Scientific studies on heat pump

Heat pump has become a system that has become increasingly used due to reasons such as the increase in fuel prices, the environmental damage of other fossil fuel-based heating systems, and the increasing energy consumption in response to the rapidly increasing human population. . In these systems, soil, water or air is used as a heat source. Since the temperature change of soil varies less throughout the year than air and water, its use is greater. In addition, the soil temperature is colder in summer and warmer in winter than the outside air. Due to such advantages and low cost of soil, studies on this subject are increasing day by day.

The energy sources we use change in parallel with the changing technology. While wood and similar fuels, which are easy to obtain from nature, were previously used, coal and, more recently, oil and natural gas began to be used. Under today's conditions, almost all our energy needs are met by fossil fuels and their derivatives. In addition, some of the energy used is provided by solar energy and a very small part by nuclear energy. The fact that fossil fuels will soon be depleted raises the question of how energy will be met. In addition to the problem of depletion of fossil fuels, the increase in their prices causes the need to find new alternative resources and develop the existing ones.

These harmful systems that cause environmental pollution also negatively affect the ecological balance. It leaves bad effects on living and non-living things. The 'greenhouse effect', which is strengthened as a result of the rapid increase in carbon dioxide and other greenhouse gas emulsions released into the atmosphere, primarily the use of fossil fuels, and other compounds that cause depletion of the ozone layer, respectively, cause global warming and an increase in ultraviolet rays reaching the earth. As a result, the damage to nature disrupts the ecological balance by causing the extinction of living species.

On the other hand, environmental problems arising from the production, conversion, transmission and depletion of energy, as we mentioned before, and the protection of the environment are the issues of energy policies and practices of the countries of the world. has begun to be taken into more and more emphasis in the program. In parallel with this, it is becoming increasingly important to meet Turkey's rapidly growing energy needs cheaply as well as to control environmental pollution (Niğdelioğlu, 2006).

Energy resources are becoming more expensive and scarce; Pollution arising from the energy, industry and transportation sectors has made it necessary to take measures to protect the environment in our country, as in the world. Since the main purpose of energy policies is to protect and improve the environment while strengthening socio-economic development, our country approaches the environment, which is increasingly being taken into consideration in the energy policies and programs of the world's countries, with a parallel view to other countries, and believes in the necessity of protecting and improving the environment. It carries out various activities and takes precautions to reduce environmental pollution and greenhouse gas emissions (Niğdelioğlu, 2006)

Such problems and efforts in these energy sources used are the result of new alternative energy sources. revealed his quest. New energy sources include sun, wind, wave, biomass, geothermal energy, soil, rock and groundwater. Our country is also trying to benefit from these new energy sources. Among these, the system we see most frequently is solar energy systems, and geothermal energy has begun to be used in many areas such as electricity generation, cooling, heating and hot water needs, greenhouse cultivation, etc. (Güven, 2002). The system that attracts our attention the most is geothermal energy. The reason is that our country is the seventh country in the world in terms of geothermal resources.

Soil is a system used in the heating and cooling of commercial buildings, various engineering structures and the production of domestic hot water by using the energy that can be recovered from the heat obtained by the earth from the sun's rays. The use of “Welded Heat Pump” (TKIP) is increasing. The operating principle of the system is based on the transfer of heat. Since TKIP systems are systems that provide heating and cooling with electrical energy, they have been used for a long time in Scandinavian countries, especially in the USA, Canada, Germany and Sweden, as an environmentally friendly system. TKIPs produce more effective results in the use of energy because the temperature inside the soil changes steadily and they keep their performance at a high level in cold climates (Şahin et al., 2007).

If the heat pump is defined simply, it transfers heat from one environment to another. carrying system. The system gets its energy from electricity. The thermodynamic law that heat cannot be created or destroyed, and that heat can only be transported, defines the way the heat pump works. In heat pumps, soil, water or air are used as heat sources. In case of using soil as a heat source; Both the appropriate value of the soil to meet the required heat need and the high heating effect coefficient cause the efficiency to increase.

The term heat pump is new to most people in the heating industry. However, the refrigerators, air conditioners, dehumidifiers and freezers in our homes are products of the same logic. Since their working principle complies with the logic of transporting heat, they can be grouped under the title of "heat pump". If cooling machines are used for heating or heating and cooling purposes, they are called heat pumps. As an example, let's consider the refrigerators used in our homes. In refrigerators, the interior environment where the food is stored is cold, and the pipes behind it are hot because they release the heat into the environment. Almost every person is aware of this phenomenon and wonders where this heat comes from. As seen in the example, cooling machines produce heat and cold at the same time. As can be understood, when we talk about heat pumps, we refer to cooling machines. So, heat pumps are a concept that has been known for a long time, so it is not a new technology for the 90s. Heat pump technology was logically first developed in the 18th century. The heat pump will have a huge role in the use of heating purposes from now on, as it has with the rising trend it has followed in cooling until today (Ünlü, 2005).

