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ABSTRACT
solar air conditioning refers to any a
conditioning (cooling) system that uses solar powe
PRESENTATIONOFPAPERSONSOLARAIRCONDITIONING
Authors
NVH SRIRAM,
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This can be done through passive solar,solar
thermal energy conversion
and photovoltaic conversion (sun to electricity). The
U.S. Energy Independence and Security Act of
2007[1]created 2008 through 2012 funding for a
new solar air conditioning research and
development program, which should develop and
demonstrate multiple new technology innovationsand mass productioneconomies of scale. Solar air
conditioning will play an increasing role in zero
energy and energy design.
In particular, in hot and humid summers, an
important proportion of the overall electric power is
dedicated to satisfy air conditioner loads. Outdoor
weather conditions are crucial in determining
residential energy consumption for heating,
ventilation and air-conditioning (HVAC) household
appliances. In this paper we address the modeling of
outdoor weather conditions impact onpredominantly air conditioner residential load. The
main emphasis is on the temperature and humidity
segregated load influence where the socioeconomic
and life style of the consumer is isolated from the
load model. Important field data has been collected
for several hot and humid consecutive months
covering a wide range of outdoor temperature and
humidity. After recognizing that humidity can be
divided into three different comfort levels, three-
dimension analysis of the data have been conducted
and mathematical relations have been extracted to
represent the dependencies of the real power with
both humidity and temperature. The investigations
have shown the sensitivity of the load to
temperature and humidity to be in good compliance
with the expected natural load behavior.
Every air-conditioning system needs some fresh air
to provide adequate ventilation air required to
remove moisture, gases like ammonia and hydrogen
sulphide, disease organisms, and heat from
occupied spaces. However, natural ventilation is
difficult to control because urban areas outside air isoften polluted and cannot be supplied to inner
spaces before being filtered. Besides the high
electrical demand of refrigerant compression units
used by most air-conditioning systems, and fans
used to transport the cool air through the thermal
distribution system draw a significant amount of
electrical energy in comparison with electrical
energy used by the building thermal conditioning
systems. Part of this electricity heats the cooled air;
thereby add to the internal thermal cooling pe
load.
In addition, refrigerant compression has both dire
and indirect negative effects on the environment
both local and global scales. In seeking f
innovative air-conditioning systems that mainta
and improve indoor air quality under potentiamore demanding performance criteria witho
increasing environmental impact, this pap
presents radiant air-conditioning system which us
a solar-driven liquid desiccant evaporative cool
The paper describes the proposed solar-driven liqu
desiccant evaporative cooling system and t
method used for investigating its performance
providing coldwater for a radiant air-conditioni
system in Khartoum (Central Sudan). The results
the investigation show that the system can opera
in humid as well as dry climates and that employi
such a system reduces air-conditioning peelectrical demands as compared to vapo
compression systems.
Introduction
Air-conditioning has been achieved reliably a
efficiently over the last few decades due to t
popularity gained by vapour compression machinas a result of halogenated hydrocarbons discove
The need to conserve high grade energy a
reducing the harm effects of halogenat
hydrocarbons, such as; the contribution to t
Earths ozone layer depletion and global warmi
due to emissions of halogenated hydrocarbo
during production and use, necessitate explori
alternative techniques. Evaporative cooling, a ve
simple, robust and low cost cooling technolo
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basically achieved by evaporation of water in air is
one proposition. Evaporative water coolers (cooling
towers) are devices utilizing the direct contact
between water and atmospheric air to cool water by
evaporating part of the sprayed water in the air.
Despite its potential to reduce cooling energy and
peak energy demand, cooling towers are not widely
used in many areas because of their decliningcooling capacity
with increasing outdoor humidity.
In liquid desiccant evaporative cooling (LDEC)
process air is used, dehumidified by a desiccant
solution, to cool water by direct evaporative cooling
(both require no refrigerant). LDEC is considered to
be a modification of direct evaporative cooling that
can cater for different climates. Unlike vapor
compression cooling which rely on high energy
technology, desiccant evaporative cooling relies on
desiccant dehumidification (low energy technology)to provide dry air required for ventilation and
evaporative cooling. Solar energy or any other type
of energy that might otherwise be wasted provides
the heat energy required for regenerating the
desiccant used by the desiccant dehumidifier
during the cooling season (summer) and heating
the water circulated through the radiant system
during the heating season (winter). This provides
dry ventilation air and cold water for a radiant
system, and thereby gives a solution to thermal
environment control that significantly reduceselectrical energy demands, greenhouse gas
emissions and dependence on harmful refrigerants.
As an open heat driven cycle affording the
opportunity to utilize heat that might otherwise be
wasted, a liquid desiccant evaporative cooling cycle
can be coupled with solar heating to produce dry
ventilation air and cold water for a radiant system.
