Design of a passive temperature management house using composite phase change materials

Human progress and the increase in industrial output have led to a gradual acceleration in energy consumption. At the same time, there is a growing demand for a higher quality of life, with the fundamental requirement for human comfort being within an appropriate temperature range. To achieve this, various methods of temperature management in buildings have been devised. Many of these involve active temperature management methods through the combustion of fossil fuels or the use of air conditioning for temperature control. Fossil fuels persist as a predominant source of heating energy, posing the risk of potential fuel shortages and contributing to anthropogenic greenhouse effects [1]. These active methods of building temperature management not only accelerate the depletion of existing energy resources but also cause environmental harm, failing to meet the requirements of green and sustainable development. Currently, building energy consumption constitutes 40 % of the annual energy consumption in human activities [2]. Moreover, it is anticipated to increase by an additional 28 % by the year 2035 [3]. The majority of energy consumption in building energy usage is concentrated in building temperature management, with 60 % of the energy devoted to heating and cooling [4]. Heating and domestic hot water loads constitute the largest proportion of building energy consumption [5]. Hence, there is a pressing demand for a building temperature management method that is low-energy or even zero-energy [6]. Thermal energy storage (TES) technology provides flexibility for buildings, allowing the storage of excess heat during low loads and its release during high loads. This flexibility helps buildings adapt to varying energy demands at different times. Phase change materials (PCMs) release or absorb significant latent heat during phase transitions and can be utilized for storing thermal energy [7]. PCMs are commonly classified into organic and inorganic PCMs. The main characteristic of organic PCMs is their high stability [8] and long cycle life [9,10], as well as their small degree of supercooling, making them the mainstream choice for thermal management applications [11]. Inorganic PCMs typically refer to hydrated salts or molten salts. While inorganic PCMs are cost-effective, they tend to have a large degree of supercooling and are prone to phase separation, issues that still need to be addressed. Due to their recyclability, environmental friendliness, and high latent heat, PCMs have been applied in various fields, including battery thermal management [[12], [13], [14], [15]], infrared stealth field [[16], [17], [18]], industrial waste heat recovery [[19], [20], [21]], and building thermal management [[22], [23], [24], [25], [26]].

In the field of construction, PCMs can be integrated with walls [27,28], ceilings [29,30], floors [31], and glass [32], effectively reducing the thermal management energy consumption of buildings while maintaining a comfortable living environment for humans. Heating and domestic hot water account for the largest portion of building energy consumption [5]. Therefore, using passive technologies to replace or supplement existing heating methods, such as radiators and air conditioning, can save a significant amount of energy. There is a need for a passive thermal management approach specifically designed for winter conditions in cold regions. Solar energy is becoming increasingly important as a clean energy source in today’s society. It is a renewable and pollution-free form of energy that harnesses power from solar radiation without producing harmful waste or greenhouse gases in the process. The primary uses of solar energy involve converting it into electrical energy [33]and thermal energy [34]. Among these, converting solar energy into thermal energy is widely applied in fields such as seawater desalination and thermoelectric conversion. By combining photothermal conversion materials with PCMs, it is possible to directly store thermal energy during the solar energy conversion process. In addition, during harnessing solar energy by PCMs, the photothermal conversion capability is another key point. Traditional fillers to enhance photothermal conversion performance, such as Ag [35], Au [36], and MXene [37], are expensive and have complex preparation processes. Carbon materials, on the other hand, are abundant, inexpensive, and also exhibit excellent photothermal conversion performance. Liu et al. [38] carbonized ZIF-67 grown on agricultural waste to encapsulate paraffin, achieving excellent thermal energy storage and release for photothermal, magnetothermal, and electrothermal conversion. Li et al. [39] created scalable, highly conductive phase change composites by aligning graphite nanoplatelets to enhance heat transfer for photothermal conversion. While PCMs combined with photothermal materials have been used for thermal storage, their complex preparation and high cost limit their application in building thermal management. Thus, developing cost-effective cPCMs with high photothermal efficiency and simple preparation methods is essential.

Currently, researchers have conducted several studies on the use of PCMs for passive temperature management in buildings. They have identified suitable PCMs such as paraffin wax [40] and CaCl₂·6H₂O [41], which have appropriate phase change temperatures and high latent heat. Most of the current research focuses on encapsulating these PCMs and then mixing the cPCMs with building materials to create composite materials with thermal storage capabilities, thereby managing the temperature of buildings. Cao et al. [42] prepared a cPCM using methyl palmitate, disodium hydrogen phosphate dodecahydrate, and sodium carbonate decahydrate as the main PCMs. In simulated house temperature tests, compared to foam materials, the cPCM extended the heating time by 7.64 times and the cooling time by 4.96 times. Ali et al. [43] used recycled expanded glass (REG) as a support material combined with n-octadecane (nOD) and added it to cement mortar to prepare thermal storage cement. The temperature difference results (−10.60 °C cooling during the day, 4.00 °C heating at night) suggest that REG/nOD has potential for sustainable buildings. Güliz et al. [44] incorporated microencapsulated PCMs into wood fiber starch, and in hot environments, the maximum temperature difference on the inner surface was 7.03 °C, demonstrating good building temperature management capabilities. Radiative heat transfer has been widely validated in previous studies for building thermal management. For example, Gür et al. [45] integrated radiators with PCM and demonstrated through simulations that natural convection and radiative heat transfer in a closed space can effectively manage indoor temperatures. Similarly, Tang et al. [46] combined solar heat pumps with PCM flooring, proving through both experiments and simulations that radiant heating systems are feasible in practice. These studies support the viability of using radiative heat transfer for indoor temperature regulation.

Although this strategy endows building materials with some thermal storage capabilities, combining them with building materials generally reduces the original mechanical properties of the construction materials. Furthermore, using only PCMs makes it difficult to achieve phase change cycles in prolonged low-temperature environments, thereby hindering effective thermal management. Therefore, our team proposes combining photothermal conversion materials with PCMs to serve as a passive thermal energy input. To maximize the thermal storage density per unit volume, we encapsulate high-density hydrated salt PCMs in radiators. These two modules work together to maintain a comfortable living temperature for humans.