Page 17 - Low Temperature Energy Systems with Applications of Renewable Energy

6 Low-Temperature Energy Systems with Applications of Renewable Energy

On the basis of the information obtained and the process flow diagram, the relative
sizes of energy flows and losses are estimated and lists of main energy consumers are
compiled. In determining the power consumed by end-users, it is advisable to use addi-
tional meters or other measuring devices. In case of estimating electric power flows in
the absence of stationary meters, portable electric meters should be used, the applica-
tion of which does not require the breakdown of electrical networks.
In the process of inspecting the production site (a compressor shop, a refrigerator as
a whole), it is necessary to study all stages of the technological production process and
to calculate the balance of energy flows and materials at each stage. When determining
the flow rate of heat and cooling agents, refrigerants, and cooling water in the absence
of stationary meters and flow meters, it is expedient to use flow meters with external
high-frequency sensors, for which there is no need to be in direct contact with the
measured flow of substances. The information relating to the consumed and installed
capacity of the equipment (compressors, pumps, fans, heaters) can be obtained from
the passport data of the equipment manufacturers, but this information should be
used with caution as this equipment could be upgraded or reconstructed during oper-
ation. Also, one should take into account the nature of the production process (round
the clock, continuous or discrete with a certain period); technicians, technologists, op-
erators and process managers are the ones best able to answer these questions.
After the identification of main energy consumers, it is desirable to carry out an
assessment of energy consumed. If consumers are particularly large or complex,
then further distribution of energy consumption is required to improve the quality of
energy efficiency measures.

1.4 Energy-saving cooling and heat pump systems

1.4.1 Physical principles of heat pumps and cooling systems

Thermodynamic principles of heating and cooling require that work must be per-
formed on a system that transfers heat from a body with a lower temperature to a
body with a higher temperature, in accordance with the Second Law of thermody-
namics [12,13]. In the engineering device performing this task, the thermodynamic
properties of a working medium are changed during the processes of decreasing and
increasing the temperature.
Lowering the temperature of a working fluid in refrigeration machines may be
effected by using various thermodynamic processes, such as: (1) the Joule-
Thompson effect, i.e., a flow throttling valve; (2) Ranque-Hilsch vortex tube, i.e., a
means of producing a cold and a hot stream from a compressed gas; (3) an expansion
process performing external work; (4) the Peltier effect, i.e., a thermoelectric phenom-
enon; (5) the magneto-caloric effect, i.e., adiabatic demagnetization; and (6) gas
desorption. The first one, namely, a throttle valve, is the simplest and the most
commonly used in practical vapor-compression systems.