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New Termsinternal factors Sources of heat generation from within abuilding, including people, lights, and machinery.external factors Sources of heat generation from outside afacility, including wind, solar radiation, transmission, andleakage.Solar radiation is the heat generated and released by the sun aselectromagnetic waves. This heat is greater in the east in the morning andwest in the afternoon. The sun’s radiation can penetrate glass, and can be usedas a heat source to warm interior space.Transmission is the heat transfer process of moving heat through walls andwindows into or out of a facility. Different materials transfer heat at differentrates. When the outside temperature is above the inside temperature, heattransfers into the facility through the outside structure. When the outsidetemperature is lower than the inside temperature, heat will be transferred outof the building. This is why offices and rooms in a house can become so warmin the summer and so cold in the winter.Leakage occurs when pressure differences in a building cause air to infiltrateor exfiltrate through cracks in walls, doors, windows, and roof equipmentpenetrations.New Termssolar radiation The heat generated by the sun. Energyemitted from a source in the form of rays.transmission The heat transfer process of moving heatthrough walls and windows into or out of a facility.leakage The escaping of heat through cracks in walls,windows, doors, or any other opening in the structure of afacility.12Lesson 1-

Cooling and Heating LoadsCooling load is the total heat gained from the sum of internal and externalfactors. This heat must be removed by cooling the zone or building. Abuilding may have different cooling load ratings for different zones within itbecause of different internal and external factors in any area at any giventime.Heating load is the total heat lost from the sum of internal and externalfactors. This heat must be replaced by adding heat back to the various areas inthe facility that are cooler than the desired setpoint.Lesson - 113

New Termscooling load The total heat gained from internal andexternal factors.heating loadfactors.The total heat lost from internal and externalsetpoint The desired temperature that is monitored by athermostat or other type of sensor.Installing the HVAC SystemThe general contractor is responsible for the completed construction of abuilding. For large-scale building projects, the general contractor hiressubcontractors to help complete the project. The general contractor hires amechanical or HVAC contractor to professionally install the HVAC system.The HVAC contractor works with a consulting mechanical engineer todesign the HVAC system. The mechanical engineer creates the contract orengineering drawings of the HVAC system for a building depending on theneeds of the owner, the facility’s function, the comfort factors, and theinternal and external design factors. The HVAC contractor takes theengineering drawings and creates shop drawings to be used as guidelines forthe workers installing the HVAC system. The HVAC contractor hires workersto install the HVAC system and procures equipment.After the HVAC system is installed, the Balancing contractor is responsiblefor testing, adjusting, and balancing (TAB) the HVAC system to verify thatthe system operates correctly.14Lesson 1-

New TermsHVAC contractor Also known as the mechanicalcontractor, responsible for the installation of the HVACsystem.consulting mechanical engineer Engineer responsible fordesigning the plans and specifications for installation of anew HVAC system.engineering drawings The plans and specifications for theinstallation of a new HVAC system.shop drawings The HVAC contractor’s larger-scaled, andmore detailed, plans and specifications that are given to theworkers to use as instructions for the installation of an HVACsystem.ReviewDesign is important to the successful operation of an HVAC system. Theoccupants’ needs will be met if the designer considers both internal andexternal factors.People, lights, and equipment are internal factors that affect the temperature,humidity, and air quality in a facility.Wind, solar radiation, transmission, and leakage are all external factors thataffect the temperature, humidity, and air quality in a facility.Internal and external factors cause a facility to lose or gain heat. The totalheat gained is the cooling load, and the total heat lost is the heating load.The HVAC contractor is responsible for the installation of the HVAC system.A consulting mechanical engineer designs the HVAC specifications and theHVAC contractor creates shop drawings from the specifications that theworkers use as installation instructions.Lesson - 115

Exercises: 1.21. Identify the following HVAC design factors as Internal or External bycircling the correct factor ternalExternalSolar nternalExternal2.Fill in the blanks below with the correct word(s) to make the followingstatements true.The is the total heat lostfrom internal and external factors.The is the total heatgained from internal and external factors.The is responsible forcreating the engineering drawings.The is responsible forcreating the shop drawings.3. Describe a setpoint.16Lesson 1-

1.3 ComfortComfortComfort is a subjective feeling. Because individuals perceive comfortdifferently, comfort cannot be measured directly. Variables that affect aperson’s comfort are indoor air quality and body heat loss. While anindividual person’s comfort level encompasses many complex factors, HVACsystems function primarily to maintain thermal comfort.Thermal comfort will exist when someone is surrounded by an environment ofproper temperature, relative humidity, air quality and distribution that allowsthem to give up their body heat at the same rate it is produced. A person’sbody generates heat as it performs routine bodily functions such as theoxidation of food substances or body fat. As the body is producing heat, itwill also be losing it through the process’ of radiation, conduction orconvection. The average temperature of the human body depends upon abalance between the sum of the heat generated by the body and the sum of theheat loss to the surrounding air.New Termsradiation The process of heat being given off from the bodyin electromagnetic ray form as it produces heat from internalchemical reactions or body processes.conduction The process of heat being transferred bymolecule to molecule through direct contact.convection The process of heat being transferred by a fluid.HeatHeat is a form of energy that can exist on its own and can be moved from onelocation to another. Heat is not matter; it does not exist as a solid, a liquid, orgas, and so it cannot be measured by weight or volume. When we think ofheat, we tend to think of temperature, but temperature does not really measureheat content. Instead, temperature indicates the average velocity of theLesson - 117

