditioned to a certain level of temperature, humidity, and cleanliness. The capital and operating costs of a heating, ventilating and air-conditioning system are much higher than for a central heating system, especially if the cooling is done with electricity. To ensure the correct maintaining, operating, cleaning, and servicing of such a system, professional service personnel are required. Owners of apartment buildings, office buildings, or commercial facilities usually contract a professional service agency. Incorrect maintenance can lead to hygiene problems such as microbial contamination (e.g. Legionella bacteria, see also course module "Plumbing Installation") in air washers or mold in filter media. The use of chlorinated water or the disinfection of cooling water with biocides against bacterial and fungal contamination can also pose problems. The cooling water used in air conditioning should have drinking water quality.
Sick building syndrome (SBS), an internationally recognized disease that is widely discussed among health care professionals and climatologists, is attributed especially to air-conditioning systems.
Despite these problems, many large buildings such as high-rise buildings, hospitals, schools, office and administration buildings, theaters, movie theaters, or warehouses cannot do without it, neither in summer (overheating) nor in winter (ventilation, indoor air humidity, temperature control).
With air-conditioning systems, the close connection between climate and building type (building materials) is lost. The attempts at trying to fix with technology what was not considered as part of a climate-aware design are often lacking.
There are more and more commercial buildings that employ promising heating and ventilation concepts that manage without a traditional HVAC system. This is a result of the rising energy costs and the worldwide debate about the sick building syndrome. In addition to other strategies, there are, for example, natural ventilation systems, or in- floor, in-wall, and ceiling heating and cooling systems such as the so-called concrete core activation system (see also course module "Heating and Ventilation"). In order to accomplish such a feat, however, dedicated heating and ventilation engineers as well as the architects must all work closely together during the planning stage.
Regarding indoor air quality, the German Workplace Ordinance (ArbStättV) has the following to say:
"The employer shall have...air-conditioning and ventilation system installations professionally maintained and the functionality of the system checked at regular intervals."
"The employer shall provide workspaces with...adequate air space.
44 "The size of the required air space of a given room shall be calculated based on the physical activity level and number of employees, as well as any other persons present." "It must be possible for employees to open, close, adjust, or secure windows, skylights, and ventilation equipment in a safe manner."
"In enclosed workspaces, sufficient fresh air conducive to health must be provided, thereby taking into consideration methods of operation, the physical activity level and number of employees, as well as any other persons present."
"If an air-conditioning and ventilation system is necessary for the operation of the workplaces, it must be in working order at all times." "Any malfunctioning must be reported by an automatic warning system." "Precautions must be taken to ensure that employees are safeguarded against health hazards in the event of the malfunctioning of the system".
"If air-conditioning or mechanical ventilation installations are used, the employer shall ensure that employees are not exposed to drafts that cause discomfort."
"Any deposits or contaminants in air-conditioning and ventilation systems whose air can pose an immediate threat to the employees' health must be removed immediately."
The German Workplace Ordinance implements the European directive "Concerning minimum safety and health requirements at the workplace." The Ordinance is meant to improve occupational health and safety. Because, according to official statistics, every fourth employee must leave the workforce prematurely due to illness or accident (source: Hauptverband der gewerblichen Berufsgenossenschaften, today called "German Social Accident Insurance"). In Germany, about 1 million work-related accidents and about 60,000 occupational diseases are entered into the statistics registers every single year, and this is only the tip of the iceberg. For the direct consequences of occupational injuries and illnesses alone, costs are in the double-digit billions (source: German federal government report on the status of occupational health and safety) Moreover, the national economy is burdened with expenditures for premature retirement and work-related diseases.
The German Workplace Ordinance forgoes specifying detailed measurements regarding distances, lengths, or minimum air space sizes. Consequently, the responsibility lies with the employer. In order to create healthy and safe workspaces, employers must also meet other laws, regulations, and standards such as the German Hazardous Substances Ordinance, the Technical Rules of Hazardous Substances exposure limits TRGS 900, Occupational Noise and Vibrations Ordinance (LärmVibrationsArbSchV), and building codes.
45 Summary of ventilation types
Natural ventilation
• Natural air infiltration (= diffusion, joints, etc.) • Window ventilation (ventilation through joints and open windows) • Automatic window ventilation (power modules for automatically tilting windows) • Ventilation with trickle vents • Stack ventilation
Controlled ventilation
More about this in course module "Heating and Ventilation"
Air conditioning
In new or renovated buildings—but also in some older buildings—natural air infiltration and the air infiltration through joints will not be sufficient. It is recommended to have a blower-door test (= test of wind tightness) and/or CO2 measurements to assess the situation.
As a minimum, such buildings should be equipped at least with trickle vents or automatic window ventilation. A simple exhaust fan with supply air openings would be better because this way it is easier to regulate the air exchange rate in accordance with the air supply required. In order to save energy, in many cases it is best to choose a ventilation system with heat recovery. For various reasons, building biology environmental consultants prefer recommending decentralized ventilation units.
Manual window ventilation is only an alternative when it is applied in an older building whose basic air exchange rate is sufficient due to leakage or the occupants are well informed about ventilation and willing to regularly and actively open windows. Ventilation behavior can be best checked and optimized by using a CO2 meter and a humidity meter (hygrometer). Quick cross ventilation by opening windows (and doors) wide is the most effective and, at the same time, most energy-efficient way of ventilation.
Windows only have to be opened when rooms are being used or when an excessive amount of humidity in the air or building components must be reduced.
46 Building materials and indoor climate
Building materials and how important they are for the indoor climate have already been discussed in various contexts throughout this course module. And it has been shown that they influence almost all climate factors to one degree or another:
• Temperature of air and surfaces • Air humidity and material moisture • Air movement • Natural air infiltration through diffusion and leaks • Indoor electromagnetic quality • Odor of indoor air • Absorption of air pollutants • Growth of bacteria, mold, and insects such as mites • Overall atmosphere and its impact on the occupants' well-being
This is a short overview of how building materials affect the indoor climate, whereby a critical analysis of common building practices is compared to ideal solutions (for more details, see the following course modules).
Critical analysis of common building practices
The existing conditions in almost all new construction, but also in most of the retrofit situations, usually do not meet building biology requirements and extensive remediation efforts may become necessary as a result. Among other things, the following causes contribute to this development:
• Insufficient research and consideration of all climate factors—not just individual aspects—and how they are related to building materials
• Predominant use of hard and/or synthetic building materials (example reinforced concrete: high thermal conduction, low diffusion and absorption capacity, only slightly hygroscopic, scent and color unpleasantly "cold," problematic regarding electromagnetic pollution, long lasting building moisture in new construction).
• Sometimes the proportion of window areas is too large. Especially in the case of poorly insulated glazing (U-value >1.3 Wm2K), no constant temperature levels within a given room; air movement (drafts); overheating of indoor air (in winter, due to heating; in summer, due to solar exposure); reduced diffusion, hygroscopicity, and absorption of remaining wall surfaces.
47 • Installation of vapor barriers: prevents diffusion and filtering of the air, lowers indoor air humidity, and increases the risk of moisture damage / mold.
• Impairment of fresh air supply
• Use of synthetic materials for flooring, wall finishes, sound and thermal insulation, furnishings, adhesives for wood products, glues, varnishes, paints, wood preservatives, cleaners, etc. This can lead to the following disadvantages:
– Insufficient buffering of indoor humidity – Accumulation of toxins in indoor air – Growth of harmful microorganisms (molds, yeasts, bacteria) – High static electricity, decrease in negatively charged oxygen – Odor pollution
48