CAREL is a world leader in control solutions for air-conditioning, refrigeration and heating, and systems for humidification and evaporative cooling. We design our products to bring energy savings and reduce the environmental impact of machinery and systems. Our solutions are used in commercial, industrial and residential applications.
Worldwide data centre power consumption is estimated to account for around 2-3% of the earth’s total electricity usage. As a result of this astonishing level of energy consumption, high-efficiency solutions need to be increasingly adopted. In particular, free cooling and evaporative cooling technologies are among the most promising cooling solutions for data centres, especially recently-designed sites; as these adopt cold aisle and hot aisle separation, higher supply air temperatures are allowed, as specified by the well-known ASHRAE TC 9.1 thermal guidelines. In recent years, different solutions have been developed for both direct (DEC) and indirect evaporative cooling (IEC); the best option depends on weather conditions and installation constraints, always keeping into account the balance between energy saving and business continuity, which is essential in mission-critical applications.
Different technologies can be applied to data centre cooling following the recommended conditions suggested by ASHRAE depending on outdoor air temperature and humidity.
Among these solutions, in recent years IEC has been particularly interesting, due the development of different configurations and the improvement of the main technologies; as the number of installations grows, the entire industry is striving to improve those technologies and move to the next level.
The system consists of an AHU that recirculates the air from the data centre, and uses an outdoor airflow to cool it via an air-to-air heat exchanger. This “secondary” air stream flows through the heat exchanger unit without entering the data centre, thus avoiding the introduction of contaminants in the air: during winter the outdoor air is cold enough to provide cooling. In the summer, the evaporative cooler reduces the “secondary” air temperature, while at the same time increasing its humidity until saturation, with maximum cooling of the recirculated air yet without affecting its moisture content. A cooling coil (direct expansion or chilled water) can deliver supplementary cooling capacity if needed, as well as providing redundancy. The air is delivered into the cold aisles and distributed through grills or diffusers, and the return fan then draws in air from the hot aisles.
An example of an IEC installation
The overall efficiency of the this kind of unit depends on the performance of the individual components: the heart of the system is the heat exchanger and the adiabatic humidifier.
1. The heat exchanger: nowadays there are different types of heat exchangers, however the most suitable technology is the aluminium-coated cross-flow heat exchanger, as this brings several advantages:
Best dry efficiency, meaning evaporative cooling is only used when necessary, thus optimising its water usage effectiveness (WUE);
It guarantees the best air and water tightness: in particular the latter is important to prevent any water ending up in the server room. This characteristic makes the cross-flow heat exchanger the most suitable technology, when compared with the heat wheel, which cannot avoid cross contamination (and makes it virtually impossible to use evaporative cooling);
It can withstand a high differential pressure between the two air flows, allowing a more flexible layout of the two air flows with their own air speed and pressure;
It can withstand ice formation due to its elastic modulus, as the cooling unit operates all year long and needs to be reliable over time;
It can be washed with a high water pressure without damage, offering high reliability over time;
It can withstand all types of water, thanks to its coated surface.
2. The adiabatic humidifier: there are different ways to perform evaporative cooling on the secondary air flow. One technology uses the so-called “wet pad”, cardboard or plastic media soaked with water that the air flows through, thus absorbing moisture and thereby being cooled. An alternative way is to spray water into the airstream, creating small droplets to facilitate evaporation; in particular, some systems use a pump to pressurise the water up to 15 bars, atomising it through nozzles, with consequently effective absorption for an optimal cooling effect.
IEC with pressurised water on the left and wet pad on the right
The advantages of a pressurised system are:
Better absorption efficiency due to the smaller droplets;
Better temperature control, as the pump is controlled by inverter and can thus modulate the amount of sprayed water; furthermore, the reduced inertia of the system allows a faster response, which is paramount for supply temperature control;
Reduced pressure drop compared to wet pad systems, which means a lower TCO due to lower fan power consumption;
Reduced maintenance, as the wet pad needs to be replaced periodically;
Possibility to easily create redundancy by doubling the spray systems: a double wet pad means either two ducts or double the pressure drop;
Possibility to wet the surface of the HX, if the type of HX allows, giving cooling potential due to evaporation by contact.
The following chart shows the comparison between evaporative cooling only (i.e. wet pad) or including the possibility to wet the surface at the same saturation level with a spraying system: the minimum improvement is 25%.
Comparison in terms of data centre air temperature difference between the configuration with the WET PAD and the medium-pressure adiabatic humidifier (MP HUMIDIFIER)
The Polytechnic University of Milan has carried out a research project to examine the best arrangement of medium-pressure adiabatic humidifier and heat exchanger in order to obtain optimal water distribution on heat exchanger plates with limited water consumption. Medium-pressure adiabatic humidifiers allow different layouts to be adopted in order to find the best configuration. Different configurations were investigated experimentally, with performance measured in different operating conditions: humidification from the top, side, bottom, top at 45° and bottom at 45°.
The results show the highest cooling capacity is obtained with the vertical orientation of heat exchanger plates and water/secondary air supplied from the top: there is pre-humidification at the inlet to the heat exchanger, and water evaporation is distributed evenly across the heat exchanger. The nozzles in counter-flow to the air further increase the cooling capacity of the entire system. Performance of the systems not shown in the graph can be derived: the 45° top configuration has performance that lies midway between the top and the bottom arrangements.
Medium-pressure adiabatic humidifier and heat exchanger arrangements
Comparison between different configurations of the medium-pressure adiabatic humidifier + heat exchanger
At the same time, the influence of the aluminium coating on the heat exchanger in the IEC systems was investigated. Two different materials were compared, one hydrophobic (EPOXY protection) and one hydrophilic-adsorption (called BLUE, due to its typical colour), in the same conditions. The results highlight that the Blue material enhances the cooling capacity of the IEC system by up to 10%. This increase is due to its special coating, comprising two different components: the hydrophilic surface that increases the contact angle of the water droplets, and the adsorption matrix that retains water on the surface. The combination of these two characteristics enhances the wettability of the plate, a more uniform water film is formed on the plate during the adiabatic process, and the wet bulb temperature is more easily reached over the entire surface. Compared to the standard solution with epoxy protection, the hydrophilic-adsorption coated heat exchanger reduces the WUE, in the same conditions, making it a solution to the most challenging market demands.
