Renewable Energy: Benefits, Issues, and Solutions for Using Geothermal Heat and Groundwater (Open Loop Method)

Geothermal energy and groundwater heat, which are renewable energies, are a heat source that is "cool in summer and warm in winter"

Generally speaking, earth temperatures tend to remain stable at around the annual average temperature of the region. Once you reach a depth of about 10m or more below the surface, you are less susceptible to temperature changes at the surface, and the temperature barely changes between summer and winter. Once you reach a depth of 200m or more, the temperature begins to rise due to geothermal influences. At depths between 10m and 200m, which is in between, a constant temperature is maintained throughout the year. Although it differs by region, in Honshu it is generally around 12-18°C.
This temperature is cooler than the outside temperature in summer and warmer than the outside temperature in winter. This is particularly excellent as a heat source for air conditioning, and by using it effectively, energy saving in air conditioning can be achieved.

Difference between closed loop and open loop (groundwater heat utilization)

There are various methods for utilizing geothermal energy, which is a renewable energy source, but the most common is the geothermal heat pump method, which uses a heat pump to recover geothermal heat and supply it at the required temperature. Geothermal heat pump methods are further classified into two types depending on the heat recovery method.

1. Closed loop method
Currently, this is the most common method in Japan. Pipes (U-tubes, etc.) for heat recovery are buried underground, and a refrigerant (antifreeze) is circulated through them to send heat to the heat pump. Since the refrigerant piping path is closed, this is called the closed loop method.

2. Open loop method (utilizing groundwater heat)
In this method, groundwater is pumped up without using a refrigerant, and is used as it is as a refrigerant to send groundwater heat to the heat pump. Since the groundwater is at almost the same temperature as the ground, it can also be used as a refrigerant. The groundwater that carried the heat is released (returned underground or discharged, etc.), so it is called an open loop method.


Closed loop and open loop (From the Geothermal Energy Promotion Association website)

Renewable energy: Is using geothermal and groundwater heat expensive? Here's why

As shown in the figure, geothermal heat pumps almost always refer to closed loop systems. They are attractive because they are highly energy-efficient and can be installed anywhere, even among renewable energies, and are a heat source that is expected to become more widespread as a national policy. However, it cannot be said that they are widely used, and the main reason for this is their high cost. The reasons why geothermal heat pumps, especially closed loop systems, are expensive are as follows:

1. The cost of burying pipes is extremely high
In order to indirectly capture geothermal heat using a refrigerant, it is necessary to circulate it underground for a longer distance than you might imagine. A rough calculation shows that a total underground extension of about 100m is required for a heating capacity of 10kW (about 66m² of an office). This excavation alone would cost several million yen, making it a very expensive form of air conditioning. Even if you take into account the reduction in electricity bills due to energy conservation, it will take more than 20 years to recover the investment, which is only a disadvantage economically. Currently, in order to overcome this, efforts are being made to reduce the excavation depth and bury the refrigerant horizontally, and subsidies are becoming more generous, but this still does not provide a fundamental solution.

2. There are few dedicated heat pumps
Heat pumps used for geothermal energy use are called "water-cooled" because they use liquid as a heat source, unlike the "air-cooled" types commonly used in air conditioners and freezers. There are few options for water-cooled types, especially in Japan, and there are only a handful of manufacturers that produce models suitable for geothermal energy use. The market is still immature, and the price of the machine itself is one of the factors that increases the cost.

The spread of geothermal heat pumps (Ministry of the Environment, 2017)

On the other hand, groundwater heat utilization (open loop method) is the most profitable renewable energy.

In terms of profitability, it is very difficult to introduce a closed-loop system, but the open-loop system that utilizes groundwater heat is a more profitable system than other renewable energy sources.The secret is as follows.

1. Drilling costs are lower than with the closed-loop method.
In contrast to the closed loop, where the larger the facility capacity, the higher the drilling costs become, in the case of groundwater heat utilization, all that is required is to secure the required amount of water, so even for a large-capacity facility, only one well plus a few extra is required. This makes drilling costs overwhelmingly cheaper, and keeps implementation costs down.

