Design and Construction of Bioclimatic Wooden Greenhouses, Volume 3 E-Book

Gian Luca Brunetti

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 382

Veröffentlichungsjahr: 2022

Beschreibung

This book is the third of four dealing with bioclimatic design and construction by focusing on the most basic and polyvalent of modern environmental systems: the bioclimatic greenhouse, the "Swiss-army chainsaw" of architecture. More specifically, this third volume focuses on how the envelope of bioclimatic wooden greenhouses may be designed and built. In more general terms, it helps us to consider how to design and build the transparent and opaque enclosures of bioclimatic, low-energy architecture, with low environmental impact. This multi-volume book covers both free-standing greenhouses that can naturally heat and cool themselves, and lean-to greenhouses that support the natural heating and cooling of buildings; this includes both agricultural greenhouses and greenhouses suited to host people. As a result, it is a trans-disciplinary work deriving its areas of concern from a broad range of study areas, spanning from environmental, to constructional, to structural, drawing the clarity of the approach from the fact that the topics are presented by a single author with a single voice and a designer's mindset. To achieve this, the book adopts a composite set of explanatory strategies and communication registers - including extensive support by 3D construction drawings and examples - and presents not only stateof-the-art solutions, but also experimental ones.

Leseprobe

Table of Contents

Cover

Title Page

Copyright Page

Introduction

1 Prolog – Overview of Types of Transparent Enclosures

1.1. Risks of condensation on transparent enclosures

1.2. Essentials on glass panel enclosures

1.3. Essentials on synthetic panel enclosures

1.4. Curtain walls

1.5. Glazing with glass panels

2 Transparent Plastic Enclosures

2.1. Materials for synthetic panels

2.2. Commonalities between flat polycarbonate, acrylic or fiberglass panels

2.3. Installation of multi-wall polycarbonate or acrylic panels

2.4. Connection of mullions and/or transoms to the transparent panels by means of pressure caps

2.5. Further considerations related to solar shading

2.6. Thermal insulation

2.7. Movable insulation

2.8. Solar reflectors

2.9. Mechanical systems for operating the openable frames

2.10. Opaque envelopes

2.11. Thermally broken external balconies

2.12. Paints, stains and preservatives

3 Film-enclosed Greenhouses

3.1. Characteristics of polyethylene films

3.2. Alternatives to polyethylene films

3.3. Strategies for installing the films

3.4. Specific challenges in polyethylene-enclosed wooden greenhouses

3.5. Multiple polyethylene film layouts

3.6. Film-enclosed greenhouses for hot climates

3.7. Framed structural layouts adopting combinations of portal frames

3.8. Bamboo greenhouses

Conclusion

References

Index

Summary of Volume 1

Summary of Volume 2

Summary of Volume 4

Other titles from iSTE in Civil Engineering and Geomechanics

End User License Agreement

List of Tables

Chapter 2

Table 2.1.

Thermal resistances of cavities of different radiative properties

...

List of Illustrations

Chapter 1

Figure 1.1

Solutions using glazing glue or putty to hold the transparent pan

...

Figure 1.2

Typical wooden curtain wall configuration featuring aluminum pres

...

Figure 1.3

Connection of a structural glass panel to the frame in a curtain

...

Figure 1.4

Joint perpendicular to a roof slope, solved without a pressure ca

...

Figure 1.5

Multi-wall polycarbonate panels. Photo: MaterialScience100, 2014,

...

Figure 1.6

This is the most typical configuration of a curtain wall at a hor

...

Figure 1.7

The configuration seen in this horizontal section is the same as

...

Figure 1.8

The configuration for enclosing the roof is completely similar to

...

Figure 1.9

A solution for the construction of the corner between two façades

...

Figure 1.10

This is another symmetric solution that does not require a speci

...

Figure 1.11

The closure of the angle can be obtained by pressing down rigid

...

Figure 1.12

Another symmetric solution for the corner: pressing down two woo

...

Figure 1.13

This solution is similar to the previous one, but it is asymmetr

...

Figure 1.14

This solution is similar to the previous one, but increases the

...

Figure 1.15

This is a further lapped-mullion solution, obtained by shifting

...

Figure 1.16

This is a symmetric solution that requires a special mullion for

...

Figure 1.17

Thermally insulated transition between a greenhouse roof and a f

...

Figure 1.18

With respect to the previous solution, this one integrates a gut

...

Figure 1.19

In this solution, the gutter has been partially recessed beyond

...

Figure 1.20

In this case, there is a header joist that can be used to work a

...

Figure 1.21

The placement of the framing elements in this solution is opposi

...

Figure 1.22

Gable wall to roof connection. Legend. 1. edge rafter; 2. vapor

...

Figure 1.23

This solution has thicker insulation than the previous one. Addi

...

