Page 51 - Low Temperature Energy Systems with Applications of Renewable Energy

Principles and operation of refrigeration and heat pump systems 39

firstglance,solutionallowstheproblemsofenergysaving,reducingtheproductcost,etc.,to
be solved effectively. Such decisions are encouraged by financial circumstances as well; for
example, when different tariffs for electricity are set for over a 24-h period, it is profitable to
produce (accumulate) cold at night, and use it during the day.
Of course, in the above considerations, it is assumed that the requirements for the
modes of refrigeration processing or storage technology of food products, for air pa-
rameters in air conditioning systems, for characteristics of boiling processes, conden-
sation of a cooling agent in refrigeration units, etc. are not violated and are fulfilled,
even when using cooling systems with cold productivity being less than the peak
values. This aspect is very important because it can happen for certain businesses
that the cost of losses of food product and the lowering of its quality can exceed the
achieved energy saving on the total electricity consumption for the cold production.
Therefore, the design and operation of cooling systems with cold storage accumu-
lators requires careful calculation of the plans of the cooling system operation, the
sequence of refrigeration processing, the storage of various types of products (nominal
and for every day), heat loads for heat exchange equipment, heat flows from the envi-
ronment, necessary volumes of the accumulator (mass of an accumulated cooling
agent), dynamics of changes in the temperature of the cooling agent in the accumulator
and in the system of its circulation, kinetics of phase transformations in the cooling
agent and other characteristics of the cooling system.
Reducing the required amount of an accumulator can be achieved by not only cool-
ing a cooling agent, but also through use of the exo- or endo-thermic effects of phase
transformations (water-ice) or chemical reactions (aqueous solutions of crystallo-
hydrates). In air-conditioning systems, water-cooling machines that operate with un-
even loads are used. The choice and sizing of equipment relative to peak loads leads
to an increase in equipment productivity and the provision of comfortable conditions.
Cold accumulators and heat accumulators are used at peak loads in heating systems
(Fig. 1.21).

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Fig. 1.21 Thermal Battery™ cooling system consisting of Trane air-cooled chillers, Trane
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controls and Ice Bank energy storage tanks; photo by Trane, used with permission [31].