Thermal manikin experiments for the investigation of simultaneous radiant temperature asymmetry and warm floor exposures
Edit Barna* and László Bánhidi
Budapest University of Technology and Economics, Hungary
*Corresponding email: barna.edit@epgep.bme.hu
SUMMARY
In these days, one task of HVAC designers is to produce energy efficient buildings. At the same time they have to provide a thermally comfortable environment for the occupants. These requirements lead to the development of such systems like for example the low temperature heating and high temperature cooling systems that affect the occupant’s heat exchange with his surroundings via radiation. With regards to the above described systems, the combined effect of two local discomfort parameters is studied in this paper, namely radiation temperature asymmetry and warm floors. The European standard CR 1752 deals with these parameters separately and no data are available on how many people are dissatisfied due to multiple exposures. The paper summarizes the results of climate chamber measurements with a thermal manikin that is simultaneously exposed to cold wall and warm floor. The presented results are to be applied for the coming human subject experiments.
KEYWORDS
Asymmetric radiation, Combined effect, Local discomfort, Thermal manikin, Warm floor
INTRODUCTION
Energy efficiency, not without a point, is becoming the main concern of the building industry lately. Energy efficiency has to be reached for different cases: for newly built commercial and office buildings, which often have extensive glass facades, for family houses and for buildings that are under renovation processes. Energy efficiency can be accomplished among other factors by insulating the building envelope and by designing a heating/cooling system, which will require minimum energy input.
Recently, low temperature heating and cooling systems (water based heating/cooling panels, TABS, floor heating) are becoming more and more popular in the case of newly built buildings. These systems use as much renewable energy (solar, heat gains from room equipment and from occupants) as possible, thus satisfying the demand for energy saving.
These systems all work via radiation, and it is a question whether local discomfort parameters will be of concern or not.
The effect of radiation on thermal comfort is included in the European standard CEN CR 1752 (1998) at several points. As a mean radiant temperature (MRT) it is present in the equation of predicted mean vote (PMV) for global thermal comfort. Furthermore, it appears within the local discomfort parameters as asymmetric radiation or warm/cold floor. So far, satisfying the limitations prescribed by the standard, these parameters have been only taken into account and were calculated separately, even though they may be present in the indoor environment simultaneously.
Indoor Air 2008, 17-22 August 2008, Copenhagen, Denmark - Paper ID: 479
Until recently only very few research studies dealt with multiple short-term exposures, eg.
combined effect of temperature, indoor air quality and noise were studied by Balazova et al.
(2007) and Clausen et al. (2005). Berglund et al. (1987) evaluated the subjective human response to low-level air currents and asymmetric radiation. Olesen et al. (2002) and Toftum (2002) outlined in their papers the need for further investigations regarding combined effects of local discomfort parameters.
The aim of this paper is to present the results of climate chamber experiments with a thermal manikin, in which the manikin was simultaneously exposed to two local discomfort parameters, namely warm floor and a cooled wall. The measurements were conducted in order to acquire heat loss data for each body segment in the combined environments. The obtained data helped in describing those body parts that might be most affected by the multiple exposure. Results of the measurements are to be compared with sensation and comfort votes that will be collected from the coming human subject experiments. The overall aim is to create the relationship between combined exposure to asymmetric radiation and warm floor and thermal satisfaction with such environment.
METHODS
Measurements were carried out in a 3.8 m (L) x 3.1 m (W) x 2.5 m (H) climatic chamber that is located in a room, thus being sealed from outdoor conditions. The chamber’s walls and floor can be heated by circulating water. The circulating water temperature can be controlled in order to provide the required surface temperatures. One of the walls was cooled and the floor was heated during the experiments.
Two comfort environments with uniform temperatures (air and surface temperatures being equal) and eight different surface temperature combinations were tested with a thermal manikin (Table 1). Throughout condition 1 to 8 air temperature was tried to be kept close to 23°C, so that comparison to the uniform 23°C environment would be possible. The manikin was seated in front of a desk facing the cooled wall, in the middle of the chamber (Figure 1).
Table 1. Examined surface temperature conditions.
Cond.
1
Cond.
2
Cond.
3
Cond.
4
Cond.
5
Cond.
6
Cond.
7
Cond.
8
Base 1
Base 2 Cooled wall
temp. (°C) 16 16 16 16 18 18 18 18 20 23 Heated floor
temperature
(°C) 20 23 26 29 20 23 26 29 20 23
Figure 1. Experimental setup (side view – top view); position of the manikin compared to the cooled wall.
The manikin used in the experiment is an average-sized male with 18841 cm2 of total surface area. It is divided into 18 segments; the segments cannot be controlled separately and the manikin’s software can only work in ‘heating to a fixed set point’ mode. Throughout exposures the heat loss and the equivalent homogenous temperature (EHT) of each body segment could be registered. The manikin was wearing a clothing ensemble that had a clo value equal to 1.
