HVAC System Flashcards
HVAC?
heating ventilation air conditioning
what are hvac designed for
- thermal conditions
- adequate amount of outdoor air
what does a hvac system consist of
- controls
- min of one fan to move air
- provision for introducing outdoor air
- filter
- coil for heat and cooling air
- distribution system
why is the location of air intakes important
- because of the potential to permit contaminates from the area
- usually 1/3 up building
- usually found next to loading docks or on roofs near exhausts
what is the mixing plenum
- it is where return and outdoor air mix
- since rain and snow can be sucked in there should be floor drain
- if drain is connected to sewer line must have water trap
what is a outdoor air damper?
opens and closes to control air volume passing through inlet
what do air filters do?
they deliver clean air
what do the coils in the hvac system do
either cool or heat air coming in
what is the purpose of cooling coils
- cool air
- dehumidify air as water condenses
what is purpose of heating coils
- heat the air
- provide thermal comfort
where must coils be?
- accessible
- clean
- have sufficient capacity to give thermal comfort
- located centrally throughout building
what are condensate drain pans for?
- collect moisture under cooling coils
- must be properly sloped towards the drain line
- should be kept clean
what is the supply air fans
the driving force to distribute air into building
return-air fan, what do, what is?
- draws air out of building and deliver it to air-handling unit and exhausted outside
- relationship to air supply is important as resulting pressure can introduce air into air-handling unit
boiler?
- generates heated water for thermal conditioning and hot-water needs
- fossil fuels or electric
- generate combustion products that may become indoor contaminants
chilllers
- provide chilled water to meet cooling loads
- required for thermal comfortable conditions
hvac system produce what?
- heating
- cooling
- heat transfer fluids
- control delivery to a space to maintain stable condition
heating and cooling produced by what
- refrigeration devices
- furnaces
- boilers
movement of heat transfer fluids are preformed by what?
- ductwork
- grillers
- diffusers for air
- pumps
- piping system for water
name a heating and cooling control device
space thermostat
heating and cooling system, explain them
- very temp of air supply with a constant flow
- vary flow of air supply with constant temp
- vary flow and temp of air supply
what is a zone?
- one area that is controlled by a single thermostat
single zone system
house with furnace controlled by a single thermostat
two zone system
house with two furnaces each controlled by a separate thermostat
two types of hvac controls, which is better
- manual
- automatic
- automatic controls system more precisely and reliably for comfort, safety, and efficiency
the control systmes control?
- temp sensor
- pressure sensor
- flow rate sensor
- humidity sensor
- speed sensor
- time with clock sensor
what are basic control devices?
- sensor
- controllers
- actuators
sensors?
- measure and monitor variables
- signals are input into controller
controller?
- provide decision for function of control system
- determines if signal is sent or not
actuators?
provides physical control of equipment by valves or dampers
thermostats?
sense and respond to temp
- signals sensors and controller
humidistats?
sense and respond to humidity
- either relative or absolute
constant temp variable volume?
- used for zone control
- simple residential system, maintains the temp set on thermostat
- turns of when the temp is achieved
single zone constant air volume
- simple system used in commercial building
- fans run constantly and provide ventilation
- air is supplied at a constant rate, to achieve the desired temp
cooling coil uses what to cool?
- refrigerant
- cold water
how does heat get produced by hvac system?
- furnace and space heater heat air
- fuels burnt to heat water or produce steam to heat air
- electric heat up coil to heat air
- boilers heat by hot water or steam
air-handling system components
- fan sections,
- cooling section
- heating section
- humidification section
- filter section
- air mixing section
- discharge air plenum
- other components
what is contaminates are in outdoor air?
- gas, liquid, solid particles
- bacteria
- viruses
fans in hvac system
moves air in the system either ventilate heat or cool
- all have rotating impeller blades, increases kinetic energy of air
- increase of energy is converted into pressure
ductwork includes
- supply duct
- return duct
- outside air
- relief air
- exhaust air ducts
ducts made from what material?
- galvanized steel
- aluminum
- stainless steel
what shapes can ducts be?
- rectangular
- round or flat oval
how does insulation in a duct work?
- applied to interior of duct (rectangle)
- applied external as fiberglass or blanket (round)
- external more expensive
- for thermal and acoustic
rectangular duct used for what?
- used for low-velocity applications
round or flat oval used for what?
- medium high velocity
what do air devices do?
supply and remove air from building
name air devices?
- diffusers
- grilles
- registers
what are diffusers for?
- to get rid of any drafts areas creating hot or cold spots
- it controls air quantity and direction
what is the coanda effect?
- allows air to fall gradually and mix with room air ver large area
- without this the chilled air will fall straight to the ground creating a cold spot
- this is called dumping creating uncomfortable draft
