Chapter 1 THERMAL, ENVIRONMENTAL, AND COMFORT CONCEPTS

body heat generation and heat transfer is influenced by two additional factors that are not related to the environment but rather to the occupant:

- Activity Level - Clothing Level

Environmental factors affecting occupant comfort are typically grouped into four classifications:

- Air Temperature - Relative Humidity - Air Movement - Mean Radiant Temperature

A typical home in a heating climate will consume about -- million BTU of heating energy over the heating season

100

psychometric chart

A graphical representation of the thermodynamic properties of moist air. It describes the relationships between psychrometric variables.

What standard defines defines effective temperature (ET) as an arbitrary, experimentally determined index used to rate the various combinations of dry bulb temperature, relative humidity, radiant conditions, and air movement that create the same thermal sensation?

ASHRAE Standard 55-1992

What standard explains the operative temperature as being based on an arbitrary set of indexes that combine into a single number the effects of dry bulb temperature, radiant temperature, and air motion on the sensation of warmth or cold felt by the human body.

ASHRAE Standard 55-2004

What standard specifies a comfort zone representing the optimal range and combinations of thermal factors (air temperature, radiant temperature, air velocity, humidity) and personal factors (clothing and activity level) with which at least 80% of the building occupants are expected to express satisfaction?

ASHRAE Standard 55-2004

quantity of heat is measured in ____ or ______.

BTU (british thermal units)/Joules

The unit of specific heat in the engineering system is ? per ? per degree temperature change (Btu/lb °F) or ? per ? per degree temperature change (J/kg °C).

Btu/pound/Joules/pound

The heating (?) value of a fuel, including food, is the ? of heat produced by its ? under specified conditions.

Calorific/quantity/ combustion

____ removes heat by the movement of air around the body because of the difference between skin and air temperatures.

Convection

Power

Defined as the measure of energy consumed over a period of time. When energy is extracted, converted into a useful form, and used in an application, power is the result.

____ of moisture from the body is affected by the relative humidity of the surrounding air, air velocity, and the skin wetness

Evaporation

What kind of chart is used to trace a process undergone by an air/water-vapor mixture?

Psychrometric Chart

? and ? occur by a change dry bulb temperature alone; that is, moisture is not added or removed.

Sensible heating/cooling

Psychrometric

Study of the thermodynamic properties of gas-water vapor mixtures under varying temperatures and pressures.

latent heat of vaporization

The amount of energy required to change a unit mass of a substance from liquid to gas

latent heat of fusion

The amount of energy required to change a unit mass of a substance from solid to liquid

sensible heat

The heat energy that causes a change in temperature of a substance but does not contribute to a change in state

Body metabolism

The human body is constantly generating heat through metabolic activity

ASHRAE Standard 55-2004

Thermal Environmental Conditions for Human Occupancy, specifies combinations of indoor space environmental and personal factors that will produce thermal environmental conditions where 80% of the occupants do not express dissatisfaction with the room conditions; that is, the given condition is not acceptable to 20% of the occupants.

_____________, specifies combinations of indoor space environmental and personal factors that will produce thermal environmental conditions where ?% of the occupants do not express dissatisfaction with the room conditions; that is, the given condition is not acceptable to ?% of the occupants.

Thermal Environmental Conditions for Human Occupancy/80/20

How are temperature scales defined?

They are defined by using the point at which ice melts and water boils at the standard atmospheric pressure.

What is commonly used to measure environmental related heat stress?

Wet Bulb Globe Temperature used to prevent heat stroke during physical exercise or while at work.

A straight line between two points on the psychrometric chart represents...

a change in the condition of air

Thermal sensation

a conscious feeling graded on a scale: cold,cool,slightly cool, neutral, slightly warm, warm, and hot.

Phase Change

a reversible physical change that occurs when a substance changes from one state of matter to another

What are other conditions that affect overall thermal comfort?

activity level, level of clothing, temperature and relative humidity of the room air, air velocity, types of heating and cooling systems, and types and materials of construction.

