Self-Adaptive Membrane

MASTER IN ADVANCED ARCHITECTURE Digital Digital Matter - Intelligent Constructions

2014 /15 SELF-ADAPTIVE MEMBRANE KINETIC PASSIVE SYSTEM

BARCELONA BARCELONA

MASTER IN ADVANCED ARCHITECTURE

SELF-ADAPTIVE MEMBRANE

Research Studio: Digital Matter- Intelligent Constructions

Director: Areti Markopoulou Faculty Assistant: Alexandre Dubor Assistant: Carlos Bausá Martínez

Nohelia Gonzalez Shreyas More

INDEX Abstract

05

Introduction

07

01 State of the art

The Air Flow(er)

Adaptive Skins

Smart Screen 02 Thesis project

08 10 12 14 16

03 Material research

Nitinol SMA (Shape Memory Alloy)

The loop movement

18 20 24

04 Nitinol Joints

Design of joints Conclusions

27 30 39

05 Application on fabrics

Elastic responses on fabrics

SMA in metal rings

Lever machine principle

40 42 44 50

06 Embedding lenses

62

07 Design system

Activation of Nitinol

Design application

76 78 80

08 Passive model

Joint design in the system

Distribution of forces

Project costs

86 88 91 96

09 Conclusion

98

10 References

100

6

Abstract On the advanced approach of architecture some designers have been trying to fill the gap between the kinetic responsive and the totally passive systems. Performative models applied in architecture have been always designed for being electrically driven. The systems in the sustainable category, in spite of reducing the energy expended by automatically respond when the climate conditions are advantageous or disadvantageous for the quality of the controlled environments, still require electricity to work. Even though an improvement is achieved, it seems contradictory that electricity is still needed.

Right now there are two well defined study lines that barely merge. These are the completely passive systems and the performatives. Although it is true that classical passive systems have shown amazing results of the level of comfort of controlled environments, nowadays there seems to exist the need for merging these classical systems with the available technology in order to change the direction of the sustainable design.

Taking advantage of the technology embedded on the smart materials, there is constantly growing possibility to create a new path among the existing design lines, in order to evolve the concept of sustainability, not only for the highly developed areas but also for creating an impact on the underdeveloped communities.

Architecture have been constantly, although not uniformly, evolving and, in an era where the change has been triggered and the sustainability is steering the path, the change is in our hands.

7 05

06

Introduction Avant-garde architecture has been hindered by the lack of cost-efficient manufacturing techniques and limited access to information [1]. In the contemporary time there are innumerable intelligent architectural systems widely used in construction as facades for shading, lighting, and humidity control which have many ways to monitor the mechanism that brings about change in the system to obtain responses. The advantage of these responsive technologies is that they are adaptive to time and changing situations, which can actively address to problems and resolve them. Such systems in architecture are very essential to maximize the efficiently of performance and not having to depend on man force for controlling the machinery.

By the other hand, according to the International Energy Agency (IEA) 47% of the world‘s energy consumption corresponds to indoor environmental comfort control systems [2].

Classic passive systems, applied in the architectural scale, such as cross-ventilation and facade orientation have been one of the responses to the energy problem. However, these systems are not enough.

Moreover, there are many products on the market that use sensors, processors, controls, and motors to automatically close/open blinds when a room becomes too warm/cool. One of the advantages of these automatic systems is that they can help conserve energy that is expended on cooling. However, motorized shades consume electricity in order to operate, and there is no zero-power system existing on the market [3].

The following research is based on how a particular smart material, such as Nitinol Shape Memory Alloys (SMAs), can regulate heat gain and help to conserve energy expended on heating ventilating and air conditioning (HVAC). Our main objective is to develop a system capable to automatically respond to the heat parameter, simply by changing its shape when the rays of sun hits it.

07

Smart materials such as Nitinol and other shape memory alloys have been started to be widely used in the architectural scale. Moreover, many designers that have experimented with this SMAs have used electrically driven systems.

As a base for our research, three projects that use SMAs as actuators were chosen. The aim of all the three projects is to work passively under the heat parameter where in two of three cases, the final prototypes were not tested under real conditions, using an external source of heat as heatguns to simulate it. Since commercial SMA springs activation temperature goes from 20 to 80 degrees, reducing its strength with the reduction of temperature, it is a challenge o the use of it completely passively.

In spite of the effort for developing sensible zero energy systems, the use of SMA is restricted in terms of strength and activation temperature. Projects that have used high temperature, thus strong SMA, stayed on the protorype stage; such is the case of the Air Flower [4] and Adapative Skins [5], where the testing stage was never performed under real conditions. By the other hand, completely passive projects like Smart Screen [3] that perform under environmental temperature are restricted by the stenght of the SMA and the small movement that this creates.

08

01

STATE OF THE ART

09

The Air Flow(er) Lift Architects The Air Flow(er) is an energy independent thermally active ventilation device which behaves like a flower, whose “petals� open wide when exposed to warmer temperatures. It aims to regulate airflow and interior temperatures without electricity.

