Modeling of driveway as a solar collector for improving efficiency of solar assisted geothermal heat pump system: a case study

Abstract

It is well known that rooftop solar thermal panels increase both power rates of circulation pumps and initial investment cost of solar assisted ground source (geothermal) systems. To avoid both of them it means that the unnecessary energy consumption rates of circulation pump(s) and their initial capital cost, rather than installing rooftop solar thermal panels, driveways can be used as solar collectors for improving efficiency of geothermal heat pump systems (GSHP) and declining initial capital cost of SAGSHPs. Mainly this idea was first put in the middle by Jefferson W. Tester. In this paper, we will examine modeling of driveway as solar thermal panel to enhance efficiency of solar assisted geothermal heat pump system (SAGSHP) depends on its different operating types; yet we will give only a case that is investigated theoretically for solar assisted geothermal heat pump systems.

Introduction

GSHP applications have been increased all over the world, since they have huge energy savings in air conditioning of buildings and these systems make it possible to evaluate both shallow geothermal resources and shallow soils as energy resources. Moreover, they have indirect benefits on reduction in NO_x, CO₂, SO₂, etc emissions. These are well known environmental air pollutants.

Typical SAGSHP systems consist of solar thermal panels, heat pump coupled with horizontal or vertical ground heat exchangers. For SAGSHP applications in heating and cooling of buildings, the containment of solar thermal panels becomes an integral part of the projects, yet they can be problematic, since they require storage tanks and special attention to the design of ground and solar heat exchangers for charging and discharging, other considerations include possible water leakages bad effects to building roof, cost, short and long term cycling stability, space requirements, sometimes solar thermal panels and their storage tanks can be exposed wind that occurs the heat losses etc. Hence, shallow soils could be an alternative solution instead of solar thermal panels. In this paper, we will examine modeling of driveway as solar thermal panel to enhance efficiency of solar assisted geothermal heat pump system (SAGSHP) which depends on its different operating types, yet we will give only a case that is investigated theoretically for solar assisted geothermal heat pump systems.

Before layout ground heat exchangers, defining of shallow soil temperatures is very important in terms of layout pipes that would be solar collector. In the past over 30 years, researchers have actively considered using soils for thermal energy storage applications e.g., [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. In many cases a detailed investigation of the soil properties and long term soil temperature measurements as a function of time at different depths of the research area is needed in order to determine design parameters and feasibility of a system [11].

Elsayed presented long-term analyses to predict the optimum tilt angle of an absorber plate at any surface azimuth angle and his analyses include the effects of number of glass covers, latitude angle, monthly average clearness index, month, and ground reflectivity [4].

Optimum collector slope for a liquid base active solar heating system employing flat-plate collectors was investigated by Iqbal [5]. Measurement of absolute spectral reflectivity was analyzed by Gier et al. [6]. Kusuda presents in a clear and orderly fashion all the factors which need to be considered in an earth sheltered house in his work [7]. They enhanced a model which is based on the transient heat conduction differential equation using the energy balance equation at the ground surface as boundary condition. The energy balance equation involves the convective energy exchange between air and soil, the solar radiation absorbed by the ground surface, the latent heat flux due to evaporation at the ground surface as well as the long-wave radiation [8]. Soil can be used as heat reservoir for building heating or cooling purposes, as the underground temperature is different from the ambient air temperature. Ambient air is heated or cooled when flowing along a tube installed underground, and this air with changed temperature is introduced in the building. This problem can be studied in many ways, the main differences being the objectives and the considered details of the flow and temperature fields. In the present work a thermodynamic analysis is made, and important criteria are obtained in what concerns both the construction parameters (diameter and length of the tube installed underground) and the operation parameters (mass flow rate and heating or cooling effect) [9]. Mihalakakou׳s study deals with two methods for modeling and estimating the daily and annual variation of soil surface temperature [10].

However, none of them is related to utilization of asphalt as cover of solar collector idea. Mainly this idea was first put in the middle by Jefferson W. Tester, and also this idea came from commercial heated driveway system to melt snow and ice in winters. In this work, the obtained results are based on the authors׳ assumptions and their past experimental and field experiences.