modelISO9806HeatLoss

Calculate the heat loss of a PVT collector using ISO9806:2017

Extends from IDEAS.Fluid.SolarCollectors.BaseClasses.EN12975HeatLoss.

Information

This component computes the heat loss from a solar thermal or PVT collector according to ISO 9806:2017. It builds on the structure of the IDEAS.Fluid.SolarCollectors.BaseClasses.EN12975HeatLoss model, but extends it with the wind‑ and long‑wave irradiance‑dependent loss mechanisms defined in ISO 9806:2017.

The base EN12975HeatLoss model includes only the linear (a1) and quadratic (a2) temperature‑difference heat‑loss terms from EN 12975. These describe the main convective and radiative losses of glazed collectors, but they do not account for wind‑driven or long‑wave radiation effects.

The ISO 9806:2017 quasi‑dynamic formulation adds the additional coefficients used here to represent wind‑dependent heat loss and long‑wave irradiance exchange. These effects are essential for accurately modeling unglazed collectors, where wind and sky radiation strongly influence thermal losses.

The thermal losses in the extended model are calculated for each segment i ∈ {1, ..., nseg} as:

Qlos,i = Ac / nseg · [ a1 · ΔTi + a2 · (ΔTi)2 + a3 · ur · ΔTi + a4 · (EL − σ · Ta4) + a6 · ur · G + a7 · ur · (EL − σ · Ta4) + a8 · (ΔTi)4 ]

where:

  • ΔTi = Tm,i − Ta: temperature difference between the mean fluid temperature in segment i and the ambient temperature
  • a1: heat loss coefficient (W/m²·K)
  • a2: temperature dependence of the heat loss coefficient (W/m²·K²)
  • a3: wind dependence of the heat loss coefficient (J/m³·K)
  • a4: sky long-wave irradiance dependence
  • a6: wind dependence of thermal zero-loss efficiency (s/m)
  • a7: wind dependence of long-wave exchange (W/m²·K⁴)
  • a8: higher-order radiation loss coefficient (W/m²·K⁴)
  • ur: wind speed normal to the collector plane
  • EL: long-wave irradiance from the sky
  • G: global solar irradiance on the tilted collector plane
  • Ta: ambient air temperature
  • σ: Stefan–Boltzmann constant (5.67×10⁻⁸ W/m²·K⁴)

This model captures additional wind- and long‑wave irradiance‑dependent heat‑loss mechanisms defined in ISO 9806:2017, allowing the collector performance to be represented more realistically under varying outdoor conditions than when using only the EN 12975 a1 and a2 terms.

Implementation Notes

The heat-loss block inherits from IDEAS.Fluid.SolarCollectors.BaseClasses.EN12975HeatLoss to reuse its interface and segment-wise structure. Only the heat‑loss equations and parameters are replaced to match the ISO 9806:2017 formulation.

References

  • ISO 9806:2017. Solar thermal collectors — Test methods. ISO.

    • Parameters

    TypeNameDefaultDescription
    Modelica.Units.SI.CoefficientOfHeatTransfera1Linear heat loss coefficient
    Reala2Quadratic heat loss coefficient
    Reala3Wind speed dependence of heat loss
    Modelica.Units.SI.DimensionlessRatioa4Sky long-wave irradiance dependence
    Reala6Wind speed dependence of thermal zero-loss efficiency
    Reala7Wind speed dependence of IR radiation exchange
    Reala8Radiation losses

    Components

    TypeNameDefaultDescription
    Modelica.Blocks.Interfaces.RealInputwinSpePlaWind speed parallel to collector plane
    Modelica.Blocks.Interfaces.RealInputHGloTilGlobal irradiance on the tilted plane
    Modelica.Blocks.Interfaces.RealInputHHorIRLong-wave (sky) irradiance [W/m2]

    Revisions

    • March 11, 2026, by Lone Meertens:
      Updated thermal formulation from ISO 9806:2013 to ISO 9806:2017. This is for #1473.
    • July 7, 2025, by Lone Meertens:
      First implementation PVT model. This is for #1436. .