Hydrophilic-adsorption coated heat exchanger (left) and a detail of its plate (right)
Comparison in terms of cooling capacity between an IEC system with epoxy and hydrophilic-adsorption coated (BLUE) heat exchangers
Different types of water can be used
It is better to use bigger nozzles and to check and clean the rack very often
Aluminium plate can be used. Casing with epoxy protection
With softened water some dust can settle on the plate. Regular maintenance is needed
B∙Blue protection on the aluminium plates is needed as well as epoxy protection on the side plate
Higher price. Up to 5 times higher than mains water.
Deionised water is acidic. B∙Blue protection is needed to avoid corrosion
Ever since around 1750, fossil fuels have been used as the easy-to-get energy source; after all, they have been plentifully available with low extraction effort until now, so why not use them?
Yes, why not? Thanks to fossil fuels, mankind has improved living conditions in developed countries and increased its wealth practically without interruption, with the idea that such growth can be sustainable and continuous becoming a frequently proposed view among economists and governments. In fact, this is physically not possible.
Growth implies the use of resources to produce goods and run services, however resources are finite: for instance, the amount of fossil fuels is limited, albeit vast, as is that of mineral ores. The fact that the natural resources of our planet are limited is easy to understand: our planet is finite, which means that, theoretically, we could use up all the resources as it contains and no more. As growth is based on resources, it therefore cannot be continuous.
Let’s look at some numbers in this regard.
Fossil fuels have been used at an impressive rate. It took the Earth around 500 million years to produce fossil fuels, and so far we have used up around 250 million years of reserves in 250 years: an astounding average consumption of 1 million years of reserves for every calendar year. No surprise then that we are quickly depleting them.
From “Are you ready for the exponential era?” by Hans van der Loo, Chairman Advisory Board, Institute for Integrated Economic Research
Yet, one could argue, half of the reserves are still available, so why worry about the future? First of all, because the planet’s population is increasing, so higher amounts of fuels will be required, and this will reduce available deposits more quickly; secondly, because, in general, the less of a natural resource is available, the higher the effort needed to extract and use it (in economic terms, this means that the Energy Returned On Energy Invested, ERoEI, decreases).
We can now bring together the information presented above to draw some conclusions:
Our population is growing and is expected to reach 9.7 billion in 2050, up from 7.6 billion (estimated) in 2020
The finite resources of our planet are being used at increasing rates:  From Supplementary Table 18 of “A low energy demand scenario for meeting the 1.5 °C target and sustainable development goals without negative emission technologies” by Arnulf Grubler and others, in Nature Energy volume 3, pages 515–527 (2018))
From the presentation “2050 ENERGY EFFICIENCY VISION - RESOURCE EFFICIENCY IN CIRCULAR ECONOMY AND ENERGY EFFICIENCY POLICIES” by Jaap Strengers, Associate Partner SYSTEMIQ, made during the International Resource Panel (IRP) on 31 January 2018 in Brussels
The efforts to extract and use resources are increasing for the same unit output (the ERoEI is decreasing)
Pollution is increasing
The foreseeable consequences are:
Once the ERoEI becomes too low, the current growth of developed countries will slow down and reach a trough, to be possibly followed a new growth some years later. This has already happened in the past, because continuous growth is physically impossible; nowadays in particular, the use of resources is further strained by developing countries that are growing and justly claiming a larger part of the pie
From “Are you ready for the exponential era?” by Hans van der Loo, Chairman Advisory Board, Institute for Integrated Economic Research
If we are wise enough at a planetary level, we will invest in more efficient use of resources for a more sustainable future, meaning slower growth but also less sudden slow-downs
The possible ways forward are:
Reduce as much as possible energy usage for the same unit output, that is, maximise energy efficiency both at a product and system level. This will also reduce the GHGs indirectly generated by power plants still running on fossil fuels
Maximise the use of renewables instead of fossil fuels, because these are always available (or, at least as long as the sun shines and the Earth’s inner core generates heat, but this should happen for several millions, if not billion, of years after we have gone). Note, however, that given the stochastic nature of renewables compared to fossil fuels, we need to reach the point of being able to generate at least 5 times as much energy, with the surplus to be stored and used when energy cannot be generated, because either the sun is not shining or the wind is not blowing; this implies the development of energy-storage solutions with a capacity high enough to be small and suitable for use in homes and vehicles, for instance
From “Are you ready for the exponential era?” by Hans van der Loo, Chairman Advisory Board, Institute for Integrated Economic Research
Minimise the use of raw resources and, at the same time, maximise their re-use once embedded in products. Mr. van der Loo has proposed to pass from the typical 3 Rs (the top three in the image) to 10 Rs:
Is CAREL on track?
CAREL had been well on track years before these concepts became part of common language (or have yet to do so in some unfortunate cases) because we have been and are always promoting energy efficiency both at a product level and at a system level, thanks to our innovative control and monitoring solutions, as well as water-conscious evaporative cooling systems. This as regards topic 1 above.
Regarding topics 2 and 3, we are following both the developments of the relevant EU Directives (in particular, the RED, on renewables, and the EPBD, on the energy efficiency of buildings) and the important Circular Economy policy that is aimed, to the maximum feasible extent, at the re-use of resources embedded in products and systems.
However small it may be, we are doing our part to help all of us not be at stake.
In recent years we have witnessed increasing awareness of climate issues, both among individuals and governments. The focus is on reducing the climate-changing impact of human activities, in terms of emissions and consequently primary energy consumption, relating to both industrial and other activities. In this regard, the European Union has set the goal to reduce primary energy consumption by at least 20% by 2020, through Directive 2010/31/EU, whose scope is broad and covers different sectors. However it is the residential sector that is most affected: contrary to what we might think, households make the same contribution as industry in terms of primary energy consumption, and consequently emissions of climate-changing gases. The figure below illustrates that around 50% of our energy consumption can be attributed to these two sectors, with transport accounting for 33%.