Figure 1.24

Uninsulated version of the previous solution

Figure 1.25

Different from the previous solutions, this one, thanks to the a

...

Figure 1.26

This solution is the insulated version of the previous one

Figure 1.27

This solution features thicker insulation than the one in the pr

...

Figure 1.28

Connection between a glazed roof and an uninsulated building wal

...

Figure 1.29

The connection of the rafters with the wall is here realized wit

...

Figure 1.30

Connection between the wall and the glazed roof insulated at the

...

Figure 1.31

This solution is similar to the previous one, but in this case,

...

Figure 1.32

Connection between a transparent roof and a transparent back wal

...

Figure 1.33

This solution is insulated only externally to the edge beam

Figure 1.34

In this solution, the vertical plate receiving the rafters is sh

...

Figure 1.35

Transition between an opaque roof covered with profiled sheets a

...

Figure 1.36

The only part of the transition that has a transverse channel is

...

Figure 1.37

Connection between the wall of a building and a gable wall of an

...

Figure 1.38

Connection between an externally insulated wall of a building an

...

Figure 1.39

Thermally improved connection between an externally insulated ve

...

Figure 1.40

Angles traversing the pressure caps to anchor some additional fa

...

Figure 1.41

Anchorage of additional façade systems to a curtain wall by mean

...

Figure 1.42

Transparent panels held in place by Z-shaped steel connectors. I

...

Figure 1.43

In this example, the Z-shaped connectors are positioned in groov

...

Figure 1.44

The rationale for the installation of glass panels as overlapped

...

Figure 1.45

In this solution, the fixed window frames have been kept flush w

...

Figure 1.46

This figure shows that an ordinary window (seen from the outside

...

Figure 1.47

In this configuration (seen from the outside), the windows have

...

Figure 1.48

In this solution (which is being seen from the outside), the fix

...

Figure 1.49

This solution (seen from the inside) is a variant of the previou

...

Figure 1.50

This solution is a variation from the previous one. Here, the wi

...

Figure 1.51

This solution is a variation of the previous one where additiona

...

Figure 1.52

A double façade made of recycled windows built in the context of

...

Figure 1.53

In this solution, a wide astragal has been added to the outside

...

Figure 1.54

In this solution, the window frames have been anchored at the ou

...

Figure 1.55

A greenhouse built with the principle of façades of windows. Pho

...

Figure 1.56

Connection between the fixed window bay and the curtain wall. Le

...

Figure 1.57

In this solution, the joint of the fixed window below the pressu

...

Figure 1.58

In this case, there are two windows, one on top of the other, an

...

Figure 1.59

This is a variant of the solution above in which insulation has

...

Figure 1.60

In this configuration, because two windows are adjacent to the p

...

Figure 1.61

In this solution, the window has been stepped back and heightene

...

Figure 1.62

In this solution, the window frames have been integrated into th

...

Figure 1.63

In this example, the façade is not built as a curtain wall, but

...

Figure 1.64

In this case, the façade frame constituted by mullions and trans

...

Figure 1.65

This solution is a variation from the previous one. Here, the wi

...

Figure 1.66

In this configuration, the glass holders have substituted the wi

...

Figure 1.67

A simple fixed frame. It can be obtained with battens of 6x5 cm,

...

Figure 1.68

This double-step lock creates only one position for hosting a ga

...

Figure 1.69

This arrangement of the frames occupies more space than the prev

...

Figure 1.70

This solution improves on the one above thanks to the double gas

...

Figure 1.71

These two solutions are similar to the two previous ones, but th

...

Figure 1.72

This solution, openable towards the inside, has frames with thre

...

Figure 1.73

This solution, openable towards the inside, has two equalization

...

Figure 1.74

In this case, openable towards the inside, the two equalization

...

Figure 1.75

These solutions are similar to the previous ones, but they are o

...

Figure 1.76

In this example, an ordinary fixed window has been combined with

...

Figure 1.77

An openable window can be integrated into the curtain wall of a

...

Figure 1.78

A wooden stop can be used in place of the rigid plastic foam sto

...

Figure 1.79

As an alternative, the fixed frame can be shaped so as to have t

...

Figure 1.80

Integration of a casement window openable towards the inside int

...

Figure 1.81

Anchoring of a hopper window, seen from indoors

Figure 1.82

The detail in the vertical section can be arranged in a very sim

...

Figure 1.83

When windows are positioned above and below a transom, the joint

...

Figure 1.84

Here, the top joint of the window is protected by an internal fl

...

Figure 1.85

The joint below the transom of the movable frame of a hopper win

...

Figure 1.86

In this arrangement, the window frame is shifted towards the rea

...

Figure 1.87

In this case, the window frame is shifted towards the rear zone

...