This can significantly reduce cooling electrical
energy demands in comparison with conventional
vapour compression refrigeration, and should in
theory be extremely environment friendly as it
eliminates greenhouse gas emissions and
dependence on harmful refrigerants. As it delivers
cold water and dry air at relatively high COP, solar-
operated liquid desiccant evaporative water cooling
would be cost effective. The objective of this paper
is to study the performance of a solar-driven
desiccant evaporative cooling system in providing
cold water for a radiant air-conditioning system in
Khartoum Sudan. In doing so, a computer progra
was used to simulate the solar-driven liqu
desiccant evaporative cooler. The comput
program was developed based on unit subroutin
constituting the solar-operated liquid desicca
evaporative cooling system components governi
equations.
System Description
The liquid desiccant evaporative water cooler, whi
is designed to serve as an open cycle absorptio
system operating with solar energy is show
schematically in. The cooler consists of nine maj
components: continuous fin tube type process a
pre-cooler, air-to water air cooler, an isotherm
vertical tube type falling film absorber, adiaba
packed bed tower regenerator, solution-to-soluti
strong solution pre-cooler and weak solution prheater, water-to-solution solution cooler, solutio
to-thermal fluid solution heater, solar collect
thermal fluid heater, counter-flow packed bed ty
evaporative water cooler and appropria
instruments for various measurements. Arab
numerals indicate working fluids states at speci
locations; thick solid lines represent air flow, th
solid and dashed lines represent solution and wat
flow respectively.
The liquid desiccant system is connected in a flo
arrangement that allows thermal fluid storage and
capable to work in two automatic modes as may
selected by the user. One automatic mode is for f
system operation in which all components includin
the thermal fluid storage circuit operate, while t
second is for solar heating only. In the full automa
mode, pump 1 pumps absorbent solution fro
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regenerator sump (state 13) through the solution-
to-solution heat exchanger where it is pre-cooled
by exchanging heat with cold solution leaving the
absorber sump. The solution then flows through the
solution-to-water heat exchanger where it is cooled
to state 9 by water from the evaporative water
cooler and supplied to the absorber distribution
system.
The cold solution to trickle down in counter flow to
air stream and collects in the absorber sump. A fan
draws ambient air through the air-to-air heat
exchanger where it is pre-cooled to state 2 and
through the air-to-water heat exchanger where it is
cooled to state 3 to the absorber chamber. In the
absorber, water vapour is removed from the
sensibly cooled process air entering the bottom of
the absorber (state 3) by being absorbed into the
absorbent solution. Part of the dehumidified air
leaving the absorber (state 4) is taken to facilitateventilation purposes while the remainder is brought
into direct contact with sprayed water in the
evaporative cooler. The temperature of the
absorbent solution in the absorber is maintained
constant using a water-to-solution heat exchanger
enclosed within the absorber chamber through
which cold water from the evaporative water cooler
is circulated. To maintain the liquid desiccant at the
proper concentration for moisture removal, pump 2
pumps weak solution from the absorber sump (state
10), through the solution-to solution heat exchangerwhere it is pre-heated to state 11 by recovering
heat from the hot solution leaving the regenerator.
The pre-heated solution is then pumped through
the solution-to-thermal fluid heat exchanger where
it is heated to the required regeneration
temperature (state 12). The hot solution then
trickles down the regenerator distribution system in
counter flow to atmospheric air entering at the
bottom of the regenerator. The vapour-pressure
difference between the ambient air and the hot
solution causes ambient air to absorb water vapour
from the solution (i.e. re-concentrate the absorbent
to state 13).
The hot air is discharged to the atmosphere while
the re-concentrated solution (state 13) is pumped
through the solution-to-solution pre-cooler and the
solution-to-water cooler to the absorber distribution
system. During solar heating, pump 4 supplies the
thermal fluid-solution heat exchanger with the
required amount of the hot thermal fluid from t
hot fluid storage tank. After it exchanges its he
with weak solution, the leaving warm solution
mixed with another amount of warm thermal flu
from the warm fluid storage tank and pump
through the solar collector heater to the hot therm
fluid storage tank. During night, pump 5 suppli
the thermal fluid-solution heat exchanger with trequired amount of hot thermal fluid from the h
thermal fluid storage and store the warm fluid in t
warm fluid storage tank. The regenerator and t
associated flow system and components are
similar towhat was shown at the absorber side. T
system regeneration side is shut down if the therm
fluid storage tank cannot supply thermal fluid
sufficiently high temperature or if the absorbe
solution concentration in the absorber pool ris
above a set limit. Psychometric cycle of process
flowing through the solar driven liquid desicca
evaporative water cooler employed solely to provicold water for a radiant system. Lines 1-2, 2
represent the path of the process air (ambient a
through the air-to-air and air-to-water he
exchangers. Line 3-4 represents the path throu
the absorber and line 4-5 the pass through t
evaporative water cooler.
