Chapter 1 hvac

Refrigeration & Air Conditioning System

BMCT 4153

Faculty of Mechanical Engineering, UTeM, Semester 1, 2012/2012

By Fadhilah binti Shikh Anuar

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Contents

1. Introduction – Malaysia and Energy Policy

2. Introduction to Heating, Ventilating and Air Conditioning (HVAC)

3. Classification of HVAC System4. Application of HVAC

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Learning Outcomes

At the end of this lecture, the students should be able to: Define air conditioning and refrigeration system. Discuss in depth the air conditioning and

refrigeration types and applications used in everyday life.

Discuss terms associated with the refrigeration system and air conditioning performance.

Describe the fundamental underlying scientific principles and theory of refrigeration system and air conditioning.

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Basic Facts of Malaysia

Population: 26,896,751 (December 2006 est.) – now estimated 28 million plus

Geographic coordinates: 2 30 N, 112 30 E

Area: total: 329,750 sq km, land: 328,550 sq km, water: 1,200 sq km

Climate: tropical; annual southwest (April to October) and northeast (October to February) monsoons

Natural resources: petroleum, timber,, copper, iron ore, natural gas, tin bauxite

Environment - international agreements:Biodiversity, Climate Change, Climate Change-Kyoto Protocol, Desertification, Endangered Species, Hazardous Wastes, Law of the Sea, Marine Life Conservation, Ozone Layer Protection, Ship Pollution, Tropical Timber 83, Tropical Timber 94, Wetlands

Export: electronic equipment, petroleum and liquefied natural gas, wood and wood products, palm oil, rubber, textiles, chemicals

Import: electronics, machinery, petroleum products, plastics, vehicles, iron and steel products, chemicals

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National Energy Policy 

OBJECTIVES Three principal energy objectives are instrumental in guiding the future energy sector development. They are:-

1. The Supply Objective (Objektif Pembekalan) To ensure the provision of adequate, secure and cost-effective energy supplies through developing indigenous energy resources both non-renewable and renewable energy resources using the latest cost options and diversification of supply sources both from within and outside the country;

2. The Utilization Objective (Objektif Penggunaan) To promote the efficient utilization of energy and discourage wasteful and non- productive patterns of energy consumption; and

3. The Environmental Objective (Objektif Persekitaran) To minimize the negative impacts of energy production, transportation, conversion, utilization and consumption on the environment.

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Strategies to Achieve National Energy ObjectivesSecure supply •Diversification of fuel type and sources, technology, maximize use of indigenous energy resources, adequate reserve capacity to cater for contingencies [adequate reserve margin for generation, upgrading transmission and distribution networks and distributed generation (islanding);

Sufficient supply •Forecast demand, right energy pricing and formulate plans to meet demand.

Efficient supply •Promote competition in the electricity supply industry.

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Cont..Cost-effective supply •Promote competition and provide indicative supply plan to meet demand based on least cost approach using power computer software such as WASP;

Sustainable supply •Promote the development of renewable and co-generation as much as possible.

Quality supply (low harmonics, no surges and spikes, minimal variation in voltage) •Match quality with customer demand with variable tariffs

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Cont..

Efficient utilization of energy • Bench marking, auditing, financial and

fiscal incentives, technology development, promotion of ESCOs, Labelling, Ratings, correct pricing, energy managers; and

Minimizing Negative

Environmental Impacts • Monitor the impacts, improve efficiency of

utilization and conversion and promote renewable.

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Energy Programmes • Centre for Education and Training for Renewable Energy and Energy Efficiency(CETREE)

•  Project on Capacity Building in Integrated Resources Planning (IRP) at Government and Related Agencies  

•  MECM's Low Energy Office (LEO) Project at Putrajaya

•  Small Renewable Energy Programme (SREP)

•  Demand Side Management (DSM) Project

• Green Building Index

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Basic Energy Efficiency Terms

Coefficient of Performance (COP) A ratio calculated by dividing the total heating capacity

provided by the heat pump, including circulating fan heat but excluding supplementary resistance heat (Btus per hour), by the total electrical input (watts) x 3.412.

Energy Efficiency Ratio (EER)A ratio calculated by dividing the cooling capacity in Btus per hour (Btu/h) by the power input in watts at a given set of rating conditions, expressed in Btu/h per watt.

Seasonal Energy Efficiency Ratio (SEER)SEER is a measure of cooling efficiency for air conditioning products. The higher the SEER rating number, the more energy efficient the unit is.

