designed porous media

DESIGNED POROUS MEDIA

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JIM PERAINO

KALEY BLACKSTOCK

&

GSD_06453 | SPRING 2015

INSTRUCTOR: SALMAAN CRAIG

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The criteria for the final project for Designed Porous Media is to create an office building for a hot climate that integrates building design with the design of thermally active surfaces to establish two convective flow regimes: an updraft buoyancy-driven flow during temperate conditions, and a downdraft cooling-induced flow during hot conditions. Critical to the project is the management of micro and macro strategies to match form to flows.

The project offered an opportunity to invert conventional design methodologies. Rather than fitting building components to an overarching architectural design, we began our project at the micro scale of the surface. Simple spiraling aluminum disks coupled with hydroponic tubing reveal the delicate physical phenomena of boundary layer dynamics. Reorienting the geometry intensifies the distinction of thermal effects caused by single geospatial maneuvers. The performance of the surfaces thus initiated a conception of the project as a human-scale composition and catalyzed the desire to maintain an intimate relationship to the thermodynamics of the surfaces as a critique of the notion of occupancy.

The building design consists of a rotating stack of L-shaped office units that join an open floor plan with a vertical chimney. The construction is lightweight and light-filled. Hung within the chimney and along the ceilings are series of thermally active surfaces that work in conjunction with insolation and the dimensions of the spaces to facilitate the two flow regimes.

A key aspect of the project was the iterative re-evaluation of the building and surface design. We constructed a series of experiments that validated the underlying intuitions of the schemes. Though each experiment employed a degree of abstraction, the act of testing the designs provided a translation between the scalar considerations of an architectural project.

i

THE BUILDING

Siting Conditions for ConceptThermal Topology and Uses

ii

THE COMPONENTS

Thermally Active Surface

iii

THE EXPERIMENTS

Macro System - Water Bath TestMicro System - Schlieren TestingSizing the systems - Calculations

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GSD 06453: DESIGNED POROUS MEDIA

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THE BUILDING Siting conditions, thermal topology and

programming for an office building design

Passive and active strategies for the optimization of thermal comfort in architectural design are often the result of layered techniques and technologies that run parallel to the design of the building. The taxing negotiation between the large scale operations of the building and the small scale components challenge ambitions of matching heat flow to architectural form. The result is often a taxonomy of building parts underpinning an absolute architectural aesthetic. A solution is to begin at the micro scale - to craft spaces that operate in tandem with the architectures of the components that generate the performance of the facility.

The mission of the project is to design an office building for a hot desert climate that couples a large-scale building design with small-scale thermally active surfaces. While conventional thermally active surfaces seem supplementary to the building geometry and consequently the macro design strategies for the building, the performance of the surfaces aims to highlight a scalar relationship between the elements of the building and the habitation of the spaces. The geometry of the building is simple - nested ‘L’-shaped single-floor spaces, joined in the formal repetition of the unit as a rotated vertical stack. Key to the geometry of the unit is the vertical chimney that houses a collection of spiraling aluminum

disks - the thermally active surfaces that create a falling colonnade of cool air for the inhabitants within, while droplets of condensation collected from the surfaces hydrate the gardens resting below. The unit is conceived of as a light-filled and lightweight structure - a glass tower wrapping pretensioned concrete cubes.

The siting of the office building in a hot desert climate questions the appropriateness of a glass and concrete tower in such extreme thermal conditions. Rather than climate mitigation, the project focuses on climate matching that couples the building design to the climate context of the site. We selected Phoenix, Arizona as our test case. Critical to the facility’s performance is the scheduling and management of the systems during the diurnal swings. The facility has two modes of operation: downdraft and updraft. During the hours when the facades are shaded from solar gains, the thermally active surfaces within the chimney create downdrafts that, in conjunction with the thermally active surfaces along the office space ceiling, condition the occupiable zones below. Inversely, during moments when the sun is perpendicular to the facades, solar gain collected within the chimney initiates a buoyancy-driven updraft that pulls fresh air through the office spaces below. As the unit rotates in the vertical

stacking of the building section, inlets and outlets of the various units are places in close proximity and yet function thermodynamically unencumbered by this geospatial perversion.

Despite the composition of the units, the individual performance of each nested ‘L’ drives the success of the project. The performance of the units is contingent on not only the ambient temperatures of the site, but also on the solar conditions that initiate the stack effect. The insolation of the chimney varies per the rotation of the unit in the vertical stacking of the spaces, providing some units with morning easterly sun or evening westerly sun and, at times, no solar gains at all as in the case of a northern facing unit. The totaling effect is a building that is in constant state of flux, with each unit operating individually per the external conditions of the unit - a prime opportunity for a fluid scheduling of programming of the ever-active facility.

