Modified calculation of solar heat gain coefficient in glazing façade buildings

ScienceDirect ScienceDirect

Energy Procedia 00 (2017) 000–000 Energy Procedia 00 (2017) 000–000

Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available

ScienceDirect ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Energy (2017) 000–000 151–156 EnergyProcedia Procedia122 00 (2017) www.elsevier.com/locate/procedia

CISBAT 2017 International Conference – Future Buildings & Districts – Energy Efficiency from CISBATNano 2017toInternational – Future Buildings & Districts – Energy Efficiency from Urban Scale,Conference CISBAT 2017 6-8 September 2017, Lausanne, Switzerland Nano to Urban Scale, CISBAT 2017 6-8 September 2017, Lausanne, Switzerland

Modified calculation of solar heat gain coefficient in glazing façade The 15th International Symposium on District Heating and Cooling façade Modified calculation of solar heat gain coefficient in glazing buildings Assessing the feasibilitybuildings of using the heat demand-outdoor Shunyao Lua, Zhengrong Lia*, Qun Zhaob, Fujian Jianga a temperatureShunyao function for a long-term heat Jiang demand Lua, Zhengrong Lia*, Qundistrict Zhaob, Fujian School of Mechanical Engineering, Tongji University, Shanghai 200092, China b a College of Architectural Urban Planning, University, Shanghai 200092,China of Mechanical University, 200092, Chinac a,b,c School a andEngineering, a TongjiTongji bShanghai b College of Architectural and Urban Planning, Tongji University, Shanghai 200092,China a

I. Andrić a

forecast

*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc

IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b

Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract In the building’s cooling load calculation, solar heat gain through the transparent envelope is calculated using the solar heat gain In traditional buildings, the window-wall ratio is small it is assumed that theisincoming radiation cannot In coefficient. the building’s cooling load calculation, solar heat gain through thesotransparent envelope calculatedsolar using the solar heat escape through the But this hypothesis is not suitable buildings glazing that facades. Modifiedsolar calculation of SHGC gain coefficient. In window. traditional buildings, the window-wall ratiofor is small so itwith is assumed the incoming radiation cannot Abstract is carried out onthe thewindow. basis of But the Radiosity-Irradiation ISO 15099 algorithms using theModified commercial softwareofMatlab. escape through this hypothesis is not Method suitable and for buildings with glazing facades. calculation SHGC The impact geometric dimensioning and absorptance surfaces isusing evaluated. The results of numerical is carried outof on room the basis of the Radiosity-Irradiation Method and of ISOinterior 15099 algorithms the commercial software Matlab. District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the calculation that atgeometric 12:00 on dimensioning June 21th, the and escaped solar energy ratio is surfaces 8.85% and modifiedThe SHGC is 0.67, which is The impactshow of room absorptance of interior is the evaluated. results of numerical greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat smaller thanshow the that original, 0.71.onInJune room geometric dimensioning, theratio depth and height affect SHGCSHGC significantly, calculation at 12:00 21th, the escaped solar energy is 8.85% and the modified is 0.67, while which in is sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, internal surfaces’ theInfloor hasgeometric greater impact on the modified SHGC otheraffect internal surfaces. smaller than the absorptance, original, 0.71. room dimensioning, the depth andthan height SHGC significantly, while in prolonging the investment return period. internal surfaces’ absorptance, the floor has greater impact on the modified SHGC than other internal surfaces. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand ©forecast. 2017 The Authors. by Elsevier districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 © 2017 TheThe Authors. Published by Elsevier Ltd. Peer-review under responsibility of Elsevier the scientific of the scientific committee of the CISBAT 2017 International © 2017 The Authors. Published by Ltd. committee buildings that vary in both construction period and typology. weather (low, medium, –high) andBuildings three district Peer-review under responsibility of the scientific committee of theThree CISBAT 2017 scenarios International Conference Future & Conference – Future Buildings & Districts – Energy Efficiency from Nano Urban Scale. Peer-review under responsibility of the scientific committee of the scientific committee the CISBAT Districts – Energy Efficiency from Nano(shallow, to Urban intermediate, Scale renovation scenarios were developed deep). To to estimate theoferror, obtained2017 heat International demand values were Conference – Future Buildings & Districts – Energy from Nano to Urbanand Scale. compared with results from a dynamic heat demandEfficiency model, previously developed validated by the authors.

