Energy Efficient Air-Conditioning
The safety and performance properties of HFC, HFC/HFO blends, HFO, and HCFO refrigerants make them suitable for use in air-conditioning systems, particularly where charge size and location exclude other options.
The main categories for air-conditioning in the EU are:
Moveable (portable) hermetically sealed units
Split systems
Multi-split systems and VRF systems (Variable Refrigerant Flow)
Chillers (central plant with secondary chilled water system)
The EPEE White Paper “Count on Cooling: A five-step approach to deliver sustainable cooling” examines the crucial role of cooling in the 21st century.’ See https://countoncooling.eu/index.php/about-epee/
Split systems, VRFs and Chillers widely use HFC, HFC/HFO, HFO and HCFO refrigerants
F-Gas Regulation 517/2014 has two use bans that apply to the air-conditioning sector:
- Movable room air-conditioning equipment (hermetically sealed equipment which is movable between rooms by the end user) that contain HFCs with GWP of 150 or more: 1 January 2020.
- Single split air-conditioning systems containing less than 3 kg of fluorinated greenhouse gases, that contain, or whose functioning relies upon, fluorinated greenhouse gases with GWP of 750 or more: 1 January 2025.
The requirement to use refrigerants with a GWP less than 750 has resulted new fluorocarbon refrigerants that have different balance of safety, technical and GWPs to replace R-410A in a range of air-conditioning applications. Ultra-low GWP HFOs and HCFOs are particularly suitable for chiller applications.
GWPs, classifications and applications for HFCs/HFOs/HCFOs and refrigerant blends subject to the F-gas Regulation can be found here.
Split systems & Multi-split systems and VRF systems (Variable Refrigerant Flow)
HFC-410A is the most widely used refrigerant for split, multi-split and VRF systems as it is non-flammable, has high volumetric capacity and good efficiency.
- HFC-32, a A2L mildly flammable refrigerant is now being used in some new equipment in all these applications in the EU. According to BSRIA “R-32 is gaining ground rapidly and in 2019 approximately 37% of all splits systems used R32 refrigerants.” Compared to HFC-410A, HFC-32 offers a reduction of GWP (F-Gas Regulation AR4 value 675 reduced from 2088), a reduction in refrigerant charge and energy efficiency improvement all contributing to reduced greenhouse gas emissions. In Japan from 2014 100% of residential split air-conditioner production was switched to HFC-32.
- HFC/HFO A2L blends such as R-454B and R-452B are being considered as HFC-410A alternatives for some air-conditioning sectors. For North American ducted systems one company has selected R-454B with a GWP of 466.
- A non-flammable HFC/IFC based blend (R-466A) containing CF3I to achieve non-flammability and with a GWP of 733 is being evaluated for performance and long-term reliability and stability as an alternative to HFC-410A for VRF systems. Initial performance testing showed very similar efficiency, cooling and heating capacity to R-410A.
Chillers (central plant with secondary chilled water system)
Chillers use a secondary chilled water system and are available in a wide range of equipment technologies from small systems suitable for small mid-sized office buildings (for example using scroll or rotary compressors) to larger systems using screw or centrifugal compressors.
For small chillers HFC-410A and HFC-134a are still widely used, but are being replaced by lower GWP refrigerants:
- For screw compressor chillers, R-513A, a non-flammable lower GWP HFC/HFO (GWP573), is being used to replace HFC-134a. HFO-1234ze(E) (GWP <1 AR5 value) is also being used as an alternative to HFC-134a.
- For scroll chillers, mildly flammable A2L refrigerants, HFC-32 (GWP 675) and R-454B (GWP 466) are being used as alternatives to HFC-410A in new systems. Additional safety measures are required to prevent the risk posed by A2L mildly flammable refrigerants. The systems are factory filled hermetically sealed chillers R-513A and HFO-1234ze(E) are being used as alternatives to HFC-134a.
Large centrifugal compressors use single component refrigerants or azeotropes and are designed specifically for the refrigerant properties. HFOs, HCFOs and R-513A/R-514A (HFO based) refrigerants are becoming the refrigerants of choice due to their ultra-low GWPs, energy efficiency, and low or non-flammability. HFC-134a continues to be used.
CHILLERS – understanding refrigerant emissions contribution to total emissions
The total greenhouse gas emissions due to the operation of a chiller are the direct emissions of refrigerant and the indirect emissions due to energy use. The switch to lower GWP refrigerants for chillers, such as HFC/HFO blends, HFOs and HCFOs, reduces the contribution of the refrigerant emissions and energy consumption is essentially the source of emissions during use for chillers with very low refrigerant emissions
Find our more
- 2018 AFCE Final Report Energy Efficient State of the Art of Available Low-GWP Refrigerants and Systems. This report can be downloaded from the AFCE (Alliance Froid Climatisation Environnement) website at http://www.afce.asso.fr/wp-content/uploads/2018/10/Final-rapport-energy-efficiency-GWP-2018.pdf
- UNEP June 2016 Report of the Technology and Economic Assessment Panel Volume 1 Progress Report
- UNEP Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee 2014 and 2018 Assessment Reports
- UNEP June 2016 Report of the Technology and Economic Assessment Panel Volume 1 Progress Report
How do we use air-conditioning
Air-conditioning is used for human comfort (domestic and commercial), in keeping hygienic conditions in hospitals, retirement homes and public buildings and ensuring controlled conditions for sophisticated computer systems (data centres). Reversible air-conditioning systems combine heating and cooling in the same system (see also the heat pumps applications section). Large numbers of installed split or multi-split or variable refrigerant flow (VRF) are reversible and operate as heat pumps when required. The issues associated with safety, refrigerant and construction are comparable to air-conditioners.