molecules of a substance, or the intensity of heat in a substance. As thetemperature of heat in a substance increases, the molecules move morerapidly. As the temperature drops, the molecules slow down. If all heat isremoved from a substance all molecular motion stops. This is called absolutezero.Temperature is generally measured in degree Fahrenheit ( F) or degreeCelsius ( C) units. For example, water at sea level has a freezing point of32 F or 0 C, and a boiling point of 212 F or 100 C. Fahrenheit is the mostcommonly used temperature scale in the United States. It is used in theremainder of this training workbook.Heat content is most frequently measured in British Thermal Units or BTUs.A BTU is the amount of heat required to raise the temperature of one pound ofwater by one degree Fahrenheit. For comparison purposes, the completeburning of a common wooden match produces approximately one BTU.The rate of heating is generally described in terms of BTUs per hour, BTU/h.This expression describes not only how much heat is present but also how fastthe heat energy is transferring.New Termstemperaturesubstance.The average molecular velocity of aBritish Thermal Units (BTU) The amount of heat requiredto raise the temperature of one pound of water one degreeFahrenheit. BTU/h is the rate of heat transfer.HumidityHVAC systems monitor and control the variables in an indoor environmentthat affect the occupants’ perceptions of thermal comfort. Temperature andhumidity impact the skins evaporation rate. If the evaporation rate to thesurrounding air is too high or too low, the body will feel uncomfortable. If theair is dry, the evaporation rate increases, so heat transfers from the body at ahigher rate. This may cause the person to feel chilly even when airtemperature is in the mid 70s.Space temperature is the temperature of the air in a building zone18Lesson 1-

Humidity slows down the evaporation process. High temperature andhumidity cause the body mechanism to work harder to disperse heat, and thebody feels uncomfortable.Relative humidity is the ratio of the amount of water vapor actually presentin the air to the greatest amount possible at the same temperature.New Termsspace temperature The actual measured temperature of theair in a space or zone under control.relative humidity The percentage of the amount of watervapor present in the air compared to the maximum the aircould possibly hold.VentilationCleanliness/ventilation relates directly to comfort. Ventilating fresh outdoorair into a facility replaces polluted air from occupants and interiorfurnishings. In most cases, outdoor air is fresher than indoor air.Contaminants such as dust and smoke can be physically removed through theHVAC system. Proper HVAC filtering and ventilation can reduce particlespresent in indoor air that irritate the eyes, nose, and lungs.ReviewComfort is not only affected by combinations of temperature, humidity, andair distribution, but also by physical activity. Comfort levels vary in as manyways as people do.Lower relative humidity levels require a higher temperature to maintaincomfort. Conversely, higher relative humidity levels require a lowertemperature to maintain comfort.Lesson - 119

Exercises: 1.31.Identify three conditions that affect the rate of body heat loss.2.Which of these conditions can be controlled by an HVAC system?3.How are these conditions adjusted to improve human comfort?20Lesson 1-

1.4 HVAC System ComponentsAir Conditioning TheoryHVAC system components transfer heat from one place to another to moveand condition indoor air. The Second Law of Thermodynamics states that heattransfers in one direction from a higher temperature source to a lowertemperature source. HVAC systems function on this principle to either addheat to or remove heat from a facility to control and maintain comfort.HVAC System ComponentsA facility’s HVAC system can consist of different parts depending on what thepurpose of the facility dictates. For example, if a facility requires the indoorspace in the basement to be cooled, the HVAC system needs to include heatrejecting equipment. Simultaneously, if the facility requires the remainingfloors to be heated and cooled, the HVAC system must not only include acooling source but a heating source as well. The mechanical componentstogether perform all functions required in a facility’s HVAC system beyondjust temperature control. HVAC system design requirements may includeheating, cooling, ventilating, humidifying, dehumidifying, pressurizing, andthe distributing of air or water.New Termheat-rejecting Equipment that removes heat from aspecified area in order to cool the temperature of that space.Lesson - 121

Table 1.2 HVAC System ComponentsTypical HVAC system componentsExampleHeat generation systemBoilerFurnaceElectric heating coilHeat rejection systemChillerWindow air unitEvaporative spray coilAir delivery systemFanSheet metal ductTerminal unitFanFilterDampersMixing boxPiping systemCoilHeat generation systems are major HVAC system components involved inmaintaining human comfort. The heat generation system is the primary sourceof heat energy for a facility. Its purpose is to transfer heat to the areas in afacility that are cooler than desired. Examples of heat generating componentsare boilers, electric heating coils, and gas-fired furnaces.Drawing courtesy of Cleaver Brooks22Lesson 1-

