solar air conditing

7/30/2019 solar air conditing

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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


8/12

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


9/12

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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10/12

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


11/12

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).


12/12

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,

from http://www.greenlaunches.com/gadgets

-and-tech/portable-solar-powered-

refrigerator-cools-like-human-body.php

Pedersen, PH. Mat J. 2006. SolarChill

vaccine cooler and refrigerator: a

breakthrough technology. Industria

Formazione. Special International Issu

Refrigeration and Air Conditioning. No. 30

Suppl. 1(No. 62006):1719

Pedersen, PH., Poulsen, S., Katic, I. (n.d

SolarChilla solar PV refrigerator witho

battery. Danish Technological Institu

Taastrup, Denmark: Solar Energy Centre,

4. Lachut, S. (2009, Jan. 8) A Portable, Sola

Powered Fridge for the Developing Wor

PSFK. Retrieved January 29, 200

from http://www.psfk.com/2009/01/a-

portable-solar-powered-fridge-for-the-

developing-world.html

UNEP 2005. SolarChill: the vaccine coo

powered by nature. Paris, France: UN

Division of Technology, Industry a

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from http://www.uneptie.org/Ozonaction/infmation/mmcfiles/4489-e-SolarChill.pdf.

Flahiff, D. (2009, Jan. 12). Student Inven

Solar-Powered Fridge for Developi

Countries. Inhabitat. Retrieved January 3

2009,

from http://www.inhabitat.com/2009/01/12/

olar-powered-fridge-by-emily-cummins/

Sanford A. Klein, Ph.D. and Douglas T. Rein

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