Carbon Dioxide as Refrigerant Applications in Mobile Air-Conditioning and Applications in Heat Pumps Petter Nekså Senior Research Scientist, Norway 1
SINTEF location, Trondheim, Norway SINTEF does contract research for national and international clients We work in close collaboration with the Norwegian University of Science and Technology (NTNU) 2
Outline Mobile air conditioning and heat pump systems Mobile Air Conditioning LCCP comparison Mobile Heat Pumps Heat Pumps and AC for space conditioning Heat pump water heaters Other heat pump applications Some additional points Conclusion 3
Mobile Air Conditioning and Heat Pumps Application with largest emissions of HFCs Second largest refrigerant emissions Sector shares in 2002, expressed in CO 2 equivalent Palandre et al, Earth Techn. Forum, Washington 2004 4
European seminar: carbon dioxide refrigerant Current thinking: Phasing of HFC-134a free systems MAC European Commission - DG Environment June 2003 100 80 Share of HFC-134a free systems 60 40 20 0 2008 2009 2010 2011 2012 5
CENTRO RICERCA 6
CENTRO RICERCA Life Cycle Climate Performance (LCCP) of Mobile Air-Conditioning Systems with HFC-134a, HFC-152a and R-744 MOBILE AIR CONDITIONING SUMMIT 2004 Washington D.C. Armin Hafner and Petter Nekså,, Trondheim Norway Jostein Pettersen Norwegian University of Science and Technology NTNU Trondheim Norway 7
Overview Origin of the COP/Capacity from measurement (experimental) data Basis for the LCCP calculations Comparison of LCCP and seasonal energy use, for various climate locations US-locations applying US FTP 75 driving cycle European countries, applying NEDC Comments Conclusion Life Cycle Climate Performance (LCCP) of Mobile Air-Conditioning Systems with HFC-134a, HFC-152a and R-744 8
CENTRO RICERCA Origin of COP/Capacity data: SAE AR CRP data for Enhanced HFC-134a (SAE ARCRP, 2002) 2002 R-744 Pilot Project data from (SAE ARCRP, 2003) Small system SAE AR CRP Phase II data for 2003 Best Technology (SAE ARCRP II, 2004, preliminary results) BT HFC-134a SAE AR CRP Phase II data for 2003 HFC-152a (SAE ARCRP II, 2004, preliminary results); (same system as BT HFC-134a) 9
CENTRO RICERCA COP data 2500 rpm 5 o C air from evaporator or equal capacity Typical efficiency at varying condenser/gascooler air inlet temperature COP 8 7 6 5 4 SAE AR CRP data +28 to +39 % +21 to +34 % - 3 to +11% COP R-744 More than 90% of operation COP is important 3 2 EnR134a 1 R-744 2002 2-slab evaporator R-744 2002 Small 0 10 15 20 25 30 35 40 Air inlet temperature, o C HFC-134a Less than 10% of operation Capacity is important Condenser/gas cooler air inlet temp. 10
Driving Cycles FTP 75 NEDC NEFZ Vehicle velocity [km/h]. 120 100 80 60 40 City Cycle Highway Cycle Vehicle velocity [km/h] 120 100 80 60 40 Urban Cycle Extra Urban Cycle 20 20 0 0 500 1000 1500 2000 2500 Time [s] 0 0 250 500 750 1000 Time [s] Applied for the US-locations Mean vehicle velocity: 48 km/h Applied for the European locations Mean vehicle velocity: 26 km/h 11
CENTRO RICERCA Chicago: Miami: Phoenix: Selected Locations & Climate Data USA: 22.000 km/year Germany: Spain: Greece: Europe: 13.321 km/year 10.738 km/year 13.321 km/year USA Midwest, Chicago USA Sourtheast, Miami USA Southwest, Phoenix Japan, Kadena Japan, Misawa United Kingdom Germany Greece Italy Spain 4500 4000 3500 35 o C 3000 Temperatures 2500 2000 1500 1000 Hours above 35 o C hardly ever occur 500 0-30 -20-10 0 10 20 30 40 50 Ambient temperature ( o C) 12
