On substances that deplete the ozone layer
Options for new equipment
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- HFC-134a and HFC blends R-407C, R-417A and R-410A
- 8.3.2 HFC-32
- 8.3.3 HFC-1234yf and other low-GWP HFC blends
- 8.3.4 R-744 (carbon dioxide)
- 8.3.5 Hydrocarbons
- R-717 (ammonia)
8.3 Options for new equipmentIn most non-article 5 countries the transfer to non-ODS refrigerants was completed several years ago. But, based on its favourable thermodynamic properties and high efficiency in heat pump applications, HCFC-22 is still in use for high and moderate temperature water and space heating heat pumps in the A5 countries. When selecting refrigerants, both the direct and indirect climate impacts must be considered (see chapter 2 and chapter 11). For heat pumps, the reduction in emission resulting from replacing fossil fuel burning may be the most important factor regarding greenhouse gas emissions. Options for new heat pumps include HFC-32, HFC-134a, R-407C, R-410A, R-417A, HFC-1234yf, new HFC blends, HC-290, HC-600a, R-744 and R-717. Studies of new low-GWP fluorochemicals (notably unsaturated HFCs – see Chapter 2 “Refrigerants”) in heat pumps are ongoing, notably in several European countries, Japan and the USA. Similar studies are underway to evaluate use or broader use of R-744 and hydrocarbons as refrigerants in several types of heat pumps, though actual product development and commercialization are limited to Europe and Japan at present.
HFC-134a, R-407C and R-410A are used widely in heat pump systems and are well commercialised globally. R-417A is used in heat pump application in existing systems as well as in new equipment. These refrigerants are being used in high to low temperature water and space heating heat pumps, in countries where HCFC-22 consumption reduction started in advance of the Montreal Protocol. These refrigerants are used mainly in Europe. In Japan R-410A is used and HFC-134a and R-410A are used in Canada and USA and to a lesser extent in Mexico and the Caribbean countries. R-407C has been used to mainly replace HCFC-22 in existing product designs because minimal design changes are required. However, the use of R-407C is declining in favour of the higher efficiency of R-410A and lower system cost. To use R-410A design changes are necessary to address its higher operating pressures and to optimise the system to its properties and thereby achieve a higher performance. Cascade heat pumps using HFC-134a and R-410A are commercialised in high temperature combined space and hot water heating heat pumps in Europe. These heat pumps have a relatively good performance and can operate without auxiliary electrical heaters. The heat pump can supply water at temperatures approaching 80 ºC. Most new heat pump products are using refrigerant R-410A because it results in more compact and efficient systems when they are optimised. Air to water split cascade systems are put on the market using R-410A for the low temperature and HFC-134a for the high temperature circuit. They guarantee high seasonal COP for colder climates even at high water sink temperatures, while keeping the required heating capacity without auxiliary electrical heaters. They are most used for combined space and hot water heating to replace existing boiler systems. Energy efficiency of R-407C systems is typically poorer than HCFC-22, although similar COPs can be achieved if the system is carefully designed. R-407C shows a pronounced temperature glide in practice, which can lead to operational difficulties. R-417A has been used by some manufactures for heat pump water heaters. R-417A provides lower capacity than HCFC-22 but has demonstrated its effectiveness at higher temperatures. As the cost of the refrigerant itself is minor in the total system cost, limited differences in refrigerant cost have a minor effect. The cost of components has a major impact. A more compact design results in general in a lower cost. For larger systems the design pressure has a larger impact on the cost than for small systems. For small and medium size systems R-410A is the most cost effective, while for large systems HFC-134a is most effective. There are no significant barriers to their use at the moment, but the high GWP of the refrigerants may put them under pressure to changes for lower GWP fluids. 8.3.2 HFC-32The use of HFC-32 in water heating heat pumps is not commercialized yet on a larger scale. HFC-32 has a higher operating efficiency than HCFC-22 and R-410A (Shigehara, 2001). It has saturation pressures slightly higher than R-410A which is approximately 60% higher than HCFC-22. The system refrigerant charge can be up to 43% less than for HCFC-22 while the energy efficiency is the same or higher (Yajima, 2000). It has better heat transfer and transport properties than R-410A due to lower molar mass. Since it has higher discharge temperatures than R-410A more accurate control of temperature is necessary especially for high temperature water heating heat pumps and low temperature heat source. The direct cost of the pure HFC-32 substance is lower than R-410A, but this has limited effect on the system cost. Based on the refrigerant properties, the equipment is more compact and consequently potentially cheaper, while mitigation devices for high discharge temperature may add some cost. The main barriers are related to the safe use of the lower flammable refrigerants (class 2L by ISO 817); see chapter 2. Standard ISO-5149 is updated in 2014 and IEC-60335-2-40 is in process of update to accommodate this new class. In general safety aspects during the lifecycle of the equipment are limited. However, some building codes do not allow the use of flammable refrigerants in certain type of buildings. If the refrigerant water heat exchanger is located in outside occupancy, the safety issue is easier to solve but frost prevention becomes an issue.