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The intended location for the building project is a hot desert climate. Typical of the cities within the latitude range of this climate type are extreme summer temperatures, at times above 40C with little to no rainfall (below 50% of the potential evapotranspiration threshold for that location). However, local geographies play a significant role in the effects of these conditions. Proximity to large bodies of water, high altitudes and urban density can temper or exacerbate diurnal swings, relative humidity levels, and direct radiation. To give comparative examples to Phoenix, Arizona, the selected test location, two additional cities - Lima, Peru and Isfahan, Iran - are presented to illustrate the range of microclimate conditions due to the geographical context of the sites. For instance, the proximity to the mountainous coast of Lima, Peru deflates seasonal temperature swings as well as provides ample cloud coverage year round, while the high altitude and clear skies of Isfahan produces great seasonal temperature shifts from winter to summer.

The effect of these seasonal and diurnal environmental changes is an altering of the performance of the passive and active systems within the design strategies. At high temperatures with low relative humidity, thermally active surfaces used to create downdrafts for cooling of occupiable spaces can be coupled with water evaporation to enhance the thermal effects of the system. Alternatively, a climate with a large seasonal temperature differences may render active systems unnecessary during shoulder or winter months. Furthermore, climates with extreme cloud coverage may require catalysts other than solar radiation to induce buoyancy-driven convective cooling.

Desert Climates: BWk (Hot Desert) and BWh (Cold Desert).

1 Wikipedia contributors, “Köppen climate classification,” Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=K%C3%B6ppen_climate_classification&oldid=660254516 (accessed May 4, 2015).2 Carrier Psychometric Chart

DRY BULB TEMPERATURE

ABSOLUTE

HUMIDITY

RELATIVE HUM

IDIT

Y

EVAPORATIVE COOLING

THERMALLY ACTIVE SURFACE + EVAPORATIVE COOLING

SITING CONDITIONS

PHOENIX, USA

LIMA, PERU

iSFAHAN, IRAN

Koppen Climate Classification Map

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PHOENIX, USA

Located at 33.45ON latitude and 340m above sea level, Phoenix exhibits typical conditions for hot dry desert climates: high levels of direct radiation, extreme diurnal swings, low relative humidity rates, and low cloud coverage.

LIMA, PERU

Located at 12OS latitude and at sea level, Lima is conditioned by the cold Humboldt current that travels north along the western coast. Flanked to the east by the Andes Mountain Range, the metropolis experiences rather consistent temperatures with frequent cloud coverage.

ISFAHAN, IRAN

Located at 32.6ON and 1590m above sea level, Isfahan exhibits conditions typical of a cold desert climate with hot summer temperatures. Low precipitation and clear skys enable solar radiation to warm summer days while the flat northern boarder allows for cold winter winds.

WINTER: 33O

WINTER: 35O

WINTER: 33O

SUMMER: 80O

SUMMER: 80O

SUMMER: 80O

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Key to the design is the optimal use of solar gains to initiate the updraft flow regime. The solar conditions for Phoenix, Arizona are typical of desert climates. High direct radiation (yellow areas in the accompanying climate graph) compared to low diffused radiation (teal) indicate little to no cloud cover with minimal variation throughout the year. Due to the rotation of the building unit, each facade except the northern facing unit, is exposed to strong solar radiation levels for a few hours of the day, giving the potential to program the units to match the convective flows initiated by the solar gains within the chimney.

SOLAR GAINS

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EAST FACADE SOUTH FACADE WEST FACADE

9:00 9:00 9:00

12:0012:0012:00

15:0015:0015:00

18:0018:0018:00

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The design strategy for the office building operates two thermal regimes: updraft created by solar radiation, and downdraft created by conditioned air. Two sets of thermally active surfaces are integrated into the design - one placed within the chimney to establish the downdrafts that preconditions

and generates fresh air flow, and one placed along the ceiling in the habitable zone to cool occupants when extreme air exchange rates are unnecessary. During the hours in which the sun is perpendicular to the facade, solar gain within the chimney establishes a buoyancy-driven updraft to circulate

air through the occupiable space. The temperature of the infiltrating external air in updraft mode is effected by the diurnal swings of the site. The rotated geometry of the building proposes a varied and scheduled use of internal spaces per the flow conditions of the units.

