1. Environmental Thermal Engineering
Lecture # 9
Min soo Kim
Mechanical & Aerospace Engineering

2. Refrigerating System Application
Lecture Supplementary Data
Refrigerating System Application
Ex) ice thermal storage system, geothermal heat pumps,
Refrigeration System using CO2

3. Ice Thermal Storage System
[빙축열 설치 사례(ASEM 컨벤션센타 33,000RTH)]

4. Ice Thermal Storage System
Introduction
In midnight (22:00∼08:00), refrigerator operates with cheap midnight electric power and stores coldness in ice storage tank, then using them for cooling in daytime. It can reduce operating hours in daytime, so driving cost is much cheaper than other systems.

5. Ice Thermal Storage System
Ice Thermal Storage – Thermal Storage using ice
Ice
Latent energy, so system is compact
Most feasible for small and moderate thermal storage systems
Less efficient as the leaving water temperature is reduced
Requires better insulation
※ Reducing delivery temperatures, so as to reduce duct sizes and fan expenses as well as do a better job at dehumidifying has encouraged the use of ice storage systems.
Other example) Chilled Water
Sensible storage
Less expensive per unit volume of storage
Most feasible for large thermal storage systems
Requires large storage tanks

6. Principle of Ice Thermal Storage System

7. Characteristics of Ice Thermal Storage System
Economic ▶ power cost reduction, power-saving effect caused by using cheap midnight electric power. High efficiency ▶ confident cooling system with cold ice wind.
▶ maximizing efficiency by controlling calorific value in heat storage tank with requirement
National ▶ national electric cost can be reduced by creating midnight load
Pollution free ▶ no pollution using clean fuel electricity.
Adaptable ▶ good adaptability for load change in future with enlargement and alteration  

8. Operating method of Ice Thermal Storage System
Midnight operation
(ice making operation)
Daytime operation
(cooling operation)
Operation in midnight is for ice making part. In this part, just outdoor unit and heat storage tank are operated. Refrigerant from outdoor unit as below zero temperature flows through coil in heat storage tank and makes ice around coil.
Operation in daytime is for cooling part with ice in heat storage tank made in midnight. In this part, just heat storage tank and indoor unit are operated. Water passing through ice in heat storage tank become cool and go into indoor unit, so make pleasant cooling.

9. Applications Commercial office buildings Convention centers
District cooling
Theaters
Retail
Institutional
Healthcare
Worship facilities
School

10. Geothermal Heat Pumps

11. What is Geothermal? Heat of the Earth [Geo (Earth) + Thermal (Heat)].
The majority of the available energy on this planet is heat energy, or thermal.
The six miles of the Earth’s crust contains 50,000 times as much energy as the
fossil fuels oil, coal and gas.
Geothermal power plant at the Geysers,
California, USA, the largest dry steam
production field in the world

12. What is geothermal heat pump?
Operates on the same principle as an air-conditioner or air-source heat pump.
Instead of transferring heat with the outside air, geothermal exchange system uses the
earth as its heat source of heat sink.
The earth connection is either a series of buried pipes (closed loop) or water wells
(open loop).
GHPs don’t create heat; they move it from one area to another.

13. Residential Geo Exchange System
Geothermal heat pump
Cooled air
is distributed
through the
house via
ductwork
Room air
returns to
air handler
Hot outside air
temperatures
Relatively cool
ground
In cold zone,
refrigerant
absorbs heat
from circulating
interior air
Note the absence of visible
outdoor equipment
Hot refrigerant flows
through coils, releasing
heat to cooler water
in ground loop
Ground loop
releases heat
to cool earth
Ground loop releases
heat to cool earth
Compressor
Residential Geo Exchange System
(Cooling Mode)

14. Geothermal heat pump
Cooling Mode
(13℃)
(18℃)

15. Residential Geo Exchange System
Geothermal heat pump
Warmed air
is distributed
through the
house via
ductwork
Room air
returns to
air handler
Cold outside air
temperatures
Relatively warm
ground
In hot zone,
refrigerant
gives up heat
to circulating
interior air
Ground loop
absorbs heat
from warm
earth
Ground loop absorbs
heat from warm earth
Compressor
Cold refrigerant flows
through coils, absorbing
heat from warmer water
in ground loop
Residential Geo Exchange System
(Heating Mode)

16. Geothermal heat pump
Heating Mode
(8.9℃)
(6.7℃)

17. Ground Coupled Heat Pump (Closed loop heat pumps)
Types of GHP systems
Ground Coupled Heat Pump (Closed loop heat pumps)
Horizontal
Vertical
Slinky

18. Groundwater Heat Pump (Open loop heat pumps)
Types of GHP systems
Groundwater Heat Pump (Open loop heat pumps)
Two well
Single well

19. Surface Water Heat Pump (Lake or pond loop heat pumps)
Types of GHP systems
Surface Water Heat Pump (Lake or pond loop heat pumps)
Indirect
direct

20. Benefits of GHP systems
Energy efficient – 25 ~ 50% better than any other HVAC system.
Low operating cost.
design flexibility.
Low environmental impact.
Low maintenance
Durability

21. Refrigeration System using CO2

22. CO2 - BACKGROUND The Ozone Story 1 “The ozone layer is a thin layer of
ozone in the atmosphere,
kilometers above the earth.”
“The ozone layer absorbs most of
the harmful ultraviolet-B (UV-B)
radiation from the sun.”
“Wonder gas” CFCs were invented
in 1928 for commercial applications.