2. More efficient than the closed loop method
In the closed loop system, in order to balance drilling costs and thermal efficiency, the refrigerant temperature never reaches the same temperature as the ground temperature. Therefore, although it is desirable to utilize heat at around 15°C, a difference of several degrees occurs, and thermal efficiency does not increase fully. In contrast, when groundwater is used, the ground temperature is supplied to the heat pump as it is, so there is no temperature loss and efficiency can be maximized.

3. Groundwater can be reused after it has been used for heat
After the heat renovation, the groundwater can be used for watering, sprinkling, melting snow, etc. By undergoing secondary treatment, it can also be used as grey water, which will help reduce water bills and ensure a lifeline in the event of a disaster.

For these reasons, groundwater heat utilization (open loop method) is an excellent method not only in terms of energy conservation effects but also in terms of profitability.

Drilling wells for groundwater heat utilization

Reasons why groundwater heat utilization is not progressing

As mentioned above, the open loop method has extremely excellent characteristics, but as can be seen from the fact that its adoption has not progressed, there are several issues that need to be addressed before it can be adopted.

1. Groundwater surveys and regulatory compliance
Groundwater reserves, water quality, and ground conditions vary from region to region, and investigations must be conducted in advance to determine whether it can be used as a heat source. However, investigations require expert know-how and are not easy.
Depending on the area, you may need to take into consideration subsidence, and use the facility in accordance with local ordinances established by the local government.

2. Machine wear due to water quality (scaling)
Groundwater contains many components such as calcium, magnesium, silica, and iron that adhere to pipes and heat exchangers. When these crystallize and adhere to the equipment, this is called scaling, and can lead to reduced performance, corrosion, and damage to the equipment. Removing these substances requires large-scale equipment and costs money, which negates the benefits of using groundwater heat.

3. Lack of compatible devices
Due to the scaling problem mentioned above, most water-cooled heat pumps have strict water quality standards, and cannot actually use groundwater directly. As a countermeasure, the dissolved components must be removed at great expense, or an additional heat exchanger must be designed to prevent groundwater from entering the heat pump directly. However, these methods result in heat and temperature losses, increasing equipment costs and negating the benefits of a closed loop. For this reason, groundwater heat utilization has only been carried out in areas with extremely good water quality.

Pipes blocked by scaling

Making groundwater heat available to more people

We have been developing various technologies and making breakthroughs to solve the problems of using groundwater heat and to enable more people to enjoy the benefits of using groundwater heat as a renewable energy source.

1. Free groundwater status survey and guarantee
We utilize our experience and know-how gained from many years of working on making groundwater potable, and even for facilities that have never had a well before, we can carry out a free water source survey, propose a groundwater heat utilization system and a well as a guarantee. This is a service that minimizes the burden and risk for those considering this.

2. The adoption of a highly durable heat exchanger and catalytic filter technology enables direct use of groundwater
Our heat pumps and heat exchangers are original products that use highly durable and chemical-resistant materials such as SUS316 and titanium, and have been used for many years in hard water areas where scaling is likely to occur. Furthermore, we have developed filters that use catalytic technology patented in eight countries around the world, and by assembling these into a series of systems, it is possible to pass water directly through the heat pump for many types of groundwater quality in Japan. Of course, there are limitations, but even in those cases, these can be overcome by installing a chemical cleaning mechanism or devising a system, and the products are so durable that they can be used even with hot spring water, wastewater, and salt water, which have harsher water quality.

3. Integrated design from heat source to equipment unit
Until now, well drilling companies, heat pump manufacturers, equipment design, etc. all worked individually, making it difficult to optimize and guarantee the system as a whole, which resulted in difficulties in installation and high equipment costs. Our company is able to design all of these systems together, allowing us to provide efficient proposals.

4. Support for applying for subsidies
Groundwater heat is also a form of renewable energy. Currently, subsidies are available for installation costs from the Ministry of Economy, Trade and Industry and the Ministry of the Environment. Our company provides support from preparing application documents to submitting reports, and the adoption rate so far is 100%. (As of February 2018)

Achieve energy savings with renewable energy! Make effective use of geothermal heat and groundwater heat

It is our hope that the use of groundwater heat, a renewable energy source with many benefits, will help the management and lives of many people.
Please consider utilizing groundwater heat for sustainable social development and sustainable business strategies.

en_USEnglish