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The boiler in this example is demand controlled, more information on this control strategy can be found in Basic boiler controls. Furthermore the distribution circuits of every branch is an active mixing, which means no primary pump is needed. The boiler however has to have a large water content because the flow through the boiler is variable and in partial load this can be nearly zero. Templates for boilers with minimal flow rate can be found in Small water content (open header) and Header configuration.
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