GROUP VI - HEATING, VENTILATING, AIR CONDITIONING (HVAC)

Metabolism

• Metabolism is the body's process of converting food into energy for functions like maintaining body temperature at 98.6°F (37°C).

• Metabolic rates differ by physical activity and gender; men generally have 30% higher rates than women.

• 1 MET (Metabolic Equivalent) unit is approximately 360 BTuh (British Thermal units per hour) for an average-sized man.

• Metabolic rate depends on activity levels, measured in MET units.

• Heat loss occurs through various methods influenced by air temperature, humidity, and surrounding surfaces.

Metabolic Rates (in MET units)

• Resting: 0.7 to 1.2

• Walking (2 to 4 mph): 2.00 to 3.8

• Miscellaneous Occupations:

  • Bakery, Lab work: 1.4 to 2.0

  • Carpentry Machine: 1.8 to 2.2

  • Sewing by hand: 4.00 to 4.8

  • Planning by hand: 5.6 to 6.4

  • Garage work: 2.2 to 3.0

  • Light Machine work: 2.0 to 2.4

  • Heavy Machine work: 1.6

  • Car driving: 1.5

  • Heavy Vehicle: 3.2

• Domestic Work:

  • Cooking: 1.6 to 2.0

  • Washing and ironing by hand: 2.0 to 3.6

• Office Work: 1.1 to 1.4

• Leisure Activities:

  • Calisthenics exercise: 3.0 to 4.0

  • Tennis: 3.6 to 4.6

  • Basketball: 5.0 to 7.6

  • Golf: 1.4 to 2.6

Thermal Equilibrium and Comfort

• Thermal equilibrium and comfort involve regulating the thermal environment for balanced heat loss to prevent body chill or excessive respiration.

• Environmental comfort includes aesthetics and acoustics.

• Factors controlled by air-conditioning systems:

  • Mean radiant temperature of surrounding surfaces

  • Temperature of the surrounding air

  • Relative humidity of the air

  • Motion of the air

  • Odors

  • Dust

Regulation of the Thermal Environment

• Heat loss by convection: Temperature difference (typically 10°F) between skin/clothing and surrounding air causes warm air to rise and be replaced by cooler air. Air temperature adjustments should be within 1–2 degrees of optimal range.

• Heat loss by radiation: Energy transfers from the warmer body/clothing to cooler surfaces in direct view. Rate of radiant heat loss depends on the temperature difference between the body's surface and surrounding surfaces.

• Mean radiant temperature (MAT) typically ranges between 70 and 80°F, lower than the average skin and clothing temperature of 85°F, facilitating heat radiation from the body.

• In winter, room surfaces influence MAT; lights raise temperatures, while outdoor exposure lowers them. Modern designs aim for MAT alignment with room air temperature through better insulation and reduced lighting.

• Circulated air enhances comfort by balancing heat and removing humidity. Air circulation rate depends on a room's heat transfer needs (typically 70 to 100 fpm).

Criteria for Thermal Comfort

• ASHRAE Standard 90-75 was adopted by the American Society of Heating, Refrigeration, and Air Conditioning Engineers in 1975 with energy conservation as its primary focus.

• Indoor design conditions:

  • Winter: 72°F (22°C) dry bulb, up to 30% maximum relative humidity if humidification is provided.

  • Summer: 78°F (25.5°C) dry bulb where comfort air conditioning is required or used.

Indoor Humidity in Winter

• Indoor relative humidity (RH) in winter should remain above 20% to prevent damage to wooden furniture and finishes; low humidity leads to shrinkage and cracks.

• Without humidification, indoor RH rarely drops below 20-30%.

• Raising RH too high in winter can lead to:

  • Condensation on glass, especially single-pane windows (minimized by heating below the glass).

  • Moisture passing through imperfect vapor barriers and condensing within walls.

