4th International Conference On Building Energy, Environment

Effects of the inner wall of the building envelope with low emissivity on the thermal comfort of human body

S.M. Lu1 ,Q.L. Meng 1,Q. Li1

1State Key Laboratory of Subtropical Building Science South China University of Technology, GuangZhou510640, China

SUMMARY Radiation heat transfer of the building envelope is an important factor affecting the indoor thermal comfort. However, to date, there is less information available about the effect of the indoor space formed by the inner wall of the building envelope with low emissivity on the thermal comfort of human body. In this study, Fanger’S PMV model was improved based on the principle of human body heat balance and the principle of radiation heat transfer and was used to investigate the effect of ε on the thermal comfort of human body and mean radiation temperature in low radiation environment during winter and summer conditions. The results showed that the relationship between the modified PMV model and ε is a parabolic curve. Further studies showed that in summer conditions, with the decrease of ε, the PMV up to 1.2 can be reduced, under the same conditions of comfort, the indoor design temperature can be increased 1 ~ 2 ℃ .Under the winter condition, with the decrease of ε, the PMV value is obviously increased, and the indoor design temperature can be reduced by 3 ~ 4 ℃ under the same comfort condition.

INTRODUCTION Radiation heat transfer of the building envelope is an important factor affecting the indoor thermal comfort. In the process of heat transfer of the envelope, the radiant heat transfer of the inner surface accounts for more than 60% of the total heat transfer of the inner surface(Liu X 2010). In the heat dissipation in the indoor environment and the human body, when the body reaches a state of thermal comfort, the heat radiation amount to 45% to 50%(Huang Q 1985). The commonly used surface of building materials usually has a strong thermal radiation absorption capacity, the surface radiation value ε range is generally between 0.85 ~ 0.95. This means that if there are indoor and outdoor temperature difference, the heat in the winter outdoor heat conduction will be a lot of heat transmitted to the outside through the building envelope; and summer just the opposite. Therefore, reducing the radiance of the inner surface of the envelope to a certain extent, can reduce the indoor surface heat transfer coefficient, can reduce indoor and outdoor heat transfer, change the internal surface temperature, and then change the human body and indoor environment, radiation heat transfer, improve indoor thermal environment comfortbal(Jelle BP 2015). However, to date, there is less information available about the effect of the inner wall of the building envelope with low emissivity on the thermal comfort of human body. In this study, Fanger PMV model was improved based on the principle of human body heat balance and the principle of radiation heat transfer and was used to investigate the effect of ε on the thermal comfort of human body and mean radiation temperature in low radiation environment during winter and summer conditions.

HUMAN BODY HEAT BALANCE MODEL AND PREDICTED MEAN VOTE In indoor heat exchange ，The body participates are as a part of the indoor environment. The effect of the indoor environment on human comfort depends on the balance between the heat generated by the body's metabolism and the amount of heat dissipated by the human body to the surroundings. This relationship can be expressed by Equation 1:.

M-W-C-R-E=S (1)

Where M is the metabolic rate;W is the effective mechanical power; C is the convective heat transfer; R is the radiation heat transfer; E is the evaporation heat; S-body heat storage.

In a stable thermal environment, only when the body heat and heat balance, that is, S = 0, the body can maintain normal body temperature. But S = 0 does not represent the human body in comfortable state. Professor Fanger believes that thermal comfort is a function of human body heat and body heat balance(Fanger 1970). On the basis of the principle of human body heat balance, combined with the experimental data and comfortable physiological conditions, collected 1396 subjects of hot and cold feeling, the establishment of PMV comfort evaluation index. The indicators are employed in ISO7730(2005) and ASHRAE Standard 55(2013), which follows the equation：

