Visualizing How Buildings Visualizing How Buildings BreatheBreathe

Presented By:Presented By:

Ahmed Mohamed GendiaAhmed Mohamed Gendia

By: Adrian Tuluca, R.A By: Adrian Tuluca, R.A

Web Address:Web Address:

http://www.architectureweek.com/articles/http://www.architectureweek.com/articles/tools_articles.html  tools_articles.html 

Topic Number: Topic Number: 169169

Date: Date: 03 January 2001 03 January 2001

IntroductionIntroductionThe constant movement of air The constant movement of air through the spaces of a building through the spaces of a building affects its thermal environment affects its thermal environment and, thus, its energy performance, and, thus, its energy performance, yet this invisible "breathing" has yet this invisible "breathing" has been difficult to understand or been difficult to understand or predict using traditional tools. predict using traditional tools. Expensive wind tunnel models Expensive wind tunnel models were used before for measurement were used before for measurement as models needed to be as models needed to be reconstructed every time a reconstructed every time a modification occurs.modification occurs.Thus Computational fluid dynamics Thus Computational fluid dynamics (CFD) emerged to describe the (CFD) emerged to describe the complex movement of air complex movement of air molecules and temperatures within molecules and temperatures within spaces.spaces.

Wind tunnel model

CFD modeling was applied to special, CFD modeling was applied to special, large-scale spaces, such as airport large-scale spaces, such as airport terminals or multistory atria. These terminals or multistory atria. These CFD models were expensive and CFD models were expensive and could take weeks to build in the could take weeks to build in the computer. computer. Now CFD is being used for all kinds Now CFD is being used for all kinds of buildingsof buildings. .

CFD is no longer the budget buster. CFD is no longer the budget buster. Small buildings can be modeled for Small buildings can be modeled for $5,000 to $10,000; a 2D CFD $5,000 to $10,000; a 2D CFD simulation can be done for $2,000 to simulation can be done for $2,000 to $4,000. $4,000. CFD uses colored

arrows to simultaneously display air speed, direction, and temperature.

There are two kinds of analysis:There are two kinds of analysis: A- Two dimensional analysis:A- Two dimensional analysis: B- 3D dimensional analysis:B- 3D dimensional analysis:

The following scenarios show a variety of The following scenarios show a variety of conditions and the different approaches conditions and the different approaches of analysis:of analysis:

Oberlin's Environmental Studies CenterOberlin's Environmental Studies Center

(1255-square-meter) (1255-square-meter) Well environmentally designed.Well environmentally designed.Highly insulated walls and roofs; energy-Highly insulated walls and roofs; energy-efficient lighting; photovoltaic panels on efficient lighting; photovoltaic panels on the roof to generate electric power…the roof to generate electric power… Fresh as no air from one space is Fresh as no air from one space is mechanically induced into another.mechanically induced into another.

For an atrium space at Oberlin College, CFD analysis modeled the path of air streams that moved from the front door to windows above the mezzanine.

CDF targets: CDF targets: 1-Minimum area of operable 1-Minimum area of operable

windows with best windows with best performance.performance.

2- Detection of most efficient 2- Detection of most efficient location of windows.location of windows.

3- Elimination of still air zones. 3- Elimination of still air zones.

Solutions:Solutions: 1-CFD studies showed that a 1-CFD studies showed that a

roof-top monitor in the atrium roof-top monitor in the atrium would provide a "chimney would provide a "chimney effect" .(too costly)effect" .(too costly)

2-CFD recommended that the 2-CFD recommended that the designers place more designers place more operable windows low on the operable windows low on the south wall to vent heat gain. south wall to vent heat gain.

Oberlin's Environmental Studies CenterOberlin's Environmental Studies Center

Analysis of the air velocity at four feet (122 centimeters) above the floor uses color to show still air (dark blue) next to fast-moving air (red) through the door. Windows were added to the building's east wall to mitigate the stagnant pocket.