LCCP Indirect Mass Direct System Mass [kg] Yearly driving distance [km/year] Fuel consumption rate for carrying and transport the AC system [litres/kg/km] Fuel consumption to CO 2 emission factor [kg CO 2 /litre of gasoline] Vehicle life [years] = Mass Contribution [kg CO 2 ] System charge [g] Yearly Leakage [g/year] * Yearly Leakage [g/year] * Life time Services [-] End of Life recovery rate [%] Global Warming Potential of Ref. Emission of producing a kg of Ref. [kg CO 2 ] Re-processing emission during the end of life refrigerant recovery [kg CO 2 ] Vehicle life [years] = Direct Impact (kg CO 2 ) * Achievable total controlled losses of 35 g/yr suggested by Fernqvist (2003), plus uncontrolled and service losses: total 60 g/yr (used in this analysis) 13
Measurement Data (Q o & COP) Driving Cycles (FTP 75 & NEDC) Elevated air inlet temperatures at idling (25% of idling time) Indirect contribution to LCCP COP = f {ambient temperature, ref. & driving cycle} Cooling demand (mid size vehicle) Annual temp. distribution Energy consumption of AC-system Indirect LCCP (TEWI) = Vehicle Life CO 2 emissions [kg CO 2 / kwh] Engine efficiency 13 0.243 0.27 14
CENTRO RICERCA En HFC134a R744 2002 LCCP comparison En HFC-134a versus 2002 R-744 US locations & US FTP75 Indirect Mass Direct -3% -39% Chicago US FTP75 Combined City & Highway driving Cycle En HFC-134a R744 2002 System Mass: 14.4 kg 16 kg Direct Leakage: 60 g/yr 50 g/yr Indirect: SAE CRP UIUC En HFC134a R744 2002-5% -20% Miami En HFC134a R744 2002 ±0% -18% Phoenix 0 1000 2000 3000 4000 5000 6000 7000 8000 LCCP 15
CENTRO RICERCA LCCP comparison En HFC-134a versus 2002 R-744 European locations & NE-Driving Cycle Indirect Mass Direct NEDC Driving Cycle European Union (93/116) En HFC134a R744 2002-13% -49% Germany En HFC-134a R744 2002 System Mass: 14.4 kg 16 kg Direct Leakage: 60 g/yr 50 g/yr Indirect: SAE CRP UIUC En HFC134a R744 2002-13% -39% Spain En HFC134a R744 2002-14% -31% Greece (Athens) (Athen) 0 1000 2000 3000 4000 5000 6000 7000 8000 LCCP 16
HFC152a HFC 134a LCCP comparison 2003 Best Technology HFC-134a versus 2003 HFC-152a US locations & US FTP75 Indirect Mass Direct -3% -31% Chicago US FTP75 Combined City & Highway driving Cycle HFC-134a / HFC-152a System Mass: 14.4 kg 14.4 kg Direct Leakage: 60 g/yr 60 g/yr Indirect: SAE ARCRP II HFC152a HFC 134a -3% -17% Miami HFC152a HFC 134a -5% -18% Phoenix 0 1000 2000 3000 4000 5000 6000 7000 8000 LCCP 17
HFC152a HFC 134a LCCP comparison 2003 Best Technology HFC-152a versus 2003 BT HFC-134a European locations & NE-Driving Cycle Indirect Mass Direct -4% -40% Germany NEDC Driving Cycle European Union (93/116) HFC-134a / HFC-152a System Mass: 14.4 kg 14.4 kg Direct Leakage: 60 g/yr 60 g/yr Indirect: SAE ARCRP II HFC152a HFC 134a -3% -31% Spain HFC152a -22% -3% Greece (Athens) (Athen) HFC 134a 0 1000 2000 3000 4000 5000 6000 7000 8000 LCCP 18
Which refrigerant will be the alternative to HFC-134a? Part of illustration from AutoBild 01/04 19
Comments 1(2) Phase II data cannot be directly compared to Phase I data, due to different system design. However, the relative LCCP improvement between HFC-152a and HFC-134a (Phase II) applied to the HFC-134a phase I data indicate that HFC-152a may approach the data of R-744. This analysis doesn t indicate that R-744 would have any problems to compete which HFC-152a. Not only hot climates should be considered in further LCCP analyses, focus should be given to vehicle population at all climate zones on earth. 20
Comments 2(2) Heat pump operation of the AC system was not considered. (Promising option for R-744 systems, even for US climates) Increased air inlet temperatures to the condenser of a car at idling are platform -specific problems. Only a few cars have this problem, others not. To assume an elevated temperature of +15 K at 25% of the idling time for the entire car fleet is a rather conservative assumption. Best Technology means best HFC 134a-system, available in 2003 as described in SAE ARCRP II (2004). HFC-152a may only be possible with an indirect system arrangement. (Hydrogen fluoride (HF) is a side product, when HFC-152a is thermally degraded. HF is highly toxic.) 21
