1. Objectives Review thermodynamics
- Solve thermodynamic problems and use properties in equations, tables and diagrams
Used prometheus

2. Systems: Heating Make heat (furnace, boiler, solar, etc.)
Distribute heat within building (pipes, ducts, fans, pumps)
Exchange heat with air (coils, strip heat, radiators, convectors, diffusers)
Controls (thermostat, valves, dampers)

3. Systems: Cooling
Absorb heat from building (evaporator or chilled water coil)
Reject heat to outside (condenser)
Refrigeration cycle components (expansion valve, compressor, concentrator, absorber, refrigerant)
Distribute cooling within building (pipes, ducts, fans, pumps)
Exchange cooling with air (coils, radiant panels, convectors, diffusers)
Controls (thermostat, valves, dampers, reheat)

4. Systems: Ventilation
Fresh air intake (dampers, economizer, heat exchangers, primary treatment)
Air exhaust (dampers, heat exchangers)
Distribute fresh air within building (ducts, fans)
Air treatment (filters, etc.)
Controls (thermostat, CO2 and other occupancy sensors, humidistats, valves, dampers)

5. Systems: Other Auxiliary systems (i.e. venting of combustion gasses)
Condensate drainage/return
Dehumidification (desiccant, cooling coil)
Humidification (steam, ultrasonic humidifier)
Energy management systems

6. Drain Pain
Removes moisture condensed from air stream
Cooling coil
Heat transfer from air to refrigerant
Extended surface coil
Condenser
Expansion valve
Controls
Compressor

7. Heating coil
Heat transfer from fluid to air
Heat pump
Furnace
Boiler
Electric resistance
Controls

8. Blower
Overcome pressure drop of system
Adds heat to air stream
Makes noise
Potential hazard
Performs differently at different conditions (air flow and pressure drop)

9. Duct system (piping for hydronic systems)
Distribute conditioned air
Remove air from space
Provides ventilation
Makes noise
Affects comfort
Affects indoor air quality

10. Diffusers
Distribute conditioned air within room
Provides ventilation
Makes noise
Affects comfort
Affects indoor air quality

11. Dampers
Change airflow amounts
Controls outside air fraction
Affects building security

12. Filter
Removes pollutants
Protects equipment
Imposes substantial pressure drop
Requires Maintenance

13. Controls
Makes everything work
Temperature
Pressure (drop)
Air velocity
Volumetric flow
Relative humidity
Enthalpy
Electrical Current
Electrical cost
Fault detection

14. Review
Basic units
Thermodynamics processes in HVAC systems

15. Heat Units
Heat = energy transferred because of a temperature difference
Btu = energy required to raise 1 lbm of water 1 °F kJ
Specific heat (heat per unit mass)
Btu/(lbm∙°F), kJ/(kg∙°C)
For gasses, two relevant quantities cv and cp
Basic equation (2.10) Q = mcΔt
Q = heat transfer (Btu, kJ)
m = mass (kg, lbm)
c = specific heat
Δt = temperature difference

16. Sensible vs. latent heat
Sensible heat Q = mcΔt
Latent heat is associate with change of phase at constant temperature
Latent heat of vaporization, hfg
Latent heat of fusion, hfi
hfg for water (100 °C, 1 atm) = 1220 Btu/lbm
hfi for ice (0 °C, 1 atm) = 144 Btu/lbm

17. Work, Energy, and Power
Work is energy transferred from system to surroundings when a force acts through a distance
ft∙lbf or N∙m (note units of energy)
Power is the time rate of work performance
Btu/hr or W
Unit conversions in Handouts
1 ton = 12,000 Btu/hr (HVAC specific)

18. Where does 1 ton come from?
1 ton = 2000 lbm
Energy released when 2000 lbm of ice melts
= 2000 lbm × 144 BTU/lbm = 288 kBTU
Process is assumed to take 1 day (24 hours)
1 ton of air conditioning = 12 kBTU/hr
Note that it is a unit of power (energy/time)

19. Thermodynamic Laws First law? Second law? Implications for HVAC
Need a refrigeration machine (and external energy) to make energy flow from cold to hot
Literature for Thermodynamics Review:
Fundamentals of Thermal-Fluid Sciences
-Yunus A. Cengel, Robert H. Turner, Yunus Cengel, Robert Turner
or any thermodynamics book

20. Internal Energy and Enthalpy
1st law says energy is neither created or destroyed
So, we must be able to store energy
Internal energy (u) is all energy stored
Molecular vibration, rotation, etc.
Formal definition in statistical thermodynamics
Enthalpy
Total energy
We track this term in HVAC analysis
h = u + Pv or H=U+PV
h = enthalpy (J/kg, Btu/lbm)
P = Pressure (Pa, psi)
v = specific volume (m3/kg, ft3/lbm)

21. Second law
In any cyclic process the entropy will either increase or remain the same.
Entropy
Not directly measurable
Mathematical construct or
Note difference between s and S
Entropy can be used as a condition for equilibrium
S = entropy (J/K, BTU/°R)
Q = heat (J, BTU)
T = absolute temperature (K, °R)

22. T-s diagrams dH = TdS + VdP (general property equation)
Area under T-s curve is change in specific energy – under what condition?

23. T-s diagram

24. h-s diagram

25. p-h diagram

26. Ideal gas law Pv = RT or PV = nRT R is a constant for a given fluid
For perfect gasses
Δu = cvΔt
Δh = cpΔt
cp - cv= R
M = molecular weight (g/mol, lbm/mol)
P = pressure (Pa, psi)
V = volume (m3, ft3)
v = specific volume (m3/kg, ft3/lbm)
T = absolute temperature (K, °R)
t = temperature (C, °F)
u = internal energy (J/kg, Btu, lbm)
h = enthalpy (J/kg, Btu/lbm)
n = number of moles (mol)

27. Mixtures of Perfect Gasses
m = mx my
V = Vx Vy
T = Tx Ty
P = Px Py
Assume air is an ideal gas
-70 °C to 80 °C (-100 °F to 180 °F)
Px V = mx Rx∙T
Py V = my Ry∙T
What is ideal gas law for mixture?
m = mass (g, lbm)
P = pressure (Pa, psi)
V = volume (m3, ft3)
R = material specific gas constant
T = absolute temperature (K, °R)

28. Mass-Weighted Averages
Quality, x, is mg/(mf + mg)
Vapor mass fraction
φ= v or h or s in expressions below
φ = φf + x φfg
φ = (1- x) φf + x φg
s = entropy (J/K/kg, BTU/°R/lbm)
m = mass (g, lbm)
h = enthalpy (J/kg, Btu/lbm)
v = specific volume (m3/kg)
Subscripts f and g refer to saturated liquid and vapor states and fg is the difference between the two

29. Properties of water Water, water vapor (steam), ice
Properties of water and steam (pg 675 – 685)
Alternative - ASHRAE Fundamentals ch. 6