                      ContentsSection 1 Environmental PhysicsSection 2 Properties of MaterialsSection 3 Fluid Flow in Pipe and Duct NetworksSection 4 Measuring Variables    Description:  The purpose of this unit is to enable you to understand the fundamental concepts of Building Engineering and be able to apply these in a vocational context.

Author:  Gates MacBain Associates

Section 1  Environmental Physics Aims and ObjectivesAt the end of this section you should be able to:Explain the concepts of basic environmental physics.

Introduction

The word physics deals with energy and how energy interacts with everything around us. In Environmental physics, we apply the laws of physics to understand the environment. This environment can be natural or man-made which is also called built environment.

In this section, you will learn some concepts of basic environmental physics which have a number of applications. The understanding of these concepts will help you to appreciate ways in which heat transfer takes place.  It is also required to design systems for human comfort.

Temperature

When we heat a substance, molecules move randomly generating energy. Temperature is a measurement of this molecular or kinetic energy. Temperature is either measured on a  Celsius scale or a Kelvin scale.

Celsius temperature (t) refers to melting point of ice and boiling point of water while Kelvin scale relates to absolute zero.

Humidity

This is a measurement of the amount of moisture in the air: how wet the air is. This wetness relates to amount of water vapours. Hence more humidity means more water vapours.

Relative Humidity measures the amount of water vapours present at a given temperature as compared with the maximum amount of vapours air can take. It is expressed as a ratio of the two quantities.

Dry bulb, Wet bulb and dew point temperatures

A dry bulb temperature refers to measurements taken with an ordinary thermometer. We can then make the bulb wet with, for example, with a gauze, and measure the surrounding temperature. As the moisture will evaporate, the readings will be lower than the actual. This gives an indication of how dry or wet the air is.

When air becomes fully saturated, the water vapour starts to condense. This temperature is called the dew point.

The publications listed contain a more detailed explanation of temperature and humidity. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand these fundamental concepts.

Energy

This is the capacity of a system to carry out work. It can take many forms: Potential energy stored in a body; Kinetic energy generated due to motion; Sound energy; electromagnetic energy; and so on.

Sources of energy can be renewable (sun, wind, water, etc) or non-renewable (oil, gas and coal).

Heat and work are two forms of energy. It flows from a hot to a cold source.

Heat flows between the system and surroundings until the two are at the same temperature. When the system absorbs heat, the process is endothermic (it feels cold). When a system produces heat it is exothermic (it feels hot).

Enthalpy

Under constant pressure, the heat absorbed or released is termed enthalpy or heat content. Enthalpy cannot be directly measured, but the change can be which is the heat added or lost by the system or change in enthalpy. It is thus the sum of the internal (heat) energy including the heat of the air and water vapours.

The publications listed contain a more detailed explanation of energy and its various forms. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand the concepts. These also highlight the difference between energy sources and explain why renewable energy is important to us. Websites PublicationsMcMullan, R. (2007) Environmental Science in Buildings. 6th edition: Palgrave Macmillan, New York (Chapter 3)Brumbaugh J E. (2004). HVAC Fundamentals, Vol 1: Heating Systems, Furnaces and Boilers, 4th edition: Wiley Publishing, Indiana (Chapter 2)Burberry, P. (1997). Environment and Services (Mitchells Building Series). 8th edition: Addison Wesley Longman Limited, England  (Chapter 2)Chadderton D V. (2007). Building Services Engineering. 5th edition: Taylor & Francis, England (Chapter 4) Video / DVDs Self-Assessment TaskExplain Absolute Zero and the difference between temperature scalesDescribe why it is important for an engineer to learn about relative humidity?Identify all possible forms of energy giving at least one example in each case.Explain the difference between renewable and non-renewable sources of.

Section 2  Properties of Materials Aims and ObjectivesAt the end of this section you should be able to:Discuss the properties of materials

Introduction

We deal with materials everyday: Whether we are at home or at work. We also have knowledge of their properties without sometimes really knowing it. For example, we know that steel is heavier and stronger than, for example, timber. We are also aware that if we keep on stretching a rubber band, it would snap.

In this section, we will look at the material properties in an easy-to-understand yet in a scientific manner. This is really fundamental for you as an engineer that you develop an understanding of these properties. This knowledge will help you in selecting the most suitable and economical materials for a given task.