In order to implement the changes needed to achieve the objectives defined by the European Union, efficiency in the residential sector is essential. Consequently, there is much more attention to NZEB (Nearly-Zero Energy Buildings). More than just an acronym, this is an actual definition agreed on by all the participating countries, specifying the technical requirements of new buildings. Indeed, starting 2020 all new residential buildings must have an energy impact, expressed in kW/m2/year, that is as close as possible to zero. To set the example, all new government buildings have needed to comply with these new regulations since 2018. So what do the NZEB requirements involve? They take into account all of the state-of-the-art technical solutions in terms of high energy efficiency. Indeed, when constructing a new building, technical, economic and environmental feasibility aspects must be factored into the design, adopting high-efficiency solutions such as:
These solutions are adopted for space heating, domestic hot water production, air-conditioning, ventilation and air handling in general. To ensure optimal, or optimised, management of the available energy resources, weighted control of the building’s technical systems is required. Such control, which can be customised to varying extents depending on the user, is based on different environmental and system parameters. Where possible, modulating operation of the units is preferable, so as to reflect the thermal load as closely as possible. Interfacing together several modulating systems, such as heat pumps combined with large ventilation systems, is complex but certainly economically beneficial. Depending on the country where new systems designed to help achieve a NZEB are installed, economic incentives may be provided to help users recoup the cost of the technical solutions adopted. It is also useful to have systems available for monitoring energy consumption, as well as sensors for monitoring environmental parameters, so as to understand the building’s effective energy consumption. Moreover, wireless monitoring can also be adopted, with the possibility of continuous remote monitoring, combined with a smart interface for viewing the data. According to Directive 2010/31/EU, these types of solutions are intended for a wide variety of applications. They can be briefly summarised as follows:
Single-family houses of different types
Hotels and restaurants
Wholesale and retail trade services buildings
It is clear therefore that the application of new high-efficiency technologies covers a complete range of different areas, with the precision of the technical solutions adopted depending on the specific need. So what is the current situation at an EU level? What progress has been made so far? According to the periodic report by ZEBRA2020, a project created to monitor the progress of NZEB implementations, the situation is quite varied.
In the figure, where the index from 0 to 1 reflects the maturity of implementation, it is clear that there is still a lot of room for the implementation of technical solutions to move towards NZEBs. Although the study showed that sourcing components is quite easy, prices are affordable and communication is effective, market penetration is not yet optimal. Indeed, it is clear that there is wide scope for improvement in the sector. National policies tend to favour implementation of these technologies. Obviously, the conclusions are based on the average data in European Union countries. The actual situation sees large differences at a local level, where high efficiency implementations are already mandatory or are about to come into force, with high market expectations. Going into more detail on the implementation of heat pumps, which represent the main technical solution from the point of view of NZEBs, research carried out by the ZEBRA2020 committee showed the following results.
Source EURAC Research, Institute for Renewable Energy, article written by Giulia Paoletti, Ramón Pascual Pascuas, Roberta Pernetti and Roberto Lollini ‘Nearly Zero Energy Buildings: An Overview of the Main Construction Features across Europe’
This highlights the air handling technologies used across a pool of NZEB buildings. 75% is accounted for by heat pumps, which are in turn divided based on the type of heat source. The most common are those with an air-cooled heat exchanger. Following these are ground-source heat pumps or units combined with recirculation of exhaust air from air handling units (AHUs). In conclusion, we can state that the efficiency of buildings, for both residential and commercial use, and in terms of insulation and primary energy consumption, represents the most effective solution for reducing emissions. Moreover, as highlighted by the first figure, this represents a major share of global primary energy consumption. To achieve the Nearly-Zero Energy Building objectives, however, high-tech system engineering solutions are needed, with the possibility for the system components to modulate the load, and therefore the energy consumed.
This is the judgement of distinguished Prof. Alberto Cavallini that is still echoing in the conference room at the Milan Polytechnic University. Even though the statement may seem a little over the top, it perfectly summarises his surprise speech during the 18th European Conference on Refrigeration and Air-Conditioning held in Milan on 6 and 7 June.
“It no longer makes sense to talk about new refrigerants, nor to wait for new ones to be developed in the future”, he stated. “Natural fluids, including hydrocarbons, ammonia and carbon dioxide, together with HFOs are the last refrigerants left that can be used for vapour compression cycles in HVAC/R”.
This is not the first time that Prof. Cavallini has given his authoritative opinion on refrigerants, however his comments are worth emphasising as, in my opinion, they perfectly sum up what was discussed at the Milan conference.
His conclusion is based not only on his decades of experience in the sector, but also on a study that analysed and classified more than 60,000 different molecules that could possibly be used as refrigerants. I did not detect any hesitation in him making this statement to manufacturers of synthetic refrigerants, intent on promoting new blends, and representatives of industry, intent on describing their current problems and their feelings of uncertainty over the long term.
Let’s then see how the conference unfolded.
300 people wanting to hear the latest news in the HVAC/R sector.
Milan offered a fabulous week of breezy sunshine as the setting for the biennial event organised by Centro Studi Galileo, with the patronage of the United Nations and the Italian Ministry of the Environment. The excellent organisation succeeded in bringing the majority of operators in the HVAC/R sector to the Milan Polytechnic: component and application manufacturers, trade associations, universities, design firms, distributors and representatives of the European commission and other institutions. I personally consider the networking opportunities and discussions to be the strength of this event.
The presentations, on the other hand, failed to meet some expectations, in particular among those who were looking for short- and medium-term solutions to the phase-out of synthetic refrigerants such as R-410A. On one hand, companies proposed their solutions focused on R-32 and R-454B, while on the other, institutions, associations and universities emphasised how the focus should now already shift to natural fluids.
