Experimental analysis of thermal performance in buildings with shape-stabilized phase change materials

Experimental analysis of thermal performance in buildings with shape-stabilized phase change materials

Accepted Manuscript Title: Experimental analysis of thermal performance in buildings with shape-stabilized phase change materials Authors: Hyun Bae Ki...

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Accepted Manuscript Title: Experimental analysis of thermal performance in buildings with shape-stabilized phase change materials Authors: Hyun Bae Kim, Masayuki Mae, Youngjin Choi, Takeshi Kiyota PII: DOI: Reference:

S0378-7788(17)31640-7 http://dx.doi.org/doi:10.1016/j.enbuild.2017.07.076 ENB 7816

To appear in:

ENB

Received date: Revised date: Accepted date:

9-5-2017 20-6-2017 26-7-2017

Please cite this article as: Hyun Bae Kim, Masayuki Mae, Youngjin Choi, Takeshi Kiyota, Experimental analysis of thermal performance in buildings with shape-stabilized phase change materials, Energy and Buildingshttp://dx.doi.org/10.1016/j.enbuild.2017.07.076 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Title: Experimental analysis of thermal performance in buildings with shapestabilized phase change materials

Highlights    

Three identical huts using varying shape-stabilized PCMs (SSPCM) levels were examined for verifying the effect of indoor thermal stabilizing. The heat-storage performance changes depending on the installation area and position, even when the same amount of PCM. The higher thermal benefit was achieved when the PCM was applied on the floor which receives direct solar radiation and when the applied area was expanded. The effect of reducing heating power was doubled when the applied area was expanded from the floor to the entire surface.

1

Experimental analysis of thermal performance in buildings with shapestabilized phase change materials 

Hyun Bae Kim a, Masayuki Mae a, Youngjin Choi a, Takeshi Kiyota b a

Department of Architecture, Graduate School of Engineering, The University of Tokyo

b

JXTG Nippon Oil & Energy Corporation

email: [email protected], Telephone: 00813-5841-6208

ABSTRACT Maintaining constant thermal conditions in building interiors requires substantial energy. Using phasechange materials (PCMs) with construction materials can improve thermal performance without increasing energy expenditure. Herein, shape-stabilized PCMs (SSPCMs) were used. We measured the thermal performance of a PCM sheet and established the melting- and solidification-temperature ranges at 19–26℃. Three identical huts were examined using varying PCM levels under natural and heating conditions. In Hut A, no SSPCM sheets were applied; in Hut B, four layers of SSPCM sheets were applied to the floor; in Hut C, one layer of SSPCM was applied to the floor, walls, and ceilings. The results demonstrated that the application of SSPCM sheets improves thermal performance. For an equal number of SSPCM sheet layers applied on each side, the floor directly exposed to solar radiation showed the highest indoor temperature stabilization effect, followed by the walls and ceilings. Compared with Hut A, which served as the reference, the total power consumption using a heater decreased by 9.2% and 18.4% in Huts B and C, respectively. The effect of reducing heating power doubled when the applied area was expanded from the floor to the entire surface. Hence, effective PCM usage can entail large-scale application of SSPCM sheets to building surfaces.

Keywords: Phase-change material; Shape-stabilized PCM; Thermal comfort; Heating load;

1

Introduction Buildings with a low thermal mass undergo frequent and severe indoor temperature fluctuations. To

maintain interior thermal conditions appropriate for human comfort, up to 65% of the energy usage in buildings is attributed to interior space heating and cooling, according to Natural Resources Canada [1]. Such exorbitant energy consumption patterns go against the great international demand for energy conservation, especially in the wake of the Paris Agreement, in which many countries pledged to reduce greenhouse gas emission by 25%–65%