THERMAL TOPOLOGY

NORTH

MORNING

MIDDAY

EVENING

EAST SOUTH WEST

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INTERIOR GARDENS

At the base of the chimney is located interior winter gardens, hydrated by condensation collected from the thermally active surfaces.

THERMALLY ACTIVE SURFACES

To establish downdraft conditions within the chimney, a thermally active surface chills incoming air. Additionally, a thermally active surface is placed along the ceiling of the occupiable zone to cool use space.

OCCUPIABLE ZONES

Office spaces, approximately 40’ x 35’. Flex spaces with activity and occupancy level determine by interior

SOLAR COLLECTION

The exterior facade of the chimney is utilized during maximum sunlit hours to initiate updraft flows. The facade facing the core of the building uses low-E coating - minimizing solar gains, while enabling light penetration across the sacked units.

LEAN

Due to the vertical stacking of the units, one edge of the chimney sets back to allow for cross ventilation for above units.

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PROGRAMMING

EAST FACING

The east-facing unit is supplied with solar gains in the morning, restricting updraft conditions to hours before noon. Due to clear skies, external temperatures are relatively low, effectively precooling inflowing air. High internal load activities should be scheduled for the mornings, particularly in the winter when updraft potential is highest and incoming air is coolest.

SOUTH FACING

The south-facing unit receives the most extreme thermal swings througout the day. During hot conditions, updraft potential is highest and most effective during the midday, encouraging the scheduling of high air exchange rate conditions to this unit during those hours. In flowing air will be hot and dry, allowing for optimal heat transfer from thermally active surfaces and additional evaporative cooling from collected condensation.

WEST FACING

The west-facing facade receives the evening sun when general temperature conditions are warmer due to the thermal mass of the building and surroundings, effectively preheating inflowing air to the occupiable zone. Updraft potential is highest during the afternoon, noting that infiltrating external temperatures remain relatively high despite the setting sun, limiting internal flow rates.

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MORNING

MIDDAY

AFTERNOON

TEMPERATURE

REL HUMIDITY

RADIATION

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THE COMPONENTS Two thermally activesurfacesto activate convective flows.

As designers, it is simple to sketch diagrams to indicate the intended performance of our structures. Rarely are we allowed the opportunity to iteratively investigate the thermodynamics of our designs. In this project, we were determined to test our ideas and validate our intuitions. In doing so, we were surprised by the range of results, not in contradicting our hypotheses, but rather they revealed our limited expectations of the performance of our designs. Furthermore, we discovered teh delicate nature of analogue research, often redesigning the test in conjunction with refining the design itself.

Our first set of experiments employed Schlieren Imaging to reveal the downdraft currents of our chilled thermally active surfaces. In this micro flow experiment, we constructed a rough prototype of our surface - two thin plastic sheets flanking a water-soaked chamois disk, wrapped in aluminum tape - that was placed in a freezer overnight. The frozen prototype was then suspended in front of a highly refractive mirror to capture the slight changes in air density due to the cooling effect of the surrounding air of our prototype. It was in this experiment that we recognized the distinct flow patterns between the vertically oriented spiral and the horizontal spiral. Columns of cool air were captured and channeled into the core of the vertical spiral

whereas chilled air dropped in streams between the disks of the horizontal spiral, thus redefining our conception of the surface as a geospatially sensitive and scalarly manipulable component.

Our second set of experiments aimed to test the macro flows of our building unit in search of evidence of updrafts and downdrafts prescribed by the thermal topology. We ran a series of water bath tests - the act of placing hot and cold steel plates adjacent to surfaces of an plexi sectional model submerged in a fish tank; small drops of diluted ink indicate the directions of flows as the water circulates through the model. These test confirmed our intuitions of the stack effect and enthralled us in the display of downdrafts. However, it was the test itself that revealed the complexity of the system - the low conductivity of the plexi, the viscosity and heat capacity of the water, and the scale of the model all greatly mitigated the results of the otherwise successful experiment.

In addition to analogue testing, we perfomred a sensitivity analysis based on heat flow equations to determine the aspects of the design most effective in inhibiting or facilitating the flow regimes. Using a mathematical model of the stack effect, we compared results of the building units with varying chimney widths and cross ventilation

opening dimensions. More akin to the digital reality that harbors our design, these abstracted values and evaluations confirmed our expections of the flows, and validated our understanding of presure systems within buoyancy-driven convective currents. Though not determinant in our design of the unit due to geometric irregularities, this series of tests did influence our concept of the chimney as a non-occupiable space.

