Radiative sky cooling-assisted thermoelectric cooling system for building applications

Radiative sky cooling-assisted thermoelectric cooling system for building applications

Journal Pre-proof Radiative Sky Cooling-Assisted Thermoelectric Cooling System for Building Applications Dongliang Zhao, Xiaobo Yin, Jingtao Xu, Gang...

2MB Sizes 0 Downloads 176 Views

Journal Pre-proof Radiative Sky Cooling-Assisted Thermoelectric Cooling System for Building Applications

Dongliang Zhao, Xiaobo Yin, Jingtao Xu, Gang Tan, Ronggui Yang PII:

S0360-5442(19)32017-1

DOI:

https://doi.org/10.1016/j.energy.2019.116322

Reference:

EGY 116322

To appear in:

Energy

Received Date:

26 June 2019

Accepted Date:

10 October 2019

Please cite this article as: Dongliang Zhao, Xiaobo Yin, Jingtao Xu, Gang Tan, Ronggui Yang, Radiative Sky Cooling-Assisted Thermoelectric Cooling System for Building Applications, Energy (2019), https://doi.org/10.1016/j.energy.2019.116322

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.

Journal Pre-proof

Radiative Sky Cooling-Assisted Thermoelectric Cooling System for Building Applications Dongliang Zhao1, Xiaobo Yin1,2, Jingtao Xu3, Gang Tan4,*, Ronggui Yang1,2,* 1 Department 2 Materials

of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA

Science and Engineering Program, University of Colorado, Boulder, Colorado 80309,

USA 3 Ruiling

Institute of Advanced Energy and Environmental Solutions, Ningbo 315000, China

4 Department

of Civil and Architectural Engineering, University of Wyoming, Laramie, Wyoming

82071, USA * Corresponding

authors: [email protected]; [email protected]

Page 1 of 35

Journal Pre-proof

Abstract Thermoelectric cooling suffers from low energy conversion efficiency (i.e., COP) which is a major bottleneck that hurdles its wide application, especially for large-scale systems. The COP of thermoelectric cooling system can be improved by integrating with other technologies. Due to its “free” nature, radiative sky cooling technology can potentially be integrated with thermoelectric cooling to obtain much higher system COP. This study introduces a novel radiative sky coolingassisted thermoelectric cooling (RSC-TEC) system. The system has four different working modes under different operating conditions. A case study has been conducted for a two-story residential building that has 223 m2 living zone area located in Los Angeles, USA. Sensitivity analysis is first performed to size the system parameters. It is shown that the RSC-TEC system with a 0.83 m3 cold storage tank, 32 m2 radiative cooling surface area, and 101 thermoelectric modules (Laird ZT8-12), could achieve annual cooling COP of 1.87. Further analysis showed that daytime and nighttime cooling of the radiative sky cooling subsystem contribute to 55.0% and 45.0% of annual cold generation (heat dissipation) respectively, which indicates the critical importance of daytime cooling. The RSC-TEC system demonstrates a potential solution for large-scale adoption of the thermoelectric cooling technology.

Keywords: Radiative sky cooling; Thermoelectric cooling; Building energy consumption; COP

Page 2 of 35

Journal Pre-proof

1. Introduction Vapor-compression technologies currently dominate the heating, ventilation, and air conditioning (HVAC) systems for residential and commercial buildings. However, refrigerants used in the vapor-compression systems have detrimental effects on the environment. As a solid state cooling technology, thermoelectric cooling has advantages of high reliability, no moving mechanical parts, no refrigerants, and quiet operation [1,2]. The potential use of thermoelectric cooling for buildings has been explored [3,4]. However, due to its low energy conversion efficiency (i.e., coefficient of performance, COP), thermoelectric cooling has been restricted to those applications where energy efficiency is not as important as energy availability, reliability, predictability, and quiet operation [5]. The COP of a thermoelectric cooling system is determined by many factors, including the performance of thermoelectric materials (ZT value), the design of thermoelectric module, the configuration of thermoelectric system (e.g., the design of hot and cold side heat sinks [6]), and the working conditions (e.g., operating electric current [7]). Quite many studies have been focused on the development of high performance thermoelectric materials [8,9], optimization of thermoelectric module configuration [10–12], along with system-level design and optimization [6,13–18] to improve the performance of thermoelectric cooling. It is of great interest to integrate thermoelectric cooling with other technologies to improve its COP, for example, phase change material (PCM) integrated thermoelectric cooling [19,20], solar assisted thermoelectric cooling [21,22], and thermoelectric cooling integrated with heat pipes [23,24] and thermosyphons [25–27]. Zhao and Tan [19] proposed a thermoelectric system integrated with PCM for space cooling. The system has 15 pieces of thermoelectric modules (Type RC12-8). A PCM cold storage unit is employed to store the cooling energy at night and then the cold storage unit works as a heat sink to reduce the hot side temperature of thermoelectric modules Page 3 of 35

Journal Pre-proof

during the day. For a 2-hour chamber (2.1 m3 volume) cooling test, the PCM-assisted thermoelectric cooling system has average COP at around 0.87, with a maximum transient COP of 1.22. Luo et al. [28] proposed an active building wall system that integrates thermoelectrics with photovoltaics (PV). The electricity generated from PV cells is used to power thermoelectric modules, which can control the heat flow through the wall. The merit of such a system exists in its self-adaptive to solar radiation. In summer, the higher the solar radiation received by PV cells, the higher the cooling capacity generated by thermoelectric modules. Simulation results showed that the system can reduce around 70% daily heat gain as compared to traditional wall on a typical summer day. Liu et al. [23] introduced a thermoelectric system integrated with heat pipes for cooling of electronic devices. The heat pipe works as a heat sink at the hot side of the thermoelectric module to dissipate heat more efficiently. With the heat pipe heat sink, the overall heat transfer coefficient times the total heat transfer area (𝑈𝐴) can be significantly improved. Radiative sky cooling cools an object on the earth by emitting thermal infrared radiation to the cold universe through the atmospheric window [29]. It consumes no electricity and has a great potential to be explored for cooling of buildings. Earlier research on radiative sky cooling has been restricted to nighttime only because solar absorption during the day offsets the radiative sky cooling effect. Recently, with radiative sky cooling metamaterial film that is capable of reflecting 96% of solar irradiation demonstrated [30], a radiative sky cooling system can be built to run 24hour continuously at both day and night [31,32]. The integration of radiative sky cooling for buildings has also been explored [33,34]. However, performance of a radiative sky cooling system is strongly affected by weather and ambient conditions. The temperature of the heat transfer fluid cooled by the radiative cooling system constantly varies with the ambient temperature [31], which makes it difficult to directly use in real-world applications without a control. More importantly,

Page 4 of 35

Journal Pre-proof

the temperature of the heat transfer fluid produced by the radiative sky cooling system is not low enough (usually 3-10°C below ambient [31]), especially during the day, when compared to the required temperature of chilled water supply for building space cooling, which is generally 7°C (44°F). Therefore, in order to make good use of radiative sky cooling in buildings, one approach is to integrate radiative sky cooling with other cooling technologies as a supplemental cooling source for efficiency improvement. Earlier study [17] showed that most of the current buildingintegrated thermoelectric cooling systems have COPs less than 1. One can expect a much higher COP for thermoelectric cooling if integrated with radiative sky cooling. This could be of interests especially if the cost of radiative sky cooling is within the acceptable range, according to our earlier economic analysis on a hybrid radiative sky cooling system [33]. In this work, we study the performance of a radiative sky cooling assisted thermoelectric cooling (RSC-TEC) system for building applications. The cooling energy generated by the radiative sky cooling subsystem can be either directly used to cool the hot side of the thermoelectric cooling subsystem or stored in the cold storage tank for later use, depending on different operation conditions. The system has four working modes: 1) cold storage mode, 2) direct radiative cooling – thermoelectric cooling mode, 3) radiative cooling – cold storage – thermoelectric cooling mode, and 4) cold storage – thermoelectric cooling mode. A case study has been conducted for a twostory residential building located in Los Angeles, USA. With 101 thermoelectric modules (Laird ZT8-12, ZT value 0.8), a 0.83 m3 cold storage tank, and 32 m2 radiative cooling surface area, the system can achieve an annual cooling COP of 1.87.