Surface temperatures were registered on each wall and the floor by using Fe-Co thermocouples. Twelve thermocouples were fixed on the cooled wall; sixteen on the heated floor and the temperature of the other walls were measured in three points respectively. Data were collected and saved in a data logger. The air temperature was also measured at head height by a thermocouple.
Data were collected from the manikin every 2 minutes after steady-state condition was reached, and average heat-loss and EHT was calculated from 30 to 45 data (covering 60 to 90 minute periods). Surface temperatures were saved every 2 minutes as well. The data from 12 sensors were averaged in case of the cooled wall, and the 16 data for the floor were treated in the same manner. Surface temperatures were logged for the same time period like the steady- state manikin data.
For the present study, heat loss data from the manikin’s different body parts were used. The measured values for condition 1 - condition 8 were compared with the values of base measurement 1 and 2.
RESULTS
Comparisons were made for the heat losses of body sections between Base 1, 2 (uniform environments) and the 8 different asymmetric conditions (See Table 1).
Figure 2 summarizes measurement results for cases when the floor temperature was kept 23°C and wall temperatures were set to 16°C and 18°C (Condition 2 and 6). The measured heat losses were compared to the uniform 23°C environment. Heat loss values were highest, between 70-90 W/m2, for the following body parts: Face, Head, Left and Right hands.
Compared to the heat losses in the uniform environment, in the case of 18°C wall, a 10 W/m2 increase could be observed, while for the 16°C wall an approximately 15-20 W/m2 increase could be registered for the head and hand regions. The lower leg region had higher, between 50-70 W/m2 heat loss values compared to the upper body parts.
Figure 3 shows the results of measurements when the floor temperature was kept 26°C and wall temperatures were set to 16°C and 18°C (Condition 3 and 7). The measured heat losses were compared again to the uniform 23°C environment. The heat loss values decreased for all problematic body parts to be between 60-80 W/m2. Greatest differences could be observed for the hands and the face, however, compared to the previous figure, the differences were only between 5-10 W/m2. The left lower thigh also showed differences compared to the base value, however this was due to the malfunction of the segment.
Heat losses by body parts - Condition 2, 6 and Base 2
0 10 20 30 40 50 60 70 80 90 100
FACE CHEST BACK LEFT UPPER ARM RIGHT UPPER ARM LEFT LOWER ARM RIGHT LOWER ARM LEFT HAND RIGHT HAND LEFT UPPER THIGH RIGHT UPPER THIGH LEFT LOWER LEG RIGHT LOWER LEG LEFT FOOT RIGHT FOOT LEFT LOWER THIGH RIGHT LOWER THIGH HEAD
Body parts Heat loss (W/m2 )
23°C (air 22.9°C) 16°C - 23°C (air: 21.9°C) 18°C - 23°C (air: 22.4°C)
Figure 2. Comparison of body section heat loss values between uniform environment (Base 2), and Condition 2 and 6.
Heat losses by body parts - Condition 3, 7 and Base 2
0 10 20 30 40 50 60 70 80 90 100
FACE CHEST BACK LEFT UPPER ARM RIGHT UPPER ARM LEFT LOWER ARM RIGHT LOWER ARM LEFT HAND RIGHT HAND LEFT UPPER THIGH RIGHT UPPER THIGH LEFT LOWER LEG RIGHT LOWER LEG LEFT FOOT RIGHT FOOT LEFT LOWER THIGH RIGHT LOWER THIGH HEAD
Body parts Heat loss (W/m2 )
23°C (air 22.9°C) 16°C - 26°C (air: 23.1°C) 18°C - 26°C (air: 23.4°C)
Figure 3. Comparison of body section heat loss values between uniform environment (Base 2), and Condition 3 and 7.
Figure 4 shows the heat loss of manikin body segments in the extreme environment when a 16°C and 18°C cold wall and a warm floor (29°C) is present. Heat loss values for the head, face and hands remained higher compared to Base 2 heat losses. In contrast, heat losses of the lower legs and feet decreased by 8-12 W/m2, compared to the base values. The left lower thigh showed once more differences compared to the base value due to the malfunction of the segment.
Heat losses by body parts - Condition 4, 8 and Base 2
0 10 20 30 40 50 60 70 80 90 100
FACE CHEST BACK LEFT UPPER ARM RIGHT UPPER ARM LEFT LOWER ARM RIGHT LOWER ARM LEFT HAND RIGHT HAND LEFT UPPER THIGH RIGHT UPPER THIGH LEFT LOWER LEG RIGHT LOWER LEG LEFT FOOT RIGHT FOOT LEFT LOWER THIGH RIGHT LOWER THIGH HEAD
Body parts Heat loss (W/m2)
23°C (air 22.9°C) 16°C - 29°C (air: 24.2°C) 18°C - 29°C (air: 24.7°C)
Figure 4. Comparison of body section heat loss values between uniform environment (Base 2), and Condition 3 and 7.