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by 2030. Large-scale application of phase-change materials (PCMs) in both residential and commercial buildings to improve thermal storage can reduce the large carbon footprint in climate control and help us realize the abovementioned goals. The specific heat of PCMs changes according to their surrounding temperature; i.e., if a PCM’s temperature moves to a phase-changing range, it will absorb or release heat by changing its phase from solid to liquid or from liquid to solid, respectively, and consequently reduce the heat flow to and from the environment. Ideally, PCMs can be used with construction materials to serve as buffers for sudden and/or severe changes in thermal conditions. Therefore, PCMs enable latent thermal storage and hence offer a large heat storage capacity when used in building materials. Since 1980, the application of various types of PCMs in buildings has been studied owing to their thermal-storage potential [2]. In early PCM research, prototypes of PCM wallboards and concrete systems were developed to increase the thermal energy storage (TES) capacity of standard gypsum wallboards and concrete blocks. Studies on the peak load transfer and solar energy utilization of these prototypes have led to great research interest. In addition, the impregnation of PCMs into building materials such as gypsum boards or concretes has been studied [3,4]. Since the appearance of the micro-encapsulating PCM (mPCM) technique, various studies on the incorporation of PCMs into architectural materials have been conducted [5,6]. Using shape-stabilized PCMs (SSPCMs) is one of the methodologies currently being used for encapsulating PCMs in order to solve the problems of leakage and volatilization [7]. SSPCMs have skeletons comprising supporting materials such as high-density polyethylene (HDPE), polypropylene (PP), and styrene–butadiene–styrene (SBS), which are immersed in paraffin (PCM). Paraffin can easily spread into a network formed by these supporting materials. Even if the operating temperature is higher than the melting point of paraffin and a phase change from solid to liquid occurs, an SSPCM can still maintain its shape [7–9]. The application of SSPCMs in building components (e.g., floors, walls, and ceilings) has been studied. Zang et al. [10] found that SSPCMs can simplify a thermal storage system because containers are not required to encapsulate the PCM. They proposed the potential applications of PCMs in buildings and for use as inner linings in walls, ceilings, and floors. Xu et al. and Lin et al. produced new SSPCM panels using different ratios of paraffin, polyethylene, and supporting materials and evaluated their thermochemical properties for heat storage [11,12]. Zhou et al. [13] simulated a middle direct-gain room using SSPCM panels as inner linings and confirmed the effects of their thermochemical properties (e.g., melting temperature, heat of fusion, and thermal conductivity), plate thickness, and location. Zhou et al. [14] showed via a simulation that using SSPCMs in the building envelopes of office buildings can reduce the indoor temperature swing and improve energy performance. Kim et al. [15] showed that a test building using EnergyPlus with hexadecane/xGnP SSPCM

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mortar reduced temperature variations and enhanced thermal inertia during the monitored period. Although SSPCMs have been studied in numerous ways [16,17], more thermal-performance evaluations via field experiments are necessary to further establish their validity and feasibility. Through field experiments, Nghana et al. [18] measured the effects of PCMs on bio-PCMs for twin side-by-side buildings. The experimental results were benchmarked using EnergyPlus and applied to real apartments to simulate summer and winter energy savings. Entrop et al. [19] used concrete containing microencapsulated PCMs to make four heat boxes with an internal volume of 1130 mm × 725 mm × 690 mm. Two of the boxes contained 4.9% of microencapsulated PCMs based on the weight of concrete, whereas the other two used plain concrete to confirm the effects of the PCMs, including the insulation effect. Castell et al. [4] produced cubicles using conventional brick comprising macroencapsulated PCMs to measure the temperatures, cooling loads, and CO2 emissions during summer. The peak temperature was reduced by more than 1°C, cooling energy consumption decreased by 15%, and CO 2 emissions decreased by 1.5 kg/yr/m2. Navarro et al. [20] made three cubicles and compared the heating energy consumption using both polyurethane alone and polyurethane with the PCMs and a reference with no insulation or PCMs. Athienitis et al. [21] found that using gypsum boards with 25% PCMs in Montreal, Canada, led to a decrease in temperature by ~4°C during the daytime and could reduce the heating load significantly at night. Ahmad et al. [22] found that an indoor temperature amplitude of ~20°C decreased in a test cell when a composite wallboard with a vacuum insulation panel and a PCM were used during summer. Barzin et al. [23] achieved cost and energy savings of up to 93% and 92% per day, respectively, using PCM-impregnated gypsum boards with night ventilation. Sage-Lauck et al. [24] simulated a house in Portland, USA, in which a 0.9 kg m−1 two-floor area of PCM was incorporated and found that the PCM could reduce the hours for which the zone was overheated by ~50%. Jamil et al. [25] used a PCM in the ceilings of two rooms and observed a reduction of up to 1.1°C in the indoor air temperature of Bed room during the day and a 34% reduction in the number of hours of thermal discomfort. Although several PCM-related field experiments have been conducted, studies on SSPCMs have been scarce. In fact, most of the studies confirm only the effects of the presence of PCMs. Even if the same amount of a PCM is used in different building components, its effect would depend on the position and installation area because PCMs store heat using direct-day solar radiation. Therefore, not only should the effects of the presence of PCM be studied but also their performance according to the installation area and positions in field experiments. When PCMs are applied to an actual house, variables such as inflow solar radiation and insulation conditions must be considered. However, in this study, basic experiments were conducted to determine the indoor stabilization

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effect and the heating load reduction effect in winter of the Japanese temperate climate depending on the PCM application area and installation area. Herein, the thermal performance of SSPCM sheets made using paraffin (comprising hexadecane and octadecane) with polypropylene and elastomer was measured in the testing huts. The technology used in SSPCMs enables the sheet-like forming of supporting materials, which can be easily attached to existing construction materials. This presents us with the largest advantage of SSPCMs yet, which is the fact that they can be applied to all buildings, even existing ones, because they can also be easily applied post-construction. The present paper investigates the possibility of using SSPCM sheets to enhance thermal comfort by stabilizing the indoor temperature and reducing the heating energy used in winter.