The active component is a Shape Memory Alloy (SMA) wire. When an SMA is in its lower temperature form, it can be easily deformed into a new shape. However, when the alloy is heated through its transformation temperature, it recovers its original shape with great force.

The four leaf prototype could be used as the operable blind or shade on either the exterior or interior face of a naturally ventilated double-skin facade system.

10

In the summer, the cavity between the inner and outer skin is vented out of the building through the automatic response to temperature. In the winter, a double-skin facade acts as a passive solar heater by using the device to seal the cavity and minimize the faรงade heat loss [4].

Air Flow (er) Lift Architects 11

Adaptive Skins Sushant Verma & Pradeep Devadass, AA School of Architecture

The project investigates responsive building skin systems that adapt to the dynamic environmental conditions. Heat is the primary parameter for regulation, leading to energy efficiency and dynamic spatial effects. A passive skin was developed using SMA springs actuators and regular springs on a tensegrity structure. Fabric pieces were attached to the model so when its active, different shadow patterns are created by the attraction of the structure elements into the heat. Heat gun was used for the performative prototype. [5]

12

Adaptive skins Verma & Devadass 13

Smart Screen Decker Yeadon LLC SmartScreen is a solar shading system that opens and closes in response to changes in ambient room temperature. The system is both a sensor and a motor so it does not require additional sensors, processors, motors, or electricity to operate.

At the low ambient room temperature (21ยบC), the screen would be fully open to absorb solar heat gain; at the high ambient room temperature (26ยบC), the screen would be fully closed to deny solar heat gain.

A customized alloy was used to work under low temperature (compared to regular SMA with activation temperatures from 60ยบC to 90ยบC). Unlike conventional SMAs that allow for a restorable deformation strain of about 7%, the customized SMAs

14

only allow about 1% strain or less. This means the system uses very little movement which has far less movement than a standard, electrically driven SMA. The R-Phase SMA actuator includes a bias spring and center piston that turns the top rod. When warmed, the SMA pushes the piston down; when cooled, the bias spring overcomes the SMA to push the piston back up and open the screen [3].

Smart Screen - Decker & Yeadon 15

The dissertation aims towards

explored in series of experiments

understanding the materiality

to understand the potentials of

of Shape Memory Alloys which

this material for use in architectu-

transforms from one form to the

ral scale.

other on the change of tem-

16

perature and the application of

The aim is to study the materia-

resultant change in form into

lity and behavior of Nitinol SMA

architectural use.

actuator under the parameter of

The main objective of the re-

heat, and design an architectural

search is the develop of a novel

application using the properties

kinetic and passive system able

of expansion, contraction and

to perform only when solar heat

weight bearing strength from

is advantageous or disadvanta-

series of investigations to control

geous. Our aim is to explore the

a responsive architectural system,

gap between the passiveness and

dependent completely on passive

the responsiveness in architecture

heating techniques.

through the development of a

Quoting Decker and Yeadon,

responsive zero energy system.

“Many designers have experimen-

Since Nitinol SMA is a thermo

ted with SMA electrically driven,

responsive smart material, the

however is not a challenge to rai-

main parameter for its activation is

se the temperature to 90 degrees

heat. This particular smart material

by using electricity� [3]. Based on

possesses a great load carrying

this challenge, we directed our

capacity when it is transforming

research in a zero energy system

back to its programmed shape

that could work as both sensor

on deformation. This capacity of

and motor responding mainly to

pulling weights on activation was

the heat of sun.

02 THESIS PROJECT

17

Shape Memory Alloy (SMA) Nickel ti-

recover, when the deformation occurs

tanium, also known as Nitinol, is a me-

at certain temperature, the recovery

tal alloy of nickel and titanium, where

comes right after it at a slightly higher

the two elements are present in roug-

temperature and the material exhibits

hly equal atomic percentages e.g. Niti-

enormous elasticity, some 10-30 times

nol 55, Nitinol 60. Nitinol alloys exhibit

that of ordinary metal. [4]. Commercial

two closely related and unique pro-

SMA springs activation temperature

perties: shape memory and supere-

goes from 20 to 80 degrees, reducing

lasticity (also called pseudoelasticity).

its restorable deformation strain of 7%

Shape memory is the ability of Nitinol

with the reduction of temperature [6].

to undergo deformation at one tem-

On this research, commercial high

perature, on a stage called martensi-

temperature (80°C) SMA springs have

te, and then recover its original, unde-

been used in order to obtain the maxi-

formed shape upon heating above its

mum strenght from them.