The combination of experiments and tests, though singular in their processes, were part of an iterative approach to the design. Rather than fine-tuning the small components to fit the criteria of the building agenda, the experiments utilized our design skills to craft the form to match the flows, and subsequently inverted the conventional hierarchy of design methodology. From the geometry of the thermally active surfaces to the dimensions of the building, each element was evaluated against a symbiotic and integrated engine of design.

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From the genesis of the project, a determining factor in the relationship between the geometry of the building design and of the thermally active surface was scalar reciprocity. The phenomenon of the surface must match the phenomenology of the space. The

design of the thermally active surface is a simple spiral of attached aluminum disks, doubled and filleted to created two crevices, one for hydroponic tubing which carries a high-heat capacity fluid, and one for the channeling of condensation down the core of the

spiral. This surface can be adjusted - coiled and uncoiled - and rotated - vertical and horizontal. The effects are distinct and can be calibrated to achieve the thermal conditions desired by the occupant.

THERMALLY ACTIVE SURFACES

HORIZONTAL ORIENTATION

VERTICAL ORIENTATION

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ALUMINUM SURFACE

Due to its high conductivity, aluminum effectively extends the surface area of the hydroponic tubing.

CONTINUOUS DOUBLE

SPIRAL GEOMETRY

For ease of construction, the thermally active surface is composed of adjoining aluminum disks, welded together.

CONDENSATION COLLECTION

Due to extreme temperature changes of surrounding air, condensation is collected in the overlapping surfaces, and channeled down to gardens below.

HYDROPONIC TUBING

Sandwiched between the aluminum disks is hydroponic tubing filled with a high heat capacity fluid (water or antifreeze). The pipe is attached to the disks with conductive caulking.

CABLE SPINE

Given that the thermally active surface is installed in both the vertical and horizontal orientations, the cable spine stabilizes the component and additionally, provides a guideline for the anchoring of the hydroponic tubing.

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THE EXPERIMENTS Schlieren testing of the thermally active surfaces

paired with water bath testing of the macro system to validatebuilding design. Calculations calibrate components and systems.

As designers, it is simple to sketch diagrams to indicate the intended performance of our structures. Rarely are we allowed the opportunity to iteratively investigate the thermodynamics of our designs. In this project, we were determined to test our ideas and validate our intuitions. In doing so, we were surprised by the range of results, not in contradicting our hypotheses, but rather they revealed our limited expectations of the performance of our designs. Furthermore, we discovered the delicate nature of analogue research, often redesigning the test in conjunction with refining the design itself.

Our first set of experiments employed Schlieren Imaging to reveal the downdraft currents of our chilled thermally active surfaces. In this micro flow experiment, we constructed a rough prototype of our surface - two thin plastic sheets flanking a water-soaked chamois disk, wrapped in aluminum tape - that was placed in a freezer overnight. The frozen prototype was then suspended in front of a highly refractive mirror to capture the slight changes in air density due to the cooling effect of the surrounding air of our prototype. It was in this experiment that we recognized the distinct flow patterns between the vertically oriented spiral and the horizontal spiral. Columns of cool air were captured and channeled into the core of the vertical spiral

whereas chilled air dropped in streams between the disks of the horizontal spiral, thus redefining our conception of the surface as a geospatially sensitive and scalable component.

Our second set of experiments aimed to test the macro flows of our building unit in search of evidence of updrafts and downdrafts prescribed by the thermal topology. We ran a series of water bath tests - the act of placing hot and cold steel plates adjacent to surfaces of a plexi sectional model submerged in a fish tank; small drops of diluted ink indicate the directions of flows as the water circulates through the model. These test confirmed our intuitions of the stack effect and enthralled us in the display of downdrafts. However, it was the test itself that revealed the complexity of the system - the low conductivity of the plexi, the viscosity and heat capacity of the water, and the scale of the model all greatly mitigated the results of the otherwise successful experiment.

In addition to analogue testing, we performed a sensitivity analysis based on heat flow equations to determine the aspects of the design most effective in inhibiting or facilitating the flow regimes. Using a mathematical model of the stack effect, we compared results of the building units with varying chimney widths and cross ventilation opening dimensions. More akin to the

digital reality that harbors our design, these abstracted values and evaluations confirmed our expectations of the flows, and validated our understanding of pressure systems within buoyancy-driven convective currents. Though not determinant in our design of the unit due to geometric irregularities, this series of tests did influence our concept of the chimney as a non-occupiable space.