Conclusion MAC LCCP 1 (2) The test data have reconfirmed that COP is no argument against R-744 systems. Fuel use of 2002 R-744 system is significantly lower than with Enhanced HFC-134a (up to 14% in Europe), even in the warm US climates (Phoenix) the total energy consumptions will be at the same level. LCCP of 2002 R-744 system is improved by 18 49 % compared to Enhanced HFC-134a system. The 2003 HFC-152a system uses 3-5.% less energy (fuel) than BT HFC 134a system. LCCP of the 2003 HFC152a system is improved by 17-40 % compared to an 2003 BT HFC-134a system. 22
Conclusion 2 (2) All data show that R-744 is able to compete, both regarding Energy efficiency and LCCP 23
Mobile Heat Pump based on reversal of AC system (Ambient air as heat source) CO 2 is an excellent refrigerant for a heat pump Alternatives heat sources: Engine heat Gas cycles Ambient air Combinations Interior heat exchanger Interior heat exchanger Exterior heat exchanger Heating operation Cooling operation 24
Why Mobile Heat Pump? Insufficient waste heat from modern fuel-injected engines, e.g. small diesels Higher demands for comfort (immediate heating expected) Safety (defrosting, defogging, driver attention) Instead of auxiliary fuel- or electricity-based heating system, use existing heat pumping circuit for both AC and HP, reducing total cost, weight and space requirements Electric vehicles have almost no waste heat 25
CENTRO RICERCA 26
Heat pump operation 100 150 125 Pressure [bar] Temperature [ C] 100 75 50 25 0 10 400 500 600 700 800 900 Specific enthalpy [kj/kg] -25 3,25 3,5 3,75 4 4,25 Specific entropy [kj/kg*k] 27
CENTRO RICERCA Heat Pumps and AC for space conditioning 28
CENTRO RICERCA Heat Pump Water Heaters The ideal application for CO 2 as refrigerant 29
Heat Pump Water Heater using the transcritical CO 2 cycle Temperature [ C] 120 100 80 60 Throttle Valve 5 6 4 Evaporator Receiver Int. Heat Exchanger 1 3 2 Compressor Gas Cooler p= 150 bar 2 40 20 0 3 4 5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 Entropy, [kj/kg K] 6 1 p= 20 bar 30
CO 2 Heat Pump Water Heaters commercialized - commercialized in Norway (Development started 1989) and Japan - based on Shecco Technology lisencees from Hydro Pronova Norway: Commercial sized system First system: AS Eggprodukter, Larvik, 22 kw heat output, 80 o C Supplies hot water with 1/5 of the electricity consumption compared www.shecco.com to resistance heating In operation since November 1999 Japan: Residential systems 4.5 kw heat output, 90 o C water Average power cons. 1,3 kw About 120.000 sold in the Japanese market in 2004 Shecco licence 2000 Finsam Denso 31
CENTRO RICERCA Brine to Water CO 2 Heat Pump System Principle [Stene, J., PhD NTNU, Trondheim, 2004] 32
CENTRO RICERCA Heat Rejection Process Combined Mode [Stene, J., PhD NTNU, Trondheim, 2004] 110 110 Temperature, T ( o C) 90 70 50 A B C CO 2-8.5 MPa (a-b-c-d) Preheating of DHW Low-temperature space heating Reheating of DHW b C a 90 70 50 30 d c B 30 10 T A A 10-10 -10 450 500 550 600 650 700 750 800 850 Specific Enthalpy, h (kj/kg) 33
CENTRO RICERCA Heat Rejection Process DHW Mode Heat Rejection Process SH Mode Temperature, T ( o C) 110 90 70 50 A C CO 2-10 MPa (a-b/c-d) Preheating of DHW Reheating of DHW c b C a 110 90 70 50 Temperature, T ( o C) 110 90 70 50 B CO 2-8.5 MPa (b-c) Low-temperature space heating b 110 90 70 50 30 10 d A 30 10 30 10 c B 30 10-10 -10 450 500 550 600 650 700 750 800 850 Specific Enthalpy, h (kj/kg) -10-10 450 500 550 600 650 700 750 800 850 Specific Enthalpy, h (kj/kg) 34
