.Buildings.Fluid.SolarCollectors.BaseClasses.EN12975HeatLoss

Information

This component computes the heat loss from the solar thermal collector to the environment. It is designed anticipating ratings data collected in accordance with EN12975. A negative heat loss indicates that heat is being lost to the environment.

This model calculates the heat loss to the ambient, for each segment i ∈ {1, ..., n_seg} where n_seg is the number of segments, as

Q_los,i = A_c ⁄ n_seg (T_env-T_flu,i) (C₁ - C₂ (T_env-T_flu,i))

where C₁ > 0 is the heat loss coefficient from EN12975 ratings data, C₂ ≥ 0 is the temperature dependence of heat loss from EN12975 ratings data, A_c is the collector area, T_env is the environment temperature and T_flu,i is the fluid temperature in segment i ∈ {1, ..., n_seg}.

This model reduces the heat loss rate to 0 when the fluid temperature is within 1 Kelvin of the minimum temperature of the medium model. The calculation is performed using the Buildings.Utilities.Math.Functions.smoothHeaviside function.

Implementation

EN 12975 uses the arithmetic average temperature of the collector fluid inlet and outlet temperature to compute the heat loss (see Duffie and Beckmann, p. 293). However, unless the environment temperature that was present during the collector rating is known, which is not the case, one cannot compute a log mean temperature difference that would improve the UA calculation. Hence, this model is using the fluid temperature of each segment to compute the heat loss to the environment. If the arithmetic average temperature were used, then segments at the collector outlet could be cooled below the ambient temperature, which violates the 2nd law of Thermodynamics.

References

CEN 2006, European Standard 12975-1:2006, European Committee for Standardization

Revisions

• December 17, 2017, by Michael Wetter:
  Revised computation of heat loss.
  This is for issue 1100.
• Jan 16, 2012, by Peter Grant:
  First implementation