Moisture Production for Various Domestic Operations (Pounds of Moisture)

• Floor mopping (7.2 sq. m. kitchen, 0.03 psf): 2.40

• Clothes drying indoors: 26.40

• Clothes Washing: 4.33

• COOKING:

  • Breakfast: 0.90

  • Lunch: 1.17

  • Dinner: 2.69

• DISHWASHING:

  • Breakfast: 0.20

  • Lunch: 0.15

  • Dinner: 0.65

• BATHING:

  • Shower: 0.50

  • Tub: 0.12

• Human contribution (family of four/hr): 0.46

• Gas Refrigeration per hour: 0.12

• House Plants (each per hour): 0.04

• Humidifier (when used per hour): 2.00

Coping with Special Conditions

• Glass is highly sensitive to weather changes, requiring solutions to manage large glass areas in different seasons.

• A sudden increase in occupants can strain air-conditioning systems.

• Buildings have a thermal lag, taking days to return to normal after a temperature drop, potentially leading to radiant chill that air temperature adjustments may not fully address.

The Recycling of Air

• Air is reusable; outdoor air is often added to circulated indoor air for heating or cooling.

• ASHRAE requirements must be met for acceptable outdoor air quality.

• In major cities, minimal treatment is usually required to meet these standards.

• In recirculated air systems, air quality standards apply to occupied spaces.

• Treated outdoor air can be reduced to 15% with odor and gas removal, or 33% with proper filtering and temperature control.

• Reducing outdoor air use saves energy: winter heating requires a 120°F rise for outdoor air but only 45°F for recirculated air; summer cooling needs a 35°F drop for outdoor air versus 15°F for recirculated air.

• In mild seasons, high outdoor airflow can cool buildings if air quality meets standard 62-73.

Heat Loss, Thermal Value of Walls and Roofs

• For energy conservation, walls, roofs, and floors exposed to the outdoors must resist rapid heat transmission.

• Insulation is crucial; vapor barriers prevent condensation or freezing in colder areas.

• Tight construction helps retain warm air and block cold air during windy conditions.

• The balance between glass and insulated walls and roofs should be considered for fuel efficiency and comfort.

Importance of Heat Conservation

• For indoor comfort during cold weather, room air must stay at a higher temperature than outdoor air.

• Controlled ventilation contributes to heat loss.

• Energy is needed to replace lost heat, so infiltration, ventilation, and transmission rates must be carefully analyzed in architectural design.

• Thermal transmission is crucial in selecting exterior construction materials; each square foot adds to long-term fuel costs.

• The key measure is the U-coefficient, quantifying heat transfer in BTUs per hour through 1 sq. ft. of surface per 1°F temperature difference.

Heat-Transmitting Rates of Opaque and Transparent Enclosing Walls

• Glass loses heat quickly under critical conditions, such as the absence of sunlight.

• When properly positioned, glass efficiently allows solar energy to enter the building during sunny hours.

Nature of Heat Flow

• Heat flows from combustion of fuel in boilers or furnaces to warm occupied spaces, minimally to the outdoors via transmission through exterior room surfaces or loss of warmed air through openings.

• Heat Transfer Methods:

  • Conduction: Heat transfers through materials from higher to lower temperatures. Poor conductors prevent heat loss.

  • Radiation: Heat radiates from warmer surfaces to the outside air. Reflective materials minimize radiation loss.

  • Convection: Heated air expands and circulates, losing heat upon contact with cooler surfaces. Preventing air currents in walls and ceilings is crucial.
    

  Heat loss by conduction at varying rates in different materials.
  

  heat loss by convection currents
  

  heat loss by radiation carries the heat across the air space.
  

  heat loss is conducted from the room air by warm air currents that strike the inside wall.
  

  Heat is conducted away from the exterior surface of the wall by the action of the wind.

Heat Flow Through Homogenous Solids

• Conductivity (Unit Conductance, K): The number of British thermal units per hour that flow through 1 sq. ft. of material, 1 inch thick, when the temperature drops 1°F under steady heat flow.

• Conductance (C): Similar to conductivity but for thicknesses other than 1 inch.

• Formula for Thermal Resistance (R): $R = L/K$, where L is the thickness of the material and K is the thermal conductivity.

