COOLING APPLICATIONS OF SOLAR SYSTEMS

Submitted to :Mr. Narender KaushikAssociate Professor,Mechanical Dept.,

Presented By :Vikram Dangi758/ME/12

VAISH COLLEGE OF ENGG.,ROHTAK

CONTENTS• Introduction• Simple Vapour Absorption System• Practical Vapour Absorption System• C.O.P of Ideal Vapour Absorption System• Properties of Ideal Refrigerant and Absorbent• Properties of Ideal Refrigerant-Absorbent

combination• Advantages of Absorption System over

Compression System• Passive Cooling

INTRODUCTION• It is a heat operated system.• It is quite similar to Vapour Compression systems.

Condensation and evaporation takes place at two different pressure levels to achieve refrigeration.• The main motive is to raise the temperature of the

refrigerant from evaporator pressure to condenser pressure.• Here refrigerant is dissolved in inert liquid in absorber and

pumped to condenser.• After raising pressure of refrigerant it is separated from

solution by heating.• After condensation in condenser, refrigerant is throttled by

expansion valve and then it evaporates in evaporator providing the refrigeration effect.

SIMPLE VAPOUR ABSORPTION SYSTEM

• Ammonia vapour from evaporator is absorbed by water in absorber. Condensation heat released is absorbed by cooling water.

• After being pumped to generator, heat is supplied which gives ammonia vapour. Weak sol. sent back to absorber.

• High pressure vapour is condensed to high pressure liquid ammonia in condenser.

• Liquid ammonia is throttled by expansion valve, and then it evaporates absorbing heat from evaporator.

Simple Vapour Absorption System

PRACTICAL VAPOUR ABSORPTION SYSTEM

Water vapours if reach condenser may block the expansion valve. Therefore, analyser-rectifier is used practically.Analyser : Strong solution flows down the trays. Due to high saturation temperature water condenses down and vapours escape through.Rectifier : A water cooled heat exchanger which further condenses water vapour. (If any left) Heat Exchanger : Used to cool weak solution from generator. It also heats the strong solution coming from pump, thereby reducing heat to be supplied at generator, increasing economy. Practical Vapour Absorption

System

LAYOUT OF VARS

COEFFICIENT OF PERFORMANCE OF IDEAL ABSORPTION SYSTEM

C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)

Various energy transfers in VARS

C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)

= C.O.P of Carnot refrigerator working b/w temperature limits &.= C.O.P of Carnot engine working b/w temperature limits &.

Thus C.O.P of ideal absorption system, = [ ] x [ ]

PROPERTIES OF IDEAL REFRIGERANT & ABSORBENT

Properties of ideal refrigerant :• It should boil b/w 2˚-10 ˚C

and condense at 40 ˚C or above. (pressure around atmospheric)• Large latent heat of

vaporization.• High critical temperature.• Low specific heat.• Stability in complete cycle.

Properties of ideal absorbent :• Greater affinity for

refrigerant.• Heat released during

absorption of refrigerant should be minimum.• High boiling point.• Low specific heat.• Chemical stability.

PROPERTIES OF IDEAL REFRIGERANT-ABSORBENT COMBINATION

• Refrigerant should have high affinity for absorber at low temperatures & less affinity at high temperatures.• Mixture should have low specific heat and viscosity.• It should be non-corrosive.• Large difference in normal boiling points of refrigerant

and absorbent.Commonly used combinations in air-conditioning applications • Ammonia-water • Lithium-bromide water

•For LiBr-water solution•It uses water as refrigerant(boiling point 100ºC) and Lithium-Bromide(boiling point 1265ºC) as its absorbent•Is used in a number of air conditioning applications. This system is useful for applications where the temperature required is more than 32ºF(0ºC).•Water used as the refrigerant in the absorption refrigeration system means the operating pressures in the condenser and the evaporator must be very low• The system can be achieved even without installing the expansion valve in the system, since the drop in pressure occurs due to friction in the refrigeration piping and in the spray nozzles.•It has lesser components than ammonia-water absorption.

LiBr-WATER COMBINATION

AMMONIA-WATER COMBINATION•Uses Ammonia(NH3, Boiling point -33.34ºC) as refrigerant and Water(Boiling point100ºC) as absorber•Most commercial and industrial refrigeration applications occur at temperatures below 32ºF(0ºC) and many are 0ºF (-17.78ºC). As a result, a fluid which is not subject to freezing at these temperatures is required. So the lithium bromide-water cycle is no longer able to achieve this conditions, because water is used for the refrigerant.•Have a disadvantage in acquiring extra parts compare to LiBr-water system but does have an advantage in operating pressure above atmospheric that avoid air leakage.

ADVANTAGES OF ABSORPTION SYSTEM OVER COMPRESSION SYSTEM

•No moving part except pump-motor, which is comparatively smaller than compressor system.•Quiet in operation, low maintenance cost.•Can work only with thermal energy as an input.•Can be built for huge working capacities. (even for above 1000 TR)•Can be operated at designed C.O.P’s or even at part loads by varying generator temperature.•Space and Auto. control requirements favour absorption system.

PASSIVE COOLING

PASSIVE COOLING •Passive cooling refers to technologies or design features used to cool buildings without power consumption, such as those technologies discussed in the Passive house project.

The term "passive" implies that energy-consuming mechanical components like pumps and fans are not used.

Passive cooling building design attempts to integrate principles of physics into the building exterior envelope to:

Slow heat transfer into a building. This involves an understanding of the mechanisms of heat transfer: heat conduction, convective heat transfer, and thermal radiation (primarily from the sun).

Remove unwanted heat from a building. In mild climates with cool dry nights this can be done with ventilating. In hot humid climates with uncomfortable warm / humid nights, ventilation is counterproductive, and some of solar air conditioning may be cost effective.

PURPOSE OF PASSIVE COOLING• Provides indoor comfort• Low maintenance• Zero/ Low energy consumption• Low running cost• Promotes healthy environment

☺Saves the Earth

SOME PASSIVE COOLING TECHNIQUES

Shading a building from solar radiation can be achieved in many ways.

Buildings can be orientated to take advantage of winter sun (longer in the East / West dimension), while shading walls and windows from direct hot summer sun. This can be achieved by designing location-specific wide eaves or overhangs above the Equator-side vertical windows (South side in the Northern hemisphere, North side in the Southern hemisphere).

(1)SHADING

VENTILATIONThe mechanical system or equipment used to circulate

air or to replace stale air with fresh air.Ventilation in buildings has three main purposes:

1. To maintain a minimum air quality2. To remove heat (or other pollutant)3. To provide perceptible air movement to

enhance thermal comfort

(2)VENTILATION

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