# Dynamic and Static Investigation of Ground Heat Exchangers Equipped with Internal and External Fins
## 1 Introduction
[24] studied the thermal performance of a double U-tube GHE and the effects of parameters such as inlet velocity, temperature, and operating distance on the temperature distribution of the soil. [PERSON] and [PERSON] [25] performed computer simulations of borehole heat exchanger to determine ground and borehole the temperature along depth using a finite difference model. [PERSON] and [PERSON] [26] performed a dynamic thermal analysis on a 4-ton residential GSHP and observed a design trade-off between cooling and heating modes. They obtained the optimal value of the evaporator area fraction in both cooling and heating modes. [PERSON] et al. [3] studied the energy savings by using GSHP systems in the residential buildings sector in cooling-dominated environments. It was found out that the energy savings by using GSHPs when compared to the conventional air source heat pump system are much higher. Similarly, [PERSON] et al. [27] performed a techno-economic analysis on a hybrid ground-source heat pump systems for cooling-dominated applications. The results of their simulation showed that a ground-source heat pump-based system helped the owner to save up to 30% of lifetime electricity consumption as compared to an air-source heat pump-based system. In contrast, the air-source heat pump-based system can have up to 10% lower total cost of ownership due to the lower upfront capital cost. A study by [PERSON] and [PERSON] [4] discussed that the commercial buildings in Dubai have fairly high occupancy, fluctuating demands, and extensively diverse cooling requirements within individual zones, which are difficult to meet effectively and efficiently with conventional HVAC systems. They concluded that there is potential for the efficient use of ground couple heat pumps (GCHPs) in Dubai commercial buildings leading to significant savings in energy usage and operating costs and substantial reduction in CO2 and NOx emissions over a 20 year life cycle as opposed to other HVAC options. The performance of fins for enhancing heat transfer of heat exchangers generally has been considered previuosly [28] and [PERSON] et al. [29] investigated the influence of internal fins on the dynamic and thermal performance of U-tube GHEs. Using fins increased heat transfer rate up to 7%. [PERSON] et al. [30] performed a numerical simulation of GSHPs with a spiral pipe and investigated the effects of a fin on the outer surface of the spiral pipes. The results showed that fins can improve thermal conductivity due to increased surface area. Previous studies have been conducted to find a method to increase the thermal efficiency of GSHP systems. These methods were based on borehole configuration, thermal properties of the ground and grout materials, and generally finding suitable solutions to reduce the borehole depth. To the best of the authors' knowledge, the impacts of internal and external fins on the thermal performance of U-tube GHEs have not been compared yet which is the aim of the current study. Moreover, both dynamic and static behavior of simple and finned U-tube GHEs will be evaluated to obtain the best efficiency. For the dynamic tests, various conditions such as short timescale response and sinusoidal response tests will be investigated for the BHE equipped with fins. The velocity of the inlet flow with the resultant flow filed patterns and the frequency of the input temperature with its effects on the response time and amplitudes are other important parameters that are added to this investigation.