Systems Simulation
The simulation process constitutes description of t
procedure used to model the system componenand a main program that integrates the
components. The main program calls the u
subroutines to link the components and form
complete cycle. Mass and energy governi
equations are written by taking each syste
component as a control volume and divide t
domain of interest into a finite number
computational cells using finite differen
technique. A mathematical solver solv
simultaneously the system components governi
equations.
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1) Active Solar Space Cooling
Solar space cooling is quite costly to implement. If
the solar system is used for space cooling only,
installed costs can run $4,000-$8,000 per ton. It is
best to use a solar system that serves more than
just the cooling needs of a house to maximize the
return on investment and not leave the system idle
when cooling is not required. Significant spaceheating and/or water heating can be accomplished
with the same equipment used for the solar cooling
system.
Figure3 Schematic of Solar Absorption Cooling
SystemT = system flow sequence
Solar-powered refrigerators
Solar-powered refrigerators are most commonly
used in the developing world to help
mitigate poverty and climate change. By
harnessing solar energy, these refrigerators are able
to keep perishable goods such as meat and dairy
cool in hot climates, and are used to keep much
needed vaccines at their appropriate temperature to
avoid spoilage. The portable devices can be
constructed with simple components and are perfect
for areas of the developing world where electricity isunreliable or non-existent. [1] Other solar-powered
refrigerators were already being employed in areas
ofAfrica which vary in size and technology, as well
as their impacts on the environment. The biggest
design challenge is the intermittency of sunshine
(only several hours per day) and the unreliability
(sometimes cloudy for days). Either batteries
(electric refrigerators) or phase-change material is
added to provide constant refrigeration.
History of solar refrigeration
"In developed countries, plug-in refrigerators w
backup generators store vaccines safely, but
developing countries, where electricity supplies ca
be unreliable, alternative refrigeration technologi
are required.[3]
Solar fridges were introduced in tdeveloping world to cut down on the use
kerosene or gas-powered absorption refrigerat
coolers which are the most common alternative
They are used for both vaccine storage a
household applications in areas without reliab
electrical supply because they have poor or no gr
electricity at all.[4] They burn a liter of kerosene p
day therefore requiring a constant supply of fu
which is costly and smelly, and are responsible f
the production of large amounts of carbon dioxid[5] They can also be difficult to adjust which c
result in the freezing of medicine.[6] There are twmain types of solar fridges that have been and a
currently being used, one that uses a battery an
more recently, one that does not.
Solar a/c using desiccants
Air can be passed over common, solid desiccan
(like silica gel or zeolite) to draw moisture from t
air to allow an efficient evaporative cooling cyc
The desiccant is then regenerated by using so
thermal energyto dry it out, in a cost-effective, lo
energy-consumption, continuously repeaticycle. A photovoltaic system can power a lo
energy air circulation fan, and a motor to slow
rotate a large disk filled with desiccant.
Energy recovery ventilation systems provide
controlled way of ventilating a home wh
minimizing energy loss. Air is passed through
"enthalpy wheel" (often using silica gel) to redu
the cost of heating ventilated air in the winter
transferring heat from the warm inside air bei
exhausted to the fresh (but cold) supply air. In t
summer, the inside air cools the warmer incomisupply air to reduce ventilation cooling costs.[3] Th
low-energy fan-and-motor ventilation system can
cost-effectively powered byphotovoltaics, w
enhanced natural convection exhaust up a so
chimney- the downward incoming air flow would
forced convection (advection).A desicca
like calcium chloride can be mixed with water
create an attractive recirculating waterfall, th
dehumidifies a room using solar thermal energy
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regenerate the liquid, and a PV-powered low-rate
water pump. (See Liquid Desiccant Waterfall for
attractive building dehumidification)The potential
for near-future exploitation of this type of innovative
solar-powered desiccant air conditioning technology
is great.
Active solar cooling wherein solar thermal collectors
provide input energy for a desiccant cooling system:
A packed column air-liquid contactor has been
studied in application to air dehumidification and
regeneration in solar air conditioning with
liquid desiccants. A theoretical model has been
developed to predict the performance of the device
under various operating conditions. Computer
simulations based on the model are presented
which indicate the practical range of air to liquid flux
ratios and associated changes in air humidity and
desiccant concentration. An experimental apparatushas been constructed and experiments performed
with monoethylene glycol (MEG) and lithium
bromide as desiccants. MEG experiments have
yielded inaccurate results and have pointed out
some practical problems associated with the use of
glycols. LiBr experiments show very good
agreement with the theoretical model. Preheating of
the air is shown to greatly enhance desiccant
regeneration. The packed column yields good
results as a dehumidifier/regenerator, provided
pressure drop can be reduced with the use ofsuitable packing.
Passive solar cooling
In this type of cooling solar thermal energy is not
used directly to create a cold environment or drive
any direct cooling processes. Instead, solar building
design aims at slowing the rate ofheat transfer into
a building in the summer, and improving the
removal of unwanted heat. It involves a good
understanding of the mechanisms ofheat
transfer: heat conduction, convective heat transfer,and thermal radiation, the latter primarily from
the sun.