Keywords: glazing façade buildings; solar heat gain coefficient; modified calculation; thermal process The results showed that when only weather change is considered, the margin of error could be acceptable for some applications Keywords: glazing façade buildings; solar heat gain coefficient; modified calculation; thermal process

(the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

* Corresponding author. Tel.: +86-021-65988869; fax: +86-021-65988869. address:[email protected] * E-mail Corresponding author. Tel.: +86-021-65988869; fax: +86-021-65988869. © 2017 The Authors. Published by Elsevier Ltd. E-mail address:[email protected] Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Cooling. Peer-review©under the scientific committee 1876-6102 2017responsibility The Authors. of Published by Elsevier Ltd. of the CISBAT 2017 International Conference – Future Buildings & Districts – Energy Efficiency Nano to Urban Scale. committee of the CISBAT 2017 International Conference – Future Buildings & Districts – Peer-review under from responsibility of the scientific Keywords: Heat demand; Forecast; Climate change Energy Efficiency from Nano to Urban Scale.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the CISBAT 2017 International Conference – Future Buildings & Districts – Energy Efficiency from Nano to Urban Scale 10.1016/j.egypro.2017.07.335

Shunyao Lu et al. / Energy Procedia 122 (2017) 151–156 Shunyao Lu et al. / Energy Procedia 00 (2017) 000–000

152 2

1. Introduction The solar heat gain through the transparent envelope is an important part of a building’s cooling load, especially in buildings with a glazing facade because of the greater window area. Some of the solar radiation enters the inner space directly. A smaller portion of the incident solar radiation is absorbed by the fenestration, part of which is transferred to the interior of the zone as infrared radiation or by convection. Solar heat gain is calculated by means of the solar heat gain coefficient (hereinafter SHGC) [1.2]. Many studies have been conducted on SHGC as it is an important thermal property parameter of the window. The hot box test was used to figure out the value of SHGC in experimental research with natural a light source [3-6] or an artificial light source [7-9]. As most of the mentioned studies of SHGC focused on fenestration, the equipped room had not been considered. Actually, the incident solar radiation could escape through the window after reflection by indoor surfaces. In traditional buildings, an assumption was made that the portion of escaped solar radiation can be ignored because the window-wall ratio is small. For example, the window-wall ratio is 0.29 and the ratio of window area to indoor surface area is 0.04 in a typical room considered by the harmonic response method [10]. The ratio of the window area to the indoor surface area is 0.154 in a room with full glazing and the escaped solar radiation cannot be ignored. Therefore the assumption that incident solar radiation cannot escape is not reasonable for glazing façade buildings. Some researchers have noticed the escaped solar radiation in glazing façade buildings. M. Cucumo [11] and J. Wen [12] calculated the room’s effective solar absorptance which was the ratio between the solar energy absorbed by the opaque walls and the solar energy entering through the windows. G. Oliveti [13] considered the solar energy absorbed by windows and presented a more accurate calculation model. In this model, the heat gain from the portion of escaped solar energy absorbed through the glazing was calculated by using the external radiative-convective heat transfer factor. Actually the radiative-convective heat transfer factor varies under different energy balance conditions and the outdoor climate is different from the indoor climate [14], so it is inappropriate to use external radiativeconvective heat transfer factor in calculation. In this paper, a solar radiation model is established to calculate the escaped solar energy in glazing façade buildings. Then on this basis, the modified calculation of solar heat gain coefficient is conducted by using mathematical models. Nomenclature A C Fi−j G H J L 𝑀𝑀1 𝑀𝑀2 N P q Q S W θ  α

surface area (m2 ) judgement factor view factor between surface i and surface j irradiation for a surface (W⁄m2 ) height of the room (m) radiosity for a surface (W⁄m2 ) width of the room (m) first surface number of the glazing last surface number of the glazing total number of divided surfaces the escaped solar energy ratio (%) absorbed solar flux for a surface (W⁄m2 ) solar energy (W⁄m2 ) solar energy sources that have passed though the glazing (W⁄m2 ) depth of the room (m) direct solar radiation’s incident angle for a surface ( °) reflectance absorptance



Shunyao Lu et al. / Energy Procedia 122 (2017) 151–156 Author name / Energy Procedia 00 (2017) 000–000