Train station. Rensselaer Train Station in Train station. Rensselaer Train Station in Albany, New York .Albany, New York .double-height waiting room, crowned with double-height waiting room, crowned with a sloped roof. a sloped roof. No natural ventilation was possible in the No natural ventilation was possible in the space because the outside air is polluted.space because the outside air is polluted.analysis of the waiting room.analysis of the waiting room.Targets:Targets:

Determine how Determine how comfortable temperaturescomfortable temperatures could be maintained without could be maintained without excessive air excessive air

flow. flow. Model was simplified to keep the cost of Model was simplified to keep the cost of the analysis down.the analysis down.

Rensselaer Train StationRensselaer Train Station

An exterior computer rendering of the Rensselaer Train Station.

It was not necessary to accurately It was not necessary to accurately predict temperatures at roof level. predict temperatures at roof level. The heat gain was accurately The heat gain was accurately calculated.calculated.CFD revealed temperature CFD revealed temperature differences ranging from 105 differences ranging from 105 degrees Fahrenheit (40 degrees degrees Fahrenheit (40 degrees Celsius) near the ceiling to Celsius) near the ceiling to 70degrees F. (21 degrees C.) at 70degrees F. (21 degrees C.) at floor level.floor level.Thus the temperature is Thus the temperature is comfortable.comfortable.

Rensselaer Train StationRensselaer Train Station

The sloped ceiling of the train station was simply modeled as rectilinear to save time and cost. The rendering of the waiting room volume shows temperature variation.

HVAC designers HVAC designers will have two will have two options:options:

(1) Specify smaller (1) Specify smaller fans fans

OROR

(2) Specify the same (2) Specify the same size of fans, but size of fans, but with variable-speed with variable-speed drives drives

Variable-speed Variable-speed drives fans is was drives fans is was found the best found the best solution as it to solution as it to meet the variable meet the variable needs of the needs of the space. space.

Rensselaer Train StationRensselaer Train Station

A streamline diagram indicates the air moving from the supply ducts to the return grilles. Notice that each streamline changes in color as its temperature changes.

Two slices through the train station space show temperature variations. The abrupt change in color indicates the location of the mezzanine.

Although CFD was born from the need to Although CFD was born from the need to model large-scale, complex spaces, model large-scale, complex spaces, there is no reason this simulation can't there is no reason this simulation can't be used to simulate small spaces, such be used to simulate small spaces, such as one room in a house. as one room in a house.

The goal was to study how changes in a The goal was to study how changes in a builder's routine construction techniques builder's routine construction techniques could lead to a more energy-efficient could lead to a more energy-efficient house .house .

(150-square-meter) prototype house in (150-square-meter) prototype house in Rochester, New York.Rochester, New York.

Modifications to more energy efficient Modifications to more energy efficient housing (low-e glazing…) housing (low-e glazing…)

First experiment involved removing the First experiment involved removing the heating supply registers from under the heating supply registers from under the windows .windows .

A Single RoomA Single Room

For the prototype house built by Ryan Homes, CFD revealed temperature variations within a bedroom. Note the temperature spike at the floor register.

Registers beneath windows Registers beneath windows mitigate air cooled by the surface of mitigate air cooled by the surface of the windows, which otherwise flows the windows, which otherwise flows to the floor and creates drafts.to the floor and creates drafts.

Efficient air distribution could be Efficient air distribution could be achieved from registers placed in achieved from registers placed in the ceiling or high on the wall.the ceiling or high on the wall.

Radiant improved to more Radiant improved to more comfortable level. comfortable level.

CFD improved the ventilation CFD improved the ventilation efficiency in the room and those efficiency in the room and those modifications were taken as a modifications were taken as a prototype.prototype.

A Single RoomA Single Room

A new location for the bedroom supply duct, near the ceiling, allows heated air to be thrown into the room at 30 degrees (0.5 radians).

CFD computer modeling has come a long way from CFD computer modeling has come a long way from the time-consuming, costly simulations that were the time-consuming, costly simulations that were the norm only a few years ago. the norm only a few years ago.

CFD is an accurate measurement tool.CFD is an accurate measurement tool.

Faster than conventional tools.Faster than conventional tools.

More illustrative.More illustrative.

Applied on different scales.Applied on different scales.

Could be used as a checking tool.Could be used as a checking tool.

Time conserver.Time conserver.

Money conserver. Money conserver.

ConclusionConclusion

THANKS…THANKS…