Figure 1.88

A window opening towards the outside is more impervious to the e

...

Figure 1.89

The strategies for anchoring a fixed frame to a façade frame do

...

Figure 1.90

The protection from water may be performed simply by the horizon

...

Figure 1.91

When a window is openable towards the outside (awning window), t

...

Figure 1.92

In the absence of a pressure cap, the horizontal joint on top of

...

Figure 1.93

In this solution, here viewed from the inside, the window is pos

...

Figure 1.94

In this arrangement, the thermal bridge shown in the previous fi

...

Figure 1.95

Construction scheme highlighting the criterion with which a skyl

...

Figure 1.96

Construction scheme highlighting the most ordinary criterion wit

...

Figure 1.97

When the skylight shoulders sit on the roof frame and the bays a

...

Figure 1.98

Variant construction for integrating a skylight frame can be int

...

Figure 1.99

In this arrangement, (a) the skylight frames, (b) the flashing p

...

Figure 1.100

Assembly scheme showing how the continuity of the flashing arou

...

Figure 1.101

This drawing refers to the flashing assembly in the previous fi

...

Figure 1.102

Here, the “shoulders” of the skylight have been lined with ther

...

Figure 1.103

The top glass sheet of the skylight should be cantilevered out

...

Figure 1.104

For improving the protection of the down-sloping joint, flashin

...

Figure 1.105

View of a channel at the side of the skylight

Figure 1.106

A channel at the side of the skylight (here seen looking upward

...

Figure 1.107

3D section of the skylight along the slope

Figure 1.108

2D section of the skylight across the slope

Figure 1.109

Relation between the angle of incidence and solar transmittance

...

Figure 1.110

Relation between the number of clear, non-low-e glass sheets in

...

Figure 1.111

Steel angle anchored to the transom to support the glazing

Figure 1.112

Relations between solar heat gain coefficients and light transp

...

Figure 1.113

On the left: 3D section of a window frame with vented double gl

...

Figure 1.114

Strategy for holding the glass panels in the absence of pressur

...

Chapter 2

Figure 2.1

An ingenious way to install polycarbonate or fiberglass sheets sp

...

Figure 2.2

Most usually, corrugated sheets – transparent and opaque – are pu

...

Figure 2.3

An example of an enclosure realized with multi-wall panels. Pavil

...

Figure 2.4

Anchorage of a multi-wall panel by means of thermally unbroken ch

...

Figure 2.5

Anchorage of a multi-wall panel by means of thermally broken alum

...

Figure 2.6

Anchorage of an alveolated panel by means of profiles connectors

...

Figure 2.7

Water “dam” constituted by the gaskets under the pressure caps in

...

Figure 2.8

On the left: multi-wall panels can be put in place as glazing pan

...

Figure 2.9

Using multi-wall panels resembles the use of multiple glass panel

...

Figure 2.10

There is the possibility of treating multi-wall panels as multip

...

Figure 2.11

Besides the possibility of being installed similarly to glass pa

...

Figure 2.12

This image features a hybrid solution: the panels of the curtain

...

Figure 2.13

In this example, both the curtain wall and the window are built

...

Figure 2.14

This super-minimal solution attainable with multi-wall plastic p

...

Figure 2.15

This solution is a variation of the previous one, not requiring

...

Figure 2.16

In this curtain wall solution, the polycarbonate multi-wall pane

...

Figure 2.17

In this variation of the solution in Figure 2.16, the intermedia

...

Figure 2.18

Detailed section of the solution in Figure 2.16 at the intermedi

...

Figure 2.19

Opening rationale for the solution in Figure 2.16

Figure 2.20

The joint of the top transom of the opening frame in the solutio

...

Figure 2.21

The protection of the top transom is also obtained here by canti

...

Figure 2.22

Miter joints are difficult to execute well with hand tools. Draw

...

Figure 2.23

Scheme of some compound window frames and similar window assembl

...

Figure 2.24

This frame is constructed with half-wood connections at the ends

...

Figure 2.25

This window frame is constructed with a lap joint and is easy to

...

Figure 2.26

A large frame is likely to take advantage of the fact that the c

...

Figure 2.27

This bracing scheme is executed with screws parallel to the fram

...

Figure 2.28

This bracing scheme is more rigid than the one in the previous f

...

Figure 2.29

Example of a simple large awning window with no rebates at the j

...

Figure 2.30

Detailed section at a labyrinth of a joint between a fixed frame

...

Figure 2.31

Another example of a simple and large awning window with no reba

...

Figure 2.32

Example of simple large hopper window with no rebates

Figure 2.33

A simple large casement window or door with no rebates

Figure 2.34

Another bracing solution for a simple large casement window or d

...

