The definition of HVAC and some basic concepts wre introduced in HVAC – Understanding the Basics. In continuing your understanding of HVAC we will discuss the scientific and engineering principles used in the design of HVAC systems.  These are principles which need to be understood by anyone seeking to have a career or run a business in the HVAC industries.   

Force [Newtons, N]

In simple terms, force is defined as a push or a pull. It is the basic phenomena of Mechanical Engineering and pertains to any object that has a tendency to set a body into motion, to bring a body to rest or change the direction of any motion.  The unit of force is Newtons [N], named after Sir Isaac Newton who pioneered the study of force and motion in the 17th century.  

indiworks A force is a push or pull

A force is a push or a pull.  Source:

Pressure [Pascals] 

Pressure is the force exerted per unit area. It may be described as the measure of intensity of a force exerted on any given point on the contact surface. Whenever a force is evenly distributed over a given area the pressure at any point on the surface is the same. It can be calculated by dividing the total force exerted on a surface by the total contact area. 

Atmospheric Pressure [Pabs]

The Earth is surrounded by an envelope of air called the atmosphere, which extends upward from the surface of the earth. Air has mass and due to gravity exerts a force called weight.  The force per unit area is the pressure. This pressure exerted on the Earth’s surface is known as atmospheric pressure

Gauge Pressure [Pgauge]

Most pressure measuring instruments measure the difference between the pressure of a  fluid  and the atmospheric pressure. This is referred to as gauge pressure.

Absolute Pressure [Pabs]

Absolute pressure is the sum of gauge pressure and atmospheric pressure. 


If the pressure is lower than the atmospheric pressure, its gauge pressure is negative and  the term vacuum is applied to the magnitude of the gauge pressure when the absolute pressure is zero (i.e. there is no air present whatsoever).


Pressure is the normal force per unit area exerted on an imaginary or real plane surface in a fluid or a gas.


Density [ρ]

It is defined as the mass of a substance divided by its volume or the mass per unit volume. 

 Density(ρ) =  mass(m) ÷ volume(V). 

Specific Volume(v) is the reciprocal of density or volume per unit mass.

  v =  V/m

Specific Weight (Ws) is defined as the weight of a substance divided by its volume or the weight per unit volume.

  Ws = m/V 


If a system undergoes a displacement under the action of a force, work is said to be done. The amount of work being equal to the product of force and the component of displacement parallel to the force. If a system as a whole exerts a force on its surrounding and a displacement takes place, the work that is done either by or on the system is said to be external work.


A body is said to possess energy when it is capable of doing work. In more general terms, energy is the capacity of a body for producing an effect. 

Energy is classified as  

1.Stored Energy for example Chemical energy in fuel and Potential Energy stored in dams 

  1. Energy in Transition for example Heat and  Work.
indiworks A body is said to possess energy when it is capable of doing work.
indiworks A body is said to possess energy when it is capable of doing work.

The three main forms of energy are potential energy, kinetic energy and internal energy. The three forms  of energy are explained below. 


A body is said to possess energy when it is capable of doing work.


Potential Energy

It is the energy stored in the system due to its position in the gravitational force field. If a heavy object such as a  building stone is lifted from the ground to the roof, the energy  required to lift the stone is stored in it as potential energy. This stored potential energy  remains unchanged as long as the stone remains in its position. 

PE  = mgH   Where H = height of the object above the datum Units Joules

Kinetic Energy

If a body weighing one kg is moving with a velocity of v m/s with respect to the observer, then the kinetic energy stored in the body is given by:        K.E      =      221mv. This  energy  will  remain  stored  in  the  body  as  long  as  it  continues  in  motion  at  a  constant  velocity.  When the velocity is zero, the kinetic energy is also zero. 

Internal Energy

Molecules  possess  mass.  They  possess  motion  of  transactional  and  rotational  nature  in  liquid  and  gaseous states. Owing to the mass and motion these molecules have a large amount of kinetic energy stored  in  them.  Any  change  in  the  temperature  results  in  the  change  in  the  molecular  kinetic  energy  since molecular velocity is a function of temperature.  



Also the molecules are attracted towards each other by forces, which are very large in their solid state and  tend  to  vanish  once  they  are  in  a  perfect  gas  state.  In  the  melting  of  a  solid  or  vaporization  of  a  liquid it is necessary to overcome these forces. The energy required to bring about this change is stored in molecules as potential energy. 

The internal energy is defined as the total energy of the body – chemical, nuclear, heat, gravitational, or any other type of energy. This energy is stored within the body which is denoted by the symbol ‘μ’. It is obvious from the above definition that it is impossible to measure the absolute value of the internal energy. However, we can measure the changes occurring in the internal energy. Since thermodynamics deals  with  the  change  in  the  internal  energy  of  the  system,  it  is  important  to  know  what  causes  the  internal energy to change. The change in the internal energy can be caused either due to absorption or release of heat in the system or the work done by or on the system., or if any matter enters or leaves the system. 


