WHAT IS HEAT?

Helping YOU find good heating engineers. We share case studies from engineers in the Guild of Master Heat Engineers to help people find top installers, help gas and oil engineers increase their knowledge around heat pumps, and provide a solution for third-sector professionals to understand the industry better.

Who Understands Heat?

There’s a lack of understanding around heat within the wide heating discourse: think tanks, policy, charities, local authorities, social housing, developers, trainers, hubs, trade bodies, engineers, manufacturers etc…

For example, earlier in the year I delivered an event at the NESTA HQ in London. In attendance were people from trade media, DESNZ, Energy Systems Catapult, Energy Savings Trust, Sustainable Energy Association as well as people from manufacturer’s marketing and comms teams.

I asked a simple question to everyone: what is the standard unit of measurement for heat. Everyone had a mini whiteboard they could write their answer on. Before I asked that question I mentioned how the meter is the standard unit of measurement for distance. For small distances we use millimetres for long distances the kilometre.

“everyone please hold up your whiteboard” I asked.

Only one person out of 40 people had written the correct answer: Joules

Everyone else had either written ‘Celsius’ ‘Centigrade’ or ‘Kelvin’

Most of the people in the room were from the comms and marketing departments so I put them at ease by explaining that most engineers, trainers, even manufacture’s technical directors also get this question wrong.

Arguably, if our country wants to ‘decarbonise heat’ then it helps if more people understand what heat actually is. And to confuse you, heat is not actually a thing.

Heat - What is it?

The cup of hot coffee in the above image contains no heat. A building never contains heat. Therefore, a building never looses it.

Heat, is a very misunderstood term. It’s ok that it’s used wrong but it helps if more people understand the term and the science. When the science is better understood persistent myths such as ‘heat pumps don’t work in uninsulated buildings’ or ‘radiators need to be hot’ will start to vanish.

Heat is not a thing, it is a process. It is not something which can be stored. Heat is the scientific term given to energy in transit across the boundary separating two systems driven solely by a temperature difference between them.

What is a boundary and what is a system?

It helps to Think Small

Most of us appreciate that everything is made up of atoms and molecules. These particles are constantly moving (kinetic energy) They are jiggling about. In the image featuring my cup of coffee we have three separate systems.

The liquid coffee

The cup

The air

Each of these three systems is essentially its own crowded dance floor.

Picture every atom and molecule as a person on that dance floor. The energy stored inside these physical systems is called internal energy, and it is made up of two distinct parts:

Kinetic Energy (Sensible): This is the speed at which the dancers are jumping, shuffling, and jiggling around. When you measure temperature with a thermometer, you aren't measuring heat. You are taking a tempo check. Temperature is purely a measurement of the average kinetic energy of those particles. In physical terms, we experience changes in kinetic energy as sensible energy: energy you can literally "sense" on a thermometer.

Potential Energy (Latent): This is the strength of the microscopic handshakes holding the dancers together. When dancers hold hands tightly, they form solids or liquids. If you add enough energy during a phase change, like boiling water or evaporating refrigerant, that energy goes directly into breaking those handshakes so the dancers can break free into a gas. Because the energy goes entirely into breaking bonds rather than making dancers jump any faster, the temperature stays exactly the same. Physics calls this hidden energy exchange latent energy.

So, internal energy is always the sum of these two things: kinetic (sensible) plus potential (latent).

Crossing the Boundary

Now, what happens when you place a hot cup of coffee on a table?

The liquid coffee (System 1) is a fast, energetic dance floor. The ceramic cup (System 2) sits next to it, and the room air (System 3) surrounds them both with much slower-moving dancers.

Where the coffee touches the cup, and where the cup touches the air, faster dancers collide with slower dancers across the boundary. Energy transfers as the faster particles knock into the slower ones, gradually balancing out the speeds until every dance floor reaches the same average tempo: thermal equilibrium.

That transaction, while energy is actively crossing the boundary driven by a temperature difference, is the only thing physics calls Heat.

Once energy crosses that boundary and stops moving, heat no longer exists. It has simply become part of the air's stored internal energy.

Objects do not hold heat. A cup of coffee holds internal energy. A building holds internal energy. A thermal store holds internal energy.

When we stop thinking of heat as a physical fluid trapped inside walls and start understanding it as a dynamic transfer process between systems, modern heating engineering starts to become a bit more understandable. We aren't trying to "trap heat", we are managing the exact rate at which internal energy crosses boundaries.

CHECK OUT THE LATEST PODCAST EPISODE AND THE VIDEO FEATURING GUILD ENGINEERS AND POLICY EXPERTS FROM INNOVATE UK AND THE EUROPEAN HEAT PUMP ASSOCIATION

In this video I interview Paul Kenny, Director General of the European Heat Pump Association and Mike Pitts, Deputy Director of Heat & Buildings at Innovate UK. They are joined by three of the Guild Engineers.

The latest BetaTalk podcast episode features Liam Knowles and Michael Waring. They explain what it is like to be a heat pump engineer during the energy transition. You can find Guild Engineers in your area on the Guild Map 

The Guild of Master Heat Engineers is supported by our Patrons.

Learn more about our Patrons here.

Nathan

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