Page 5 of 35

Journal Pre-proof

2. System description Fig. 1 shows a schematic of the proposed radiative sky cooling-assisted thermoelectric cooling (RSC-TEC) system. The system consists of a radiative sky cooling subsystem, a thermoelectric cooling subsystem, a cold storage tank, and a control subsystem. The radiative sky cooling subsystem has multiple panels with the radiative cooling metamaterial film laminated on to the top to provide 24-h continuous cooling of fluid. The thermoelectric cooling subsystem is composed of multiple thermoelectric modules connected thermally in parallel and electrically in serious, an air-cooled heat sink at the cold side, and a water-cooled plate at the hot side. The realtime feedback control subsystem includes five thermocouples, six on/off controlled valves, and two on/off-controlled pumps to automatically control the switching among four different working modes. For building integration, the radiative sky cooling subsystem is placed on a flat or lowslope building roof in order to have a large view factor from radiative cooling surface to the sky. The thermoelectric cooling subsystem functions as an indoor air handling unit, and the cold storage tank and control subsystem can be placed inside the building. Details of the control schemes are presented in Table 1. The four working modes are: 1). Mode 1: the cold storage mode stores cooling energy in the cold storage tank when there is no cooling load; 2). Mode 2: the direct radiative cooling – thermoelectric cooling mode connects thermoelectric cooling subsystem directly to the radiative sky cooling subsystem when the temperature of water in cold storage tank is high; 3). Mode 3: the radiative cooling – cold storage – thermoelectric cooling mode is turned on when radiative cooling power is greater than thermoelectric cooling load. In this case, cold storage and thermoelectric cooling work simultaneously. The radiative sky cooling subsystem, cold storage tank, and water-cooled plate are connected in series. All cooling energy generated by the radiative sky cooling subsystem are Page 6 of 35

Journal Pre-proof

eventually delivered to cool the thermoelectric cooling subsystem; 4). Mode 4: the cold storage – thermoelectric cooling mode uses the cold storage tank to cool the thermoelectric subsystem when fluid temperature at the outlet of the radiative sky cooling subsystem is high.

Fig. 1. Schematic of the RSC-TEC system for building applications.

Page 7 of 35

Journal Pre-proof

Table 1. Summary of operational modes and control schemes of the RSC-TEC system. Working

Building

Mode

cooling load

1

No

Brief description

Control

The radiative sky cooling subsystem provides P1 off, P2 on, V1-V2 on, cooling to the cold storage tank.

2

Yes

V3-V6 off

The radiative sky cooling subsystem provides P1 on, V3-V4 on, P2 off, cooling directly to the thermoelectric cooling V1, V2, V5, V6, off subsystem. The cold storage tank is bypassed.

3

Yes

The radiative sky cooling subsystem provides P1 on, P2 on, V1, V2, V5, cooling to the cold storage tank while the cold V6 on, V3, V4 off storage

tank

provides

cooling

to

the

thermoelectric cooling subsystem. 4

Yes

The cold storage tank provides cooling to the P1 on, P2 off, V1-V4 off, thermoelectric

cooling

subsystem.

The V5-V6 on

radiative sky cooling subsystem stopped working due to its high outlet temperature.

2.1 Modeling of thermoelectric cooling subsystem A steady-state energy conservation model has been applied to theoretically predict the performance of thermoelectric modules [20]. The model assumes that thermophysical properties of the thermoelectric material are temperature independent and the Thomson effect is neglected. Commercial thermoelectric module ZT8-12 from Laird technologies is used while the technical specifications of ZT8-12 are given in Table 2. The Seebeck coefficient, electrical resistance, and thermal conductance of the thermoelectric module are 0.0393 V/K, 0.9317 Ω, and 0.6244 W/K, respectively. The energy absorbed at the cold side (𝑄𝑐) and the energy released at the hot side (𝑄ℎ) are quantified by Eqs. (1) and (2), respectively. 𝑄𝑐 = 𝛼𝐼𝑇𝑐 ―0.5𝐼2𝑅 ― 𝐾(𝑇ℎ ― 𝑇𝑐) Page 8 of 35

(1)

Journal Pre-proof

𝑄ℎ = 𝛼𝐼𝑇ℎ +0.5𝐼2𝑅 ― 𝐾(𝑇ℎ ― 𝑇𝑐)

(2)

where, 𝛼 represents module Seebeck coefficient; 𝐼 is electrical current; 𝑅 denotes module electrical resistance; 𝐾 is module thermal conductance; 𝑇ℎ and 𝑇𝑐 are temperatures at hot and cold sides of thermoelectric module, respectively. Electrical power consumption of the thermoelectric module (𝑃𝑚𝑜𝑑𝑢) is: 𝑃𝑚𝑜𝑑𝑢 = 𝐼2𝑅 + 𝛼𝐼(𝑇ℎ ― 𝑇𝑐)

(3)

The cooling COP of the thermoelectric module (𝐶𝑂𝑃𝑚𝑜𝑑𝑢) is then expressed as: 𝑄𝑐

(4)

𝐶𝑂𝑃𝑚𝑜𝑑𝑢 = 𝑃𝑚𝑜𝑑𝑢

Table 2. Technical specifications of ZT8-12 from Laird technologies (evaluated at hot side temperature 300K) [35].

Item

Properties

Dimensions (L×W×H, mm)

40×40×3.8

Qmax (W)

74.7

Imax (A)

9.7

Umax (V)

15.4

ΔTmax (°C)

70.2

Module ZT value

0.80

Fig. 2 shows the performance curves of the thermoelectric module at different operating currents and different hot/cold side temperature differences (𝛥𝑇). It is clear that COP varies significantly with operating current and 𝛥𝑇. Since 𝛥𝑇 is constantly changing, real-time control of the system operating current is implemented in the model to achieve optimum system COP.

Page 9 of 35

Journal Pre-proof

Fig. 2. Performance curves of the ZT8-12 thermoelectric module from Laired Technologies under different hot/cold side temperature difference and different operation currents. The curves are calculated with hot side temperature of the module fixed at 300 K.