The combination of experiments and tests, though singular in their processes, were part of an iterative approach to the design. Rather than fine-tuning the small components to fit the criteria of the building agenda, the experiments utilized our design skills to craft the form to match the flows, and subsequently inverted the conventional hierarchy of design methodology. From the geometry of the thermally active surfaces to the dimensions of the building, each element was evaluated against a symbiotic and integrated engine of design.

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Schlieren imaging is a form of convective flow finding through a loop sequencing of a light source and a convex lens. Through extreme refractioning of light, variations in air densities are exhibited as grayscale streaks, thus illuminating convective currents from thermally disparate entities. For this test, a simplified prototype of the thermally active surface was chilled and then displayed infront of the Schlieren mirror to give evidence of the laminar and turbulent flows produced by the geometry.

• What is the effective zone of the thermally active surface?

• Does the orientation of the spiral produce different downdraft effects?

• Does a more coiled spiral (a more vertical slope of the cross-section of the spiral) enable more laminar flows down into the center of the spiral?

• In contrast, does a flatter coil have greater potential for turbulent flows?

• Does a tight spacing of the coils reduce the downdraft velocity, and/or does a widely spaced coil create potential for turbulent flows?

• Validation of the test: Does our presence affect the accuracy of the test?

SCHLIEREN TESTING

PROTOTYPE | MIRRORLIGHT SOURCE + CAMERA

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The Schlieren Test was effective in validating our intuitions about our thermally active surface. For the experiment we generated a mock-up of the surface that demonstrated the concept of the design. A series of water-soaked chamois fabric pieces cut to the shape of disks were sandwiched between thin plastic sheets, covered in aluminum tape. The prototype was placed overnight in a freezer to simulate the cooling capacity of chilled water piped through an aluminum surface.

The imaging of the prototype is compelling. Evidenced are both laminar and turbulent flows produced by the chilled prototype, as

anticipated. Surprising, however, was the performance of the surface in the horizontal orientation. We expected the coiling of the spiral to affect the laminar versus turbulent generation of flows, with a tighter coiled surface establishing more laminar flows along a more vertical surface than the flattened disks of an uncoiled surface. This in turn would not only affect the flows of currents, but the volume of air affected by the surface. When oriented in the horizontal, the degree of coiling did affect the generation of flows, but reinforced the notion that air would pass through and thus be conditioned by the surface per the characteristic length of contact with the surface.

This sparked new questions regarding our design: Does the water in the vertical thermally active surface require as low of temperatures as the horizontal surface? Should we fan out the coiling spiral (to form the profile of a tree versus a single vertical line) to reduce the characteristic length in the vertical orientation? If this test were reissued, we would consider these options. Additionally, we would restrict the interference of cross currents (produced by our body heat and by air cycles of the room) by confining the prototype within a box, able to adjust and exchange different prototypes for further testing.

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LAMINAR FLOWTURBULENCE OF

STILL AIRVOLUME OF AIR

AFFECTEDDISRUPTIVE CROSS

FLOW

VERTICAL COILED

(CONES)

More prominent along edge of spiral

Minor turbulence (difficult to determine

due to coil

Less volume, air falls mostly within core of

spiral

Coil protects air within the space of the spiral

TEST 1 - VERTICAL, COILED (CONES)

result was a narrow zone of downdraft currents around the area of the surface. A surprising result in the imaging was the degree of interference from cross currents of the ambient air and possibly from our own body heat. Nonetheless,

we were pleased to see the laminar flows dominate the currents around the geometry, with minor turbulent flows wicked away by the cross currents.

In our first iteration of the imaging experiment, we were anxious to prove our theory of downdraft columns within the core of the spiral. In this iteration, we oriented the surface in the vertical, with a tightly wound coil. The

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FLOW

VERTICAL FLAT (DISKS)

Less prominent, mostly turbulent

flows

Minor turbulence (difficult to determine

due to cross flows)

Greater volume of air around the spiral

affected

Extreme disruption from cross currents

TEST 2 - VERTICAL, FLAT (DISKS)

underneath the surface would fall out and around the geometry of the surface. Following the lessons learned from the preveious test with regards to cross currents, it is evident in the results that the flattend spiral enables a greater

potential for cross current interference with downdrafts. A tightly wound coil effectively shields its cascading column of air, whereas a flattened disk produces and enables more turbulent flows around the surface.