Density

This is a measure of mass per unit volume. It is an important concept in engineering in selection of fit-for-purpose materials. If mass in measured in kilograms (kg) and the volume in cubic metres (m³), the units of density will be kg/m³.

Stress and Strain

When we apply any force on a material, it resists that force thereby generating internal force called stress which is measured a force per unit area. If force is measured in Newton and area in mm², the unit of stress will be N/mm².

Strain is the result of the applied force or stress expressed as ratio of change in length per unit length.

If the action of the force is to stretch the resulting stress will be tensile.

If the force is pushing, the resulting stress will be compressive.

Ductility

A ductile material is the one which does not fail suddenly: it gives warning signs such as cracking.

Shear Strength

Shear is a sliding phenomenon  when one part tends to slide against the other part, which is how garden shears work cut.

Shear strength describes a materials resistance to a failure under shear.

Elastic and Plastic Behaviour

When we apply a force, the material deforms. Up till a certain point, removing the force will not result in any permanent change in the material properties This point is referred to as elastic limit. If the amount of force is increased beyond that point, material will undergo a permanent change which is what is termed as plastic behaviour.

Elasticity is measured through Youngs Modulus of Elasticity which is a ratio of stress and strain.

The publications listed contain a more detailed explanation of material properties. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand these fundamental concepts. Video / DVDs PublicationsBurberry, P. (1997). Environment and Services (Mitchells Building Series). 8th edition: Addison Wesley Longman Limited, England  (Chapter 11)Timings R L. (1998). Fundamentals of Engineering. Addison Wesley Longman Limited, England  (Chapter 6)Morgan w. et al. (2003). Structural Mechanics, 6th edition. Pearson Education Ltd. England (Chapter 7) Self-Assessment TaskProduce a table of material properties for 5 commonly found materials.Draw a stress-strain curve for a ductile and a brittle material. Explain these curves by appropriately annotations.Describing how knowledge of material properties can help us in selection of fit-for-purpose materials.

Section 3  Fluid Flow in Pipe and Duct Networks Aims and ObjectivesAt the end of this section you should be able to:Apply principles to solve problems in the flow of fluids in pipe and duct networks.

Introduction

Matter is divided into solids and fluids. Fluids can be further divided into Liquids and Gases. Water and air are two very common and important fluids.

As an engineer, you will design and construct ducts and pipe lines carrying fluids such as water, oil, gas or sewage. Therefore, it is important that you understand the rules and laws regarding fluids.

Fluid can be at rest which means it is not moving. Study of fluids in this state is called Fluid Statics. When fluid moves, its properties are studied under Fluid Dynamics. Put these two together and these collectively fall under Fluid Mechanics.

Pressure

Pressure is defined as force acting perpendicular to a unit surface area. The SI unit of pressure is Pascal (Pa) where 1 Pascal = 1 N / m².

If a force acts parallel to the area under consideration, then it has no perpendicular component and thus, there is no pressure exerted by that force on the area.

Factors affecting pressure in liquids
• Denser liquids have greater weight and therefore exert greater pressure.
• The greater the height of the liquid column the greater its weight and the pressure it exerts on its base.
• Pressure increases with the depth of the point below the free surface of the liquid.

Calculation of Pressure

In order to calculate pressure you can use the following formula:

P = r  x  g  x  h

Where               P = pressure (N/m²)
r = density(kg/m³)
g = acceleration due to gravity (m/s²)
h = head  (m)

The publications listed contain a more detailed explanation of fluid statics. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand these fundamental concepts. The web resources include a useful calculator for pressure and related calculations.

Types of fluid flow

Consider the water flowing in a river: Assume that the water has a number of layers one over the other. When the fluid flow is nice and gentle, we can say that the layers do not cross or intersect each other. This is called laminar flow.  On the other hand, if the water is stormy, the layer do cross each other. This is called turbulent flow. Between these two states the flow is transitional which means it is changing from one type to the other.

How do we know whether it is laminar or turbulent? A British engineer Osborne Reynolds did some experiments and developed the number boundaries to differentiate between laminar and turbulent flow.

