| Summary: | Hot water thermal energy stores have the potential to improve and
extend the performance of many kinds of energy system. Waperature
stratification in the store is likely to affect the system's
efficiency. A basic but accurate computer model of the hot water
store under various inlet flow conditions is a requisite means of
assesiing promising applications of hot water storage by system
computer simulation techniques.
A microprocessor-controlled test facility has been constructed to
evaluate the performance of a 3m
3
hot water store under a wide range
of inlet flow conditions, using a temperature step input approach.
Three types of inlet/outlet ports have been examined: horizontal,
vertical and distributors. The results show that two distinct
regions evolve within the store: a fully-mixed region adjacent to
the inlet port and a region of smooth 'plug-flow' in the remaining
volume of the store. The performance of the store is shown to be
defined by the initial depth of the fully-mixed region which in turn
is seen to be closely related to the buoyancy and momentum fluxes of
the inlet flow.
The behAviour of the store and the evident correlations have enabled
a one-dimensional computer model of the store to be developed, taking
into account the turbulent mixing, vertical heat conduction and heat
losses to the surrounding areas. The model has been successfully
validated against the results from the step input experiments.
The model has been integrated into a computer simulated central
heating system which incorporates a hot water store. Predictions have
been made, using the simulation, of the energy savings which may be
achieved with the use of storage in comparison to a conventional
system, and an assessment has been made of the economic viability of
the application.
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