On substances that deplete the ozone layer
Indirect impacts due to energy use
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- 11.4.1 Energy efficiency improvements
- 11.5 Equipment life cycle considerations: equipment design, operation, maintenance, and end-of-life
- 11.5.1 Equipment design
11.4 Indirect impacts due to energy useBy its very nature, the use of energy to accomplish refrigeration draws a valuable resource as the power generation systems consume fuel and, in many cases emit CO2 and other pollutants. The refrigerant selection impacts the energy consumption of the refrigeration system due to its thermodynamic nature in many ways. The indirect emissions operating the refrigeration systems during its lifetime contribute in many cases far more compared to the direct impact. The more important is the participation of renewable sources to the power grid, the less prevalent is the indirect impacts from energy use. Designing and efficiently maintaining HVAC&R systems contributes by a large factor to the reduction of GHG related to the air conditioning and refrigeration industry through cutting “indirect emissions”. Consequently, using measurement for the global warming effect of refrigerants that take into consideration indirect emissions is a more representative way for selecting environment friendly refrigerants than a simple comparison by direct emissions alone. Also the introduction of minimum energy performance standards (MEPS) has helped drive energy efficiency to higher levels than if those standards had not been applied, and that the cost of not complying with those standards will have an adverse effect on cutting GHG emissions. Energy efficiency is the measure of the amount of energy input to a machine to deliver a required output. It is measured in units of energy output or work done by the machine vs. the power input to the machine. However, energy efficiency for the HVAC industry can be measured at different levels: individual components, cooling and heating systems, or a building as a whole. The efficiency at each level contributes to that of the other level up and depends on the proper design and application of components at the particular level. Energy efficiency parameters are measured at certain conditions at which the machine is working and will have different readings if those conditions change. For most air-source air conditioning machines, this includes the ambient air conditions and the room temperature that the machine is expected to deliver. An air conditioner operating in a high ambient temperature condition will generally be less efficient than one working in an outside temperature of 35°C or below. 11.4.1 Energy efficiency improvementsThe discussion around energy efficiency is closely related to the one on alternative refrigerants. The guidelines from paragraph 15 of Decision XIX/6 require countries benefiting from investment projects, to implement conversion technologies that minimise the effects on climate. By converting to more energy efficient products, countries will minimise the consumption of electric power leading to a reduction in the carbon emissions from power plants. Emissions of CO2 in grams per kWh of electric power generated vary by fuel type or amount of renewable energy as well as plant design; emission factors are approximately 443 for natural gas, 778 for oil and 960 for coal. Depending on the sources of electric power in a particular country, each kWh saved will contribute to a reduction of up to a kilogram of CO2. An analysis by the European Commission on residential air conditioners reckons that "most of the environmental impacts (and life cycle costs - LCC) are attributable to the use-phase." (European Commission, 2009b). This shows the importance of understanding energy efficiency in any discussion about climate impact of air-conditioning and refrigeration equipment. Moreover, it is important to note that climate impact may also be reduced by the use of renewable energy sources; however, this does not mean that countries with low-carbon electric grids do not have to keep the pressure on higher energy efficiency standards especially when electric grids are regionally interconnected. 11.5 Equipment life cycle considerations: equipment design, operation, maintenance, and end-of-lifeConcepts and selection criteria for alternative refrigerants in various applications for each sector of the HVAC&R industry are presented in other chapters of this Assessment Report. The common criteria among the different sectors are the necessity to design, operate, and maintain efficient systems that operates with minimized emissions, both direct and indirect. For refrigeration and air-conditioning systems, the most important design criteria in an optimized operation is reducing indirect emissions due to energy efficiency measures over the lifetime of the equipment. In the design phase, the optimization process is a result of product innovation (such as part load design considerations of compressors, heat exchangers, and components), integration of the refrigeration equipment into the heating system for heat recovery, and utilization of power grid based controls. Those technical design criteria are linked to regulations and standards as well as voluntary agreements by industry. In U.S. buildings, space cooling and refrigeration accounted for 13.7% of the site and 21.3% of the primary energy use, in 2010 (USDOE, 2011). Additional energy is consumed for heating via reversible heat pumps, primarily in the residential sector. 