Analysing the refrigeration cycle of the gas in the operation of the heat pump in a pressure-enthalpy diagram, the electrical energy used by the compressor depends on the operating characteristics of the heat pump during a given time. Both the evaporation pressure and the condensation depend on the ambient temperature and this oscillation will affect the energy used by the compressor. The higher the difference in temperatures between the evaporation and condensation, the more energy required. The performance of a heat pump can be defined as the ratio of energy delivered in heat by the condenser to the electricity used by the compressor. This relationship is known as Coefficient of Performance (COP) (Lienard, 1995)
Coefficient of Performance (COP) = (Energy delivered ( kWh) )/(Energy consumed ( kWh))
Depending on the working conditions of the heat pump, the values of the COP can range between 2 and 5. Low temperature systems (20-40°C) such as under floor heating are the most efficient. High temperature systems such as radiators are less efficient because they work at a higher temperature. (Stevenson, 2014)
Efficiency of the Ground Source Heat Pumping System
Modern functionaries related to the Ground Source Heat Pump Systems are very much efficient as compared to the previously existing ones. As we know that the pump requires some energy to perform its designated function, so for every unit i.e. KW of the power fed into the pump in order to run it, we can extract 3 to 4 KW’s of energy to be made useful for utilization. The system’s efficiency is entirely dependent over the quality of the design and the installation of the equipment as a whole. To be precise this efficiency grid can be further enhanced using solar recharge phenomena of the ground. The coefficient of Performance i.e. COP of the heat pump system entirely is dependent over its design, formation and the quality to be the least possible one. It usually varies from 2 which is the minimum threshold (for a heat pump system using air as a working fluid) and reaches up to 4 which is quite higher on the scale (for a heat pump system with unassisted ground source) and to our surprise a value of 8 can be achieved which is only possible in the case of system empowered from the solar recharge of the ground ads mentioned earlier. (Fuhrer, 2015)
Scope of Performance
GSHP systems are quite a well-established technology as observed around the globe. Its utilizations in the Eastern Europe and other neighbouring countries have been seen occasionally. They also perform relevant to their size, i.e. a unit which may be utilized for a small building would be of the size of a full sized Refrigerator to be precise. And now going for greater utilizations, the size does not vary much i.e. they do not increase with the same ratio rather the desired output is duly achieved. Reverse cycle heat pumps i.e. (RCHP’s) deliver both the heating & cooling equally efficiently. There is a phenomena linked with this one known as Renewable Cooling (cooling from an Air Conditioner is quite low as compared to the efficiency of cooling gained from the heat exchanger with comparatively cold ground). (Lienard, 1995)
Application of Units
Because of the fact that the new building laws and regulations have been set to conserve energy, fuel and raw material so, every building being built according to these updated international building regulations is amicably well-suited for such systems to be installed. For non-compliant constructions the system is equally good but the capacity is to be enhanced accordingly. Poor constructed and old barrens may also be treated with the same but we must keep this thing in mind that the more updated the construction is, the greater would be the reward and the output. In addition to all the facts, the most important among all is that the aforementioned systems are very eco-friendly as experienced. About 40% of the harmful emissions in the atmosphere are because of the refrigerators, air conditioners and similar systems, which whenever replaced with this can be manipulated easily. Because of the fact that there is no dangerous emissions, no flammable oil, no need for the flue or chimney, so no safety checks are required so far. (Fuhrer, 2015)
Factors Effecting the Performance of GSHP
The performance and capability of a Ground Source Heat Pump is one of the top chart factors considered for calculating its efficacy. It basically depends over the constant term known as Coefficient of Performance as mentioned earlier in the heading 5 of the paper. The detailed factors are described below. (Lienard, 1995)
Inside Heat Exchanger
Heat Exchangers are not at all a complex structure but rather a simpler one indeed. It contains tubes, walls and interfaces for heat exchange purposes. So, comprising of a few components as mentioned below some dependencies are seen as follows:
Inlet Temperature
Inlet temperature of the heat exchanger also plays a very vital role in performing the task of heat exchange as serving the purpose. The main purpose of the heat exchanger is the exchange/transmission of heat from one module to another i.e. Heat transfer from higher concentration to lower. Greater the temperature difference, greater the rate of heat transfer among the equipment. Now, as the heat of the ground is to be transferred to the pumps so we have to make sure of this thing that the temperature difference of both modules is greater. So, any arrangement linking to the fact and making sure of this thing that the ground heat exchange pumps should be of colder temperature as compared to the temperature of the ground. Doing this maximum efficacy can be achieved with quite ease. (Stevenson, 2014)
Running Fluid
Working fluid is the only source capable of performing the desired task in here. Knowing the fact that only the working fluid has the capacity to absorb and carry the heat engaged from one place to other serving its purpose. So, characteristics of the fluid, its viscosity, its resilience, density, COP, boiling temperature and other physical and chemical properties are to be considered in order to choose it for application. Especially the fluid must not keep any bit of heat in any form, complete quantity of the heat must be absorbed and the transmitted amount must be the same as absorbed.