𝑃𝑃𝑃𝑃𝑃𝑃 = [0.303 · 𝑒𝑒𝑒𝑒𝑒𝑒(−0.036𝑃𝑃) + 0.028] · {(𝑃𝑃 −𝑊𝑊) − 3.05 ·10−3[5733 − 6.99(𝑃𝑃 −𝑊𝑊) − 𝑃𝑃𝑎𝑎] − 0.42 · [(𝑃𝑃 −𝑊𝑊) − 58.15] − 1.7 ·10−5 · 𝑃𝑃 · (5867 − 𝑃𝑃𝑎𝑎) − 0.0014 · 𝑃𝑃 · (34 − 𝑡𝑡𝑎𝑎) − 3.96 · 10−8 · 𝑓𝑓𝑐𝑐𝑐𝑐 ·[(𝑡𝑡𝑐𝑐𝑐𝑐 + 273)4 − (𝑡𝑡𝑟𝑟 + 273)4] − 𝑓𝑓𝑐𝑐𝑐𝑐ℎ𝑐𝑐(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)} (2)

Where M is the metabolic rate, in watts per square metre

(W/m 2 );W is the effective mechanical power, in watts per

square metre (W/m 2 ); 𝑓𝑓𝑐𝑐𝑐𝑐 is the clothing surface area factor;

𝑡𝑡𝑎𝑎 is the air temperature, in degrees Celsius (°C); t𝑟𝑟� is the mean radiant temperature, in degrees Celsius (°C); 𝑃𝑃𝑎𝑎 is the water vapour partial pressure, in pascals (Pa); ℎ𝑐𝑐 is the convective heat transfer coefficient, in watts per square metre kelvin [W/(m2K)]; 𝑡𝑡𝑐𝑐𝑐𝑐 is the clothing surface temperature, in degrees Celsius (°C).

Among them, the expression of radiation heat transfer is as follows：

𝑅𝑅 = 3.96 · 10−8 · 𝑓𝑓𝑐𝑐𝑐𝑐 · [(𝑡𝑡𝑐𝑐𝑐𝑐 + 273)4 − (𝑡𝑡𝑟𝑟� + 273)4] (3)

Professor Fanger is strictly controlled by various environmental variables, experiments conducted with convective heat transfer mainly at small air-conditioned

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4th International Conference On Building Energy, Environment

environment radiative heat transfer, thermal comfort analysis of experiments in this environment data subjects who feel hot, come to the human body the regression equation between the heat load and thermal sensation(Fanger 1972).

THE MODIFIED PMV MODEL From the formula (3) can be seen, Professor Fanger in the calculation of the human body on the surface of the surrounding environment of radiation cooling rate, is the human body and the environment are reduced to gray body, and are almost regarded as spherical, the two gray surface composition Of the closed system for research. The computational model simplifies the computational complexity to a large extent. Although the PMV equation introducts the mean radiant temperature.but for the mean radiation temperature calculation model, this value is equivalent to the surface temperature,which can not accurately describe the different surface emissivity ε case of radiation heat transfer. However, this calculation method has been verified feasible in the convection heat transfer mode based environment. In order to investigate the radiation heat transfer in the case of human and indoor environment with different internal surface emissivity ε, this paper assumes that the human body is in a closed hexahedron consisting of ceilings, floors and four walls. The area, emissivity, radiation intensity and surface thermodynamics temperature of the j face of the hexahedron are: 𝐹𝐹𝑗𝑗�𝜀𝜀𝑗𝑗�𝐸𝐸𝑗𝑗�𝑇𝑇𝑗𝑗 .The area, emissivity, radiation intensity and surface thermodynamics temperature of the human body are: 𝐹𝐹𝑝𝑝�𝜀𝜀𝑝𝑝�𝐸𝐸𝑝𝑝，𝑇𝑇𝑝𝑝 . 𝜑𝜑𝑝𝑝𝑗𝑗 is the radiation angle coefficient of human body and surface .Then,the Radiation heat transfer capacity of human body and indoor environment 𝑄𝑄𝑟𝑟 is(Chen Qi Gao 1991.):