“transformation temperature“, on the

A series of weight experiments were

austenite stage. Superelasticity occurs

performed

at a narrow temperature range just

springs and SMA spring to come upon

above its transformation temperature;

the strength of each and finding a ba-

in this case, no heating is necessary

lancer for couple them afterwards.

to cause the undeformed shape to

18

on

conventional

zinc

03

MATERIAL RESEARCH

19

Nitinol SMA (Shape memory alloy) Technical specifications Density

6.45 g/cm3 (0.233 lb/cu in)

Electrical Resistivity (Austenite)

82 X 10-6 Ω.cm

Electrical Resistivity (Martensite)

76 X 10-6 Ω.cm

Thermal Conductivity (Austenite)

0.18 W/cm·K

Thermal Conductivity (Martensite)

0.086 W/cm·K

Coefficient of Thermal Expansion (Austenite)

11 X 10-6 /⁰C

Coefficient of Thermal Expansion (Martensite) 6.6 X 10-6 /⁰C Magnetic Permeability

< 1.002

Magnetic Susceptibility (Austenite)

3.7 X 10-6 emu/g

Magnetic Susceptibility (Martensite)

2.4 X 10-6 emu/g

Elastic Modulus 75-83 GPa Yield Strength 195-690 MPa Poisson‘s Ratio 0.33

20

Austenite

Martensite

At high temperatures, nitinol assumes an interpenetrating face-centered cubic structure referred to as austenite (also known as the parent phase). At low temperatures, nitinol spontaneously transforms to a more complicated body-centered tetragonal crystal structure known as martensite (daughter phase). The temperature at which austenite transforms to martensite is generally referred to as the transformation temperature. More specifically, there are four transition temperatures.

When the alloy is fully austenite, martensite begins to form as the alloy cools at the so-called martensite start, or Ms temperature, and the temperature at which the transformation is complete is called the martensite finish, or Mf temperature. When the alloy is fully martensite and is subjected to heating, austenite starts to form at the As temperature, and finishes at the Af temperature.[7]

21

Weight

00 gm

Zinc spring length 20 mm

Weight

110 gm

Zinc spring length 20 mm

Weight Zinc spring length

Expansion

00 mm

Expansion

03 mm

Expansion

Weight

00 gm

Weight

110 gm

Weight

Zinc spring length 40 mm

Zinc spring length 40 mm

Zinc spring length

Expansion

00 mm

Expansion

10 mm

Expansion

Weight

00 gm

Weight

110 gm

Weight

Zinc spring length 60 mm Expansion 22

00 mm

Zinc spring length 60 mm Expansion

19 mm

Zinc spring length Expansion

Zinc spring test series

330 gm

440 gm

220 gm

Weight

20 mm

Zinc spring length 20 mm

13 mm

Expansion

19 mm

Expansion

39 mm

220 gm

Weight

330 gm

Weight

440 gm

40 mm

Zinc spring length 40 mm

36 mm

Expansion

53 mm

Expansion

82 mm

220 gm

Weight

330 gm

Weight

440 gm

60 mm

Zinc spring length 60 mm

55 mm

Expansion

86 mm

Weight

Zinc spring length 20 mm

Zinc spring length 40 mm

Zinc spring length 60 mm Expansion

121 mm 23

The loop movement Zinc springs as counter - weight

From the series of tests on zinc and Nitinol SMA the capacities of individual springs are identified. This is further coupled together to obtain results when zinc and nitinol is connected in series.

Zinc springs form 20 mm to 60 mm springs were tested in conjunction with SMA springs, resulting the 20 mm test failed since the tension on the hot stage was greater than the system strength. The optimum result with the greatest loop displacement couples a 20 cm SMA spring with a 30 cm zinc spring (a proportion of 40-60%). The displacement ends being 34% of the length of the system.

When the SMA is cold, the zinc spring pulls the nitinol in martensite state. At this phase the zinc spring is active. In application of heat, the Nitinol SMA contracts to reach austenite state and stretches the zinc spring untill the spring is cold again.

This results in a loop movement of the central point of the spring. Depending on passive heating, the idea is to use this loop movemet to creat a change in the system in hot environmental conditions and undo the change when the environmental conditions are cold again.

24

Nitinol SMA spring test series

SMA length 20 mm

SMA length 20 mm

SMA length 20 mm

Weight

110 gm

Weight

220 gm

Weight

Expansion

00 mm

Expansion

10 mm

Expansion

330 gm

SMA length 20 mm Weight

440 gm

22 mm

Expansion

60 mm

Nitinol SMA - zinc spring test series

SMA length Zinc Length

20 mm 30 mm

Displacement 68 mm

SMA length

20 mm

SMA length

20 mm

SMA length

20 mm

Zinc Length

40 mm

Zinc Length

50 mm

Zinc Length

60 mm

Displacement 62 mm

Displacement 56 mm

Displacement 44 mm 25

26

04

NITINOL JOINTS

27

Open assembly of joints with heat actuator Length of zing spring

40 mm

Length of nitinol spring

20 mm

Total extension 54 mm Time to austenite state (contraction)

23 s (21.29 %)

Time of Martensite (expansion)

1 min 25s (78.71%)

Total time 1 min 48 s

Open assembly of joints with electricy as actuator Length of zing spring

40mm

Length of nitinol spring

20mm

Total extension 54mm Time to austenite state (contraction)

09 secs (7.43 %)

Time of Martensite (expansion)

2 mins 1 s (91.67%)

Total time 2 mins 10 s

Closed assembly of joint in aluminum tube Fails due to excessive heating of metal

28

1. Joint at cold temperature

Zinc- contracted (active spring)

Nitinol expanded

Puling joint when the nitinol contracts away from the system mobile point Pushing joint when the nitinol contracts towards the system mobile point 2

Joint at hot temperature

Nitinol- contracted (active spring)

Zinc- expanded

Illustration showing movements of

the spring in two states 29

Design of joints Basic linear actuator After different lengths of springs were studied to obtain maximum displacement, the best result was concentrated on a joint.

