Criteria for a comfortable indoor environment in buildings

J. therra. Biol. Vol. 18, No. 5/6, pp. 545-549, 1993

0306-4565/93 $6.00+ 0.00 Copyright © 1993Pergamon Press Ltd

Printed in Great Britain. All rights reserved

INDOOR CLIMATE CRITERIA FOR A COMFORTABLE INDOOR ENVIRONMENT IN BUILDINGS BJARNE W. OLESEN* and JULIE SEELEN Indoor Environment Program, College of Architecture and Urban Studies, Virginia Polytechnic Institute and State University, 206 W. Washington, Blacksburg, VA 24061-0547, U.S.A. Abstract--l. The major purpose of buildings is to provide a healthy and comfortable environment for occupants. 2. The indoor environment is a complex system including factors like thermal, visual and acoustic conditions, indoor air quality, electromagnetic fields, static electricity and vibration. 3. To obtain an indoor environment that is acceptable in terms of health as well as comfort, criteria for these factors need to be established. 4. The present paper gives an overview of the criteria recommended in current existing standards and guidelines. 5. As most studies to date have focussed on thermal conditions and indoor air quality, these two factors are described in more detail. Key Word Index: Comfort; indoor environment; criteria; standards

INTRODUCTION The major purpose of buildings is to provide a healthy and comfortable environment for occupants. In most parts of the world, people spend more than 9 0 0 of the day indoors, i.e. at home, at the work place, during shopping or during transportation. To design and construct a healthy and comfortable environment, criteria that define an acceptable environment are needed. These criteria should be usable during the design process and should be able to be objectively measured, once the building is finished. The indoor environment is a complex system including factors like thermal, visual, and acoustic conditions, indoor air quality, electromagnetic fields, static electricity and vibration. The influence of these factors on human beings have been studied extensively and for several of these factors guidelines for design and measurements have been established. The present paper gives an overview of the criteria recommended in current existing standards and guidelines. During the 70s and 80s most focus has been given to the thermal conditions and the indoor air quality, therefore these will be described in more detail. The perception of the indoor environment is a combination of factors and solving a problem with *Address for correspondence: D. F. Liedelt "VELTA", P.O. Box 5209, Robert-Koch-Strass¢ 11, D-2000 Norderstedt, Germany.

one factor may result in unacceptable conditions due to another factor. In poor designed HVAC system you often may have to choose between an uncomfortable warm environment or a neutral, comfortable thermal environment; but with an uncomfortable noise level from the fans and the risk of draught. The requirements for increased amount of fresh air to improve the indoor air quality, may result in higher air velocities and then a risk of draught. The artificial light in a building will influence the thermal load and then the thermal environment. It is therefore important to take this interrelation into account. Today we do not know very much of the combined influence and there does not exist a common comfort index for the indoor environment. INDOOR AIR QUALITY An often used guideline is A S H R A E Standard 62-89 "Ventilation for acceptable Indoor Air Quality" (ASHRAE, 1989). This standard defines acceptable indoor air quality as, air in which there are no known contaminants at harmful concentrations, and in which a substantial majority ( > 80%) of the people exposed do not express dissatisfaction. A S H R A E 62 specifies two procedures for estimating the required ventilation rate (amount of outdoor air). The ventilation rate procedure is probably used during the design of 95% of the HVAC systems. This method specifies the amount of outdoor air as l/s per 545

546

BJARNEW. OLESENand JULIESEELEN

person for different types of spaces. For some situations the ventilation rate is specified as l/s per m 2. The ventilation rate in this procedure is mainly based on occupancy level and it is assumed that the air provided dilutes the air contaminants so the indoor concentrations will not be harmful or cause significant discomfort to the occupants. The basic requirement is 7.5 I/s per person and in office spaces 10 i/s per person. The basic value, 7.5 l/s per person, is based on studies on a person's perception of body odor (Cain et al., 1983; Fanger and Berg-Munch, 1983). At this ventilation rate, 80% of visitors, i.e. people just entering the space, can be expected to express satisfaction with the indoor air quality. If carbon dioxide is used as an indicator, 80% satisfied corresponds to a level of 1000 ppm, assuming the outdoor level is 350 ppm. The other procedure to estimate the required ventilation rate is the indoor air quality procedure. The amount of outdoor air, needed to bring the concentration of any contaminant below recommended limit values, is calculated with: O = G / ( C i - Co) x I/Ev