Ground source heat pump has been in America and Europe since 1995. It has improved the most at 59% or 9.7% per year. Its installation capacity in 26 countries in the world is 6850 MW and annual energy use is 23214 TJ / year. The number of installed systems is around 500,000 according to 2000 data (Lund and Freeston, 2000; Ünlü, 2005). In addition, geothermal heat pumps came to the fore in our country in 2001-2002 and were put into practice for heating and cooling purposes in many residences. However, TKIP manufacturing is not yet available in our country and package type TKIPs imported from abroad are used.

TKIP was designed to transfer the heat energy stored in the geomass from the earth to living spaces when the sun's rays hit the earth. TKIP uses the soil as a heat source or heat well. The fact that the soil temperature remains partially constant from the surface to the depths and that this temperature is closer to the temperature required for human comfort conditions than the ambient temperature makes this type of heat pump application attractive. Due to this close to constant temperature, higher values ​​in the performance of the cycle are achieved with ground source heat pumps, even in regions with harsh climates. Although heat pumps that use air as a source are widely used, they have some disadvantages such as operating at low efficiency and causing undesirable loads on electrical feeders, especially in regions with cold and variable climates. These types of undesirable factors are eliminated by using TKIP. As can be understood, higher performance is achieved with TKIP compared to air source heat pumps (Ünlü, 2005).

The most important difference of TKIP from other heat pump systems is that TKIP systems provide heat by providing contact between the heat carrier fluid and the geomass. It requires a 'Ground (soil) Heat Exchanger' system that allows heat transfer. The high installation cost resulting from the installation of these heat exchangers in the ground can be considered a disadvantage of ground source heat pumps. However, the operating costs of these heat pumps remain lower than other heat pump types. Ground heat exchangers can be placed horizontally or vertically within the geo-mass (Ünlü, 2005).

Considering that 1/3 of the energy produced by ground source heat pumps is paid for, compared to alternative systems, not only the consumer but also the state also receives outsourced energy. It has been proven that it will provide a great advantage in energy purchasing policies and thus heat pump technology is encouraged and supported by states (Ünlü, 2005).

Turkey, solar and It is a country very rich in wind. So far, solar energy has only been used for water heating in our southern regions with very low efficiency. For our country, which does not have the luxury of wasting this wealth, wind and sun, which are inexhaustible resources, are candidates to be the main energy and electricity sources in the coming years. With the widespread use of alternative energy sources, a different world view will dominate our daily lives. In such an environment, the level of welfare will be determined by the most efficient energy user, rather than the one who consumes the most energy. As a similar understanding prevails in Turkey, the importance of renewable energy resources will increase even more (Ünlü, 2005).

There are many studies in the literature regarding TKIP Systems. These studies are explained chronologically below.

In his study, Kersten (1949) explained experimental equations to determine the soil heat conduction coefficient, depending on the soil dry density and moisture content values ​​(Ünlü, 2005).

Ingersoll (1954) showed that the Kelvin Line Source Theory can be used to examine the heat transfer in pipes placed underground to draw or throw heat. Shelton (1975) examined the heat transfer in an underground heat storage and the soil around the storage (Ünlü, 2005).

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Kunze and Forsgren (1978), in their study classifying geothermal resources according to temperature, have temperatures between 50-80ºC for sources below 50ºC for geothermal heat pump applications and above 130ºC for direct use. states that the resources are suitable for electricity production (Ünlü, 2005).

Greistad and Torabramians (1981), in his research titled TKIP optimization, states that geothermal water flow rate is significantly effective on equipment (evaporator), energy and water costs (Ünlü, 2005).

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Lund and Kangas (1983) presented the net energy analysis of a solar heated system with seasonal heat storage. This analysis was carried out for Finnish climatic conditions (Ünlü, 2005).

In his study by Mathen (1984); It determined the annual performance levels of 10 TKIPs in operation and determined the net energy savings by comparing them with conventional heating systems (Ünlü, 2005).

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Lund and Östman (1985) developed a three-dimensional numerical model of seasonal heat storage in the soil using vertical pipes (Ünlü, 2005).

Hugnes et al. (1985) reported results from a multi-phase demonstration project to evaluate the technical and economic potential of TKIPs for housing in upstate New York City. In this context, heating-cooling performance and integrated domestic hot water were observed during 1982-1984 (Ünlü, 2005).

Franck and Berntsonn (1985) used vertical pipes up to 10-40m deep for seasonal storage in the soil. presented some of the main results obtained from two experimental installations in line with a large research program carried out in Sweden in the field of solar-assisted heat pumps (Ünlü, 2005).

Catan and Baxter (1985) examined the economically optimum analysis of TKIPs in northern climate applications (Ünlü, 2005).

Goswami and Dhaliwal (1985) 1.83 m They presented heat transfer analysis of techniques that use subsurface soil temperature at or greater depth. With the help of a computer simulation developed in this study, the temperature of the air passing through the underground pipe was calculated (Ünlü, 2005).

