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Future Secondary Fluids for indirect refrigeration systems

The F-gas Regulation has set a clear goal for the entire refrigeration industry to reduce the amount of GWP fluorinated greenhouse gases. Natural refrigerants with very low GWP values such as carbon dioxide, propane and ammonia have excellent properties and the only disadvantages are flammability and toxicity in case of ammonia. In order to increase the use of these refrigerants, and to reduce climate impact, it is important to find environmentally friendly and energy efficient secondary fluids for indirect systems with low pumping power and good heat transfer properties.

Funded by: Swedish Energy Agency (Termo Program) and KYS Kylbranschens Samarbetsstiftelse (Swedish Refrigeration Foundation)

Time period: 2018-07-01 – 2020-12-31

Project partners:

  • Avantherm AB
  • Bengt Dahlgren AB
  • Danfoss
  • Svensk Energi & Kylanalys AB
  • Gränges AB
  • NIBE
  • Nowab AB
  • Stainless Engineering AB
  • Rydell & Lembke Kyl & Vermeteknik AB
  • Temper Technology AB
  • Waren International AB
  • WILO Sverige.


The goals of the previous EffysExpand project were to validate properties of alternative ethyl alcohol and propyl alcohol blends, propose the most suitable corrosion inhibitors compatible with ethyl alcohol based secondary fluids. Moreover, this project had a strong focus on investigating the effect of different corrosion inhibitors on thermophysical properties and heat transfer. Additionally, numerous synthetic iso-paraffins and organic formate and acetate salts have been investigated.

This project helped manufacturers to improve their commercial ethyl alcohol based products on Swedish market by providing the thermophysical properties of actual secondary fluids with denaturing agents. Results were published during numerous conferences and started a new discussion in other European countries as well as in USA to modify their regulations regarding the type and concentrations of denaturing agents in order to obtain better thermal performance of ground source heat pumps and other indirect refrigeration systems. Moreover, the goal of launching the first ethyl alcohol based product with compatible corrosion inhibitor not only in Sweden but also on European market was achieved.

Furthermore, these results proved that additives such as corrosion inhibitors actually have a big impact on thermophysical properties even if added in small concentrations. This study is the first to indicate that especially adsorption corrosion inhibitors affect the least the thermophysical properties when added in small concentrations as well as provide an excellent corrosion protection for many different metal alloys simultaneously. Therefore, adsorption corrosion inhibitors are highly recommended for commercial secondary based fluids. Unfortunately, more environmentally friendly sugar based corrosion inhibitors like sodium gluconate appear to have a significant effect on thermal conductivity (14% lower thermal conductivity).

The tests conducted for different synthetic paraffins showed that composition, fractionation methods and molecular weight can affect the thermophysical properties of the final product. It was found that the molecular weight can significantly affect the thermal properties and short chained iso-paraffins are the most suitable for low temperature applications. Further tests helped to select the most promising iso-paraffin blends for different applications and the first three commercial iso-paraffin based products for very wide temperature applications were launched on the Swedish market.  

Finally, the results showed that different types of cation (e.g lithium, sodium, ammonium, cesium) can affect properties in different ways and more research is needed to find future salt based secondary fluids. Among all the investigated alternative formate and acetate salts, cesium formate and ammonium formate solutions showed the best performance at low temperatures by providing the lowest viscosity in case of cesium formate and low viscosity, high specific heat capacity and thermal conductivity in case of ammonium formate. Cesium acetate proved to be a good and cheaper alternative to cesium formate, which maintained its good properties with high density and low viscosity but about 16% lower heat transfer than cesium formate. In addition, cesium formate was found to be least corrosive among all formate and acetate salts tested. This study gives a new benchmark to create better blends of different salts that will give better performance and result in lower corrosion character.

Aim and objectives

The objective of this project is to validate properties of alternative formate and acetate salts and their mixtures by measuring their basic thermophysical properties. This knowledge can be beneficial for both manufacturers, who can improve their products, and for customers as a basis for the design of indirect refrigeration systems and their components. In addition, stronger emphasis is placed on properties such as environmental friendliness and low fire hazard. The project will provide recommendations to manufacturers regarding alternative acetate and formate salts that can be used together and improve thermophysical properties. This research will contribute to the development of the next generation of secondary fluids. The project will focus more on glycols with green corrosion inhibitors in order to reduce environmental and health impact in the event of leakage. Another important part of the project is the development of a new type of alcohol based secondary fluid with pine oil or terpineols having higher flash point and shorter degradation time for special applications. The project will in addition include the filling, deaeration and cleaning procedures when converting different indirect systems in order to reduce the risks of corrosion in the future. 


  1. Ignatowicz M. Barcarolo L., Melinder Å., Molinaroli L., Palm B. 2019. Cesium and ammonium salts as low temperature secondary fluids, 25th IIR International Congress of Refrigeration, August 24-30th, Montreal, Canada, DOI: 10.18462/iir.icr.2019.1185

MSc thesis reports:

1. Study of high flash point ethyl alcohol based secondary fluids applied in Ground Source Heat Pumps systems - Luis Enrique Carrion Domenech, 2019

2. Aqua ammonia as secondary fluids in ice rink applications – Brianna Kilberg,2019.

Project contact persons

PARMENIDES – Plug & plAy EneRgy ManagEmeNt for hybriD Energy Storage
HYSTORE - Hybrid services from advanced thermal energy storage systems
Open-source models for holistic building energy system design at scale
Tank to Grave Management of new Low-GWP Refrigerants (Hantering av nya låg-GWP köldmedier från installation till destruktion)
Novel tool and guidelines for designing ground source heat pumps (GSHPs) in densely populated areas
Data driven lab for building energy systems
Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family buildings
Smart Control Strategies for Heat Pump Systems
Open-source models for holistic building energy system design at scale
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Solar photovoltaic systems in Swedish cooperative housing (completed)
Smart Control Strategies for Heat Pump Systems (completed)
Creating and Understanding Smart Innovation in Cities
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Accelerating innovation in buildings
High-Resolution GIS District Heating Source-Load Mapping
Digitalization and IoT technologies for Heat Pump systems
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Wuxi Sino-Swedish Eco-City Project (completed)
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Future Secondary Fluids for indirect refrigeration systems
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