Heat is one of the many forms of energy. This is evident from the fact that heat can be converted into other  forms  of  energy  and  that  other  forms  of  energy  can  be  converted  into  heat.  Heat  as  molecular  energy is universally accepted and heat as internal energy of the matter is thermodynamics.


Source: lorecentrarg



Since all other forms of energy may be converted into heat, it is considered to be energy in its lowest form. The availability of heat energy to do work depends on temperature differential. 

Heat Capacity

It  may  be  defined  as  the  energy  that  must  be  added  or  removed  from  one  kilogram  of  a  substance  to  change  its  temperature  by  one  degree  Centigrade.  In  refrigeration  technology  heat  capacity  is  used  to  determine how much heat should be removed to refrigerate various products.

Sensible heat  (QS) 

Heat which results in an increase or decrease in the temperature without it changing its phase is called sensible heat. A change in sensible heat is given by the equation when there is a change in temperature 


QS = m× CS (T2 – T1)       Note:      CS is the heat capacity at constant pressure  m = mass of the substance in kg                     (T2 – T1) = Temperature difference in °C

Latent Heat (Ql)

Latent heat is the heat at which a substance changes its phase without any increase or decrease in the temperature. It is the amount of heat required to change the state of a substance.


QL = m×Cw(w2 – w1)       Note:      Cw is the heat capacity of moisture m = mass of the substance in kg                (w2 – w1) = change in moisture content in g/kg 

Total Heat (Qt)

Total heat is the sum of sensible heat and latent heat. Heat measurements are taken above a specified datum.  These  measurements  with  water  are  at  zero  degrees  C,  since  below  this  temperature  water  is  solid. For  example:  The  sensible  heat,  latent  heat  and  total heat for steam are shown in the fig below

indiworks Total heat is the sum of sensible heat and latent heat
indiworks Total heat is the sum of sensible heat and latent heat

Source: crediblecarbon

Temperature and its measurement

Temperature  is  a  property  of  matter.  It  is  the  measure  of  intensity  of  heat  contained  in  matter  and  its  relative value. A substance is said to be hot or cold when its temperature is compared with some other reference  temperature.  A  high  temperature  indicates  a  high  level  of  heat  intensity  or  thermal  pressure  and a body is said to be hot. 


Like  other  forms  of  energy  heat  can  be  measured  because  it  has  quantity  and  intensity.  Heat  is  not  visible but manifests itself in its effects on various substances either by changing its state or by creating relative degrees of sensation when in contact with the human body.

indiworks Internal energy is the combination of potential and kinetic energy
indiworks Internal energy is the combination of potential and kinetic energy

Souce :energyeducation


Since  temperature  is  a  measure  of  heat  content,  the  temperature  can  be  measured  by  measuring  the  effects of heat on different properties of matter as follows; • Addition of heat increases the volume of the substance or pressure at constant volume. This property is used for measuring the temperature with the help of a mercury thermometer. •  With  the  increase  in  temperature,  the  resistivity  of  metals  increases  which  is  utilized  in  resistance thermometers •   If  two  junctions  made  of  two  dissimilar  metals  are  maintained  at  different  temperatures,  a  current flows in the circuit. This property is used in measuring with a thermocouple. 


When  the  temperature  of  a  substance  increases,  the  color  also  changes.  This  property  is  used for measuring the temperature in radiation pyrometers

Pressure and temperature relationship 

Water  boils  at  1000C  when  the  pressure  on  it  is  atmospheric  at  sea  level.  If  the  pressure  is  increased  above  the  atmospheric  pressure,  i.e.  in  a  deep  mine  shaft  the  boiling  point  increases  and  when  the  pressure is reduced below atmospheric, i.e. on top of a mountain, it reduces.  Boiling water does not necessarily have to be hot because if there is vacuum, water boils at a very low temperature.  The  same  is  true  when  it  comes  to  other  liquids,  such  as  various  refrigerants.  These  refrigerants have the same properties as water except their boiling point ranges are lower. This pressure temperature relationship is used in most air conditioning and refrigeration systems.

indiworks Pressure is directly proportional to temperature
indiworks Pressure is directly proportional to temperature


HVAC – Understanding the Basics

What is HVAC?

HVAC, short for Heating, Ventilation and Air Conditioning, is a sub-specialty of Mechanical Engineering which relates to controlling the temperature, pressure and humidity of air within an enclosed volume of space.  HVAC brings together Thermodynamics, Fluid Mechanics as well as Heat and Mass Transfer from a mechanical perspective and, with current advances in technologies, requires Mechanical Engineers and Technicians to also understand Instrumentation and Control.  HVAC systems comprise of all the components and equipment that are needed to ensure that the climate in an enclosed space is controlled within the limit of the specified conditions. These components include: cooling towers, air-handling unit, compressors, pumps, ducts and many others. 

