1、Volume 12, Number 2, April 2006 An International Journal of Heating, Ventilating, Air-conditioning and Refrigerating Research American Society of Healing, Refrigerating and Air-Conditioning Engineers, Inc. HVAC accepted Octoher 4, 2005 Thiry subjects (1 7 female) were exposed forjve hours in a clima
2、te chamber at 22C (71.6“F) to clean air at 594, i.%, 2594, and 35% RH. A comparable group was similarly exposed to air polluted by carpet and linoleum to the 35% RHcondition and to 18T, 22C and 26C (64.4“F, 71.tF, and 78.8F) at an absolute humidity equal to 15% RH at 22C (71.6“F). They par- formed s
3、imulated oflce work to ensure that they kept their eyes open and reported sick building syndrome (SBS) symptom intensiv on visual-analogue scales. Nine objective tests of eye, nose, and skin function were applied. Subjecctive discomfort, though sign$cantly increased by low humidity, was slight even
4、at 5% RH. More rapid blink rates were observed at 5% than at 35% RH (P 0.05), and tearjlm quaLi consequently, this standard does not specify a minimum humidity level. However, non-thermal comfort factors such as skin drying, irritation of mucus membranes, may place limits on the acceptability of ver
5、y low humid- ity environments. AN SVASHRAE Standard 62- I989 (ASHRAE 1989) recommended an opti- mum indoor humidity range of 30% to 60% RH, while later revisions (Standards 62.1 and 62.2) no longer recommend a lower humidity limit. The low relative humidity limits originally pre- scribed in both of
6、these ASHRAE standards may have been intended to minimize dry skin, eye irritation, respiratory infections, allergy and asthma, viability and virulence of bacteria and viruses, ozone production, etc. More recently, a large-scale field investigation found that the sensation of dryness indoors is not
7、associated with physical air humidity in the range of 10% to David P. Wyon is a professor, Lei Fang is an associate professor, Love Lagercrantz is a PhD candidate, and P. Ole Fanger is a professor at the International Centre for Indoor Environmeni and Energy, Department of Mechanical Engi- neering,
8、Technical University of Denmark. 20 1 202 HVAC Wyon 1992; Nor- dstrm et al. 1994), other research has shown that complaints of stuffiness and high humidity usually increase with increasing humidity (e.g., Berglund and Cain 19891). In a recent review of factors affecting airliner cabin air quality, N
9、agda and Hodgson (2001) concluded that there is experimental evidence that exposures of more than four hours to 10% RH and below has negative effects on the eyes, nasal passages, and skin, as is often reported by flight crew. However, they consider that there is as yet no evidence that would jus- ti
10、fy taking steps to raise aircraft cabin humidity levels from the current average level of about 15% RH to the highest level that would still avoid condensation and corrosion of the airframe (24% RH), a change that could easily be achieved by slightly reducing the outside air supply rate. Laboratory
11、and field studies have found that decreasing humidity has a positive effect on the perception of air quality (Fang et al. 199Xa, 199Xb, 1999), whether or not the air is clean, Air pollution is clearly important in determining sensations of dryness, irritation, respiratory infec- tions, and allergies
12、, and as raised air temperatures and air velocities increase the evaporative power of the air, they will obviously dehydrate skin and mucous membranes. Any of these fac- tors in combination with low air humidity may give rise to dryness problems, and contact lens wearers and people with allergies ar
13、e currently considered to be particularly sensitive (Wolkoff et al. 2005). The existing experimental evidence for the effect of low humidity on discomfort, symptoms, and long-term health is thus insufficient and inconsistent. Many of the observed effects of low humidity were confounded with other fa
14、ctors such as indoor air pollution and temperature. In ASWRAE W-1160, the results of which are reported here, a series of climate chamber experi- ments were undertaken to provide rational limiting criteria for low indoor air humidity. The pri- mary focus was on buildings, but a secondary objective w
15、as to study the negative effects that might occur during short-term exposure to very low humidity levels in aircraft. The findings were validated in a field intervention experiment in winter in an office building in northern Swe- den. METHOD Experimental Design ifahoratory Experiment. A total of AO
16、subjects were exposed tn two levels of air pollutionl four levels of absolute air humidity, and three air temperatures for five hours, in groups of six. Thirty subjects (17 female) were exposed for five hours to clean air at 5%, 15%, 25%, and 35% RH at 22C (71.6“F), with 60 Lis per person (127 cfmip
17、) outside air. A further 30 subjects (15 female) were similarly exposed to 18T, 22T, and 26C (64.4“F, 71.6“F, and 78.8F) with absolute humidity of 2.4 g/kg (16.8 gdlb) dry air, corresponding to 15% RH at 22C (71.6“F) and to 35% RH at 22T (71.6“F), the 10 L/s per person (2 I .2 cfm/p) of outside air