For example, a sign of poor thermal design is an
attic that gets hotter in summer than the peak
outside air temperature. This can be significantly
reduced or eliminated with a cool roofor a green
roof, which can reduce the roof surface temperature
by 70 F (40 C) in summer. A radiant barrier and an
air gap below the roof will block about 97%
downward radiation from roof cladding heated
the sun.
Passive solar cooling is much easier to achieve
new construction than by adapting existi
buildings. There are many design specifics involve
in passive solar cooling. It is a primary element
designing a zero energy building in a hot climate.
Solar thermal cooling
Active solar cooling uses solar thermal collectors
provide thermal energy to drive thermally driv
chillers (usually adsorption or absorpti
chillers). The Sopogy concentrating solar therm
collector, for example, provides solar thermal he
by concentrating the suns energy on a collectio
tube and heating the recirculated heat transfer fluwithin the system. The generated heat is then us
in conjunction with absorption chillers to provide
renewable source of industrial cooling. The so
thermal energy system can be also used
produce hot water.
There are multiple alternatives to compressor-bas
chillers that can reduce energy consumption, wi
less noise and vibration.Solar thermal energy c
be used to efficiently cool in the summer, and al
heat domestic hot water and buildings in the winte
Single, double or triple iterative absorption coolincycles are used in different solar-thermal-cooli
system designs. The more cycles, the more efficie
they are.
Efficient absorption chillers require water of at lea
190 F (88 C). Common, inexpensive fla
plate solar thermal collectors only produce abo
160 F (71 C) water. In large scale installatio
there are several projects successful both technic
and economical in operation world wide includi
e.g. on the headquartes ofCaixa Geral
Depsitos in Lisbon with 1579m solar collectors a545 kW cooling power or on the Olympic Saili
Village in Qingdao/China. In 2011 the most powerf
plant at Singapores new constructed United Wor
College will be commissioned (1500 kW).
These projects have shown that flat plate so
collectors specially developed for temperatures ov
200 F (featuring double glazing, increased backsi
insulation, etc.) can be effective and cost efficien[8] Evacuated-tube solar panels can be used as we
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Concentrating solar collectors required for
absorption chillers are less effective in hot humid,
cloudy environments, especially where the
overnight low temperature and relative humidity are
uncomfortably high. Where water can be heated
well above 190 F (88 C), it can be stored and used
when the sun is not shining.
The Audubon Environmental Center in Los Angeleshas an example solar air conditioning installation.
The Southern California Gas Co. (The Gas
Company), and its sister utility, San Diego Gas &
Electric (SDG&E), are also testing the practicality of
solar thermal cooling systems at their Energy
Resource Center (ERC) in Downey, California. Solar
Collectors from Sopogy and HelioDynamics were
installed on the rooftop at the ERC and are
producing cooling for the buildings air conditioning
system.
In the late 19th century, the most common phasechange refrigerant material for absorption cooling
was a solution ofammonia and water. Today, the
combination oflithium and bromide is also in
common use. One end of the system of
expansion/condensation pipes is heated, and the
other end gets cold enough to make ice. Originally,
natural gas was used as a heat source in the late
19th century. Today, propane is used in recreational
vehicle absorption chiller refrigerators. Innovative
hot water solar thermal energy collectors can also
be used as the modern "free energy" heat source.For 150 years, absorption chillers have been used to
make ice (before the electric light bulb was
invented). This ice can be stored and used as an
"ice battery" for cooling when the sun is not shining,
as it was in the 1995 Hotel New Otani in Tokyo
Japan. Mathematical models are available in the
public domain for ice-based thermal energy storage
performance calculations. The ISAAC Solar Icemaker
is an intermittent solar ammonia-water abs
Photovoltaic solar cooling
Photovoltaics can provide the power for any type ofelectrically powered cooling be
it conventional compressor-based or
adsorption/absorption-based, though the most
common implementation is with compressors which
is the least efficient form of electrical cooling
methods.For small residential and small commercial
cooling (less than 5 MWh/yr) PV-powered cooling
has been the most frequently implemented solar
cooling technology. The reason for this is debated,
but commonly suggested reasons include incenti
structuring, lack of residential-sized equipment f
other solar-cooling technologies, the advent of mo
efficient electrical coolers, or ease of installati
compared to other solar-cooling technologi
(like radiant cooling).
Since PV cooling's cost effectiveness depen
largely on the cooling equipment and given the po
efficiencies in electrical cooling methods un
recently it has not been cost effective witho
subsidies. Pairing PV with 14 SEER and less coole
is the least efficient of all solar cooling method
Using more efficient electrical cooling methods a
allowing longer payback schedules is changing th
scenario.