The 6 Most Important Parts of Your HVAC System

Technician trying to understand what is HVAC? Source: Byrd HVAC


HVAC is such an essential aspect of modern human society that there are entire industries which would not exist without it.  This is due to HVAC systems being found in: high-rise buildings, restaurants, markets, medical and clinical environments, cars, logistics vehicles, airplanes, boats and many other places.  In most buildings HVAC accounts for 60-80% of all building costs according to Oaklins Netherlands.  According to Grand View Research, the HVAC industry has a $106,6 billion value market size as of 2020 and is expected to grow by 6.2% from 2021 to 2028.  It is no wonder than any Mechanical Engineer, either student, graduate or consultant interested in specialising in HVAC would have a lucrative career ahead of them.


Source: Oaklins Netherlands


It is near impossible to find an industry which does not rely on HVAC systems in some way or another and in most industries HVAC is a necessity to comply with regulatory requirements.  But before we get into the technical aspects of this industry we need to point out that there are not enough Engineers and Technicians being trained to specialise in HVAC and most Mechanical professionals enter the Engineering field without knowing about HVAC as a specialty.  In order to change this we thought to share information and trends regarding the HVAC Industry.  As most academic programmes don’t train Engineers on HVAC in undergrad, future HVAC specialists only become exposed to HVAC when in industry.  To fill this gap we intend to inspire a generation of Mechanical Engineers who will begin their studies and training with the intention of becoming HVAC Engineers.  With our articles on HVAC we intend to bridge the gap between studying, working in and being a consultant in the HVAC Industry.  In order to do this we will be covering the following topics:

  • HVAC Fundamentals
  • Psychometry
  • Human Comfort Requirements
  • Calculation of Heating and Load
  • HVAC Equipment and Systems
  • Design of Ducting
  • Distribution of Air-flow
  • Variable Air Volume Systems
  • Refrigeration
  • Instrumentation and Control of HVAC Systems
  • Environmental Impact of Air Conditioning
  • Installation, Commissioning, Operation, Testing and Maintenance of HVAC Systems
  • Fault Finding and Troubleshooting of HVAC Systems

Parts of Furnace



It you are curious about this omnipresent industry then the IndiWorks Engineering Blog is the perfect place for you.  In our first article we will cover:

  • Principles of Thermodynamics
  • Laws of Thermodynamics
  • Fundamentals of Heat Transfer
  • Fundamentals of Fluid Flow



We start with the above concepts because these are the basic principles covered in Mechanical Engineering and are a familiar starting point to all Mechanical professionals.  After covering these known topics we shall then be able to venture into the less familiar and eventually into the unknown of Heating, Ventilation and Air-conditioning.

Gain More Business – Industrial Marketing and Selling

Three years ago I made the conscious decision to sacrifice my Engineering training in order order to develop my Sales and Marketing abilities.  It is a decision that I am happy to have made as in that time I gained certification in a highly specialised standard of Sales called Integrity Selling as well as completed the Sales Consultant Development Training.  Skills which I am now able to use as an Engineering Consultant.  The training I underwent entails 3 years of grueling Sales Development consisting of almost 100 courses.  These consisted of the following topics:

  • Strategic Selling
  • Negotiation
  • Business Acumen
  • New Technologies(Virtual Reality) 
  • Industry Ecosystem

Each of these courses has three levels; Foundation, Advanced and Master.  To give an example; under Strategic Selling the courses under each of the three levels were broken down as follows:

  • Foundation
    • Capital Equipment Lifecycle Management
    • Sales Enablement
    • Sales Fundamentals
    • Sales Management Simplified
    • Virtual Selling for Sales Professionals
    • Players Won’t Play if Coaches Don’t Coach
    • Integrity Selling in a Changing Environment
    • Selling with Integrity
  • Advanced
    • Creating a Positive Customer Experience
    • Empathy for Sales Professionals
    • Identify Sales Growth Opportunities
    • Sales Coaching
    • Sales Strategies and Approaches in a New World of Selling
    • Customer Behaviour Styles: Talker, Doer, Supporter, Controller
    • Pre-Call Planning and Post-Call Analysis
  • Master
    • Sales Closing Strategies
    • The Persuasion Code – The Neuroscience of Sales
    • Becoming Head of Sales – Developing Your Playbook

   For three years my day to day involved going to clients; doing Sales Calls; contract management; product presentations; sales administration; placing orders on behalf of clients; distributing marketing material; coordinating logistics with supply chain; delivering products to clients and ultimately giving technical advise and consultation to end-users as they make use of the product.  But it was during this time that I learnt the most valuable skill in Sales – the well known “Sell Me a Pen” exercise.  Being an Engineer I learnt something even more valuable and that is the best way to sell someone a pen is to explain to them how the pen is designed; how and where it is manufactured and take them to see the extensive logistics it takes to get their highly valued pen to them.  While it might not always be possible to show them physically – taking them on a virtual whirlwind tour in their mind is enough to get your clients to walk the journey with you by being a part of it through supporting your business.  With this in mind this is why I have decided to write a series of articles on how you can gain more business as an Engineer or Technician by understanding Industrial Marketing and Selling.