Air Spaces

• Air spaces reduce heat transfer in buildings; insulating value is influenced by position, heat flow, and surface materials, not just thickness.

• Reflective surfaces, such as aluminum foil, minimize radiant heat transfer. One side is sufficient.

• Typical air space thicknesses for insulation evaluation are 0.5 and 0.75 inches.

Effects of Air Motion

• Interior air convection transfers heat to cooler surfaces; surface conductance is called hi (i for interior), varying by location.

• Exterior wind increases heat loss by carrying away heat from warmer surfaces; conductance is called ho (o for outside).

• Both hi and ho measure heat transfer per unit area and temperature difference, independent of material thickness.

Transmission Through Building Units

• Determining the conductance factor C of homogenous materials not 1 inch thick requires reference to tables on thermal properties.

Residential Heat Gain

• Heat gain calculations involve multiplying areas, linear footage, and air infiltration rates by heat transfer factors.

• Heat gain calculations use a 25°F temperature difference (100°F outdoor, 75°F indoor).

• Occupant heat gain is factored in; each person contributes approximately 650 Btuh.

• Solar heat gain includes transmission through materials and direct solar radiation through glass, often reduced by shading coefficients.

• Humidity from indoor activities necessitates a 30% addition to sensible heat gain to account for latent heat.

• Heat gain through insulated slab edges is generally considered negligible.

Non-Residential Heat Gain Calculations

• Components of the cooling load:

1. Transmission through walls and roof

2. Transmission through glass

3. Occupants

4. Infiltration or ventilation

5. Appliances

6. Lights

Reflective Insulating Glass

• PPG Solarban 490 is a high-performance, double-glazed window unit designed for energy efficiency.

• Features a metallic-reflective coating on the outer pane and a dry air space between two clear glass panels.

• Results in soft bluish-gray transmitted light and significantly reduces solar heat gain.

• Reduces peak summer solar heat gain by 86% compared to standard clear glass.

Solar Energy and Energy Conservation

• Solar energy is becoming more popular due to rising oil, natural gas, and coal prices.

• Solar power is non-polluting, sustainable for billions of years, and abundant.

Two Ways of Heating or Cooling a Building Utilizing Solar Heat

• Passive Solar Design: Employs no sophisticated collectors or expensive technology.

• Active Solar Design: Uses technologically designed solar buildings for harnessing, absorbing, transferring, and storing solar energy.

Natural Thermosiphoning and Damper

• Natural thermosiphoning of air through solar collectors without auxiliary power.

• Heated air or water expands and rises, drawing cooler air or water from storage.

• A damper controls overheating and can operate manually or automatically based on indoor and outdoor conditions.

Heat Storage

• Avoiding transport systems of ducts, pipes, fans, and pumps saves money, simplifies operation/maintenance, and increases comfort/efficiency.

• Heat storage wall absorbs heat, heating the air which rises and enters the room. Concrete absorbs some heat while simultaneously heats the air which rises and enters the room. Heat migrates slowly inward and radiates into the building after sunset.

Heat Cooling Ventilation Energy Resources:

• Natural Materials

• Fossil Fuels: Gas, oil, and coal

• Hydroelectric power

• Nuclear Plants

• The Heat Pump

• Solar Energy

• Geothermal Energy

• Trash

Energy Requirements

• Dense human occupancy provides body heat, reducing heating needs.

• Heat pumps interchange thermal gain with cooler areas.

• Computers and business machines can provide heat.

• Smaller windows and reflective insulating glass change energy dynamics.

• Yearly energy studies in commercial and institutional buildings involve trade-off budgets.

Combustion, Chimneys, and Fuel Storage

• Fuels need oxygen to burn, requiring air intake (twice the size of the flue) from outside.
  
  *Poor burning wastes energy and creates soot; effective burning requires proper boilers/furnaces/burners and airflow adjustment.

• Carbon becomes carbon monoxide or carbon dioxide when burned; carbon dioxide produces more heat.

• Chimneys should be constructed of proper materials, such as a terra cotta lining surrounded by bricks and a space filled with non-flammable material for safety, flue size/height depend on boiler/furnace type (traditional heights are 35–40 feet).

