1. Introduction to Energy Management

2. Week 3 Managing Human Comfort

3. Thermal Comfort Factors
Influenced by
Metabolism
Migration
Heat flow
Clothing
BH040

4. Metabolism Metabolism affects perception of thermal comfort
Muscular activity
Digestive process
Daily cycle
Health
Age
Gender
BH024

5. Migration
Body attempts to maintain core temperature (98.6ºF) by shifting blood flow
Vasodilation
Vasoconstriction
BH024

6. Heat Flow Multiple mechanisms Convection Conduction Radiation
Evaporation
BH030

7. Heat Flow – Convection
Air movement caused by pressure and density changes
Wind is formed by air moving from high to low pressure areas
Warming air rises
Cooling air falls
BH030

8. Heat Flow – Conduction
Caused by direct contact between two objects of different temperature
Heat always flows from warm to cool
BH030

9. Heat Flow – Radiation
Radiant heat is exchanged by two objects of different temperatures
Heat always flows toward cooler object
Surface temperature controls interaction
Seasonally variable
BH030

10. Radiant Heat Flow
Season variations can change direction of radiant heat flow

11. Mean Radiant Temperature (MRT)
MRT approach is used in Europe as a means to lower operating temperatures

12. Heat Flow – Evaporation
Water changes from liquid to gas and this phase change extracts heat
Respiration
Perspiration
BH030

13. Clothing Compounds and/or mitigates the effects of other mechanisms
BH049

14. Managing Human Comfort
Defining Human Comfort
Reciprocative Factors
Diet, activity, clothing, exposure, etc.
Physical Factors
Air temperature, relative humidity, etc.
Organismic Factors
Age, sex, genetics, body type, etc.

15. STANDARDS
Think of some building standards where the facility serves different activities

16. Managing Human Comfort
Metabolism and Heat Loss from People
Food metabolically converted to heat energy
The body cools itself
Evaporation (latent heat loss)
Radiation (radiant heat loss)
Convection (sensible heat loss)

17. Evaporative Heat Loss Radiant Heat Loss Convective Heat Loss
Managing Human Comfort
Evaporative Heat Loss
Evaporating perspiration from the body
Radiant Heat Loss
MRT – Mean radiant temperature
Average temperature of surrounding surfaces
Convective Heat Loss
Loss of heat to surrounding air

18. Factors Affecting Metabolic Heat Loss
Managing Human Comfort
Factors Affecting Metabolic Heat Loss
Evaporative losses depend on:
Skin surface temperature of the person
Relative humidity
Dry bulb temperature of the air
Velocity of the air

19. Radiation losses depend on:
Managing Human Comfort
Radiation losses depend on:
The mean radiant temperature (MRT)
Average temperature of exposed skin
Surface emissivities
Convection losses depend on:
Dry bulb temperature of the air
Velocity of the air
Average temperature of exposed skin

20. Extreme Heat Managing Human Comfort
Physiological Reactions to Thermal Extremes
The body reacts to protect its vital organs
Extreme cold
Leads to frostbite and hypothermia
Reduced evaporation heat loss from skin
Extreme Heat
Leads to heat stroke or brain injury
Increased evaporation heat loss

21. Managing Human Comfort
Designing for Metabolism and Sedentary Activity
Metabolic rates change with activities
HVAC designers usually select “average” activities
Sedentary activities are chosen for office environments
Sedentary activity generates about 400 Btu/hr

22. Defining Thermal Comfort
Managing Human Comfort
Defining Thermal Comfort
Create an energy-balanced environment
When a person loses metabolic heat at the same rate at which it is gained
The ASHRAE thermal Comfort Standard
Standard
Generally acceptable comfort ranges

23. Estimating Metabolic Heat Transfer Rates
Managing Human Comfort
Estimating Metabolic Heat Transfer Rates
At 75ºF MRT, 40% Humidity, Air velocity of 40 fpm
Evaporative transfer rate is 100 Btu/hr
Radiation transfer rate is 150 Btu/hr
Convective transfer rate is 150 Btu/hr
MRT is below air temperature in the winter
MRT is above air temperature in the summer

24. Designing for Thermal Comfort
Managing Human Comfort
Designing for Thermal Comfort
Weather conditions/Geographical location
Building use and occupancy
Architectural details
Heating/cooling sources
Heating/cooling distribution systems
HVAC system controls

25. Managing Human Comfort
List the factors that affect people’s comfort
Explain the role of metabolism in thermal comfort
List three means of losing metabolic heat
Compare the effects of air conditions on metabolic heat transfer
Describe how the body reacts to thermal extremes

26. Managing Human Comfort
After completing this chapter, you will be able to:
Understand how metabolism and activity affect thermal design
Cite ASHRAE standards for thermal comfort
List considerations for estimating metabolic heat transfer rate
Identify the factors that designers can manipulate to achieve thermal comfort