HVAC Systems Flashcards
2 types of hvac systems
water & air
direct expansion system (DX)
AKA incremental unit
self contained, passes non-ducted air over evaporator to cool air. ventilation comes from outside air
IAQ+
Diff size units. smaller = 1 room. larger =several rooms.
add heting coil & can do heat & cool
All Air System
heat is transported to/from space via supply/return ducts
most basic form = constant volume single duct system
air is heated in a central furnace/cooled in central AC & distributed via duct through house.
one central T-stat can’t be zoned
larger style all air system
variable air volume (VAV)
high velocity dual duct
reheat (constant volume) system
multizone system
variable air volume (vav)
same single duct system, but at a new zone there is a t-stat that controls damper in duct to adjust amount of air. not great for highly specialized spaces but good for basic
high velocity dual duct
two ducts run side by side, 1 hot air, 1 cold air.
meet at mixing both & specific temp is created to serve dedicated space.
diff temps can be created in diff zones
not very efficient, sometimes have to reheat/recool if gets too far away from central point
reheat (constant volume) system
return air & outside air are mixed, humidity & temp are controlled. sent thru building at low temp/constant volume. before enters into space, air is reheated locally with either elec coil in duct (zone reheat) or heated water pipes (terminal reheat). can use an economizer cycle to draw in fresh outdoor air for cooling
multizone system
central mixing unit with cool/warm air coils to produce separte hot/cold air streams. dampers mix air before going into space
duct sizes can get large if have alot of zones
all water systems
fan coil unit is needed 7 connected to water pipe circuits.
very effecient, easily controlled.
can’t control humidity
air-water systems
uses central air system to provide humidity control & ventilation
heating/cooling provided by fan coil units in each space.
often used when return air cannot be recirculated due to contamination concern (ie hospital)
induction system - adds an induction to loop to attenuate noise before entering space
electric systems
radiant heating, even, comfortable heat
not economical, usually just for supplemental
Apartment hvac systems
closed loop hjeat pump, fan coil
theatre hvac
constant volume single duct, VAV, multizone
commercial (small) hvac
VAV, multizone
hotel hvac
closed loop heat pump, fan coil, constant volume single duct
hospital hvac
constant volume single duct, dual duct increased velocity, constant volume terminal reheat, multizone, all water induction
office building hvac
VAV, multizone, all water induction, fan coil
residential hvac
direct expansion, constant volume single duct, all water induction, electric
school hvac
constant volume single duct, VAV
economizer cycle
use outdoor air when cool enough to mix with recirculated indoor air
dual condenser cooling
refrigerate equipment uses 2 condensers instead of 1, or chillers.
more efficient
gas fired absorption cooling
powered by natural gas instead of relying on elec or refrigerants
solar powered absorption cooling
powered by solar instead of relying on elec or refrigerants
dessicant
material that absorbs water
