IAED 204

Construction and Materials II

Spring 2015

HVAC SYSTEMS

HVAC SYSTEMS

(HVAC) system integrates mechanical equipment into one complex system that is designed to provide thermal comfort and air quality throughout a building.The temperature, humidity, purity, distribution, and motion of air within interior building spaces are all controlled simultaneously by an HVAC system. These systems use air, water, or both to distribute heating and cooling energy. Systems include furnaces that supply hot air and boilers that heat water or produce steam. Some systems include electric heaters that use electrical resistance to convert electricity to heat.

HVAC SYSTEMS

HVAC systems can have CENTRALIZED or LOCAL EQUIPMENT.LOCAL EQUIPMENT:Advantages:Because climate is such a strong factor in small buildings and heating and cooling needs may vary room by room, localized equipment rather than a centralized system may be the better choice. • A local system can respond more rapidly to individual room

needs and scheduling differences. • No large central equipment spaces are needed, as equipment

can be distributed throughout the building or over the roof in the case of low-rise buildings.

HVAC SYSTEMS

LOCAL EQUIPMENT:Advantages:• Distribution trees are shorter, and breakdowns are localized. • Control systems are greatly simplified. • Energy is conserved when heating and cooling is used only as

needed.Disadvantages:• The noise from many machines all over the building can be

objectionable. • The presence of maintenance workers within occupied areas can

be disruptive. • Multiple pieces of equipment mean many filters to clean and

change to assure air quality. • There is less opportunity to use waste energy than with a

centralized system.

HVAC SYSTEMS

CENTRALIZED EQUIPMENT:Advantages:• The equipment has its own space, and does not take up room

within occupied spaces.• Maintenance need do not interrupt room activities. • Energy recovery from boilers and chillers is possible in a central

equipment room. • Centralized mechanical spaces concentrate the noise and heat

for easier control. • Air intakes can be high above street pollution, and regular

maintenance of centralized air filtering equipment results in longer equipment life.

HVAC SYSTEMS

CENTRALIZED EQUIPMENT:Design and Some Disadvantages:• Mechanical rooms need to be centrally located near the area

served, with direct access to the outside for fresh air and for installation and removal of equipment.

• Achieving both a central location and outside access is often difficult. • Rooms for heating, cooling, and air handling equipment need

ceilings around 3.7 meters high.• Distribution trees of centralized systems are larger and controls

are more complex than for localized systems.• Breakdown of a single piece of equipment may affect the entire

building. • Energy is wasted when the entire system is activated to serve

one zone.

HVAC SYSTEMS

INTERIOR DESIGN:OFFICES:• Uniform ceiling heights, • lighting placement,• and HVAC grille locations

increase flexibility in office arrangements and extend the building’s useful lifespan.

HVAC SYSTEMS

INTERIOR DESIGN:OFFICES:Four basic types of office space can be interchangedwithin a flexible overall plan. These include • Enclosed offices; • bullpen offices with repeated, identical

workstations with desk-height dividers; • uniform open plan offices with higher partitions; • and free-form open plan offices with partitions of

varying heights.

HVAC SYSTEMS

INTERIOR DESIGN:OFFICES:The design of the air-circulation and ventilation systeminteracts with the layout of furniture. Even furniture like filing cabinets and acoustic screens less than 1.5 meters high can impede air circulation, especially if they extend to the floor. Some sources recommend an open space of at least 25 to 51 mm at the base for furniture pieces. If walls or full-height partitions enclose spaces, each enclosed space should have one supply vent and one return or exhaust vent.

TYPES OF HVAC SYSTEMS

TYPES OF HVAC SYSTEMS

Direct Refrigerant Systems are heating and cooling systems that respond directly to the needs of individual zones.The other three, all-air, air and water, and all-water systems, produce heating and cooling in a central location, far from some zones. Air-handling equipment for these last three systems is either central or located on each floor.

HVAC SYSTEMS

Design Issues:• Exposing the mechanical system within the space

permits easy access for maintenance, repair, and alteration.

• Exposed systems may add visual interest. Office buildings sometimes expose the HVAC system in corridors and service areas, but conceal it in offices.

Centre Georges Pompidou in Paris, designed by Piano +Rogers, Architects.

Centre Georges Pompidou in Paris, designed by Piano +Rogers, Architects.

HVAC SYSTEMS

Design Issues:• The location of centralized HVAC equipment in a large

building has implications for the building’s space use and function.

• The heat, noise, moisture, air motion, and vibration from equipment may annoy adjacent floors or neighboring buildings.

• Mechanical floors can be used to separate floors of apartments from floors of offices, isolating daytime-use spaces from housing used more heavily at night.

• Very large buildings often require several intermediate mechanical floors.

HVAC SYSTEMS

Design Issues:• Basement locations offer noise isolation, utility

access, and support for heavy machinery. • Rooftops provide access to air for rejecting excess

heat, plus unlimited headroom. However, top floor spaces often bring top rental fees, which are lost when these spaces are devoted to mechanical equipment.

TYPES OF HVAC SYSTEMS

HVAC SYSTEMS: HVAC EQUIPMENTUNITARY AIR-HANDLING UNITUnitary HVAC systems combine heating, cooling, filtration, humidity management, and air-handling functions in a single, unified package.• Unitary air-handling units are installed on the roof directly above

the space to be air-conditioned, or mounted on a concrete pad along the exterior building wall. Rooftop units may be placed at intervals along long buildings.

• Unitary air-handling units are self-contained, and are used where the utility services of individual tenants are metered separately.

• Packaged systems with vertical shafts that connect to horizontal branch ducts can serve buildings up to four or five stories high.

• They have a life of about 10 years and require little maintenance.

HVAC SYSTEMS: HVAC EQUIPMENTUNITARY AIR-HANDLING UNIT

HVAC SYSTEMS: HVAC EQUIPMENTCOMPUTER ROOM UNITSComputer room units use a highly reliable air-handling unit with extremely precise temperature, humidity, and dust controls for sensitive electronic equipment, all located in the space served.

HVAC SYSTEMS: HVAC EQUIPMENTCENTRAL AIR-HANDLING UNITSCentral air-handling unit systems are found in large buildings with multiple zones of at least 450 square meters and in tall multistory buildings.Hospitals with stringent air quality controls use centralair-handling systems exclusively. • Large central air-handling unit systems require routine

daily checking and regularly scheduled maintenance. • They are built on site, and take longer to install than

prefabricated units, but may be more energy efficient. • Central air-handling systems have a 20- to 30-year life

expectancy.

CENTRAL AIR-HANDLING UNITS1. In air-handling unit systems for large

buildings, air is passed over the air-handling unit’s heat exchanger coil, which contains steam or hot water pipes.

2. Heating is transferred to the air, then to ducts and into the spaces where it will be used.

3. The air distributed from the central air-handling unit ends up in the building’s individual occupied spaces.

Small terminal units may be mounted directly below a window or in openings in the exterior wall of each space served. Window mounted units typically are used to retrofit existing buildings.

HVAC SYSTEMS: HVAC EQUIPMENTHVAC systems are made up of a number of separatepieces of equipment:1. Pre-heaters warm air that is below 0°C to a temperature slightly above freezing before it is sent on for other processing.2. Blowers (fans) supply air at a moderate pressure, to create the forced drafts that operate the HVAC system.3. Humidifiers maintain or increase the amount of water vapor in the air.4. A chilled water plant powered by electricity, steam, or gas delivers chilled water to the air-handling equipment for cooling, and pumps condenser water to the cooling tower to dispose of excess heat.

HVAC SYSTEMS: HVAC EQUIPMENT5. The boiler generates hot water or steam for heating,and requires fuel and air supplies. Hot water (hydronic)heating is more common than steam heat today.6. The furnace generates hot air for heating and requires fuel and air supplies. 7. The fan room contains air-handling equipment in largebuildings. Sometimes individual fan rooms are locatedon each floor or in each zone.8. Chimneys exhaust gases from the burning fuel.9. Cooling towers extract heat from the water that has been used for cooling by blowing air over the water to create water vapor and liberate the latent heat. They are typically located on the roof.

HVAC SYSTEMS: HVAC EQUIPMENT10. Special control equipment in HVAC systems for large buildings maintains comfort through central monitoring and coordination of equipment and building conditions. Controls increase fuel economy by running equipment in the most efficient way, and act as safety devices to limit or override mechanical equipment in emergencies.

HVAC SYSTEMS: Distribution TreesCentralized HVAC systems distribute heating and cooling through systems called distribution trees. Distribution trees take up a lot of space, both horizontallyand vertically. They need to be coordinated with the lighting, ceiling design, and other interior design elements. Like trees in nature, distribution trees have roots—the machines heating or cooling the air or water. The trunk of the tree is the main duct or pipe from the mechanical equipment to the zone served. The tree’s branches are the many smaller ducts or pipes leading to individual spaces.

HVAC SYSTEMS: Distribution TreesAn HVAC system can distribute heating and cooling by means of air, water, or both.• All-air systems have the largest trees, followed by air and water systems.

Air systems use ducts, which are bulky and have a significant visual impact.

• All-water systems with local control of fresh air have the smallest distribution trees. Water systems use pipes, which take up less space, and are easier to integrate with the building’s structural columns.

All-air systems provide the best comfort of these three systems. The air is heated or cooled, humidity controlled, and filtered, and fresh outdoor air is added, all under controlled conditions. Within each zone, supply registers and return grilles ensure a stream of conditioned air to all areas.

HVAC SYSTEMS: ALL-WATER DISTRIBUTION SYSTEMSAll-water systems are a simpler alternative for heating and cooling than all-air systems. The distribution trees are slim.Water systems provide temperature control only. Air quality is provided by windows or infiltration, or by a separate fresh air supply system.Water for the HVAC system is heated in a boiler tobetween 71°C and 121°C. Cold water is cooled in a chiller to 4°C to 10°C.Once the water is heated or chilled, it is then piped to a fan-coil unit (FCU) or radiant panel for both heating and cooling. An FCU contains an air filter and a fan for drawing a mixture of room air and outdoor air over coils of heated or chilled water, then blowing it back into the space.

HVAC SYSTEMS: ALL-WATER SYSTEMS

HVAC SYSTEMS: AIR-WATER DISTRIBUTION SYSTEMSAir-water systems provide superior comfort control. The water distribution tree does most of the heating or cooling.A small centrally conditioned airstream filters, controls humidity, and adds fresh air.Air is not recirculated in air-water systems, making this a good choice for hospitals and other facilities where contamination may be a problem. Exhaust air is returned via return air ducts, making energy recovery possible, or is exhausted locally.