𝑄𝑄𝑟𝑟 = ∑𝐶𝐶0 𝜑𝜑𝑝𝑝𝑝𝑝𝐹𝐹𝑝𝑝�(

𝑇𝑇𝑝𝑝100)4−(

𝑇𝑇𝑝𝑝100)4�

1+𝜑𝜑𝑝𝑝𝑝𝑝��1𝜀𝜀𝑝𝑝−1�+

𝐹𝐹𝑝𝑝𝐹𝐹𝑝𝑝

( 1𝜀𝜀𝑝𝑝−1)�

𝑛𝑛𝑗𝑗=1 (4)

In the steady state heat transfer condition, the inner surface temperature of the envelope is related to the indoor and outdoor air temperature, the heat transfer resistance of the envelope and the heat transfer coefficient of the inner and outer surfaces. Assumed the inner surface temperature of the envelope j as tj, the expression is as follows:

tj =𝑡𝑡𝑖𝑖 −𝑅𝑅𝑖𝑖𝑅𝑅0

(𝑡𝑡𝑖𝑖 − 𝑡𝑡𝑒𝑒) (5)

where Ri = 1αn

; R0 = 1K

; R0 = Ri + ∑R + Re； Where αn is the total heat transfer coefficient for the inner side of an exterior wall, W / (㎡K); K is the heat transfer coefficient of envelope.Re is the total heat transfer resistance for the outside of an exterior wall, Ri is heat transfer resistance for the inner side of an exterior wall,ti is the indoor air calculation temperature (℃), te is the outdoor air calculation temperature (℃). C0 = 5.67W/(m2 ∙ K4) The total heat transfer coefficient:

αn = αc + αr (6)

Where αr is the radiant heat transfer coefficient and αc is the convective heat transfer coefficient，αc =k �(tj − ta)4 (Tao W 2010).

In the closed space, the air flow rate is very small, the convective heat transfer coefficient is very small, the main radiation heat transfer. Therefore, the overall heat transfer coefficient of the inner surface of wall can reduce depending the low-e surface .The total heat transfer coefficient for the inner side of an exterior wall can be lowered by 31.5%for an emissivity of 0.62 and 36.8% for an emissivity of 0.53 compared to αn(Hugo G. 2001.); For an example calculated by the Fraunhofer Institute for BuildingPhysics, Stuttgart, Germany (Oswald et al 1996) the R value of a brick wall could beincreased by 8% for an emissivity of 0.62 and by about 11% for an emissivity of 0.53. For any surface j in the inner surface of the envelope, the external radiation heat transfer coefficient αrj is expressed as:

αrj = � Tj100

�4− ∑ Bji n

i=1 � Ti100

� , j = 1,2, … . . n. (7)

Bji = φjiεi + ∑ φjk(1 − εk)Bkink=1 ; i = 1,2, … . . n (8)

Where Bji is the absorption factor, that is, the radiant heat which emitted by the surface Fj and absorbed by the surface Fi; its value includes the sum of the radiant heat of the radiation reflected by Fj. Taken equation 2-7 is into Equation 2-6 to obtain the total heat transfer coefficient of the inner surface of the envelope j:

αnj = αj + αr = � 𝑇𝑇𝑝𝑝100

�4− ∑ 𝐵𝐵𝑗𝑗𝑖𝑖 𝑛𝑛

𝑖𝑖=1 � 𝑇𝑇𝑖𝑖100

� + k �(θj − ta)4 （k=2.0,2.5,1.3） (9)

Taken equation 2-9 is into Equation 2-5 to obtain the surface temperature expression for surface j:

tj = ti −(𝑡𝑡𝑖𝑖−𝑡𝑡𝑒𝑒)

1+��θj+273

100�4−∑ Bji n

i=1 � Ti100

�+ k ��θj−ta�4 � (∑R+Re)

(10)

Let Tj = tj + 273 ， Tp = tcl + 273 ， 𝑡𝑡𝑖𝑖 = 𝑡𝑡𝑎𝑎 ； bring the formulas 2-9, 2-10 into 2-4 to obtain the heat transfer between the body and the envelope: Qr =

