Indoor Air Quality Flashcards
What is heat
Heat is a form of energy and causes the random vibration of molecules of a substance. Adding heat to a substance increases its molecular motion and potential energy.
What is cold
Cold is a term denoting the relative absence of heat. Absolute zero (-460 F -273 C)
What is temperature
Temperature is the measure of the intensity of heat of a substance or the measure of its molecular speed expressed in degrees
How do you change between C and F
C to F multiply 1.8 then add 32
F to C subtract 32 multiply by .556
Thermodynamics
The branch of science dealing with the mechanical action of heat.
The laws of thermodynamics
- Energy can neither be created or destroyed but can be converted from one type to another.
- Heat always travels from a warm object to a colder one.
What are the methods of heat transfer
Conduction
Radiation
convection
Latent heat of evaporation
What is conduction
This is the transfer of heat through a substance
What is convection heat.
Convection is the transfer of heat by natural motion of a fluid medium, either liquid or gas. The liquid or gas is first heated and this causes it to expand and become less dense thereby giving it more volume. The air becomes lighter and rises. Gravity furnace.
What is radiation
This is the transfer of heat by energy waves similar to light waves or radio waves. Ex. Sun’s heat is radiation transfer
What is sensible heat
The heat required to produce a change in temperature of a substance, but not a change in state. It can be measured with a thermometer or sense of touch.
Latent heat
The amount of heat required to change the state of a substance without changing its temperature. It is measured in btus.
What is latent heat of evaporation
The amount of heat required to change a liquid to a gas without changing its temperature
Specific heat
The number of btus required to raise the temperature of 1 pound of that substance 1 degree F Water has a specific heat of 1.0.
Define humidity
It is the quantity of water in a particular volume of air. Humid air is less dense than dry air.
What is the study of the properties of air?
Psychrometrics
What are the properties of air that can be controlled
Dry bulb temp Wet bulb temp Dew point temp Relative humidity Grains of moisture per pound of dry air Specific volume Enthalpy
Dry bulb temp
A measurement of the temperature of the air as recorded by a standard thermometer.
Wet bulb temp
The measurement of sensible heat minus the heat that is lost during the evaporation of the water of the wick.
What is dew point
The temperature that moisture will start to condense from the air
Relative humidity
A measure of the amount of water air can hold at a certain temperature. Warmer air can hold more moisture than cold air.
Define saturated air
When the air contains the max amount of vapour possible for a particular temperature. Warm air can hold more vapour. Ex. Summer is more humid
What measures wet and dry bulb and applies them to a chart
Sling psychrometer. It can also measure relative humidity.
Hydrometer are instruments that measure humidity.
True
What is effective temperature
Temperature of saturated air which gives the same physical feeling of warmth.
Types of humidifiers
Pan style Drum style Disc wheel Flow through Steam
Three types of heat exchangers for hrv’s
Plate
Heat pipe
Rotary wheel
What must a make up sir system due
Provide the needed amount of air exchange
Distribute outdoor air where it is needed
Be quiet
Not interfere with the other systems in the house
What 3 ways can filters be tested?
By the average synthetic duct weight arrestance test, by the atmospheric dust spot test, and by the fractional efficiency test.
One micron equals .0001 millimeters or one millionth of a meter.
True.
What are fibrous media filters?
These are the least expensive and most widely used. It is produced with woven fibers, screen, or other materials with a light coating of oil to help the dust stick. They trap particles as small as 10 microns.
What are pleated media filters?
Made up of a tighter woven fabric. The pleats switch back and forth to increase the surface area causing a decrease in resistance to air flow as well as an increase in life span. Low velocity systems. Captures 3 to 10 microns.
Describe electrostatic filters.
As air passes over the media, it becomes statically charged. The airborne particles will be attracted to the fibers that have a charge opposite to their own. 10 microns. Low velocity. The charge or efficiency will become weaker as humidity increases.
Electronic air cleaners
Also known as two stage electrostatic precipitators. The wires give the particles a positive charge. Collector plates are negatively charged. As small as .5 microns.
What are HEPA filters?
Stands for high efficiency particular arrestance. They are a throwaway extended medium dry type filter. Contains ultraviolet lights. Used in medical facilities. Catches as small as .3 microns
What factors determine thermal comfort?
Air temperature and air movement.
Explain stratification?
When air is allowed to remain still it will create different temperatures at different levels. Cooler air has higher density, so it settles to the lower portions of the room. The air will also become stale and stagnant.
Air flowing across the surface of the skin will cause you to feel cooler than you actually are. What is this called?
Wind chill. Wind chill is based on the rate of heat loss from exposed skin caused by air movement. As the air speeds up, it draws more heat from your body making you feel cooler. This is why blower and fan size is important as to not cause noise or drafts.
There is no known risk of hearing loss at 70 dB or lower.
True. Occupational limit is 70 dB.
How is fan noise affected?
Fan noise is very much depandant on the diameter and the rotational speed of the fan. Generally a large diameter fan running at a lower resolution per minute will produce a lower frequency and lower noise level.
Air flow in empty straight ducts produces a relatively small amount of turbulence and noise. Noise levels will increase by 18dB when air speed is doubled.
True.
How many dB will occur when air speed is doubled in bands, branch junctions, or sudden changes in direction. What can be done to reduce this?
15 to 20dB. Use larger radius elbows turning vanes, or splitters.
What else can cause a significant increase in noise levels?
Fire dampers
Volume dampers
Air extractors
What is crosstalk?
It is another form of noise that can travel through the duct bypassing the noise insulation created by the walls. It occurs when sound, from other rooms, travels through the ductwork. Acoustical duct lining will help with this.
Exposure to indoor air pollutants (iap) can be up to 100 times greater than outdoor air.
True.
What are the three types of indoor air pollutants?
Particulates
Bioaerosols
Volatile organic compounds (VOC)
What are particulates in indoor air?
These include dirt, dust, fibers, and tobacco smoke. Airborne particulates can range from .1 to 100 microns in size. 99% of the particles are one micron or smaller which are called ultrafine particles.
What are bioaerosols?
These are particles of organic matter such as bacteria, molds, fungi, and dust mites. Bioaerosols range from .1 to 10 microns with majority smaller than 1 micron.
What are volatile organic compounds?
These include harmful or irritating derivatives of alcohols, ketones, hydrocarbons, and aromatics such as formaldehyde or benzene. They can come from tobacco smoke and are often created from the release of gases from man made products such as carpet or house hold chemicals. Tobacco has over 200 VOC’s.
It is estimated that more than 70 percent of all indoor air quality related problems involve the operation and maintenance of the HVAC system.
True.
