Automatic sizing

How the sized component variants automatically determine nominal volume flow and nominal power from the building's connection load - and when individual variants make sense

Overview

The consumer components come in two variants:

  • sized (auto-sized) – nominal volume flow and nominal power are determined automatically from the connection load of the respective building
  • individual – all nominal values are entered by hand

Sized variants exist for the simple heat exchanger, the transfer station and the source-side heat pump.

Recommendation: use the sized variants almost always. A single plant can thereby be assigned to all consumers of the network – from the single-family house to the commercial operation – and every transfer station is automatically sized to match its building.

What is computed automatically

The automatic sizing takes place when the simulation model is generated, individually for each consumer node. The nominal volume flow follows from the building’s connection load and the nominal temperature difference of the network:

V˙nom=Pconnectionρ⋅cp⋅ΔTnetwork\dot V_{nom} = \frac{P_{connection}}{\rho \cdot c_p \cdot \Delta T_{network}}

with the density ρ\rho and the heat capacity cpc_p of the network fluid. Depending on the component, further quantities are added:

Component (sized)Determined automatically
Simple heat exchangerNominal volume flow
Transfer stationNominal volume flow and nominal heating power (= connection load)
Source-side heat pumpNominal volume flow and maximum heating power (from the building demand; for heat pump consumers corrected by the COP, since only the evaporator power is extracted from the network)

Only the parameters that do not depend on the building remain to be set by the user – in particular the nominal pressure loss as well as model-specific quantities such as the logarithmic temperature difference of the transfer station or the COP polynomial of the heat pump.

Data sources

Thus the sizing of the transfer stations is automatically consistent with the pipe sizing: both start from the same spread.

In practice:

For an entire network, a single sized transfer-station plant is usually sufficient: assign it to all consumers, and every station sizes itself automatically based on the connection load of its building – from the single-family house to the commercial operation. You only need a separate plant per building size for the individual special cases further below.

When to use the individual variant?

The individual variants are intended for special cases:

  • Recalculation of a specific station with datasheet values (e.g. an existing transfer station with a known nominal power and known pressure loss)
  • Deviating sizing of individual consumers, e.g. deliberately over- or under-sized stations
  • Components without a building reference, e.g. a heat exchanger inside an energy-plant assembly for which there is no connection load

For individually parameterized consumers, a separate plant must be created and assigned per building size.

Notes

  • For sized components, entered values for nominal volume flow or nominal power are ignored – the automatically computed values are always decisive.
  • Check the temperature difference of the network: if the actual spread during operation deviates significantly from the nominal value, the automatically sized volume flows are correspondingly too large or too small.
  • Pipes and pumps are not sized automatically – pipes via the pipe sizing, pumps via the pump sizing.

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