In the second iteration, we uncoiled the surface to create flat disks in the vertical orientation. We anticipated that this configuration would create a large zone of air movement around the surface as turbulent flows generated

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TEST 3 - HORIZONTAL, COILED (CONES)




FLOW

HORIZONTAL COILED

(CONES)

Eddies are created by interferring laminar and turbulent flows

Greater presence of turbulence

Less great - air passes through surface zone once but hindered by

coil

Less prominent, only occurs after passing

through spiral

with adjacent flows, creating eddies underneath the surface. It is clear in this test that the slope of the surface affects the creation of laminar flows along the face of the surface. Despite graviational pull, the currents cling to the underside of the slanted surface. However, like

the previous iterations, it is difficult to determine how much of the flows are caused by additional cross flows from the ambient air and adjacent body heat.

In this iteration, we rotated the orientation of the surface to the horizontal and moderately coiled. the geometry. Evident in the video is the laminar flows along the edges of the surface. As the cool currents slip off the edges of the disk, they collide

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TEST 4 - HORIZONTAL, FLAT (DISKS)




FLOW

HORIZONTAL FLAT (DISKS)

More laminar flow at the bottom of the

spiral

Less prominent, mostly laminar along

surface of spiral

Greater - air passes through surface zone

once

Less prominent, only occurs after passing

through spiral

that channel the downdraft into the coil of the spiral, the horizontal orientation contains a significantly shorter characteristic lenght. Also evident is the influence of the flattening of the surface in the creation of more vertical surfaces. The result is more laminar flows along

the face of the surface. However, it is difficult to discern between possible cross currents from the ambient air from the currents established by the cooling effect of the surface.

In this iteration of the horizontal orientation, we compressed the coil so as to create disk-like surfaces (more vertical slopes of the surface). Evident in the video is the constant flow of air through the space of the surface. As compared to vertically oriented surfaces

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Water Bath Testing is a proof of concept for the convective flows created within the building’s geometry, actuated by thermally active surfaces. In this test, a scaled model of the building unit is placed within a body of water. Hot and cold surfaces are placed adjacent to specific surfaces in the model simulating occupancy or thermally active surfaces. Ink is introduced to record the flows of the water caused by the hot and cold surfaces.

• Will flows occur within the model with just occupancy simulated (testing of the stack effect)?

• What flows occur when assummed conflicting flows are simulated (occupancy plus downdraft created by cold thermally active surface within the chimney)?

• Will flows occur when simulated surfaces are within close proximity (occupancy plus thermally active surface along ceiling of occupiable zone)?

• Validation of the test: Does the width of the model to width of the tank affect the performance of the test?

WATER BATH TESTING

10 GALLON TANK1/8” PLEXI MODEL

DILUTED INK

To visualize the convective flows, a few drops of ink were introduced at the source of the flows.

INFARED CAMERA + THERMOMETER

Each test logged the various plate temperatures to maintain consistency accross the trials.

1/2” STEEL PLATES + FOAM

By heating (via the hot plate to the left) and chilling steel plates, we simulated solar gains and thermally active surfaces. Each plate was insulated by foam to direct heat flow to the interior of the plexi model.

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The results of the trials of the water bath test were very compelling. Overall, we produced flow regimes as anticipated by the conditions set for for each trial. However, we were surprised by the many aspects that influenced the performance of the test. For instance, the low conductivity of the plexi tempered the heat exchange between the water and the model. A solution could be the removal of plexi in plate locations for heightened plate to water contact.

However, the high heat capacity of water quickly cools or warms the plate thus abruptly shortening the test. Another concern that emerged during the experiment was the influence of the ink injection velocity on the recorded flows. In a few cases, the force of the dispensed ink reverberated off the plexi, producing contrasting flows. While care was taken in dispensing the ink, it is recommended that a constant flow of dye be supplied during the experiment.