∑

C0 φpjFp

⎣⎢⎢⎢⎢⎡

(tcl+273100 )4−(

ta+273−(ta−te)

1+��tj+273100 �

4−∑ Bji

ni=1 �

Ti100� + k �(tj−ta)4 �(∑R+Re)

100 )4

⎦⎥⎥⎥⎥⎤

1+φpj��1εp−1�+

FpFj

(1εj−1)�

nj=1

(11) In the radiation-based environment ， the mean radiation temperature is an important factor affecting the human body thermal comfort. When the air flow rate is less than 0.2 m / s, the effect of air temperature and mean radiation temperature on indoor thermal comfort is equally important. The mean radiation temperature of the body and the envelope is related to the position of the person in the room, the emissivity of the surface, and the surface temperature. Fanger (Fanger 1970) proposed the angle coefficient to determine the mean radiation temperature between the body and the surface:

𝑇𝑇𝑟𝑟� = (∑ 𝐹𝐹𝑝𝑝−𝑗𝑗𝑛𝑛𝑗𝑗=1 𝑇𝑇𝑗𝑗4)1/4 (12)

ISBN: 978-0-646-98213-7 COBEE2018-Paper159 page 477

4th International Conference On Building Energy, Environment

Where 𝑇𝑇𝑟𝑟� is the mean radiant thermodynamics temperature (K); 𝑇𝑇𝑗𝑗 is surface thermodynamics temperature of the j face (K). 𝐹𝐹𝑝𝑝−𝑗𝑗 is the angle coefficient of human body and plane j. Observed formula 12 found that the mean radiation temperature of the human body and the environment is only related to the surface temperature and the angle coefficient, which can be regarded as the mean temperature of the inner surface of the envelope, and the surface material is approximately black Set up. Therefore, the expression of this mean radiation temperature can not accurately express the different surface emissivity ε situation. According to the definition of the mean radiation temperature, it is assumed that each surface of the envelope is a constant gray body, and ε = α. The emittance, effective radiation and thermodynamic temperature of the jth surface are εj, Ej and Tj, respectively. Then the human body feels the mean radiation temperature of is:

𝑇𝑇𝑚𝑚4 = 1𝜎𝜎

∑ 𝐸𝐸𝑗𝑗𝑛𝑛𝑗𝑗=1 𝐹𝐹𝑝𝑝−𝑗𝑗 (13)

𝐸𝐸𝑗𝑗 = 𝜀𝜀𝑗𝑗𝜎𝜎𝑇𝑇𝑗𝑗4 + (1 − 𝜀𝜀𝑗𝑗)∑ 𝐸𝐸𝑛𝑛𝑖𝑖=1 𝑖𝑖 𝐹𝐹𝑗𝑗−𝑖𝑖 (14)

t𝑟𝑟� = 𝑇𝑇𝑚𝑚 − 273 (15)

The formula 2-13 into 2-2, the PMV formula in the radiation heat transfer part of the whole R replaced by the 𝑄𝑄𝑟𝑟, and the modified equation PMVεget:

PMV = [0.303 · exp (−0.036M) + 0.028] · {(M − W) − 3.05 ·10−3[5733 − 6.99(M − W) − 𝑃𝑃𝑎𝑎] − 0.42 · [(M − W) −

58.15] − 1.7 · 10−5 · M · �5867 − 𝑃𝑃𝑎𝑎� − 0.0014 · M · (34 −

𝑡𝑡𝑎𝑎) − ∑𝐶𝐶0 𝜑𝜑𝑝𝑝𝑝𝑝𝐹𝐹𝑝𝑝�(

𝑡𝑡𝑐𝑐𝑐𝑐+273100 )4−(

𝑡𝑡𝑝𝑝+273

100 )4�

1+𝜑𝜑𝑝𝑝𝑝𝑝��1𝜀𝜀𝑝𝑝−1�+

𝐹𝐹𝑝𝑝𝐹𝐹𝑝𝑝� 1𝜀𝜀𝑝𝑝−1��

𝑛𝑛𝑗𝑗=1 − 𝑓𝑓𝑐𝑐𝑐𝑐ℎ𝑐𝑐(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)} (16)