18、for this set of four exposures being first passed over a realistic quantity of carpet and linoleum (Table 1). These conditions were established simultaneously in two adjacent climate chambers (exposure VOLUME 12, NUMBER 2, APRIL 2006 203 Table 1. Environmental Conditions for the Climate Chamber Expo
19、sures Temperature 18OC (64+4F) 22OC (71.6F) 26C (78PF) Humidity 0.8 g/kg (5.6 grlb) dry air (5% RH) L ratio 2.4 g/kg (16.8 grlb) dry air (15% RH) H L, H H at 22T (71dF) 4.1 gkg (28.7 gdlb) dry air (25% RH) 5.7 g/kg (39.9 gr/lb) dry air (35% RH) L L, H NB: H: high level of atr pollution, .e., low ven
20、tilation rate of 10 L/s per person (2i cfmip), with pollution sources. L: low levet of air pollution, 1.e high ventilation rate of 60 L/s per person (1 27 cfm/p), with no pollution sources. chambers). A third chamber was used for the medical examinations (examination chamber). The temperature and hu
21、midity in the examination chamber were kept constant at 22.510.3“C (72.5+0.5“F) and 40% RH (+3%) throughout the experiment. Subjects were exposed at the same time of day and on the came day of the week, the four conditions occurring in balanced order over an experimental period of four successive we
22、eks. This design permits within-subject com- parison of (I) four levels of humidity (5%-35% RH) at 22C (71.6“F) in clean air (30 subjects), (2) three levels of temperature in the range IX“C-26“C (64.4T-78.8“F) in polluted air (30 more subjects) at constant absolute humidity, (3) 35% and 15% RH at 22
23、C (71.6“F) with 30 subjects exposed at each level of air pollution, and (4) 35% and 15% RH at 22OC (71.6F) with 60 sub- jects available for this comparison when both groups are pooled, regardless of air quality. Between-subject comparisons of clean with polluted air at 22C (71 .6“F), with RH at eith
24、er 35% or 1596, are also available. Field Intervention Experiment. Steam humidification was temporarily installed in an office building in stersund in northern Sweden (latitude 63“N) so that it could be applied to either of two adjacent floors. The intention was to raise the indoor air humidity from
25、 its naturally occur- ring low levei to about 30% RH. A crossover experiment, with two weeks in each condition, was carried out over a period of six weeks in midwinter, but the outdoor temperatures that year were not cold enough for low humidity conditions to occur indoors for long enough to create
26、a useful reference condition. No further mention will be made of this part of the project. Exposure Chambers The two chambers used for the experiments (Toftum et al. 2004) are identical in size: L x W x H = 5.4 x 4.2 x 2.5 m3 (212.6 x 165.4 x 98.4 in). They can be controlled independently to provide
27、 the following range ofconditions: air temperature 15C to 40C (59F to 104F) with an accuracy of h0.25“C (10.45“F), air humidity normally 30% to 70% (rt3%) RH, and outside air ventilation rate 12 to I80 L/s (25 to 381 cfm). Samples of building or furnishing materials can be placed in a miniature “roo
28、m“ in the air supply system of each chamber. Rotating desic- cant wheel dehumidifiers were installed for the experiment, each able to convert air at 8*C (46.4“F) and 5.5 gikg (38.5 gr/lb) to 30C (86F) and O. 15 gikg (1 .O5 gdlb) at the maximum out- door air flow rate of 180 Lis (38 I cfm). The hot d
29、ry air that resulted was then cooled by a cool- ing coil. If the outdoor air temperature and humidity were above these values, the intake air was cooled and dehumidified by an initial cooling coil before reaching the dehumidifier. This made it possible to extend the chamber humidity range down to 5%
30、 RH at 22C (71.6“F). 204 HVAC 3.9, 23.6 and 43.3 in.), were measured at each workstation before the experiment started to check that thermal conditions were uniform. Ozone concentration inside the chamber and in the outdoor air was measured every day by a Seres ozone monitor (OZ 2000) to investigate
31、 whether low relative humidity affects ozone levels indoors, as ozone has both direct and indirect irritant effects on the mucous membranes of the eyes, nose, throat, and respiratory tract. The concentra- tion of airborne dust and the distribution of particle size were measured under each condition
32、by a Grimm dust monitor (1.106) to determine whether decreasing relative humidity reduced the size of airborne particles and thereby increased their penetration into the airways. Subjective Ratings Subjective assessments of perceived air quality, thermal sensation, and the reported intensity of sick
33、 building syndrome (SBS) symptoms were obtained using visual-analogue scales (War- gocki et al. 1999), which in this experiment were marked by the subjects on a computer screen, using a mouse. The results were quantified and stored automatically by the computer. Objective Medical Tests after each ex
