A recent focal point of solar domestic hot water research has been on cost reduction. The market share of SDHW systems can only increase if they are less expensive and simpler to install. Because the heat exchanger commonly included in SDHW systems represents both a significant cost and a significant thermal performance penalty, it is a good candidate for replacement or removal. However, the decision to remove the heat exchanger from the system requires that some other method be used to protect the system from freezing temperatures. While many technologies have been proposed as solutions to the freeze protection problem, less research has been focused on characterizing the locations in which freeze protection needs to be a concern. This paper proposes that the piping to and from the collector is the critical feature of an SDHW system with regards to freeze protection. The collector itself is a fairly well insulated box. The piping, however, is more difficult to protect. Insulation is difficult to form around elbows and T-pieces while long sections are well exposed to wind. Both steady state and transient models are developed and verified against experimental and theoretical results. The models are then used to predict the amount of time required to form an ice blockage in a section of pipe exposed to extreme ambient conditions. Various pipe diameters and insulation levels are studied. The range of pipes studied is from 3/8" pipe with 3/8" insulation to 1" pipe with 2" insulation.
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