Refrigerants are key components, responsible for the efficient working of heat pumps. The choice of selection and usage plays an important role in this. Hence it is important to understand clearly about refrigerants.
What are refrigerants?
The working liquids which are used in the process of the refrigeration cycle are called refrigerants. They are commonly used in air conditioning systems and heat pumps. Since refrigerants are toxic, flammable and cause ozone layer depletion they are highly regulated by concerned authorities. You may have a question! If refrigerants are toxic, then how can I choose them? An ideal and user-friendly refrigerant should be non-corrosive, non-toxic, non-flammable, with no ozone depletion. Let us have a look at how refrigerants work in the heat pump.
How refrigerants work in heat pumps?
As we saw above refrigerants are most importantly used in the refrigeration cycle. Apart from different types of heating and cooling system, all refrigerants work in a similar manner. Refrigerants will pass between the main components of the compressor, condenser, expansion device and the evaporator and remove unwanted heat from one location to another. The common types of refrigerants will have a low boiling point compared to water. This will make them evaporate in a short time and with minimum use of thermal energy.
Importance of refrigerant used in heat pumps
- Toxicity level is low.
- Non-flammability property.
- It has zero ozone depletion potential.
- Very low global warming potential.
- Excellent thermodynamic properties and low energy requirements.
Criteria for selection of refrigerants for heat pumps
Before looking into the selection criteria of refrigerants for heat pumps, let us see the characteristics of an ideal refrigerant.
- It has a normal boiling point below 0 degree Celsius.
- Ideal refrigerants are non-toxic and non-flammable.
- It will be easily detectable in case of leakage.
- Affordable and recyclable.
- Stable usage under operating conditions.
- Eco-friendly and low gas flow rate.
Here comes the major criteria for selection criteria for refrigerants in heat pumps:
Condensation pressure will vary for different refrigerants at a given temperature. Certain refrigerants will have very high temperature and the pressure will become too high. In that case, those refrigerants cannot be used for heat pumps. On the other hand, low pressure also has a risk side. Low pressure needs high volume thus needs a higher investment.
In a refrigerant, the critical temperature is the temperature above which a refrigerant gas (vapour) cannot be liquefied, irrespective of pressure. The refrigerant will reach a supercritical area (the area where pressure and temperature are above critical point) after a certain temperature. Then the fluid and gaseous phase of the refrigerant cannot be no longer distinguished in the supercritical area.
The energy efficiency varies according to the choice of refrigerants used.
Synthetic vs natural refrigerants
The contribution of synthetic refrigerants to greenhouse gas incase of leakage will be high. The effect will be 3000 times higher as compared to CO2.
How are refrigerants denoted?
There are specific codes used to denote refrigerants. The code will begin with letter “R” denoting refrigerant following numbers. The codes will also depict the properties of a particular refrigerant. The general code of refrigerants is Rxyz.
Where R(number of C atoms-1)(number of H atoms -1)(number of F atoms).
Let us look into the codes of few refrigerants.
R400-series: Zoetrope mixtures which do not have an evaporation point but rather an evaporation range. The Evaporation will not take place on a fixed temperature but will take place during the increase of temperature to a few degrees.
R500-series: Azeotrope mixtures that has a fixed evaporation point.
R600-series: Organic refrigerants.
R700-series: Inorganic refrigerants.
Common types of refrigerants used in heat pumps
R134a type refrigerant can be used for medium-sized and large heat pump systems. It has higher efficiency when compared to refrigerants R407c and R410a but has lower efficiency compared to NH3 refrigerant. Since it has low-pressure investment cost will be high.
R407c and R410a
These are commonly used in small and medium-sized heat pumps. Both the refrigerants are widely used for dual purpose installations. R410a will reach a supercritical state above a 71 °C temperature. Efficiency is higher and investment is low compared to R13a.
R600 (butane) and R600a (isobutane)
These refrigerants are usually deployed for temperatures higher than 80 °C. In case of refrigerants R600 and R600a the increase of pressure with temperature is much lower. Since these are fire explosive, installations should be safely done.
When it comes to industrial usage R717 is the most suitable refrigerant for heat pump. The efficiency of Ammonia is high can be easily applied below 80 °C temperature. The most impressive feature of Ammonia is that it is a natural refrigerant and does not contribute to the greenhouse effect. It is inflammable and toxic. On the other hand, due to its odour, the leakage can be easily sensed. It should be installed according to PGS-13.
I hope the above blog has given you a reasonable knowledge about refrigerants.
Thinking of installing a suitable heat pump along with a suitable refrigerant for your business?
Aspiration Cleantech Ventures provides hyper-efficient heat pumps for heating process in industries. For industries that stick to green energy initiatives, we offer heating solutions that provide long term predictable low-energy costs on a unique monthly performance-based energy payment. We avoid expensive and dirty fossil fuels by adopting proven technologies to both unutilized space and complex applications.
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