Heat rejection systems, or the cooling system, is another major HVAC systemcomponent involved in maintaining comfort. It transfers heat from where it istoo warm to an area where it is needed or not objectionable. Examples of heatrejection components are a chiller, a window A/C unit, and an evaporativespray coil.Drawing courtesy of The Internet Encyclopedia of ScienceAir delivery systems provide the means for transferring heated and chilled airthroughout a facility. Air delivery systems typically combine outside andrecycled building air, filter it, add or remove heat from it, and often timeshumidify or dehumidify it before transferring the air throughout the facility.This system usually consists of a fan that blows air through sheet metal ducts.The ductwork is like an artery that supplies air to all the rooms in a facility.Lesson - 123

Terminal units are the last piece of equipment involved in the delivery offresh air to a facility. After the heated or cooled air passes through the airdelivery system, it disperses through the terminal units. Terminal units areusually located in the spaces they condition. Examples of terminal units areunit ventilators, fan coils, VAV boxes.Pumping systems force a fluid, usually water, through a piping system. Thefluid is the control agent that transfers energy from primary energy sources,such as heat generating systems or cooling systems, to air delivery systemsand/or terminal units. The heat energy transfers from the control agent to theair through a coil. A coil is an arrangement of tubes with heat transfer finslocated in the air stream. Hot water coils release heat into the air in a heatingsystem. Chilled water coils absorb heat in a cooling system. A car radiator is acommon example of a heat transfer coil.24Lesson 1-

New Termfluid A substance such as a liquid, gas, or steam that cantake on the shape of its container.ReviewHeat always travels from a warmer object to a cooler object. HVAC systemsprovide the means to transfer heat.An HVAC system consists of different system components that give it theability to function as it is designed to maintain comfort.A typical HVAC system consists of a heat generating device, a cooling systemdevice, ducts to transfer the conditioned air, pipes to transfer heat through afluid, and terminal units that disperse conditioned air into the spaces where itis needed.Lesson - 125

Exercises: 1.41. Whatis the Second Law of Thermodynamics?2.What are the basic system components of a typical HVAC system?3. Match the letter of the correct HVAC system component to itscorresponding function description.Function Description26AnswerHVAC System ComponentPrimary source for heat energy.A. Air delivery systemEnables the transfer of heated and cooled air.B. Heat rejection systemSmall version of an air delivery system.C. Pumping systemPrimary source for cooling energy.D. Heat generation systemEnables the transfer of heat through a fluid.E. Terminal unitLesson 1-

1.5 HVAC System ControlComponentsAn HVAC system’s automatic controls are vital to the overall functionality ofthe system. The control components regulate a facility’s HVAC system so thatit maintains desired comfort levels, conserves energy, reduces labor costs, andmaintains safe equipment operating conditions.Automatic Control SystemsAutomatic controls regulate environmental conditions of the control zone toensure that the HVAC system maintains comfort. When the system detects thetemperature is too hot or too cold, meaning the load in the space has changed,the controls activate the HVAC system to add or remove heat from thebuilding to maintain comfortable conditions.New Termsload Heat that is lost or gained.Energy is conserved when the controls maintain interior conditions withinpredetermined limits. The HVAC system can reset setpoints based on outsidetemperatures in anticipation of load changes, allow the use of outside air tocool inside the building to conserve energy and employ other energyconservation strategies.The automatic controls also keep HVAC system equipment operating safely.If the equipment is allowed to operate unsupervised, serious damage canoccur. For example, boilers and chillers must have the proper supportequipment operating before they are enabled.Automatic Control System ComponentsControl system components work together to gather data about facilityconditions, measure it, and transfer energy from one location to anotherthrough the HVAC system. The three main elements of a control system are aLesson - 127

sensor, a controller and controlled device. Two additional elements that arealways assumed present in the control system are the controlled medium andcontrol agent.Table 1.3 Control System ElementsControl system elementsDescriptionSensorMeasures a controlled variable (temp,press, etc.)ControllerCompares the setpoint to control point andadjusts the controlled deviceControlled deviceRegulates the flow of the control agent(valve, damper, etc.)Controlled mediumFluid that transfers the energy to or fromthe process or zone (air in the air handler)Control agentTransfers the required energy to or fromthe controlled medium (steam in theheating coil)All three basic components of an HVAC control system are necessary to makeautomatic control of the system possible. The sensor measures a controlledvariable such as temperature or pressure or level. The sensor then transmitsthat information to the controller. The controller compares the measuredcontrol point against the desired setpoint and generates an output to bring thetwo closer together. The controlled device regulates the amount of controlagent to the desired amount.28Lesson 1-

Automatic Control System ClassificationAutomatic control systems can be class

Understanding HVAC Fundamentals 1.1 HVAC System Functions 5 HVAC System Types and Applications 7 1.2 Designing the HVAC System 11 HVAC Design Factors 11 Cooling and Heating Loads 13 Installing the HVAC System 14 1.3 Comfort 17 Comfort 17 Heat 17 Humidity 18 Ventilation 19 1.4 HVAC System Components 21 Ai