The thermoelectric cooling subsystem consists of thermoelectric modules and heat exchangers at both hot and cold sides. Energy balance equation for the air-cooled heat sink at the cold side is given as: ∂𝑇ℎ𝑠

(𝑚𝑐𝑝)ℎ𝑠 ∂𝑡 = ―

(𝑇ℎ𝑠 ― 𝑇𝑐) 𝑅ℎ𝑠 ― 𝑐

+

(𝑇𝑎𝑖𝑟,𝑖𝑛 ― 𝑇ℎ𝑠) 𝑅ℎ𝑠 ― 𝑎𝑖𝑟

+ ℎ𝑝𝑙𝑎𝑡𝑒 ― ℎ𝑠(𝐴ℎ𝑠 ― 𝑛𝐴𝑚𝑜𝑑𝑢)(𝑇𝑝𝑙𝑎𝑡𝑒 ― 𝑇ℎ𝑠)

(5)

where the term at the left hand side is the rate of energy change of the cold side heat sink. At the right hand side, the first term denotes the cooling power generated by all thermoelectric modules, the second term represents the cooling energy absorbed by circulating air, and the third term is thermal loss from the hot side to cold side through the insulated area. The thermal insulation material is 4-mm-thick EPDM foam rubber sheet, which has a thermal conductivity of 0.043 W/(m·K) [36]. ℎ𝑝𝑙𝑎𝑡𝑒 ― ℎ𝑠 is the heat transfer coefficient between water-cooled plate and air-cooed Page 10 of 35

Journal Pre-proof

heat sink, W/(m2·K), which is determined by thermal conductivity and thickness of the insulation material. 𝑇ℎ𝑠 is the mean temperature of the heat sink, 𝐴𝑚𝑜𝑑𝑢 is the area of a single thermoelectric module and 𝑛 is the total number of thermoelectric modules. 𝐴ℎ𝑠 is the total base area of the heat sink, which equals to the base area of the water-cooled plate. 𝑅ℎ𝑠 ― 𝑐 is the thermal resistance between the heat sink and the cold side of thermoelectric module, K/W, 𝑅ℎ𝑠 ― 𝑎𝑖𝑟 is the thermal resistance between air-cooled heat sink and circulating air, K/W. 𝑅ℎ𝑠 ― 𝑐 and 𝑅ℎ𝑠 ― 𝑎𝑖𝑟 can be estimated from manufacturer datasheet [37]. The water-cooled plate at the hot side is assumed adiabatic to the ambient air and its energy balance can be expressed as:

(𝑚𝑐𝑝)𝑝𝑙𝑎𝑡𝑒

∂𝑇𝑝𝑙𝑎𝑡𝑒 ∂𝑡

=

(𝑇ℎ ― 𝑇𝑝𝑙𝑎𝑡𝑒) 𝑅ℎ ― 𝑝𝑙𝑎𝑡𝑒

― (𝑚𝑐𝑝)𝑤(𝑇𝑝,𝑜𝑢𝑡 ― 𝑇𝑝,𝑖𝑛) ― ℎ𝑝𝑙𝑎𝑡𝑒 ― ℎ𝑠(𝐴ℎ𝑠 ― 𝑛𝐴𝑚𝑜𝑑𝑢)(𝑇𝑝𝑙𝑎𝑡𝑒 ― 𝑇ℎ𝑠) (6)

where the term at the left hand side is the rate of energy change of the water-cooled plate. At the right hand side, the first term represents the hot side heat dissipation by all thermoelectric modules, the second term is heat absorbed by circulating water, and the third term is the heat transfer from the water-cooled plate to air-cooled heat sink through insulated area. 𝑇𝑝𝑙𝑎𝑡𝑒 is the mean temperature of the water-cooled plate. 𝑅ℎ ― 𝑝𝑙𝑎𝑡𝑒 is the thermal resistance between hot side of the thermoelectric module and water-cooled plate, K/W, which can be estimated from manufacturer datasheet [38]. 𝑇𝑝,𝑖𝑛 and 𝑇𝑝,𝑜𝑢𝑡 are inlet and outlet water temperatures of the water-cooled plate.

Page 11 of 35

Journal Pre-proof

2.2 Modeling of the radiative sky cooling subsystem The radiative sky cooling subsystem consists of multiple water-cooled panels connected in parallel, as shown in Fig. 1. The net cooling power of the subsystem can be expressed as: 𝑃𝑛𝑒𝑡 = 𝑃𝑟𝑎𝑑 ― 𝑃𝑎𝑡𝑚 ― 𝑃𝑛𝑜𝑛 ― 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑣𝑒 ― 𝑃𝑠𝑜𝑙𝑎𝑟

(7)

where 𝑃𝑛𝑒𝑡 is the net cooling power generated by the radiative sky cooling subsystem. 𝑃𝑛𝑜𝑛 ― 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑣𝑒 is the non-radiative heat transfer between radiative cooling surface and ambient air. and 𝑃𝑠𝑜𝑙𝑎𝑟 is the total solar radiation absorbed by the radiative cooling surface. The net cooling power generated by the radiative cooling subsystem equals to the cold gain of the heat transfer fluid: 𝑃𝑛𝑒𝑡 = (𝑚𝑐𝑝)𝑤(𝑇𝑟𝑎𝑑,𝑖𝑛 ― 𝑇𝑟𝑎𝑑,𝑜𝑢𝑡)

(8)

where 𝑚𝑤 is the circulating water flow rate in the radiative sky cooling subsystem, 26.5 L/(h·m2), which is obtained from our earlier experimental study [31]. The radiative cooling power of the radiative cooling surface can be obtained by integrating the spectral radiance over the entire spectrum and the hemisphere: ∞

𝑃𝑟𝑎𝑑(𝑇𝑠𝑢𝑟𝑓) = 𝐴∫𝑐𝑜𝑠𝜃𝑑Ω∫0 𝐼𝑏𝑏(𝜆,𝑇𝑠𝑢𝑟𝑓)𝜀𝑠𝑢𝑟𝑓(Ω,𝜆)𝑑𝜆

(9)

𝜋

where ∫𝑑Ω = ∫ 2𝑑𝜃𝑠𝑖𝑛𝜃∫2𝜋𝑑𝜙 is the angular integral over a hemisphere, 𝜀𝑠𝑢𝑟𝑓(Ω,𝜆) is the 0 0 emissivity of the radiative cooling surface as a function of direction and wavelength, 𝐼𝑏𝑏(𝜆,𝑇𝑠𝑢𝑟𝑓) =

2ℎ𝑐2

1

𝜆5 exp (ℎ𝑐 (𝜆𝑘 𝑇 𝐵 𝑠𝑢𝑟𝑓) ― 1)

is the spectral radiance of blackbody at surface temperature 𝑇𝑠𝑢𝑟𝑓, 𝜆 is

wavelength, and 𝐴 is the total radiative cooling surface area, ℎ is the universal Planck constant and

Page 12 of 35

Journal Pre-proof

equals to 6.626 × 10-34 J·s, 𝑐 is the speed of light in vacuum (2.998 × 108 m/s), 𝑘𝐵 is the universal Boltzmann constant, which equals to 1.381 × 10-23 J/K. Similarly, the absorbed atmospheric radiation, depending on emissivity of both the radiative cooling surface and the atmosphere, is given by: ∞