For example, a 100,000 BTU U.S. Energy Star rat
air conditioner with a high seasonal ener
efficiency ratio (SEER) of 14 requires around 7 kW
electric power for full cooling output on a hot da
This would require over a 7 kW solar photovolta
electricity generation system (with morning-t
evening, and seasonal solar tracker capability
handle the 47-degree[vague] summer-to-wint
difference in solar altitude). The photovoltaics wou
only produce full output during the sunny part
clear days.
A solar-tracking 7 kW photovoltaic system wou
probably have an installed price well over $20,0
USD (with PV equipment prices currently falling roughly 17% per year). (New advances in ing
manufacturing have dropped raw silicon (refin
sand) costs... leading to lower crystalline silico
with the advances places like www.sunelec.com c
sell inferior strip amorphous silicon modules f
$1.20-1.50/kwh of raw modules; infrastructur
wiring., mounting and NEC code costs may add
to an additional cost; for instance a 3120 watt so
panel grid tie system has a panel cost of $0.99/wa
hour peak, but still costs ~$2.2/watt hour pea
Other systems of different capacity cost even morlet alone battery backup systems, which cost eve
more. Due to the advent of net metering allowed b
utility companies, your photovoltaic system c
produce enough energy in the course of the year
completely offset the cost of the electricity used
run air conditioning, depending on the amount
your electric costs you wish to offset.
A more efficient air conditioning system wou
require a smaller, less-expensive photovolta
http://en.wikipedia.org/wiki/Southern_California_Gashttp://en.wikipedia.org/wiki/San_Diego_Gas_%26_Electrichttp://en.wikipedia.org/wiki/San_Diego_Gas_%26_Electrichttp://en.wikipedia.org/wiki/Sopogyhttp://en.wikipedia.org/w/index.php?title=HelioDynamics&action=edit&redlink=1http://en.wikipedia.org/wiki/Phase_changehttp://en.wikipedia.org/wiki/Phase_changehttp://en.wikipedia.org/wiki/Refrigeranthttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Lithiumhttp://en.wikipedia.org/wiki/Bromidehttp://en.wikipedia.org/wiki/Propanehttp://en.wikipedia.org/wiki/Photovoltaicshttp://en.wikipedia.org/wiki/Radiant_coolinghttp://en.wikipedia.org/wiki/BTUhttp://en.wikipedia.org/wiki/Energy_Starhttp://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratiohttp://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratiohttp://en.wikipedia.org/wiki/KWhttp://en.wikipedia.org/wiki/Solar_trackerhttp://en.wikipedia.org/wiki/Wikipedia:Manual_of_Stylehttp://en.wikipedia.org/wiki/Wikipedia:Manual_of_Stylehttp://en.wikipedia.org/w/index.php?title=Solar_altitude&action=edit&redlink=1http://en.wikipedia.org/wiki/Southern_California_Gashttp://en.wikipedia.org/wiki/San_Diego_Gas_%26_Electrichttp://en.wikipedia.org/wiki/San_Diego_Gas_%26_Electrichttp://en.wikipedia.org/wiki/Sopogyhttp://en.wikipedia.org/w/index.php?title=HelioDynamics&action=edit&redlink=1http://en.wikipedia.org/wiki/Phase_changehttp://en.wikipedia.org/wiki/Phase_changehttp://en.wikipedia.org/wiki/Refrigeranthttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Lithiumhttp://en.wikipedia.org/wiki/Bromidehttp://en.wikipedia.org/wiki/Propanehttp://en.wikipedia.org/wiki/Photovoltaicshttp://en.wikipedia.org/wiki/Radiant_coolinghttp://en.wikipedia.org/wiki/BTUhttp://en.wikipedia.org/wiki/Energy_Starhttp://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratiohttp://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratiohttp://en.wikipedia.org/wiki/KWhttp://en.wikipedia.org/wiki/Solar_trackerhttp://en.wikipedia.org/wiki/Wikipedia:Manual_of_Stylehttp://en.wikipedia.org/w/index.php?title=Solar_altitude&action=edit&redlink=1 -
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system. A high-quality geothermal heat
pump installation can have a SEER in the range of
20 (+/-). A 100,000 BTU SEER 20 air conditioner
would require less than 5 kW while operating.
Newer and lower power technology including
reverse inverter DC heat pumps can achieve SEER
ratings up to 26, the Fujitsu Halycon line being one
notable example, but its requirements of 200-250v
AC input makes its use in the USA in smaller grids
newer.
There are new non-compressor-based electrical air
conditioning systems with a SEER above 20 coming
on the market. New versions of phase-change
indirect evaporative coolers use nothing but a fan
and a supply of water to cool buildings withoutadding extra interior humidity (such as at McCarran
Airport Las Vegas Nevada). In dry arid climates with
relative humidity below 45% (about 40% of the
continental U.S.) indirect evaporative coolers can
achieve a SEER above 20, and up to SEER 40. A
100,000 BTU indirect evaporative cooler would only
need enough photovoltaic power for the circulation
fan (plus a water supply).
