Announcement

1. Announcement First Exam is on March 21 Examples are posted on the course website !

2. Lecture Objectives • Learn about • Heating Systems • Cooling Systems

3. HW2 Help session • HW2 Due March 5th • On Monday morning from 8 to 10 am, and (??? afternoon hours) we will have TA office hours to help with specific questions for this HW2

4. Heating systems

5. Choosing a Heating System • What is it going to burn? • What is it going to heat? • How much is it going to heat it? • What type of equipment? • Where are you going to put it? • What else do you need to make it work?

7. Choosing a Fuel Type • Availability • Emergencies, back-up power, peak demand • Storage • Space requirements, aesthetic impacts, safety • Cost • Capital, operating, maintenance • Code restrictions • Safety, emissions

8. Selecting a Heat Transfer Medium • Air • Not very effective (will see later) • Steam • Necessary for steam loads, little/no pumping • But: lower heat transfer, condensate return, bigger pipes • Water • Better heat transfer, smaller pipes, simpler • But: requires pumps, lower velocities, can require complex systems

9. Steam Systems • Steam needs bigger pipes for same heat transfer • Water is more dense and has better heat transfer properties

10. What About Air? • Really bad heat transfer medium • Very low density and specific heat • Requires electricity for fans to move air • Excessive space requirements for ducts • But ! • Can be combined with cooling • Lowest maintenance • Very simple equipment • Still need a heat exchanger

12. Furnace • Load demand, load profile • Amount and type of heat • Response time • Efficiency • 80 – 85 % is typical • Electricity is ~100 % • Combustion air supply • Flue gas discharge (stack height)

13. Choosing a Boiler • Fuel source • Transfer medium • Operating temperatures/pressures • Equipment • Type • Space requirements • Auxiliary systems

14. Water Boilers Types • Water Tube Boiler • Water in tubes, hot combustion gasses in shell • Quickly respond to changes in loads • Fire Tube Boiler • Hot combustion gasses in tubes, water in shell • Slower to respond to changes in loads

16. Electric Types • Resistance • Resistor gets hot • Typically slow response time (demand issues) • Electrode • Use water as heat conducting medium • Bigger systems • Cheap to buy, very expensive to run • Clean, no local emissions

17. Auxiliary • Burner type (atmospheric or power vented) • Feedwater systems • Returns steam condensate (including accumulator) • Adds water to account for blowdown and leaks • Preheats the water • Removes dissolved gasses • Blowdown system • Periodically drain and cool water

18. Auxiliary • Water treatment • Dissolved minerals and gasses cause: • Reduced heat transfer • Reduced flow (increased pressure drop) • Corrosion • Treatment options • Chemical (add bases, add ions, add inhibitor) • Temperature (heat to remove oxygen)

19. Location • Depends on type • Aesthetics • Stack height • Integration with cooling systems

20. Cooling Systems

21. Compressor 2) Condenser 3) Evaporator 4) Air handler 5) Reversing valve and expansion valve www.srpnet.com/energy/pumpworks.aspx

22. Vapor Compression Cycle Expansion valve Indoor 75°F Outdoor 105°F

23. Vapor Compression Cycle (DX Cooling Machine) High pressure, high boiling/condensing point DB = 77 °F WB = 64 °F 56 °F 69 psig 110 °F ~200 psig 92 °F DB = 60 °F WB = 53 °F orifice capillary tube TXV Low pressure, low boiling point

24. Refrigeration Cycle

25. Thermodynamics - review

26. Enthalpy: h [J/kg, Btu/lb] Temperature change ΔT Δh = cp ΔT – only for the same phase (air, water) What if we have change of the phase -evaporation or condensation? Entropy: s [J/kgK, Btu/lb°F] Δh =T Δs for evaporation or condensation Thermodynamics - review

27. What is the COP? • Congressional Observer Publications • California Offset Printers, Inc • Coefficient of Performance • Slang for a policeman

28. COPCoefficient of Performance

29. Reading Assignment Tao and Janis Chapter 3,4,5

30. HW3 Solution