In domestic dwellings, air-conditioning equipment typically consists of direct units, and may be portable units (rolled from room to room, with a flexible pipe to discharge heat e.g. through a window), or small split units through to multi-split systems for whole dwellings.
Smaller commercial offices and retail buildings can have very sophisticated Variable Refrigerant Flow (VRF) systems which can change refrigerant flow to each indoor unit in response to the system demand. In addition, VRF systems can be configured to have cooling or heating functionality for each indoor unit independently allowing simultaneous cooling and heating for different indoor areas, in response to requirements such as occupancy and heat load from equipment or sunlight, and shade. VRF systems allow for heat recovery and are very efficient.
Chillers use a secondary chilled water system and are available in a wide range of equipment technologies from small systems to larger systems that are used in a wide range of sectors, particularly for large buildings, building complexes, data centres and district cooling systems. Data centres are becoming increasingly important and widely installed. Large data centres use massive amounts of energy to process and store data. Similar quantities of energy can be required for cooling to maintain the required data operating temperature. (see separate applications page for further information). District heating and cooling can significantly improve energy efficiency and reduce energy consumption compared to alternative heating and cooling approaches (see separate applications page for further information). Chillers are designed for high reliability and a long service life and may stay in service for up to 40 years depending on the compressor type. Refrigerant emissions are significantly lower today for newly installed chillers compared to systems installed 10 or 20 years ago. Already the global warming impact for a chiller is dominated by the energy use with the contribution due to emissions of HFC refrigerant being about 1 to 3%. The use of lower GWP refrigerants, in particular very low GWP HFOs and HCFOs reduces this considerably to much less than 0.1% of the global warming emissions. In addition, the focus on energy consumption is driven by the EU ecodesign regulation for air heating and cooling products (EU) 2016/2281 which sets minimum efficiencies for chillers.
Chillers – understanding metrics for total emissions
The total greenhouse gas emissions due to the operation of a chiller are the direct emissions of refrigerant and the indirect emissions due to energy use. The switch to lower GWP refrigerants for chillers, such as HFC/HFO blends, HFOs and HCFOs, reduces the contribution of the refrigerant emissions and energy consumption is essentially the source of emissions during use for chillers with very low refrigerant emissions.
The total greenhouse gas emissions during operation of a chiller is known as TEWI (Total Equivalent Warming Impact). Refrigerant recovery at end of life is included. A more complete understanding of the emissions related to the manufacture and use of a chiller is the LCCP or Life Cycle Climate Performance. The LCCP models can be extremely detailed, accounting for all CO2 contributions from CO2 emissions from the use of energy (indirect) and CO2 equivalent emissions from other operations (direct CO2eq) from “cradle” (refrigerant and product manufacturing), through use (including servicing and potential leak rates by type of product), to “grave” (recycling and disposal) for a product. For large centrifugal chillers, due to the long use phase (20-40 years) the emissions due to equipment manufacture and equipment disposal are extremely small (<1%) as a percentage of total LCCP. Life Cycle Assessment extends the LCCP approach to the other relevant aspects that concern the environmental impact of a technology.
The main contributor to LCCP is energy use, typically >95% for a HFC chiller with a 5% annual refrigerant leakage rate, assuming effective end-of-life recovery of refrigerant. Reducing the annual leakage rate to 1% reduces the refrigerant contribution to emissions from about 5% to about 1% (but actually dependent on climatic conditions and primary energy source). State of the art chillers may have annual leakage rates as low as 0.1%.
With extremely low refrigerant emission rates, energy consumption is essentially the source of emissions during use, and refrigerant selection takes into account energy efficiency, safety, reliability and technical performance. Lower GWP HFCs or HFC/HFO refrigerants further reduce the contribution due to refrigerant emissions compared to currently used HFCs.
The switch, where technically appropriate, to HFOs or HCFOs with extremely low GWPs, reduces the contribution of the refrigerant emissions to the LCCP to close to zero. Very low refrigerant leakage rates minimise refrigerant use, maximise resource efficiency and help maintain optimum chiller performance. The chiller in use emissions are effectively only from energy consumption, which in turn depends on the chiller design, its energy efficiency with the selected refrigerant, the ambient conditions, the overall installation and control systems, and the primary energy mix used to generate the electricity consumed. When nuclear or renewable primary sources are used to generate the grid electricity, virtually no GHGs are emitted.
References
Assessment Of Life Cycle Climate Performance (LCCP) Tools For HVAC&R Applications With The Latest Next Generation Refrigerant Technology, Purdue University Purdue e-Pubs International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 2014
2018 RTOC Assessment Report