Sığ kuyu toprak kaynaklı ısı değiştiricilerin tasarımında mevsimlere bağlı atmosferik koşulların etkisi
Effects of seasonal atmospheric conditions on the design of shallow ground-source heat exchangers
Yazar: FERHAT CAN KOÇAK
Danışman: DR. ÖĞR. ÜYESİ SEVAN KARABETOĞLU
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı / Enerji Bilim ve Teknoloji Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Enerji = Energy

Özet:
Isı değiştiriciler geleneksel ısıtma sistemlerine alternatif olarak ortaya çıkmış doğal ya da özel bir sistemden (kazan, fırın vb.) ısı enerjisini toplayan sistemlerdir. Topladığı bu enerjiyi daha sonra evler, küçük işletmeler veya büyük hacimli endüstriyel tesisler gibi birçok farklı uygulama ve alanda kullanabilen cihazlardır. Isı pompaları genellikle ısı enerjisini topladığı kaynağa göre farklı şekillerde sınıflandırılırlar. Doğal kaynaklardan enerji toplayan sistemler hava, su ve toprak kaynaklı olarak isimlendirilirler. 
Hava kaynaklı ısı pompaları, dışarıdaki havadan ısıyı toplayarak ve iklimlendirilmesi sağlanmak istenen iç mekana bir fan yardımıyla ileterek ilgili ortamın ısıtılmasını veya soğutulmasını sağlayabilir. Su kaynaklı ısı pompaları ise çeşitli su kaynaklarından (deniz, göl, nehir vb.) ısıyı toplayarak çeşitli uygulamalarda kullanılabilir. 
Toprak kaynaklı ısı pompaları ise toprağın sahip olduğu ısı enerjisini toplayarak binaların ısıtılması ve/veya soğutulması için kullanılan cihazlardır. Toprak, gün boyunca güneş enerjisini emerek depoladığı için alternatif ısı pompası kaynaklarına göre daha kararlı bir duruş sergiler. Toprak kaynaklı ısı pompalarının genel çalışma prensibi toprak altına yerleştirilen bir döngü sistemi yardımıyla dolaşan bir ısı taşıyıcı sıvı kullanılmasıdır.  Genellikle kapalı döngü sistemler kullanılmakla beraber açık döngü sistemler de kullanılabilmektedir. Toprak kaynaklı ısı pompaları, yüksek verimlilik ve düşük işletme maliyetleri nedeniyle giderek daha popülerlik kazanmaktadır. Bununla birlikte kurulum maliyetleri ve doğru boyutlandırmanın çok önemli olması sebebiyle tasarımların hassas bir şekilde ele alınması gerekmektedir.
Toprak kaynaklı ısı pompaları açık ve kapalı sistemler olarak ayrılmanın dışında sığ kuyu kaynaklı ve derin kuyu kaynaklı olarak ikiye ayrılmaktadırlar. Bu tez çalışması kapsamında sığ kuyu kaynaklı ısı değiştiricilerinin tasarımı üzerine odaklanılmaktadır.
Bu kapsamda ilk olarak sığ kuyu kaynaklı ısı değiştiricilerinin çalışma prensipleri incelenmiştir. Yer altı toprak sıcaklığı, toprağın derinlerine inildikçe nispeten sabit kalmakta ve bu da sıcaklık farkı kullanılarak ısının aktarılmasına olanak sağlamaktadır. Daha sonra sığ kuyu kaynaklı ısı değiştiricilerinin tasarım parametleri belirlenmiştir. Bu parametreler, sıcaklık farkı, su debisi, boru malzemesi, boru uzunluğu ve boru çapı gibi değişkenleri içermektedir. Bu faktörler, sığ kuyu kaynaklı ısı değiştiricilerinin verimlilik ve performans değerleri üzerinde önemli bir etkiye sahip olmaktadır. Bu tez çalışması içerisinde özellikle mevsimsel etki nedeniyle oluşan yüzey ve toprak sıcaklık farkı ve boru uzunluğu üzerinde durularak sığ kuyu çalışmalarının limitlerinin belirlenmesi amaçlanmıştır. Bu limitler belirlenirken COMSOL programı kullanılarak simülasyon çalışmaları gerçekleştirilmiş ve parametrelerin etkisi incelenmiştir.

