Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 71

K −1 ); h p_f is the heat transfer coefficient absorber-fluid (Wm −2 K −1 ); S is
the solar radiation absorbed per unit area of the absorber (Wm −2 ); T f is the
temperature of the fluid (K); T g is the temperature of the glass cover (K);
T p is the temperature of the absorber (K); t is time (s); and v f is the fluid
velocity (ms −1 ).
Praene, Garde, and Lucas (2005) proposed a version of this model for direct
flowvacuumtubesdetailingtheenergyexchangesbetweentheabsorberand
the glass envelope and then performed a sensitivity analysis of the collector
parameters, such as the exchange coefficients and thermal capacity.
Bourdoukan et al. (2008) presented a model for vacuum tube collectors
with heat pipes.
2.2.2.3 Thermal Storage Tanks
Both short-term thermal storage and long-term (seasonal) storage concepts
are in development for use in solar systems. In the case of “short-term”
thermal storage (i.e., hours to days), the use of water as a storage medium
has been shown to be a readily available, cost-effective solution. It is
important however, to ensure that the storage system is designed to
maximize available energy and exergy by avoiding mixing and promoting
stratification. The development and characterization of a new multitank,
sequentially stratified thermal storage for use in medium-sized solar
domestic hot water heating systems is described by Cruickshank and
Harrison(2008,2010).Thisworkdemonstratedmodular,scalable,low-cost
thermal storage for water heating systems, but still requires further
development for use in combi-systems in low-energy buildings.
Producing domestic hot water (DHW) using solar energy is the most
common application for solar thermal collectors. A typical solar domestic
hot water system consists of a solar thermal collector, a circulating pump,
and a hot water storage tank as shown in Figure 2.20 .