Warm Air Heating

• Air heating ensures uniform temperatures, cleaning via filters, and fresh air intake.

• Central cooling can be added if ducts are designed for it.

• Humidifiers add humidity, while cooling systems dehumidify in summer.

• Supply registers should be placed in the floor below glass areas, especially for winter. Return grills should be on high interior walls to pick up warm air for recooling.

• Balanced designs place the furnace near the center of the house.

• The furnace should burn fuel at a rate offsetting hourly heat loss, with an air delivery rate that transmits heat effectively at the planned temperature rise.

• The motor and blower must be strong enough to overcome air friction in the supply and return ducts, furnace, filters, registers, and grills.

Furnace

• A typical furnace includes a fan (blower), motor, filters, oil burner, and heat-transfer surfaces. A humidifier can be added.

• Air enters through the blower and is forced into the warming chamber.

• Different styles include U-path flow, in-line flow, straight-line flow, and vertically upward, horizontal, or vertically downward (counterflow).

Ducts

• Ducts are constructed of sheet metal or glass fiber, either round or rectangular.

• Suggestions to reduce duct noise:

1. Do not place the blower too close to a return grill.

2. Select quiet motors and cushioned mountings.

3. Do not permit connection or contact of conduits or water piping with the blower housing.

4. Use canvas-asbestos flexible connection between bonnet and ductwork.

Duct Sizing

• Example: For a main duct in a low-velocity, warm air system delivering 1,600 cubic feet per minute (cfm), an acceptable velocity would be 800 ft. per minute (fpm). The area of the duct in square inches would be determined based on these values.

Dampers

• Dampers balance the system and adjust it to the desires of the occupants. Splitter dampers are used where branch ducts leave the larger Trunk ducts.

• Each riser can have its flow controlled by an adjustable damper in the basement at the foot of the riser. Labels should indicate the room's served.

Air Control Ducts

• Air Adjustment by Opposed-Blade Dampers

• Air adjustment by Splitter damper

• Conventional Turns in Ducts

• Right-angle Turns with turning Vanes (More Compact Method)

Registers

• Supply registers should have dampers and vanes to disperse air and reduce velocity quickly. Divert air half to the right and half to the left, while corner registers should direct all air away from the corner.

• Return grills are slotted in walls and grid-type in floors.

• All registers and grills must be tightly connected to the duct.

Controls

• The burner is controlled by a thermostat in a thermally stable location in or near the living room, protected from drafts, direct sunlight, and nearby air registers.

• The fan switch in the furnace bonnet has a cut-in temperature between 80 and 95°F.

• The burner and blower continue running while heat is needed. Blower keeps running until the furnace temperature drops below the fan switch's cut-in temperature.

• If the temperature exceeds 200°F, a high-limit switch turns off the burner for safety and comfort.

• A stack temperature control in the breaching turns off the fire if ignition fails.

Resourcefulness in the Design of Warm Air Systems

• In 1900, warm air heating systems began replacing open fires. An iron furnace was positioned in the middle of the basement and hand-fired with coal. It was encased in sheet metal, with an opening near the bottom to draw cool air from the basement. A short duct at the top of the enclosure directed warm air by gravity to a large grill in the middle of the parlor floor.

• In the 1961, basements became less common, leading to the rise of subslab perimeter systems in basementless houses. These systems retained previous features, delivering air upward across glass and returning it through high-return grills.

• In the 1970s, oil and gas became scarce, leading to the adoption of electricity and eliminating the need for combustion, chimneys, and fuel storage. Horizontal electric furnaces appeared in shallow attics or above furred ceilings, delivering air down from ceilings to warm exterior glass and returning it through door grills and open plenum space.

• Zone C duct layout: Heating-ventilating unit C serves classrooms 1 and 2. Warm air is delivered downward across cool glass through two 12 x 5 in. registers and horizontally into the space through two 12 x 5 in. registers in the common duct face. Return air exits through 18 x 18 in. door grills and is drawn into the unit via a 30 x 24 in. ceiling grill.