34、posure. Eye (Wyon and Wyon 1987): 1. Tearfilm stabil this is believed to be due to the higher dehumidifier purging temperatures needed to produce the low humidity condition. Subjective Ratings lowing significant changes occurred as humidity decreased: Comparing the 35%, 25%, 15%, and 5% RH condition
35、s at 22C (7 I .6”F) in clean air, the fol- I. Humidity ratings decreased (P and an increase in reading speed with temperature (P was measured under the six conditions, the values encountered proved to be close to those of the air temperature (/tg - !,I 5 i “C) in the same places and under conditions
36、 with low air velocity (V, I 0.2 mis). Table 1. Characteristics of Measuring Instruments . Quantity Measuring Range Accuracy Air temperature, “C 10-30 *0.2* Mean radiant temperature, “C I O40 IO.5 Air velocity (for ambient measurements), mis 0.05-1 k(D.03 i. 3% Y,) Air velocity (for diffuser measure
37、ments), mis 0.05-3 k(0.03 + 3% Y,) Relative humidity, % 30-70 I3 Surface temPerature. “C 0-5 O *os VOLUME 12, NUMBER 2, APRIL 2006 22 1 The following internal heat sources were established for the tests: four microcomputers (390.4 W), four simulators in light activity (399.6 W), 16 fluorescent tubes
38、 (696 W), and 80 lightbulbs (2,723 W) performing 4,209 W internal toad (121 .O0 W/m2). Since there is basically no heat exchange between the inside and the outside of the test chamber, the internal thermal load can be considered constant for all six conditions. Variables such as air temperature (ta)
39、, air relative humidity (RH), air velocity (Va), globe temperature (Q-globe temperatures were measured for the determination of mean radi- ant temperatures, -radiant temperature asymmetry (t,), and floor temperature (t,) were mea- sured under each condition established in the environment. Measuremen
40、ts were made at 20 points previously determined (Figure 4), covering the whole room area (test chamber), that is, occupation zones (workstations with simulators SI to S4), the peripheral zone (next to the light panel), and circulation zones. In the occupation zones, measurements were made at three p
41、oints around each simulator, equidistant 33 cm from its center (Pi to P12). In addition, measurements were obtained at four other points (P17 to P20) placed in the center of the diffusers, which allowed the determination of air velocity and temperature profiles. To accomplish the measure- ments at e
42、ach point, the transducers were placed at six heights above the floor (0.10, 0.60, 1.10, 1.70, 2.00, and 2.35 m). In parallel with the measurements of comfort variables, other variables related to system function were continuously measured and monitored during each test to ensure that the conditions
43、 created in the environment remained constant; measured values are shown in Table 2. Under the same six thermal conditions, in the second stage a sarnpie of people evalu- ated the environment answering questions about their thermal sensations. The results allowed the definition of comfort parameters
44、 adequate for users of office build- ings with the same characteristics as the evaluated environment. The sample was made up of 33 people (1 7 male and 16 female) who usually perform daily office activities. Ages varied from 20 to 40 because this is the predominant age group in contemporary Brazilia
45、n office buildings (Leite 1997). All participants are Brazilian and none practice sports frequently. At the time of the tests, none displayed a feverish state or any other kind of infectious or inflammatory disease; they were not drowsy, nor did they show any signs of malnutrition or excessive weigh
46、t. The participants wore standardized clothing (with the same fabric and models for men and women) appropriate for the thermal conditions of the tests and Brazilian customs. In two subse- Table 2. System Functioning Parameters Tests Conditions Variables c1 c2 c3 c4 c5 C6 Air ternperature-environment
47、, “C 25.8 25.2 24.1 23.2 22.1 20.8 Relative humidity-environment, % Return air temperature, “C Return air humidity, % Discharge air temperature, “C Plenum air supply temperature, “C Plenum air supply humidity, % Chilled water supply temperature, “C Chilled water return temperature, “C Static pressur
48、e-plenum, Pa 42.0 45.0 43.0 48.0 57.0 63.0 27.2 26.6 24.5 24.4 23.4 22.4 40.0 42.0 40.0 45.0 52.0 57.0 13.9 14.2 13.1 13.9 14.8 15.0 19.9 19.5 19.0 17.9 16.3 15.4 63.0 65.0 62.0 70.0 81.0 86.0 9.0 9.0 8.0 8.9 9. I 9.0 13.8 14.1 12.9 14.1 14.0 14.2 9.0 9.6 11.2 13.7 18.1 18.9 222 HVAC I, = 0.7 clo fo
49、r C3 and C4; I, = I. 1 cio for C5 and C6. The referred IL/ is the sum of each garments IC, in compliance with IS0 9920 (IS0 1995) and Olesen (1 985 j in ASHRAE (200 1). For the tests, the sample was divided into groups of four (most of the time two men and two women) and subjected to two thermal conditions a day with a reduction in temperature of IT in the subsequent condition. For each test, the people entered the chamber and randomly occupied the existing workplaces. After remaining seated for 50 minutes performing office activities, th