The joint is designed with 20mm Nitinol spring and 30mm zinc spring connected in series, following the principles of the optimum movement from the loop movement test. The central point of connection of springs is mobile which slides in either direction while the ends are constricted by an acrylic tube. The Nitinol in martensite is stretched by the zinc spring maintaining equilibrium of forces. On actuation by heat or electricity, on the austenite stage, the Nitinol contracts, displacing the central piece which lengthens the joint by 34mm in a 100 mm joint. On completion of one loop, the displaced point returns to original position.

In brief, the joint behaves as a linear actuator that can be applied in many different designs considering its proportions. In this sense, the joint can be scaled up for a greater displacement considering that this last will be submitted to a 34% of movement regarding the jointâ&#x20AC;&#x2DC;s length. By the other hand, the diameter of the actuator remains the same as it is scaled.

30

6

5

4 3

2

Assembly of joints

1- Joint cap 2- 10 mm nitinol spring 3- Intermediate movable part A

1

4 - Intermediate movable part B 5- 15 mm zinc spring 6- 100 mm x 12 mm acrylic tube 7- Wire to positive battery source

7

8

8 - Wire to negative battery source 31

Nitinol Zinc Joint inside acrylic casing

32

After finalizing a basic casing for the joint, different treatments were tested in order to increase the inside temperature of the joint for reaching the activation temperature (75 -80 째C) of the SMA that is been used.

33

White Joints Test for reflection of light using cylindrical lens

0 min

20 min

Time taken for austenite initiation

20 min 0 sec

Maximum movement of joint

0 mm

Joint Section

Active Joint

34

Black Joints Test for absorption of heat using cylindrical lens

0 min

20 min

Time taken for austenite initiation

14 min 43sec

Maximum movement of joint

08 mm

Joint Section

Active Joint

35

Airtight black Joints Test for rise in temperature in air-tight apparatus using cylindrical lens

0 min

20 min

Time taken for austenite initiation

07 min 02 sec

Maximum movement of joint

08 mm

Joint Section

Active Joint

36

Brass powder filled Joints Test for effect of foreign material introduction using cylindrical lens

0 min

20 min

Time taken for austenite initiation

04 min 04 sec

Maximum movement of joint

08 mm

Joint Section

Active Joint

37

38

1

2

contracted spring

expanded spring

contracted spring

expanded spring

Conclusions It is a challenge to heat over 75째C degrees by using just the power of sun even in hot climates. For this reason, different methods were tested to increase the temperature inside the joint. Among these methods the casing treatment plays a main roll.

Light and heat are both different types of energy, however, light energy can be transformed into heat energy. While dark colors absorb all wavelength of light and transform them into heat, light colors reflect them.

Using this theory as a base, a white coating was used in order to reflect light into the spring. Nevertheless, in 20 minutes under the sun no activation was visible. On this account, black coating was used to absorb light and increase the overall temperature inside the acrylic casing. Since the results showed an activation and contraction of 8 mm in 14 minutes and 43 seconds, a black and airtight joint was tested for avoiding the escape of hot air, showing a reduction of 55 % of the time. Also, a foreigner material with lower heat capacity than air, such as brass, was tested showing an 8 mm contraction in 4 minutes and 4 seconds.

As result, we concluded that the brass introduction in the joint could accelerate the responsiveness on the joint. However, none of the previous experiments showed enough contraction to achieve the optimum movement of 34% of the joint. For this reason, additional methods were tested.

1

Air Specific heat Capacity 1.005 KJ/Kg K

2

Percentage Contraction in sun 21.31%

Brass Specific heat Capacity 0.380 KJ/Kg K

Percentage Contraction in sun 48.99% 39

05

APPLICATION ON FABRICS

41

Elastic responses on fabrics SMA joint in tensile structures

42

0%

activation of nitinol joints

30%

100%

in-between openings

70.69% in-between openings

60%

activation of nitinol joints

46.66% in-between openings

100%

activation of nitinol joints

activation of nitinol joints

40.63% in-between openings

Objective To control different degrees of apertures between the fabric by activation of linear nitinol joints on passive heating. The aim is to be able to control a facade system which controls solar gain in the interior spaces using a complete passive system.

