Modifications to the TRNSYS Thermal Storage Tank Model
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Date
1994Author
Schmid, Michael
Publisher
University of Wisconsin-Madison
Metadata
Show full item recordAbstract
Solar energy is a time-dependent energy resource. The demands for energy are also time
dependent but in a different fashion than the solar energy supply. Consequently, energy has to
be stored if solar energy is to meet substantial portions of these energy needs. One of the
most economically feasible methods of solar storage is a fluid storage tank.
Before choosing the proper size and performance of a thermal fluid storage, it is important to
make calculations with the whole system. The TRNSYS software package has been used
extensively for thermal system analysis. It has a modular structure and consists of individual
subroutines which represent real physical devices or utility components. The components can
be connected together to form complex systems.
One of these components is the TYPE 4 multi-node model. The tank is modeled as N fully
mixed volume segments. The degree of temperature stratification, which increases the
effectiveness of a storage tank, is determined by the choice of N. Higher values of N result in
more stratification.
Although the current TYPE 4 tank model has been proven to be an accurate component, it
has some limitations. Outlet flows are fixed at the tank top (load flow) or tank bottom
(collector flow). The tank has always two inlets and two outlets. Inlet flow rate from one
source are automatically the outlet flow rate to the same source. The output of the losses to
the exhaust of a gas auxiliary heater are added to the losses to the environment. Only tanks of
circular cross section can be used.
The goal of this project is to modify the current TYPE 4 model. The new TYPE 4 includes
several new features which make the tank more versatile. Inlet and outlet positions can be
located anywhere in the tank. Inlet flow rates from one source do not have to be
automatically equal the outlet flow rate. Also the tank need not have two inlets and two
outlets; it can have less than four flows, and still satisfy a mass balance for the whole tank.
The losses to the exhaust flue of an optional gas auxiliary heater are output separately from the
losses to the environment. The cross section of the tank can be circular or rectangular. The
new model calculates the difference in static pressure between the top of the tank and each
inlet and outlet position. This option is needed to simulate a thermosiphon system. Further,
the conduction between the tank segments (nodes) is considered. Since tanks may destratify
more rapidly due to natural convection a user specified parameter has been added to the
conduction coefficient.
Subject
Thesis (Diplomarbeit)--University of Wisconsin--Madison, 1994.
Dissertations Academic Mechanical Engineering.
University of Wisconsin--Madison. College of Engineering.
Permanent Link
http://digital.library.wisc.edu/1793/7879Description
73pp.
Citation
Schmid, M. (1994). Modifications to the TRNSYS Thermal Storage Tank Model. Master's Thesis, University of Wisconsin-Madison.