(1)

where: Q = ventilation rate required (l/s); G = contaminant load (g/s or I/s); Ci = allowable concentration of contaminant (g/l or ppm); Co = outdoor contaminant concentration at air intake (g/1 or ppm); Ev = contaminant removal effectiveness (ventilation effectiveness). To use this procedure effectively, information is needed on the relevant contaminants, recommended limit values, and emission rates for typical building materials and furnishings. An important source of pollution is environmental tobacco smoke (ETS). Given normal rates of smoking a 20% dissatisfaction criteria corresponds to a fresh air supply of 20 l/s per person (Cain et aL, 1983). The indoor concentration of Volatile Organic Compounds (VOC's) is becoming a more important issue, but there is not enough data available yet to establish a guideline. The humidity also influences the indoor air quality:

high humidity can support growth of organisms like fungi and dust mites, while low humidity may increase the risk for getting common cold and static electricity or dust in the air. A S H R A E 62-89 recommend a relative humidity in the range 30-60%. Only a few contaminants are listed in the standard. The annex to the standard and other sources, like W H O (1987) and EEC (1991, 1992), list information on radon, combustion products, environmental tobacco smoke (ETS), formaldehyde, volatile organic compounds, micro-organisms and particulates. More information is needed for other indoor air contaminants. In many studies it has been difficult to find or measure the causes for indoor air quality problems. Some researchers have then used the human nose as measuring instrument. With this method and the introduction of the Olf-Decipol units (Fanger, 1988; Fanger et al., 1988a), it has been demonstrated that the major contributors to the indoor air pollution level are building materials, furnishings and the HVAC system. An EEC guideline (EEC, 1992) uses this concept to calculate the required ventilation rate using similar equation as shown above. This guideline gives three levels of perceived indoor air quality and required ventilation rate for comfort as shown in Table 1 (together with corresponding CO2 levels). The guidelines also include tables for typical sensory pollutant loads caused by the building (olf/m 2 floor), occupants (off/occupant), outdoor air quality (decipol), and anticipated levels of contaminant removal effectiveness of spaces ventilated in different ways. This method is included as an alternative method in the German Standard (DIN, 1993). The NKB guideline (1991) and DIN 1946 (1993) also recognize that the building itself contributes to the contaminant load along with occupants, etc. NKB specifies as a basic value 0.7 1/s m 2, and an additional 0.35 l/s per person for sedentary activity. However, the total level must never be lower than 7 l/s per person in non-smoking spaces and 20 1/s per person in spaces where smoking is allowed. Table 2 shows a comparison between the above mentioned standards.

Table 1. Three levels of perceived indoor air quality, the CO2concentration above outdoor air level, and example of required ventilation rate. (EEC Report 11, 1992) Perceived air quality Quality level (category) A B C

% Dissatisfied

Decipol

[CO2] above outdoor level ppm

I0 20 30

0.6 1.4 2.5

350 650 1200

Required ventilation rate l/s olla 16 7 4

SThe ventilation rates given are examples referring exclusively to perceived air quality. They apply only to clean outdoor air and a ventilation effectiveness of one.