Conclusion The technique of direct application of nitinol joints on fabric is inefficient as the openings are controlled from 100% to 40% due to the limited displacement of each points on the surface of fabric.

43

SMA in metal rings Integration of counter force

44

In order to integrate the responsive SMA joint into the design module, a metallic ring with plastic recovery force was used to substitute the counterforce of the zinc spring. The recovery thereof was tested by measuring the deformation during the active and inactive state of the SMA spring.

Different diameters on the same metallic strip thickness were tested to find the right counterbalance for the maximum loop movement.

a a

b

b

length a

length b

Static state

150 80

Dynamic State

165 48

Difference

15 40

Static state

105 72

Dynamic State

116 45

Difference

11 27 45

Static Fabric 0% activation of nitinol 31.89% opening

Heating Bottom right 100% activation of nitinol 34.51% opening

Heating Top right 100% activation of nitinol 34.51% opening

Heating Top left 100% activation of nitinol 34.51% opening

Heating Bottom left 100% activation of nitinol 46

34.51% opening

Objective Replacing linear nitinol joints with metal rings performing as the countering forces to retract nitinol to original position on cooling to control apertures on passive heating of nitinol spring.

Conclusion The technique of direct application of nitinol joints on fabric is inefficient as the openings are controlled from 31.80% to 52.07% due to the limited displacement of each points on the surface of fabric.

47

48

49

Lever machine principle SMA positioned in a pantograph system

50

The lever machine is one of the six simple machines identified by Renaissance scientists and it consists of a beam or rigid bar pivoted on a fulcrum. It is used to move an object at a second point by a force applied at a third. In an ideal system, the power into the lever equals the power out, and the proportion of output to input force is given by the proportion of the distances from the fulcrum to the points of application of these forces. This is known as the law of the lever [8].

T1= M1 a = M2b = T2

a

b

Since material testing on SMA springs showed great pulling force but relatively short movement, the lever principle was applied in a simple pantograph system where the movement was generated in a central piece which is smaller than the surrounding pieces. In this case, greater force, yet smaller distance, is needed for opening and closing the system.

51

Displacing one point on arc

Displacing two points on

Displacing two points

(open state)

arc (intermediate state)

linear (closed state)

Each single unit has 4 control points at the 4 corners of the frame. Together in a pair, 8 control points can be moved to deform the overall geometry which responds to the needs of the interior space.

By pulling the strings of the fabric using nitinol joints, the angle of the facade at unit level can be controlled to redirect light in the desired direction.

52

Facade iterations

100% Open

75% Open

25% Open

100% Closed

When outside temperature above 35

Actuation temeprature reached

Initiating the system of joints to control the apertures

The facade system is an assembly of units interconnected with Nitinol springs which activate when the temperature of the environment reaches a temperature to heat up the nitinol.

Each two units in the facade have the apparatus based on the lever principle that moves thanks to the Nitinol and zinc springs. For this particular purpose the joint was deconstructed, being placed the SMA springs in the central area, for closing when heated and the zinc springs on the edges for pulling the system to open.

53

System depth changing with seasons The depth in the facade system changes with the needs of controlling the interior spaces. The smart mechanism in the desgin can be connected with learning computers to facilitate different changes in system when the system needs to be override or in cold seasons.

In summer solstice the facade is at its maximum depth and the fabric can be directed towards the light ray to harness diiffused sunlight. and control the amount of heat and light directly coming in.

In winter solstice, the facade is shallow to harness most light and heat while the opening can be controlled to regulate the amount of wind entering in.

A catalog with all the possible movement combinations for each season was developed in order to understand what the system could offer as response to the environmental conditions. In spite of the many combination, in the catalog it can be observed the repetition of shadow and light patterns, which means that the effect of them for the interior climate control was restricted.

The main limitations on this design was that the complexity of it did not respond to the benefits achieved by it. Also, forces as friction and the torque produced by the tensile fabric prevented the membrane from the optimum performance.

54

Galapagos results Exterior

Interior

Increased shading Environmental heat and light Environmental air temperature

Summer solistic - 21st June Increased shading Reduced heat and light Cooler air temperature

Light harness factor 1.97%

Winter solistic - 22nd December Reduced shading Environmental heat and light Environmental air temperature Light harness factor 28.43%

Reduced shading Reduced heat and light Cooler air temperature

Exterior

Exterior on sun

Exterior on shadow

Interior

Interior on sun

Interior on shadow 55

56

Percentage changes with orientation and seasons

57

58

The mechanism of facade includes nitinol and zinc spring ap-

paratus connected to deployable frame which slides over the tracks and closes. The fabric stretched over the two frames behaves as a solar shading in summer and reflects the light from its surface in winters.

59

60

61

The primary actuator for the designed responsive system is the environmental condition of heat. The actuating temperature of Nitinol springs ranges from 45-80 degrees Celsius. In order to make the Nitinol responsive at temperatures over 35 degrees Celsius, lenses are embedded in the system to amplify the heat inside the tubes.

