Energy supply with R290 heat pumps
Specialist article in the HLH
The use of regenerative heat generation systems and the associated reduction in CO2 emissions are important goals for the future. Heat pumps with natural refrigerants play a decisive role in this. A look at a current project in the Stuttgart suburb of Leonberg shows the decisions that engineers and specialist planners are currently facing and the background information that can be used to create a sensible and long-term solution for the customer.
In the middle of Leonberg in Baden-Württemberg, the terraced new building of one of the world’s largest automotive suppliers is currently under construction. The building, with a roof height of over 26 meters, will be the new workplace for around 2,000 employees. The first floor will house a daycare center and a restaurant, while the rest of the new building will be used for administrative and research activities. Since 2020, the company has been able to claim that all of its more than 400 locations are climate-neutral. Accordingly, the focus for the new building in Leonberg was also on sustainability and energy efficiency. The heating and cooling requirements are to be covered by air-cooled chillers and water-cooled heat pumps. But what needs to be considered here and what optimizations influence the efficiency of the project?
From the hole in the ozone layer to the eternal chemical
The choice of refrigerant is an unavoidable and essential part of any project. There is a wide range on offer, as is the current uncertainty. The EU Parliament is seeking to amend the so-called F-Gas Regulation. Regulation (EU) No. 517/2014 on fluorinated greenhouse gases has been in force since 1 January 2015 and aims to reduce emissions of fluorinated greenhouse gases in the EU by 70 million tons of CO2 equivalent to 35 million tons of CO2 equivalent by 2030. These targets are now to be adjusted again and deadlines shortened – with a significant impact on refrigerants used in heat pumps.
But let’s start by looking at refrigerants in the 1970s. It is well known that chlorofluorocarbons (CFCs such as R12) are largely responsible for the depletion of the ozone layer. After this was proven, the use of CFCs was banned. They were replaced quite quickly because partially fluorinated hydrocarbons (HFCs) were already convincing substitutes with similarly good thermodynamic properties. What nobody had any idea of at the time, however, was the greenhouse gas effect of these substances. In 1997, the United Nations Kyoto Protocol classified HFCs and PFCs as greenhouse gases. Ultimately, this was an important step towards protecting the earth from chemically produced, environmentally harmful refrigerants. With the original F-Gas Regulation from 2006, its new edition from 2014 and the expected amendment at the beginning of 2024, there have been and will be further components that will continue to restrict the use of fluorinated gases. This is already having an impact on availability and prices. According to the draft currently being discussed in the European Parliament, F-gases with a global warming potential (GWP) greater than 150 will no longer be allowed to be used for maintenance and service from 2030. There is also a general ban on new stationary refrigeration systems with fluorinated refrigerants from 2025, which has been increasingly discussed since this year because a new negative property of these HFCs and PFCs has been identified under the generic term PFAS (per- and polyfluoroalkyl substances). These are fluorine-containing substances in refrigerants that are extremely persistent and also pose a risk to humans by poisoning the environment. A far-reaching ban on these “eternal chemicals” is currently being examined by the EU.
Alternative: Natural refrigerants
In light of the uncertainties outlined above, the use of natural refrigerants is becoming increasingly important. At this year’s ISH, numerous manufacturers presented heat pumps with a propane refrigerant circuit. Propane (R290) is a hydrocarbon with outstanding thermodynamic properties and high environmental compatibility (GWP of 3). It is therefore not subject to any bans under EU regulations.
Although the refrigerant propane is a flammable gas (classified as safety classification A3 according to ISO 817 and ANSI/ASHRAE 34), with the necessary knowledge, precautions can be taken with R290 systems to avoid any risks in this regard. It is important that the systems are designed in such a way that they comply with the legal standards and specifications. In order to make a leak as unlikely as possible, all connections must be technically tight in the long term. Should a leak nevertheless occur, the plant safety concept, which is also applied in Leonberg, comes into effect. Here, the systems are continuously monitored with a gas sensor that is linked to a two-stage system.
There must be a certain ratio for a flammable air-propane mixture. The lower limit is a propane content in the air of around 1.7 percent by volume, the upper limit is around 10.8 percent by volume. The first stage of the concept switches with the built-in gas sensor, which detects at ten percent of the lower limit, i.e. 0.17 percent by volume. The machine housing with the refrigerant-carrying parts is then ventilated by a generously dimensioned ATEX fan. The escaping propane is thus discharged into the environment in a non-flammable concentration and further diluted. When the 20 percent threshold is reached, all non-ATEX-certified electrical components are de-energized. All safety-relevant components are designed in ATEX and remain in operation.
It is often possible to install a propane system outdoors. This should be used whenever possible. Propane is very volatile, so there can be no build-up of propane if the system is installed correctly outdoors. Today, there are also solutions for indoor applications, either by designing special machine rooms or by using systems with a low refrigerant charge and a ventilated housing, which can be expanded on a modular basis.
But let’s start by looking at refrigerants in the 1970s. It is well known that chlorofluorocarbons (CFCs such as R12) are largely responsible for the depletion of the ozone layer. After this was proven, the use of CFCs was banned. They were replaced quite quickly because partially fluorinated hydrocarbons (HFCs) were already convincing substitutes with similarly good thermodynamic properties. What nobody had any idea of at the time, however, was the greenhouse gas effect of these substances. In 1997, the United Nations Kyoto Protocol classified HFCs and PFCs as greenhouse gases. Ultimately, this was an important step towards protecting the earth from chemically produced, environmentally harmful refrigerants. With the original F-Gas Regulation from 2006, its new edition from 2014 and the expected amendment at the beginning of 2024, there have been and will be further components that will continue to restrict the use of fluorinated gases. This is already having an impact on availability and prices. According to the draft currently being discussed in the European Parliament, F-gases with a global warming potential (GWP) greater than 150 will no longer be allowed to be used for maintenance and service from 2030. There is also a general ban on new stationary refrigeration systems with fluorinated refrigerants from 2025, which has been increasingly discussed since this year because a new negative property of these HFCs and PFCs has been identified under the generic term PFAS (per- and polyfluoroalkyl substances). These are fluorine-containing substances in refrigerants that are extremely persistent and also pose a risk to humans by poisoning the environment. A far-reaching ban on these “eternal chemicals” is currently being examined by the EU.
