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32 Cards in this Set
- Front
- Back
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What does relative humidity measure?
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The ratio of moisture in the air compared with the maximum possible.
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What is the target comfort zone?
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B/T 25-70% relative humidity and
B/T 68-79F Actually aim for 50% relative humidity |
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What are the 3 main thermal loads on SFH & other skin load dominated (SLD) bldgs?
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30% envelope (HE thru envelope, conductivity)
25% outside air 25% solar radiation |
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Typically high-rise bldgs and bldg with deep thick floor plates are dominated by _________ ____________.
What are the sources of 2 main internal thermal loads? |
internal loads (ILD)
Lighting and eqpt, people |
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What is the R value?
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Resistance to heat exchange,
Reciprocal of conductivity |
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Name 3 sources of heat flow through the envelope.
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Temperature difference (2 way)
Solar radiation (1 way, in only) Air infiltration (2 way) |
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What is the U-value, and how is it calculated?
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Thermal transmittance
Reciprocal of the sum of the R-values |
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What is the unit of measurement for heat loss/gain?
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BTU/hr
or watts |
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At high angle of incidence, how much sunlight is reflected?
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Most of it.
When sun is coming straight at window, 90 deg angle |
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What are 4 main sources of (accidental) air infiltration?
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1. Floors, walls, ceiling, 31%
2. Ducts, 15% 3. Fireplace, 14% 4. Plumbing, 13% |
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The best solution for the correct number of zones for comfort is a balance between ____________ & _____________.
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cost
complaints |
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What are three typical ways to base the zoning of space?
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By use,
By variance in thermal loads, By quality of space |
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HVAC systems are primarily focused at acheiving these four goals: 1) temperature control, 2) ___________ control, 3) air movement and 4) air filtration.
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humidity
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The target level of relative humidity in building interiors is typically ______ percent.
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50
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Which of the three thermal load categories involves only heat gain rather than heat flow?
Temperature difference, Solar radiation, Air infiltration, All, None |
Solar radiation
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The core of a typical internal load-dominated building is always in cooling mode regardless of the local climate and season.
TRUE FALSE |
True
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What are the all-air systems?
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Single duct, constant air volume (CAV)
Multi-zone, constant air volume (CAV) Single duct, variable air volume (VAV) Double/dual duct |
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What are pro and cons of double dust system?
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PROs Most comfortable
CONS Smaller ducts, higher velocity, fans spinning Noise, cost |
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What is main disadvantage of all-water system?
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No ventilation.
Requires a separate ventilation system to change air and improve quality of air. |
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A __________ system is a self-contained, simplified system with both cooling and heating capbilities
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packaged
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Name and explain 4 main components of chilled water plant.
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1. Compressor - ^ pressure, reduce vol of refrigerant vapor.
2. Condenser - refrigerant is changed from gas to liq, same p, using cooled water loop. 3. Expansion Valve - reduce p, incr vol to drop temp 4. Evaporator/Chiller - removes heat from water loop, changes from liq to gas. |
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How does cooling tower work?
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Warm water returned from water loop is spray into top of tower and drops through baffles, with outside air forced by fan through baffles and droplets to coll water. Temp drops as it travels down and pools at bottom.
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How does air handling unit work?
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Filter, pre-heat to above freezing, finned cooling coil for cooling and dehumidification, reheat for main heating. Supply fan, either serial or centrifugal.
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What are disadvantages of washing filter?
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Adds humidity
Could spread bacteria |
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What are commonly used types of filters?
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1. Arrestance - gauzy filter to pick out particles.
2. Electrostatic - electromagnetic field to draw particles into filter. |
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Describe components of ductwork.
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Ducts - high or low velocity, rectangle or round, stepdown volume to maintain air flow rate.
Registers and diffusers - supply side, register may have flow controller. Grills - return air side |
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What are two options for ductwork tree placement?
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Vertical or horizontal
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How many BTU/hr is 1 ton?
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12,000
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In western cities, the most prevalent HVAC system is _________________.
CAV, VAV, dual duct, 2 pipe water, 4 pipe water, air-water, roof-top units |
variable air volume
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The component within an all-water system which is used to condition the air is called a "______ _______ unit".
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fan coil
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The compressor within the chilled water plant converts the refrigerant from a low pressure liquid to a high pressure liquid.
TRUE FALSE |
FALSE.
It's vapor. |
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A component of the chilled water plant called a __________ __________, is commonly located on the roof and cools condensing water for use in the condenser.
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cooling tower
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