Criteria for a comfortable indoor environment

547

Table 2. Required ventilation rate in l/s m 2floor area, calculatedusing methods specifiedin the different standards and guidelines EEC Report No. 1It

Building Category Single office 10 m2 no-smoking Large office no-smoking

Occupant load

ASHRAE 62-89

pcrson/m2

l/s m2

0.I

1,0

Category 1/s m 2 A

B

C

NKB Publication 61E

DIN 1946 (1993)

l/s m2

l/s m2

1.1

1.1

0.9

1.7

1.4

1.7

10.5

8.3

3.5

4.2

3.3 1.4 0.8

2.8 0.07

1.2

0.7

0.7 Large office 20% smoking Auditorium

4.0 0.07

1.7

0.7

1.0 26.7 1.5

12

11.4

6.4 School classroom

10.0 0,5

4

4.3 2.4

'For the EEC-guideline low emission building materials (0.1 olf/m2) are assumed.

THERMAL ENVIRONMENT Thermal sensation is influenced by the following factors: activity level, thermal insulation of clothing, air temperature, mean radiant temperature, air velocity and humidity (water vapor pressure). These factors can be combined in many ways to provide an acceptable thermal environment. ISO 7730 standardizes an analytical method based on the PMV-PPD index (Fanger, 1982), which integrates the above six parameters into one value on a 7 point scale: + 3 hot, + 2 warm, + 1 slightly warm, 0 neutral, - 1 slightly cool, - 2 cool, - 3 cold. The quality of the thermal environment may also be expressed as the Predicted Percentage of Dissatisfied, PPD index, which is related to the PMV value. A PMV value of zero is equivalent to thermal neutrality. Dissatisfaction may be caused by warm, or cool discomfort for the body as a whole (general thermal discomfort, thermal neutrality). However, thermal dissatisfaction may also be caused by an undesirable warm or cold exposure of one part of the body (local thermal discomfort). Therefore, an additional requirement for thermal comfort is necessary, namely that no local thermal discomfort exists. Local discomfort may be caused by an asymmetric radiant field, local convective cooling, i.e. draught, contact with a warm or cold floor, or by a vertical air temperature difference. One of the most critical factors is draught. Many people are very sensitive to air velocities and therefore, draught is a very common cause for occupant complaints in ventilated and air conditioned spaces. Research (Fanger et al., 1988b) has shown that

fluctuations of the air velocity have a significant influence on a person's sensation of draught. The fluctuations may either be expressed by the standard deviation of the air velocity or by the turbulence intensity Tu, which is equal to standard deviation divided by the mean air velocity, v a (SDva/v,). The percentage of people feeling draught ( P D ) may be estimated from the equation: P D = (34 - ta)(va - 0.05)°6223(3.143 + 0.3696 Tu v,)

(2) where: v~=mean air velocity (3rain) m/s; Tu = turbulence intensity of air velocity (3 rain); ta = air temperature, °C. The criteria for the thermal environment can also be calculated for different quality levels. Table 3 gives an example of three quality categories, with category B as the equivalent of recommendations in A S H R A E Standard 55-1992 (ASHRAE, 1992) and ISO 7730 (ISO, 1993). The criteria for the three quality levels are shown in Table 4 and 5, calculated based on the PPD index and studies of the relation between local discomfort parameters and the percentage of dissatisfied (Fanger et al., 1985, 1988a, b; Olesen, 1977, 1991; Olesen et al., 1979). OTHER FACTORS INFLUENCING THE INDOOR ENVIRONMENT

Lighting

Lighting in a building influences safety, work performance, pleasantness in a space. It has been fairly well established that working environments lit uniformly to less than 200 lux tend to be rated

BJ~NE W. OT~_qmNand JULIESEELEN

548

Table 3. Three quality categories of the thermal environment Thermal state of the body as a whole

Quality category A B C

Predicted percentage of dissatisfied (PPD) <6% <10% <15%

Local discomfort

Predicted mean vote (PMV)

Percentage of dissatisfied due to draught

Percentage of dissatisfied due to vertical air temperature difference

-0.2 < PMV < +0.2 -0.5 < P M V < +0.5 -0.7 < PMV < +0.7

<10% <15% <25%

<3% <5% <10%

Unsatisfactory (Saunders, 1969). For general offices an illumination of 500 lux is recommended (CIBSE, 1984). To improve the visual conditions at a working desk it is often much more efficient to improve the contrast. Especially at VDU terminals it is important to avoid veiling reflections from luminaries or windows. Discomfort from glare occurs when the luminance in one direction of the visual field is much higher than the average luminance (CIBSE, 1985). Wilkins et al. (1989) reported that the 100 Hz light modulation influences the number of headaches by susceptible individuals. This number was substantially reduced where this modulation was absent e.g. fluorescent lamps controlled by electronic ballast operating at high frequency or daylight.

