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