23. CO2 - BACKGROUND The Ozone Story 2 CO2 - BACKGROUND
“...use of CFCs increases rapidly...”
“Scientists discover a link between
CFCs and ozone layer depletion.”
“If the ozone layer depletes, more
harmful UV-B radiation will reach the
earth through the damaged ozone
layer.”

24. CO2 - BACKGROUND The Ozone Story 3 CO2 - BACKGROUND
“In 1978, the United States of America,
Canada, Sweden and Norway ban the
use of CFCs in aerosols.”
“Parties agree to completely phase out
CFCs by the year 2000, and to establish
a Multilateral Fund to assist developing
countries. US$240 million was allocated
for ”
“In 1992, it was decided that the
developed countries phase out
HCFCs by 2030, freeze methyl
bromide by 1995 and that the
phase out of CFCs be brought
forward to 1996.”

25. CO2 - BACKGROUND The Global Warming Process GLOBAL WARMING
Global Temperature
Change( )
Green Gas

26. CO2 - BACKGROUND Preservation Measures of Ozone Layer Destruction
Prohibition on use of high Ozone depletion potential refrigerant
(CFC, HCFC)
Development of alternative refrigerant (HFC)
Replacement of natural refrigerant carbon dioxide (CO2), hydrocarbon (HC), ammonia (NH3), water, air etc.

27. CO2 - BACKGROUND Carbon Dioxide (CO2) Refrigerant Advantages
Not toxic, Odorless, Non flammable, Non explosive
Global Warming Potential(GWP) : 1
Ozone Depletion Potential(ODP) : 0
Large refrigeration capacity, Small compression ratio
Possibility of device weight lightening,
availability with low price
Good suitability with metal material
Advantages
Low critical temperature(31 ℃), high working pressure
Disadvantages

28. CO2 - Property cf. Table. Thermophysical properties of carbon dioxide
Property Value
Chemical formula CO2
Molecular weight (kg/kmol) †
Critical temperature (K) †
Critical pressure (MPa) †
Critical density (kg/m3) †
Normal boiling temperature (K) †
†: McLinden et al.(1998)
Table. Thermophysical properties of carbon dioxide
cf.

29. CO2 - Property Fig. Saturation Pressure
Fig. Volumetric Cooling Capacity

30. CO2 - Property Heat Rejection Temperature Profile Compression Process
“Gliding” temperature gives small approach
Low pressure ratio gives high efficiency

31. CO2 Circuit

32. CO2 Heat Transfer HEAT TRANSFER CHARACTERISTICS OF CO2
(Experimental Study)
Gas cooler:
High performance heat exchanger
Evaporator:
Compressor:
High efficiency and low leakage
Accumulator tank integrated with inner heat exchanger
and Expansion Valve
1. An experimental study on the
characteristics of evaporation
heat transfer of carbon dioxide 2.
An experimental study on
heat transfer characteristics
during gas cooling process
of carbon dioxide
Gas cooler:
High performance heat exchanger

33. (Evaporation Test at SNU)
CO2 Heat Transfer
View of Test Rig
(Evaporation Test at SNU)
Preheater
Test section T
Heat exchanger`
Subcooler
Reservoir
Pressure
relief valve
Mass flow meter
CO2
Pump
Syringe pump

34. CO2 Heat Transfer View of Test Rig (Gas Cooling Test at SNU) Hot Bath
Magnetic
Gear Pump
Liquid
Receiver
Subcooler
Cool Bath
Mass Flow Meter
Preheater
Heat
Exchanger
Charging
Port
Pressure
Relief Valve
Strainer
Water
Circulation Pump
Hot Bath
Test Section (8 Subsections)

35. INFLUENCE OF INLET PRESSURE
CO2 Heat Transfer
Fig. P = 8.0 MPa
INFLUENCE OF MASS FLUX
INFLUENCE OF INLET PRESSURE
Fig. G = 337 kg/m2s

36. CO2 Heat Pump System Schematic Diagram of Experimental
Setup for CO2 Vapor Compressor System
Metering
Condenser/Gas Cooler
Evaporator
Compressor
Expansion Valve
Mass
Flow Meter
Liquid Receiver
Heat Exchanger
Internal
Pump
Heater
Reservoir
Heat
Exchanger
Chiller T P DP 1 2 4 5 6 3

37. CO2 Applications PRESENT APPLICATIONS FOR TRANSCRITICAL CO2 CYCLE
HEAT PUMP (HOT WATER HEATER, AIR HEATING SYSTEM)
VEHICLE AIR CONDITIONING

38. CO2 Applications
VEHICLE AIR CONDITIONING

39. CO2 Applications
VEHICLE AIR CONDITIONING