One especially important speech was made by Niccolo Costantini, Policy Officer for the European Commission on Climate Action. He openly criticised the excessive emphasis on solutions with refrigerants that still have a high GWP (> 400), including those mentioned above. He also underlined how the Commission has given the CEN/TC 182 committee a mandate to analyse the safety of HVAC/R equipment, with the focus on flammable category A3 fluids, i.e. natural fluids such as propane. A Commission mandate symbolises the strong desire to encourage the sector to adopt these types of solution.
Moreover, as Didier Coulomb from the International Institute of Refrigeration (IIR) pointed out, CO2 emissions from the refrigeration sector are constantly growing and account for 7.8% of total emissions. This explains the pressure that institutions are putting on the players in this sector, as well as partially the results of the recent European elections, in which environmental policies were at the fore.
Still on the subject of refrigerants, the University of Padova proposed some interesting in-depth studies. In particular, Prof. Del Col has carried out work on zeotropic mixtures, i.e. composed of components with differing volatility and whose behaviour in heat exchangers is quite different from that described by traditional calculation models, giving lower performance than is expected in theory.
GWP reduction has always a cost
So why are we worried about volatility issues now? Probably because the current attempt to propose mixtures of different fluids in order to lower the GWP means giving with one hand and taking away with the other.
Take R-410A for example. This is a mixture composed of equal parts of R-32 and R-125. It is not flammable, due to R-125 that compensates for the flammability of R-32. It is not zeotropic, as the two components have practically the same high volatility and for the same reason it has high pressure, useful for reaching low temperatures. Consequently, it has an excellent operating range, excellent efficiency, and it is no coincidence that it is the most widely-used refrigerant today. However, it has a GWP of 2080 and is destined to be phased down.
To reduce its GWP, the percentages of R-32 can be increased up to 100%. R-32 is a flammable fluid with a GWP of 675, which is still quite high.
This can be mixed with R-1234yf, which has a GWP of 4. One of the possible mixtures obtained, R-454B, has a GWP of 465, the same flammability, yet is zeotropic and sees a decline in efficiency and a loss of pressure due to the low volatility of R-1234yf compared to R-32.
To recoup pressure and lower the GWP, more R-1234yf and a small part of carbon dioxide (CO2) can be added. This for example gives R-455A, a flammable gas with a GWP of 146, so finally a low value, yet with lower performance as the CO2 behaves in a diametrically opposite manner to the R1234yf, meaning a decline in heat exchange.
In summary, lowering the GWP means chemically increasing flammability and creating problems in terms of volatility, efficiency or operating range. Give with one hand and take away with the other.
Hence the sensible drive to work with pure natural fluids, such as propane, ammonia and even CO2. These have been known for over a century, have been adopted as a standard in various refrigeration applications and can now represent a long-term alternative for all other applications.
Naturally, this is not part of the plans of the companies that manufacture synthetic refrigerants. For example Jean De Bernardi from Honeywell proposed R-466A with a GWP of 750, and HDR-147, a provisional name, with a GWP of 400. Beyond the considerations I have described above, many of those attending the conference fear that the introduction of new mixtures is now lagging behind the phase-down process. In fact, it takes from three to four years to complete compatibility testing with components, especially compressors and valves, in order to obtain the required certification. In four years’ time in Europe, the planned average GWP will need to be around 400, and in seven years less than 300.
Will energy saving be a “new low GWP refrigerant”?
The final topic and one very dear to me is energy efficiency. To say that energy efficiency is more important than the type of refrigerant used in an HVAC/R application has generated quite an exchange of opinions on my Twitter account. Indeed, both Andrea Voigt of the European Partnership for Energy and Environment (EPEE) and Didier Coulomb himself stressed that the emissions produced by the refrigeration sector are mainly indirect (63%), or due to power consumption.
I therefore continue to stress that a well-built, high-efficiency system with a low refrigerant charge and reduced leaks emits much less CO2 even when working with high GWP refrigerants, compared to a system whose only target is to use a low GWP refrigerant, while neglecting the rest.
The fashion industry is not alone in evolving cyclically over decades with the same products. Even engineering at times brings back to light old things that perhaps had not been so successful in the past.
This is the case of CO2, which attracted a great deal of attention in the early 20th century and, following a long break of roughly 50 years, has come back at the beginning of the 21st century as a promising new refrigerant. After its consolidated use in refrigeration, with the development of highly-efficient compressor rack solutions, it is now the turn of CO2 being used for passenger comfort in transport.
The milestone is European Union Directive 2006/40/EC on “Mobile Air Conditioners” or MACs fitted in passenger cars (category M1 vehicles) and light commercial vehicles
“To reduce emissions of fluorinated greenhouse gases from MACs, the European Directive introduces a gradual ban on these gases in passenger cars. Fluorinated greenhouse gases with a global warming potential (GPW) higher than 150 will no longer be used in MAC systems. By reducing these emissions, the Directive contributes to the EU’s strategy for climate action.”
The EU has not been mandating any one preferred gas for the transition to low GWP refrigerants, but rather has left it to the automotive industry to develop solutions that meet the target set by the directive. The automotive industry thus came out with R1234yf as the most likely and adaptable substitute to R134a. However, this is slightly flammable and thus requires further precautions for application in passenger cars and light commercial vehicles. Modern cars typically employ a refrigerant charge of 200 g to 300 g, which is still manageable for an A2L classified “ASHRAE Standard 34” refrigerant such as R1234yf. This is not the case though for larger systems, such as buses and trains, where the refrigerant charge is typically above 5 kg. Managing such quantities of a flammable refrigerant is quite complicated, and requires special care in the design and installation of the air-conditioning system aboard the vehicle.
It is clear that CO2 air conditioners operate in transcritical mode, due to the low critical temperature (31°C) compared to all other refrigerants. A transcritical cycle means the gas discharged by the compressor cannot be condensed by a heat exchanger. Moreover, a transcritical CO2 cycle reaches very high working pressures, i.e. more than 100 bars, up to 10 times higher than the pressure in R1234yf systems. This means that components such as the compressor and condenser (which for CO2 is actually a gas cooler), need to be designed for high capacities and high pressures. This gives a much heavier unit compared to those operating on R134a or R1234yf.
