Investigation of thermo-mechanical performance of PCM incorporated Geothermal Energy Pile (PCMinGEEP)

政府间气候变化专门委员会（IPCC）的最新报告《全球变暖1.5摄氏度》强调，现在需要采取“迅速而深远”的行动来遏制碳排放，以限制全球变暖和气候变化的影响。脱碳加热是将在减少碳排放中发挥关键作用的行动之一。气候变化委员会指出，在实现低碳供暖家庭目标方面进展不足，需要立即关注以满足我们的碳预算。众所周知，冬天地面比空气暖和，夏天地面比空气凉爽。因此，我们的祖先在地下建造洞穴和家园，以保护他们免受极端寒冷/炎热的天气。地热能桩（GEEP）主要由桩基础、换热回路和热泵组成。热交换回路通常由高密度聚乙烯管制成，并携带热交换流体（水和/或乙二醇）。回路连接在钢筋笼上，安装在建筑物的混凝土桩基础上，通过热泵提取浅层地面能量，在冬季为建筑物供暖。在夏季，当热量从建筑物中收集并储存在地下时，循环就被逆转了。GEEP可以在供暖脱碳方面发挥重要作用，因为它利用了我们脚下可用的可持续地热能。高昂的初始成本仍然是热泵技术应用的主要挑战。在GEEP的情况下，初始成本可以降低，如果混凝土的热容量得到改善，环路长度可以因此减少。这可以通过在混凝土中加入相变材料（PCM）来实现。PCM有一个特殊的特性，即在相变过程中（固变液或液变固），它吸收或释放大量的能量。该项目旨在通过结合GEEP和PCM两种技术开发一种创新的解决方案，以获得更多的单位环路长度的热能，从而显著降低GEEP的成本。PCM过去从未与GEEP一起使用过，因此明显的研究问题,思想(1)如何在具体注入PCM(2)什么是PCM在混凝土强度和工作性的影响(3)PCM将如何影响负载容量山绵羊山绵羊的主要目标是支持结构(4)多少热能可以(5)将会发生什么,周围的地面温度山绵羊(6)要花多少钱(7)是否会减少混凝土的碳足迹。我们的目标是通过采用可持续和环保的PCM并将其浸渍在由废物（如粉煤灰，矿渣，玻璃）制成的轻质骨料（LWAs）中来回答上述所有研究问题。使用由废物制成的LWAs有三个优点：第一，LWAs将取代混凝土中的天然骨料，因为天然骨料具有碳强度；第二，LWAs具有多孔性和轻质性，因此可以吸收大量的PCM，减轻混凝土的重量；第三，废物的再利用。实验室规模的混凝土GEEP将由PCM浸渍的LWAs制成，并在加热和冷却负荷下进行测试，以研究热（传热）和机械（负载能力）性能。将进行广泛的实验和数值研究，以设计和开发包含GEEP的新型PCM，该PCM可以为供暖和制冷提供可再生的地面能源。

The latest report of Intergovernmental Panel on Climate Change (IPCC) 'Global warming of 1.5C' emphasises the need for 'rapid and far-reaching' actions now to curb carbon emission to limit global warming and climate change impact. Decarbonising heating is one of the actions which is going to play a key role in reducing carbon emission. The Committee on Climate Change states that insufficient progress has been made towards the low carbon heating homes target that requires immediate attention to meet our carbon budget.It is well known fact that the ground is warmer compared to air in winter and cooler in summer. Therefore our ancestors build caves and homes underground to protect them against extreme cold/hot weather. Geothermal energy pile (GEEP) basically consists of a pile foundation, heat exchanging loops and a heat pump. Heat exchanging loops are usually made of high density polyethylene pipes and carry heat exchanging fluid (water and/or ethylene glycol). Loops are attached to a reinforcement cage and installed into the concrete pile foundations of a building to extract the shallow ground energy via a heat pump to heat the building during winter. The cycle is reversed during summer when heat is collected from the building and stored in the ground. GEEP can play an important role in decarbonising heating as it utilises the sustainable ground energy available under our feet.High initial cost remains the main challenge in deploying heat pump technology. In the case of GEEP, the initial cost can be reduced, if the heat capacity of the concrete is improved and loop length can thus be decreased. This can be achieved by incorporating phase change material (PCM) in the concrete. PCM has a peculiar characteristic that it absorbs or releases large amount of energy during phase change (solid to liquid or liquid to solid). This project aims to develop an innovative solution by combining two technologies GEEP and PCM to obtain more heat energy per unit loop length which would reduce the cost of GEEP significantly. PCM has never been used with GEEP in the past, therefore obvious research questions that come to the mind are (1) how to inject PCM in concrete (2) what would be the effect of PCM on concrete strength and workability (3) how PCM would affect load capacity of GEEP as primary objective of the GEEP is to support structure (4) how much heat energy would be available (5) what would happen to the ground temperature surrounding GEEP (6) how much it would cost (7) whether it would reduce carbon footprint of concrete. We aim to answer all the above research questions by employing sustainable and environmental friendly PCM and impregnate it in light weight aggregates (LWAs) made with waste material (e.g. fly ash, slag, glass). There are three advantages of using LWAs made from waste: first LWAs will replace natural aggregate in concrete as natural aggregates are carbon intense, second LWAs are porous and light so they can absorb large amount of PCM and reduce the weight of concrete, third reuse the waste. Laboratory scale concrete GEEP will be made with PCM impregnated LWAs and tested under heating and cooling load to investigate thermal (heat transfer) and mechanical (load capacity) performance. Extensive experimental and numerical study will be carried out to design and develop novel PCM incorporated GEEP which can provide renewable ground energy for heating and cooling.