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Experimental Setup and Data Analysis Procedure The effectiveness of SSPCM sheets was examined in three identical lightweight huts. Hut A has no

SSPCMs sheets installed and is used as the reference; Hut B is equipped with four layers of SSPCM sheets on its floor; and Hut C has one layer of SSPCM installed on the floor, walls, and ceilings. The tests were driven by three aspects. First, the basic approach of the experiment was to examine the effectiveness of SSPCM sheets by comparing the heat flows in Huts A, B, and C. Second, the thermal performance and heat storage when using a similar number of SSPCM sheets in Hut B (6.65 MJ) and Hut C (6.74 MJ) were investigated with respect to different covering areas, with Hut A being the reference. Finally, the stabilization effect of the sheets on indoor temperature was evaluated using a heat flow meter on each side of Hut C, where one layer of SSPCM was installed. The experimental results obtained regarding these three aspects led us to discover highly efficient practical applications of SSPCM sheets. When installing a PCM in a house, the furniture and carpet appliances affect the amount of solar radiation that reaches the PCM directly; moreover, the thermal performance of the PCM is likely to vary according to the number of occupants. However, this study focuses on limiting the variables and comparing performance the same amount of PCM used in different areas.

2.1

Overview of the experimental facility In November 2014, three identical test huts were constructed in Chiba Prefecture, Japan (shown in Fig.

1). All of them had southward-facing windows and doors (designed to exhibit the same thermal performance as a northern wall) on their northern walls. To balance the solar radiation conditions in the three huts, two walls of

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were built on the west side of Hut A and on the east side of Hut C using the same construction materials. Table 1 presents the construction details of the building envelope and the thermal properties of the materials. The windows used in the test huts were made of triple glazing resin, which is highly efficient for heat-release acquisition (Uw: 1.32W/m2∙k, Solar Heat Gain Coefficient: 0.41). In an actual house, east- and west-facing windows play an important role in determining the heating and cooling loads. However, this study investigated the effect of PCM application on the south-facing window during winter. The U-value of the south-facing wall is designed to meet low-energy housing standards so that the window-to-wall area ratio does not differ significantly from that of the existing direct-gain houses; in the present study, the ratio is taken to be 0.68 [26]. Recently, in accordance with performance enhancement (high insulation) of the housing envelope in Japan, PCM was applied to a highinsulation house with better heat insulation than the insulation standard proposed in the Japanese architectural standards [27]; this study investigated the possibility of a non-heating house using direct gain.

Hut A

Hut B

Hut C

Fig. 1. Exteriors of the test huts.

Table 1 Construction details of the building envelope and thermal properties of the materials used. Component

Assembly detail

Thickness

Conductivity

Volumetric specific heat

(U-value)

solidification range (℃)

(mm)

(W/m-K)

(kJ/m3-K)

Wall

Fiber-reinforced cement siding

15.0

0.28

1600

(0.218W/m2K)

Air cavity Extruded foam polystyrene

50.0

0.28

25

Plywood

10.0

0.16

720

Extruded foam polystyrene

120.0

0.03

25

Veneer core plywood

12.0

0.16

720

SSPCM sheet Plywood

None or 2.5 mm 9.0

0.16

720

Ceilings

Fiber-reinforced cement siding

15.0

0.28

600

(0.166 W/m2K)

Air cavity

6

Extruded foam polystyrene

170.0

0.03

25

Veneer core plywood

12.0

0.16

720

SSPCM sheet

None or 2.5 mm

Plywood

9.0

0.16

720

Floor

Extruded foam polystyrene

170.0

0.03

25

(0.164 W/m2K)

Structural plywood

24.0

0.16

720

Veneer core plywood

6.0

0.16

720

SSPCM sheet

None, 2.5 mm, or 10.0 mm

Plywood

15.0

0.16

720

2.2

SSPCM installation The SSPCM sheets (Fig. 2) used herein were made of paraffin (hexadecane and octadecane)-based PCM

mixed with polypropylene and elastomer to keep their shape stabilized. The thermal properties of the sheets are shown in Table 2. To examine the effects of SSPCM sheet application and those of different SSPCM sheet application areas, no SSPCMs sheets were installed in Hut A, whereas a four-layer SSPCM sheet (6.65 MJ) was installed on the floor of Hut B, and one-layer SSPCM sheets were mounted on the walls, floors, and ceilings (6.74 MJ in total) of Hut C, as shown Fig. 3.

SSPCM sheet

SSPCM sheet 2.5mm

Ply wood

Fig. 2. SSPCM sheet installation behind ply wood.

Table 2 Thermophysical properties of the SSPCM sheets. Approximate

Approximate

Density

Specific heat

Latent heat

Thermal conductivity

melting range (℃)

solidification range (℃)

(kg/m3)

(kJ/kg∙K)

(kJ/kg)

(W/m∙K)

19.0–26.0

20.0–25.0

868

3.26

62.24

0.12

7

+



+

+

Wall

Hut B



Floor

• •

+

Ceiling

Wall

+



Hut C

Wall

+



Floor

+

Floor





Ceiling

Ceiling

Hut A



+

+





PCM installed area : 0m 2 PCM installed latent heat : 0MJ Pl ywood

• PCM installed area : 12.32m 2 • PCM installed area : 49.95m 2 • PCM installed latent heat : 6.65MJ • PCM installed latent heat : 6.74MJ Th e rmocouple H e at Flow sensor SSPCM sheet 2.5mm Direction :

+

positive

− negative

Fig. 3. Cross-section of SSPCM sheet installation.