By way of comparison, while an R134a air-conditioning unit with a capacity of 20 kW, such as those typically used on buses weighs 100 to 150 kg, the same unit running on CO2 could weigh even twice as much and require more complexity.
Comparison table between CO2 and R1234yf
The scenario for CO2 is more favourable when it comes to electric mobility. Due to the little or no heat loss from the electric engine, there is almost no heat supplied by the vehicle’s engine, whereas in conventional vehicles this is produced in massive amounts by the internal combustion engine. As a result, the vehicle’s air-conditioning system also needs to provide heating, and is therefore upgraded to a reverse-cycle system (cooling and heating), namely a heat pump, in the transport sector.
This represents a clear advantage for CO2 due to its intrinsic property of operating at very low temperatures (-20°C) compared to R134a and R1234yf, which are limited to roughly 0°C. CO2 indeed adapts to a wider operating temperature range. Despite the complications of building a heat pump operating in transcritical mode, which is essential to obtain a decent level of efficiency especially in mild climates, these complications are still less intricate than the flammability issues that a refrigerant such as R1234yf would bring to system design.
The inclusion of CO2 in class A1 “ASHRAE Standard 34” means CO2 is certified as a refrigerant that is non-flammable and non-toxic in moderate concentrations.
In the EU, some governments have attempted measures to foster the adoption of e-mobility for public transport, and some manufacturers have followed by putting forward new vehicle proposals on the market.
One of these, as of 2020, is the German “Blue Angel” eco-label (RAL-UZ 59b), which will be awarded only to buses with mobile air-conditioning using non-halogenated refrigerants such as CO2.
In conclusion, CO2 heat pumps are a viable solution for heating and cooling public transport using electric vehicles. Whether e-mobility will take over from conventional fuel-injection systems is another story: this will also depend on geopolitics (with the environment at stake).
The recent growth in the use of social networks is significantly affecting our lives, at times negatively and at times positively. One of the main merits of social media is undoubtedly the extra knowledge and awareness of a wide variety of topics that previously had not been on our radar, as well as the possibility to debate these in detail. One of the topics that continues to attract more and more attention is the environment, in all its various facets: excessive consumption of disposable plastic, pollution caused by fossil fuels, noise pollution, global warming, the greenhouse effect, massive deforestation and the consequent increased dangers for fauna and flora, and so on.
We are all in our own small way overwhelmed by all of this information that, in one way or another, has nonetheless made us more aware of our own impact on the environment, thus helping us act in the most informed way possible. Responsible waste collection and recycling, the choice of cars with hybrid drives or running on natural gas, and the use of recycled products are all actions that allow us to change the impact we have on the environment we live in.
It is worth asking, then, whether governments and companies are also making decisive moves towards achieving a future goal of total environmental sustainability. The answer is certainly yes, even though we cannot be sure if and to what extent such moves will be sufficient to guarantee a future where our impact on the environment is truly sustainable. We can also ask whether the timeline is reasonable; are we too late, and have we already reached a point of no return?
Whatever the case, national and international companies and governments have adopted, or are now adopting, many different policies to reduce environmental impact. Take for example manufacturers, a category that includes companies in the HVAC/R business: what policies have been adopted? A few decades ago, many companies started independently implementing actions aimed at respecting the environment, both for ethical reasons and for purely commercial purposes. Indeed, increasing awareness of respect for the environment can help sway customers to choose a certain product over another. Some companies therefore got off to an early start in this area. However, even though the inclusion of environmental issues in the narratives presented by large companies is a competitive factor, not all companies have chosen to do this, and consequently to ensure more decisive action, governments and organisations have over time introduced specific legislation and regulations. International treaties such as the Kyoto protocol, the climate alliance, etc. are just some examples of agreements between countries. The European Union has also already begun to issue regulations to counteract negative effects on the climate. In recent years, regulations have been introduced that specifically affect the companies that manufacture electronic products for HVAC/R: the main two are the REACH regulation and the RoHS directive.
The REACH regulation, by definition, is applicable directly by law in the various Member States, including Italy. The RoHS directive has been implemented by Italy and is applied through national legislation.
Both of these regulations impose restrictions on the use of specific materials. Such restrictions are aimed at preventing any potentially harmful materials from negatively affecting the environment and consequently the health of people. REACH mainly involves chemical substances (“REACH is a European Union regulation dating from 18 December 2006 that addresses the production and use of chemical substances “) while the RoHS directive is aimed at electronic components (“EU legislation restricting the use of hazardous substances in electrical and electronic equipment”). In the electronics business this is also known as “lead free”, because in its first revision it specified the exclusion of lead in components. At the time this was a true revolution, as almost all electronic components at the time contained lead; since then, component manufacturers have needed to find alternative solutions to make such products. Manufacturing companies have similarly needed to adopt purchasing policies for totally “lead free” material. Compliance with the RoHS directive is not simple, as there is the need to verify that all raw materials fulfil the requirements of the standard, and strict procedures have to be implemented regarding the introduction of new components, in order to avoid the use of non-compliant materials. In addition to all of this, the standard is dynamic, meaning it is periodically updated with the addition of restrictions on the use of further hazardous elements. All this involves the need to adopt appropriate procedures to ensure real-time verification that the raw materials used meet the requirements of the standard. If they don’t, the raw materials can no longer be used to manufacture the products.
What does this mean in practice? Firstly, it is impossible not to comply, as it is not a question of voluntary fulfilment of certain requirements, but rather clear laws that must be obeyed. This means companies can have a more sustainable impact on the environment. Indeed, considering that in the product’s life cycle and above all on its disposal there are no longer any toxic substances present, no further damage will be done.
... we can add that factories should now also deliver well-being in the environment we live in!
I recently went to Brussels for the annual event organised by EHPA (European Heat Pump Association), with two topics in mind: the heat pump as a service, and the importance of its integration from a demand/response perspective. I went back to the office after three days of networking with some certainties and some ideas to examine further.