𝑃𝑎𝑡𝑚(𝑇𝑎𝑚𝑏) = 𝐴∫𝑐𝑜𝑠𝜃𝑑Ω∫0 𝐼𝑏𝑏(𝜆,𝑇𝑎𝑚𝑏)𝜀𝑠𝑢𝑟𝑓(Ω,𝜆)𝜀𝑎𝑡𝑚(Ω,𝜆)𝑑𝜆

(10)

where 𝑇𝑎𝑚𝑏 is ambient temperature, 𝜀𝑎𝑡𝑚(Ω, 𝜆) is the atmospheric emissivity and is a function of precipitable water [39]. The total solar radiation absorbed by the radiative cooling surface (𝑃𝑠𝑜𝑙𝑎𝑟) can be calculated by: 𝑃𝑠𝑜𝑙𝑎𝑟 = 𝐴𝜆𝐼𝑠𝑜𝑙𝑎𝑟

(11)

where 𝜆 is the solar absorption coefficient, which is 0.04 for the metamaterial-based radiative cooling surface [30]; and 𝐼𝑠𝑜𝑙𝑎𝑟 is the incident solar irradiation. The non-radiative heat transfer between the radiative cooling surface and ambient air is calculated as: 𝑃𝑛𝑜𝑛 ― 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑣𝑒 = 𝑈𝐴(𝑇𝑎𝑚𝑏 ― 𝑇𝑠𝑢𝑟𝑓)

(12)

where 𝑈 is the overall heat transfer coefficient between radiative cooling surface and ambient air. From our previous study [31], the overall heat transfer coefficient of the radiative cooling surface change with local wind speed can be obtained as 𝑈 = 2.5 + 2𝑣.

Page 13 of 35

Journal Pre-proof

2.3 Modeling of cold storage tank A one-dimensional heat transfer model is used to predict temperature change in the cold storage tank. Though two- or three-dimensional models can provide more accurate flow and temperature characteristics, they are not practically applicable to simulate the annual behavior in the cold storage tank due to computational cost [40]. The cold storage tank is assumed to be a vertical cylinder tank that is divided into ‘𝑘’ equal volume layers. Cooled heat transfer fluid enters the bottom of the tank and is assumed to well mix with the initial ‘𝑚’ bottom layers. Physical properties of water are assumed to be independent of temperature. Temperature of each layer after the injection of cooled inflow follows the following set of equations at each time step 𝑛: 𝑇(𝑖,𝑛) = {[𝑉(𝑖) ― ∆𝑉/𝑚]𝑇(𝑖,𝑛 ― 1) + (∆𝑉 𝑚)𝑇𝑖𝑛} 𝑉(𝑖)

for 𝑖 ≤ 𝑚

(13)

𝑇(𝑖,𝑛) = {[𝑉(𝑖) ― ∆𝑉]𝑇(𝑖,𝑛 ― 1) + ∆𝑉𝑇(𝑖 ― 1,𝑛 ― 1)} 𝑉(𝑖)

for 𝑖 > 𝑚

(14)

where 𝑉(𝑖) is the volume of each layer, which equals to the total volume divided by total layers, ∆𝑉 is the volume flow into the tank at each time step, 𝑇(𝑖,𝑛) is the temperature of the 𝑖 th layer at time step 𝑛.

2.4 Initial sizing of the system A few parameters need to be sized before conducting system simulation: (1) the surface area of the radiative cooling subsystem, (2) the volume of the cold storage tank, and (3) the number of thermoelectric modules. These parameters are initially sized according to the cooling load profile on the design day. The total radiative cooling surface area can be estimated based on the daily average cooling load on the design day, as given below:

Page 14 of 35

Journal Pre-proof

24

𝐴𝑅 =

∑𝑗 = 1𝑞𝑐𝑜𝑜𝑙𝑖𝑛𝑔_𝑙𝑜𝑎𝑑,𝑗 𝑞𝑛𝑒𝑡 × 24 × 𝐷𝑓

(15)

where 𝑞𝑛𝑒𝑡 is the daily average net cooling power of the radiative cooling surface that can be calculated from Eq. (7); 𝐷𝑓 is the design factor (e.g., 1.15 for cooling as suggested by ASHRAE [41]); and 𝑞𝑐𝑜𝑜𝑙𝑖𝑛𝑔_𝑙𝑜𝑎𝑑,𝑗 is the cooling load of the building in hour 𝑗 (1 ≤ 𝑗 ≤ 24). The volume of the cold storage tank can be sized as: 24

𝑉𝑡𝑎𝑛𝑘 =

∑𝑗 = 1max[(𝑞𝑐𝑜𝑜𝑙𝑖𝑛𝑔_𝑙𝑜𝑎𝑑,𝑗 ― 𝑞𝑛𝑒𝑡),0] × 3600

𝑤𝑐𝑝,𝑤∆𝑇

(16)

where 𝑤 is the density of water, 𝑐𝑝,𝑤 is the specific heat of water, and ∆𝑇 is the average daily cold storage temperature difference (daily maximum minus daily minimum). The number of thermoelectric modules is determined by: 24

𝑁𝑚𝑜𝑑𝑢 =

∑𝑖 = 1max(𝑞𝑐𝑜𝑜𝑙𝑖𝑛𝑔_𝑙𝑜𝑎𝑑,𝑖) 𝑄𝑐

(17)

where 𝑄𝑐 is the cooling power of a single thermoelectric module at the maximum cooling load hour on the design day, which can be obtained from Fig. 2 with an estimated temperature difference across the thermoelectric module. The two on/off controlled pumps are assumed to have rated power consumption of 60 W, which is based on our earlier experimental work on radiative sky cooling system [31]. Once the system is preliminarily sized, sensitivity analysis is conducted to optimize the system parameters. Full system simulations are then performed for a residential building to analysis annual energy consumption and cooling COP.

Page 15 of 35

Journal Pre-proof

3. Case study for a residential building in Los Angeles, California 3.1 Residential building model The modeling procedure described above for the RSC-TEC system is coded in MATLAB and applied to a model residential building, as shown in Fig. 3. Here the two-story prototype building has two thermal zones: a conditioned living zone (223.1 m2 area, 481.7 m3 volume) and an unconditioned attic zone (111.5 m2 area, 85.1 m3 volume). The building enclosure, constructions, and HVAC system all comply with the ASHRAE standard 90.1-2013, and the weather data from the Los Angeles international airport is used in the simulation. Los Angeles is selected in this study because it is the second most populated city in the US, and more importantly, the cooling load is not too high in the summer which matches well with the low-energy-density (generally less than 100 W/m2) characteristic of radiative sky cooling. Indoor temperature is set at 24 °C. The whole building simulation software EnergyPlus [42] developed by the U.S. Department of Energy is used to calculate the annual cooling load and energy consumption. The reference cooling system for comparison is a regular air conditioning unit. The hourly ambient dry-bulb temperature of Los Angeles and annual hourly cooling load of the residential building calculated using EnergyPlus are plotted in Fig. 4. The hourly cooling load, local weather conditions, radiative cooling metamaterial properties, and parameters of the RSC-TEC system are then used as input files into the RSC-TEC MATLAB model to calculate annual cooling energy consumption and COP.

Page 16 of 35

Journal Pre-proof

Fig. 3. Schematic of the prototype residential building simulated.

Fig. 4. Hourly ambient dry-bulb temperature and cooling load of the residential building for a whole year in Los Angeles.