2.3

Instrumentation A weather station that measures ambient temperature, humidity, and wind velocity and direction was

located on the western side of Hut A. Pyrheliometers were installed inside Hut C to measure vertical and horizontal solar radiation. Fig. 4 shows the layout of the thermocouples and heat-flow meters installed in the huts. Thermocouples were installed on each surface and at different heights (100, 600, 1100, and 1700 mm) to measure the indoor temperature at five locations (east, west, north, south, and center). At the center point of each side, heat-flow meters (30 mm × 30 mm) were placed on the SSPCM sheets to examine the amount of heat absorbed or released. Thermocouples and heat-flow meters were mounted on both sides of the huts, where the SSPCM sheets were attached. The results of experiments were evaluated during January 15–19 and February 3–9 under both natural and heating conditions, as given in Table 3. The extra-heating condition was achieved using a ceramic heater that was activated from 0600 to 2400 during the measurements. The indoor heating was set at 20 ℃ by the Japanese low-energy standards [28].

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Ceiling

Thermocouple

Thermocouple: both surface of the PCM Heat flow meter

Heat flow meter: both surface of PCM Room air temperature point (100,600,1100,170mm)

North

Globe temperature

Ceiling West

East 1700mm

3804mm

2700mm

2700mm

600mm

3804mm

Floor Window

2600mm

1820mm

South

1100mm

N

Floor

100mm

Fig. 4. Layout of the thermocouples and heat flow meters installed in the huts

Table 3 Experiment schedule and conditions Measurement period

Evaluation period

Heating

(2016)

(2016)

Set temp. (℃)

Natural condition

Jan. 13-Feb. 2

Jan. 15-19

-

Heating condition

Feb. 3-9, Feb. 16-25

Feb. 3-9

20.0

3

Results and Discussion The experiments examined SSPCM sheets installed in the three huts. First, under the natural condition,

the possibility of enhancing SSPCM sheets to improve their thermal comfort via indoor temperature stabilization was investigated. The heat-storage performance of the SSPCM sheets was investigated via indoor temperature and heat flow monitoring. The reliability of the experiment was ensured using heat balance. Second, the heatenergy-saving effect of the SSPCM sheets was examined in winter. The application of PCM can affect the increase or decrease in both summer and winter heating loads; however, the present study focuses on stabilizing the room temperature and reducing the heating load in winter by using PCM in an experimental hut. However, in the present study, the number of variables associated with the house was limited for the sake of a quantitative comparison of the PCM installation conditions. The experiment was focused on the possibility of applying PCM in the Japanese climate and on improving indoor-temperature 9

stabilization in winter as a consequence of doing so.

3.1

Natural conditions From January 15–19, the experiment was performed under the natural condition. The change in the air

temperature was calculated using an average of 20 thermocouple positions. Fig. 5 shows the weather conditions (horizontal solar radiation and outdoor temperature) and the average indoor temperature of each hut during the measurement. The average temperature of Hut A without PCMs is 21.1℃; that of Hut B, with four layers of SSPCM sheets installed only on the floor, is 21.6 °C; and that of Hut C, with one layer installed on the floor, wall, and ceiling is 22.0 °C. The temperatures of Huts B and C are 0.5 °C and 1.0 °C higher than that of Hut A, respectively. The temperature differences between Huts B, C, and A during the same period are shown in Fig. 6. Compared with Hut A, the maximum peak indoor temperature decreases during the daytime by 2.3 °C (mean 1.4 °C) and by 3.1 °C (mean 2.3 °C) on January 19 in Huts B and C, respectively. The solar radiation during measurement reaches its peak of 20.70 MJ/m2 on January 19. Compared with Hut A, the maximum nighttime temperature increases by 1.9 °C (mean 1.7 °C) on January 18 and by 2.6 °C (mean 2.3 °C) on January 17 in Huts B and C, respectively. Overheating did not occur on January 18, when the weather was cloudy and solar radiation was the minimum at 0.97 MJ/m2; however, the heat stored by the PCM on January 17 decreased the indoor temperature throughout the day in Huts B and C. Therefore, the stabilization effect of indoor temperature was confirmed through a decrease in the indoor temperature corresponding to the installation of the SSPCM sheets. The peak temperature of Hut C was about 0.9 °C lower than that of Hut B, and the nighttime temperature of Hut C was increased about 0.9 °C than Hut B. This means that for the same amount of PCM, different installation areas exhibit different thermal performances.

Horizontal solar radiation

35

Temperature [oC]

30

Outdoor tempetature

Hut A

Hut B

Hut C

1600 1400

Phase change range

25

1800

1200

20

1000

15

Solar_horiz.

Solar_horiz.

Solar_horiz.