EHPA Forum 2019 was held on 15 and 16 May at “The Egg“, an industrial building in the heart of Brussels dating back to 1925 and renovated in 2009 as a multifunctional centre to host different kinds of events. The event was attended by representatives of European industry associations, utilities and heat pump and component manufacturers, with the aim of examining the 2018 market data, available technologies and successful cases.
Before the opening of the Forum, EHPA invited its members to a mini workshop lasting just over an hour, entitled “Innovation in the Heat Pump sector”.
The cost of innovation
The workshop involved representatives of some of the most important manufacturers of components for heat pumps: Alfalaval (heat exchangers), Grundfoss (pumps), Emerson and Bitzer (compressors), Sanhua (valves), Honeywell (refrigerants) and Carel (control systems). We answered questions on innovation from the moderator, Marek Miara from Fraunhofer ISE, a person with considerable experience in the sector, and from the audience.
The discussion immediately focused on the topic of refrigerants. The most innovative technologies mentioned, including variable-capacity compressors and pumps and machine learning control systems, are designed to guarantee correct operation, efficiency and operating range of the heat pumps that are currently on the market and converted to work with low environmental impact refrigerants. These include flammables (propane, R-32, HFO mixtures such as R-452B and R-454B), the low-pressure HFOs suggested by Honeywell, highlighting the availability of some non-flammable options (R-1233zd for high temperatures), and finally CO2.
It was agreed that current heat pumps are not lacking in terms of technology, actually, quite the opposite. A SCOP* of 5 achieved by many units on the market it is more than sufficient to justify the investments made in these technologies. A heating capacity as high as 5 kW can be obtained from 4 kW of direct renewable energy (the outside air that the heat pump draws its energy from) and 1 kW of electricity, which is also partly renewable, depending on the percentages of production in each country. Why then are we demanding more innovation? Higher efficiency?
One answer lies in the topic that captured the audience’s attention: cost.
In 2019, the cost of heat pumps is still the main concern among consumers and therefore manufacturers. This is indeed a barrier to the uptake of this technology, and seemingly can only be overcome by economies of scale that bring significant reductions in production and component costs. 10%? 20%? None of the speakers was willing to say a precise number. However, there don’t seem to be any alternatives, and indeed it is unlikely that a technical innovation could solve this problem.
I thus brought this topic up: how long will we continue to worry about the cost of heat pumps? Why not start considering them as a service (indoor comfort and hot water production) rather than an asset?
This way of looking at the application is first and foremost in line with the future structure of Western society, as reported in the New York Times, which will be based on use and not ownership. It also allows companies operating in the production and installation of heat pumps to take on the initial costs of the systems, the aforementioned barrier that consumers complain about. These companies could then profit from the benefits of a high-efficiency system, equipped with predictive maintenance and self-optimisation technologies. Finally, it is in line with a market context in which utilities, i.e. the companies that supply energy/gas/water services, are beginning to extend their field of expertise.
The question therefore is: why fight over costs/prices in a “battlefield” that is on the edges of the service war? Why not take advantage of more energy-intensive home units (indoor comfort) to expand the range of skills and manage energy flows in the home using heat pumps, rather than considering these to be simply units managed by others?
A one-hour workshop and the pleasant networking dinner that followed was enough to win some endorsements, but not to find an answer.
Subsidies, success stories and demand/response in the path of heat pumps
The next morning, the forum commenced with the topic of “gender diversity”. It was in fact introduced by three women representing three different generations and how they see the present and the future. A different approach to the sector will most likely come from a different managerial class, one that is younger and more varied than the one I am part of today. Over the two days, several success stories were presented, regarding both industrial/commercial and home applications. The most deserving initiatives received the “Heat Pump City of the Year Award“, won this year by the city of Tampere in Finland for the design of a building served by heat pumps that use soil, waste water, exhaust air and solar panels as their source. All of these initiatives can help encourage the practical use of this technology to replace traditional gas-fired systems, yet on their own are not sufficient to bring more widespread use.
We then talked about the subsidies that exponentially increase sales. Some good examples are the schemes in the Netherlands, presented by Frank Agterberg from DHPA, and especially in France, where a heat pump will soon cost just € 1 for less well-off families and will be subsidised 50% for everyone else, as reported Valérie Laplagne from AFPAC.
(by Valérie Laplagne, AFPAC. Double digital growth: France, first Heat Pump market, in Europe)
As we all know, however, the subsidy solution requires policies that are focused on environmental sustainability and are currently not a priority on the agenda of most European governments nor indeed elsewhere in the world.
Last but not least, the topic of availability and cost of electricity in the coming years was discussed. There is a growing need to better manage electrical appliances, both to optimise costs and due to lack of availability, as well as to exploit all those solutions that are capable of returning energy to the system or guaranteeing operational flexibility.
Marco Gazzino from Enel, an energy multinational, presented their “Enel X” management system. Stéphane Dufour from Teko, a service company, proposed their “Energy Solutions”.
Both speakers predicted that the operation of units such as heat pumps will be controlled by a YES/NO signal. This is due to the absence of data communication standards that can allow more advanced management, as well as to guarantee compatibility with whatever technology is installed.
For this reason I emphasised the importance of shifting the focus from unit to service, from installation costs to operating costs, from circuit components to management technologies, such as machine learning, so as to place heat pumps at the forefront of the complex landscape that awaits us.
Unfortunately, I have the feeling that there is not sufficient awareness of this yet and that the puzzle will need to be completed by someone else.
*Seasonal Coefficient Of Performance, a number that represents the weighted efficiency in different climate and load conditions, and summarises the performance of a heat pump. A SCOP of 5 is equivalent to producing an average heating capacity of 5 kW, while consuming 1 kW of electricity
In the age of technological development, connectivity has certainly played a primary role, transforming both the functioning of devices and systems and the way in which people interface with them.
The new millennium has marked the arrival of a surprising evolution, a series of major changes that have created a new model of society and brought about a true digital revolution: this is the era of expansion of global interconnection.
In less than forty years, technological development has radically changed how some tools are used, and without showing signs of slowing down, is moving into a new digital era, characterised by industry 4.0, IoT and 5G, which will again lead the coming technological generations to change how they use certain tools.
