HVAC: Heat Transfer Principles

• HVAC & Plumbing as a lesson
• This lesson covers Structures & Building Systems

Lesson 1: Principles of Heat Transfer

• By the end of this lesson, you will be able to describe the principles of heat transfer, thermal concepts, and temperature
• Thermal equilibrium occurs when objects reach the same temperature, stopping heat transfer
• Heat moves from warmer objects to cooler ones

3 Ways to Transfer Heat

• Conduction, Convection, and Radiation are the three ways to transfer heat

Conduction

• Conduction is the flow of heat through a solid
• Heat energy travels through collisions between atoms/molecules
• Conduction happens easier in solids and liquids because their particles are closer than in gases
• Energy transfer via conduction is faster with a bigger temperature difference where substances touch

Thermal Conductivity

• Thermal conductivity determines the amount of conduction in a material
• Materials that conduct heat include: Aluminum, copper, graphite, steel
• Materials that resist heat include: Air, glass, wood, rubber, paper and plastic
• Thermal Conductivity is measured in Joules per second per meter per Celsius (J/s m°C)
• Copper equals 386 J/s m°C
• Water's value is 0.56
• Wood's value equals 0.10
• Fiberglass' value is 0.048 making it a great insulator
• Air is excellent at 0.023, but only when it is still

Convection

• Convection involves heat transfer through fluid movement, whether liquid or gas
• A fluid heated carries thermal energy with it
• As a fluid heats, above a surface it expands, becomes less dense, and consequently rises

Radiation

• Heat travels via electromagnetic waves

Evaporation

• Evaporation is another method of heat transfer where a liquid removes heat as it evaporates

Thermal Concepts - Heat

• Quantity of heat (Q) is measured in British thermal units (Btu) and joules
• A Btu is the heat needed to raise 1 lb (0.45 kg) water temperature from 59.5°F (15.3°C) to 60.5°F (15.8°C)

Thermal Concepts - Heat - Units

• 1 Btu = 1055 joules (J) = 252 calories (c) = 0.293 watt-hour (W-hr.)
• 1 watt-hour (W-hr.) = 3.413 Btu
• 1 therm (natural gas) = 100 000 Btu
• 1000 Btu = 1 Mbtu = 1kBtu
• 1 000 000 Btu = MMBtu 1000 kBtu

Thermal Concepts - Temperature

• Temperature (T) measures the average kinetic energy linked to atoms and molecules' motion in a substance
• Temperature gauges the intensity of heat
• A thermometer is what measures temperature
• Fahrenheit (°F), Rankine, Celsius (°C) and Kelvin

Lesson 2: HVAC & Plumbing

Objectives

• An understanding of HVAC, design process with HVAC, basics of HVAC, and understanding HVAC drawings are the objectives of the lesson

HVAC

• HVAC means Heating, Ventilation, and Air Conditioning
• “H” is the heating system designed to add thermal energy and maintain a selected air temperature
• “V” is the ventilating system that introduces fresh air without changing its temperature
• “AC” is the air conditioning component that should filter out particulates like water, dust, and pollution

ASHRAE

• ASHRAE: American Society of Heating, Refrigeration and Air Conditioning Engineers
• They state HVAC should achieve four objectives: temperature, humidity, circulation, and quality

Design – Architectural Team

• The Architectural Design Team designs buildings and enclosed spaces, and coordinates with Mechanical Engineers
• Each space may require a different mechanical design

Design – Mechanical Team

• The Mechanical Team determines systems for buildings designed by the Architectural team

Introduction to HVAC

• The basics include: Goals of an HVAC system, parts of the HVAC system, and HVAC system in operation

Goals of HVAC

• An HVAC system aims to control air temperature, humidity and quality efficiently
• Air temperature and humidity affects comfort, productivity, and health, and are adjusted using thermostats and humidistats
• Air circulation is needed to circulate fresh air into a space, alleviate carbon dioxide buildup, and circulation of pollutants, dust, contaminants
• Air Filters are important to the circulation of air, also maintenance on ducts and filter replacement
• Efficient systems include Heat Recovery Ventilators (HRV) exchanges heat with fresh air
• Energy Recovery Ventilators (ERV) exchange heat and humidity with fresh air
• Variable Air Volume (VAV) boxes maintain constant temperature with varying airflow

Parts of an HVAC System

• Roof Top Units (RTU) provides conditioned air to buildings
• Ducts are connected to the RTU and distributes air to spaces
• HVAC systems are distributed through distribution trees
• Distribution trees take up space both Horizontally and Vertically in a building and is different per space according to its load
• Residential systems use a furnace
• Commercial systems use RTUs
• Ducts come round or rectangular
• Dampers control air flow to accommodate different zones and Prevent the spread of fire

Zones

• Zones are areas that require separate control
• Dampers in the ducts regulate and redirect air to zones
• Allows for customized temperatures
• Grilles, registers, and diffusers (GRD’s) allow air to enter a space
• Grilles contain louvres to deflect air
• Registers have adjustable dampers
• Diffusers are ceiling mounted and spread air throughout space linearly

Mechanical HVAC Plans

• Engineers, Architects, and mechanical contractors create HVAC plans
• Architectural Technologists must be able to interpret basic HVAC plans
• Ceiling plans show HVAC ducting and ceiling diffusers
• Revit models can be shared with mechanical consultants to input their requirements
• HVAC plans are drawn at the same scale as floor plans
• Commonly 1/4”=1’-0” (1:50) or 1/8”=1’-0” (1:100)
• HVAC ductwork and ceiling grilles are designed and drawn over the floor plans
• HVAC drawings employ basic symbols to show components
• Ceiling ductwork has a central main supply, shown in single lines with sizes noted