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No. 10 on the list of the Greatest Engineering Achievements of the 20th Century

These cooling technologies have altered our lifestyles completely: Buildings are climate-controlled & comfortable Fresh foods & milk are kept in

refrigerators/freezers Food can be transported over long distances

without spoiling Building designs - changed completely Environment for industrial processes are

controlled

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Applied to processes by which air in occupied spaces is maintained at acceptable conditions (temp, humidity and freshness)

Space Conditioning

Heating Ventilating Air Conditioning

HVAC

Refers to all process used in changing states of conditioned air in an HVAC system

Often used to describe just the cooling and dehumidification aspects of overall HVAC system

Air Conditioning

Definitions

Fields of refrigeration and air conditioning are interconnected

Heating, humidifying and air quality control

Industrial Refrigeration, incl

food preservation, chemical and

process industries

Cooling and Dehumidifying operations

in air Conditioning

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Largest application of refrigeration process of cooling (used for air-conditioning)

Additionally used frequently in industrial applications (food preservation, food processing, heat removal in chemical plants etc)

Air conditioning needs more than a cooling process

Thus AC includes the entire heating operation, as well as velocity regulation, thermal radiation and air quality (incl removal of vapors and foreign particles)

Confort Air-conditioning:

The process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution to meet comfort requirements of the occupants of the conditioned space

HVAC Broad Field, available engineering focus on space conditioning but there are numerous other applications

Office Buildings Retail Facilities (Stores, Shopping

Malls) Places of Assembly Educational Facilities Health Facilities

General Commercial Sector

Automotive Truck Aircraft Ships

Speciality Areas

Human Comfort criteria for each of these applications are similar

But differences in levels of acceptable temperature and outdoor ventilation required

Same basic equipment may be used in different applications

Control Techniques specialized

Performance criteria different for each system

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Industrial Facilities Air treatment also required Each area has special and different

needs

INDUSTRY REQUIREMENTChemical/Painting Large amounts of outdoor air

Paper Industry Drying Systems (produces very humid air)

Plastics Plant Dry and Tightly Controlled Conditions required

Food Industry Freezing, Drying, Preserving foods requires air treatment (correct temp and humidity required)

A/C of Medium/Large Buildings Summer cooling systems standard in

large buildings Also needed to remove heat generated

by people, lights, equipment etc

Some form of central system serves building

One or more water-chilling plant/heater (boiler)

Conditioned spaces served by one or more air-supply/return system

Hot water may be piped to HE in conditioned space

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Single Storey Commercial Buildings Often served by rooftop units Simple to install Various duct lengths can be used Incorporates filter, supply fan, heater (gas-

fired/electric), ventilation dampers and controls

Hospitals Special Requirements: 100% outdoor air must be used Humidity levels are limited in ORs to avoid static

electricity Design of an energy efficient system meeting all

the requirements quite a challenge

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Industrial Air ConditioningProviding a certain level of comfort for workers in hostile environments, but also control air conditions to be favourable for specific industrial processes

Spot Heating/Cooling

Environmental Laboratories

Printing Textiles

Precision Parts and Clean

RoomsPhotographic

Products

Residential Air Conditioning Usually a DX system Central/Unitary system compressor and condenser is

located outdoors (called a condensing unit), and evaporator coil in the interior air ducts

Combined heating and cooling Heat Pumps (cycle can be reversed evaporator becomes condenser)

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Food Industry Air blast Freezing Contact Freezing Immersion Freezing

Freezing

Fruits and Vegetables should be frozen quickly after harvesting

Refrigerated Warehouses (-20 to -23CStorage

Food moves from Refrigeration Warehouses to food marketsRefrigerated Display Cases (3-5C) for dairy products-20 for frozen products and ice cream

Distribution

Milk,ice cream and cheeseFood Processing

Concentrated fruit juices, beer and wineFreeze Drying (product is frozen and water removed by

sublimation)Beverages

Special Applications

Drinking Fountains Dehumidifiers Ice Makers

Ice Skating Rinks Construction

Desalting of Seawater

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Typical Air Distribution SystemHVAC System Continuously circulates air

through building

Cooling mode air supplied to building is cool and dry (must remove heat

and moisture)

Heating Mode air supplied is warm to balance heat losses

Pollutants generated by Occupants and processes

removed thruogh air exchange with outside (exhaust duct and

dampers)

Air exchange with outside leads to additional heating/cooling requirements.