3.2 Sensitivity analysis To evaluate the impacts of the cold storage tank volume, the radiative cooling surface area, and the thermoelectric modules number on the annual cooling electricity consumption and COP of the proposed RSC-TEC system, sensitivity analysis has been carried out. Here July 21st is selected as the design day to initially size the system. From Eqs. (15) - (17), the initial calculated Page 17 of 35

Journal Pre-proof

number of thermoelectric modules is 84, the radiative cooling surface area is 21 m2, and the volume of the cold storage tank is 1.04 m3. For sensitivity analysis, the parameter variation range analyzed for the number of thermoelectric modules is from 30 to 120, the radiative cooling surface area is from 10 to 40 m2, and the volume of the cold storage tank is from 0.5 to 2.0 m3. The annual cooling electricity consumption and annual COP of the RSC-TEC system are taken as the performance indices. Fig. 5 shows the trend of annual COP varying with tank volume, radiative cooling surface area, and number of TE modules. Fig. 5(a) shows the system performance variation with varying cold storage tank volume when the number of thermoelectric module is set as 84 and the radiative cooling surface area is set as 21 m2. It shows that the change of tank volume has relatively small impact on the annual cooling electricity consumption. Similarly, the system COP has been slightly enhanced from 1.43 to 1.58 (10.5% increase) when the tank volume increases from 0.5 to 2.0 m3, which suggests that system performance is not very sensitive to the change of tank volume. Fig. 5(b) shows the system performance variation with varying radiative cooling surface area while the number of thermoelectric module is fixed at 84 and cold storage tank volume maintains at 1.04 m3. The annual COP increases dramatically from 0.46 to 1.99 (332% increase) when radiative cooling surface area increases from 10 to 40 m2. Fig. 5(c) shows the system performance variation with varying number of thermoelectric modules and the other two parameters remain at 21 m2 and 1.04 m3 respectively. Annual system COP varies significantly from 0.81 to 1.66 (105% increase) with the increase of thermoelectric modules from 30 to 120. From Figs. 5(b) and (c), performance of the system is much more sensitive to the radiative cooling surface area and the number of thermoelectric modules.

Page 18 of 35

Journal Pre-proof

Fig. 5. Sensitivity analysis on three system parameters. (a) Sensitivity analysis of tank volume to annual space cooling electricity consumption and system COP with 84 thermoelectric modules and 21 m2 radiative cooling surface area. (b) Sensitivity analysis of radiative cooling surface area to annual space cooling electricity consumption and system COP with 84 thermoelectric modules and 1.04 m3 tank volume. (c) Sensitivity analysis of number of thermoelectric (TE) modules to annual space cooling electricity consumption and system COP with 21 m2 radiative cooling surface area and 1.04 m3 tank volume.

Page 19 of 35

Journal Pre-proof

The quantitative sensitivity analysis is conducted with the input parameters perturbed by ±20% and ±50% from the initial values. Results are shown in Fig. 6. It confirms that the annual COP is not sensitive to the variation of tank volume. Increasing the tank volume by 50% only results in 2.4% improvement in annual COP. Decreasing the tank volume by 20% only results in 1.2% degradation of annual COP, which suggests that the tank volume can be decreased for cost saving. Compared to tank volume, annual COP is much more sensitive to the surface area of the radiative cooling subsystem and the number of thermoelectric modules. Increasing the radiative cooling surface area by 50% could improve annual COP by 20.8%. Increasing the number of thermoelectric modules by 20% could result in 8.1% increase in annual COP; however, it is not desirable to increase the number of thermoelectric modules by 50% as it only contributes to an extra increase of 1.2% (9.3% increase in total).

Fig. 6. Sensitivity analysis showing the impacts on annual COP from three system parameters.

With sensitivity analysis, the final adopted system parameters are 0.83 m3 (20% decrease from initial calculation) water tank volume, 32 m2 (50% increase from initial calculation) radiative Page 20 of 35

Journal Pre-proof

cooling surface area, and 101 thermoelectric modules (20% increase from initial calculation). These parameters are used in the following system performance analysis.

3.3 System operation on typical summer and winter days

Fig. 7. Performance of the RSC-TEC system on typical summer days (July 20-26).

System operation analysis is performed for typical summer and winter days. The summer operations from July 20 to 26 are plotted in Fig. 7. Daily maximum solar irradiations are between 600 - 850 W/m2 and daily maximum ambient temperatures are between 22 and 26°C on these days. Water temperatures decrease in the cold storage tank are observed every night to the early morning of next day (Mode 1). The daily lowest achievable temperature in the cold storage tank is generally Page 21 of 35

Journal Pre-proof

2-3°C below daily lowest ambient temperature [Fig. 7(a)]. Water temperatures in the tank start to increase in the morning to early afternoon (Mode 3 and 4). When tank temperature is higher than ambient temperature in the afternoon and evening, the cold storage tank is bypassed and the radiative sky cooling subsystem is directly connected with the thermoelectric cooling subsystem for heat dissipation (Mode 2), which suggests that on high cooling load days, the cold storage tank is often bypassed due to its high water temperature. The hot side and cold side temperatures of the thermoelectric subsystem are plotted in Fig. 7(c). The hot side temperature fluctuates due to water temperature change in the cold storage tank. The temperature differences between hot and cold side are between 7-22°C. System performance on typical winter days (January 20-26) is shown in Fig. 8. Daily maximum solar irradiations are between 500 - 900 W/m2 and daily maximum ambient temperatures are between 15 and 28°C on these days, as shown in Fig. 8(a). It can be observed that daily maximum ambient temperatures increase during these days and a similar trend can be found for daily cooling loads, as shown in Fig. 8(b). When there is no cooling load (Jan 20 and Jan 21) or cooling load is small (Jan 22 and Jan 23), water temperatures in the cold storage tank are low and remain nearly constant. Very limited cooling energy charging is needed and the system operates primarily on Mode 1. However, when cooling load increases on Jan 24 and Jan 25, water temperatures in the tank also increase rapidly. When water temperature in the tank is higher than the ambient, system operates at Mode 2 and Mode 3. The hot and cold side temperatures of the thermoelectric subsystem are plotted in Fig. 8(c). Essentially, the higher the temperature in the cold storage tank, the larger the temperature difference between hot and cold side, and therefore the lower the cooling COP.

Page 22 of 35

Journal Pre-proof

Fig. 8. Performance of the radiative sky cooling assisted thermoelectric cooling (RSC-TEC) system on typical winter days (January 20-26). Very limited electric power input is needed when ambient temperatures are low.

3.4 Annual system performance Annual system performance has been analyzed for the final adopted system parameters: 0.83 m3 water tank volume, 32 m2 radiative cooling surface area, and 101 thermoelectric modules. Fig. 9(a) shows the monthly cooling load and electrical power consumption and Fig. 9(b) shows monthly COP variation throughout a typical year. It can be seen that COP of the RSC-TEC system presents a significant variation across different months, which is due to the changes of ambient

Page 23 of 35

Journal Pre-proof

temperatures and cooling loads. When ambient temperatures and cooling loads are high in summer, heat dissipation for the RSC-TEC system is more challenging, which is due to larger temperature difference across the thermoelectric modules. The system operates at COP close to 3.0 from November to March, but dropped to a lowest value of 1.22 in September, with an annual COP of 1.87.