Abstract:
In the modern era, with the growing awareness of climate change, enviromental problems, increasing population and the need for sustainable practices; energy efficiency and reviewing energy consumption parameters has become a priority. Improving energy efficiency has environmental, economic and social benefits such as lowering energy bills and operational costs, make room for employment, increasing comfort and support healthy life standarts, etc. By prioritizing energy efficiency, we can create more sustainable and comfortable for both living and working environments while minimizing our carbon footprint.
Considering buildings are one of the biggest contributors to energy consumption and greenhouse gas emissions, energy efficiency and effective energy management techniques need to be prioritized in this area. Optimizing building energy use involves a comprehensive approach that includes architectural design, advanced building systems, and energy-efficient technologies. This requires the integration of renewable energy sources, the use of energy-efficient building materials, the implementation of smart control systems, and the promotion of behavioral changes among building residents. The goal is to eliminate energy waste, reduce CO2 emissions, and improve overall energy performance. With a growing focus on sustainability, laws and regulations are being developed to promote energy efficient building designs, retrofitting existing buildings, and the implementation of renewable energy sources. Therefore, research and development in building energy management systems and energy-efficient technology has grown more important. Additionally, there is an urgent need to focus on improving building energy performance through effective design, construction, and use of energy-efficient technologies and practices.
Due to their numerous advantages, heat exchangers are an attractive choice for a variety of applications and they play a crucial role in improving energy efficiency in buildings. Heat exchangers are devices that have emerged as an alternative to traditional heating systems and collect thermal energy from a natural or special system (boiler, furnace, etc.). The application areas can be diversified as residential buildings, small businesses and large industrial facilities where it can use the energy it collects.
Heat exchangers allow for more efficient use of available heat energy sources, which contributes to energy conservation and reduced environmental impact. They also enable the efficient transfer of heat across different fluids or other sources, resulting in more efficient heating, cooling, and ventilation systems. Heat exchangers, for instance, allow in the exchange of heat between incoming fresh air and outgoing polluted air in HVAC (Heating, Ventilation, and Air Conditioning) systems, so optimizing energy conservation. Furthermore, heat exchangers are adaptable in their applications meeting a wide range of heating and cooling requirements in the residential, commercial, and industrial sectors. 
Heat exchangers can also help sustainability and the transition to a greener future by extracting heat from renewable energy systems like solar thermal systems, geothermal heat pumps or waste energy sources to improve energy use and reduce dependency on traditional energy sources.
Buildings can recover and reuse waste heat by using heat exchangers, lowering the need for additional energy inputs. They can be customized to meet unique needs, assuring optimal performance and cost-effectiveness. In addition to increasing heat transfer efficiency and providing temperature control, they ensure that energy is not wasted in buildings as much as possible while maintaining comfort levels. As a result, using heat exchangers in building design and retrofitting projects is critical for creating sustainable and energy-efficient surroundings. 
Heat pumps are generally classified based on the source of heat energy from which they obtain. These sources are offen classified as air, water, or ground-based. Air-source heat pumps extract heat from the surrounding air to provide heating or cooling for indoor spaces through the use of a fan. Water-source heat pumps, on the other hand, gather heat from various water sources such as seas, lakes, or rivers for diverse applications. 
Ground source heat pumps also known as geothermal heat pumps are devices that collect the thermal energy that the soil contains, which can be used for heating, cooling and providing hot water in residential, commercial or industrial buildings. Since the soil stores solar energy throughout the day, it is more stable than alternative heat pump sources. The general operating principle of ground source heat pumps is to use a heat-carrying liquid that circulates through a loop buried underground. Although closed loop systems are more common, open loop systems can be employed as well. In addition to being classified as open and closed systems, ground source heat pumps are also divided into shallow well and deep well systems. 