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Understanding Heating and Cooling Equipment Performance Ratings

SEER – The Seasonal Energy Efficiency Ratio is a representation of the cooling season efficiency of a heat pump or air conditioner in cooler climates. It applies to units of less than 65,000 Btuh capacity

EER – The Energy Efficiency Ratio is a measure of a unit’s efficiency at full load conditions and 95 degrees outdoor temperatures. It typically applies to larger unit over 65,000 Btuh capacity.

HSPF – The Heating Season Performance Factor is a representation of the heating efficiency of a heat pump in cooler climates.

COP – Coefficient of Performance is the measure of heating efficiency of a heat pump at a constant temperature of 47 degrees.

Btuh – Btuh or Btu/h is a rate of heating or cooling expressed in terms of British Thermal Units per Hour.

Ton – One ton of cooling is the energy required to melt one ton of ice in one hour. One ton = 12,000 Btuh

2. Introduction to HVAC

Heating, ventilation & Air conditioning (HVAC) is the technology of indoor and automotive environmental comfort.

HVAC system design is a major sub discipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer.

Refrigeration is sometimes added to the field’s abbreviation as HVAC & R or HVACR.

HVAC is important in the design of medium to large industrial and office buildings where safe and healthy building conditions are regulated with respects to temperature and humidity, using fresh air from outdoors.

Air conditioning

It refers to the control of temperature, moisture content, cleanliness, air quality, and air circulation as required by occupants, a process or a product in the space. ~ by Willis Carrier

Based on ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) standard, indoor comfort conditions that are thermally acceptable to 80% or more of a commercial building’s occupants.

Generally, these comfort conditions are called as the “comfort zones” – temperature between 68 – 75 deg F for winter and 73-78 deg F during summer. Room air relative humidity is 50% and moving at a slow speed (velocity) of 30 feet/min or less.

Acceptable range; temp: 70 to 75 deg F, relative humidity: 40 to 50%

Refrigeration

It has many definition. Generally, as any process of heat removal. It is also defined as that branch of science which deals with the process of reducing and maintaining, the TEMPERATURE space or material below the temp. of the surroundings.

Therefore, the heat must be removed from the body. The heat is transferred to another whose temperature is below that of the refrigerated body.

Relationship of the refrigeration & air-conditioning fields

Cooling & dehumidifying operations in air conditioning

Heating, humidifying, and control of air quality

Industrial refrigeration,

including food preservation, chemical and

process industries

Air conditioningRefrigeration

Refrigerating agent

In any refrigerating process, the body used as the heat absorber or cooling agent is known as Refrigerant. another sub topic in this subject

According to the effect of heat absorbed by the refrigerant, all cooling processes may be classified as either SENSIBLE or LATENT.

Sensible process – when the absorbed heat cause an increase in the TEMPERATURE of refrigerant

Latent process – when the absorbed heat cause a change in physical state of the refrigerant.

Common HVAC units and dimensions

Unit in HVAC, include both; English and SI units.

Examples: gpm (gallons per minute) for liquid volume flow rates cfm (cubic feet per minute) for air volume flow rates in.wg (inches water gauge) for pressure

measurement in air-flow systems ton (12,000 Btu per hour) for the description of

cooling capacity or rate ton-hr (12,000 Btu) for cooling energy

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Air Conditioning Functions

1. Provide the cooling and heating energy as required

2. Condition (process) the supply air by:(a) heat or cool,(b) humidify or dehumidify,(c) clean and purify, and(d) attenuate any objectionable noise produced by the HVAC&R equipment

3. Distribute the conditioned air, containing sufficient outdoor

air, to the conditioned space.

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Air Conditioning Functions

4. Control and maintain the indoor environmental parameters

within predetermined limits between the conditioned space and surroundings, which include:

a) temperature,b) humidity,c) cleanliness, d) air movement, e) sound level, and f) pressure differential.

Energy versus power

Power is the rate at which energy is produced or consumed. With all other factors being equal, the electrical power (kW) required by an HVAC system or component depend on size.

Size = capacity = load = demand The energy (kW-hr) used by an HVAC

system depends not only on the size, but also the on the fraction of capacity or load at which the operating and the amount of time that it runs.

Example 1

Determine the July electric utility bill for a facility that used 112,000 kw-hrs during that month and which had maximum power usage of 500 kw during the peak periods of time in that month.

The utility has a fixed ‘meters’ charge of $75 per month and charges of flat rate of 5 cents per kw-hr for energy and $12 per kw for maximum power usage during peak periods in July.

Answer- Example 1

The monthly bill is made up of a fixed meter charge, a charge for energy, and a charge for peak demand.

