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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 and others, 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. The system with all options is visualised in the figure below.

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  1. BTES 1.0

  2. Heat Pump (HP)

  3. Boiler

  4. Chiller

  5. Low Temperature (LT) heating equivalent end-unit

  6. High Temperature (HT) cooling equivalent end-unit

  7. Hot storage vessel

  8. Cold storage vessel

  9. Dry Cooler (DC) used in different ways

To optimise the system, the user should first check if the BTES system cant deliver more cooling to the system than it already does, and check if the heat pump cant deliver more heating. So the first step is to optimise the heating and cooling contribution of the heat pump and BTES system. More information on hydraulic configurations can be found in Hybrid production Heating.

If for instance there is a lot of simultaneous heating and cooling, it might be more optimal to bypass the BTES system. In this case, the heating and cooling produced by the heat pump will both be used directly instead of using indirect cooling by first storing the cold produced by the heat pump inside the BTES system. Because less energy is stored in the BTES, the thermal losses decrease as well.

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After the system is optimised by increasing the BTES and/or the heat pump contribution, the thermal balance of the BTES system should be optimised. To clarify all the different options, the BTES system is deemed either too cold or too hot.

BTES too cold

If the BTES system is too cold the following things can be done:

  1. If there is no dry cooler or any regeneration unit available, the heat pump can be limited in storing cooling inside the BTES system. This option is suboptimal because the heat pump is a preferable production unit. If the heat pump is limited, it won’t deliver anymore heating to the building, resulting in a lower heating contribution of the heat pump and a higher contribution of the boiler.

  2. A dry cooler or any other regeneration unit can be used to release the excess cooling to the ambient air instead of storing it in the BTES system. In this case, the heat pump sort of works like an Air Source Heat Pump (ASHP) instead of a Ground Source Heat Pump (GSHP).

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  3. A dry cooler is used to release the excess heat stored in the BTES system when there is no cooling demand.

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BTES too hot

If the BTES system is too hot the following things can be done:

  1. If there is no dry cooler or any regeneration unit available, the BTES system can be limited in supplying cooling to the building. This option is suboptimal because the cold used from the BTES system is prefered over the produced cooling by the chiller. If the BTES system is limited, it won’t deliver anymore cooling to the building, resulting in a lower cooling contribution of the BTES system and a higher contribution of the chiller.

  2. A dry cooler or any other regeneration unit can be used to deposit cooling from the ambient air in in the BTES system (which is the same as blowing away the excess heat inside the BTES system).

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Notice that implementing a dry cooler between the cold thermal store and the BTES system increases the flexibility of the installation because it can be used to prevent a BTES which is too cold or too hot (option 2 in both cases).

Free cooling

Controls: default without all bells and whistles but with the boiler and chiller

Boiler and chiller can be removed, …

More information on BTES BC, HP, boiler, chiller, configurations

HT cooling + HT and LT heating separate

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