10

13.41MJ/m2

19.52MJ/m2

6.17MJ/m2

Solar_horiz. 20.70MJ/m2

Solar_horiz. 0.97MJ/m2

5

800 600 400

0

200

-5

0

15-Jan-16

16-Jan-16

17-Jan-16

18-Jan-16

19-Jan-16

Fig. 5. Weather conditions and indoor temperature (average of 20 points).

10

Solar radiation [W/m 2 ]

40

Temperature [o C]

4 3 2 1 0 -1 -2 -3 -4

Temperature decline in nighttime

Hut B - Hut A

Hut B-Hut A: 1.6oC

Hut C - Hut A

Hut C-Hut A: 2.5 C o

Over heating reduction

Temperature decline in nighttime

Over heating reduction

Hut B-Hut A: -1.6oC

Hut B-Hut A: 1.9oC

Hut B-Hut A: -2.3oC

Hut C-Hut A: -2.2oC

Hut C-Hut A: 2.5oC

Hut C-Hut A: -3.1oC

15-Jan-16

16-Jan-16

17-Jan-16

18-Jan-16

19-Jan-16

Fig. 6. Indoor-temperature difference (average of 20 points).

Fig. 7 shows the average surface temperatures of five points on the floors and ceilings and three points on the east wall. The average floor-surface temperatures of Hut A, B, and C are 20.5℃, 21.3℃, and 21.4℃, respectively. Similarly, the average surface temperatures of the east walls are 20.7℃, 21.4℃, and 21.6℃ and the average surface temperatures of the ceilings are 20.5℃, 20.9℃, and 21.1℃, respectively. The average temperature differences are the largest on the floor, followed by the east walls and ceilings. The maximum surface-temperature differences between Hut A and Huts B and C are 2.3℃ and 2.5℃ on the floors, 2.7℃ and 4.5℃ on the east walls, and 2.3℃ and 4.2℃ on the ceilings. The surface-temperature difference of more than 2 °C on the east walls and ceilings of Hut A and Hut B reduces the variation in the indoor temperature and affects the surface temperature.

Temperature [oC]

35

Hut A

Floor surface temperature:

Hut A-Hut B: 2.2oC

30

Hut A-Hut C: 2.4oC

Hut B

Hut C

Hut A-Hut B: 2.2oC

25

Hut A-Hut C: 2.5oC

20 15 10

Hut B-Hut A: 1.8oC

Hut B-Hut A: 2.3oC

Hut B-Hut A: 2.3oC

Hut C-Hut A: 2.3oC

Hut C-Hut A: 2.5oC

Hut C-Hut A: 2.4oC

16-Jan-16

15-Jan-16

17-Jan-16

19-Jan-16

18-Jan-16

(a) Floor-surface temperature of each hut (Average of five points) Temperature [oC]

35

Hut A

East wall surface temperature:

Hut A-Hut B: 1.4oC

30

Hut A-Hut C: 3.2oC

Hut B

Hut A-Hut B: 1.9oC

25

Hut A-Hut C: 4.5oC

20 15 10

Hut B-Hut A: 1.8oC

Hut B-Hut A: 1.9oC

Hut B-Hut A: 2.0oC

Hut C-Hut A: 2.3oC

Hut C-Hut A: 2.7oC

Hut C-Hut A: 2.6oC

15-Jan-16

16-Jan-16

17-Jan-16

18-Jan-16

(b) East-wall surface temperature of each hut (Average of five points)

11

19-Jan-16

Hut C

Temperature [o C]

35

Hut A-Hut C: 3.0oC

25

Hut A

Ceiling surface temperature:

Hut A-Hut B: 1.5oC

30

Hut B

Hut C

Hut A-Hut B: 2.1oC Hut A-Hut C: 4.2oC

20

Hut B-Hut A: 1.5oC

15

Hut C-Hut A: 2.0oC

10

15-Jan-16

Hut B-Hut A: 1.6oC

Hut C-Hut A: 2.3oC

Hut B-Hut A: 1.7oC Hut C-Hut A: 2.2oC

16-Jan-16

17-Jan-16

18-Jan-16

19-Jan-16

(c) Ceiling-surface temperature of each hut (Average of five points) Fig. 7. Average surface-temperature difference in each hut (January 14–19)

The difference in the maximum floor-surface temperature between the four layers of SSPCM sheets installed in Hut B and the one layer installed in Hut C was not greater than 0.2 °C. This phenomenon is further explained by comparing the heat flow through the floor, walls, and ceilings of each hut. The effects of PCM application and the differences corresponding to the amount of PCM are shown in Fig. 8 (direction of heat flow is the same as that shown in Fig. 3). The SSPCM sheets absorbed the solar heat coming through the windows via indoor air; this prevented the huts from overheating. Thus, the floors of Huts A, B, and C had a positive heat flow of 1.70 MJ/m2, 2.93 MJ/m2, and 1.85 MJ/m2, respectively, during measurement. Conversely, the indoor temperature dropped at nighttime because the buildings lose heat in the absence of solar radiation from sunset to sunrise. The direction of heat flow was from the SSPCM sheets to the indoor air via radiation, leading to a decrease in temperature at nighttime. The floors of Huts A, B, and C had negative heat flows of 0.41 MJ/m2, 1.65 MJ/m2, and 0.54 MJ/m2, respectively. The floor-surface temperature difference between Huts B and C was not large; however, the heat flow was higher in Hut B by ~75%. The data obtained in the experiments indicate that the heat flow in the Hut B and C with PCM was larger than that in the Hut A without PCM and that the heat absorbed or released increased according to the amount of PCM used. Hut C where the same amount of SSPCM sheets (one layer) installed each surface on the floor, wall, and ceiling had a positive heat flow of 1.85 MJ/m2, 1.50 MJ/m2, and 1.44 MJ/m2, and a negative heat flow of 0.54 MJ/m2, 0.18 MJ/m2, and 0.34 MJ/m2, respectively. The results show that when the same amount of PCM was installed on each side, the stabilization effect of the indoor temperature was the highest on the floor directly exposed to solar radiation, followed by the wall and ceiling.