Vertical
Fluid temperature distribution, when taken into account along the borehole depth, back then, there was presented a new model for the same purpose. A new three quasi-dimensional model was presented which is also known as the vertical heat transfer pump. In this model more efficient heat transfer is possible as the surface area of contact is greater as compared to the other scenario. Moreover, greater differences in the temperatures can be observed in this model and overall efficacy increase of sixty percent is seen. (Stevenson, 2014)
Heat Exchanger
Diameter
Physical properties pertaining to the heat exchanger are very important to consider while selecting one. Out of which the diameter of the tubes from the heat exchanger no matter what type is it of is a key responsibility. The diameter of the exchanging tubes plays a very vital role no matter what. As a matter of fact the diameter of the tubing has a direct relation with the heat exchange i.e. greater the dia., greater is the exchange rate, provided the flow also upholds the diameter. Smaller diameters and higher velocities add up to the necessity of heat flow. When the diameter increases, the velocity of the flow should also increase so as to overcome the increase in the diameter. But generally greater diameter means greater surface area for heat exchange. (Lienard, 1995)
Material of Pipe
To choose the material for the piping, tubing of the heat exchanger, some factors are to be kept of foremost importance. Best of the conductors is to be used for this purpose. As, we know that copper is one of the best available conductors in the periodic table so it is considered to be the best one for the purpose. Now a days, many composites and other materials are used instead of copper, keeping in view the condition that the desired properties must be observed. The reason for the material to be the best conductor is that whenever it is made to absorb the heat it should absorb all of it, and whenever it is subjected to transfer the heat to inspect for exchange it must transfer all the heat leaving none behind. (Lienard, 1995)
Arrangement
There are metallic tubes inside the heat exchangers that carry fluids in and out in all types of flows. There are various kinds of arrangements described in the literature and are used practically for the purpose. Counter-Current Exchange, Current Exchange, Parallel, Perpendicular, Shell Tube, Tube-Tube, Shell-Shell heat exchangers are available in the market and are detailed in the literature. The main difference is based upon the flow of current through them. The current for the flow of fluid, the absorbent, the working fluid. So it is important to keep all the required considerations into account while designing the said. (kreith, 2000)
Pitch
The distance in between the centres of the placed tubes in the heat exchangers is called as the pitch of the heat exchanger. Usually it is kept to about 1.25 times the external diameter of the heat exchanger tubes. Main variable features for the heat exchangers can be varied by varying the pitch of the tubes of the heat exchanger like shell side pressure drop and velocity of shell side fluid etc. (Fuhrer, 2015)
Outside Heat Exchanger
Concrete
Concrete outside the heat exchanger is considered to be an essential tool for the transferability and its efficacy. As it is well known that the thermal stability, thermal resistibility and thermal capacity of the concrete is much higher as compared to other materials to be considered for the coating. Along with a well-known fact that it is strong, it is also used in the ceiling and rooftops and for constructing the buildings because it resists a hell lot amount of heat. It directly depends upon the thickness of the concrete wall or sheathing, greater the sheathing, greater will be the heat/thermal resistibility and vice versa. So concrete is the best option to be used in this place instead.