This context inevitably requires product manufacturers and service providers to focus on two fundamental concepts:
Reliability, security and robustness of connectivity;
Simplicity in the management of technological complexity.
While on one hand the margins for error are becoming more and more restricted - take for example the first self-driving cars or remote surgery - on the other, in a context where primary needs are now satisfied, the need for simple and satisfying use has acquired a key role.
It is therefore essential to simplify the interaction between people and machines as much as possible, focusing our attention on users, who, with their needs and skills, should never feel frustrated by aspects that limit what they can do.
The latest generation of mobile devices, such as smartphones and tablets, are the point of access to a myriad of tasks that in the past were very time consuming; today, however, dedicated apps let us complete a payment, send an email or photo and access real-time information with a simple click.
Applications designed and developed for specific tasks, according to the type of user, help improve access to content and the user experience. Although this way of doing things still has a high switching cost for past generations, who are often unable to adapt their behaviour to the new technological context, current generations are ever more demanding, yet they both share the fact of being able to enjoy simple and immediate interaction.
This is precisely the goal of usability, namely “to make the underlying technology invisible, transparent to the user, who should be able to concentrate exclusively on the purpose rather than the means”.
For the HVAC/R sector too, the use of mobile devices that integrate connectivity via NFC, Bluetooth and WiFi technologies has meant tasks that were previously done manually are now much more efficient. Configuring a unit before meant scrolling through a menu of parameter codes that, without the support of a printed manual, were hard to understand. Today, dedicated apps make it possible to extend the product’s traditional user interface to the screen of a mobile device. Thus, thanks to a specific design, a whole series of information is available at a simple glance, including identification of the unit, its technical specifications and operating conditions.
This reduces the access barriers and extends the user’s range of possibilities by being able to interact with the unit via a well-known tool: their smartphone. The possibility of configuring the connected unit or changing its settings to improve performance, as well as sending specific notifications, are just some of the possibilities that are available today. These possibilities are of particular benefit to those involved in technical service. Technical personnel can be sent a detailed report on a fault, for example, meaning they can understand the origin of the problem before going on site and thus carry out more targeted actions to solve the problem and complete the task much more quickly.
QR codes, RFID or NFC mean the unit’s characteristics are immediately available, such as serial number, documentation, spare parts, traceability or even simply the log of all maintenance carried out. With cloud computing services, then, the possible scenarios and benefits grow exponentially. Data acquired in the field can be used to represent, on specific dashboards, an aggregate analysis of the performance achieved, or processed using machine learning algorithms that can predict malfunctions and implement the required countermeasures in advance. Complex topics that, when represented in detail and intuitively in graphic form, are accessible to everyone.
This changes the perception of usability from a simple additional feature to an essential element for evaluating the performance of a given product: the resulting benefits are not exclusively linked to extra revenues, but also increased productivity, considering the savings in time and effort. Usability engineering will therefore be increasingly the subject of discussion: a complex activity that requires care and method through a continuous sequence of phases (analysis, design, prototyping and testing), with the goal of reducing the barriers of the digital divide. Pursuing usability is today a fundamental asset to guarantee the success of a product, as it aims to build a world that is more human than technological, reducing the waste of resources and increasing user satisfaction.
The speed of progress today makes it difficult even to imagine what it will be possible to do tomorrow, however we can certainly expect a future in which artificial intelligence and augmented reality will allow us to use the displays of mobile devices and wearable devices to access additional information superimposed over the reality we see. While today we can already access multimedia content, such as images and videos that can be activated using a simple camera, new real time interactions via voice commands and 3D displays will represent the new frontier in usability.
The technological applications of engineering generally derive from a common approach: understanding how a phenomenon works and then describing it through equations. These equations are the models used as the basis for designing, improving and configuring specific solutions to satisfy a specific need. Take a car engine: to achieve the highest performance, it’s important to know how much power it can deliver, at how many revs, consuming how much fuel. In practical terms, we experience the result of this every time we drive: when we press the accelerator and expect the car to go faster. Even though we don’t have a precise equation in mind, we do expect an effect (extra speed) relating to a certain input (how hard we press the accelerator). All of these variables are clearly related and can be described by equations that designers know and apply. This simple example illustrates how thorough knowledge of the behaviour of a machine is important for optimum use and essential for correct design and configuration.
As regards the refrigeration sector, one of the main components of a refrigeration circuit is the compressor. Being the most highly-stressed, most complex and most expensive component, as well as the one that consumes the most energy, it is natural that it is the subject of special attention. Mathematical models are constantly used in the refrigeration and air-conditioning industry to determine the characteristics of compressors: when configuring a system, it is essential to identify which compressor best responds to the load requirements, simulating operation using these models. While in the example of the car the parameter in question was the increase in speed based on pressure on the accelerator, in the case of a compressor we need to know the refrigerant flow, cooling capacity, power input and current draw depending on the operating speed and the refrigerant suction and discharge conditions.
Nonetheless, the compression process involves certain dynamics that complicate its modelling. In an ideal case, with various boundary conditions that simplify the problem, the physics of compression would be able to predict the exact conditions of the fluid. Unfortunately, these limits are too rigid for real conditions; dissipative phenomena, complex fluid dynamics and the characteristic properties of gases are just some of the factors that cause real behaviour to deviate from the ideal situation.
Practical tests are thus used to define the operation of a compressor: tests are conducted in the laboratory in order to verify what actually happens in certain operating conditions and how the compressor behaves.
The US association AHRI (Air Conditioning, Heating, and Refrigeration Institute, one of the leading organisations in the sector) has defined guidelines to follow when testing compressors in its publications “AHRI Standard 540” and “AHRI Standard 570” (for carbon dioxide). The conditions under which the tests are to be performed are described in detail, in terms of ambient conditions, system configuration and the method used to acquire the data. The operating points measured thus become valid in general terms and can be used with confidence, due to the uniformity of the acquisition method.
