1. First Exam is on March 21 Examples are posted on the course website !
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 Storage Cost Code restrictions
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 But !
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 Efficiency Combustion air supply
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 Fire 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 Electrode
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 Treatment options
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

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. Thermodynamics - review
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

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

28. COP Coefficient of Performance

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

30. HW3 Solution