Hot Water and Steam Boilers: Types of Steel and Cast Iron Boilers

1. Oil-Fired Steel Boiler: A refractory chamber receives the hot flame of the burner, where combustion continues in the chamber and fire tubes. Smoke exits through the rear breaching. Water surrounding the chamber absorbs the generated heat. If a domestic hot water coil is used, a larger boiler is selected. An aquastat (water thermostat) activates the burner when the boiler water cools, maintaining a hot water reservoir for heating.

2. Gas-Fired Cast Iron Hot Water Boiler: Cast iron sections contain water that is heated by gas from below the unit. Output is related to the number of sections. It may be considered a "package" unit because the connected circulating pump stands ready to move water through convectors or baseboards.

3. Oil-Fired: Package-type sell boiler.

4. High-Output Cast Iron Hot Water Boiler: Primary and secondary air for combustion may be regulated at the burner unit. Flame enters the refractory chamber and continues around the outside of the water-filled cast iron sections. For large buildings using steam as a primary heating medium, one or several such boilers may be used. The relative lightness of this boiler type makes this package type suitable for use on upper floors of tail buildings.

5. Convertor Steam to Hot Water: When, in a building rising primary steam boilers, secondary circuits using hot water for heating are required, a convertor is used. It is considered a heat exchanger may also be used to transfer heat from steam to domestic water.

6. Electric Boilers: For hot water heating are of high capacity output. Electric steam boilers are also commonly used in large buildings.

7. Coal-Fired Steam Boiler: use of coal is achieved, a return of this variation of equipment is seen

Hot Water Heating Systems

• There are four principal methods of arranging the piping for the circulation of hot water to the heating elements located in the spaces to be heated.

Series Perimeter Loop

• This series loop system usually runs at the perimeter of the house. The water flows to and through each baseboard or intube in turn. Obviously the water at the end of the circuit is a little cooler. Values at each heating element are not possible since any value would shut off the entire loop. Adjustment is by a damper at each baseboard, which reduces the natural convection of air over the fins. For long runs or lengths of water circuit, the pipe size can be increased.

One-Pipe System

• This is a very popular choice. Special fittings, act to divert part of the flow into each baseboard. A value may be used at each one to allow for reduced heat or a complete to conserve energy, an advantage that the loop system does not provide. However, this one pipe system uses a little more piping and is thus not as economical to install as the loop system in which piping is minimal.

LEGENDS:

• (a) Boiler

• (b) Compression tank

• (c) Circulator (pump)

• (d) Hot water main

• (e) Runout (branch)

• (f) Control valve

• (g) Air vent

• (h) Baseboard heating unit

• (i) Special return fitting

Two-Pipe Direct Return

• This system is not favored because the path of water through baseboard No.1 is much shorter than that through the others, especially No.5 baseboard No.5 could easily be undesirably cool, since it is short-circuited by the others.

Two-Pipe Reverse-Return

• Except for the necessary air cushion in the upper part of the compression tank above the boiler, air must not be allowed to accumulate at high points in the piping or at the convector branches. These air vents relieve these possible air pockets, which would otherwise make the system air-bound and inoperative.

• If a system is to be drained and left idle in a cold house, water trapped in low points could freeze and burst the tubing or pipings. Operable drain values must be provided at such locations and, of course, at the bottom of the boiler.

Special Fitting

• For one-pipe systems. Venturi-type jet tee used here. In the return branch connection to the main it induces flow through the convector by retarding the flow to force water into the supply branch and producing a jet to reduce the pressure in the main following the return branch.

Hydronic and Electrical Controls

• A. Compression Tank

• B. Air Control Fittings

• C. Pressure Relief Valve

• D. Ott Burner

• E. Stack Temperature Control

• F. Dra'n Valve

• G. Aquastat.

• H. Remote Switch.

• I. Junction Box and Relays.

• J. Thermostat.

• K. Electrical Power Source.

• L. Hot Water Supply.

• M. Hot Water Return.