Lund and Friends (1987) carried out a computer simulation of a solar heating system with seasonal heat storage for the climatic conditions of Tashkent ( Ünlü, 2005).

Eskilson and Hellström (1987) developed an analysis for a 25-well heat storage. Approximately a constant 100 kW of heat energy was added to the tank for a few days, and the inlet and outlet temperatures of the heat-carrying water were measured in 25 parallel wells (Ünlü, 2005).

Claesson and Eskilson (1988) As a heat source They gave information about the thermal analysis and sizing rules of heat exchangers placed in the ground during heat withdrawal in heat pumps where soil is used (Ünlü, 2005).

Kavanaugh and Pazent (1990) studied the operation of water/air heat pumps using river water as the heat source and heat sink. He also made suggestions regarding the selection of the heat pump, pumping systems, pipeline layout and river size/depth characteristics (Ünlü, 2005).

Martin (1990) used the heat pump system with a single-pipe horizontal soil heat exchanger. conducted studies to determine the effect of changes in parameters (Ünlü, 2005).

Sulatisky and Van Der Kamp (1991) in Canada (Saskatchewan) evaluated five ground source heat pumps for residential use (Ünlü, 2005).

Kavanaugh (1992) conducted studies to determine the acceptability and operating characteristics of vertical ground source heat pumps in southern climates (Ünlü, 2005) .

Meloy (1992) worked on the conversion of the Cowlitz County Courthouse to a well source heat pump system with downwell water cooling. and stated the problems encountered during the transformation (Ünlü, 2005).

Rafferty (1992) identified two 360 tons (11266 KW) power plants with a groundwater temperature of 22ºC and a 156 tons (549 KW) power plant with a groundwater temperature of 13ºC. explained experiences from different groundwater source heat pump systems (Ünlü, 2005).

Dvorov and Ledentsova (1994), in their study examining the economic and technical aspects of geothermal heat use for Russia, revealed that it is more economical to utilize low-temperature sources with a heat pump instead of direct heating using sources at temperatures of 80ºC and above. (Ünlü, 2005).

Bloomquist and Schuster (1994) in their study examining the historical development of geothermal resource use in America; revealed the importance of geothermal heat pump applications both today and in the future (Ünlü, 2005).

Sullivan (1994) stated in his article that geothermal heat pumps, which first appeared in the 1940s, are now available in 35,000 units per year in America. (Ünlü, 2005).

Healy and Ugursal (1997) using a computer model, He worked on determining the effects of different system parameters on the performance of TKIPs. He also conducted an economic analysis to evaluate the feasibility of using a TKIP where conventional heating/cooling systems and an air source heat pump are used (Ünlü, 2005).

Spikler (1998) studied the design of a vertical ground source heat exchanger, using the thermal conductivity test and the effect of different filling materials used in vertical ground source heat exchangers (in four different hole diameter layouts) (Ünlü, 2005).

Den Braven (1998) examined and listed the availability of antifreezes used in TKIP's soil heat exchanger in America. He stated that almost half of the states in America do not have any rules or recommendations that include antifreeze materials for TKIPs (Ünlü, 2005). examined the performance of a hybrid heat pump (in which the amount of ground heat exchanger required was reduced) (Ünlü, 2005).

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In parallel with the studies carried out abroad, some studies are also carried out in our country.

Koyun and Diz (2000) In their study, they examined its change depending on time and depth. Depending on the physical properties of the soil, the values ​​of soil temperature at different depths during the year were obtained through mathematical expressions (Ünlü, 2005).

Işık and Friends (2000) In their study; The performance of water-water and air-water source heat pumps in simultaneous heating and cooling conditions has been experimentally investigated. (Ünlü, 2005).

In the study of Kıncay and Temir (2002), heat loss and heat gain values ​​of a villa in Hadımköy, Istanbul were found and dimensioning calculations were made for both heating and cooling with a vertical type ground source heat pump. (Ünlü, 2005).

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Kaygusuz et al. (1992) conducted a study on the adequacy of energy storage and solar-assisted heat pump for domestic heating in the Black Sea region (Güven, 2002).

Taner (1986) from Anadolu University and Kılkış (1981) from METU. Articles have been prepared about ground source heat pumps (Güven, 2002).

Hepbaşlı (1985), 'heat pump systems and housing In his master's study titled 'Heating', he studied residential heating with soil-water heat pump, using soil as the heat source (Güven, 2002).

Ataman examined this subject as his master's thesis in 1991. In the study, heating of a house built in Göztepe with a ground source heat pump was discussed (Güven, 2002).

Oksay and Babür from METU, in 1985, used the devices in the METU Mechanical Engineering Department laboratories to create a connection between soil and air. They designed and built a working heat pump. The ground source heat pump performance was experimentally examined with a heat pump consisting of two circuits (Güven, 2002).

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Since ground source heat pumps have not yet reached the production stage within the borders of our country, they are supplied from outside as package type, which causes an increase in investment costs.