Not all trials were logged due to time constraints. Those in black are reviewed in further detail on the following pages. In each trial, we recorded and maintained temperatures of each critical medium: - water = 75OF - occupancy plate = 95OF - chilled plate = 65OF - heated plate = 125OF

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE

HORIZONTAL THERMALLY

ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 0 - - - WARM CONTROL

TRIAL 1 HOT - COLD WARM SUN, TAS-H, OCCUPIED

TRIAL 2 HOT - - WARM SUN, OCCUPIED

TRIAL 3 HOT - COLD WARM SUN, TAS-H, LOW-OCCUPANCY

TRIAL 4 - COLD COLD WARM TAS-V, TAS-H, OCCUPIED

TRIAL 5 - COLD - WARM TAS-V, OCCUPIED

TRIAL 6 - COLD COLD WARM TAS-V, TAS-H, LOW-OCCUPANCY

TRIAL 7 - - COLD WARM TAS-H, OCCUPIED

TRIAL 8 - - - WARM OCCUPIED

TRIAL 9 - - COLD WARM TAS-H, LOW-OCCUPANCY

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expectations with an exceptional display of updraft flows. We were concerned about the aggressive injection of ink into the model, wondering if the vertical flows from the base of the model were due to the reverberation of the ink off the floor or caused by the

updraft currents themselves. Overall, the control trial of occupancy-induced convective flows was successful.

In this trial we had an inital expectation of gentle updraft flows established by a warm occupancy plate in the office space. As ink is injected, the flows would migrate up towards the ceiling and gradually up and out of the chimney. The result of the trial confirmed our

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 0 - - - WARM CONTROL

TRIAL 0 - CONTROL

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be quickly exhausted by the updraft currents of the chimney. Though this cycle did occur, we were disappointed in the speed of the currents. We questioned the efficacy of the layered plexi-plate-foam, wondering if the low conductivity of the plexi abated heat

exchange between the plate and the water. Additionally, we considered the need to redesign the foam supports in the model to create a more watertight connection between the plate and the plexi surface.

In the first trial to simulate the use of a thermally active surface (horizontal) in conjunction with radiation-induced stack effect, we anticipated a slight downdraft of currents in the occupiable zone, forcing lateral flows into the lower register of the chimney that would

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 1 HOT - COLD WARM SUN, TAS-H, OCCUPIED

TRIAL 1 - SUN, TAS-H, OCCUPIED

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a vertical flow of currents up to the ceiling of the occupiable space, which are then quickly exhausted through the chimney. The results were not as clear and successful as expected. The cycle did occur as anticipated, however at slower flow rates than desired. We concluded

that the low conductivity of the plexi is a determining factor in the performance of the flow regimes.

Given the performance of the first trial, we wanted to test the most extreme updraft condition to investigate the effect of the low conductivity of the plexi. In this trial we simulated a solar radiation-induced updraft boosted by internal occupancy loads. We anticipated

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 2 HOT - - WARM SUN, OCCUPIED

TRIAL 2 - SUN, OCCUPIED

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gentle downdraft of currents within the chimney, that are slowly elevated by the occupancy plate and exhaused through the window. The downdraft did occcur with slight upticks in the occupancy area, however there was no visible exhaust through the window. It is

important to note that in this trial, the abrupt injection of ink initially created backflow out of the chimney.

Trial 5 inverts the flow regime of trial 2, by replacing the solar hot plate with a chilled plate to simulate a thermally active surface. Given that the plexi deters heat transfer, we anticipated slower flow rates for the subsequent trials. In this iteration, we expected to see a

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 5 - COLD - WARM TAS-V, OCCUPIED

TRIAL 5 - TAS-V, OCCUPIED

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the occupiable zone, supplied by a downdraft from the chimney. We did not expect exhaust to occur out the window. The trial performed as expected with a stagnation of flows at the occupiable zone. Furthermore, the test recorded an elegant column of

cascading currents that culminated at the base of the chimney, encouraging our design strategy of a winter garden placed below the thermally active surfaces.

In this trial, we investigated the effects of both thermally active surfaces on convective currents within the unit to simulate conditions in which extreme cooling is needed with little air exchange. In this iteration, we anticipated a cycling of currents at

TRIAL 6 - TAS-V, TAS-H, OCCUPIED

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 6 - COLD COLD WARM TAS-V, TAS-H, OCCUPIED

32 FRESH N’ FOLD

within the room as the slow downdrafts of the chilled horizontal plate counteract the slow updrafts from the occupancy plate. The trial performed as expected with exceptional clarity. We conclude from these stagnation trials that the weight of the horizontal plates provides

a better contact and thus heat exchange between the plate, plexi and water.

In trial 7 we extened our investigation of stagnating currents in the occupiable zone. In this iteration we simulated a condition of slight cooling by the horizontal thermally active surface with little need for high air exchange rates. We anticipated circulating currents

TRIAL 7 - TAS-H, OCCUPIED

SOLAR PLATE

VERTICALTHERMALLY

ACTIVE SURFACE


ACTIVE SURFACE

OCCUPANCY PLATE

SIMULATION STUDY

TRIAL 7 - - COLD WARM TAS-H, OCCUPIED

33

In addition to analogue testing of our systems, we performed a sensitivity analysis to determine which aspects of

the design most affected the convective flows within the units. The following calculations inspect varying chimney

widths and cross-ventilation opening dimensions in the throttling of air movement through the building.