• N. Draft Adjuster.

• O. House Cold Water Main.

• P. Flow Control Valves.

• Q. Temperature/Pressure Gauge.

• R. Pressure Reducing Valve

• S. Shutoff Valves.

• T. Circulator.

Circulating Pump

• A centrifugal pump is selected to overcome the friction-of-flow in the piping and fittings and to deliver water at a rate sufficient to offset the hourly heat loss of the house or buildings.

Fireplaces

Conventional Masonry Fireplace

• This is often used where there is wide space and you can afford it. But conventional fireplaces are about 10% efficient. That is, 90 percent of the fire's heat goes up the flue.

Heat Circulating Fireplace

• This give off as much radiant heat as conventional types, but to this they add circulating air warmed by convection. These fireplaces have a double or triple·wall fire box with an intervening air space several inches wide. Vents at the bottom of the fire box draw cool air into this space between the inner and outer walls, where it is warmed. The heated air rises by convection to be expelled through vents located aboye the firebox opening or far· ther away-even to other rooms through ducts.

• Heat circulating fireplaces provide at least twice as much heat well-<lesigned conventional fireplaces. or are 25 to 30 percent efficient.

Pre-Built Fireplaces

• This type of fireplace makes it possible to install a wood burning fireplace with- out concrete footings, without a masonry chimney, at lower cost, and in a room where structural considerations would otherwise rule out a fireplace.(usually for apartment dwellers, vacation homes, or remodelled and additional rooms).

• freestanding metal fireplace - attractively metal, with striking an unusual shapes available. (Wrought iron or copper is preferred).

How a Conventional Fireplace Works

• Masonry Fireplaces are about 5,000 pounds (227 kilos)-usually are found on the ground floor, through can be stocked one above the other in two storey buildings.

Angles Maximize Reflected Heat to Room

• Side Splayed 3" To 5" For Each Foot of Depth Or At About 15°

• Cricket or saddle so that rainwater will not accumulate at the back of the fireplace.

Fireplace Furnishings and Accessories:

• FIRE LIGHTER-to start a fire (small pieces of pine resin wood or "saleng" is effective)

• COAL HOD OR WOOD CARRIER-to carry and hold fuel.

• TONGS, LOG FORK, and SHOVEL-feed the fire poker-stirs the fire.

• Bellows-useful in stimulating the air Flame.

• Metal Hoods: Decorative and Functional

Suggested Width of Fireplace Opening Appropriate to a Size of a Room

Hydronic Heating Design and Zoning

• Hydronic heating systems or Radiant Heating, can be installed in floors or ceiling using baseboard hydronic heaters or radiators to distribute heat evenly. A home heating system that uses hot liquid, typically water, to provide space heating. The liquid is heated and pumped through pipes to distribute heat to the house. The cooled liquid returns to the heater, and the process repeats.

Hydronic Heating Design and Zoning Calculations

• TOTAL EQUIVALENT LENGTH - IS THE LENGTH OF THE CIRCUIT THROUGH WHICH THE WATER IS CIRCULATED PLUS A LENGTH EQUIVALENT TO THE RESISTANCE OFFERED BY THE FITTINGS, BOILERS, ETC.

• PRESSURE DROP IN THE PIPE - THIS DROP DUE TO THE FRICTION EXPRESSED IN MIL-INCHES OF WATER PER FOOT OF PIPE, IS THE DIFFERENCE IN PRESSURE CAUSED BY FRICTION IN 1 FT. OF THE PIPE AND PRESENTS THE STATIC HEIGHT OF WATER IN THOUSAND OF AN INCH CAPABLE OF BEING SUSTAINED BY THIS DIFFERENCE IN PRESSURE

• TOTAL FRICTION HEAD - EXPRESSED IN FEET, THIS HEAD IS THE COLUMN OF STATIC WATER THAT COULD BE SUSTAINED BY THE DIFFERENCE IN PRESSURE IN THE ENTIRE SYSTEM OWING TO FRICTION.

