ARCH 4521 Etech Midterm: Key Terms & Definitions

absolute humidity

the mass of water for a given mass of air

measure of water vapor/moisture in the air

adiabatic process

any process acting on closed system without adding/subtracting heat

ex: vertical flow of air in the atmosphere-air expands and cools as it rises

air barrier

a material or system in a building that prevents uncontrolled air from moving through the building envelope (walls, roofs, and floors)

air conditioning

system for controlling humidity, ventilation, and temperature in a building

albedo

reflection coefficient measured across a range of frequencies

ex: in architecture this relates to the reflection coefficient across the visible spectrum of sunlight

balance point

outdoor temperature that would not require heating or cooling for a building

bar effect

Wind speeds up and becomes turbulent as it flows over and around a long building.

bioclimatic chart

A diagram used in architecture to determine the best design strategies for maintaining indoor comfort based on temperature and humidity.

btu

british thermal unit- unit of heat; amount of heat required to raise temp of one pound of water by one degree F

channel effect

as the airs path compresses the wind moves with more velocity

chilled beams

HVAC systems that use chilled water to cool indoor spaces through ceiling-mounted units.

climate

outdoor environment

Clo

amount of clothing required by a resting person to be indefinitely comfortable at ambient conditions (70 degrees)

condensation

conversion of vapor or gas to a liquid

conductance (C)

how easily heat or electricity flows through a specific object
Depends on the material and its dimensions

conduction

transfer of heat through direct contact between materials or objects.

conductivity (k)

a material’s ability to conduct heat or electricity. it is a property of the material itself.
it does not depend on the material’s size and shape.

higher conductivity = heat or electricity travels through it more easily

convection

transfer of heat by a moving fluid medium

convective loop system

air circulating in an enclosed space, rising on the warm side and sinking on the cold side, which carries heat across the space.

Shorter version: Convective loop = air rising warm, sinking cool, carrying heat across a cavity.

cooling degree day

a measure of the cooling requirement of a climate, found by adding up the degrees the daily average temperature is above 65°F.

corner effect

velocities of wind increase around corners of tall buildings

cosine effect

a given beam of sunlight will illuminate a larger area as the sun gets lower in the sky

decoupled ventilation

separating the systems that control heating and cooling from those that control ventilation and humidification

ex: different exhaust supply systems for each (balance on/off systems)

dedicated outdoor air system

type of HVAC system that consists of two parallel systems

1. dedicated system for delivering outdoor air ventilation, that handles both the latent and sensible loads of conditioning the ventilation air

2. parallel system to handle the loads generated by indoor/process sources

direct gain system

passive heating technique generally used in cold climates

ex: sunlight admitted into the living spaces through openings

displacement ventilation

air distribution technology that introduces cool air into a zone at low velocity

dry bulb temperature

temperature reading from a standard thermometer

emissivity

ability of a material to emit radiation

ration of the energy emitted to the energy emitted from a black body

enthalpy

sum of sensible and latent energy

entropy

measure of the unavailable energy in a closed system

usually considered to be a measure of the systems disorder

first law of thermodynamics

energy can neither be created nor destoryed, only changed

gap effect

wind through gaps increases velocity

heat

thermal energy that is being transferred

heat capacity

The amount of energy required to raise the temperature of 1 kg (or 1 g) of a substance by 1 °C (or 1 K)

heat island effect

built up areas that are hotter than nearby rural areas, due to human activities.

The temperature difference is usually larger at night than during the day

heating degree day

a measure of the time in days multiplied by the difference between outdoor temp and a set temp (often 65 degrees)

HDD is a measure of the heating requirement of a climate

humidity

the concentration of water vapor present in the air

infrared light

a type of radiant energy that is invisible to human eyes but that we can feel as heat

insulation

materials used to reduce the rate of heat transfer

internal load dominated building

where most of the heat comes from inside the building rather than from the outdoor environment.

kWh

energy of 1,000 watts of work done over 1 hour. A watt is equal to 1 joule per second

latent heat

energy/heat related to substance change- condensation, evaporation, freezing, melting etc.

latent heat capacity

amount of heat required to convert 1g of ice to 1g of water (not full definition)

144 btu/lb for ice melting to water

970 btu/lb

long wave radiation

the energy radiating from the Earth as infrared radiation at low energy to Space.

low e-coating

helps keep indoor temp consistent by reflecting the interior temperatures back inside

mean radiant temperature

the weighted mean of the temperatures surrounding a point or object

-so if a point is half surrounded by an object at 30F, and half an object at 120F, then it would be 75F

-can be approximated in two dimensions

micro climate

the climate of a very small or restricted area, especially when it differs from the climate of the surrounding area

Ex: urban heat island

mixed-air system

HVAC system that uses a mixture of new outdoor air, and recycled indoor air that has already been heated or cooled

night insulation

moveable insulation for windows to keep heat in at night

passive heating key design issues

solar aperture, conservation, thermal storage, component integration, local climate

aperture, absorber, thermal mass, distribution, control

perm-rating

standard measure of water vapor in a material

phase change

transition from one state to another

phase-change material

substance which releases/absorbs sufficient energy at phase transition to provide useful heat/cooing

ex: by melting a solid the temperature is capable of storing and releasing large amount of energy compared to sensible heat storage

process dominated building

building where most of the heating or cooling demand comes from equipment, machinery, or industrial processes rather than people or outdoor temperatures.