Fixed monthly meter charge =$75.00 Energy charge (112,000 kw-hrs x 0.05$/kw-hr)

= $5600.00Demand charge (500 kw x $12.00/kw) = $6000.00

TOTAL monthly electric bill = $ 11,675.00

Heat transfer

Heat naturally flows from a higher energy level to a lower energy level. In other words, heat travels from a warmer substance to a cooler substance.

When there are temperature difference, heat transfer will occur.

The greater the temperature difference, the greater the heat transfer

Types of heat transferThree types of heat transfer:- conduction, convection, radiation.

1 - Conduction (solid body with another solid body ) Heat energy traveling from one molecule to another. Example: heat exchanger, home

furnace

Different transfer rate, depends on the material/ solid body types.

2 - Convection (solid body with flowing medium) when some substance that is readily movable such as air, water, steam ,refrigerant moves

heat from one location to another.

HVAC system uses convection in the form of air, steam ,water, refrigerants in ducts and piping to convey heat energy to various parts of the system.

Natural convection – when air is heated, it rises Forced convection – when a fan or pump is used to convey heat in fluids such as air and

water.

3 – Radiation (solid body with another solid body, have space between them ) Heat transferred by radiation travels through space without heating the space.

Example: The space heater does not heat the air (the space) but heats the solid objects that come into contact with the heat rays.

Heat content and specific heat

The heat content of a substance = enthalpy, h Unit enthalpy: Btu/lb or Btu/lb deg F

Specific heat (Fahrenheit scale) is the amount of heat necessary to raise the temperature of 1 lb of a substance of 1 deg F

Example: specific heat of water is 1 Btu/lb deg F specific heat of air is 0.24 Btu/lb deg F

Heat Measured in Hvac Systems

SENSIBLE HEAT

Sensible heat is heat from people, lights, motors, heating equipments, and outdoor air.

E.g. A seated person in an office gives off approximately 225 Btuh of sensible heat into the conditioned space.

Enthalpy units of sensible heat are in Btu/lb deg F.

The change in the sensible heat level as measured with ORDINARY THERMOMETER is sensible temperature.

Sensible temperature is measured in degrees Fahrenheit and it is indicated as dry bulb (db) temperature.

Heat Measured in Hvac Systems

LATENT HEAT

Latent heat (hidden heat) is ; heat that is known to be added to or removed from substance but no temperature change is recorded.

E.g. Heat released by boiling water (involve physical change only; from liquid vapour)Once water is brought to the boiling point, adding more heat only makes it boil faster, it does not raise the temperature of water.

Enthalpy units of latent heat are in Btu/lb deg F.

Level of latent heat is measure in deg Fahrenheit and it is indicated as dew point (dp) temperature.

Heat Measured in Hvac Systems

TOTAL HEAT

Total heat = Sensible heat + Latent Heat Measure in deg F and it is indicated as wet bulb (wb)

temperature.

Total heat level is measured with an ordinary thermometer but the thermometer tip is covered with a sock made from water-absorbing material.

Enthalpy is in Btu/lb deg F.

A seated person gives off approximately 450 Btuh of total heat (225 Btuh sensible heat + 225 Btuh latent heat).

Heat Load

The rate of at which heat must be removed from the refrigerated space or material in order to produce or maintain the desired temp.

The heat load is the SUM of..(a) Heat leaks through walls, doors, and

window(b) Heat that must be removed from the

refrigerated product(c) Heat that must be removed from the people

working in space, by electric lights etc.

Unit of refrigeration In MKS*, the unit of refrigeration used is ton. In SI , system , kW is used as the unit of

refrigeration.

Definition of the capacity of the system. It is the rate at which it will remove heat from the refrigerated space, usually stated in kJ/hr on in terms of its ice melting equivalent.

Before the era of mechanical refrigeration, ice was widely used as a cooling medium. Now, the cooling capacity of the mechanical refrigeration is compared with ice- melting equivalent.

When one-ton ice melts in one day, it will absorb,

900 x 335 = 30, 1500 kJ/day where 900kg = 1 short ton, 335 kJ/kg = Latent heat of ice.

Heat absorbed/hr = 30, 1500/24 kJ/hr

Heat absorbed/sec = 30, 1500 / (24 x 3600) kJ/sec = 3.5 kJ/sec = 3.5 kW

*MKS is the system of units based on measuring lengths in meters, mass in kilograms, and time in seconds. 

A capacity of 1 ton

So, a mechanical refrigerating system having the capacity of absorbing heat from the refrigerated space at the rate of 3.5kW is cooling at a rate equivalent to the melting of 1 ton ice in 24 hr and is said to have a capacity of 1 ton.

