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The boiler will act as a top-up installation. This means that if the heat pumps are not able to reach the desired installation supply temperature, the boilers will turn on and increase the supply temperature to the required level. The major difference between connection the boilers via a shunt connection in the supply and connection the heat pump via shunt in the return line is whether the installation volume flow rate will be circulated completely through the heat pump’s storage tank. In cases of a variable flow system where the installation volume flow rate is limited, implementing heat pumps directly and the boilers via shunt might improve the relative contribution of the heat pump. However, this is very case dependant dependent and should be checked with simulations. A possible negative consequence is that the storage tank experiences a higher volume flow rate in design conditions, This could negatively affect the stratification of the buffer vessel and increase the amount of heat pump start/stops.
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