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
Central all water systems: fan coil terminal
- Hot or chilled water are piped to terminals where a fan mixes room air and outdoor air and blows it across the coils and into the room
- No fan rooms or ducts
- Individually controlled rooms good for schools offices apartments, usually on exterior wall
- Humidity hard to control
- High maintenance
Can vary in configurations (wall clg vertical horizontal)
Central all water system: closed loop heat pump
- Water to air pump in each space provides heating cooling and fresh air
- Uses cooling tower boiler or bypass depending on season
- Usually used for hotels or overheated areas like kitchen
- Efficient - overheated rooms can be used to heat under heated rooms
- Expensive to install and may not be worth energy savings
High maintenance
Central all water systems: hydronic convectors
- Hot water from boiler is circulated to fin tube convectors that heat vertical fins.
- Fins draw in cool air heat it and release it back to room
- Used when cooling is not required or used as supplement to other system
Economical to instal and operate
Local systems: packaged terminal units and through wall systems
- Typically used for dorms apartments motels ect
- Readily available and usually cheaper
- Mainenance is high and equipment does not always last long
Noisy and inefficient
Passive heating use vs mechanical system use
- Passive better in small/ medium buildings that are sited efficiently
- Mech better for large buildings with high ratio of interior volume to exterior surface area
Mech also better for humidity and air quality control as well as high loads and acoustic control
- Mech better for large buildings with high ratio of interior volume to exterior surface area
Forced air heating and cooling
- Furnace heats hot air (gas oil or electric) and is circulated by fan and ductwork
- Cooling capability may be added with coils adjacent to furnace
- Most versatile and widely used system for small buildings
- Can control multiple zones up to 10000 sqft
- Quiet and efficient
- Can control humidity and air quality
- Multiple zones hard to create
Heat pump = variation, not good for extreme climates
Hydronic / forced hot water heating
- Flame or electric coil heat water in boiler, water is pumped through fin tube conductors, heated fins draw cool air in, heat it, and blow it out top
- Any type of building
- Quiet, easily zoned for room to room contorol
- Cooling and humidity control done by other system
- Occupy a lot of wall space and can interfere with furniture
Radiant heated floors/clgs as variation
Active solar heating
tive solar heating
- South facing solar collectors, pump or fan sends heated air/liquid to storage in basement, fan circulates indoor air through heat exchanger filled with stored heat and distributes heated air
- Good for sunny climates
- No fuel required only elec for fans
- Initial cost is high
Usually requires back up heating, cooling is done separately
Packaged evaporative cooler
- Fan blows warm dry outside air through wetted pad, cool humid air is distributed in
- Used to cool in locations where humidity control is not an issue
- Cooling cost is low
Separate heating is necessary
Electric baseboard convectors
- Electric resistance wires in enclosure are installed at perimeter of room & heat air through convection
- Any type of building
- Each room has temp control
- No chimney
- No control of humidity or IAQ, no cooling
Electricity is inefficient for heating
Electric fan forced unit heaters
- Fan draws in room air and heats it by passing it over elec resistance wires and blowing it back to room
- Non chimney, temp control, small, does not interfere with furniture
Noisy,no humidity or quality control
- Non chimney, temp control, small, does not interfere with furniture
Electric radiant heating
- Heating wires are embedded in floor or ceiling
- Used for residences or nursing homes
- Slow to react
Cooling and humidity not included
Wall furnace and direct vent space heaters
- Self contained wall furnaces
- Usually on exterior wall
- Direct vent is more efficient
- Inexpensive a
Vent to outdoor, unattractive, humitity and cooling separate