62

06

EMBEDDING LENSES

63

Casting and production process

Since the produced lenses are customized, the focal length was adapted to the current needs. In that sense, the lenses are made with a focal length of 100 mm and 50 mm to focus light at different distances.

Two different techniques were used to cast and produce various types of lenses for finding the highest increase on the temperature by the use of them. The first technique, in the case of linear lenses, a methacrylate tube of an specific diameter (consistent with the focal length) was use to directly pouring liquid plastic and obtaining the lens.

PLA printing, covered with plastic film

Methacrylate tube used as mold for linear lenses

Acetone was used on an ABS printing for removing the layers 64

By the other hand, for more complex geometries, the pieces with the final required shape were 3D printed using Makerbot Replicator for the subsequent casting.

In the case of the plano convex lenses with focal point a PLA piece was printed and the layering texture of the 3D printer was removed by using plastic film. The Film was tighten in order to interpolate the layers and create a smoother surface. After casting, some texture still was observed however the focal point of the lens remain clear. Furthermore, the Fresnel lenses were printed with ABS filament. Since acetone is a solvent for ABS, after the printing, the piece was placed on a metallic cap of a container whose walls were cover with paper tissue and subsequently soaked in acetone. The container was closed and after 40 minutes the fumes solved the top layer of the piece turning it smoother and shiny. However, since the pieces were printed with a 5% infill, after the process the internal structure comes out creating a curvature on the surface.

The concave molds are made using rubber silicon in a container by pouring the liquid in container and immersing a convex surface at the top of the liquid surface or attaching it in the bottom.

Once the rubber is solid (14 hours later), the convex surface is removed to obtain a depression in the mold. After the mold is ready, liquid plastic is poured into it to form a singly convex lens.

65

Hand-made plano convex lenses

Temperature range without lens Date 13-03-2015, 12:40 hrs

Base temperature in Sun

25.10 0 C

Base temperature in shadow

24.40 0 C

Minimum reach in Sun (Tube)

33.30 0 C

Minimum temperature in shadow (Tube) 27.00 0 C Difference (Outside to Inside)

07.30 0 C

Temperature range without lens Date 13-03-2015, 12:40 hrs

Base temperature in Sun

44.50 0 C

Base temperature in shadow

25.40 0 C

Minimum reach in Sun (Tube)

55.50 0 C

Minimum temperature in shadow (Tube) 53.00 0 C Difference (Outside to Inside) 66

08.50 0 C

Arduino connected with thermistor for temperature readings inside the tube joint

Singly convex lens converging light to single focal point to accentuate the temperature inside the nitinol tube joints 67

68

Plano convex lenses Controlling specific points of the SMA to compress

69

Hand-made plastic lenses Plano convex lens

Rise in temperature at focus 6.3째 C

Plano convex lens

Rise in temperature at focus 4.8째 C

Spherical Fresnel lens

Rise in temperature at focus 7.6째 C

The use of lenses showed a significant increase of the temperature inside the joint. Being identified the Fresnel lenses as the most optimal solution. However, casting problems reduced their capacity. Commercial Fresnel lenses, nevertheless, demonstrate being more responsive and effective, besides the power can be controlled by reducing the surface area.

70

Commercial Fresnel lenses

Complete Fresnel lens Surface area of lens

468 cm2

Duration of test

10 sec

Initial temperature

42.60 oC

Final temperature

69.33 oC

Difference temperature

27.73 oC

Partial Fresnel lens 1 Surface area of lens

12 cm2

Duration of test

10 sec

Initial temperature

36.86 oC

Final temperature

45.66 oC

Difference temperature

08.80 oC

Partial Fresnel lens 2 Surface area of lens

4.55 cm2

Duration of test

10 sec

Initial temperature

33.66 oC

Final temperature

39.90 oC

Difference temperature

06.24 oC

71

Customized depth of lenses according to their location

Openings

Nitinol Spring

Openings

Deep Facade for increased shading Facade system- Open

72

Openings

Nitinol Spring

Openings

Shallow Facade for increased day light Facade system- Open

73

Lenses orientation and sun path Direction of solar rays

09:00 hrs

12:00 hrs

15:00 hrs

Day light hrs

74

Lenses work receiving perpendicular rays of light and directing them to a single point, increasing their intensity. Since rays need to be perpendicular, rigid lenses must be either placed in different positions for the activation at different hours in the day or follow the sun path. This last method would mean electricity is needed for the system to perform. However, by using flexible Fresnel lenses, a curved surface can be created in order to respond perpendicularly to the rays without the need of extra movements. The curvature, focal length and area of the lens can be adapted in order to respond to the design needs. Fresnel lenses have proved to be the most appropriate solution to increase the temperature since a small surface is powerful enough to activate the 80 째 C Nitinol SMA and its flexible complexion allows to create curved sections of lenses that are able to capture different sun rays angles besides perpendicular. Inasmuch as every part of one lens surface direct the light to one specific point, a large lens can be cut in sections and reorganized to cast focal points of light in a single line. This method was used for the prototype..

