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Performance Metrics for Room Air-Conditioners: Energy, Comfort and Environmental Impacts RESEARCH

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Performance Metrics for Room Air-Conditioners: Energy, Comfort and Environmental Impacts RESEARCH Performance metrics for room air-conditioners: energy, comfort and environmental impacts RESEARCH NIDHI RAI JAIN RAJAN RAWAL VISHNU VARDHAN SHUBHASHIS DEY *Author affiliations can be found in the back matter of this article ABSTRACT CORRESPONDING AUTHOR: Nidhi Rai Jain India’s current standards and labels for room air-conditioners (RACs) account for energy Centre for Advanced Research efficiency, but omit other important criteria that could influence product development in Building Science and Energy, and consumer choice: thermal comfort and environmental impact. This study proposes CEPT University, Ahmedabad, comprehensive RAC evaluation criteria by accounting for the operational energy, thermal India comfort and environmental impact through the metrics of the Indian seasonal energy [email protected] efficiency ratio (ISEER), cooling seasonal energy consumption (CSEC) and total equivalent warming impact (TEWI), respectively. It uses five RAC product cases based on the Indian RAC market to demonstrate the enhanced evaluation criteria across the climatic conditions KEYWORDS: of 55 Indian cities subject to static and adaptive (air-conditioned, AC; and mixed-mode, air-conditioning; energy MM) thermal setpoints. The analysis yields a significant difference in the number of RAC efficiency; environmental impact assessment; global operational hours between the static and adaptive (AC and MM) methods, resulting in a warming potential; indirect difference in the overall performance of RACs across varied climatic contexts. emissions; room air- conditioners; thermal comfort; PRACTICE RELEVANCE India RACs are increasingly being adopted as a standard method of active cooling with the modernisation of small and medium-sized commercial and residential spaces in TO CITE THIS ARTICLE: Jain, N. R., Rawal, R., India. However, current standards and labels only provide a partial evaluation of RAC Vardhan, V., & Dey, S. (2021). performance. This study targets three aspects of RAC performance in energy, comfort Performance metrics for room and environmental impacts. It demonstrates that existing RAC performance standards air-conditioners: energy, in India can be improved to account for climatic variability and environmental impact in comfort and environmental addition to the existing understanding of energy efficiency. The outcomes of this study impacts. Buildings and Cities, 2(1), pp. 666–687. DOI: https:// can serve as inputs to standards and labelling programmes by improving the component- doi.org/10.5334/bc.127 level energy efficiency of RACs, educating the end-users on optimising their thermal setpoints for improved performance, and supporting the development of RACs with low/zero global warming potential refrigerants. 1. INTRODUCTION Jain et al. 667 Buildings and Cities The final energy use in buildings has increased by 20% in the last decade; in 2019, it resulted in DOI: 10.5334/bc.127 28% of the global energy-related CO2 emissions (International Energy Agency (IEA) 2020). Heating, ventilation and air-conditioning (HVAC) is the most energy-intensive process in conventional buildings. Refrigerant-cooled split and window-type residential room air-conditioners (RACs) have been adopted for cooling purposes globally. In 2017, residential buildings accounted for approximately 70% of building energy consumption (IEA 2018). Developing countries such as India are the prime drivers of the growth in the adoption of RACs. The energy demand for Indian buildings is projected to grow by more than five times by 2100 primarily due to RACs (Chaturvedi & Shukla 2014; US Energy Information Administration n.d.). This necessitates the adoption of RAC-centric energy efficiency policies to help limit global warming (CLASP 2017; Graham & Rawal 2019). Therefore, there are three pertinent questions for this study: • How much energy does the RAC consume? • What is the thermal comfort with RAC operation? • What is the environmental impact of the RAC? The current standards and labelling (S&L) in India address the first question through the lens of energy consumption. However, they do not account for the ability of RAC to provide thermal comfort or its environmental impact through direct and indirect emissions. This poses a gap in the understanding of the true performance of RACs. This study attempts to address the aforementioned questions using three metrics to account for the energy efficiency, thermal comfort and environmental impact associated with RACs. Energy efficiency is assessed as the Indian seasonal energy efficiency ratio (ISEER), thermal comfort is assessed as the cooling seasonal energy consumption (CSEC), and the