.Buildings.Fluid.SolarCollectors.BaseClasses.ASHRAEHeatLoss

Information

This component computes the heat loss from the solar thermal collector to the environment. It is designed for use with ratings data collected in accordance with ASHRAE Standard 93. 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 = -slope A_c ⁄ n_seg (T_env-T_flu,i)

where slope < 0 is the slope for the heat loss, as specified in the 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

ASHRAE uses the collector fluid inlet temperature to compute the heat loss (see Duffie and Beckmann, p. 293). However, unless the environment temperature which 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.

References

J.A. Duffie and W.A. Beckman 2006, Solar Engineering of Thermal Processes (3rd Edition), John Wiley & Sons, Inc.
ASHRAE 93-2010 -- Methods of Testing to Determine the Thermal Performance of Solar Collectors (ANSI approved)

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