psychrometer

a hygrometer consisting of a wet-bulb and a dry-bulb thermometer, the difference in the two thermometer readings being used to determine atmospheric humidity.

psychrometric chart

graphical representation of the processes of air

radiant barrier

installed in homes, usually in attics, primarily to reduce summer heat fain and reduce cooling cost

radiation

transfer of energy by electormagnetic waves (light)

ex: when molecules on the surface of a substance vibrate they emit radiant energy in the form this

reheat

the process of adding energy back into an air control system

reflectivity

the property of reflecting light or radiation, especially reflectance as measured independently of the thickness of a material.

relative humidity

the ratio of the actual amount of water vapor in air to the maximum amount of water vapor that such air could contain at the same temp, if it were saturated

roof pond

passive cooling technique based upon the increased heat capacity of cheap and widely available water

row effect

the reduction in wind speed as air passes through rows of buildings or trees, compared with the open-field wind velocity.

r value

R-value measures how well a material resists heat flow. The higher the R-value, the better it insulates.

second law of thermodynamics

heat transfer takes place in one direction only- from a hotter to a cooler body, or generally from a higher state of order to a lower state

sensible heat

heat related to temperature change

solar heat gain coefficient

fraction of solar radiation admitted through a window, door or skylight

short wave radiation

radiant energy with wavelengths in the visible, near-ultraviolet, and near-infrared spectra

skin dominated building

energy usage is mostly influenced by the impact of the outside climate on the buildings outer structure or "skin"

solar flux

concentrated sunlight, a measure of how much light energy is being radiated in a given area

solar spectrum

the entire span of electromagnetic wavelengths that the sun emits; includes radio waves, microwaves, infrared light, visible light, ultraviolet rays, x-rays, and gamma rays.

source energy

represents the total amount of raw fuel that is required to operate the building

specific heat capacity

the amount of heat energy required to raise the temperature of one gram of substance by one degree celcius

stack effect

results when air in the building warms, becomes more buoyant than the outside air and rises to escape out of openings high in the building

sunpath diagram

sunspace

an interior space designed to collect solar heat, and used as an extension of the occupied space only when the weather permits

temperate zone

moderate climate zone between the polar zones and the tropics

temperature

A measure of the average energy of motion of the particles of a substance.

3 personal influences of thermal comfort

• Activity level (metabolism)

• Physiological adaptation

• Clothing

• Cultural norms

4 environmental influences of thermal comfort

-Air Temperature

-Mean Radiant Temperature

-Relative Humidity

-Air Movement

thermal comfort

the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation

thermal lag

the delay of heat transmitted through a wall

thermal storage wall

solar energy is collected and transferred predominantly by natural means; uses natural convection, conduction, or radiation to distribute thermal energy through a structure

transmittance

(t) the ratio of incident radiant energy that is transmitted, or which passes through a material (number between 0 and 1)

trombe wall

a passive solar building design where a wall is built on the winter sun side of a building with a glass external layer and a high heat capacity internal layer separated by a layer of air.

turbulence

violent or unsteady movement of air or water, or of some other fluid

ultraviolet light

form of radiation which is not visible to the human eye

u factor

A measure of the heat transmission through a building part (as a wall or window) or a given thickness of a material (as insulation) with lower numbers indicating better insulating properties.

vapor permeance

a materials ability to allow water vapor to pass through it

vapor retarder

a material or system that adequately retards the transmission of water vapor

helps prevent water vapor from moving into building assemblies

ventilation

the intentional introduction of outdoor air into a space mainly used to control indoor air quality by diluting and displacing indoor pollutant

can also be used for purposes of thermal comfort or dehumidifcation

venturi effect

Reduction in pressure of a fluid resulting from the speed increase as fluids are forced to flow faster through narrow spaces.

visible light

portion of the electromagnetic spectrum that is visible to the human eye

usually defined as having wavelengths in the range of 400-700 nanometer

visible transmittance

amount of light in the visible portion of the spectrum that passes through a glazing material

a higher this means there is more daylight in space

wake effect

area of reduced wind speed and turbulence that forms behind a building or obstacle.

weather

the state of the atmosphere at a place and time as regards heat, dryness, sunshine, wind, rain, etc.

weather barrier

part of the wall assembly; it prevents the passage of moisture, rain and wind through the walls and roof, and protects vulnerable building components from deterioration

wet bulb temperature

The lowest temperature that can be obtained by evaporating water into the air.

-always less than dry bulb temp

-the drier the air, the bigger difference between them

wind rose

a graphic tool used to view how wind speed and direction are typically distributed at a particular location

windbreak

Row of trees or hedges planted to partially block wind flow and reduce soil erosion on cultivated land.

-enhance crop production, protect people and livestock, and benefit soil and water conservation