Where,

𝑡𝑡𝑐𝑐𝑐𝑐 =

35.7 − 0.028 · (M − W) − I𝑐𝑐𝑐𝑐 ·

{∑𝐶𝐶0 𝜑𝜑𝑝𝑝𝑝𝑝𝐹𝐹𝑝𝑝�(

𝑡𝑡𝑐𝑐𝑐𝑐+273100 )4−(

𝑡𝑡𝑝𝑝+273

100 )4�

1+𝜑𝜑𝑝𝑝𝑝𝑝��1𝜀𝜀𝑝𝑝−1�+

𝐹𝐹𝑝𝑝𝐹𝐹𝑝𝑝

( 1𝜀𝜀𝑝𝑝−1)�

𝑛𝑛𝑗𝑗=1 + 𝑓𝑓𝑐𝑐𝑐𝑐ℎ𝑐𝑐(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)}

(17)

ℎ𝑐𝑐=�2.38(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)0.25 ; when 2.38(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)0.25 ≥ 12.1�𝑣𝑣𝑎𝑎𝑟𝑟

12.1�𝑣𝑣𝑎𝑎𝑟𝑟; when 2.38(𝑡𝑡𝑐𝑐𝑐𝑐 − 𝑡𝑡𝑎𝑎)0.25＜12.1�𝑣𝑣𝑎𝑎𝑟𝑟

(18)

𝑓𝑓𝑐𝑐𝑐𝑐=�1.0 + 1.29𝐼𝐼𝑐𝑐𝑐𝑐 ; when 𝐼𝐼𝑐𝑐𝑐𝑐 ≤ 0.0781.05 + 0.645𝐼𝐼𝑐𝑐𝑐𝑐 ; when 𝐼𝐼𝑐𝑐𝑐𝑐＞0.078 (19)

Pa = 𝜓𝜓 ∗ exp (16.6536 − 4030.183

𝑡𝑡𝑎𝑎+235) (20)

DISCUSSION In order to study the effect of different internal surface emissivity on the thermal comfort of human body under steady state heat transfer. The envelope is set to a non-transparent structure that does not project solar radiation. A typical room for the study, the room size of 4.5 m* 3 m * 3 m. Assume that the vertical surface of the wall, the ceiling and the ground surface material have the same surface emissivity. Taking into account the combined effect of the outer surface of the envelope and the convective heat transfer and solar radiation of the outdoor air, in order to reduce the temperature of the different inner surfaces due to the building orientation and the amount of solar radiation, the

outdoor design temperature is replaced by the outdoor integrated temperature. In summer conditions te = 45 ℃∑𝑅𝑅 = 3.6;In winter conditions te = -10 ℃, ∑𝑅𝑅 = 4.5. In order to study the effect of the internal surface emissivity on the thermal comfort of the human body in summer, it is necessary to determine the parameters of the formula PMVε first. ∑𝑅𝑅 = 4.5，ψ = 50%, Var = 0.15m / s, M = 69.78W / ㎡, W = 0, Icl = 0.08 ㎡ ℃ / W, 𝜀𝜀𝑝𝑝= 0.97.

𝐹𝐹𝑝𝑝=feff fcl AD (20)

Where Fp is the effective radiation area of the human body; feff is the effective radiation area coefficient,%; the human body attitude is different, the effective radiation area coefficient is also changing. Fanger by photography, obtained: standing feff ≈ 0.725; sitting feff ≈ 0.696; for the case of ignoring the attitude, take 0.71. fcl is the clothing area coefficient, that is, the surface of the human body with the naked body surface area ratio,%; generally take 1.1.. AD for the human body surface area, according to Dubois formula (Dubois 1916):

AD=0.020𝑤𝑤0.425𝐻𝐻0.725 (22) Where H is the person's height, m; m is the person's

weight, kg; According to the State Sports General Administration, the Ministry of Education, the Ministry of Health and other countries in 2014 National System Bulletin of Chinese men mean height of 1.697, the mean weight of 70.3kg, the mean height of 1.584 women, the mean weight of 57.8kg, so that the mean height of the Chinese H = 1.64m, the mean weight of W = 64.06kg. So you can calculate AD = 1.694m2, 𝐹𝐹𝑝𝑝 = 1.323.

