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solares energia
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Chapter 6Chapter 6
Solar Cooling SystemSolar Cooling SystemSolar Cooling SystemSolar Cooling System
Outline Outline
Overview
Solar space cooling and refrigeration
Review of refrigeration cycles
Calculation of cooling loads
Vapor-compression refrigeration cycle Vapor-compression refrigeration cycle
Absorption refrigeration cycle
Solar desiccant dehumidification
OverviewOverview
Solar cooling
At times when solar energy is most available (e.g. summer months), comfort cooling is most needed
Solar collector works more efficiently when ambient temperature is higher
Two principle methods
Refrigeration
Vapor-compression refrigeration cycle
Absorption refrigeration cycle
Evaporative cooling vaporization of moisture
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Power cycle Refrigeration/Heat pump cycle
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Ideal refrigeration cycle Carnot refrigeration cycle
CH
C
TT
T
=
max
CH TT
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Vapor-compression refrigeration system
Dry compression
Expansion valve
instead of turbine instead of turbine
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Vapor-compression refrigeration system
Evaporator ( : refrigeration capacity)
Compressor
41hh
m
Qin =&
&
hhWc =&
inQ&
Compressor
Condenser
Expansion valve
12hh
m
Wc =&
&
32hh
m
Qout =&
&
34hh =
12
41
/
/
hh
hh
mW
mQ
c
in
==
&&
&&
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Ideal vapor-compression refrigeration cycle
12s: isentropic compression
2s3: heat transfer out (constant p) 2s3: heat transfer out (constant p)
34: throttling process (adiabatic)
41: heat transfer in (constant p)
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
More realistic refrigeration cycle
CT =CH
C
TT
T
=
max
Solar space cooling and refrigerationSolar space cooling and refrigeration
Review of refrigeration/heat pump cycle
Actual vapor-compression refrigeration cycle
12:
23: HH TT >
0>s
23:
34: throttling process
41:
Superheated vapor condition
Subcooled liquid condition
HH TT >
CC TT
Solar space cooling and refrigerationSolar space cooling and refrigeration
Absorption process (Absorber)
Refrigerant + absorbent
exothermic
Review of refrigeration/heat pump cycle Absorption refrigeration
exothermic
Regeneration process (Generator)
Endothermic
Pumping liquid instead of compressing gas
Solar space cooling and refrigerationSolar space cooling and refrigeration
Calculation of cooling loads
Cooling requirement maintain the interior at a specified temperature and humidity
Consideration
Heat transfer through the building structure (windows, walls, roof)
Including solar load for unshaded/partially-shaded windows/walls
Heat gains resulting from infiltration/ventilation
Heat gains from internal sources
Usu. calculated on the basis of peak load
Solar space cooling and refrigerationSolar space cooling and refrigeration
Calculation of cooling loads
Heat transfer through windows/walls/roof:
Sensible cooling load due to infiltration and ventilation
Latent heat due to infiltration and ventilation
Solar space cooling and refrigerationSolar space cooling and refrigeration
Calculation of cooling loads
Example
Determine the cooling load for a building in Houston, Texas, on July 30th at solar noon.
Solar space cooling and refrigeration Solar space cooling and refrigeration
Vapor-compression refrigeration cycle
COP = Useful cooling energy
Net energy supplied by external sources
Solar space cooling and refrigeration Solar space cooling and refrigeration
Absorption refrigeration cycle
Common refrigerant-absorbent pair:
H2O LiBr
NH3 H2O
Solar space cooling and refrigeration Solar space cooling and refrigeration
Absorption refrigeration cycle
Ammonia-water refrigeration system
Solar space cooling and refrigeration Solar space cooling and refrigeration
Absorption refrigeration cycle
Solar space cooling and refrigeration Solar space cooling and refrigeration
Absorption refrigeration cycle
Solar desiccant dehumidificationSolar desiccant dehumidification
Desiccant air-conditioning
Address the issue of thermal comfort by modifying the water vapor content in a space
Sensible cooling cooling of the space air
Latent cooling control of the air humidity
Air dehumidification By cooling the air below its dew point and removing moisture by condensation
By adsorption through a desiccant material
Solar desiccant dehumidificationSolar desiccant dehumidification
Desiccant air-conditioning
Combination of solar desiccant system and vapor compression system Pre-treating ventilation air
Saving energy
Solar desiccant dehumidificationSolar desiccant dehumidification
Desiccant air-conditioning
Two types of desiccant system
Liquid desiccant cooling
Solid desiccant cooling