Selecting Systems Flashcards
Central system vs local system
- Central systems
○ Quieter, more energy efficient, better indoor air quality, last longer, easier to service- Local
Less space, no ductwork, more economical to buy and install, good for spaces that require individual temp control
- Local
Fuels
- Best to use steam or hot water bc no chimney is needed and equipment is more compact
- Electricity is clean and compact and quiet, less efficient for heat
- Gas requires no onsite storage
Oil in tank is used when more economical than gas
All air system
○ Fan circulate conditioned air to and from spaces along ductwork
○ Good quality of interior air
Precise control of humidity and filtration
Air and water system
○ Air is ducted to spaces ○ Heated water and chilled water piped to each space to modify air temp at each outlet ○ More compact than all air systems ○ Better for individual control More complicated more maintenance
All water system
○ Air is circulated locally ○ Onlly chilled/heated water are furnished to each space ○ Only piping reqd no ducts ○ Better for individual control More complicated more maintenance
Central all air system: Single Duct Variable Air Volume
- Air is conditioned at central source and distributed
- Controlled by regulating volume of air discharged
- Usually best for large biuldings
- Adv
○ Local temp control at moderate cost
○ Self balancing - Disadv
○ Limited range in heat / cooling
○ Cannot heat one part of a building and cool the other - Has a lot of equipment, packaged system can be used for smaller buildings
Multiple packages good for servicing large horizontal buildings
Single duct variable air volume reheat system
- Air psses through a reheat coil before distributed locally
○ Coil may be electric or hot water from boiler- Controled by local thermostat allows for more variation in vav system
Efficient bc reheat is not activated unless vav system is incapable of meeting temps
- Controled by local thermostat allows for more variation in vav system
Variable air volum induction system
- Used when limited available space for ducts
Small volume of high velocity air is mixed with air from the room and redistributed
Dual duct variable air volume system
- Dual duct work and not energy efficient
Two side by side ducts are mixed
Central all air system: single duct constant air volume
- Air is conditioned (and contains outdoor air) at a central source
- Supply and return fans circulate air through ducts, controlled by master thermostat
- Used for large open areas with few windows (lobbies stores halls)
- High air quality
- Simple and easy to maintain
Single zone
CAV alt: furnace
Indoor unit that is a source of heat and a fan in one box, limited to small buildings
CAV alt: constat air volume reheat system
- Same as CAV unitl it enters local duct work for each zone, then it is passed through a reheat coil
- Local thermostat for each room allows for more control
- Used for precise control and constant airflow for labs and Ors
Wasteful bc air is first cooled then heated
CAV alt: multizone system
- Several ducts from a central fan
- Air is either blended or regulated
Require lots of space - restrict to few zones and short runs
- Air is either blended or regulated
Central air and water system: air water induction system
- Fresh air is conditioned at a central source and circulated through small high velocity ducts
- Mixture of primary air and room air is passed over a coil that temps the water
- Good for offices, interiors with wide range of heating and cooling but humidity control is not required
- Good for local temp control
- Smaller than all air, no fans in spaces
Complicated system, noisy, not energy efficient, not really used today
Fan coil unit (air water variation)
- Use a fan to blow air through coils instead of relying on induction of primary air
Can circulate without primary air
