1. Announcement Field trips: Thursday 8 am on UT Campus Meet at the main entrance of ECJ (2 nd floor) Friday 8 am St. Edward's University Meet at the main entrance

2. Final Project Report Due: Tuesday, May 6 Report Presentation: TBD

3. Lecture Objectives: Introduce Low temperature Energy Systems – Stirling engines Energy mesurment

4. Low temperature energy systems Waist heat is part of almost every CHP Many new micro CHP system use Stirling engine http://www.viessmann.com

5. Stirling cycle Closed Cycle Engine No phase change Working fluid: air, hydrogen, or helium

6. Stirling engine Theoretical efficiency of up to 25% (for 500ºC) Real efficiency in residential application between 6-8%

7. When using gas good for micro-generation where heat is needed around the year

8. Thermal energy measuring technique for energy management systems Measuring of temperatures Water, glycol, steam, air,…. Measuring of flow rates same list of fluid Issues: Accuracy Frequency Time integration

9. 9 Resistance Temperature Devices Resistance temperature devices (RTDs) 10 year ago -most commonly applied T-sensing device Nearly linear (positive) T coefficient of metals Platinum = very popular will not oxidize (change resistance) --- stable highly accurate Thin-film platinum RTDs = ± 0.1 o K Also: rhodium-iron, nickel, tungsten, copper Simple circuit design w/ good sensitivity Requires transducers Response time depends on ……

10. 10 Thermistors Themistors = thermal resistors Element: semi-conductor compounds (metal oxides) Change resistance w/ T (negative T coefficient) Significant change in R vs. T relative to RTDs RTDs: order 0.1 ohm/ o C Thermistors: order 10 ohm/ o C Highly non-linear T vs. R curve see ASHRAE PDS IV document (pg. 2-9)

11. 11 RTD vs. Thermistor

12. 12 Thermocouples Two wires of dissimilar metals joined at two ends – solder, weld, twist One end heated – small current generated V based on temperature difference and material props V proportional to T difference Voltage often order µV (e.g., 50 µV/ o C) Less precise than RTDs Thermopiles = bunch of thermocouples (to order mV) See Table 2 of ASHRAE Handbook Ch 14

13. 13 Thermocouples Gas hot water heater - Pilot flame sensor

14. 14 Type of thermocouples T - Copper - Constant K – Al - Chromium

15. Turbine flow meters

16. Vortex flowmeter For given geometry V~f You measure sped of pressure oscillations (frequency)

17. Doppler/Transit-Time Ultrasonics

18. Magnetic