In the series I will be covering topics such as; What is Marketing? How Marketing in Engineering is Different to Traditional Marketing, Types of Advertising: Direct Mail; Web and Email; Telemarketing etc., Sales Management, Building Relationships, Public Presentations, Resellers, The pain points of getting your messaging to your customer; the pain points of not hearing your customer, researching and finding new business clients, market research and other topics.  This is by far not an extensive list of all the information you may need at your disposal, but it is enough for you to startup.  We shall start by defiining Marketing from the persective of an Engineer.


The Definition of Marketing – According to an Engineer
Philip Kotler Marketing 5.0 Technology for Humanity. Source:

“The art and science of finding, keeping and growing profitable customers” – Philip Kotler


Most people do not see or know that there is a difference between selling and marketing – from the get-go, or in Engineering terms from First Principles it is critical to have an understanding of the subtle difference between Sales and Marketing.  The first thing to dispel from your mind is that marketing is selling, this couldn’t be further from the truth – though it is an integral part of advertising; marketing is not just selling and selling is a very important part of marketing – but only just a part of of it.  Philip Kotler put it best as in the opening line to this article.  To understand is from the point of art and science is to intimate that Marketing is the bringing together of creativity and empirical methods in order to serve a need of a person, a group of people or society at larger and that in itself is the defined role of what an Engineer does.

Dilbert cartoon Depicting How Engineering relates to Sales and Marketing. Source:

I want you to understand the definition of marketing from the above perspective lest you think that marketing is merely: “The whole process of persuading  customer that they are better off buying my goods or services, now and in the future”.  With that being said; for the sake of following a set standard let us go with the definition of Marketing as given by the Institute of Marketing Management which defines it as:   “The assessment and creation of demand, the utilization of the resources of production and distribution and to meet that demand at a planned profit”.  This definition is best from the view point of an engineering or technical professional as it brings home the point that production plays a critical role and effects the entire value chain of supplying the customer with their desired product.  It drives home the notion that marketing is not just a department whose sole job is to bring in sales, but rather marketing can act as the main motivator for personnel on the production floor.  Marketing is about making them know that their relentless pursuit to producing the highest level of quality is directly tied to the needs and wants to the customer of the company.  By making this direct correlation you imbue the understanding that the same pride which they feel when they produce a product that meets all quality standards on the factory floor is the same sense of pride that their customer feel when they use the product in their home or place of work.  Once you are able to make production personnel have a sense that the company’s end-users are their customers you would have achieved the goal of making marketing an organisation-wide endeavour.  The success of any marketing campaign is attained when every member of the organisation is included in the commercial efforts relating to the product or service being marketed.


New Product Introduction Lifecycle. Source:

New product introduction is probably the most understood need for marketing by technical professionals and engineers.  Without marketing customers would not be aware that a product exists – this is always the case when it come to the improvement of an existing technology.  If it were not for marketing the latest feature which engineers spent months in R&D working on would never be known to the end-user whom they painstakingly designed it for.  And without previous sales of the product they would not be able to begin on their next improvement and so the cycle goes.  This shows how critical a role marketing plays in Engineers being able to justify the need to invest in R&D for an improvement  in technology and marketer s do this by creating a demand for the need of the new feature and the benefits thereof.  


Engineer presenting product to clients.
Engineer presenting product to clients. Source:

Now that you have gotten an idea of how and why marketing can get just as complex as engineering, it is important to apply the same principles in find a solution to engineering problems.  In this case the problem is attempting to change or maintain the perceptions of a customer about our company and ultimately our products and services in order for them to be more likely to make use of our products and buy our services.  In order to break down this complex into its smaller sub-systems you need to ask the following pertinent questions:

  • Who are my customers?
  • What are my customers looking for above everything else?
  • How can I help them get what they need and want?
  • What knowledge do I have that can help them make the best decisions in meeting their current needs?
  • What are they happy or unhappy about?
  • What are the short-term trends in my industry?
  • What are the long-term advances in my industry?

Answering the above questions is the most advantageous way to start any marketing endeavour.  These questions can be asked in many different forms and different books, articles or people will ask them in various ways.  The way in which you ask them has to ultimately be with the goal of sharing your engineering and technical expertise in a way that helps your potential and actual customers gain the level of understanding which you have regarding the product, service or solution needed.