Transferring Heat Instead of Creating It: Say Hi To Heat Pumps
Heat pumps and how they're pumping it up for the planet 🌎
Welcome to Part Two of our Distributed Energy Resources (DERs) series! Today we will focus on heat pumps, how they work, and their benefits and risks.
Let’s not waste any more words and dive right into it!
What Are Heat Pumps?
Heat pumps are electrical systems that can heat or cool a building. They look similar to traditional air conditioning units and are usually located outside of a building. They can also be used for heating water, creating steam, or heating materials in commercial or industrial applications.
Heat pumps don’t actually create heat. They transfer hot air from a source to where it’s needed. Within the pump, the heat is increased (more on how later on) and sent to its final destination.
There are three different kinds of heat pumps. They differ in the origin of their heat source:
Heat pumps using surrounding air (~ 85% of heat pumps installed)
Heat pumps using geothermal energy
Heat pumps using heat from water or factory waste
Hybrid heat pumps are conventional gas furnaces combined with heat pumps. But we’re trying to move away from traditional heating systems and go full green, so let’s not focus on these today.
How Heat Pumps Work
Heat pumps move a fluid through a circular system, taking on and releasing heat in a recurring cycle. Through this process, the fluid changes its state from liquid to gas and back. Depending on the need, it’s either compressed or expanded in order to transfer heat.
The first magic ingredient in heat pumps is the fluid. It’s a refrigerant (a fluid chemical with a very low boiling point). Having a lower boiling point means it takes much less energy to achieve a state change. The fluid changes its state from liquid to gas throughout the cycle and releases or absorbs heat as required. Refrigerants are used in fridges and traditional air conditioners as well.
The second magic ingredient is the second law of thermodynamics, which basically says that hot wants to move to cold. Just open your front door during winter and experience how the hot air inside your home rushes outside to chase the cold.
The Cycle
There are four crucial steps in the circular process of a heat pump:
Evaporation: The refrigerant flows through a heat exchanger and picks up heat from outside air. In this step, the liquid changes its state from liquid to gas.
Compression: The gas enters the compressor where it’s compressed. This increases pressure and the boiling point. The result: the gas is warmer than the indoor room temperature.
Condensation: The warm gas passes through another heat exchange and flows past a relatively colder room. Gas releases heat into the room aided by a fan.
Expansion: The gas goes through an expansion valve which expands the gas back into a liquid state. The gas is ready to pick up heat from the outside air again and the cycle starts from the beginning.
If you want to cool your home, the cycle reverses. Pretty amazing stuff.
Energy Efficiency
When talking about heat pumps, we have to talk about energy efficiency. Energy efficiency describes the process of using less energy to do the same task e.g. heating a home. For example, the most efficient gas furnaces convert 98% of the fuel used into heat. Therefore, 2% of the fuel is lost.
One of the most impressive factors about heat pumps is their efficiency. They can achieve energy efficiency rates of 300-400%!
300-400%?! How is that possible?
Thank you, second law of thermodynamics. Heat pumps take advantage of this law and are able to output more energy in the form of heat than they require to run.
For example, using 1 kilowatt hour (KWh) of electricity to power the pump can output 3-4 KWh of energy in the form of heat. That is CRAZY! How is that not more widely known?
The Myth of Cold Climates and Heat Pumps
Cool story so far! But how can this work when it’s cold outside? How can heat be transferred when there is not heat? This is one of the most frequent questions asked about heat pumps. Let’s take a look at it.
From a scientific perspective, even on the coldest days there is energy in the air. Looking at our world on a microscopic level, there are molecules in our air. When it’s hot, the molecules move faster. When it’s cold, the molecules move slower. Slower, but they are still moving. By offering the outside air something colder to move towards, heat pumps are capable of picking up energy even when it’s cold outside.
Look at Norway for instance. Last time I checked, it’s pretty cold in Norway for most of the year. In the winter months, Norway as an average temperature of 2 degrees Celsius (35 degrees Fahrenheit ; varies by region).
But Norway has the highest heat pump penetration worldwide. More than 60 out of 100 households have a heat pump. Through smart policy and the right incentives, Norway functions as a role model example of a successful transformation towards cleaner heating, ventilation, and air conditioning (HVAC) systems.
Yes, heat pumps are less efficient and require more electricity to operate in colder climates, but they still work tremendously well. Some are more efficient in colder climates than others, so it’s important to pick the right heat pump when upgrading your HVAC system at home.
Heat pumps are killing two birds with one stone: electrifying heating and cooling systems AND avoiding emissions. Win-win situation. Case closed.
I can only recommend checking out this great article from MIT Technology Review to dive a bit deeper.
Benefits of Heat Pumps
Heat pumps come with great advantages. Here are some highlights:
Cheaper in the long run
Significantly more energy efficient than traditional HVAC systems
Cheaper electricity bill (see: energy efficiency)
Run on electricity —> No CO2 emissions
Safer than gas furnaces
Risks of Heat Pumps
Nothing in this world is risk-free. Neither are heat pumps. Here are some risks:
High upfront cost (take advantage of tax rebates)
Not all houses can retrofit a heat pump
Less efficient in extreme cold (though conventional HVAC systems also struggle in extreme cold)
Refrigerants are potent greenhouse gases, hence secure handling is crucial to avoid leaks
Where we are now
Heat pumps are getting more and more popular. Several countries just set new records for heat pump sales in 2023. Just like solar panels, heat pumps are constantly improving. New refrigerants are being developed, more efficient compressors and heat exchangers are being built, and more workers are being trained to install the systems. Government incentives are doing their part to speed up deployment.
The transition is happening. Sometimes slower than we want it to, but it is happening. Heat pumps are picking up steam (literally) and are going to play a key part in the green transition. Their versatility and efficiency outperform any other known form of HVAC. Economically, it just makes sense as well.
Heat pumps are an essential part of turning every home into an independent little power plant. Powering a heat pump with rooftop solar and a connected battery system is a step towards a cheaper, greener, and more reliable energy supply. Heating and cooling buildings are responsible for 10% of global greenhouse gas emissions. It’s about time we change that.
That’s it for this week, lovely people.
Let me know in the comments below if you have a heat pump and what your take is. And if you don’t comment because you don’t have a heat pump, just get one. Or tell your landlord to get one. And show him this article. Both are worth it.
Stay electric,
Basti