From energy perspective recirculate as much as conditioned air as possible

Mixture of return air ventilation air passes through a series conditioning equipment: Filters remove dust and particles Cooling coils placed after filters to cool and dehumidify the air Heating coils humidification equipment heat the air and add

moisture in the winter

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Separate supply and return fans are used in the main supply and return air ducts

Operated so that building is at a pressure higher than the outdoor to prevent infiltration.

Introduction of the outside air must be controlled by the ventilation system

Air-distribution system can serve various zones within a building

This is termed an all-air system space conditioning is provided ONLY by air processed at a central location and then distributed

Quite common in commercial buildings relatively low cost and simplicity

All-water systems used to distribute cold and/or hot water (or steam) to heat

exchangers located in various zones to provide local cooling and heating

Local Thermostat controls water quantity flowing through heat exchanger

Ventilation of outside air to each zone is provided locally Air-water systems

Combination of centrally cooled and ventilated air as in all-air systems, with hot water coils in each coil for heating

Zone: region of a building with its own temperature control, usually through a local thermostat

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EquipmentHeatingDepending on requirements steam or hot water to HEs from a boiler (natural gas,

oil or electricity) Fuel-fired furnace Electric resistance heaters in duct

Cooling Typically a vapour-compression system to chill water certain cases absorption chillers sometimes used

Direct Expansion (DX) Evaporator of VC-system is in the supply duct and cools

and dehumidifies air directly Residential/Small Commercial Applications

Equipment (2) Large Commercial applications: Centrally located chiller systems

distributes chilled water to cooling coils for cooling and dehumidifying air.

Coils may be located centrally (all-air) or locally (all-water)

Heat Rejection Process: Condenser is used, may transfer heat directly to

ambient air using a evaporative condenser water is sprayed into air stream before passing over condenser surfaces

Large systems condenser is water cooled heat transfer to environment through cooling towers (water is cooled by evaporation into ambient air)

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DX System Evaporator located in main supply air duct with a heat

exchanger for a furnace (central air system) Single thermostat is used to cycle compressor and

furnace on and off to maintain setpoint temperature Compressor and condenser are located outside

building When condenser and evaporator are not located in the

same package split system Packaged system - incorporates all of the VC system in

a single package e.g. rooftop units

Equipment (3) Chilled water and hot-water/steam equipment often used

in large commercial buildings to serve a number of AHU (air handling units)

Combination of a fan, filter, heating coil, cooling coil, humidifier, ventilation dampers and controls

Usually pre-assembled and purchased as built-up air handling units

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History Keeping cool obsession with

humans for centuries Evaporative cooling: Dates back to Egyptians (wet

mats over doorways) Slaves would fan clay jars filled

with water Native Americans: water trenches

beneath huts American West wet sheets on

sleeping porches

Some Roman Emperors (Elagabulus) had snow hauled from the mountains to cool their summer villa and to chill their drinks

Middle East wind towers (from medieval Persia) used to cool buildings. Small Windows captures gusts of wind and funnel them downwards

Hand fans (made of feathers, bamboo or plant fronds) fashion accessory (Queen Elizabeth I). Imported from China

Wealthy roman citizens pumped cool water from aqueducts into villas, circulated through pipesin the walls,

lowering room temperatures

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.1902 Comfort cooling system installed at the New York Stock Exchange1902 First office building with an air-conditioning system installed

1904A self-contained mechanical refrigerator is displayed at the St. Louis World's Fair

1906 First office building specifically designed for air conditioning.1906 Patent filed for "dew point control" system

1907Air-conditioning equipment installed in dining and meeting rooms at Congress Hotel in Chicago

1914Aircooled, electric, self-contained household refrigerating unit is marketed

1927 Gas-fired household absorption refrigerators become popular

1927First refrigerator to be mass produced with a completely sealed refrigerating system

1930 Smaller air-conditioning units appear on trains1928 Chlorofluorocarbon (CFC) refrigerants are synthesized

1931"Hot- Kold" year-round central air-conditioning system for homes on the market

1931 A heat pump air-conditioning system in Los Angeles office building1936 Albert Henne synthesizes refrigerant R-134a

1969More than half of new automobiles are equipped with air conditioning

1987 Minimum energy efficiency requirements set1987 The Montreal Protocol1992 Minimum energy efficiency standards set for commercial buildings

Self-study: Read through chapter 1 in MQuiston