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What is a CO2 Heat Pump?

What is a CO2 Heat Pump?
Apr 29 2024

Traditional Heat Pumps use refrigerant to change stages based on pressure, transferring heat from inside a building and out (and vice versa in the winter). One of the big costs to heat pumps is Freon, which is expensive, as well as the copper lines running through a building to transfer the heat around via Freon.

There is a new technology breaking that uses CO2 to act as the refrigerant. It is exciting, and we will discuss some reasons it may or may not break out into the US anytime soon.

A Very High Efficiency HVAC system has an air sourced heat pump with an ERV (Energy Recovery Ventilator) and is the cornerstone of our offerings to commercial and public buildings in Illinois. CO2 based heat pumps have the potential to drive the costs down even further on this exciting approach.

How Does a Heat Pump Work?

A heat pump operates on a very clever principle that allows it to move heat, rather than generate it directly. This makes it a much more efficient way to heat and cool your commercial building compared to traditional systems like furnaces, boilers and air conditioners. But how exactly does it achieve this?

The key component in a heat pump is refrigerant, a specially chosen liquid that can easily absorb and release heat. The refrigerant circulates through a closed loop system within the heat pump. By changing the pressure of the refrigerant, the heat pump can manipulate its ability to absorb and release heat.

heat pumps using CO2 as a refrigerant

Here’s where the magic happens. In heating mode, the heat pump absorbs heat from the outside air, even when it’s cold outside. Even though the air might feel chilly to us, it still contains some thermal energy. The refrigerant, in its low-pressure state, is able to efficiently capture this heat. Then, the refrigerant is compressed, which significantly increases its temperature.

Finally, the hot refrigerant transfers its heat to the interior of your building, warming you up. The cooled refrigerant then circulates back outside to pick up more heat, and the cycle continues. This process is essentially the reverse of what happens in your refrigerator, where heat is extracted from the inside to keep your food cold.

How is CO2 a Good Refrigerant?

Carbon dioxide (CO2) is emerging as a strong contender in the world of refrigerants, and for good reason. Compared to traditional refrigerants, CO2 boasts several properties that make it an environmentally friendly and efficient choice. Let’s delve into the reasons why CO2 stands out.

Firstly, CO2 is a champion for environmental sustainability. Unlike many conventional refrigerants, CO2 has a zero Ozone Depletion Potential (ODP) and an ultra-low Global Warming Potential (GWP) of 1. This means it doesn’t contribute to the depletion of the ozone layer or significantly enhance greenhouse gas effects. In a world increasingly focused on combating climate change, CO2 presents a much greener alternative. And unfortunately, the world has more CO2 than in the past centuries because of how much fossil fuels we have burned.

Beyond its environmental benefits, CO2 shines in terms of performance. It boasts excellent heat transfer properties. CO2 can absorb and release heat very effectively, leading to faster cooling and heating cycles in refrigeration systems. This translates to improved efficiency and lower energy consumption for your building. Additionally, CO2’s high density allows for smaller pipes and compressors to be used in refrigeration systems, making them more compact and potentially less expensive.

school energy efficiency
Recent Air Sourced Heat Pump Project by Verde in Oak Park, IL

What are the Downsides of Using CO2 as Refrigerant in a Heat Pump System?

It’s important to acknowledge that CO2 does have some drawbacks. Due to its high operating pressures, CO2 systems require sturdier components compared to traditional refrigerants. This can translate to higher upfront costs for installation by welding steel vs brazing copper refrigerant lines. Additionally, CO2’s effectiveness can be reduced in very cold climates, as it can transition from a liquid to a gas state at higher temperatures than some other refrigerants.

However, some new companies like Tequs in Norway are combining the promise of hydronic systems (hot water) with CO2 Heat Pump systems. The CO2 refrigerant is contained within the outdoor heat pump system, and ultra hot or cold water is piped through the building to indoor fan coil units, or even into existing ductwork systems. This exciting system has a lot of potential, possibly lower costs for installation, and far lesser environmental impact over Freon. And, way less energy usage like all heat pump systems.

How Can You Use Hydronic (Hot Water) in a Heat Pump System?

Heat pumps are renowned for their efficient heating and cooling capabilities. But what if you crave the even distribution of heat and the silent operation offered by hydronic systems, traditionally reliant on boilers? The good news is, you can have the best of both worlds! Here’s how heat pumps can seamlessly integrate with hydronic systems.

The magic lies in air-to-water heat pumps. Unlike traditional air-source heat pumps that directly blow heated or cooled air throughout your home, air-to-water models extract heat from outdoor air and transfer it to a circulating water loop. This heated water then becomes the workhorse, silently flowing through your existing hydronic system’s network of pipes and radiators.

The benefits of this synergy are numerous. Firstly, heat pumps excel at extracting heat from even moderately cold outside air, making them efficient in most climates. This warm water then feeds your existing hydronic system, which is a master at evenly distributing heat throughout your home. Radiant floor heating, for example, provides a comfortable warmth that rises gently from the ground, eliminating drafts and hot and cold spots.

Furthermore, this marriage of technologies leverages the strengths of each system. Heat pumps are known for their efficiency, especially compared to traditional electric resistance heating. By using this efficient heat source to power your hydronic system, you can significantly reduce your energy consumption and enjoy lower running costs. Additionally, hydronic systems are inherently quiet, as they rely on the silent circulation of water. This, combined with the quiet operation of modern heat pumps, creates a remarkably peaceful heating and cooling experience.

The potential benefits of improved efficiency, even heat distribution, and quiet operation make the combination of heat pumps and hydronic systems a compelling choice for many Illinois buildings. And since 60% of our buildings are going to need to transition away from natural gas by 2050 – we need every trick in our toolbelt to get there. Using Hot and Cold water lines combined with heat pumps is a great strategy to get there.

Overall, CO2 presents a compelling option for the future of refrigeration. Its environmental benefits, exceptional heat transfer properties, and potential for efficiency gains make it a strong contender. While some challenges exist, ongoing advancements in technology are continuously improving CO2 systems, making them a viable and sustainable solution for a variety of commercial and residential applications.

Reach out to Verde for an energy efficiency assessment today for your commercial building in Illinois.



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