ANALISIS DEL OBJETIVO N° 01

Kerka and Humphries (1956) experimented with odours and there relationship with the thermal environment using three pure vapours and cigarette smoke. A trained panel o f humans was used to ascertain the odour intensity from odorants generated within a chamber. The judges consisted o f 6 members o f staff from ASHRAE’s research building who entered the test chambers by being called away from the general work situation. An odour intensity scale was adopted;

C h a p te r 2 - H u m an P e r c e p tio n o f In d o o r A ir Q u a lity and O d o u r Air Quality Percentage Dissatisfied Stuffy 6 Not Stuffy 0 100 20 21 22 23 24 25 26 27

Air Quality Judgements DPT2.2°C —

DPT

re

- ‘ DPT 11.rc

Air Temperature (oC) DPT: Dew point temperature

Occupants at 1 met, ventilation rate 15 1/s.p

Figure 2.26: Stuffy and air quality acceptability responses at 1 met Source: Berglund and Cain 1989

C h a p te r 2 - H u m a n P e r c e p tio n o f In d o o r A ir Q u a lity an d O d o u r

Degree of Odour Intensity Description

0 Odourless

1 Threshold

2 Definite

3 Strong

4 Overpowering

The three pure odorants were tested; iso-valeric acid (“sour and footy”), methyl salicylate (“fragrant and cool”), and pyradine (“burnt and nauseating). Cigarette smoke was also evaluated by using an irritation scale:

Degree, Odour or Irritation Description

0 Im perceptible odour, or irritation

1 Perceptible odour, or irritation, but n ot o b jection able

2 M oderate odour, or irritation, little or no objection, a cc ep ta b le level 3 O bjection able odour, or irritation; condition regarded with disfavour

4 Strong odour, or irritation, but endurable

5 Very strong odour, or irritation, in tolerable

Ventilation rates were held constant and only temperature and humidity altered. They found that an increase in humidity lowered the perception o f odour intensity at constant temperature although not to the same degree for all odorants. Tobacco smoke odour intensity was found to decrease with increasing temperature. Ventilation rates between 25 and 150 1/s per cigarette were needed to maintain the perception o f air at or below ‘moderate’ on the irritation scale. The results were plotted on a psychrometric chart where the boundaries o f each category scale were displayed (Figure 2.27). The discussion following the paper raised the point that these result are contrary to popular belief that hot humid room are perceived as less inviting. The authors responded by suggesting that in real buildings concentrations o f odorants would increase with temperature and possibly humidity whereas these test kept the odour concentration constant.

These findings were also confirmed by Kuehner (1956) who also discovered that the vapour pressure between inside and outside a room will increase the loss o f odour from a space. Furthermore he found that high humidities increased the volatilisation o f odours from building materials and fittings which will tend to increase the intensity o f odour in these situations.

C h a p ter 2 - H um an P ercep tion o f Indoor A ir Q u a lity and O d o u r

Relative Humidity

9p%^ 7p%^ 5p%

IsoV alenc Acid at Concentration

= 0.0067 mg/m Sub-Threshold

Ventilatim Rate = 147 I/s

/ / / T hreshold/ Threshold to Definite Definite Definite to Strong 20% 13% 0 5 10 15 20 25 30 35 40 45

Dry Bulb Temperature (°C)

Relative Humidity

90®o 70% 5 0 %

/ / / /

Methyl Salicylate at Concentration = 1.14 mg/m’ Ventilation Rate = 147 1/s Ibreshold to Definite Definite g ^ ^ D e f m it e to Strong 30% 13% 0 5 10 15 20 25 30 35 40 45

Dry Bulb Temperature (°C)

R elative H um idity " 7 0 % 5 0 % Cigarette bunting rate = 3 min/cm , ^

Ventilation Rate = 9 2 1/s / P e r c e p t i b l e to M oderate Odour / . / 23 1/cigarette M oderate Odour M oderate to O bjectionable Odour 0 5 10 15 20 25 30 35 40 45

Dry Bulb Temperature (°C)

Figure 2.27: Odour categories plotted on pychrometric charts indicating human response to odour at different ambient temperatures and humidities. Source: Kerka and Humphries 1956

C h a p te r 2 - H um an P ercep tio n of Indoor A ir Q u a lity and O d o u r

Imagine that you during your daily work would be exposed to the air from the diffusers.

How acceptable is the air quality?

T CLEARLY ACCEPTABLE

JUST ACCEPTABLE JUST NOT ACCEPTABLE

CLEARLY NOT ACCEPTABLE

Figure 2.28: Continuous air quality scale (Source: Fang et al 1996)

_______________ C h a p te r 2 - H u m a n P e r c e p tio n o f In d o o r A ir Q u a lit y an d O d o u r _______________

A very important experiment has recently been carried out using between 30 and 40 untrained persons to evaluate the quality o f air emitted from a chamber containing building materials (Fang et al 1996). Care was taken to use the same quantity o f materials and ventilate the chamber with air at the same temperature and humidity. However, the exhaust air could be re-conditioned to vary its temperature and humidity. This exhaust air was channelled to a port for evaluation by the untrained panel. Panel members voted on a continuous scale (Figure 2.28). The results indicate that the acceptability o f the air declined with increased temperature and relative humidity for the same pollution load. The authors show a linear relationship between enthalpy and acceptability (Figure 2.29). The relative humidity effect seems to contradict the finding o f Kerka and Humphies (1956). Previous studies, described above, have measured odour responses with changing relative humidity and temperature. This study has specifically measured indoor air quality acceptability. It may be argued, therefore, that odour responses are independent o f the air’s temperature whereas indoor air quality acceptability is not. This is particularly difficult to accept as humans do not appear to be equipped with any specific sensory mechanism to distinguish between odour and air quality acceptability. However, consideration o f much o f the research carried out into the human perception o f indoor air quality, and discussed above, shows that humans are likely to be influenced by several non-physiological factors such as the phraseology, the context o f the experiment, the range o f stimuli offered, signal to noise ratios etc. Nonetheless the results from these experiments are important as they question the results obtained from the auditoria studies used in the development o f the olf and decipol which do not appear to have made allowances for the ambient relative humidity or air temperatures. Furthermore, the effect o f the respondent’s physical environment has not been considered. It may be that a person exposed to cold-dry air will consider warm-humid air as more acceptable than someone who judges the warm-humid air after being exposed to even warmer air.

C h a p te r 2 - H u m a n P e r c e p tio n o f In d o o r A ir Q u a lity and O d o u r

0.2

u u

m ÛO

Enthalpy (kJ/kg)

pollution level 1, (background air): r = 0.975, p<0.001 pollution level 2, (wall paint): r = 0.955, p<0.001 pollution level 3, (carpet): r = 0.958, p<0.001 pollution level 4, (floor varnish): r = 0.959, p<0.001 pollution level 5, (sealant): r = 0.957, p<0.001

Figure 2.29: Perceived air quality and acceptability as a function o f the enthalpy of clean air and air polluted by different materials. Source: Fang et al 1996

_______________ C h a p te r 2 - H u m a n P e r c e p tio n o f In d o o r A ir Q u a lity an d O d o u r _______________