The aforementioned standards also define how to use the data acquired to construct equations that describe a certain parameter: mass flow, cooling capacity, power input and current draw are calculated using a combination of evaporation temperature, condensing temperature and ten empirical coefficients derived from experimental data.
This model is widely used in industry, and is the de facto industry standard. By its very nature, however, it is a completely empirical model: it is in essence the mathematical curve that best approximates the experimental data, without any real physical meaning to support the equation. This makes it versatile, as while maintaining the same mathematical structure, it can describe different parameters, such as flow-rate and capacity. At the same time, however, the scope of the model is limited to the areas covered by the operating points used to extrapolate the equation.
A different approach involves the use of semi-empirical equations. These are derived from the physical equations that describe ideal compression (i.e. not accounting for dissipative phenomena and assuming the gas to have specific properties) yet readjusted using coefficients that compensate for the imperfections in real operation. This approach is frequently adopted in the scientific community and can be used to accurately describe a phenomenon that is coherent with the physics that govern it. Two examples are the Navarro et al. model and the Li model. The former expresses the flow-rate of refrigerant handled by the compressor as a function of the ratio of suction and discharge pressures, evaporation temperature and refrigerant superheat. Three coefficients are derived from the experimental data and are used to adapt the equation based on the compressor and the fluid used. The Li model, on the other hand, expresses the power consumption of the compressor as a function of suction pressure, discharge pressure and volumetric flow-rate. Three empirical coefficients are obtained, together with the power dissipated, by fitting experimental data and completing the equation.
The AHRI curves are the preferred choice, as within their range of validity they guarantee considerable precision due to their extensive experimental basis. However, due to the need for expensive testing, they are not always available. In this case, referring to the semi-empirical models described in literature can give acceptable results with less experimental data, due to their basis in physics.
Comparison between AHRI equation, Navarro model and sperimental mass flow data, as a function of evaporation temperature at suction pressure (with constant rotation speed and discharge pressure)
As mentioned at the beginning, experience acquired in the laboratory has a direct impacts on the market and the end customer. From scientific research to everyday life, the gap is much narrower than it would seem: it is also thanks to compressor modelling that after a hard day’s work we can go home to find a nice cold beer in the fridge.
Navarro-Peris, E.; Corberán Salvador, JM.; Falco, L.; Martínez Galván, IO. (2013). New non-dimensional performance parameters for the characterization of refrigeration compressors. International Journal of Refrigeration Liao, S.M. & Zhao, T & Jakobsen, A. (2000). Correlation of optimal heat rejection pressures in transcritical carbon dioxide cycles. Applied Thermal Engineering AHRI Standard 540, 2015. Standard for positive displacement refrigerant compressors and compressors units AHRI Standard 570, 2012. Standard for performance rating of positive displacement carbon dioxide refrigerant compressors and compressor units
If I were asked to choose just one feature that makes a car more luxurious than another, before engine power or the beauty of the design, I would certainly answer the comfort felt inside the car when driving. Indeed, it is no coincidence that comfort can be defined as the purely subjective sensation experienced by a user that represents their perceived “level of well-being”. We could therefore ask: “What features are essential to ensuring a comfortable passenger compartment?” A relaxing and comfy seat, a wide windscreen that offers a perfect view of the landscape and sufficient space for passengers would all be correct answers, yet these are undoubtedly secondary to correct climate control in the compartment and good sound insulation. In fact, anyone who gets into a luxury car immediately appreciates the plush interiors, yet at the end always perceives the quality of the thermal-acoustic insulation offered during the drive when compared against a more economical car.
There are many sources of noise heard in the passenger compartment when driving: most are generated by the combustion engine, yet there are also others, such as the aerodynamic noise due to the motion of the car itself, the noise generated by the rolling of the tyres on the asphalt, the noise created by the movement of the suspension and by other parts of the car, such as the air-conditioning. Considering that the automobile market is progressively shifting towards electric vehicles in place of internal combustion engines, it is clear that what were initially secondary disturbances are now becoming the major cause of discomfort when driving. In an electric car, the primary demands for thermal and acoustic comfort are therefore more in conflict with each other than before, and in-depth analysis of the system is needed to find a compromise.
The noise generated by the air-conditioning system is partly due to vibrations along the entire air-conditioning circuit. Just like in homes, in fact, this circuit comprises an evaporator, a condenser, an expansion valve and a compressor. The latter has the task of pumping the refrigerant around the circuit so as to complete the thermodynamic cycle needed to create cooling in the passenger compartment. To do this, it uses a rotor that revolves around a static element, the stator. This rotational movement invariably generates vibrations that, just like the refrigerant, are carried along the ducting. The vibrations then propagate in the air, and on reaching the ears of the passengers and the driver, creating a feeling of disturbance. This type of noise, due to the shaking of mechanical parts, is called structure-borne.
Unfortunately, this is not the only type of acoustic stress that occurs when the air-conditioning is turned on. Just like what happens with a wind instrument, where air is blown into pipes of different shapes to create a pleasant sound, the air-conditioner fan forces air into the ducting, thus “playing” music that in this case is not very pleasant to the ear. This is known as air-borne noise.
However, a good design engineer knows that, in the worst cases, “simple” abatement of these two types of noise may not be sufficient to stay under the deciBel limit threshold. Just like in any enclosed place, the effect of acoustics in cavities needs to be taken into account: when an acoustic vibration enters an enclosed space, it starts to “bounce” off the boundary walls, creating resonance zones, i.e. zones where the perceived noise is higher. This physical effect can in some cases be beneficial: take for example an auditorium, where the aim is to have a room designed to exploit these effects and ensure the actor’s voice is heard loud and clear by the audience. In a passenger compartment, however, this type of effect is likely to amplify the annoyance to passengers and the driver, leading to a worse driving experience and reducing perceived comfort.
Today more than in the past, at the dawn of the inevitable and much-desired era of electric vehicles, it is becoming increasingly clear how this will lead to a complete reversal in the way a car is conceived, designed and perceived. Many of the aspects until now considered as secondary or negligible will be at the forefront, and only the companies that succeed in changing their way of thinking will be able to ride this new wave, without being crushed by it.