Civil Engineering Reference
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provides a more accurate internal (source location) temperature than a
one-dimensional model.
To calculate the heat flow from the fluid to the system, the active BITES
system is treated as a heat exchanger (EERE, 2013). The source location
temperature is obtained using CTF/QTF time-series coefficients. One
important assumption is made for the heat exchanger treatment: the system
temperature along the length of the tubing/air channel is constant during
one time step. The NTU method is chosen for heat exchange calculation
between fluid and solid.
In TRNSYS, there are currently two models for hydronic systems:
quasi-analytical formulation and a two-dimensional finite difference model
(see Leaf House case study,
Chapter 7
). The quasi-analytical formulation is
developed to calculate the internal and surface temperatures of the radiant
systems based on room air and inlet water temperature and flow rate.
Three-dimensional heat transfer is taken into account.
2.2.3.4 Nomenclature
Variables
Specific heat ( )
Thermal capacitance ( )
Index of adjacent node or boundary surface
Mass flow rate (
)
Time
Temperature (K)
Thermal conductance per unit area (
)
Conductance per meter length (
)
Conductance (
)
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