Re = (rvd) / m
Re = Reynolds Number
r= Density of water
v= Velocity
m = Viscosity
d = Diameter

For values of Re less than 2000, the flow is called laminar while a value more than 4000 will indicate a turbulent flow. Flow is called transitional for intermediate values.
Generally in science, we assume that mass and energy is never lost: it changes from one form to the other. For example, water stored in a reservoir has energy called Potential Energy. When we let this water move, this energy changes to pressure, velocity, etc.

Laws regarding fluid flow follows this principle of conservation. Examples are Bernoullis theorem and Continuity Equation.

Bernoullis Theorem

It describes relation among the pressure, velocity, and elevation or height  in a moving fluid. It states that the total energy of the flowing fluid remains constant

Potential energy + Pressure energy + Kinetic energy = Constant

Continuity Equation

When a fluid is in motion, it must move in such a way that mass is conserved. Continuity equation is a statement of the principle of mass conservation for a flow, with one inlet and one outlet.

The publications listed contain a more detailed explanation of fluid dynamics. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand the concepts and their application. Websites PublicationsMcMullan, R. (2007) Environmental Science in Buildings. 6th edition: Palgrave Macmillan, New York (Part II Resource 5) Video / DVDs Self-Assessment TaskDescribe the significance of each factor in calculating pressure.Describe the difference between laminar and turbulent flow giving examples.Discuss the applications of Bernoullis theorem and continuity equation.

Section 4  Measuring Variables Aims and ObjectivesAt the end of this section you should be able to:Apply methods of measuring different variables in the building services environment.

Introduction

The main aim of a building services engineer is to ensure that the systems are designed to provide optimum human comfort. To do so, the engineer has to measure a few things before suggesting a solution such as humidity. As these change with the weather, conditions within a building and other factors, we call these variables.

In this section, you will learn about measuring some of these variables.

Relative Humidity

This can be measure using the formula:

Relative Humidity = 100 [Actual Vapour Pressure (Pa)/ Saturation Vapour Pressure (Pa)]Or R.H = 100 (AVP / SVP)

Flow rate

Flow rate or Discharge (Q) is the volume of liquid flowing per second. If the volume (V) is measured in cubic metres, the unit is cubic metres per second (m³/s)

To calculate Flow Rate, you can use the following formula:

Q = Volume / time or Q = V / t

The amount of liquid flowing in a pipe also depends on the area of the pipe (A) and the velocity of the liquid flow (v). To calculate, you can use the formula:

Q = Velocity x Area or Q = A x V

Head loss

When a fluid moves, it looses head. To calculate, you can use Darcy Formula if the pipe is flowing full or Chezy Formula if it is an open channel.

Chezys Formula

It expresses a relationship between the fall in height of a channel and the velocity of flow that it produces.

V = c√(mi)

Where

V = average velocity of flow (m/s)
M = hydraulic mean radius = cross section area of flow (m²) / wetted perimeter (m)
I  = Hydraulic gradient = loss of pressure head (m) / horizontal length of flow (m)
C  = Chezys coefficient for a particular pipe

Darcys Formula

This formula is used to predict the Pressure Head loss from a liquid flowing in a full pipe due to friction between the liquid and the pipe surface

H = 4fLv² / 2gD

Where
H =  Loss of pressure head (m)
L =  Length of pipe (m)
v  = Average velocity of flow in pipes  (m/s)
D =  Internal diameter of pipe (m)
g  =  Gravitational acceleration (9.81m/s²)
f  =  Darcys frictional coefficient (this is  dimensionless with no units)

The publications listed contain a more detailed explanation of measuring these variables. You are strongly advised to read these before attempting the tasks.

Some useful websites and video resources are listed with self explanatory titles which will help you understand the concepts and their application. The web resources include some useful calculators. Websites PublicationsMcMullan, R. (2007) Environmental Science in Buildings. 6th edition: Palgrave Macmillan, New York (chapter 3 and Part II Resource 5)Burberry, P. (1997). Environment and Services (Mitchells Building Series). 8th edition: Addison Wesley Longman Limited, England  (Chapter 2) Video / DVDs Self-Assessment TaskDescribe the significance of the factors considered in Chezys and Darcys formulae for calculating head loss.Describe the process in determining  Relative Humidity, Flow Rate and Head loss.       Site Map           