12

Heat flow [W/m 2 ]

80 70 60 50 40 30 20 10 0 -10 -20

15-Jan-16

Hut A floor

Hut A ceiling

Hut A east wall

Positive heat flow :

1.70 MJ/m2

1.24 MJ/m2

1.10 MJ/m2

Negaitive heat flow :

0.41 MJ/m2

0.02 MJ/m2

0.07 MJ/m2

16-Jan-16

17-Jan-16

18-Jan-16

19-Jan-16

(a) Heat flow comparison for Hut A

Heat flow [W/m 2]

80 70 60 50 40 30 20 10 0 -10 -20

15-Jan-16

Hut B floor

Hut B ceiling

Hut B east wall

Positive heat flow :

2.93 MJ/m2

1.45 MJ/m2

1.14 MJ/m2

Negaitive heat flow :

1.65 MJ/m2

0.00 MJ/m2

0.06 MJ/m2

16-Jan-16

17-Jan-16

19-Jan-16

18-Jan-16

(b) Heat flow comparison for Hut B

Heat flow [W/m 2]

80 70 60 50 40 30 20 10 0 -10 -20

15-Jan-16

Hut C floor

Hut C ceiling

Hut C east wall

Positive heat flow :

1.85 MJ/m2

1.50 MJ/m2

1.44 MJ/m2

Negaitive heat flow :

0.54 MJ/m2

0.18 MJ/m2

0.34 MJ/m2

16-Jan-16

17-Jan-16

18-Jan-16

19-Jan-16

(c) Heat flow comparison of Hut C Fig. 8. Heat flow comparisons for each hut (January 14–19)

To evaluate thermal comfort, factors such as temperature distribution, humidity, room temperature, and radiation temperature should be considered. In the present study, however, we focused on using the PCM to stabilize the room temperature. The indoor temperature in the test huts was classified as either below 18.0℃, between 18.0℃ and 25.0℃, or above 25.0℃ by globe temperature. The proportion of temperature range in each hut is shown in Fig. 9 [29]. Regarding the comfort zone between 18.0℃ and 25.0℃, the highest cumulative percentage in the period was recorded in Hut C (floor, wall, ceiling), followed by Hut B (floor), and then Hut A (blank). Specifically, in the case of a cloudy day with almost no solar radiation (January 18), compared with Hut A, the indoor temperatures in Huts B (floor) and C (floor, wall, and ceiling) were higher by ~28% and ~47% because of the amount of heat stored by the PCM the previous day. This demonstrates the stabilizing effect of indoor-temperature comfort offered by SSPCM sheets. The results of Predicted Mean Vote (PMV) calculation

13

show that Hut A is −0.42, Hut B is −0.28, and Hut C is −0.20 (air temperature and mean radiant temperature: measurement value, relative humidity: 50%, air speed: 0.1 m/s, clothing level: 1.0, metabolic rate: 1.1) [30]. The evaluation of thermal comfort using PMV also confirmed the effects of the SSPCM sheets and the effect of the installation area.

below 18℃

Above 25℃

47%

29%

0%

34%

34%

25%

92%

91%

94%

46%

51%

33%

74%

67%

56%

Hut A Hut B Hut C 15-Jan-16

Above 18℃ below 25℃

Hut A Hut B Hut C

Hut A Hut B Hut C

Hut A Hut B Hut C

16-Jan-16

17-Jan-16

18-Jan-16

Hut A Hut B Hut C 19-Jan-16

Fig. 9. The proportion of temperature range in each hut

Fig. 10 shows the heat balance from January 15 at 00:00 to January 19 at 24:00. The amount of solar radiation passing through the windows was measured using the vertically installed pyrheliometer in hut C. The internal heat gains of various heat sources, such as the heater, measuring instruments, and lights, were measured using the wattmeter of each hut. The transmission heat loss through the windows was calculated using the difference between the internal and external temperatures and the U-value of the windows. The transmission heat loss through the floor, walls, and ceilings was measured using the heat-flow meters on each side of the huts. The infiltration load was calculated to be 0.1 ACH. The error range of the heat balances in Huts A, B, and C was within ~2%, thereby confirming the reliability of this experiment.