A less-expensive partial-power photovoltaic system
can reduce (but not eliminate) the monthly amount
of electricity purchased from the power grid for airconditioning (and other uses). With American state
government subsidies of $2.50 to $5.00 USD per
photovoltaic watt,[17] the amortized cost of PV-
generated electricity can be below $0.15 per kWh.
This is currently cost effective in some areas where
power company electricity is now $0.15 or more.
Excess PV power generated when air conditioning is
not required can be sold back to the power grid in
many locations, which can reduce (or eliminate)
annual net electricity purchase requirement.
(See Zero energy building)The key to solar air conditioning cost effectiveness
is in lowering the cooling requirement for the
building. Superior energy efficiency can be designed
into new construction (or retrofitted to existing
buildings). Since the U.S. Department of Energy was
created in 1977, their Weatherization Assistance
Program[18] has reduced heating-and-cooling load on
5.5 million low-income affordable homes an average
of 31%. A hundred million American buildings still
need improved weatherization. Carele
conventional construction practices are s
producing inefficient new buildings that ne
weatherization when they are first occupied.
It is fairly simple to reduce the heating-and-cooli
requirement for new construction by one half. Th
can often be done at no additional net cost, sin
there are cost savings for smaller air conditionin
systems and other benefits.
Since U.S. President Carter created the Solar Ener
Tax Incentives in 1978, hundreds of thousan
ofpassive solar and zero energy buildings ha
demonstrated 70% to 90% heating-and-cooling lo
reductions (and even 100% reduction in som
climates). In contrast, well over 25 million neconventional U.S. buildings have ignored we
documented energy efficiency techniques sin
1978. As a result, U.S. buildings waste more ener
(39%) than transportation or industry.[1
their architects and builders had listened to the U
Department Of Energy presentations at the Nation
Energy Expositions three decades ago, Americ
buildings could be using $200 billion USD le
energy per year today.
Geo thermal cooling
Earth sheltering or Earth cooling tubes can ta
advantage of the ambient temperature of the Ear
to reduce or eliminate conventional air conditioni
requirements. In many climates where the major
of humans live, they can greatly reduce the build u
of undesirable summer heat, and also help remo
heat from the interior of the building. They increa
construction cost, but reduce or eliminate the co
of conventional air conditioning equipment.
Earth cooling tubes are not cost effective in hhumid tropical environments where the ambie
Earth temperature approaches human temperatu
comfort zone. A solar chimney or photovolta
powered fan can be used to exhaust undesired he
and draw in cooler, dehumidified air that has pass
by ambient Earth temperature surfaces. Control
humidity and condensation are important desi
issues.
http://en.wikipedia.org/wiki/Geothermal_heat_pumphttp://en.wikipedia.org/wiki/Geothermal_heat_pumphttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-16http://en.wikipedia.org/wiki/KWhhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Zero_energy_buildinghttp://en.wikipedia.org/wiki/Efficient_energy_usehttp://en.wikipedia.org/wiki/U.S._Department_of_Energyhttp://en.wikipedia.org/wiki/Weatherizationhttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-17http://en.wikipedia.org/wiki/Passive_solarhttp://en.wikipedia.org/wiki/Zero_energy_buildinghttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-18http://en.wikipedia.org/wiki/Architecthttp://en.wikipedia.org/wiki/Construction_workerhttp://en.wikipedia.org/wiki/Earth_shelteringhttp://en.wikipedia.org/wiki/Earth_cooling_tubeshttp://en.wikipedia.org/wiki/Solar_chimneyhttp://en.wikipedia.org/wiki/Photovoltaichttp://en.wikipedia.org/wiki/Geothermal_heat_pumphttp://en.wikipedia.org/wiki/Geothermal_heat_pumphttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-16http://en.wikipedia.org/wiki/KWhhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Zero_energy_buildinghttp://en.wikipedia.org/wiki/Efficient_energy_usehttp://en.wikipedia.org/wiki/U.S._Department_of_Energyhttp://en.wikipedia.org/wiki/Weatherizationhttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-17http://en.wikipedia.org/wiki/Passive_solarhttp://en.wikipedia.org/wiki/Zero_energy_buildinghttp://en.wikipedia.org/wiki/Solar_air_conditioning#cite_note-18http://en.wikipedia.org/wiki/Architecthttp://en.wikipedia.org/wiki/Construction_workerhttp://en.wikipedia.org/wiki/Earth_shelteringhttp://en.wikipedia.org/wiki/Earth_cooling_tubeshttp://en.wikipedia.org/wiki/Solar_chimneyhttp://en.wikipedia.org/wiki/Photovoltaic -
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A geothermal heat pump uses ambient Earth
temperature to improve SEER for heat and cooling.
A deep well recirculates water to extract ambient
Earth temperature (typically at 6 to 10
gallons[vague] per minute). Ambient earth temperature
is much lower than peak summer air temperature.