Fig. 9. Annual system performance of the radiative sky cooling assisted thermoelectric cooling system. Simulation is performed for the system with 101 thermoelectric modules, a 0.83 m3 cold storage tank, and 32 m2 radiative cooling surface area. Monthly COP varies significantly in different months due to different cooling loads and ambient temperatures. The annual COP of the system is 1.87.

Page 24 of 35

Monthly Cold Generation (MJ)

Journal Pre-proof

4000 Radiation Convection

3000 2000 1000 0 -1000

Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec

Month Fig. 10. The contributions from radiative cooling and convective cooling respectively. While radiative cooling always contributes to cold generation throughout the year, convective cooling only contributes to cold generation in summer months.

Analysis has been performed for the contributions of different heat transfer mechanisms on the radiative sky cooling subsystem. Fig. 10 shows the monthly total cold generation (i.e., heat dissipation) through the radiative cooling surface. A negative cold generation means that the radiative cooling surface is heated up by the ambient. It can be observed that surface radiation heat transfer contributes to cold generation throughout the year, but this is not the case for convection heat transfer. Convection heat transfer contributes to cold generation in months from June to September because water temperature in the cold storage tank is high compared to ambient temperature [see Fig. 7(a)], in other words, the radiative cooling subsystem operates under aboveambient cooling conditions more frequently. From October to May, convection heat transfer has negative impact on cold generation because the radiative cooling subsystem more frequently operates under sub-ambient cooling conditions. Page 25 of 35

Monthly Cold Generation (MJ)

Journal Pre-proof

3000 2500

Day Night

2000 1500 1000 500 0

Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec

Month Fig. 11. The monthly cold generation contributed by daytime and nighttime radiative sky cooling respectively. Daytime radiative sky cooling contributes significantly in summer months. Daytime and nighttime radiative sky cooling contribute 55.0% and 45.0% of annual cold generation respectively.

In the earlier studies, radiative sky cooling systems work only at night because the daytime solar absorption offsets the radiative sky cooling effect. Net radiative cooling power can be achieved during the day only recently due to the superior solar reflection of the radiative cooling metamaterial [30]. Here, analysis was performed to quantify daytime and nighttime contribution to total cold generation (i.e., heat dissipation) of the radiative cooling subsystem. Fig. 11 shows the monthly cold generation during the day and night, respectively. It is clear that the daytime contribution is negligible in winter because the nighttime cold storage could handle majority of the cooling load. However, daytime radiative sky cooling becomes much more critical in summer days when cooling loads are high, especially from July to September, which is due to the insufficient cold storage at night and the system operates more frequently in direct heat dissipation mode [Mode 2 as shown in Fig. 7(b)]. In short, daytime radiative sky cooling contributes Page 26 of 35

Journal Pre-proof

significantly to annual cold generation in the proposed RSC-TEC system. If the radiative sky cooling subsystem operates at night only, larger cold storage tank and larger radiative cooling surface area will be needed to achieve a comparable annual COP. Daytime and nighttime radiative sky cooling contributes 55.0% and 45.0% of annual cold generation (heat dissipation), respectively.

3.5 The effect of ZT values on system performance ZT value of the thermoelectric module plays an important role in determining the annual system COP. Though current commercial thermoelectric module only has a ZT value at about 0.8, there are significant efforts in improving module ZT through both using advanced thermoelectric material and better module design. Thermoelectric modules with improved ZT values can be anticipated in the near future. Here, we analyze the performance of the RSC-TEC system with improved ZT values. Fig. 12(a) shows the monthly system COPs with thermoelectric modules that have ZT values of 0.8, 1.5, and 3.0, respectively. The monthly COP variations under the three ZT values show a similar trend throughout the year, with winter COPs much higher than the summer COPs. Corresponding annual COPs are 1.87, 2.85, and 3.59 for ZT values of 0.8, 1.5, and 3.0, respectively. As a comparison, the monthly COPs of the reference vapor compression system are also given in Fig. 12(a). Monthly COPs of the vapor compression system is more stable than those of the thermoelectric cooling system in a year. Annual COP of the vapor compression air conditioning system is 3.52 in Los Angeles, which suggests that thermoelectric modules with a ZT value of 2.0 assisted by the radiative sky cooling can be comparable to the current vapor compression system, as shown in Fig. 12(b).

Page 27 of 35

Journal Pre-proof

Fig. 12. Performance of the RSC-TEC system with improved thermoelectric module ZT values. Simulations were performed with 101 ZT modules, 0.83 m3 cold storage tank volume, and 32 m2 radiative cooling surface area. By using a thermoelectric module that has ZT value 2.0, annual COP of the radiative sky cooling assisted thermoelectric cooling system will be comparable to the predominant vapor compression air conditioning system.

We note here that the use of thermoelectrics for building cooling has been proposed by many earlier researchers. Thermoelectric systems can be either integrated with building envelope (e.g., windows, walls, roof, and ceiling) or with building energy systems (e.g., ventilation system) [3]. The comparison is made here between the proposed RSC-TEC system and some other buildingintegrated thermoelectric cooling technologies based on cooling capacity and COP, as shown in Table 3. Since both cooling capacity and COP are affected by many factors, in order to make a fair comparison between different technologies, all necessary operation parameters are given alongside with the cooling capacity and COP values. It can be observed that the COP of the proposed RSCTEC system is significantly higher than those of the earlier studies.

Page 28 of 35

Journal Pre-proof

Table 3. Comparison of the proposed RSC-TEC system with some earlier building-integrated thermoelectric cooling technologies (listed in chronological order).

Brief description

Module number

Cooling capacity

and type

(W)

Solar cell powered

Number determined

thermoelectric cooling

by cooling capacity

ceiling combined with

and operating voltage

displacement ventilation

(9500/127/060 B)

change material for building

Reference and Year

0.9 (5-6 V voltage, 570 (maximum)

A thermoelectric cooling system integrated with phase

Cooling COP

average of a 3-hour

Liu et al.

experiment)

[43], 2014

0.87 (average of a 2210 (maximum)

15 (RC12-8)

hour experiment)

Zhao et al. [19], 2014

165 (average)

cooling Total cooling

A thermoelectric cooling system driven by a

0.45 (average of July –

capacity 35.77 kWh September), simulation

6 (not specified)

from July to

photovoltaic system

He et al. [44], 2014

September 0.75-0.78 (7.2 V

Thermoelectric cooling unit performance under real

500 (7.2 V 16 (RC12-8)

voltage), 620 (12 V

conditions

voltage)

voltage) and 0.620.66 (12 V

Ibañez-Puy et al. [45], 2017

voltage), experiment

A thermoelectric air duct system that cools airflow to

15 (TEC1-12730)

517 (maximum)

reduce room temperature

simulation

Radiative sky cooling assisted thermoelectric cooling system

1.15 (6 A current),

Up to 3000 101 (ZT8-12)

(Varying with

Irshad et al. [46], 2017

1.87 (annual average), simulation

This work

ambient conditions

3.6 The effect of climate zones on system performance To show the climate adaptability of the RSC-TEC system, more cases have been studied for the same building (in Fig. 3) in different climate conditions, including Phoenix, Arizona (hotPage 29 of 35

Journal Pre-proof

dry climate), Denver, Colorado (cold climate), and Miami, Florida (hot-humid climate). Note that in different climate conditions, parameters of the RSC-TEC system are also different, as shown in Table 4. These parameters are sized according to the procedures provided in Sections 2.4 and 3.2. The required radiative cooling surface area in Phoenix and Miami is larger than roof area (i.e., 120 m2) due to large cooling load requirement. In this case, the radiative cooling subsystem can be placed on the ground near the residential building. The monthly COP variation are calculated and plotted in Fig. 13(a). Annual system COPs are 0.96, 1.46, and 1.49 for Phoenix, Denver, and Miami respectively. Note that though Denver located in cold climate, a small cooling load still exists in winter due to occasional warm days. It can be seen that the system has better annual performance in mild climate area, i.e., Los Angeles. For Phoenix and Miami, high ambient temperature in summer limits the capability of the radiative sky cooling subsystem from producing low temperature cooling water.

