DUAL SOURCE systems in geothermal applications
A still little known heat pump usage is its use in hybrid applications. The meaning of "hybrid" leads to simultaneous, or intermittent use of multiple sources of exchange. Hybrid application generally occurs when several sources of different nature coexist, since usually one of them is hydrothermal (including geothermal) and an aerothermal type.
The reason for using a hybrid system is sought in the need or the opportunity to exploit the different characteristics of the different exchange systems. The case analyzed concerns the most used typology: a system consisting of a geothermal field coupled with an aerothermal exchanger.
Most geothermal systems use closed-loop vertical probes. They have almost universal application, they are relatively easy to design and are often the first and only geothermal option considered. However, barriers to their wider use are important.
- High cost or limited budget for drilling ( which is the largest part of the cost )
- Insufficient space to properly displace the entire probes field. Significant power plants require considerable spaces and these are not always available.
In both cases, we have an inadequate geothermal exchange source. The impasse can be effectively overcome by adopting the hybrid scheme, which through the aerothermal component fills the residual gap and allows the geothermal part to be used for its more productive use. As a further positive consequence, an important improvement in return on investment has to be emphasized.
Once the hybrid option has been chosen, the designer must adequately integrate the two different sources. The most rudimentary solution is to use two separate heat pumps. The first one dedicated to the geothermal circuit and the second to the aerothermal circuit. The disadvantages of this approach lie mainly in the higher cost to buy the units and above all to set up a regulation system that governs the coexistence of two systems with different characteristics. In addition, the control system must be designed to maximize the performance of the entire system.
Fortunately, all this is already an integral part of the COMPOUND DUAL SOURCE units!
- Only one unit can simultaneously handle both plant types.
- It is not necessary to adopt an external regulation system as the COMPOUND units are natively equipped with an internal adjustment system designed for this purpose.
- The WTMC control system that manages the COMPOUND units already has the algorithms needed to obtain the maximum efficiency of a hybrid system.