A number of other unsaturated chemicals are being identified in the patent literature as possible low-GWP refrigerants for heat pumps. Blends with HFC-32 or HFC-125 may make it possible to approach the properties of HCFC-22 or R-410A, but it results in a higher GWP than pure HFC-1234yf. As sample supply of these refrigerants is very limited, it is too early to judge whether any of these chemicals will be commercialised and will show acceptable performance and competitiveness in heat pump systems. Due to the price competitiveness pure HFC-1234yf is not considered as a future solution. For water heating and space heating heat pumps using HCFC-22, R-410A, R-407C, significant design changes would be required to optimise for HFC-1234yf. Some of the required changes include larger displacement compressors, larger diameter interconnecting and heat exchanger tubing and additional heat exchanger surface to offset lower heat transfer and higher flow resistance. The heat transfer is expected to be lower than for R-410A systems because of its lower saturation pressure. The relatively higher pressure drop in the refrigerant pipes and heat exchanger will result in poor efficiency at high temperatures typical for heat pump water heaters. As a new molecule due to a different manufacturing process, the HFC-1234yf and other Low-GWP HFC blend refrigerants has significant higher cost than that of HFC-134a. Components cost will be similar to HFC-134a, but the flammability will have effect for larger systems due to the pressure vessel codes. The same restrictions as for HFC-32 apply (see Annex to Chapter 2). 8.3.4 R-744 (carbon dioxide)In the past, R-744 was not used in water and space heating heat pumps because of its high pressure characteristics (Fernandez, 2008). Development of R-744 heat pumps started around 1990 (Nekså, 1998). R-744 heat pump water heaters were introduced to the Japanese market in 2001, with heat pumps for heating of bath or sanitary water as the main application. Space heating heat pumps that operate at lower water temperatures in combination with hot water heating have also been developed, but the numbers sold are less. R-744 operates at very high pressures; approximately 5 times higher than HCFC-22 and 3.5 times higher than R-410A. This is an advantage enabling more compact system designs. The low critical temperature of R-744 results in trans-critical operation. R-744 refrigerant has been used primarily in storage type heat pump water heater applications. Continued growth of market for domestic hot water heat pumps is expected in Japan, Asia and to some extent in Europe. Recently, R-744 heat pumps for domestic space heating application have been developed in Europe for use in cold climates if combined with very high temperature radiator type space heating. For commercial buildings with combined radiator and air heating systems, R-744 is a very promising refrigerant (Nekså, 2002). This also holds for new low energy buildings where the domestic hot water demand is large compared to the space heating requirement. It is not known what level of market penetration R-744 space heating heat pumps will experience. The ultimate market acceptance will be determined by the system economics, energy labelling and minimum energy efficiency requirements. R-744 as refrigerant enables domestic water heating up to temperatures as high as 90 ºC without use of an auxiliary electrical heater. R-744 may give a high performance when it is used with low temperature sources and high temperature sinks with a certain temperature difference between inlet and outlet water temperature (Steene, 2008). This makes it well suited for use in storage type heat pump water heaters in which low temperature inlet water is heated to a high temperature for thermal storage of domestic hot water. Compared to HFC refrigerants design modifications are required to get equivalent performance with R-744 for space heating alone (Nekså, 2010). To obtain high efficiency for domestic space heating application is challenging if the difference between the high and low water temperature of the heat sink is low. System designs enabling a low water return temperature are then required (Nekså, 2010) or introduction of work recovery components, e.g. ejectors or expanders may overcome the energy efficiency barrier, but the cost for it may make the product less competitive. The cost of the working fluid is low. However, because of the high pressure, certain types of systems require more robust designs for pressure safety which adds cost, while specific tube dimensions are much smaller compared to current technology which gives the advantage of compact tubing and insulation material. The main barrier is cost of the system and energy efficiency in some applications.
At present HC-290 systems are sold in a limited number of low charge level heat pump water heater installations in Europe. While, for hydronic systems, with ventilated enclosures configuration, larger refrigerant charges are allowed. Use in Europe has declined due to introduction of the Pressure Equipment Directive (Palm, 2008) but some compressor manufacturers are now offering compressors for HC-290 applications. The efficiency of HC-290 and HC-1270 in heat pumps is known to be good (Palm, 2008). The direct cost of the substance is favourable. Based on the refrigerant properties the equipment cost is similar to HCFC-22 while mitigation devices for safety add some cost. The main barriers are related to the safety. For systems with parts, which are located in occupied spaces, the allowable charge quantity is limited, whereas for systems located outside, there are no major restrictions. The necessity to ensure that technicians are appropriately trained to handle the flammability of hydrocarbons is a main barrier. For equipment manufacturers the liability aspects combined with the costs for safety measures are the main barriers to extend the use of hydrocarbons.
R-717 is used mainly for large capacity systems. It has also been used in a small number of reversible heat pumps and sorption ones. It is not expected to be used in small capacity water and space heating heat pumps. The energy efficiency of R-717 heat pumps is known to be very good. Crucial problems in commercial ammonia direct expansion system is oil return so as to achieve good heat transfer in the evaporator. These problems can be solved by use of oil which is soluble in ammonia (Palm, 2008). The cost effectiveness is unfavourable for non-industrial process use due to equipment and/or installations costs. The main barriers are related to safety aspects (see Annex to Chapter 2) during the life cycle of the equipment and the minimal capacity required for cost-effectiveness and certain national regulations controlling installation, even though it has been shown that small capacity heat pump systems can be designed to operate with very low charge of ammonia (100 g of ammonia for 9 kW heating capacity (Palm, 2008). The main obstacle for the commercialization of small capacity heat pump systems is the limited supply of components. Particularly, there are no hermetic or semi-hermetic compressors for ammonia available and ammonia is incompatible with copper.
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