The BTES 1.0 templates are divided into different types of regime temperature combinations for heating and cooling end-units. To clarify this aspect the different templates are the following.
LT heating + HT cooling
Working principle
The working principle of a geothermal system is divided into two main operating conditions, winter and summer. Of course, if there is both heating and cooling demand at the same time, both conditions are active.
Winter
In the winter, when there is heating demand, the heat pump will supply heating to the building. When the heating provided by the heat pump is insufficient, the boiler will deliver the remaining required heating. While the heat pump is delivering heat, it’s also extracting heat from the BTES system on the evaporator side. Extracting heat is the same as injecting cold, so in this operating condition the BTES system will cool down.
BTES 1.0
Heat Pump (HP)
Boiler
Low Temperature (LT) heating equivalent end-unit
Hot storage vessel
Cold storage vessel
Summer
In the summer, when there is cooling demand, the cooling stored in the BTES system (in the winter) will be used to cool down the building. If the delivered cooling from the BTES system is insufficient, the chiller will deliver the remaining required cooling. When cooling is extracted from the BTES system en supplied to the building, the BTES system will heat up, increasing its overall temperature.
BTES 1.0
Chiller
High Temperature (HT) cooling equivalent end-unit
Thermal balance soil
The soil temperature without an ATES or BTES system would be almost constant throughout the year. If an ATES or BTES system is used, and we start in January, the temperature of the soil would gradually drop in the winter months because heat is extracted from the soil (= injecting cold). In the summer months, the soil temperature will gradually rise because the cold is extracted from the soil to cool down the building. After the summer, the winter comes again, meaning the temperature will drop again. This is visualised in the figure below.
If the same amount of cold is extracted from the soil, as there is injected, the temperature at the end of the year would be exactly the same as in the beginning. This is called a thermally balanced soil.
However, if more cold is injected than there is extracted, the temperature would gradually drop every year. This is visualised in the graph below which shows the soil temperature in a 3-year simulation. In this case, the BTES is after a few years too cold.
The same thing can be said if the extracted cold is larger than the injected cold. The temperature will gradually rise every year.
A thermal imbalance of the soil reduces the system efficiency of the system because of the increasing thermal losses in the soil and the lowered SCOP value of the heat pump. It can even lead to a thermal breakdown of the system, meaning no cold can be injected or extracted anymore.
For this reason, more options are available in the template to give the user some strategies to make sure the thermal balance is met with an optimal system efficiency.
BTES 1.0
Heat Pump (HP)
Boiler
Chiller
Low Temperature (LT) heating equivalent end-unit
High Temperature (HT) cooling equivalent end-unit
Hot storage vessel
Cold storage vessel
Dry Cooler (DC) used in different ways
HT cooling + HT and LT heating separate
HT cooling + HT and LT heating together
LT heating + LT and HT cooling separate
LT heating + LT and HT cooling together
HT and LT heating separate + LT and HT cooling separate
HT and LT heating together + LT and HT cooling separate
HT and LT heating separate + LT and HT cooling together
HT and LT heating together + LT and HT cooling together