Equations for the following calculations can be found in Section 4.3.1: Distributed Heat and Cooling in Buoyancy Effects of Natural Ventilation by Torwong Chenvidyakam.

CALCULATIONS

External Temp T_ext 298 K

CHIMNEY HEIGHT ‐ m

OPENING ‐ 1 ‐ m²

Porocity ratio 1

Effective opening area

‐ m²

OPENING ‐ 2 ‐ m²

Porocity ratio 1


‐ m²

CHIMNEY WIDTH ‐ m²

Porocity ratio 1


‐ m²

OCCUPIED AREA ‐ m²

Lights/Computers 75 W/m²

OCCUPANCY ‐ people

Load per person 75 W

Occupant density m² pp

Occ. heat density W/m²

Total heat density W/m²

Cooling : Heating 0.01 ‐

Cooling density 0 W/m²

g 9.8 m²/s

β ##### 1/K

ρ 1.205 kg/m³

c 1005 J/kg‐K

1. Inputs

Geometry

Heating Loads

Cooling Power

Constants

1

T_ext 298 K

25 C

77 F

CHIMNEY HEIGHT

‐ m

OPENINGS ‐ m²

HEATING LOADS

‐ W

COOLING LOADS

‐ W

g β 0.034 m²/s‐K

ρ c 1211 J/m³‐K

2. Input summaryExternal Temperature

Geometry

Heating & Cooling

Constants

1

T_int ‐ K

T_int ‐ C

T_int ‐ F

Q ‐ m³/s

per person ‐ l/s

velocity ‐ m/s

Internal Temperature

Fresh Air Flow

3. Results

1

OPENING 2

OPENING 1

CHIMNEY WIDTH

OCCUPIABLE AREA

CHIMNEY HEIGHT

34 FRESH N’ FOLD

CHIMNEY HEIGHT

CHIMNEY WIDTH

OPENING 1 OPENING 2 OCCUPANCYINTERNAL

TEMPFRESH AIR

FLOW

48’

1.5’

20%(6.68m2)

20%(6.68m2)

HIGH (40p) 25.004 C 4.2 m2/s

LOW (5p) 25.003 C 3.9 m2/s

10%(3.34m2)

HIGH 25.033 C 3.4 m2/s

LOW 25.028 C 3.1 m2/s

10%(3.34m2)

20%HIGH 25.033 C 3.4 m2/s

LOW 25.028 C 3.1 m2/s

10%HIGH 25.1 C 3.0 m2/s

LOW 25.086 C 2.8 m2/s

5’

20%

20%HIGH 25.001 C 4.9 m2/s

LOW 25 C 4.6 m2/s

10%HIGH 25.016 C 3.7 m2/s

LOW 25.014 C 3.4 m2/s

10%

20%HIGH 25.016 C 3.7 m2/s

LOW 25.014 C 3.4 m2/s

10%HIGH 25.066 C 3.1 m2/s

LOW 25.056 C 2.9 m2/s

In the calculation study, we were interested in two key results - the internal temperature and the fresh air flow rate. We anticipated that a narrower chimney would increase air flow through the occupiable space due to the Bernoulli effect within the chimney. This would however affect internal temperatures, creating temperatures closer to that of the external air. Additionally, we anticipated that narrower openings at the occupiable level would discourage air flow out through this opening, as the difference in pressure and temperature in the chimney would induce a buoyancy driven convective flow.

The above results give evidence to the abstraction of the formulas when applied to the unit geometry. It is clear, for instance, that the opening dimension are not contingent on their spatial location, but rather it is the relative dimension (and porosity) that determine the flow rates. We did see slight differences in both internal temperatures and fresh air flow rates due to chimney widths, with a narrower chimney producing both higher temperatures and flow rates. However, we also noticed that the change in occupancy in conjunction with varying chimney widths did not produce any

drastic distinctions - additional internal loads do not intensify changes in temperature or flow rates in a narrow versus wide chimney.

As stated, the geometry of our unit type does not match perfectly to the mathematical model and therefore the results provide guidelines rather than rules for refining of the building design. However, the model did reveal the sensitivity of the overall scheme to macro changes in the design.

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designed porous media

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