Chapter 13: Mechanical and Electrical Systems Flashcards
What is an all-air HVAC system?
Heats spaces by conditioned air alone. Heat is transported to the space with supply and return air ducts.
Residential: Forced-hot-air furnace; boiler powered by oil or gas heats air that is distributed throughout the house in ductwork. Return air ducts in each room collect the cooled air and return it to the furnace for reheating. AC is connected to same ductwork.
Commercial: Variable air volume (VAV), high-velocity dual duct, constant volume with reheat, and multizone systems. Registers are connected to the supply air ductwork and can be adjusted to control the direction of air flow and the volume of air coming through them. Separate ductwork is not used for return air, but grilles are simply placed in the suspended ceiling to collect return air. The mechanical system draws the return air back to a central collecting point where it is then returned through ducts to the building’s heating plant.
What is a plenum?
The space between the suspended ceiling and the structural floor above. At the locations where the fire wall is penetrated, fire dampers are required that automatically close in the event of a fire.
What factors determine the location of air registers?
Supply air registers are often connected to the main ductwork with flexible ducting. This allows some adjustability in the exact location of an air register if its location is in conflict with some other ceiling-mounted item.
Because return air grilles are generally not connected to ducts in commercial construction, they may also be relocated if overall circulation is maintained. Mechanical engineer should be consulted.
How does an all-water heating system work?
Uses some type of coil unit called a convector in each space through which hot water is circulated. The hot water heats the fins of the coil unit, and air is heated as it is drawn over the fins. The air may be circulated by convection, as with most baseboard residential fin-tube radiators, or by forced circulation created with a fan.
Where are ducts and pipes located in residential construction?
Typically run within the walls and floor joists. Occassionally horizontal ducts in a house must be run below the floor joists and a dropped ceiling, or furred down space must be built to conceal them.
Where are ducts and pipes located in commercial construction?
Horizontal ducts are normally run in the plenum and vertical ducts are normally run within their own chases. In a multistory building, a chase runs continuously through the floors. Large, horizontal ducts may occupy most of the vertical distance between a suspended ceiling and the structure above.
What is a mixing box?
Located in the plenum, a mixing box adjusts the quantity or temperature of air going into a space from the main air supply line, reduces the velocity of air, and attenuates noise. Lines from thermostats are connected to the mixing boxes.
6-18” high
24-60” long
14-66” wide
How does a mixing box work in a VAV system?
The VAV box, as it is called, varies the quantity of air. One duct leads in and one or several lead out and are attached to the registers mounted in the ceiling. A VAV box is typically placed above the ceiling, within or near the space it serves.
How does a mixing box work in a dual-duct system?
It mixes cool air and hot air coming into it from two separate ducts and distributes the mixed air to ducts serving individual rooms or spaces.
How does a mixing box work in terminal reheat systems?
The box contains a hot-water coil that provides additional heat to the air stream. These can easily be identified by the air ducts and copper pipes leading into them.
What is access flooring?
A false floor of individual panels raised above the structural floor with pedestals in commercial construction. Can be used for HVAC ductwork.
What is a chase wall?
Consists of two runs of studs separated by several inches, the exact dimension being determined by the largest pipe or duct that has to be concealed. Commonly used between back-to-back commercial toilet rooms where extensive plumbing work and toilet carriers are required.
What is a toilet carrier?
A steel framework that is bolted to the floor inside a pipe chase and carries the weight of wall-hung toilets.
What are the requirements of a plenum when used as return air space?
No combustible materials such as wood or exposed wire with the space. Fire-rated dividers must be installed to limit the spread of fire and smoke horizontally.
What is an access door?
Small steel doors with frames taht are opened by using a thumbturn or key to access valves, fire dampers, heating coils, mechanical equipment, electrical junction boxes, communication junction boxes, and similar devices.
What is the interior designer’s responsibility when it comes to design related to the ceiling?
The interior designer should coordinate the locations of supply air diffusers and return air grilles with other ceiling items, such as lights, sprinkler heads, smoke detectors, speakers, and the like so the ceiling is as functional and well planned as possible.
How do window coverings related to the HVAC system?
Window coverings can affect the HVAC load in a space and may interfere with supply air diffusers or other heating units near the window. Also there should be at least 2” between the glass and any window covering and 1 1/2” clearance above the sill to avoid excessive heat build.
How should HVAC be considered in space planning and furniture placement?
Consider locations of floor registers, fin-tube baseboard radiators, and other equipment. Consult engineer if there’s a capacity or area change.
How do mechanical and electrical services pose problems with acoustics?
When an office wall intersects an exterior wall with a convector running near the floor. The opening in the convector that allow warm air to circulate also allow sound to penetrate and travel inside the convector, past the partition, and out the openings on the other side.
What can be done to prevent acoustical problems with convectors?
- Acoustical insultation
- Metal plate over openings at partition loaction; neoprene pad behind openings
- Caulk all gaps with acoustical sealant
- Remove fins at partition location and fill gap with 1/2” gypsum wallboard on each side of acoustical insulation
- Acoustical sealant below gypsum wallboard