When ground source heat pumps operate in heating mode, the fluid circulates through the pipes and takes heat energy from the soil. The fluid absorbs heat energy from the warmer underground and transports it to the heat pump unit inside the building. The fluid transfers heat within the heat pump unit to a refrigerant, which is a cooling agent such as hydrofluorocarbon (HFC) or carbon dioxide. The refrigerant evaporates from a low-pressure liquid to a high-pressure gas, allowing it to absorb a considerable quantity of heat energy from the fluid. The heated refrigerant is then forced through a compressor, where its temperature and pressure are further increased. The heated, high-pressure refrigerant is then sent to a second heat exchanger, where it is transferred to the building's heating system, such as underfloor heating or radiators. Heat is transferred from the refrigerant to the building's heating system, which warms the interior space. At the same time, the refrigerant returns to its initial low-pressure liquid condition after releasing its heat energy, and the cycle repeats.
In cooling mode the process works in reverse. The fluid absorbs heat from the building's interior space and transmits it to the refrigerant in the heat exchanger. The refrigerant then transports the heat to the ground, where it is released and cooled.  
Ground source heat pumps are becoming increasingly popular due to their high efficiency and low operating costs. However, due to installation costs and the importance of correct sizing, designs must be handled with care. Before using ground source heat pump systems, especially in shallow wells and horizontal applications where ground temperature vary seasonally, more accurate models should be developed and the level of accuracy should be increased during the design phase. Instead of sizing based on an assumed average ground temperature value for the entire year, utilizing analytical and numerical model results for different scenarios will enable a more realistic design.
In this context, the goal of the thesis is to design a ground source heat pump working in shallow wells and to estimate efficiency limits of this systems. First, the operating principles of shallow well ground source heat exchangers are examined. 
 Then, the design parameters of shallow well ground source heat exchangers are determined. These parameters include variables such as temperature difference, water flow rate, pipe material, pipe length, and pipe diameter. 
Ground temperatures based on measurement data will be treated as time-dependent initial and boundary conditions in this study, and an annual performance analysis for heating and cooling modes of ground source heat exchangers will be conducted. Different outdoor conditions will be determined, and the results of analytical and numerical modeling for different size and type of heat exchanger design parameters will be compared. As a result, a realistic sizing model method will be developed. The system was run with continuous charge and discharge phases. There is also stand by periods between each charging and discharge cycle. The charging period is 4 months and the discharge period is 7 months, based on the climatic features of the Sarıyer Istanbul region. The graphs and change values for annual average temperature change and radiation are obtained from the NASA database. The charging, discharging, and stand by periods of the system have been identified using these graphics. These factors have a significant impact on the efficiency and performance values of shallow well ground source heat exchangers. 
The soil temperature is the key parameter for evaluating the performance of ground-based heat exchangers. The temperature of the soil at the surface is directly influenced by the ambient temperature, resulting in a time-dependent variation in heat transmission. In this context, the time-dependent heat conduction equation will be solved analytically for 2D and 3D domains separately using both the constant temperature and constant heat flux methods. The boundary conditions used in this analysis will be time-dependent, where the temperature distribution obtained at the end of the previous period will be considered as the initial condition for the next period. To validate the results of the analytical model, numerical models with high mesh density will be created for the same geometries. 
In this thesis, the limits of shallow well operations were determined, especially by focusing on surface and soil temperature differences due to seasonal effects and pipe length. Mathematical modeling and COMSOL program were used to perform simulation studies and examine the effect of parameters. The accuracy of the Comsol simulation model applied has been demonstrated by using the mathematica application to solve heat transfer equations that have been approved in previous studies. The effectiveness of ground source shallow well heat pumps was investigated by simulating the confirmed comsol model, over a wide range of variables. The points to consider in the design of an optimum shallow well source heat pump system have been disclosed by analysing the data.