14

Hut A

Hut B

Hut C

20.76

21.06

20.96

6.83

7.13

7.04

13.93

13.93

13.93

-1.45

-1.50

-1.54

-6.00

-6.33

-6.14

-3.22

-2.12

-2.17

-2.57 -1.16 -2.39 -1.93 -2.30

-2.67 -1.09 -2.74

-2.72 -0.94 -2.04 -2.15

21.04

21.18

25

Heat Gain [MJ]

20

15 10 5

Heat Loss [MJ]

0 -5

-10 -15 -20

-25

-2.31 -2.43

-2.34

20.04

From J an. 15th 00:00 to the 19th at 24:00

Solar radiation through windows

Internal heat gain

Infiltration load

Transmission heat loss through window

Transmission heat loss through floor

Transmission heat loss through ceiling

Transmission heat loss through south wall

Transmission heat loss through north wall

Transmission heat loss through east wall

Transmission heat loss through west wall

Fig. 10. Heat balance in each hut

To compare the heat performances of Huts B C, the amount of heat stored (heat absorbed or released) by the SSPCM sheets was calculated using heat flow meters (300 mm × 300 mm) installed on both sides of the SSPCM sheets from January 15 (0:00) to January 19 (24:00). The PCM absorbs heat from three sources during the daytime. One source is the external transmission load. The others are the internal heat gain and solar radiation. The total heat absorbed by the PCM is the sum of the heat absorbed from these three heat sources. The PCM loses heat to the internal ambient air regardless of its exchange pattern with the external side, i.e., whether the heat is moving from the outside to the PCM or radiating in both directions (to both inside and outside). The values heat absorbed or released calculated by the heat flow meters on each side were multiplied by the area (m2) of the installed SSPCM sheets (Hut B floor: 12.32 m2, Hut C floor: 12.32 m2, walls: 21.48 m2, ceilings: 13.25 m2). Fig. 11 shows the amount of heat stored by the SSPCM sheets in each part of Huts B and C; 32.33 MJ of heat was absorbed and 29.67 MJ of heat was released by the floor of Hut B, where SSPCM sheets with a latent heat of 6.65 MJ were installed over an area of 12.32m2. In the same period, 39.72 MJ of heat was absorbed and 38.09 MJ of heat was released by the floor, wall, and ceiling of Hut C, where SSPCM sheets with a latent heat of 6.74 MJ were installed over an area of 49.95 m2. In Huts B and C, which had a similar amount of SSPCM sheets installed, heat absorbance increased by 23.6% and heat release increased by 25.5% owing to the difference in installed areas. The results show that the heat-storage performance changes depending on the installation area and position even when the same amount of PCM is installed in the building.

15

Hut B

Hut C

35

29.74

30

24.07

Heat Absorbed [MJ]

25

8.28

20

15

13.44

24.07

10 5

8.01

Heat Released [MJ]

0

-8.25

-5 -10

-23.74

-15

-13.84

-20 -25

-7.69

23.74

-30 -35

29.78

From J an. 15th 00:00 t o the 19th at 24:00

Heat radiant Ceiling

Heat radiant Wall

Heat radiant Floor

Heat absortion Floor

Heat absortion Wall

Heat absortion Ceiling

Fig. 11. Amount of heat absorbed or released by the installed SSPCM sheets.

3.2

Heating condition From February 3–9, the heater was operated with a heating set point of 20.0℃ from 6:00 to 24:00 for

comparing the heat load of Hut A, B, and C. Fig. 12 shows the weather condition and the indoor temperature of each hut. During measurement, daytime overheating occurred only on February 5, 7, and 9, and the peak indoor average temperatures were compared. Compared with Hut A, the maximum peak indoor temperatures in Huts B and C decreased by 2.2℃ and 3.1℃, respectively, on February 5. From February 3–9, the heater operation reduced the temperature decline at night. The maximum nighttime temperature increased by 1.7℃ on February 3 in Hut B and by 2.3℃ on February 9 in Hut C when compared with Hut A.

Horizontal solar radiation

35

Temperature [oC]

30

Outdoor tempetature

Hut A

Hut B

Hut C

1200

20

Solar_horiz.

15 10

Solar_horiz.

Solar_horiz.

9.36MJ/m2

12.03MJ/m2

16.47MJ/m2

1600 1400

Phase change range

25

1800

Solar_horiz.

Solar_horiz.

Solar_horiz.

4.43MJ/m2

16.53MJ/m2

11.68MJ/m2

Solar_horiz. 17.28MJ/m2

1000 800 600

5

400

0

200

-5

0

3-Feb-16

4-Feb-16

5-Feb-16

6-Feb-16

7-Feb-16

8-Feb-16

Fig. 12. Weather conditions and indoor temperature (average of 20 points).