153 3

2. Calculating models 2.1. Solar radiation modeling inside the room The solar radiation model is established on the basis of the radiosity-irradiation method (RIM) [15] and view factor theory [16]. The model subdivides the finite areas forming the room into a number of rectangular grid surfaces. This algorithm is developed on these hypotheses: (1) each divided wall is considered as a single surface and the absorbed solar radiation would be distributed over the whole surface uniformly. (2) All internal walls are treated as a Lambert surface: i.e. a perfect uniform and diffuse emitter, absorber and reflector of radiant energy, their parameters are of the same except glazing surface. (3) The direct solar radiation is traced from the point where it leaves the glazing until its first encounter with a surface where upon it undergoes diffuse reflection. a

b

Fig. 1. (a) radiosity for internal surface j; (b) raidosity for the interior surface 𝑘𝑘 of the glazing.

The irradiation for surface i is:

(1)

The radiosity for surface 𝑖𝑖:

(2)

𝐺𝐺𝑖𝑖 = ∑𝑁𝑁 𝑗𝑗=1 𝐹𝐹𝑖𝑖−𝑗𝑗 𝐽𝐽𝑗𝑗

𝐽𝐽𝑖𝑖 = 𝜌𝜌𝑖𝑖 𝑆𝑆𝑏𝑏,𝑖𝑖 𝑐𝑐𝑐𝑐𝑐𝑐𝜃𝜃𝑖𝑖 + 𝑆𝑆𝑑𝑑,𝑖𝑖 + 𝜌𝜌𝑖𝑖 ∑𝑁𝑁 𝑗𝑗=1 𝐹𝐹𝑖𝑖−𝑗𝑗 𝐽𝐽𝑗𝑗

Sb,i and Sd,i are the solar beam and diffuse energy sources that have passed though the glazing. As shown in Figure 1, Sb,i is non-zero only for surfaces that are irradiated directly by the solar beam energy and Sd,i is non-zero only for the interior surfaces of the glazing. Since Eq. (x) is a linear algebraic equation, the solar radiosity 𝐽𝐽𝑖𝑖 could be written as the sum of a solar beam radiosity 𝐽𝐽𝑏𝑏,𝑖𝑖 and a solar diffuse radiosity 𝐽𝐽𝑑𝑑,𝑖𝑖 : 𝐽𝐽𝑖𝑖 = 𝐽𝐽𝑏𝑏,𝑖𝑖 + 𝐽𝐽𝑑𝑑,𝑖𝑖 The solar beam radiosity 𝐽𝐽𝑏𝑏,𝑖𝑖 is:

(3)

𝐽𝐽𝑏𝑏,𝑖𝑖 = 𝐶𝐶𝜌𝜌𝑖𝑖 𝑆𝑆𝑏𝑏,𝑖𝑖 𝑐𝑐𝑐𝑐𝑐𝑐𝜃𝜃𝑖𝑖 + 𝜌𝜌𝑖𝑖 ∑𝑁𝑁 𝑗𝑗=1 𝐹𝐹𝑖𝑖−𝑗𝑗 𝐽𝐽𝑏𝑏,𝑗𝑗

(4)

𝐽𝐽𝑑𝑑,𝑖𝑖 = 𝑆𝑆𝑑𝑑,𝑖𝑖 + 𝜌𝜌𝑖𝑖 ∑𝑁𝑁 𝑗𝑗=1 𝐹𝐹𝑖𝑖−𝑗𝑗 𝐽𝐽𝑑𝑑,𝑗𝑗

(6)

𝑞𝑞𝑖𝑖 = 𝛼𝛼𝑖𝑖 (𝑆𝑆𝑏𝑏,𝑖𝑖 𝑐𝑐𝑐𝑐𝑐𝑐𝜃𝜃𝑖𝑖 + 𝐺𝐺𝑖𝑖 )

(7)

Where 𝐶𝐶 is judgement factor that representing whether surface 𝑖𝑖 is irradiated or not. 16 judgment points are chosen on each surface by meshing. If 𝑚𝑚 point is irradiated by solar beam, the judgment factor is: 𝐶𝐶 = 𝑚𝑚/16 (5) The solar diffuse radiosity 𝐽𝐽𝑑𝑑,𝑖𝑖 is: The solar beam radiosity 𝐽𝐽𝑏𝑏,𝑖𝑖 and the solar diffuse radiosity 𝐽𝐽𝑑𝑑,𝑖𝑖 are calculated by solving the N*N equations with using Matlab. The absorbed solar flux for surface 𝑖𝑖 is: The escaped solar radiation is: 𝑀𝑀

