Modeling of heat exchange with the ground and analyses of energy use for a frost proof leisure building with active solar heating
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Requirements regarding efficient energy use and reduction in CO2 emissions are becoming increasingly strict. The building sector accounts for a large part of CO2 emissions and the potential for reductions within this sector should be considerable.This thesis is a continuation of the author's project thesis. The main focus is to improve the earlier model emphasizing the modeling of the interactions between the leisure home building and the ground. The goal is to develop a prototype of a leisure home where sanitary installations are kept frost proof throughout the year without the use of primary energy sources or electricity, minimizing net CO2 emissions. The building envelope is constructed of poorly insulated log walls. The sanitary installations are placed in a thermally insulated internal zone, and an active solar heating system is developed to transfer heat into the ground in this internal zone. The intention is to store the heat, transferred to the internal zone during sunny periods, in a thermal mass under the cabin. This would then passively arise during cold periods, maintaining frost proof conditions. The leisure home is planned to be located in the southern mountain regions of Norway. Different simulation tools were considered for modeling the leisure home and its energy system. The dynamic simulation tool ESP-r was chosen, and an improved model from the project thesis was developed. Different methods and theories concerning how the solar heating system and the ground could be modeled have been studied. The interactions between the building and the ground were modeled by implementing a new basement zone for the leisure home, and defining a BASESIMP configuration as boundary conditions for the surfaces adjacent to the ground. BASESIMP performs quasi 3-dimensional calculations for the heat transfer between the building and the ground. Since the heat storage is not taken into account in the BASESIMP configuration, the storage is represented in the ground construction; the basement floor of the inner zone. The solar heating system is represented in a control loop. The control loop injects electric heat into the basement floor for a given period each day. The electric data is based on solar radiation data, and the time intervals for when heat is injected into the floor are determined from when solar radiation is available in the day. Climate data from Östersund, Sweden has been used as an approximation as there was no available climate file for the southern mountain regions of Norway. Different system parameters have been changed to investigate the influence they have on the temperature conditions in the internal zones throughout the year. The internal zones maintain much more stable temperatures throughout the year than the outer zones. This shows that isolating the frost proof zones in the leisure home, represent a major advantage in the design process. The ground construction in the basement floor of the inner zone has been modeled as a thermal mass with high density and high specific heat capacity. This dense thermal mass is modeled to account for the whole area under the cabin. A south facing solar collector with an area of 4 m2 and an inclination of 70 ° indicates that the temperature in the internal zones stays above 4.2 °C throughout the year, subject to the given ground conditions and without collecting heat during May until August. The delivered energy to the ground construction in the basement floor of the inner zone for a year under the given conditions and with a collector efficiency of 45 % turned out to be 878 kWh.Heat transfer from the ground into the internal zone turned out to have a significant heat contribution in cold periods. Results also showed a noticeable potential for seasonal storage of the energy extracted from the solar heating system.For further studies, the interactions between the heat storage and the surrounding ground should be studied in a 3-dimensional conduction program. Insulation regarding snow should also be implemented in a future model to study the effect of extra insulation on the ground surface.