Atmospheric air

air found in the atmosphere, is a mixture of several constituent gases, water vapor, and contaminants such as dust, pollen, and smoke. It consists of nitrogen, oxygen, and other trace gases.

The two basic mechanisms that the body uses to involuntarily adjust body temperature are ? and ?

change of metabolism and change in the rate of blood circulation near the surface of the skin.

Heat loss from the body is transferred to the surroundings thru ___, ____, and ______.

convection, radiation, evaporation

The property of specific heat capacity of a substance is measured in Btu per ? per degree temperature change (Btu/ft3 °F).

cubic foot

when heat is removed the temperature of the substance typically ?

decreases

With a decrease in air pressure, density of air ?. Similarly, with an increase in air pressure, density ?.

decreases/increases

Latent Heat is the "___" quantity of heat absorbed or released when a material changes phase without a change in temperature.

hidden

Heat always flows from a substance at a ? temperature to the substance at a ? temperature, ? the temperature of the lower temperature substance and ? the temperature of the higher temperature substance.

higher/lower raising/lowering

? and ? involve adding or removing ? and therefore involve ?

humidification/dehumidification/moisture/ latent heat

as heat is added to a substance its temperature typically ?

increases

wet bulb globe temperature (WBGT)

is an index of various environmental factors (air temperature, humidity, radiant heat, and ventilation) that can be easily measured in the workplace.

thermometer

is an instrument that measures the temperature of a body or substance in a quantitative way.

Specific heat capacity (C)

is defined as the amount of heat required to change the temperature of a specific volume of substance one degree.

Specific heat (c)

is defined scientifically as the amount of heat that must be added or removed from one pound of substance to change its temperature by one degree.

Heat

is the agitation or motion of atoms and molecules. thermal energy in motion.

Temperature (T)

is the measure of the average kinetic energy associated with the chaotic microscopic motion of atoms and molecules within a substance.

Latent heat

is the release or storage of heat associated with change in phase of a substance, without a change in the substance's temperature.

Dry Bulb Temperature (DBT)

is the temperature of the mixture of air and moisture at rest. Expressed in units of Fahrenheit and Celsius

Sensible heating is "sensible" because ...

it can be observed by the sense of touch.

If conditions are to the ___ of the comfort zone, then there is a need to increase ____ (e.g., by increasing dry bulb temperature).

left/heating

WBT is the ? temperature that air can be theoretically ? by the evaporation of water

lowest/cooled

Mean Radiant Temperature (MRT)

of a space is a measure of the combined effects of the temperatures of surfaces within that space; it is a weighted average of the various radiant influences in a space.

Mass Density (ρ)

of a substance is the mass per unit volume.

Density is expressed in units of ?

pounds per cubic foot (lb/ft3) or kilograms per cubic meter (kg/m3).

Energy is ___ when a substance changes from a gas to a liquid or liquid to a solid.

released

If conditions are to the ____ of the comfort zone, then there is a need to ____cooling (e.g., by decreasing dry bulb temperature or increasing airflow).

right/increase

When Heat is added to a substance it may changes its state from a ___ to a _____ or from a _____ to a ____. WHen heat is removed from a substance it may change its state from a ____ to a _____.

solid/liquid/ liquid/gas gas/liquid

heat index

sometimes called the apparent temperature, is a measure of the contribution that high ambient air temperature and high humidity (expressed either as relative humidity or dew point temperature) make in reducing the body's ability to cool itself.

Energy is __ when a substance changes from a liquid to a gas or a solid to a liquid

stored

Heat is ______ or _____ whenever a substance changes phases.

stored/ released

dew point temperature DPT

temp of the air/water-vapor mixture when it is fully saturated.

Relative Humidity (RH)

the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

thermal comfort

the condition of mind that expresses satisfaction with the thermal environment

wet bulb temperature (WBT)

thermometer with a wetted cloth sock covering its bulb as fast-moving air passes across it.

wind-chill factor

used to describe the effect of the combination of low temperature and air movement in outdoor environments.

When does sensible heating not occur?

when the substance undergoes a change in state from a sold to a liquid, a liquid to a gas, or visa versa.