2 𝜏𝜏 𝐺𝐺 𝑄𝑄𝑜𝑜𝑜𝑜𝑜𝑜 = ∑𝑖𝑖=𝑀𝑀 1 𝑖𝑖 𝑖𝑖

(8)

The escaped solar radiation ratio is defined as the ratio of escaped solar energy to the incoming solar energy and is calculated by:

Shunyao Lu et al. / Energy Procedia 122 (2017) 151–156 Shunyao Lu et al. / Energy Procedia 00 (2017) 000–000

154 4

𝑌𝑌 =

𝑄𝑄𝑜𝑜𝑜𝑜𝑜𝑜

𝑄𝑄𝑏𝑏 +𝑄𝑄𝑑𝑑

(9)

× 100%

2.2. Heat transfer modeling of glazing The heat transfer processes for the band of solar wavelengths below 3μm and the band of longer wavelengths are highly different. First, an optical analysis determines how much of the solar radiation is absorbed at each of the glazing layers and how much is transmitted through the glazing system. Second, a heat transfer analysis is used to impose an energy balance on each glazing layer. The net heat transfer from any glazing layer must equal to the amount of absorbed solar radiation. Heat transfer in a glazing system includes longwave radiative exchange and conductive heat transfer. ISO 15099 algorithms are used in this paper.

Fig. 2. Energy balance for n-layer glazing system.

Fig. 2 shows the numbering system, boundary conditions and energy balance for each layer in the glazing system. The amount of solar energy absorbed by each layer is calculated with the algorithm presented by Wright, J. L [17]. The heat flux across the gap between layer 𝑖𝑖 − 1 and 𝑖𝑖 is: 𝑞𝑞𝑖𝑖 = ℎ𝑐𝑐,𝑖𝑖 (𝑇𝑇𝑓𝑓,𝑖𝑖 − 𝑇𝑇𝑏𝑏,𝑖𝑖−1 ) + 𝐽𝐽𝑓𝑓,𝑖𝑖 − 𝐽𝐽𝑏𝑏,𝑖𝑖−1

(10)

𝑞𝑞𝑖𝑖 = 𝑆𝑆𝑖𝑖 + 𝑞𝑞𝑖𝑖+1

(11)

The solution (i.e. temperatures at each glazing surface and corresponding radiant fluxes) is generated by applying the following four equations at each layer: 𝐽𝐽𝑓𝑓,𝑖𝑖 = 𝜀𝜀𝑓𝑓,𝑖𝑖 𝜎𝜎𝑇𝑇𝑓𝑓,𝑖𝑖 4 + 𝜏𝜏𝑖𝑖 𝐽𝐽𝑓𝑓,𝑖𝑖+1 + 𝜌𝜌𝑓𝑓,𝑖𝑖 𝐽𝐽𝑏𝑏,𝑖𝑖−1

𝐽𝐽𝑏𝑏,𝑖𝑖 = 𝜀𝜀𝑏𝑏,𝑖𝑖 𝜎𝜎𝑇𝑇𝑏𝑏,𝑖𝑖 4 + 𝜏𝜏𝑖𝑖 𝐽𝐽𝑏𝑏,𝑖𝑖−1 + 𝜌𝜌𝑏𝑏,𝑖𝑖 𝐽𝐽𝑏𝑏,𝑖𝑖+1

𝑇𝑇𝑏𝑏,1 − 𝑇𝑇𝑓𝑓,1 =

𝑡𝑡𝑔𝑔,𝑖𝑖

𝑘𝑘𝑔𝑔,𝑖𝑖

(𝑞𝑞𝑖𝑖+1 + 0.5𝑆𝑆𝑖𝑖 )

(12) (13) (14)

The equations (11)-(14) contain black emissive power (Ebf,i = σTf,i 4 , Ebb,i = σTb,i 4 ) and are nonlinear. They would become linear only if solved in terms of black emissive power instead of temperature. Therefore it is necessary to define two new quantities: Convection heat transfer coefficient based on emissive power: ℎ̂𝑖𝑖 = ℎ𝑐𝑐,𝑖𝑖

𝑇𝑇𝑓𝑓,𝑖𝑖 −𝑇𝑇𝑏𝑏,𝑖𝑖−1

𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 −𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖−1

(15)

Conduction heat transfer coefficient based on emissive power:

𝑘𝑘𝑔𝑔,𝑖𝑖 ∙ ℎ̂𝑔𝑔,𝑖𝑖 = 𝑡𝑡𝑔𝑔,𝑖𝑖

𝑇𝑇𝑏𝑏,𝑖𝑖 −𝑇𝑇𝑓𝑓,𝑖𝑖

𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 −𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖

(16)

By application of black emissive power terms and heat transfer coefficients based on emissive power, heat fluxes across gas spaces (13) can be written as:



Shunyao Lu et al. / Energy Procedia 122 (2017) 151–156 Author name / Energy Procedia 00 (2017) 000–000

155 5

𝑞𝑞𝑖𝑖 = ℎ̂𝑖𝑖 [𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 − 𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖−1 ] + 𝐽𝐽𝑓𝑓,𝑖𝑖 − 𝐽𝐽𝑏𝑏,𝑖𝑖−1

(17)

𝑞𝑞𝑖𝑖 = 𝑆𝑆𝑖𝑖 + 𝑞𝑞𝑖𝑖+1

(18)

And the basic energy balance equations (11)-(14) are transformed into the following system:

𝐽𝐽𝑓𝑓,𝑖𝑖 = 𝜀𝜀𝑓𝑓,𝑖𝑖 𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 + 𝜏𝜏𝑖𝑖 𝐽𝐽𝑓𝑓,𝑖𝑖+1 + 𝜌𝜌𝑓𝑓,𝑖𝑖 𝐽𝐽𝑏𝑏,𝑖𝑖−1

(19)

ℎ̂𝑔𝑔,𝑖𝑖 (𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 − 𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 ) = 0.5𝑆𝑆𝑖𝑖 + ℎ̂𝑖𝑖+1 (𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖+1 − 𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 ) + 𝐽𝐽𝑓𝑓,𝑖𝑖+1 − 𝐽𝐽𝑏𝑏,𝑖𝑖

(21)

(20)

𝐽𝐽𝑏𝑏,𝑖𝑖 = 𝜀𝜀𝑏𝑏,𝑖𝑖 𝐸𝐸𝑏𝑏𝑏𝑏,𝑖𝑖 + 𝜏𝜏𝑖𝑖 𝐽𝐽𝑏𝑏,𝑖𝑖−1 + 𝜌𝜌𝑏𝑏,𝑖𝑖 𝐽𝐽𝑓𝑓,𝑖𝑖+1

This system of 4n equations can be solved using iterative solution algorithm that is comprised of following steps: (1). Assumption for initial glazing layer temperatures. (2). Calculation of the corresponding sets of ĥi and ĥg,i based on temperatures. (3). Solution of the system of linear equations and definition of new sets of temperatures at each glazing layer. (4). Convergence checking (comparison of new sets of temperatures to old sets). If each temperature in the new set is not equal to the corresponding temperature in the old set within defined tolerance (e.g., 10−4 K), the new sets are used to replace the old sets and the calculation proceeds to the second step. 3. Results The standard size of the room is 3m×4.5m×3m (width×depth×height). For the south facing room located in Shanghai, the glazing consists of double-glass pane windows. The original SHGC is 0.71. The solar transmittance of the glazing is 0.6, the absorptance is 0.33 and the reflectance is 0.07. The absorptance of the floor surface is 0.8 and the reflectance is 0.2, other internal surfaces of the room are assigned a solar absorptance of 0.4. Modified SHGC calculations are carried out to find the effect of room parameters, for instance, room geometric dimensioning and absorptance of interior surfaces. 3.1. Room geometric dimensioning The size scale of the standard room is 1:1.5:1, the width, depth and height were changed separately in the calculation process and the results are shown in Table 1. Table 1. Modified SHGC with different room geometric dimensioning.