Table 4. Parameters of the radiative sky cooling assisted thermoelectric cooling system in different climate conditions. Radiative cooling

No. of thermoelectric

Volume of water

surface area (m2)

modules

tank (m3)

Los Angeles

32

101

0.83

Phoenix

219

293

3.6

Denver

84

171

2.1

Miami

147

198

2.9

Location

Page 30 of 35

Journal Pre-proof

Fig. 13. Climate adaptability of the RSC-TEC system. (a) Monthly averaged COP variation of the RSCTEC system in 4 different climate conditions. (b) Monthly averaged cooling load of the two-story residential building in 4 different climate conditions.

4. Conclusions This study presents a novel radiative sky cooling assisted thermoelectric cooling (RSCTEC) system for building applications. The radiative sky cooling subsystem can provide 24-h continuous cooling by using the recently-developed thin film metamaterial that has an averaged infrared emissivity > 0.93 and reflects approximately 96% of solar irradiance during the day [30]. The cooling energy generated by the radiative sky cooling subsystem can be either directly used to cool the hot side of the thermoelectric system or stored in a cold storage tank and used later, depending on different operation modes. A case study has been conducted for a residential building that has 223.1 m2 living zone area located in Los Angeles, USA. Sensitivity analysis is first performed to size the system parameters. With a 0.83 m3 cold storage tank, 32 m2 radiative cooling surface area, and 101 thermoelectric modules (Laird ZT8-12, ZT = 0.8), the RSC-TEC system can achieve annual system COP of 1.87. It should be noted that the monthly system COP varies Page 31 of 35

Journal Pre-proof

significantly in different months, which is due to different cooling loads and ambient temperatures. Analysis shows that daytime and nighttime radiative sky cooling contributes 55.0% and 45.0% of annual cold generation (heat dissipation), respectively, suggesting that the daytime radiative sky cooling plays a significant role. Finally, the performance of the system can be further improved with higher ZT values. With thermoelectric modules having a ZT value of 2.0, the annual COP of the RSC-TEC system could be comparable to the vapor compression air conditioning system. The results in this work have demonstrated the feasibility of integrating radiative sky cooling with thermoelectric cooling for residential building applications.

References [1] Zhao D, Tan G. A review of thermoelectric cooling: Materials, modeling and applications. Appl Therm Eng 2014;66:15–24. doi:10.1016/j.applthermaleng.2014.01.074. [2] Qian S, Nasuta D, Rhoads A, Wang Y, Geng Y, Hwang Y, et al. Not-in-kind cooling technologies: A quantitative comparison of refrigerants and system performance. Int J Refrig 2016;62:177–92. doi:10.1016/j.ijrefrig.2015.10.019. [3] Zuazua-Ros A, Martín-Gómez C, Ibañez-Puy E, Vidaurre-Arbizu M, Gelbstein Y. Investigation of the thermoelectric potential for heating, cooling and ventilation in buildings: Characterization options and applications. Renew Energy 2019;131:229–39. doi:10.1016/j.renene.2018.07.027. [4] Irshad K, Habib K, Saidur R, Kareem MW, Saha BB. Study of thermoelectric and photovoltaic facade system for energy efficient building development: A review. J Clean Prod 2019;209:1376–95. doi:10.1016/j.jclepro.2018.09.245. [5] Dresselhaus MS, Chen G, Tang MY, Yang RG, Lee H, Wang DZ, et al. New Directions for Low-Dimensional Thermoelectric Materials. Adv Mater 2007;19:1043–53. doi:10.1002/adma.200600527. [6] Lu X, Zhao D, Ma T, Wang Q, Fan J, Yang R. Thermal resistance matching for thermoelectric cooling systems. Energy Convers Manag 2018;169:186–93. doi:10.1016/j.enconman.2018.05.052. [7] Manikandan S, Kaushik SC, Yang R. Modified pulse operation of thermoelectric coolers for building cooling applications. Energy Convers Manag 2017;140:145–56. doi:10.1016/j.enconman.2017.03.003. [8] Kim SI, Lee KH, Mun HA, Kim HS, Hwang SW, Roh JW, et al. Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics. Science 2015;348:109–14. doi:10.1126/science.aaa4166.

Page 32 of 35

Journal Pre-proof

[9] Gao C, Chen G. Conducting polymer/carbon particle thermoelectric composites: Emerging green energy materials. Compos Sci Technol 2016;124:52–70. doi:10.1016/j.compscitech.2016.01.014. [10] Wang T-H, Wang Q-H, Leng C, Wang X-D. Parameter analysis and optimal design for two-stage thermoelectric cooler. Appl Energy 2015;154:1–12. doi:10.1016/j.apenergy.2015.04.104. [11] Erturun U, Erermis K, Mossi K. Influence of leg sizing and spacing on power generation and thermal stresses of thermoelectric devices. Appl Energy 2015;159:19–27. doi:10.1016/j.apenergy.2015.08.112. [12] Lin S, Yu J. Optimization of a trapezoid-type two-stage Peltier couples for thermoelectric cooling applications. Int J Refrig 2016;65:103–10. doi:10.1016/j.ijrefrig.2015.12.007. [13] Lv S, He W, Jiang Q, Hu Z, Liu X, Chen H, et al. Study of different heat exchange technologies influence on the performance of thermoelectric generators. Energy Convers Manag 2018;156:167–77. doi:10.1016/j.enconman.2017.11.011. [14] Sadighi Dizaji H, Jafarmadar S, Khalilarya S, Moosavi A. An exhaustive experimental study of a novel air-water based thermoelectric cooling unit. Appl Energy 2016;181:357–66. doi:10.1016/j.apenergy.2016.08.074. [15] Hu HM, Ge TS, Dai YJ, Wang RZ. Experimental study on water-cooled thermoelectric cooler for CPU under severe environment. Int J Refrig 2016;62:30–8. doi:10.1016/j.ijrefrig.2015.10.015. [16] Yu J, Wang B. Enhancing the maximum coefficient of performance of thermoelectric cooling modules using internally cascaded thermoelectric couples. Int J Refrig 2009;32:32– 9. doi:10.1016/j.ijrefrig.2008.08.006. [17] Irshad K, Habib K, Thirumalaiswamy N, Saha BB. Performance analysis of a thermoelectric air duct system for energy-efficient buildings. Energy 2015;91:1009–17. doi:10.1016/j.energy.2015.08.102. [18] Shen L, Pu X, Sun Y, Chen J. A study on thermoelectric technology application in net zero energy buildings. Energy 2016;113:9–24. doi:10.1016/j.energy.2016.07.038. [19] Zhao D, Tan G. Experimental evaluation of a prototype thermoelectric system integrated with PCM (phase change material) for space cooling. Energy 2014;68:658–66. doi:10.1016/j.energy.2014.01.090. [20] Tan G, Zhao D. Study of a thermoelectric space cooling system integrated with phase change material. Appl Therm Eng 2015;86:187–98. doi:10.1016/j.applthermaleng.2015.04.054. [21] Liu Z, Zhang L, Gong G, Li H, Tang G. Review of solar thermoelectric cooling technologies for use in zero energy buildings. Energy Build 2015;102:207–16. doi:10.1016/j.enbuild.2015.05.029. [22] Alomair M, Alomair Y, Mahmud S, Abdullah HA. Theoretical and Experimental Investigations of Solar-Thermoelectric Air-Conditioning System for Remote Applications. J Therm Sci Eng Appl 2015;7:021013-021013–10. doi:10.1115/1.4029678. [23] Liu D, Cai Y, Zhao F-Y. Optimal design of thermoelectric cooling system integrated heat pipes for electric devices. Energy 2017;128:403–13. doi:10.1016/j.energy.2017.03.120. [24] Sun H, Lin B, Lin Z, Zhu Y, Li H, Wu X. Research on a radiant heating terminal integrated with a thermoelectric unit and flat heat pipe. Energy Build 2018;172:209–20. doi:10.1016/j.enbuild.2018.04.054.