Figure 1. In the air conditioning control temperature of 26 ℃ , the envelope surface temperature of different areas

The mean radiation temperature in the Fanger classical equation is determined by the mean temperature of the inner surface. In order to study the outdoor environment on the indoor environment in the air conditioning environment. According to the "Civil Building Thermal Design Code GB50176-2016" in the provisions of the use of norms with the thermal calculation software Kvalue to calculate the typical air conditioning and refrigeration area of the envelope surface temperature, mainly used to determine the different outdoor climate Of the inner surface of the envelope. It can

26

26.2

26.4

26.6

26.8

27

27.2

Inte

rnal

surf

ace

tem

pera

ture

Inner surface maximum temperature

Inner surface minimum temperature

The average temperature of the inner surface

ISBN: 978-0-646-98213-7 COBEE2018-Paper159 page 478

4th International Conference On Building Energy, Environment

be seen from Figure 1 in the comfort range of 26 ℃, the wall temperature will be due to outdoor temperature changes. The internal surface temperature is higher than the indoor air temperature 0.5 ~ 1.2 ℃ internal surface temperature than the indoor air temperature higher than 1.1 ℃, or even more. In the same comfort conditions, according to the mean radiation temperature and indoor air temperature is inversely proportional to the relationship, if the mean radiation temperature decreased by 1 ℃, then the air temperature can be increased by 1 ℃. Figure 2 shows the change of PMV with the emissivity of the inner surface when the air temperature is 26 ℃, 27 ℃ and 28 ℃ under summer conditions. It can be seen from Fig. 2 that the PMV-ε curve is in the parabolic form as a whole. When ε≥0.1, the PMV value decreases with the decrease of ε. Compared to ε = 1, the PMV value can be reduced by about 0.3. When ε <0.1, the PMV value increases rapidly with the decrease of ε. In the air temperature of 27 ℃, ε = 0.4 PMV = 0.58 <0.8 can be considered in the comfort range. That is, if the inner surface emissivity is reduced to 0.4, the air comfort temperature can be increased by 1 ° C. Studies have shown that the air design temperature increased by 1 ℃, can save about 8%. However, after ε <0.4, the PMV value rises, because the low emissivity also has too high reflectivity, and reflects the heat of the indoor heat source back into the room. Therefore, the low emissivity of the inner surface heat transfer at the same time has to block the outdoor heat to the indoor transmission and indoor heat to the role of outdoor transmission. Therefore, the PMV value appears in parabolic form, there is an optimal value to balance the transmission of two kinds of heat.

Figure 2. Effect of emissivity ε on PMV in summer condition：from top to bottom,ta=28℃，ta=27℃，ta=26℃.

Figure 3. Effect of emissivity of inner surface on the mean radiant temperature in summer condition ： from top to bottom,ta=18℃，ta=17℃，ta=16℃.

Figure 3 shows the relationship between the surface emissivity and the mean radiation temperature in summer conditions. As can be seen from Figure 3, the curve as a whole is a parabolic form. When ε ≥ 0.1, with the decrease of ε, the mean radiation gradually decreases, usually down 0.5 ~ 1 ℃. When ε <0.1, with the decrease of ε, the mean radiation temperature gradually increased. This shows that in the indoor heat environment, reduce the inner surface of the envelope radiation emissivity ε, can reduce the mean radiation temperature, improve the body and the environment of radiation heat transfer, improve human thermal comfort.

