Using a geothermal system for heating a residential idea

Project Info


Our company was requested to design a power system for a 3 stage building with 300 m2 area using the local geothermal power. Geothermal power is one of the most important sources of power for the industrial as well as residential needs. Like other renewable sources of energy, it is a cost-effective solution for its utilizing the thermal energy of the earth.


The first step in making the design was checking the regional soil properties. After careful investigation on the structural properties of the soil and the soil type, the design team came up with a plan for powering the compound. Based on the result of the investigation, the design team determined the best depth inside the soil for burying the pipes under the ground. The existence of a sand layer also helped the team to consider a better option.
The other issue that was to be determined was the heating load of the residential facility. Having calculated this figure and knowing the soil temperature, the design team managed to obtain COP (coefficient of performance) for the system.
COP is defined by the ratio of heat dissipation and the electrical power intake for the system and indicates the efficiency of a heating and cooling machines.
In other words, COP means that for each KW heating consumption how much electrical or other sources of energy you must pay and this is very important to achieve a cost-effective solution.
In making the calculations, the following initial data were considered:

 1. The wall and the ceiling were in a rectangular shape
 2. The windows’ size 1 x 1.5m
 3. For calculation of u value, the standard of BS EN was used with the following material
     a. Sandstone brick
     b. Combination of Plywood- Shit for the ceiling
     c. Combination of sandstone brick with glass for the wall
     d. Reinforced concrete for the wall and ceiling
     e. Polycarbonate for the ceiling
 4. Also, the following thicknesses were considered
     a. The thickness of the brick wall = 20 Cm
     b. The thickness of the plywood = 2 Cm
     c. The thickness of Shit = 1 Cm
     d. The thickness of the concrete wall/ceiling = 1 Cm

Other considerations were the followings:

 1. The largest load in this system was a hot tub that consumed 164 KW electricity.
 2. The input temperature of the pump was equal to the Soil temperature in a depth of 100 Cm which was at least 6.9℃; however, the required underground temperature was 23℃, which was considered for other rooms except for the greenhouse that was considered to be 26℃.
 3. On the other hand, since the output temperature of the heat pump should have been higher than the room temperature but not more than room temperature +12 ℃, the output temperature was taken to be at most 35℃.


Since the output temperature of the other heat pumps was considered to be 35℃ and the required temperature for the hot tub was to be 50℃, another heat pump with an output temperature of at least 60℃ was considered in the final plan.
After careful calculations and considering different options and scenarios, the design team found out the best solution for positioning the pipe under the ground at a distance of 1m. This solution succeeded to reach the value of 11.7 for the COP. This meant that it was possible to produce 11.7 times more heat with the same cost paid for the electricity consumption. In other words, by consuming 1 kW electricity, it was possible to produce 11 KW heat.
This project took about one month and according to the calculations, the design could lead to a considerable reduction in the electrical power consumption of the system and its cost and based on that, the client started its installation through a local company.

B. Lee
April 30, 2018
Mechanical Engineering