= 1 ton refrigeration (1TR)

1 Ton = 3.5kJ/sec = 3.5 kW = 210 kJ/min = 12,600 kJ/hr

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Thermodynamics Laws

Zeroth – standard measurement, Ta=Tb, Ta=Tc, then Ta=Tc

First – energy balance (quantity) Energy In = Energy Out

Second – energy quality, ds=dQ/T Third – Absolute zero

Zero Kelvin

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Thermodynamics Properties

Basic properties Pressure, p Temperature, T Specific volume, v Specific Enthalpy, h Specific Entropy, s Specific Internal energy, u

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Properties diagram

p-v gives work, W T-s gives Heat, Q h-s, extensively used in steam generation

processes p-h (Mollier diagram), used extensively in

refrigeration system Psychrometric chart (inverse of p-h

diagram), used extensively in Air Conditioning system

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p-v

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Psychrometric chart

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Selection Criteria for A/C

1. Performance requirements: -on comfort, noise, control options, flexibility and meeting

requirements of local regulations/codes2. Capacity requirements

-range of capacity, multiple units, zoning, etc.3. Spatial requirement

-plant room space, space for ducting and piping (vertical shafts), space for terminal equipment

4. Costs-initial cost, operating cost and maintenance cost

5. Energy consumption -for both economic and environment reasons

6. System qualities -aesthetics, life, reliability and maintainability

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3. Classification of HVAC

HVAC SYSTEMS

Central chilled Water AC system

All air system

Air-watersystem

Direct ExpansionSystem

All watersystem

InductionFan coilTwo-pipeThree-pipe

Single zoneReheatVAVDual ductMultizone

Fan coil unitCentral chilled waterWater cooling tower

Window unitUnitary & rooftopSplit type & packageHeat pump

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HVAC System

1. Individual Systems : a self-contained , factory-made air conditioner to serve one or two rooms (e.g. room/ window air conditioner and split-type units). (Direct expansion system)

2. Unitary Packaged Systems: similar in nature to individual systems but serve more rooms or even more than one floor, have an air system consisting of fans, coils, filters, ductwork and outlets (e.g. in small restaurants, small shops and small cold storage rooms).

3. Central (Hydronic) Systems: basically consists of three major parts: (Central chilled water AC system)

a. Air system – air handling units (AHU), air distribution (air duct) system and terminals.

b. Water system – chilled water system, hot water system, condenser water system.

c. Central plant – refrigeration (chiller) plant, boiler plant.

DIRECT EXPANSION SYSTEM- HVAC SYSTEM -

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Self Contained Air Conditioning Unit

1. Window-mounted and floor - mounted units.

2. Split type conditioner

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Split Unit Type

In the split system, the indoor air handler comprises controls and the air system, containing mainly:a. fans, b. filters, and c. DX coils.

The outdoor condensing unit is the refrigeration system, composed of

a. compressors and b. condensers.

Rooftop packaged systems are most widely used.

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CENTRAL CHILLED WATER AC SYSTEM

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Central Air conditioning

In larger buildings and particularly in multi-story buildings, the split-system approach begins to run into problems. 1. running the pipe between the condenser and the

air handler exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor)

2.amount of duct work and the length of ducts becomes unmanageable.

Hence, chilled-water system is introduced. However need to use ‘cooling tower’

Distribution systems for chilled water and heating water in CENTRAL A/C

Cooling Tower…

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Cooling Tower

Used to dissipate the heat from the outside coil, hence improved systems efficiency

Cooling tower creates a stream of lower-temperature water.

Water runs through a heat exchanger and cools the hot coils of the air conditioner unit.

Costs more to buy the system initially, but the energy savings can be significant over time (especially in areas with low humidity): pay back time is fairly short (6-12 months).

Cooling tower working principle schematic diagram

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Central System A/C system – An example

Central (hydronic) air conditioning system consists of:a) an air system, b) a water system, c) a central heating /cooling plant, and d) a control system.  

Note:  HVAC water-distribution systems = Hydronic system

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a) Air System

An air system is sometimes called the air-handling system.

An air system function is to:• Condition• Transport• distribute the conditioned, • Recirculating outdoor, and exhaust air and • Control the indoor environment according to requirements.

Major components of an air system are:1. air-handling units (AHU)2. supply/return ductwork3. fan-powered boxes4. space diffusion devices and 5. exhaust systems.

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Cont.

An AHU usually consists of:1. supply fan(s), 2. filter(s),3. a cooling coil,4. a heating coil, 5. a mixing box, and other accessories.

