Thermal Systems

1. Heat Pumps

2. Introduction
• Introduction to Heat pump
• Parts of a Heat pump Working of Heat pump
• Thermodynamics Process Terms associated with Heat pump
• Application of Heat pump Types of Refrigerant
• Why CO2 ?
• Properties of CO 2 as a Refrigerant
• Advantages of heat pumps with CO2 refrigerant
• Conclusion

3. • A heat pump is a device that transfers heat energy from a heat source to a
heat sink against a temperature gradient. Heat pumps are designed to move
thermal energy opposite the direction of spontaneous heat flow. A heat
pump uses some amount of external high-grade energy to accomplish the
desired transfer of thermal energy from heat source to heat sink.

4. Parts of a heat pump
• Expansion Reversing valve
• Evaporator
• compressor
• Condenser

5. • The Refrigerant is the liquid/gaseous substance that circulates through the
heat pump alternately absorbing transporting and releasing heat. The
Reversing valve controls the direction of flow of the refrigerant in the heat
pump and changes the heat pump from heating to cooling mode or vice
versa.

6. • Working of heat pump Heat pumps mainly consists of operation Heating
cycle Cooling cycle Defrost cycle

7. THE HEATING CYCLE
• Working of heat pump During the heating cycle, heat is taken from outdoor
air and "pumped" indoors. The liquid refrigerant passes through the
expansion device, changing to a low-pressure liquid/vapour mixture. This
vapour passes through the reversing valve to the accumulator, which collects
any remaining liquid before the vapour enters the compressor. The reversing
valve sends the gas, which is now hot, to the indoor coil, which is the
condenser. Below this outdoor ambient temperature, the heat pump can
supply only part of the heat required to keep the living space comfortable,
and supplementary heat is required.

8. • Working of heat pump Cooling cycle The cycle described above is reversed
to cool the house during the summer. The unit takes heat out of the indoor
air and rejects it outside. As in the heating cycle, The liquid refrigerant
absorbs heat from the indoor air and boils,. This vapour passes through the
reversing valve to the accumulator, which collects any remaining liquid, and
then to the compressor.. The heat from the hot gas is transferred to the
outdoor air, causing the refrigerant to condense into a liquid. This liquid
returns to the expansion device, and the cycle is repeated. The heat pump
also dehumidifies the indoor air

9. • Defrost cycle Working of heat pump If the outdoor temperature falls to near
or below freezing when the heat pump is operating in the heating mode,
moisture in the air passing over the outside coil will con dense and freeze on
it. This frost build up decreases the efficiency of the coil by reducing its
ability to transfer heat to the refrigerant While heat pump is cooling the air in
the ductwork. The heating system would normally warm this air as it is
distributed throughout the house .

10. THERMODYNAMIC PROCESS
• Reversed Carnot cycle Reversed Carnot cycle is an ideal refrigeration cycle
for constant temperature external heat source and heat sinks.

11. THERMODYNAMIC PROCESS
• Reverse Brayton cycle This is an important cycle frequently employed in gas
cycle refrigeration systems. This may be thought of as a modification of
reversed Carnot cycle, as the two isothermal processes of Carnot cycle are
replaced by two isobaric heat transfer processes.

12. Coefficient of performance (COP)
• Coefficient of performance (COP): Terms associated with heat pump It is
the ratio of heat removed from the substance to the work supplied COP= It
is a measure of a heat pump’s efficiency The Higher the COP, the more
efficient the heat pump works

13. • Btu/h (British thermal unit per hour) : is a measure of the output of a
heating or cooling system, in one hour Ton: is a measure of heat pump
capacity equivalent to 3.5 kW or 12000 Btu/h Balance point : is the
temperature at which the amount of heating provided by the heat pump
equals the amount of heat lost from the house Terms associated with heat
pump

14. HEATING OF INTERIOR
ENVIRONMENTS
• Heat pumps may be used also solely for heating the internal environment.
Space heating Sanitary water heating Process heating Dehumidification Heat
recovery Application of heat pump

15. COOLING OF INTERIOR
ENVIRONMENTS
• Heat pumps are mainly used for cooling the internal environment as an
alternative source over conventional system Air-conditions Cold storage
Industrial use Application of heat pump

16. Refrigerants
• Types of refrigerants Ammonia Sulphur-di-oxide Carbon-di-oxide Freon i)
Freon-12(R-12) ii)Freon-22(R-22)

17. Why CO 2 ??
• Carbon dioxide is very abundant in the environment. It is a natural
refrigerant known and used in the past. Carbon dioxide has an ozone
depletion potential (ODP) of zero . It has a low replacement cost. In
addition to its basic environmental properties, carbon dioxide is non- toxic. It
carries an A1 safety classification (the same as most fluorocarbon
refrigerants), indicating that it has low toxicity and is non-flammable

18. • It is an inert product, compatible with all common materials encountered in
a refrigerating circuit, both metals and plastics or elastomers. the density of
carbon dioxide is around 1.98 kg/m 3 , about 1.67 times that of air. high
working pressures At low concentrations, the gas is odourless high discharge
temperature NBP of CO2 is 195.4K Properties of CO 2 as a refrigerant

19. • No Fumes, odours and smoke Energy efficient The other challenge is that
CO2 refrigerant cycles operate at far higher pressure than standard vapour-
compression-cycle equipment A new generation of CO2 based heat pumps
could avoid the high global warming potential much higher temperatures
Advantages of heat pumps with (CO2) refrigerant

20. Conclusion
• The natural fluid Carbon Dioxide displays some excellent properties in the use as a
refrigerant in compression-type refrigerating or heat pump systems: it offers unequalled local
and ecological safety, widespread availability at low cost, with no need for recycling and
containment. Because of its low critical temperature (around 31 °C), CO2 does not compare
favourably against traditional refrigerants, as far as energy efficiency is concerned, when
simple theoretical cycle analyses are carried out. But this situation can be mitigated, and in
some cases completely reversed, by proper design of the system aimed at fully exploiting the
unique characteristics of CO2 and/or the exclusive features of transcritical cycles, which
bring about important factors that improve the practical performance of CO2 systems. A
widespread research activity is underway world-wide for the application of CO2 in many
areas with promising results, including mobile and residential air conditioning, heat pumps,
and water chillers, commercial and marine applications).