Percentage of dissatisfied due to warm or cool floor <8%

<3%

<10% <15%

<5% <10%

Vibration Building vibration may affect occupants and reduce comfort and work efficiency. Complaints are likely to arise, when the vibration levels are only slightly greater than the threshold value (minimum vibration perceived by humans). The levels of complaint and acceptable limits for building vibration are given in a British Standard BS 6472 (BS, 1984).

Acoustics The acoustical requirements in a room are normally given in A-weighted sound pressure levels, dB(A). For small offices and conference rooms 35-40 dB(A) is recommended and for landscape offices 40-45 dB(A). The reverberation time influences both aural comfort and speech intelligibility (ISO/TR 3352, 1974). In some cases where major tonal components are present or in cases of low frequency noise, it may be necessary to give additional requirements limiting a single octave or terz-band-noise.

Electromagnetic fields There has been concern expressed over the possible health effects (cancer) due to extremely low frequency electromagnetic fields (<500 Hz), that may occur near high voltage power lines. Studies have also raised the possibility of an increased risk of illness for those working with visual display units. However, on the basis of current data, there has been no consensus on the role of electromagnetic fields.

Air ions It has been suggested that negative ions tend to produce sensations of freshness and well-being and that positive ions tend to cause headache, nausea and general malaise. Present study results on the effects of air ions is inconclusive (Hamilton and Kew, 1985).

Static electricity Static electricity can lead to discomfort due to shocks. Shocks may occur when occupants are not

Table 4. Operative temperature ranges and mean air velocity (3 min) during winter and summer in offices and similar spaces with occupants having light, mainly sedentary activity (1.2 met), for three quality categories of the thermal environment Operative temperature range (oc) Quality category A B C

Percentage of dissatisfied due to radiant asymmetry

Corresponding mean air velocity limit (m/s)

Winter (1 clo)

Summer (0.5 clo)

Winter

Summer

22 ± 1.0 22±2.0 22 + 3.0

24.5 + 0.5 24.5± 1.5 24.5 + 2.0

0.11 0.15 0.22

0.13 0.18 0.26

It is assumed that turbulence intensity is 40%.

Criteria for a comfortable indoor environment

549

Table 5. Permissible vertical air temperature difference between head and feet (i.1 and 0.1 m above the floor) permissible floor temperatures, and permissible radiant temperature asymmetry for three quality categories (Table 3)

Quality category A B C

Vertical air temperature difference

Range of surface temperature of the floor

Radiant Temperature Asymmetry Warm ceiling

Cool wall

Cool ceiling

Warm wall

<2°C <3°C <4°C

21-27°C 19-29°C 17-31°C

<3°C <5°C <7°C

<8°C < 10°C <13°C

< 12°C <14°C < 18°C

< 17°C <23°C <35°C

adequately earthed via the floor covering. In general, shocks are unlikely to occur above 40% relative humidity. To solve the problem, improving the floor covering is better and more economical than increasing the humidity in the room.

CONCLUSIONS

Well established guidelines are available for the thermal, aural and visual environment. Instruments, to perform the necessary measurements, and design models, to estimate most of the parameters, are available for these three factors. In the 90s most of the studies will focus on indoor air quality and related subjects like ventilation, air distribution, filter techniques, emission from building materials, carpets and furniture, dose-response studies, etc. It is, however, important to realize that all factors are related and comfort perceived by occupants is a combination of all the factors.