• REQUIRED FLOW - THE WATER FLOW IN GALLONS PER MINUTE TO BE CIRCULATED TO MAKE UP THE HOURLY HEAT LOSS AND THE SELECTED DROP IN THE WATER TEMPERATURE.

• REQUIRED VOLUME OF EXPANSION TANKS - THIS IS RELATED TO THE VOLUME OF WATER IN THE SYSTEM AND THE OVERALL RISE IN TEMPERATURE FROM COLD WATER SUPPLY TEMPERATURE TO BOILER WATER OPERATING TEMPERATURE

• PUMP RATING - THE PUMP SIZE IS SELECTED ON THE BASIS OF THE REQUIRED FLOW AND THE TOTAL FRICTION HEAD.

Electric Resistance Heating

• Floor Type. This procedure permits a method of operation that can contribute to the saving of energy. Temperature in rooms that are not in use, can be lowered or the room units turned off by means of a switch. Thus the rooms actually occupied would be the only ones to draw full energy. Baseboard and drop-in-units have a fast response.

• Ceiling Type

Refrigerated Cooling for Houses

• COOLING/HEATING by a combined Hydronic and Air System- This system combines a perimeter hot water heating pipe with an overhead air-handling system. A boiler with a tankless coil supplies domestic hot waters. The heat output supplies both perimeter loop and a coil in the air-handling unit of the duct system. The total heating load is met by the combination of radiant heat generated by the perimeter loop and heated air from the overhead air-handling system. The perimeter loop consists of only 1/2 or 3/4 inch copper tubing imbedded 4 inch below the top floor slab to kill the cold slab effect having the capacity of 35° F.

• AIR-TO-AIR COOLING- Houses are cooled by a rather simpler arrangement of the refrigeration cycle. The circuit of a refrigerant in compression, condensing, and evaporation, in which the condenser heat is carried away by the water, and the evaporation process draws heat out of water in another circuit to produce chilled water.

Central-Station Air Conditioning

• In a central station air conditioning system, all the components of the systems are grouped together in one central room and conditioned air is distributed from central room to the required places through extensive duct work.

• Complete air conditioning requires a source od heating such as a boiler, furnace, a method of cooling such as the refrigeration cycle, equipment for introducing moisture and for removing it, filter or air washing devices to clean the air and, for proper air distribution, flowers, ducts, and registers.

Principles of Central Cooling

1. COOLING BY COMPRESSIVE REFRIGERATION: The compressive refrigeration cycle is a scheme for transferring heat from one circulated water system (chillled water) to another condenser water. Is is necessary to consider the means for producing cool air, or the chilled water by which air may be cooled. Occasionally ground water is obtainable at temperature low enough for direct use but generally the use of refrigeration machine or other special cooling device is necessary.

2. UNIT OF REFRIGERATION: The requisite capacity of a refrigerating machine in tons may therefore be found by dividing the total heat gain in building on Btuh by 12,000. A ton of refrigeration is the cooling effects obtained when 1 ton of 32°F in 24 hrs.

3. COOLING by ABSORPTION: Suitable for installations up to 1,000 tons capacity, the external connections of this devide are similar to the centrifugal-refrigeration. Its a motive power steam used in regenerative process to strengthen a salt solution. Producing chilled water and has a cycle, of the condensing water that must be cooled.

4. PRINCIPLES OF CENTRAL COOLING: In larger buildings and those with varied and diverse occupancy, it is usually preferred to centralize the refrigeration plant. The condenser is cooled by water circulated to an outdoor cooling tower and the evaporator produces chilled water. The latter is then pumped to wherever it is needed in the building.

5. CENTRAL STATION CONDITIONING: When heat is needed in winter the air circulated through the room or other spaces must be heated. cooling coil in the air stream and the addition of the preheating and reheating coils, supplied with steam from a steam boiler.

Process/Absorption-Refrigeration Cycle

1. The salt solution in the absorber soaks up some of the water remaining is thereby cooled by evaporation.

2. Evaporator Coil and Pump Added-Water from this tank is pumped to a spray header which wets the coil.

3. Solution Pumps and Generator Added-To keep the