However the most optimal solution is using linear lenses capable to concentrate light in an uniform line, heating the SMA spring evenly and taking its performance to the maximum. This lenses are also available in the market only less frequently..

Focal point Fresnel lenses

Focal line Fresnel lenses

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The advantages of using fabric in the system relies in the application of a flexible material onto which rigid structural elements can be seamlessly planted to achieve complex organic movements. It also eliminates additional joinery allowing complex geometries without increasing the intricacy and weight of the system. Tension elements are also added in order the allow the deformation of the system and its recovery.

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07

DESIGN OF SYSTEM

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Actuation of Nitinol Deploying surface folds using nitinol springs

Linear displacement was applied to simple geometries to study its behaviour in the fabric-rigid elements system. This particular case is a flexible geometry which can be deformed into many possibilities by simply changing the position of the actuators or activating specific points. In this case, SMA was used on 3 points and the deployment was performed by passage of current.

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However, since passive systems can be hard to control, a more restricted geometry was needed in order to have a prediction of the different possible scenarios of actuation. In this sense, various tessellations were explored. A particular tessellation that deploys and expands to create volumetric space was chosen for further development.

On the closed stage, a flat surface built out of square elements is created, whereas the open stage creates a dome - like deformation, revealing the triangular portions of the structure, increasing its height and creating volume. Actuators were located in the center of each set of component to allow/ restrict the movement. and tension elements were set on the edges to enable the recovery of the geometry into its original shape.

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Design application Structural application in three scales

The characteristics of the system, passively kinetic and the movement achieved by using fabric as joinery reduces the possible scale of the structure. For this reason three reasonable small scale applications, at the same time catalogued as small, medium and large, were chosen as design system.

Since the geometry is the same for all of them, the main purpose is to achieve non-uniform deformation which responds to the solar path.

In this sense, when solar heat is greater in some areas than the others, the geometry tends to expand towards that direction. This action could be defined as heliotropism.

The reaction can be applied for different needs depending on the scale however, all of them related with the heat parameter. While in a garment scale it performs to cast shadow over the body, on an architectural scale it creates either small and temporary spaces, suitable for one person or applied in panels on a facade it creates a second skin with variable surface area and volume.

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Smart garments Small scale

In a small scale application, garments were seen as a suitable option. The device, made of light structural inside panels embedded into two fabrics, create an uniform surface that opens up when solar rays reach it, creating a self-adaptive hat that provides shadow only when is needed.

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Stand - alone single person unit Medium scale

The volumetric properties of the geometry can be exploited with structural proposes.

Since the actuation in mainly passive, it can always be open to unpredicted behaviours, for this reason, as a structural piece the geometry is capable of deforming in a small scale. A stand alone single person unit fits the expansion capacities, offering a space created only when sun touches the surface of the flat geometry. It is as a shelter that only appears when is needed. When the geometry is flat, the sun rays hits it evenly, however, when it starts deforming the rays will only reach specific areas, creating different volumetric shapes that correspond directly with the sun path. The entire geometry becomes a motor and a sensor that reacts under the light / heat parameter.

The geometry layering is composed first by a fabric sheet that works as joinery and protection for the inside area. The panels that define the geometry gather energy from the same activation parameter, heat, and this one is stored and transmitted to the inhabitant for simple task like charging devices such as a computer or a mobile.

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01 Nitinol joints -

04

SMA springs with zinc springs 03 02 Binding folds integrated component with nitinol joints

03 Collapsing folds-

02

01

Porous energy absorptive cells for ventilation and storing heat

04 Deploying geometry composite of materials

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Ventilation building skin or roofing system Large scale

In a building scale the structure becomes a skin or additional roof system for passive ventilation and cooling. Set into panels, the skin performs locally adapting its shape according to the position of the sun.

By using the passive SMA joint and the loop movement, no sensors, motors or electricity are necessary in order to respond to the climate conditions.

On this scale, the system can ventilate areas, gather / release heat energy or both. In this sense, only as a skin, the energy exchange happens because of the amount of surface exposed to the sun and the difference on the materials that are temporarily revealed and those which are revealed all the time. By the other hand, as a roof system, the volumetric property of the structure also allows the management of hot/cold masses of air by altering the proportions of the space.

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1 01 Close surface A flat and standard height roof accumulates masses of hot air and prevent them from escaping.

2 02 Open Surface A volumetric roof increases the height of the space and the porous revealed surface allows the hot air to escape.

On a warm climate, hot air accumulates and since it expands, it becomes lighter and moves to the highest points of the room. While this happens, the sun heats the geometry and this starts opening. When opening, not only volume is created to take the hot air higher, leaving room for colder air in the habitable height, but also, a porous area on the geometry is revealed in the process. At this point, the hot air escapes until sun leaves and the geometry closes again.

On cold climates, the exposed flat surface material gathers heat warming the air and avoiding it to escape from the room.

