Chapter 10 Flashcards
Conditions of a comfort zone
Temperature, humidity, cleanliness, freshness, motion of air without objectionable noise
What is the intended design of air duct systems?
They are designed to meet standards for air capacity, air velocity, and noise intensity and to fit within the space available for installation
The pressure of the HVAC air distribution system is only ______ atmospheric pressure
Slightly above
What is the relationship among aspect ratio, duct construction, and cost?
Ducts with high aspect ratios have greater perimeters, requiring more sheet metal to construct them and resulting in higher friction-induced pressure losses. The additional material required for ducts with high aspect ratios causes higher construction costs
How do fire dampers help prevent the spread of fire?
It closes automatically when excessive heat is detected.
How does air balancing affect air distribution throughout a building?
Distributes air evenly. Use independent firm to assess.
What are the 4 types of thermal units and how does each control the quantity and regulate the temperature of air?
1) Dual duct - receive hot air and cold air through separate supply ducts and discharge hot, cold, or mixed air to satisfy requirements of the space
2) Single Duct - either receive air at a variable temperature that is adjusted to take care of a cooling load, or they are supplied with constant temperature cold air and use a heating coil to reheat the cold air to the required temp.
3) Variable Air Volume (VAV) - temp is controlled by regulating the volume of air first rather than by controlling the temp of the air introduced into the space. Typically 55 degree air to all spaces at all times. When room temp is satisfied, the VAV box will hold the last volume of air delivered.
4) Induction - contains air supply and a heating and cooling coil. They receive primary air at a constant temp and high pressure from a single duct
What are the 4 common types of air distribution devices and how do they differ?
1) Sidewall grilles
2) Slot diffuser - max 3 in height
3) Ceiling diffuser - up to 48x48
4) Air distributing ceiling - rare and mostly used in data centers
Types of fans
1) Centfrifugal - air flows radially (along radius through the impeller - MOST COMMON; classified by blade design
2) Axial flow - Air flows axially (in a straight line through the impeller) ; classified by the functions they perform NOT by blade design
Types of coils
1) Finned tube coils - most widely used bc they are compact and easily installed
2) Air Washers - disadvantage is in chilled water piping design can create system imbalance - places chilled water in contact with the air
3) Sprayed coils -
Classifications of air filters
1) Viscous impingement -
2) electrostatic
3) fibrosis -
4) carbon -
Parking garage ventiliation
rate specified is 1 cfm psf