Soil
Three main types of soils are seen commonly in the literature i.e. (Silty Loam, Silty Clay & Sand). Their saturation and moisture vary differently depending upon the topography of the climate. Heat Exchangers in this application depend upon its coefficient of performance. Now, when we see the factors for the COP we find it quite obvious that greater the soil moisture, greater the cop and the conductivity of the soil. So it is quite a genuine practice and is preferable too to keep the soil moisture content high for best performance and results of the equipment. (Fuhrer, 2015)
Environmental
Keeping in view all of the above mentioned factors it is quite obvious that environment has to play a very well suited role in its performance. Temperatures, dust, physical conditions and other common factors are to be kept in consideration for better performance. Environment has some other factors involved which affect the performance of the heat exchanger such as, air temperature or dry bulb temperature, the sun i.e. temperature of the environment, the factor of humidity & evaporation i.e. the wet bulb temperature, air movement i.e. the air flow rate or the flow rate of the air, workload i.e. the pace at which the heat or coldness is being released to work upon, clothing i.e. a lot of clothes makes the heating and cooling more difficult and acclimatization. By acclimatization we mean the human body factors i.e. the performance of sweat glands, because greater the sweating capacity greater would be the cooling feeler, reduction in heart rate, decreased heart rate makes the body less fatigued and help in cooling it down etc.
Except for them, a number of other factors that are involved in the heat transfer inside a heat exchanger can be enumerated e.g. area of contact (as described), thermal conductivity, temperature difference, thickness of material, Specific heat capacity of all the metals and fluids involved, viscosity to be precise, flow rate of the working fluid, insulation and fouling factor etc.. A number of which have been already described in detail in the above text.
Energy Piles
Energy pile is another name for the Heat Exchanger Pile which comprises of a bunch of wires, cables and piles of heat exchanger tubes clogged together in the form of a cluster. They are used to enable heat exchange with the surrounding soil and ground surface. They have dual functionalities i.e. they perform two functions at a time which are; first one is to transfer the load from the construction site to the layer of the bearing and second one is the one of our interest i.e. heat exchange from the soil. Energy pile is a much updated, latest, promising and most efficient environment friendly practise to ensure the process of heating & cooling the buildings, houses and units. Boreholes along with these kinds of energy piles when join hands with the ground source heat pumps consume the renewable energy i.e. Geothermal Energy from the earth’s core, under the earth’s surface for being utilized as the air conditioning utility as described above. For this purpose, we require proper size, dimensions, designing, array management, positioning, and pattern to jot out the best out of it all.
The working of the energy piles is a process that depends over the annual seasons to go i.e. there is a configuration for the summers, whereas there is some other configuration for the winters to be precise.
In winters, usually the water is colder i.e. lower in temperature as compared to the natural temperature of the soil so to nullify the effect, heat is removed from the working fluid (what so ever it may be depending upon the application and utilization of the heat exchanger) using the heat pump and a higher temperature is provided to the heating. (Lienard, 1995)
Whereas on contrary to that in summers, the water is warmer than the soil underneath so the heat in the water is dissipated to the soil for the heat exchange to take place.
A general construction chart is shown in the figure above which depicts the basic arrangement and construction of an energy pile heat exchanger system. Going from 1 and ahead we can see the process of piling as; 1, 2 and 3 is the screwing in phase i.e. the soil is being displaced by screw heads to guide the tube to correct depths down the surface. Till 3 the tubes are settled and now in 4, the screwing out takes place, generally the concrete is pumped into the borehole across the auger and the pins are pulled out. In 5 & 6 the reinforcements are seen which contain the heat exchanger pipes ad wires and cables for the performance of the dedicated task. (Stevenson, 2014)
Fields of Application
Applications of energy piles are the same as of the ground source heat pups or the heat exchangers or the air conditioning units as described;
They are frequently used in the “Zero Energy Buildings”. Basically zero energy buildings are the buildings, houses and units in which the total amount of energy or power consumed per year is almost equal to the amount of energy produced or generated through every possible renewable energy source i.e. Ground Source Heat Pumps and others. So such buildings are an ideal application for such tech.
Moreover, they are one of the ideal solutions for the utilization as heating & cooling of the units.
The best utilization for the energy piles is that it is used in coupling in the geothermal heat pumps as they act best in this form.
Environmental Impact
Energy piles are very fruitful in every aspect including the environment as well;
They are produced with integrating with the existing equipment and components and low to no maintenance is required in this lieu.
This is a completely pro-ecological system i.e. no licensing procedures are required for proving them to be environment friendly.
This has proven itself to be very much environment friendly and quite a sustainable idea i.e. carbon dioxide emissions can be reduced up to 40 % using this technique.
The last but not the least we can save energy grid up to 45% at all times using this technique.