Figure 4 Effect of emissivity ε on PMV in winter condition：from top to bottom,ta=18℃，ta=17℃，ta=16℃.

In the calculation of winter conditions, the impact of the inner surface emissivity on the thermal comfort of the human body, compared with the summer conditions, the need to change the following parameters: Icl = 2.33, te = -10 ℃. Figure 4 shows the variation of PMV value with the emissivity of the inner surface when the air temperature is 16 ℃, 17 ℃ and 18 ℃ under winter conditions. It can be seen from Fig. 4 that the PMV-ε curve is in parabolic form as a whole, and the PMV value increases with the decrease of ε. And ε= 0.05 is a turning point. Indicating that the smaller the ε in the winter, the higher the indoor comfort. Compared with ε = 1, the PMV value can be increased by about 0.3 to 0.8. In the comfort area of PMV≥ -0.5, when ε≤0.05, the winter air design temperature can be reduced by 2 ℃. When ε ≤ 0.4, the winter air design temperature can be reduced by 1 ℃ . Reduce the winter interior design temperature can save winter heating energy consumption. It can be seen from the curves of Fig. 2 and Fig. 4 that the effect of reducing the temperature of the inner surface on the winter comfort is more obvious. According to Holker's law, the smaller the surface emissivity ε, the greater the reflectivity. Therefore, the lower the emissivity of the inner surface, the heat generated by the indoor heat source more reflected back to the room, in the same comfort, the indoor temperature with the decrease of ε increased. This principle in the summer conditions seem unfavorable, in fact, indoor air conditioning in the summer as a cold source, will be more cold source

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0.01 0.05 0.1 0.2 0.4 0.6 0.8 1

PMV

ε

ta=26℃

ta=27℃

ta=28℃

25

25.5

26

26.5

27

27.5

28

0.01 0.05 0.1 0.2 0.4 0.6 0.8 1

The

mea

n ra

dian

t tem

pera

ture

ε

ta=28℃

ta=27℃

ta=26℃

-1-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.1

00.10.20.30.4

0.01 0.05 0.1 0.2 0.4 0.6 0.8 1

PMV

ε

ta=16℃

ta=17℃

ta=18℃

ISBN: 978-0-646-98213-7 COBEE2018-Paper159 page 479

4th International Conference On Building Energy, Environment

back to the room. Within a certain range, the indoor temperature decreases as ε decreases.

Figure 5 Effect of emissivity of inner surface the mean radiant temperature in winter condition ： from top to bottom,ta=18℃，ta=17℃，ta=16℃.

Figure 5 is the winter operating conditions, the relationship between the surface emissivity and the mean radiation temperature. It can be seen from Figure 5, the mean radiation temperature and the internal surface emissivity is basically a linear relationship. With the decrease of ε, the mean radiation temperature increased by about 3 ~ 4 ℃. Under the same comfort conditions, the mean radiation temperature for each rise of 1 ℃, the air temperature can be reduced by 1 ℃(Atmaca I et al.2007.). This shows that in the winter according to the mean radiation temperature changes, the indoor air design temperature can be reduced by about 3 ℃ , which will greatly reduce the winter heating energy consumption.

RESULTS In summary, on the basis of the theory, reducing the inner surface of the envelope low emissivity, can reduce the inner surface heat transfer coefficient, improve the total thermal resistance of the envelope, improve the indoor space of the winter and summer climate, improve indoor comfort degree. In the same comfort range to increase or decrease the air design temperature, and thus energy-saving building heating or cooling energy consumption. From the current theoretical results, reduce the internal surface emissivity in the winter effect is more obvious. But also need to carry out experiments to verify the specific results of the field, there are studies that the inner surface of the envelope structure of low-radiation materials in the summer to improve the human body with excellent thermal comfort. However, the effect of reducing the radiance of the inner surface for the comfort of a naturally ventilated room has not yet been studied specifically, and this will be the next step.

ACKNOWLEDGEMENT Fund Supported: National Natural Science Foundation of China (No. 51590912).

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