16% in Germany have been reported (Arnemann, 2013), while the EU estimates that 55% of the primary energy in used by heating (Hudson, 2014). Buildings account for 40% of the world’s energy use with the resulting carbon emissions substantially more than those in the transportation sector (WBSCD, 2009). Estimated energy saving potential with available state-of-the-art technology is around 35-40% (FKT, 2009) per annum. A study by the German Research Council shows that it will be technically possible to achieve potential energy savings of 40% until 2020, if accompanying political measures are taken (FKT, 2012). In emerging markets like Brazil, RAC sales rocketed from 1 million units in 2003 to 3.3 million units in 2012 (Eletrobras Procel, 2013). As examples, the following energy savings achieved by voluntary agreements have been documented: - Supermarket refrigeration: 5.5%/year (period 2004-2012 (Heinbokel, 2011) - Domestic refrigeration: 27% over 10 years (Preuß, 2011); 40 % over 7 years (Silva, 2003) - Refrigeration in air conditioning systems: 2%/year (Brinkmann, 2009) In the position paper (FKT, 2012) by the German Research Council it is stated that considerable energy savings can be achieved through the optimum design of a system rather than just optimizing the design of components. Other savings can be obtained from the control, operation, and maintenance of the system. The same study found that savings up to 40% can be achieved through: - Efficient control, operation and design of systems (around 10%) - Reduction of effective temperature differences on heat exchangers (around 12%) - Use of efficient drives (around 3%) - Reducing cooling / heating demand (around 7%) - System improvement by designing in compliance with the annual temperature profile, use of heat recovery, thermal storage (around 8%) In Europe, the successful implementation of energy savings through commitments by the industry and by Eco-Design Requirements (European Commission, 2009b) in relation to the foreseeable requirements from the legislature led to a significant competitive advantage for manufacturers undertaking those voluntary commitments. As for the direct effect of the refrigerants used, here too there are opportunities to improve the life-cycle sustainability of refrigeration systems. As discussed in Section 11.6, if a refrigerant with poor environmental properties is used, careful management of that refrigerant is necessary throughout the lifecycle of the equipment. This entails designing equipment for low leaks, maintaining and operating equipment to prevent emissions, and finally properly recovering the refrigerant when the equipment is disposed or replaced. 11.5.1 Equipment designFrom an engineering point of view, the design of components such as compressors or electrical drives has a possibility for limited improvement of a few percentage points in terms of efficiency compared to ideal theoretical efficiency. Main improvements can be made through controls and smart electronic integration, minimized heat exchanger temperature differences and other measures described above. To address the direct effect, equipment can be designed to use alternative low-GWP refrigerants and/or to reduce emissions. These types of improvements are either driven by cost, product innovation or by enforced standards requirements. Environmental sustainability, including efficiency and refrigerant management considerations, can be achieved at different levels in the design phase by taking the following technical and regulatory criteria into consideration: Technical considerations:
Regulatory considerations:
The decision of which equipment to use during the design stage is often faced by competing targets: low first cost investment versus high energy efficiency affecting the cost of energy over the lifetime of the system and the GHG emission. To resolve this conflict between low first cost, operating cost and refrigerant emissions, new financing methods and evaluation criteria for the technical operation of systems in terms of their contribution to the environment are being developed. These financial mechanisms can contribute significantly to the reduction of energy consumption and refrigerant emissions and thus to system design. To be really relevant, these mechanisms must be able to account for an adequate balance between life cycle cost and LCCP. Refrigerant selection Sustainability aspects are being included as regulatory requirements (EU F-gas law) and third party standards such as the US AHAM Refrigerator Sustainability Standard (AHAM, 2012). A lifecycle approach is typically used to provide a complete analysis of the impact on the environment over the expected lifetime of the product containing refrigerant. Many of the factors that influence energy efficiency are included in Table 11-1 “Refrigerant Selection Criteria”. The efficiency of components, as well as efficiency losses such as pressure drops, have a large effect on the overall energy efficiency of the application. Energy efficiency in turn has a significant impact on the Total Equivalent Warming Impact (TEWI), the mass of refrigerant needed, the use of resources such as fuel, and end of life disposal requirements. Energy consumption is greatly affected by the selection of refrigerants, especially considering the lifetime of the equipment. For example, a typical 10 kW cooling capacity system with a SEER of 13 in the USA will use over 44000 kWh over its lifetime based on the life cycle cost estimator proposed by the U.S. Energy Star Program (Energy Star, 2014). This system will typically have 2 kg of refrigerant charge. The CO2 emissions due to the energy consumption of 44000 kWh are 30.3 metric tonnes of CO2, based on the USA power grid, which is 45 % coal-based. The equivalent CO2 emissions due to the direct release of the refrigerant charge are 2.7 metric tonnes, which is less than 10 % of the lifetime CO2 emissions. Design considerations for safety can sometimes counter the design for energy efficiency and lead to more CO2 emissions. For example, isolating heat exchangers for sake of safety or toxicity can affect the heat transfer efficiency either positively or negatively. Refrigerant criteria and properties provide a basis for the selection of a refrigerant in an application in support of the intermediate factors. Properties and selection criteria of significance are shown in Table 11-1. Table 11-1: Refrigerant selection criteria
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