Different room width

Different room depth

Different room height

L (m)

W (m)

H (m)

Escaped solar energy ratio

Modified SHGC

Correction factor

1.5 3 4.5 6 7.5 9 3 3 3 3 3 3 3 3 3 3 3 3

4.5 4.5 4.5 4.5 4.5 4.5 1.5 3 4.5 6 7.5 9 4.5 4.5 4.5 4.5 4.5 4.5

3 3 3 3 3 3 3 3 3 3 3 3 1.5 3 4.5 6 7.5 9

9.0% 8.8% 9.0% 9.0% 9.1% 9.2% 13.7% 10.1% 8.8% 8.4% 8.2% 8.1% 7.40% 8.8% 9.7% 10.5% 10.9% 11.3%

0.672 0.673 0.672 0.672 0.671 0.671 0.651 0.667 0.673 0.675 0.675 0.676 0.679 0.673 0.669 0.665 0.663 0.661

94.3% 94.4% 94.3% 94.3% 94.3% 94.2% 91.3% 93.6% 94.4% 94.7% 94.8% 94.9% 95.3% 94.4% 93.9% 93.4% 93.1% 92.8%

156 6

Shunyao Lu et al. / Energy Procedia 122 (2017) 151–156 Shunyao Lu et al. / Energy Procedia 00 (2017) 000–000

3.2. Absorptance of interior surfaces The floor’s material is always different from the walls and ceiling, and the beam solar radiation irradiates on the floor mostly. As a result, the floor’s reflectance and the other internal surfaces’ reflectance were studied separately and the results are shown in Fig. 3.

Fig. 3. Modified SHGC with different surface absorptance.

4. Conclusions The modified solar heat gain coefficient is smaller than the original SHGC obviously. For instance, in a glazing façade building with double glasses, at 12:00 in June 21th, the escaped solar energy ratio is 8.85% and the modified SHGC is 0.67, while the original SHGC is 0.71. Therefore, the correction factor is 94.4%. The modified SHGC varies with different building construction parameters. In room geometric dimensioning, the width has little influence on the modified SHGC, but the depth and height affect SHGC dramatically. In internal surfaces’ absorptance, the floor has greater impact on the modified SHGC than other internal surfaces. References [1] ASHRAE. 2013 ASHRAE Handbook—Fundamentals. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 2013. [2] National Fenestration Rating Council. NFRC 200-2004, Procedure for Determining Fenestration Product Solar Heat Gain Coefficient and Visible Transmittance at Normal Incidence. [3] Klems. A new method for predicting the solar heating gain of complex fenestration systems: Ⅰ. Overview and derivation of the matrix layer calculation [J]. ASHRAE Transactions 100(1): 1065-1072. [4] Klems. A new method for predicting the solar heating gain of complex fenestration systems: Ⅱ. Detailed description of the matrix layer calculation [J]. ASHRAE Transactions 100(1): 1073-1086. [5] Wang, R. G., Shen, T. X., Regenerated energy utilization and building energy saving, Beijing: China Architecture & Building Press, 20014. [6] Xie Y., Measurement study and apparatus development on solar heat gain coefficient of window [D], School of environmental science and Engineering, 2006. [7] National Fenestration Rating Council. NFRC 200-2004, Procedure for Interim Standard Test Method for Measuring the Solar Heat Gain Coefficient of Fenestration Systems Using Calorimetry Hot Box Methods. [8] A.H.Elmahdy. Heating Transmission and R-value of Fenestration Using IRC Hot Box[J]. ASHRAE Transactions 1991(1):631-637. [9] A.H.Elmahdy. Heating Transmission and R-value of Fenestration Using IRC Hot Box: procedure and uncertainty analysis[J]. ASHRAE Transactions 1992(1): 838-845. [10] Cao S. W., Room thermal process and air-conditioning load [M]. Shanghai: Shanghai Scientific and Technological Literature Press, 1991. [11] M. Cucuno, D. Kaliakatsos, V. Marinelli. Stimating effective solar absorptance in rooms[J], Energy and Buildings, 1995. 23: 117-120. [12] Jin Wen, Theodore F. Smith, Absorption of solar energy in a room[J]. Solar energy, 2002. 72(4): 283-297. [13] Giuseppe Oliveti, Natale Arcuri, Roberto Bruno, Marilena De Simone. An accurate calculation model of solar heat gain through glazed surfaces [J]. Energy and Buildings, 2011. 43: 269-274. [14] ISO 15099-2003, Thermal performance of windows, doors and shading devices——Detailed calculations. [15] Sparrow E. M., Cess R. D., Radiation heat transfer. Hemisphere. Washington. 1978. [16] Ehlert J. R., Smith T. F., View factor for rectangular perpendicular and parallel plates with varying position and size having parallel boundaries. J. Thermophysics and Heat Transfer. 1993. 7(1): 173-175. [17] Wright, J. L., Calculating centre-glass performance indices of windows [J], ASHRAE Transaction. 1998. 104(1): 1230-1241.