And, much higher than the lowest extreme winter
air temperature. Water is 25 times more thermallyconductive than air, so it is much more efficient
than an outside air heat pump, (which become less
effective when the outside temperature drops).
The same type of geothermal well can be used
without a heat pump but with greatly diminished
results. Ambient Earth temperature water is
pumped through a shrouded radiator (like an
automobile radiator). Air is blown across the
radiator, which cools without a compressor-based
air conditioner. Photovoltaic solar electric panels
produce electricity for the water pump and faneliminating conventional air-conditioning utility bills.
This concept is cost-effective, as long as the location
has ambient Earth temperature below the human
thermal comfort zone. (Not the tropics)
Solar Mechanical Refrigeration
Solar mechanical refrigeration uses a conventional
vapor compression system driven by mechanical
power that is produced with a solar-driven heat
power cycle. The heat power cycle usually
considered for this application is a Rankine cycle in
which a fluid is vaporized at an elevated pressure by
heat exchange with a fluid heated by solar
collectors. A storage tank can be included to provide
some high temperature thermal storage. The vapor
fl ows through a turbine or piston expander to
produce mechanical power, as shown in Figure. The
fluid exiting the expander is condensed and pump
back to the boiler pressure where it is aga
vaporized.
The efficiency of the Rankine cycle increases w
increasing temperature of the vaporized flu
entering the expander, as shown in Figure. (bo
line). The Rankine cycle efficiency in Figure westimated for a high-temperature organic flu
assuming that saturated vapor is provided to a 70
efficient expander and condensation occurs at 35
(95F). The efficiency of a solar collector, howeve
decreases with increasing temperature of t
delivered energy. High temperatures can
obtained from concentrating solar collectors th
track the suns position in one or two dimension
Tracking systems add cost, weight and complex
to the system. If tracking is to be avoide
evacuated tubular, compound parabolic
advanced multi-cover flat plate collectors can used to produce fluid temperatures rangi
between 100C 200C (212F 392F).
The efficiency of solar collectors depends on bo
solar radiation and the difference in temperatu
between the entering fluid and ambient. Figure
also shows approximate solar collector efficienci
as a function of fluid delivery temperature for
range of solar radiation values. The over
efficiency of solar mechanical refrigeration, defin
as the ratio of mechanical energy produced to tincident solar radiation, is the product of t
efficiencies of the solar collector and the pow
cycle. Because of the competing effects w
temperature, there is an optimum efficiency at a
solar radiation. However, the optimum efficien
would be a maximum of 4.5% for the conditio
assumed in Figure. This efficiency is significan
lower than that which can be achieved with no
concentrating PV modules. Solar mechanic
systems are competitive only at high
temperatures for which tracking solar collectors a
required. Because of its economy-of-scale, th
option would only be applicable for lar
refrigeration systems (e.g., 1,000 tons or 3,5
kWT.
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Absorption Refrigeration
Absorption refrigeration is the least intuitive of the
solar refrigeration alternatives. Unlike the PV and
solar mechanical refrigeration options, the
absorption refrigeration system is considered a
heat driven system that requires minimal
mechanical power for the compression process. It
replaces the energy-intensive Compression in avapor compression system with a heat activated
thermal compression system. A schematic of a
single-stage absorption system using ammonia as
the refrigerant and ammonia-water as the absorbent
is shown in Figure Absorption cooling systems that
use lithium bromide-water absorption-refrigerant
working fluids cannot be used at temperatures
below 0C (32F).
The condenser, throttle and evaporator operate in
the exactly the same manner as for the vaporcompression system. In place of the compressor,
however, the absorption system uses a series of
three heat exchangers (absorber, regenerating
intermediate heat exchanger and a generator) and a
small solution pump. Ammonia vapor exiting the
evaporator (State 6) is absorbed in a liquid solution
of water-ammonia in the absorber. The absorption
of ammonia vapor into the water-ammonia solution
is analogous to a condensation process. The process
is exothermic and so cooling water is required
carry away the heat of absorption.
The principle governing this phase of the operati
is that a vapor is more readily absorbed into a liqu
solution as the temperature of the liquid solution
reduced. The ammonia-rich liquid solution leavi
the absorber (State 7) is pumped to a highpressure, passed through a heat exchanger a
delivered to the generator (State 1). The minimu
mechanical power needed to operate the pump
given by Equation 1, the same equation that appli
to the minimum power needed by a compress
However, the power requirement for the pump
much smaller than that for the compressor since
the specific volume of the liquid solution, is muc
smaller than the specific volume of a refrigera
vapor.
It is, in fact, possible to design an absorption syste
that does not require any mechanical power inp
relying instead on gravity. However, grid-connect
systems usually rely on the use of a small pump.
the generator, the liquid solution is heated, whi
promotes desorption of the refrigerant (ammon
from the solution. Unfortunately, some water also
desorbed with the ammonia, and it must
separated from the ammonia using the rectifi
Without the use of a recifier, water exits at State
with the ammonia and travels to the evaporatwhere it increases the temperature at whi
refrigeration can be provided. This soluti
temperature needed to drive the desorption proce
with ammonia-water is in the range between 120
to 130C (248F to 266F).