REFERENCF~

ASHRAE (1989) ASHRAE Standard 62-1989: Ventilation for acceptable indoor air quality. Atlanta. ASHRAE (1992) ASHRAE Standard 55-1992: Thermal environmental conditions for human occupancy. Atlanta. BS 6472 (1984) British Standard Guide to the evaluation of human exposure to vibration in buildings (1 Hz to 80 Hz). London, U.K. Cain W. S., Leaderer B. P., Isseroff R., Berglund L. G., Huey R. J., Lipsitt E. D. and Perlman D. (1983) Ventilation requirements in buildings: control of occupancy odor and tobacco smoke odor. Atmos. Envir. 17. CIBSE (1984) Code for Interior Lighting. London, U.K. CIBSE (1985) Technical Memoranda TM 10: Calculation of Glare Indices. London, U.K. DIN (1993) DIN 1946: Ventilation and air conditioning: Technical health requirements (in German). Deutsches Institut fiir Normung, Berlin, Germany. EEC (1991) Report No. 10: Effects of Indoor Air Pollution on Human Health. European Concerted Action (COST 613). Commission of the European Communities, Luxembourg. EEC (1992) Report No. 11: Guidelines for Ventilation Requirements in Buildings. European Concerted Action (COST 613). Commission of the European Communities, Luxembourg.

Fanger P. O. (1982) Thermal Comfort. Krieger, Malabar, FL. Fanger P. O. (1988) Introduction of the oil and the decipol units to quantify air pollution perceived by humans indoors and outdoors. Energy Build. 12, 1~. Fanger P. O. and Berg-Munch B. (1983) Ventilation and Body Odor. In Proc. of Am. Engineering Foundation Conference on Management of Atmospheres in Tightly Enclosed Spaces. ASHRAE, Atlanta. Fanger P. O., Lauridsen J. and Clausen G. (1988a) Air pollution sources in offices and assembly halls, quantified by the olf unit. Energy Build. 12, 7-19. Fanger P. O., Melikow A. K., Hanzawa H. and Ring J. (1988b) Air turbulence and sensation of draught. Energy Build. 12. Fanger P. O., Ipsen B. M., Langkilde G., Olesen B. W., Christensen N. K. and Tanabe S. (1985) Comfort limits for asymmetric thermal radiation. Energy Build. 8, 225-226. Hamilton G. and Kew J. (1985) Negative air ionization in buildings. Technical Note TN 4/85. BSRIA, Bracknell, UK. ISO/TR (1974) ISO/TR 3352: Acoustics" Assessment of noise with respect to its effect on the intelligibility of speech. International Standard Organization, Geneva, Switzerland. ISO (1993) ISO 7730-1984: Moderate thermal environmerits--Determination of the PMV and PPD indices and specification of the conditions for thermal comfort (Revised version 1993). International Standards Organization, Geneva (Switzerland). Olesen B. W. (1977) Thermal comfort requirements for floors. International Institute of Refrigeration. In Conf. Proc. Commissions BI, B2, El, Belgrade, Vol. 4, pp. 307-313. Olesen B. W. (1991) The thermal factors are critical for design of HVAC systems. Env. Int. 17, 217-223. Olesen B. W., Scholer M. and Fanger P. O. (1979) Discomfort caused by vertical air temperature differences and comfort. In Conf. Proc. Indoor Climate 1979,pp. 561-579. Danish Building Research Institute. Saunders J. E. (1969) The role of the level and diversity of horizontal illumination in an appraisal of a simple office task. LRT 1, 37-46. NKB (1991) Publication No. 61E: Indoor Climate--Air Quality. Nordic Committee on Building Regulations, Espoo (Finland). WHO (1987) Air Quality Guidelines for Europe. World Health Organization Regional Office for Europe, Copenhagen (Denmark). Wilkins A. J., Nimmo-Smith I., Slater A. I. and Bedocs L. (1989) Fluorescent lighting, headaches and eyestrain. Lighting Res. Techn. 21, 11-18.