.Buildings.Fluid.SolarCollectors.BaseClasses.EN12975SolarGain

Information

This component computes the solar heat gain of the solar thermal collector. It only calculates the solar heat gain without considering the heat loss to the environment. This model performs calculations using ratings data from EN12975. The solar heat gain is calculated using Equation 559 in the referenced EnergyPlus documentation. The calculation is modified somewhat to use coefficients from EN12975.

The equation used to calculate solar gain is a modified version of Eq 559 from the EnergyPlus documentation. It is

QFlow[i] = Ac/nSeg FR(τα) (K (τα),Beam GBeam (1-shaCoe)+KDiff G Diff),

where QFlow[i] is the heat gained in each segment, A c is the area of the collector, nSeg is the number of segments in the collector, FR(τα) is the maximum efficiency of the collector, K(τα),Beam is the incidence angle modifier for beam radiation, GBeam is the current beam radiation on the collector, shaCoe is the shading coefficient, KDiff is the incidence angle modifier for diffuse radiation and GDiff is the diffuse radiation striking the surface.

The solar radiation equation indicates that the collector is divided into multiple segments. The number of segments used in the simulation is specified using the parameter nSeg. The area of an individual segment is identified by dividing the collector area by the total number of segments. The parameter shaCoe is used to define the percentage of the collector which is shaded. The main difference between this model and the ASHRAE model is the handling of diffuse radiation. The ASHRAE model contains calculated incidence angle modifiers for both sky and ground diffuse radiation while this model uses a coefficient from test data for diffuse radiation.

The incidence angle modifier for beam radiation is calculated using Eq 555 from the EnergyPlus documentation, as

K(τα),Beam=1+b0 (1/cos(θ)-1)+b1 (1/cos(θ)-1)2,

where K(τα),Beam is the incidence angle modifier for beam radiation, b0 is the first incidence angle modifier coefficient, θ is the incidence angle and b1 is the second incidence angle modifier coefficient.

This model reduces the heat gain rate to 0 W when the fluid temperature is within 1 degree C of the maximum temperature of the medium model. The calculation is performed using the Buildings.Utilities.Math.Functions.smoothHeaviside function.

References

EnergyPlus 7.0.0 Engineering Reference, October 13, 2011.
CEN 2006, European Standard 12975-1:2006, European Committee for Standardization

Contents

NameDescription
 MediumMedium in the system

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