CENTRO RICERCA Laboratory Testing of a Prototype Plant The CO 2 heat pump unit: 7 kw total heating capacity Hermetic rolling piston compressor Counterflow tube-in-tube evaporator Counterflow tube-in-tube tripartite gas cooler LPR system with back-pressure valve Energy well as heat source Operating Conditions: Evap. temp.: -10, -5 and 0 C SH system: 33/28, 35/30 and 40/35 C DHW system: 60, 70 and 80 C 35
Preliminary Conclusions (1) The SPF of an integrated CO 2 brine-to-water heat pump system may be competitive to the state-of-the-art systems as long as: The annual DHW heating demand constitutes minimum 25 to 30% of the total annual heating demand of the residence The return temperature for the SH system is sufficiently low (< 30 C) The inlet water temperature from the DHW tank is low (< 10 C) During operation in the Combined mode and the DHW mode, the outlet water temperature from the DHW tank have a significant impact on the COP of the CO 2 heat pump unit. Consequently: The design and operation of the DHW tank is of crucial importance in order to minimize mixing and conductive heat transfer in the tank during the tapping and charging periods 36
CO 2 -Heat Pump Dryer 37
Reversible air/air heat pump Principle 4-WAY VALVE COMPRESSOR OUTDOOR HEAT EXCHANGER RECEIVER INDOOR HEAT EXCHANGER NON-RETURN VALVE EXPANSION VALVE INTERNAL HEAT EXCHANGER NON-RETURN VALVE EXPANSION VALVE 38
Development of reversible air-air heat pumps Heat pump mode competitive Cooling mode currently less efficient, inefficient hx s in reversed mode operation 39
Space heating in commercial buildings CO Heat Pump System 2 Evaporator Gas Cooler Water Heater HX Hot Water Storage Tank Auxiliary System Simulation show better SPF if airheating represents more than 30% of the heating demand (rest hydronic) Temperature Throttling Distribution Cooling Compression Water Heating Radiator Air heater In Norway typically 50% of the heating demand is for airheating Evaporation Entropy, s Space Heating 40
CENTRO RICERCA CO 2 -heat pumps for commercial buildings Serie- kontra parallellkobling av varmelaster ved bruk av CO2-varmepumpe Serial- vs parallel connection of heat loads Temperatur [ C] 140 120 100 80 60 40 20 0 COP = h / w Ventilation serial Ventilasjon (seriekoblet) h2 h1 Ventilasjon (parallellkoblet) Ventilation parallel Radiator Radiators -20 w -40 450 500 550 600 650 700 750 800 850 Entalpi [kj/kg] 41
CENTRO RICERCA The design of the total system should be adapted to the refrigerant 42
Improvements Cycle improvements can be implemented more or less easy and reduce losses differently depending on the refrigerant Multistage compression Liquid subcooling Suction gas heat exchange Expander Ejector Optimisation is very much driven by economy, not only a technical fact From Denso ejector development 43
Closing conclusions The revival of CO 2 as a refrigerant started in Europe more than 15 years ago, and there has been a strong development of new technology worldwide using this refrigerant in several application areas since then. Developments which initially were driven primarily by environmental concerns have often resulted in disclosing additional advantages by using CO 2, such as higher COP, higher cooling and heating capacity, better comfort, and added possibilities of heat recovery. Cost- and energy efficient systems have been developed and commercialised for some applications and more seems to come in the near future. With increasing focus on climate gas emission reductions, strict regulations on the use of HFC chemicals may be expected, possibly followed by phase-out targets and dates as announced by some European countries. These trends will clearly drive the interest in the direction of natural refrigerants in general and CO 2 in particular. 44
CENTRO RICERCA R-744 COP Thank you very R-134a much! Condenser/gas cooler air inlet temperature 45