16

9-Feb-16

Solar radiation [W/m2 ]

40

Fig. 13 shows the power consumption of the heater. The heater, which started operation at 06:00, raised the indoor temperature, which dropped during the night, to the set point. The heater was shut down owing to the temperature rise caused by solar radiation during the daytime. The heater was restarted around 20:00 to 24:00 after the sunset when the indoor temperature was lower than the set point. On February 6, the room temperature decreased rapidly because of cloudiness and insufficient solar radiation; thus, the heater was restarted around 16:00. At nighttime on February 7 and 9, the solar radiation was sufficient; therefore, the heaters did not need to be reactivated.

Power consumption [W]

300 250 200

Hut A

Hut B

Hut A: 2.36MJ

Hut A: 1.78MJ

Hut A: 1.66MJ

Hut A: 0.75MJ

Hut A: 1.56MJ

Hut A: 1.51MJ

Hut A: 1.54MJ

Hut B: 2.27MJ

Hut B: 1.81MJ

Hut B: 1.62MJ

Hut B: 0.38MJ

Hut B: 1.56MJ

Hut B: 0.93MJ

Hut B: 1.34MJ

Hut C: 2.09MJ

Hut C: 1.75MJ

Hut C: 1.62MJ

Hut C: 0.34MJ

Hut C: 1.52MJ

Hut C: 0.87MJ

Hut C: 1.27MJ

150

Hut A: 1.26MJ

Hut A: 0.89MJ

Hut A: 1.96MJ

Hut A: 0.02MJ

Hut B: 1.22MJ

Hut B: 0.89MJ

Hut B: 1.87MJ

Hut B: 0.00MJ

Hut C: 0.83MJ

Hut C: 0.58MJ

Hut C: 1.61MJ

Hut C: 0.00MJ

100

Hut C

50 0

3-Feb-16

4-Feb-16

5-Feb-16

6-Feb-16

7-Feb-16

8-Feb-16

9-Feb-16

Fig. 13. Power consumption of the heater.

The total power consumption of the heater in Huts B and C decreased by 9.2% (13.89 MJ) and 18.4% (12.48 MJ) in Hut C, respectively, compared with Hut A (15.30 MJ), as shown Fig. 14. Because of a reduction in the temperature decline in the SSPCM sheets at night, the heater power consumption from 0:00 to 06:00 decreased by 11.3% (9.91 MJ) and 9.48% (9.46 MJ) in Huts B and C, respectively, compared with Hut A (11.17 MJ) during the morning. Using the heat stored during daytime, the SSPCM sheets reduced the heater power consumption by 3.6% (3.98 MJ) in Hut B and by 26.9% (3.08 MJ) in Hut C compared with Hut A (4.13 MJ) when the heater started to operate after sunset (from 18:00 to 24:00). Via monitoring, it was discovered that the SSPCM sheets were effective in reducing the power consumption of the heater. This effect became double when the applied area was expanded from only the floor to the entire surface.

17

Hut A

Total power consumption by heater [MJ]

18

Hut B

From Feb. 15th 00:00 t o t he 19th at 24:00

15.30

Hut C AM (0:00-12:00) PM (12:00-24:00)

13.89 (9.2%)

15

12.48 (18.4%)

4.13 12

3.98 (3.6%)

3.02 (26.9%)

9

6

11.17

9.91 (11.3%)

3

9.46 (15.3%)

0

Fig. 14. Total power consumption of the heater.

4

Conclusions This study demonstrated stabilization of the indoor room temperature and reduction in the power

consumption for heating in winter by installing a PCM (paraffin-based SSPCM sheets) that uses direct solar radiation falling on the floors, walls, and ceilings of a building. The effectiveness of SSPCM sheets in achieving the abovementioned objectives was examined in three identical lightweight huts, namely Hut A (reference hut, no PCM, 0 MJ), Hut B (with PCM on the floor, 6.65 MJ), and Hut C (with PCM on the floor, wall, ceiling, 6.74 MJ). From January 15–19, experiments were performed under the natural condition. The maximum peak indoor temperature decreased by 2.3℃ and 3.1℃during the daytime, and the maximum nighttime temperature increased by 1.9℃ and 2.5℃ during the night time in Huts B and C, respectively, compared with Hut A. For the same amount of PCM, different installations areas exhibited different thermal performances. In Huts B and C, which had a similar amount of SSPCM sheets installed, heat absorbance increased by 23.6% and heat release increased by 25.5% owing to the difference in installed areas. From February 3–9, the heater was operated with a heating set point of 20.0℃ from 6:00 to 24:00. The total power consumption of the heater in Huts B and C decreased by 9.2% (13.89 MJ) and 18.4% (12.48 MJ), respectively, compared with Hut A (15.30 MJ). Through monitoring, an SSPCM sheet was discovered to effectively reduce the heater power consumption. This effect was doubled when the applied area was expanded from the floor to the entire surface. The results show that the heat-storage performance changes depending on the installation area and position even when the same amount of PCM is installed in the building. A higher thermal benefit was obtained when the PCM was applied on the floor that received direct solar radiation and when the applied area was

18

expanded. Therefore, when using PCMs in a building, the installation area and position should be considered along with the amount of PCMs.

Acknowledgements: This work was supported by JXTG Nippon Oil & Energy Corporation, Japan.

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