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08

PASSIVE MODEL

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Joint design in the system Embbeding process Basic final joint

06

Linear Fresnel lens

05

Mobile arm

04

03

02

01

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Nitinol SMA and Zinc srpings

Anchor points for the springs

Absorbing surface (optional)

Perforated Tube for ventillation

Joint embbeded with absorbing surface

Joint embbeded without additional surface

A basic and general joint was design with the aim of being adaptable to many different situations where a linear actuation movement is required. For the best performance and most compressed design, linear Fresnel lenses with an approximated focal point of 2 cm are required. Focal length may depend on the design where the joint is applied, while the need of an absorbing surface is subject to the size of the system, since the potential of the lenses depend on the surface area exposed to the sun.

For the study case explored in the research no additional surface was needed since the Fresnel lens area is enough to increase the temperature to 80 째C. For this reason, the system was even more compressed and the loop movement was embedded in a square as thick as the SMA actuator spring.

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Joint embbeded in geometry

05

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Linear Fresnel lens

04

Mobile arm

03

Nitinol SMA and Zinc srpings

02

Anchor points for the springs

01

Case study geometry

Distribution of forces Expanding joint system SMA springs naturally contract when heated. However, the system requires to be open when the rays of sun reaches it. For this reason, the state 0 of the model, before adding the joints its open. By adding a tensile force on the edges of the structure the volume is created. In addition an expanding joint was used, so when the joint is inactive the cable inside it will tense and close the structure and when it is active it will lose the cable allowing the geometry to open.

Active joint - expanding mode

Inctive joint - contracting mode

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Activated passive model.

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Solar rays are magnified by the Fresnel lenses, heating the SMA springs to 80째 C. The contraction of the Nitinol releases the tension induced on the edges of the structure allowing it to open and expand, creating volume and increasing its height in the process 93

Inactive passive model.

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Project’s costs Retrieving with passive environmental control systems In spite of the common believe that smart materials such as Ntinol SMA applied in architecture trigger project’s costs turning it into an unachievable and expensive solution, by the punctual and strategic location of such materials, great results can be accomplished. When system of this kind implemented in architecture, it is important to find the right balance between the impact of the reduction of the expended energy and the energy expended on the system’s production.

The price of commercial SMA spring varies depending on the thickness, length and temperature. The springs used in the project (0,75 mm thickness and 2 cm long springs) have an approximated cost of 10 $, while Fresnel lenses have a cost of 1,5 $. Therefore, the price for the kinetic passive core of the system is 11,5 $ for a 20 by 20 cm panel. Thus, the cost of the developed prototype (80 square centimetres) is around 184 $ and which means 287 $ per square meter, By the other hand, conventional solar panels, the closest approach to a “passive” system capable to respond performatively by using sensor, motors and processors though the electricity generated have an approximated cost of 900 $ per square meter [5]. However, the comparison may be complicated since the standard price for this systems is calculated from kWh and not surface area.

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The approach of working with SMA

the increase of weight and other

Nitinol is mainly to use its smart

complicated joinery. For the na-

properties on a passive system

med reasons the system has been

that works only with solar energy

used in relatively small scale.

and that behaves as a sensor and

By the other hand, the system is

a motor. By using this smart ma-

restricted to 34% of linear mo-

terials we were able to develop a

vement of the total length of

zero energy system, in this case

the joint. However, SMA springs

applied into a structural prototype,

connected in series can be used

but that can be adapted into dif-

to achieve greater displacement

ferent designs that requires linear

as springs connected in parallel

displacements.

can be used to achieve greater

The advantage of a passive - ki-

force of pulling.

netic structure is that it can reduce

As

the amount of energy expended

veloped a novel and sustainable

on climate control of interior areas,

method for kinetic systems which

adapting and responding to many

does not require electricity to per-

different conditions. By the other

form, exploiting the properties of

hand, this represents a system

a commercial smart material and

that can ,not only complement a

helping the climate control without

building design, but also added

the need of any motor, sensor,

to existing structures with lack of

processor or control.

sustainable characteristics.

We believe that the research can

Nonetheless, the system is being

be taken further in other to sur-

limited by the passive condition,

pass the limitations and that can

since is not fully controllable. Also,

be widely apply in real contexts,

the joinery system implanted, a

overcoming the prototype stage

fabric as the element that hold to-

and transforming in tangible ans

gether the system, is used to avoid

sensible architecture.

contribution

we

have

de-

09

CONCLUSION

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100

1

Responsive skin. Aalto University Digital Design Laboratory, ADD.

2

International Energy Agency.

3

SmartScreen: Controlling Solar Heat Gain with Shape-Memory System.

Martina Decker, Peter Yeadon, 2009.

4

Air flower. Lift Achitects.

5

Adaptive skins. Sushant Verma, Pradeep Devadass, 2011 - 2013.

6

International Organization on Shape Memory and Super Elastics technologies.

7

Nitinol Devices and Components.

8

A Simple Lever, Stephen Wolfram.

10

REFERENCES

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