Temperatures in this range can be obtained usi
low cost non-tracking solar collectors. At the
temperatures, evacuated tubular collectors may
more suitable than fl at-plate collectors as their e
ciency is less sensitive to operating temperatu
The overall efficiency of a solar refrigeration syste
is the product of the solar collection efficiency an
the coefficient of performance of the absorpti
system. The effi ciency of an evacuated tubu
collector for different levels of solar radiation an
energy delivery temperatures is given in Figurea
energy delivery temperatures is given in Figu
5.The COP for a single-stage ammonia-water syste
depends on the evaporator and condens
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temperatures. The COP for providing refrigeration at
10C (14F) with a 35C (95F) condensing
temperature is approximately 0.50. Advanced
absorption cycle confi gurations have been
developed that could achieve higher COP values.
The absorption cycle will operate with lower
temperatures of thermal energy supplied from the
solar collectors with little penalty to the COP,although the capacity will be signifi cantly reduced.
Conclusions
An overall system coefficient of performance
(COPsys) can be defined as the ratio of refrigerationcapacity to input solar energy. The COP sys is low
for all three types of solar refrigeration systems.
However, this dentition of efficiency may not be the
most relevant metric for a solar refrigeration system
because the fuel that drives the system during
operation, solar energy, is free. Other system
metrics that are more important are the specificsize,
weight, and, of course, the cost. A number of
barriers have prevented more widespread use of
solar refrigeration systems.
First, solar refrigeration systems necessarily are
more complicated, costly, and bulky than
conventional vapor compression systems because of
the necessity to locally generate the power needed
to operate the refrigeration cycle. Second, the
ability of a solar refrigeration system to function is
driven by the availability of solar radiation. Because
this energy resource is variable, some form of
redundancy or energy storage (electrical or thermal)
is required for most applications, which further adds
to the system size and cost. The advantage of solar
refrigeration systems is that they displace some or
all of the conventional fuel use. The operating costs
of a solar refrigeration system should be lower than
that of conventional systems, but at current and
projected fuel costs, this operating cost savings
would not likely compensate for their additional
capital costs, even in a longterm life-cycle analysis.
The major advantage of solar refrigeration is that it
can be designed to operate independent of a utility
grid. Applications exist in which this capability
essential, such as storing medicines in remo
areas.
Of the three solar refrigeration concepts presente
here, the photovoltaic system is most appropria
for small capacity portable systems located in are
not near conventional energy sources (electricity gas). Absorption and solar mechanical systems a
necessarily larger and bulkier and require extensi
plumbing as well as electrical connections.
situations where the cost of thermal energy is hig
absorption systems may be viable for larg
stationary refrigeration systems.
The solar mechanical refrigeration systems wou
require tracking solar collectors to produce hi
temperatures at which the heat power cyc
efficiency becomes competitive. If the capital co
and effi ciency of tracking solar collectors can
significantly reduced, this refrigeration syste
option could be effective in larger scale refrigerati
applications.
Advantages & disadvantages of sol
refrigeration
Advantages Cost effective
Live wherever you want
Reduce your carbon footprint
Reduce your carbon footprint
Low on maintenance
Disadvantages
The installation cost is high
Also the power is not available througho
the year. (It may be available for 300 da
/year).
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References
Burton, A. 2007. Solar Thrill: Using the sun to
cool vaccines. Environmental Health
Perspectives. 115(4): 208211
Brooke, C. (2009, Jan. 8) Amazing solar-
powered fridge invented by British student in
a potting shed helps poverty-stricken
Africans. Mail Online. Retrieved January 30,2009,
from http://www.dailymail.co.uk/sciencetech/
article-1108343/Amazing-solar-powered-
fridge-invented-British-student-potting-shed-
helps-poverty-stricken-Africans.html
Ecofriend (2009, Jan. 8). Eco Tech: 21-year-
old student invents portable solar-power
frige. Retrieved January 29, 2009,
from http://www.ecofriend.org/entry/eco-
tech-21-year-old-student-invented-portable-
solar-powered-fridge/ Greenlaunches.com. (2009, Jan. 8) Portable
Solar powered refrigerator cools like human
body. Retrieved January 29, 2009,
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-and-tech/portable-solar-powered-
refrigerator-cools-like-human-body.php
Pedersen, PH. Mat J. 2006. SolarChill
vaccine cooler and refrigerator: a
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Pedersen, PH., Poulsen, S., Katic, I. (n.d
SolarChilla solar PV refrigerator witho
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PSFK. Retrieved January 29, 200
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UNEP 2005. SolarChill: the vaccine coo
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Flahiff, D. (2009, Jan. 12). Student Inven
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2009,
from http://www.inhabitat.com/2009/01/12/
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