Page 33 of 35

Journal Pre-proof

[25] Araiz M, Martínez A, Astrain D, Aranguren P. Experimental and computational study on thermoelectric generators using thermosyphons with phase change as heat exchangers. Energy Convers Manag 2017;137:155–64. doi:10.1016/j.enconman.2017.01.046. [26] Sun X, Zhang L, Liao S. Performance of a thermoelectric cooling system integrated with a gravity-assisted heat pipe for cooling electronics. Appl Therm Eng 2017;116:433–44. doi:10.1016/j.applthermaleng.2016.12.094. [27] Liu D, Zhao F-Y, Yang H-X, Tang G-F. Thermoelectric mini cooler coupled with micro thermosiphon for CPU cooling system. Energy 2015;83:29–36. doi:10.1016/j.energy.2015.01.098. [28] Luo Y, Zhang L, Liu Z, Wang Y, Meng F, Wu J. Thermal performance evaluation of an active building integrated photovoltaic thermoelectric wall system. Appl Energy 2016;177:25–39. doi:10.1016/j.apenergy.2016.05.087. [29] Zhao D, Aili A, Zhai Y, Xu S, Tan G, Yin X, et al. Radiative sky cooling: Fundamental principles, materials, and applications. Appl Phys Rev 2019;6:021306. doi:10.1063/1.5087281. [30] Zhai Y, Ma Y, David SN, Zhao D, Lou R, Tan G, et al. Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling. Science 2017;355:1062–1066. [31] Zhao D, Aili A, Zhai Y, Lu J, Dillon K, Tan G, et al. Subambient Cooling of Water: Towards Real-World Applications of Daytime Radiative Cooling. Joule 2019;3:111–23. doi:10.1016/j.joule.2018.10.006. [32] Aili A, Zhao D, Lu J, Zhai Y, Yin X, Tan G, et al. A kW-scale, 24-hour continuously operational, radiative sky cooling system: Experimental demonstration and predictive modeling. Energy Convers Manag 2019;186:586–96. doi:10.1016/j.enconman.2019.03.006. [33] Zhang K, Zhao D, Yin X, Yang R, Tan G. Energy saving and economic analysis of a new hybrid radiative cooling system for single-family houses in the USA. Appl Energy 2018;224:371–81. doi:10.1016/j.apenergy.2018.04.115. [34] Zhao D, Martini CE, Jiang S, Ma Y, Zhai Y, Tan G, et al. Development of a single-phase thermosiphon for cold collection and storage of radiative cooling. Appl Energy 2017;205:1260–9. doi:10.1016/j.apenergy.2017.08.057. [35] Thermal Wizard - Thermoelectric Modules Datasheet | Laird Thermal Systems n.d. https://www.lairdthermal.com/thermal-wizard/thermal-wizard-thermoelectric-modulesdatasheet?temid=82&ms=False&dt=20&iop=-1 (accessed April 16, 2019). [36] Rubatex R4911 EPDM Rubber Foam Sheet. MatWeb Mater Prop Data n.d. http://www.matweb.com/search/datasheet.aspx?matguid=90d8ecc8db5f409fa693166c0f1c8f 5c&ckck=1 (accessed September 25, 2019). [37] Aavid, Thermal Division of Boyd Corporation > Product n.d. https://www.shopaavid.com/Product/62725-full (accessed August 28, 2019). [38] Aavid, Thermal Division of Boyd Corporation > Product n.d. https://www.shopaavid.com/Product/416301U00000G (accessed August 28, 2019). [39] Lord SD. A new software tool for computing Earth’s atmospheric transmission of nearand far-infrared radiation. 1992. [40] Alizadeh S. An experimental and numerical study of thermal stratification in a horizontal cylindrical solar storage tank. Sol Energy 1999;66:409–21. doi:10.1016/S0038092X(99)00036-5.

Page 34 of 35

Journal Pre-proof

[41] ANSI/ASHRAE/IES Standard 90.1-2013 | Building Energy Codes Program n.d. https://www.energycodes.gov/training-courses/ansiashraeies-standard-901-2013 (accessed September 12, 2018). [42] EnergyPlus | EnergyPlus n.d. https://energyplus.net/ (accessed May 1, 2019). [43] Liu Z, Zhang L, Gong G. Experimental evaluation of a solar thermoelectric cooled ceiling combined with displacement ventilation system. Energy Convers Manag 2014;87:559–65. doi:10.1016/j.enconman.2014.07.051. [44] He W, Zhou J, Chen C, Ji J. Experimental study and performance analysis of a thermoelectric cooling and heating system driven by a photovoltaic/thermal system in summer and winter operation modes. Energy Convers Manag 2014;84:41–9. doi:10.1016/j.enconman.2014.04.019. [45] Ibañez-Puy M, Bermejo-Busto J, Martín-Gómez C, Vidaurre-Arbizu M, SacristánFernández JA. Thermoelectric cooling heating unit performance under real conditions. Appl Energy 2017;200:303–14. doi:10.1016/j.apenergy.2017.05.020. [46] Irshad K, Habib K, Basrawi F, Saha BB. Study of a thermoelectric air duct system assisted by photovoltaic wall for space cooling in tropical climate. Energy 2017;119:504–22. doi:10.1016/j.energy.2016.10.110.

Page 35 of 35

Journal Pre-proof



A radiative sky cooling assisted thermoelectric cooling (RSC-TEC) system is proposed



Sensitivity analysis is performed to size the system parameters



Annual building energy simulation is conducted with EnergyPlus and MATLAB



Annual cooling COP of 1.87 is achieved in a two-story residential building



The RSC-TEC system demonstrates a potential solution for the wide adoption of thermoelectric cooling technology