1. Class Objectives Stress the importance of HVAC
Identify and compare factors that affect thermal comfort in buildings
Calculate quantities from a psychrometric chart

2. HVAC Affects: Energy use (outdoor air quality) Peak demand
Indoor air quality
Occupant comfort and productivity
Building cost

3. Primary energy vs. End use energy
1kWh (3.6MJ) of source energy (fuel) ≠ 1kWh of electric energy
End use energy
amount of energy delivered to consumer
electric, heating, cooling
Primary energy
amount of energy
delivered to consumer
energy sources used to
produce this energy +
Example: conversion and transmission
losses in power plant
and delivery systems

4. Energy efficiency vs. Thermal efficiency
Heating the residential house
Thermal efficiency 100%
Electric
heater
Power plant
100% Primary energy (gas)
~ 33% Electric energy
End use ~ 33% For heating
Energy efficiency 33%
Thermal efficiency 75%
Furnace
heater
Transport
End use ~73% For heating
100% Primary energy (gas)
~ 97% Gas energy
Energy efficiency 73%
Page 17 Tao and Janis

5. LEED – Leadership in Energy and Environmental Design
Green building rating system
High-performance and sustainable buildings
Voluntary (at this moment) national standard
Affect
Location environment – sustainable site
Use of energy
Use of water resources
Use of building materials
IAQ
Design process

6. Thermal Comfort Combination of Human body
- Indoor environmental factors
Personal factors
Human body
- in thermal equilibrium with the environment

7. Thermal comfort equation - P.O.Fanger
Energy balance for human body
Metabolic Heat - Work = Energy that body release

8. Thermal comfort Metabolism – health condition and activity
Clothing level
Air Temperature
Mean Radiant Temperature
Air Velocity
Humidity
P.O. Fanger
PPD – Predicted Percentage of Dissatisfied
Scale 5-100%

9. Thermal comfort Factors that we control in buildings
Air Temperature
Humidity
Air velocity
Surrounding Temperature

10. Overview Psychrometric quantities Heat loss and gain
Cooling, heating, and ventilation loads
Cooling and heating equipment
Air equipment and controls

11. Willis Haviland Carrier - Carrier
1911 "Rational Psychrometric Formulae”

12. Psychrometric Chart Need two quantities for a state point
Can get all other quantities from a state point
Can do all calculations without a chart
Often require iteration
Many “digital” psychrometric charts available
Can make your own
Best source is ASHRAE Fundamentals (Chapter 6)

13. Temperature Absolute Temperature (T) (K, R)
Dry-bulb temperature (t) [°F, °C]
Wet-bulb temperature (t*)
Dew-point temperature (td)
Mean radiant temperature (tr)
Operative temperature (to)
Effective temperature (ET*)

15. Which temperature do you expect to be higher?
Wet-bulb
Dry-bulb

16. Wet-bulb temperature (t*)
Temperature measured by a psychrometer
Lower than dry-bulb temperature
Evaporating moisture removes heat from thermometer bulb
The higher the humidity
Smaller difference between wet-bulb and dry-bulb temperature

18. Dew-Point Temperature, td
Define temperature at which condensation happen
td is defined as temperature of that air at saturation
i.e. RH = 100%
Surfaces below the dew point temperature will have condensation
Measured with a chilled-mirror apparatus

20. If you have a sample of air at its dew-point temperature?
The water will condense out.
It will be pure water vapor.
Putting the sample in a sealed container and heating it will cause condensation.
Putting the sample in sealed container and cooling it will cause condensation.

21. Humidity Humidity ratio (W) [lb/lb, g/kg, grains]
[grains/lb = 1/7000 lb/lb]
Relative humidity (RH, ) [%]
Saturation

22. Humidity Ratio, W Mass of water vapor/divided by mass of dry air
Orthogonal to temperature
Not a function of temperature
Most convenient form for calculations involving airflow
Very hard to measure directly

24. Relative Humidity, RH or 
Ratio of partial pressure of water vapor to partial pressure of water vapor at same T and P at saturation
Strong function of temperature
For constant humidity ratio
Higher temperature, lower relative humidity
Saturation

26. Relative Humidity Driving force for moisture transport
Human comfort
Moisture absorption/desorption
Can be measured with
Resistive sensors
Capacitive sensors
Horse hair

27. Conclusions Define thermal comfort parameters
Define all quantities on a psychrometric chart and use it to do calculations

28. Reading Assignment Chapter 1 and
Chapter 2 (Section 2.1 & 2.2) Tao and Janis
Next class – Thursday
5 minutes quiz at the beginning of the class