Thermal Storage (EHT) Ground Source Heat Pump System

Thermal Storage (EHT) Ground Source Heat Pump System

Problems in the Promotion and Application of Shallow Ground Source Heat Pump Technology

After years of application, there are many problems with ground source heat pumps, but they are mainly manifested as:

1) Southern widespread heat accumulation

Performance: Underground heat dissipation becomes increasingly difficult in summer, and cooling towers are overloaded. The indoor temperature cannot be lowered. Even insufficient heating in winter.

2) Cold accumulation is common in the north

Performance: Underground heating in winter cannot meet the heating demand, indoor temperature cannot meet the requirements, or shutdown protection is required.

The root cause of the problem:

1. Incorrect interpretation of thermal property test data.

Under different load rate conditions, the heat exchange value varies. The lower the load rate, the greater the heat exchange value. It is necessary to combine it with the actual load rate of the building to determine the final value. Therefore, the accidental success of a certain project may be misleading.

2. Imbalance between heat dissipation and extraction. In the north, the heat generated by summer cooling is stored, resulting in a continuous decrease in ground temperature, which is increasingly insufficient to support the heating demand in winter; In the south, the heat generated by summer cooling is increasingly unable to be stored underground, resulting in a continuous rise in ground temperature and the inability of cooling towers to complete heat dissipation even when operating at overload.

3. The design quantity of the cooling tower is insufficient. The impact is limited in the north, with projects in the south being particularly evident.

4. Insufficient spacing between wells. All thermal property testing guidance data is based on the premise of safe spacing, and the testing phase is infinite. Therefore, after compressing the spacing, the heat extracted will be compressed synchronously.

5. Small heat transfer capacity of a single well: Currently, PE small-diameter pipes are used as underground heat exchangers, which have the advantages of low cost and long service life. However, the disadvantage is that the heat transfer per linear meter is relatively small, which cannot meet the design requirements of linear meter heat transfer in limited sites and fixed spacing. Meanwhile, the drilling depth and pipe depth are affected by equipment and technology, usually only reaching a depth of 120 meters.

6. If the inclination of the well is large and the spacing is small, the heat transfer will be uneven. At present, the southern market still mainly relies on crude old-fashioned low-power drilling rigs, which have the advantage of low construction costs, but the disadvantage is limited drilling depth and large slope deviation, resulting in greater horizontal displacement and uneven heat transfer, and the actual heat transfer will be reduced. On the right is a comparison of different drilling rigs.

Solution:

1. Correctly define the calorific value. The heating power and predicted power for thermal property testing should be matched as much as possible, and it is best to generate load rate data automatically. At the same time, determine the final heat exchange value based on the determined well spacing.

2. By predicting the heat dissipation and extraction, if there is insufficient heat, it is necessary to increase the contribution of heat recovery and increase the source of heat, such as thermal storage; If the heat is abundant, it is necessary to reduce the contribution of heat recovery and try to form a closed loop underground.

3. Adopting the correct cooling tower design method to prevent summer overload.

4. Adhere to the 6-meter standard spacing and increase the drilling depth to solve the site problem.

5. Develop large-scale materials to enhance the heat transfer capacity per meter.

6. Increase spacing and use high-precision drilling machines to solve uneven underground heat transfer.

7. Integrating into the energy tower can increase system flexibility and also increase heating capacity. Energy towers can also provide heat supply during the transition season.