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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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It is also possible to delete the chiller and use the heat pump as a chiller in the summer, by implementing a dry cooler on the condenser side of the heat pump. The heat pump will extract cooling from the ambient air and decrease its temperature to the required temperature for HT cooling.
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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.
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If the BTES system is too cold the following things can be done:
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.
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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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:
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.
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
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Free cooling
Controls: default without all bells and whistles but with the boiler and chiller
Boiler and chiller can be removed, …
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A dry cooler in combination with the heat pump can be used to actively store cooling in the BTES system. The heat pump will extract cooling from the ambient air via the dry cooler, meanwhile supplying the cooling to store it in the BTES system.
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If the dry cooler on the condenser side is combined with a BTES bypass, the BTES system can be limited meanwhile still delivering the necessary cooling.
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A dry cooler can also be used to directly deliver the required cooling instead of the BTES system. This is only possible if the temperature outside is low enough to deliver the required cooling, which is in most cases almost never. In this case, cooling is required when the outside temperature is low enough to deliver 14°C. When the outside temperature is that low, cooling is seldom required.
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The template is standardised with a boiler and a chiller, but it can easily be removed if it's not required. More information on BTES, heat pump, boiler and dry coolers can be found in:
Controls
Controls: default without all bells and whistles but with the boiler and chiller
HT cooling + HT and LT heating separate
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