An AHU conditions the outdoor/ recirculating air, supplies the conditioned air to the conditioned space, and extracts the returned air from the space through ductwork and space diffusion devices.

A fan-powered variable-air-volume (VAV) box, often abbreviated as fan-powered box, employs a small fan with or without a heating coil. Draws the return air from the ceiling plenum, mixes it with the conditioned

air from the air-handling unit, and supplies the mixture to the conditioned space.

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CV and VAV

Constant volume (CV) pump a constant flow of air into each room Temperature changes are effected by heating or cooling the

air Frequently mix a percentage of outside air with recycled

indoor air.

Variable volume (VAV) Maintain thermal comfort by varying the amount of

heated or cooled air supplied to each space.

Function primarily based on this mixing principle, they can also be combined with systems that change the temperature of the air they introduce into the room.

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Cont.

Space diffusion devices; slot diffusers mounted in the suspended ceiling

purpose is to distribute the conditioned air evenly over the entire space according to requirements

The return air enters the ceiling plenum through many scattered return slots.

Exhaust systems have exhaust fan(s) and ductwork to exhaust air from the lavatories, mechanical rooms, and electrical rooms.

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b) Water System

Water system includes: chilled and hot water systems chilled and hot water pumps condenser water system and condenser water pumps.

Purpose of the water system is: to transport chilled water and hot water from the central

plant to the air-handling units, fan-coil units, and fan powered boxes and

to transport the condenser water from the cooling tower, well water, or other sources to the condenser inside the central plant.

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c) Central Plant

The refrigeration system in a central plant is usually in the form of a chiller package.

Chiller packages cool the chilled water and act as a cold source in the central hydronic system.

The boiler plant, consisting of boilers and accessories, is the heat source of the heating system.

Either hot water is heated or steam is generated in the boilers.

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d) Control System

Modern air conditioning control systems for the air and water systems and for the central plant consist of: electronic sensors, microprocessor-operated and microprocessor-controlled modules

Can analyse and perform calculations from both digital and analog input signals, i.e., in the form of a continuous variable.

Control systems using digital signals compatible with the microprocessor are called direct digital control (DDC) systems.

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Cont.

DDC controllers regulate the air-handling units and the terminals.

Communicate with the central operating station through interface modules.

In case of emergency, the fire protection system detects alarm conditions.

The central operating station gives: emergency directions to the occupants operates the HVAC&R system in a smoke control mode and actuates the sprinkler water system.

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SOME COMPARISON

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4. Applications of HVAC

1. Comfort air conditioning systems and2. Process air conditioning systems.

Comfort Air-Conditioning – a process of controlling the air temperature, relative humidity, ventilation, air movement and air cleanliness of a given space in order to provide the occupants with a comfortable indoor temperature.

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Two general categories of Air Conditioning System

Air Conditioning

Human Comfort Industry

Government buildingHospital

HotelDomestic Usage

LaboratoriesPrinting

Manufacturing Textile

Clean roomPhotography

Computer LaboratoriesPower plant control room

Food industryAutomotive

Chemistry & ProcessSport- Ice sky

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Let, imagine this scenario ….. Heat gains from sunlight, electric lighting

and business machines, may cause unpleasantly high temperatures in rooms, unless windows are opened.

If windows are opened, then even moderate wind speeds cause excessive draughts, becoming worse on the upper floors of tall buildings.

If windows are opened, noise and dirt enter and are objectionable, becoming worse on the lower floors of buildings, particularly in urban districts and industrial areas.

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Cont.

The relief provided by natural airflow through open windows is only effective for a depth of about 6 metres inward from the glazing.

The inner areas of deep buildings will not really benefit at all from opened windows.

Coupled with the need for high intensity continuous electric lighting in these core areas, the lack of adequate ventilation means a good deal of discomfort for the occupants.

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Mechanical Ventilation

Mechanical ventilation without refrigeration is only a partial solution.

Must provides a controlled and uniform

means of air distribution, in place of the unsatisfactory results obtained with opened windows

Internal air/room temperatures must also suitable.

Normally room temperature will be several degrees lower than that outside

Hence natural or mechanical ventilation is needed as well as to insulate the building from heat gain.

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Sick Building Syndrome (SBS)

Sick building syndrome is very common in poorly designed air conditioned buildings due to inadequate ventilation and use of improper materials.

The sick building syndrome is characterised by the feeling of nausea, headache, eye and throat irritation and the general feeling of being uncomfortable with the indoor environment.

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Thank You