Figure 5 shows an example for the investigation of the effect of different floor temperatures.
Heat losses, when the wall temperature was set to 16°C, were compared with the 23°C uniform environment.
Heat losses by body parts - effect of floor heating
0 10 20 30 40 50 60 70 80 90 100
FACE CHEST BACK LEFT UPPER ARM RIGHT UPPER ARM LEFT LOWER ARM RIGHT LOWER ARM LEFT HAND RIGHT HAND LEFT UPPER THIGH RIGHT UPPER THIGH LEFT LOWER LEG RIGHT LOWER LEG LEFT FOOT RIGHT FOOT LEFT LOWER THIGH RIGHT LOWER THIGH HEAD
Body parts Heat loss (W/m2 )
23°C (air 22.9°C) 16°C - 23°C (air: 21.9°C) 16°C - 26°C (air: 23.1°C) 16°C - 29°C (air: 24.2°C)
Figure 5. Comparison of body section heat loss values between uniform environment (Base 2), and Condition 2, 3 and 4.
DISCUSSION
The conducted measurements had the aim of collecting objective data to describe the effect of simultaneously present cold wall and warm floor surfaces. The heat loss values, shown in Figure 2-5., prove that the most sensitive areas of the body are the head, face the left and right
hands. These body parts are more affected by heat exchange partly because they are not covered with any type of clothing.
From Figure 2 it can be seen that compared to the uniform 23°C environment all body parts had greater heat losses when a cold surface was present. The wall had a stronger influence on the hands and the head region. It can be noticed that the light heating of the floor (to 23°C) had no impact, i.e. the heat loss values of the lower leg and feet would have been expected to decrease but instead it increased. It seems that either the cold surface out ruled the effect of the floor, or the 1°C difference in the air temperature could have had such an effect.
Figure 3 contains the most accurate results for the comparison, as air temperatures for all the plotted conditions were close to 23°C. From the figure it is clear that the cold wall had significant effect on the heat loss of the hands (around 70-75 W/m2, instead of 55-65 W/m2).
In the case of the head and face the cold wall did not have a strong impact, however, values in the asymmetric environment were still higher compared to the base. It was expected that the 26°C floor temperature would produce lower heat losses for the lower legs and feet than the actual, but only few W/m2 could be observed. For the feet the same is true; it can be seen that the heated floor could compensate the cold radiant temperature from the wall as the heat loss values were the same as in the base measurement (See also Figure 5.), however it was expected that heat losses would have been lower.
Figure 4, with the most extreme conditions, clearly shows the combined effect of cold wall and warm floor. Even though air temperatures were higher compared to the base air temperature, the heat loss of the left and right hand remained higher. This can only be due to the cold wall surface. The head and face heat losses were more affected by the air temperature in this case. Furthermore, the heat loss values of the lower leg and feet were lower compared to the base. The magnitude of this heat loss difference partly was caused by the 29°C floor and the higher air temperatures.
By examining different temperature conditions, based on the results, temperatures can be selected that should be examined in the coming human subject experiment for possible cause of dissatisfaction with the environment. With the sensation and comfort votes of those experiments, relationship could be created with the objectively measured heat losses.
CONCLUSIONS
The measurements had the aim of collecting objective data to describe the effect of simultaneously present cold wall and warm floor surfaces. Findings of the thermal manikin experiments helped to select the body parts that are most probably affected by the asymmetric environment by obtaining heat loss values for each body section. These are the hands, head, lower leg and feet. Furthermore, the investigation helped in finding those temperature combinations that would be worth testing for unacceptability or comfort in the coming human subject experiments.
REFERENCES
Balazova I., Clausen G., and Wyon D.P. 2007. The influence of exposure to multiple indoor environmental parameters on human perception, performance and motivation. In:
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Berglund L.G. and Fobelets A.P.R. 1987. Subjective human response to low-level air currents and asymmetric radiation. In: ASHRAE Transactions. Part 2, pp. 497-523.
CEN CR 1752. 1998. Ventilation for Buildings: Design Criteria for the Indoor Environment
Clausen G. and Wyon D.P. 2005. The combined effects of many different indoor environmental factors on acceptability and office work performance. In: Proceedings:
Indoor Air 2005, Beijing, China, pp. 351-356.
Olesen B.W. and Parsons K.C. 2002. Introduction to thermal comfort standards and the proposed new version of EN ISO 7730. Energy and Buildings 34, pp. 537-548.
Toftum J. 2002. Human response to combined indoor environment exposures. Energy and Buildings 34, pp. 601-606.
