Challenges in Designing Low-Cost Media-Isolated MEMS Pressure Transducers for HVAC/R Applications

Transcription

1 Challenges in Designing Low-Cost Media-Isolated MEMS Pressure Transducers for HVAC/R Applications Tom Kwa, PhD CTO DunAn Sensing LLC 10 June 2015 Long Beach, California

2 Outline The need for HVAC/R HVAC/R fundamentals The developing need for pressure transducers in A/C Established media-isolated pressure transducer technologies DURAsense pressure transducer technology and performance Summary

3 The need for HVAC/R

4 Principle of natural refrigeration International College of Automotive S univ = S sys + S surr >= 0 (2 nd Law of Thermodynamics) or, heat flows from hot to cold H vap = H vapor - H liquid >= 0 (Enthalpy of vaporization) or, an evaporating liquid takes up heat

5 The fundaments of mechanical refrigeration S univ = S sys + S surr >= 0 (2 nd Law of Thermodynamics) or, heat flows from hot to cold H vap = H vapor - H liquid >= 0 (Enthalpy of vaporization) or, an evaporating liquid takes up heat P 1 H vap 1 1 ln ( ) = ( ) P 2 R T 2 T 1 (Clausius-Clapeyron Equation) or, boiling temperature increases with pressure P 1 T 1 P 2 T = (Charles Law) or, compression of a gas raises its temperature

6 Principle of compression refrigeration system

7 Simplified A/C loop flow sequence Higher refrigerant temperature (4) temperature increases with increasing pressure (4) Compressor boiling temperature increases with pressure (3) Refrigerant releases heat (1,2) heat flows from hot to cold (1) Condenser Lower refrigerant temperature (4) temperature decreases with decreasing pressure (4) Metering device boiling temperature decreases with pressure (3) Refrigerant absorbs heat (1,2) heat flows from hot to cold (1) Evaporator

8 Temperature-pressure chart of R-410A and other refrigerants Temperature Refrigerant, Pressure [PSIG] Temperature Refrigerant, Pressure [PSIG] Suction pressure Discharge pressure

9 Residential HVAC system and components

10 Pressure switches to protect the A/C system expansion valve system LPS HPS LPS=low-pressure switch HPS=high-pressure switch

11 Temperature-pressure chart of R-410A and other refrigerants 50.0 Cut-out pressure Cut-in pressure Suction pressure Discharge pressure Cut-in pressure Cut-out pressure Pressures in PSIG

12 Use of a pressure transducer to make the A/C system more efficient by minimizing superheat electronic expansion valve system Suction pressure

13 Use of multiple pressure transducers to minimize superheat and subcooling Heat release Heat absorption SP=suction pressure LP=liquid pressure

14 Use of multiple pressure transducers to maximize compressor efficiency R-410A compressor efficiency P dis =discharge pressure P suc =suction pressure Compression ratio P dis /P suc illinois.edu

15 Pressure transducer to control condenser fan speed CHP CHP=condenser head pressure WIKA

16 Challenges for HVAC/R refrigerant pressure sensors Chemically compatible with refrigerant fluids (R-410A, R-404A, refrigerant oils, acids formed due to moisture contamination) Large operating temp range (-35⁰C to 120⁰C) High burst pressure (25MPa/3,625PSIG) High dielectric withstand voltage (1.8kV) High ESD immunity (+/-2kV, +/-8kV, +/-15kV) Maintaining accuracy of +/-1%FS High reliability (>10,000,000 FS pressure cycles) Low cost (<$10)

17 Media-isolated pressure transducer technologies Silicone Oil-Fill Cavity DOES NOT MEET PERFORMANCE TARGET Piezoresistors or metal film deposited on ceramic diaphragm Strain gauges bonded on stainless steel diaphragm DO NOT MEET COST TARGET MEMS chip in stainless steel package with metal diaphragm and silicon oil

18 Media-compatible pressure sensor using DURAsense MEMS packaging technology MEMS Sensor Sensor Body Compensation Board Unique features: No oil fill No stainless steel diaphragm No welds No organic-adhesive die attach Pressure Resulting in: Compatibility with refrigerant fluids Wider temperature range Higher reliability Improved manufacturing cost

19 Construction of DunAn Sensing s DURAsense media-compatible MEMS pressure sensor U.S. Patent Application Nos.: 14/170,355; 14/170,387

20 Qualification testing methods and protocols Pressure cycling: 0 to FS, >10,000,000 cycles Temperature cycling: -40⁰C to 140⁰C Media-compatibility: HVAC/R refrigerants Vibration: 4.5g s, 20Hz to 200Hz Temperature shock: -40⁰C to 140⁰C Mechanical shock: 100g s EMI ESD Et cetera

21 Performance accuracy Achieving accuracy equal to or better than any other HVAC/R transducer on the market that meets the cost target

22 Performance before and after qualification Samples: 96 Temperatures: -40, 0, 25, 100, 140 C Pressures: 0.05, 0.66, 1.28,1.89,2.5 MPa Overall Duration 3 months Initial Final MIN MAX Average StDev UL LL Cpk LL Distribution of UL Average Shift of ~ 0.4%FS

23 Characteristics/capabilities of media-isolation technologies for pressure sensors Technology >>>>>>>>>>>> Metal thin-film sensor Microfuse sensor Oil-filled sensor Ceramic thick-film sensor DURAsense MEMS pressure sensor Measurement of absolute pressure NO NO YES OK YES Measurement of gauge pressure YES YES YES YES YES Long-term stability YES YES OK OK YES High temperature >100⁰C OK OK NO OK YES Repeatability OK OK YES OK YES Accuracy OK OK YES OK YES Reliability YES YES YES OK YES Cost HIGH HIGH HIGH MEDIUM LOW NOTE: Requirement fullfilled Requirement partly fullfilled Requirement not fullfilled Yes / Good OK / Maybe No / Bad

24 Summary Introduction of DURAsense, an innovative MEMS packaging technology which eliminates the need for the traditional method of metal diaphragm welding and oil-fill to achieve media-compatibility and can achieve an accuracy equal to or better than any other HVAC/R transducer currently on the market is compatible with refrigerant fluids has a wide temperature range has a high reliability that meets the cost target for HVAC/R

25 Contact DunAn Sensing LLC 1953 Concourse Drive San Jose, CA USA Phone: Website: