Specialization in Environmental Architecture 1: Green DesignUST College of Architecture

HeatingVentilatingAndCoolingSustainable Design Strategies

Environmental Impact of HVAC• Heating, ventilation, and air conditioning (HVAC) accounts for 50 to 60

percent of the energy used.• Chlorofluorocarbons (CFCs) are hydrocarbons, such as freon, in which

some or all of the hydrogen atoms have been replaced by fluorine atoms.• When released into the air, CFCs slowly rise through the Earth's lower

atmosphere, and up to the stratosphere (second atmospheric layer, located about 7 to 30 miles [11 and 48 kilometers] above the Earth's surface).

• The release of CFCs into the atmosphere depletes the beneficial ozone layer. However, the atmospheric impacts of CFCs are not limited to its role as an active ozone reducer.

• This anthropogenic compound is also a greenhouse gas, with a much higher potential to enhance the greenhouse effect than CO2.

• CFCs were phased out via the Montreal Protocol due to their part in ozone depletion.

Why Ventilate?

• Oxygen/Carbon Dioxide• Moisture/Water Vapour• Odor removal• Smoke removal• Particulate/Pollen• Radon• Freshness• Summer Cooling

“From the earliest times building designers have made use of naturally induced air movement to address two basic needs in buildings: the removal of foul air and moisture, and personal thermal comfort.”

Natural Ventilation

• Can save significant amounts of fossil fuel based energy by reducing the need for mechanical ventilation and air conditioning.

• Reduces greenhouse gases released into the atmosphere from electricity generating plant that produces the energy used for cooling buildings.

• Air movement within buildings removes foul air and moisture and provides cooling in summer, for human thermal comfort.

Natural Ventilation

• Natural ventilation systems rely on pressure differences to move fresh air through buildings.

• Pressure differences can be caused by wind or the buoyancy effect created by temperature differences or differences in humidity.

Cross Ventilation

• Uses high and low pressure zones created by wind to draw fresh air through a building.

• It establishes a flow of cooler outdoor air through a space; this flow carries heat out of a building.

Key Architectural Issues

• Successful cross ventilation requires a building form that maximizes exposure to the prevailing wind direction.

• Provides for adequate inlet area, minimizes internal obstructions (between inlet and outlet), and provide for adequate outlet area.

• An ideal footprint is an elongated rectangle with no internal divisions.

• Siting should avoid external obstructions to wind flow (such as trees, bushes, or other buildings).

• On the other hand, proper placement of vegetation, berms, or wing walls can channel and enhance airflow at windward (inlet) openings.

Implementation Considerations

• High inlets and outlets provide structural cooling but no air movement at occupant level

Implementation Considerations

• Clerestories do not assist in occupant level air movement. Cross ventilation through lower inlets provides occupant level air movement.

• Orientation of the building to the prevailing winds will maximize airflow

• Cross ventilation should normally be analyzed on a space-by-space basis.

• An exit opening equal in size to the inlet opening is necessary.

• Arrange spaces to account for the fact that building spaces near inlets (outdoor air) to be cooler than spaces near outlets (warmed air).

• Substantial heat sources should be placed near outlets, not near inlets.

Design Procedures

Sample Project

The building’s outer shell is fitted with alternating glass and aluminum panels, which slide open and work as ventilation elements.

Free University in Berlin designed by Foster and Partners

Free University in Berlin designed by Foster and Partners

Stack Ventilation

• Stack ventilation uses high and low pressure zones created by rising heat, causing convection currents.

• It relies on two basic principles: (1) as air warms, it becomes less dense and rises; (2) ambient (hopefully cooler) air replaces the air that has risen.

Key Architectural Issues

• A stack needs to generate a large temperature difference between exhaust air and incoming air.

• A typical stack will provide effective ventilation for areas within the lower half of its total height.

• Exterior finishes and landscaping (plants,misting,and ground covers) can lower the incoming air temperature.

• Inlet (and outlet) sizing is critical to system performance.

Stack Ventilation Configurations

Implementation Considerations

• Careful consideration to the location of intake openings and ambient air quality is important.

• Stacks tend to “blur” thermal zones, favoring spaces lower on the “ventilation chain”.

• Zoning by function and occupancy needs (both in plan and section) should be a primary schematic design consideration.

Design Procedures

• Establish a workable stack height for the project. An effective stack will usually be twice as tall as the height of the tallest space it is ventilating.

• Size the stack openings (inlet, outlet, and throat area). The smallest of the following areas will define system performance

Sample Projects

Building Research Establishment offices, Garston, Hertfordshire, UK.

Lanchester Library at CoventryUniversity, Coventry, UK.

References