environmental impact is assessed as the total equivalent warming impact (TEWI). The proposed methodology calculates the three metrics subject to the static and adaptive (air-conditioned, AC; and mixed-mode, MM) thermal setpoints of 55 Indian cities and five RAC cases. The present study is limited to small-capacity (<2.5 tons of refrigeration) RACs and two refrigerants (R410a and R32). NB: A ton of refrigeration is a unit of power used in India to describe the heat- extraction capacity of air-conditioning equipment. It is defined as the rate of heat transfer that results in the freezing or melting of 2000 lbs, or 907 kg, of pure ice at 0°C in 24 h. It is approximately equivalent to 12,000 BTU/h or 3.5 kWh. It accounts for the indoor and outdoor dry bulb temperatures to assess the thermal comfort and does not account for relative humidity (RH). It evaluates the energy-consumption-associated indirect emissions based on the emission factors identified under the Clean Development Mechanism (CDM). The study calculates the total carbon emissions based on reasoned assumptions involving leakage rate, recovery factor, refrigerant charge and operating life. The findings of this study can benefit manufacturers in producing climate-friendly and energy efficient RACs. They will help embolden the prominence of non-refrigerant-based cooling technologies. Policymakers may benefit from deriving minimum energy performance standards and devise appropriate policies. This study can also help in predicting annual energy use due to RACs, scalable from a city level to a country level. Moreover, the three metrics of ISEER, CSEC and TEWI can help acquaint the end-user with the components of RAC performance and empower them in selecting the holistically best-performing RAC. 2. LITERATURE REVIEW A quantification of RAC performance requires an enquiry from the perspectives of electrical energy consumption, thermal comfort and environmental impact. The following subsections include the findings of published research on each of the three perspectives and they discuss the relevance of this study with respect to the research gaps. 2.1 ENERGY PERFORMANCE OF RACS The energy performance of RACs is quantified as the ratio of the thermal energy output to the electrical energy input, known as the coefficient of performance (COP). COP is widely used to compare RACs since it can be measured instantaneously. The energy performance of RACs Jain et al. 668 Buildings and Cities is quantified using the energy efficiency ratio (EER), seasonal energy efficiency ratio (SEER) and DOI: 10.5334/bc.127 heating seasonal performance factor (HSPF), as defined in various studies (Abhyankar et al. 2017; Power Knot 2011; Shah et al. 2017; Waide et al. 2011). The applicability of one metric over the other differs on a case-by-case basis and test conditions. Therefore, although the aforementioned metrics represent RAC energy performance, they cannot be used interchangeably. At standard temperature conditions, EER reflects the energy efficiency of an RAC at its maximum cooling capacity; however, in real-world conditions, RACs operate at the maximum cooling capacity at the hottest outdoor temperatures, which account for a small fraction of the annual operational hours. Most of the time, RACs operate on part load. SEER captures the energy efficiency of the RAC at the peak as well as part load conditions; therefore, it serves as a more appropriate metric to assess RAC energy efficiency. SEER was first proposed under the American standard of the Air-conditioning, Heating and Refrigeration Institute (AHRI) 210/240 in the early 1970s (Waide et al. 2011). Other countries adopted similar standards for incorporating SEER (Table 1). Table 1 International CONTINENT/COUNTRY RAC STANDARD standards that calculate US AHRI 210/240-2008 room air-conditioner (RAC) performance metrics. Australia AS/NZS 3823.2-2013 Note: CSPF = cooling seasonal China GB/T 7725-2004 performance factor. Europe EN 14825-2012 India ISO 16358-1-2013 (CSPF) Japan JISC 9612:2013, JRA 4046 The Indian variant of SEER is termed the Indian seasonal energy efficiency ratio (ISEER). The formulation of ISEER followed the methodology prescribed in ISO 16358-1 (2013) while accounting for the Indian climatic context (Shah et al. 2016). It relies on a reference outdoor temperature bin distribution range of 24–43°C, as prescribed by IS1391-1992 (Parts 1 and 2) (Bureau of Indian Standards 1992a, 1992b; Ministry of Power 2017). Improving the energy efficiency of RACs in India can translate to a saving of nearly 60 GW of peak energy demand by 2030 (Phadke et al. 2014). Energy efficient RACs also reserve the potential to reduce the annual energy consumption of Indian residences by 19% by 2027. However, the literature indicates that a long payback period acts as a prominent barrier to the popularisation of the Bureau of Energy Efficiency’s (BEE) star rating
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