Refrigerant: Heat pump with propane offers advantages
When it comes to the operation of heat pumps, refrigerants play an important role. Without these substances, the heating system would not work. But what exactly are refrigerants? Why are they so important for Carrier heat pumps and what role do natural alternatives such as propane have? We provide an overview and show the advantages and disadvantages of various substances.
What are refrigerants and what do they do?
Refrigerants are synthetic or natural liquids that are used in Carrier air conditioners and heat pumps, among other things. They have special properties that enable them to transfer heat from a medium at a low temperature to a medium at a higher temperature. In the process, they undergo various phase changes, as the following overview shows:
- Heat absorption from the environment: In the first step, the refrigerant in the heat pump flows through an evaporator. This is a heat exchanger that transfers the energy from the outside air, the ground or the groundwater to the medium. It absorbs heat and evaporates.
- Pressure and temperature increase in the compressor: The refrigerant vapor then flows through a compressor. This increases the pressure, whereby the temperature also rises. This is important in order to be able to release the heat that is carried along.
- Heat transfer to the environment: The refrigerant flows through a heat exchanger again and transfers heat to the cooler environment. The heat exchanger is referred to as a condenser, as the refrigerant liquefies at this point.
- Expansion of the refrigerant: If the heat carried has been released into the environment or the heating water, the refrigerant returns to its liquid state. It flows through a special valve, where it relieves pressure and is available for the cycle again.
Please note: As the cycle can be reversed, cooling with a heat pump is also possible.
High requirements for heat pump refrigerants
In order for the refrigerant circuit to function as described, the substance must fulfill various properties. These include, for example:
- Good phase change behavior (liquid to vapor and vice versa)
- Chemically stable under all conceivable operating conditions
- Non-toxic to prevent injuries
- Ecologically beneficial in terms of GWP (global warming potential) and ODP (ozone depleting potential)
Without these features, the cooling process would not be possible in the desired form. The temperature could not be raised as desired or the output would not reach the required values.
Labeling of refrigerants explained
For clear identification, manufacturers label the substances with a standardised pattern. This consists of an R for refrigerant, a number and, in some cases, another letter. The meaning depends on the type of substance, as the following overview shows:
- Halogenated refrigerants are designated by manufacturers according to the pattern R-XYZ. The “X” stands for the number of carbon atoms. The “Y” stands for the number of hydrogen atoms and the “Z” for the number of fluorine atoms. If there is a small letter at the end, this stands for a substance with the same molecular formula but a different structure. R134a is an example.
- Inorganic refrigerants can be recognised by a three-digit number starting with 7. Typical examples are Ammonia (R717), Water (R718) and Carbon dioxide (R 744).
- Hydrocarbons are also designated by manufacturers with an “R” and three digits. These do not usually begin with the number seven and are therefore easy to recognise. Typical examples are Propene (R1270), Isobutane (R600a) and Propane (R290).
There are also mixtures of different substances, which can be recognised by an attached capital letter. Specialists distinguish between zeotropic mixtures, which change their structure due to the phase change, and azeotropic mixtures, which retain their structure.
Which refrigerants are available for heat pumps?
When it comes to selecting a refrigerant, the individual circumstances play an important role. The temperature ranges of the system (heat source, flow temperature) and the climatic effect of the substances are particularly relevant. The following table shows which refrigerants are generally suitable for heat pumps and when they should be used.
In order to reduce the environmental impact, refrigerants with very high GWP values are now subject to regulation. Due to the so-called F-Gas Regulation (EU Regulation No. 517/2014 on fluorinated greenhouse gases), many refrigerants may no longer be placed on the market without restriction. HFOs and natural refrigerants such as propane for heat pumps, on the other hand, are ecologically beneficial and inexpensive.
By the way: Carrier is increasingly relying on propane as a natural refrigerant for heat pumps.
Higher requirements for installation due to natural refrigerants
Natural refrigerants for heat pumps often have higher structural requirements. This is because the media are often flammable. Propane is a good example of this. In practice, however, the potential danger is low. After all:
- the refrigeration circuits are hermetically sealed
- only very small quantities of refrigerant are used
- there are mandatory safety distances from cellar doors and light wells
Are natural refrigerants worthwhile for the heat pump?
When it comes to use in detached and semi-detached houses, propane heat pumps such as Carrier AquaSnap 30AWH-P and AquaSnap 30AWH-NG(A) with R290 as a refrigerant are increasingly being used today. The medium has a GWP of three and is therefore three times more harmful than CO₂ when released into the atmosphere. Compared to conventional media such as R410A and R134a, however, the global warming potential is at least 590 times lower. In addition, a heat pump with R290 (propane) reaches higher temperatures. The technology is therefore perfect for both new and existing buildings, for example if you want to retrofit a heat pump.
Heat pumps with propane: advantages and disadvantages at a glance
Propane has a low GWP. It has a low global warming potential and is not affected by the F-Gas Regulation. The medium is generally inexpensive and will continue to be available in the future. Its thermodynamic properties are also an advantage. These enable efficient and reliable operation – including Carrier propane heat pumps. The following overview shows the most important advantages at a glance:
- Low operating costs thanks to high energy efficiency
- Wide range of applications thanks to temperatures of up to 70 °C
- Can also be used in old buildings without cost-intensive conversion measures
- Ecologically beneficial thanks to the low GWP of 2 to 3
- Higher subsidies for the heat pump thanks to natural refrigerants
A heat pump with propane also has disadvantages. This is because the medium is highly flammable and therefore associated with a certain hazard potential. In practice, however, this is usually irrelevant. This is due to the low refrigerant charge, hermetically sealed refrigeration circuits and higher safety precautions during installation.
Monobloc and split heat pumps with R290 available
If you want to use propane as a natural refrigerant, you have a wide choice. Both split and monobloc heat pumps with R290 are available today. The systems are available in various output ranges and therefore for many buildings and areas of application.