Figure 2.35

A stronger bracing solution for the simple large casement window

...

Figure 2.36

The simplest bracing solution for a door with no rebates. The di

...

Figure 2.37

If the internal shading devices in a direct solar gain system ar

...

Figure 2.38

Fin sizings required by solutions A, B and C in Figure 4.25, Vol

...

Figure 2.39

Different fin sizings required by the solar staircase configurat

...

Figure 2.40

Scheme of the bioclimatic zoning of the greenhouses extending th

...

Figure 2.41

The interior of a greenhouse in the social housing in Mulhouse s

...

Figure 2.42

Internal shading cloth in a post-and-cable greenhouse

Figure 2.43

Whitish shading cloth stretched below the roof space, to detach,

...

Figure 2.44

Internal shading cloth. The cloth is detached enough from the gl

...

Figure 2.45

The shading devices in this greenhouse are constituted by roller

...

Figure 2.46

Internal black curtain roller, suitable for producing convective

...

Figure 2.47

The shading “devices” that are used in this greenhouse are climb

...

Figure 2.48

Two schemes for the use of thin, vapor-permeable insulation “bla

...

Figure 2.49

Thin, vapor-impermeable reflective insulation blankets installed

...

Figure 2.50

Exterior hinged insulation panels with awning geometries are too

...

Figure 2.51

Rolling shading devices on top of a greenhouse in the botanical

...

Figure 2.52

Multi-layer insulation blankets joined by reflective tape. Photo

...

Figure 2.53

Experimental high-insulation-performance tent enclosed by reflec

...

Figure 2.54

Solar reflectors increase solar gains only when they widen the s

...

Figure 2.55

Implications of different types of reflectors (direct, on the le

...

Figure 2.56

Relation between the angle of incidence of solar radiation from

...

Figure 2.57

An opaque wall can be constructed by adding a stud frame on the

...

Figure 2.58

As an alternative, the mullions can be used as studs of the opaq

...

Figure 2.59

To superinsulate the opaque wall, cutting the thermal bridges by

...

Figure 2.60

When the opaque walls have to possess extra-strength, so as to m

...

Figure 2.61

A very sound alternative way of superinsulating the opaque walls

...

Chapter 3

Figure 3.1

The simplest and most informal opening strategy aimed at ventilat

...

Figure 3.2

This mechanical strategy requiring rotation is well suited to kee

...

Figure 3.3

A solution not requiring any sealing for avoiding water leakage b

...

Figure 3.4

Rounding the timbers at the edges of the greenhouse and smoothing

...

Figure 3.5

Assembling sequence for fixing a polyethylene film in place. From

...

Figure 3.6

Assembling sequence alternative to the previous one. From top: th

...

Figure 3.7

Technique for blocking the films without recurring to winding the

...

Figure 3.8

Where heavy rains are expected to fall and no gutters are used, r

...

Figure 3.9

A plastic envelope-inflated greenhouse in New Zealand. Photo: Eri

...

Figure 3.10

Eden Project, Cornwall. These greenhouse envelopes are constitut

...

Figure 3.11

Project for a medicine warehouse for hot climates exploiting nig

...

Figure 3.12

Single-nave greenhouse shapes suitable for favoring ventilation.

...

Figure 3.13

In large greenhouses, characterized by a low height to floor are

...

Figure 3.14

As said in the caption of the previous image, in a multi-nave (a

...

Figure 3.15

The solution above preserves the size of the inlet despite the p

...

Figure 3.16

Schematic principle for the creation of a post-and-cable polyeth

...

Figure 3.17

A post-and-cable-based polyethylene greenhouse in Almería, Spain

...

Figure 3.18

Extensive plastic greenhouses in Almeria, Spain, built in the po

...

Figure 3.19

A possibility for integrating a clerestory into a greenhouse str

...

Figure 3.20

Hot-climate greenhouse suitable for passive ventilation. This fr

...

Figure 3.21

Another example of a hot-climate greenhouse suitable for passive

...

Figure 3.22

Example of patented ventilated construction system for hot-clima

...

Figure 3.23

Yet another hot-climate greenhouse arrangement. In this case, be

...

Figure 3.24

The post-and-rafter, non-trussed type of frame shown here at the

...

Figure 3.25

Detail of an intermediate gutter in a gutter-connected multi-bay

...

Figure 3.26

Hypothesis for the wooden structure of a hot-climate greenhouse

...

Figure 3.27

Another hypothesis for the wooden structure of a hot-climate gre

...

Figure 3.28

Yet another hypothesis for the wooden structure of a hot-climate

...

Figure 3.29

Hypothesis for a hot-climate wood-framed greenhouse (Author: Gia

...

Figure 3.30

Another hypothesis for a hot-climate wood-framed greenhouse (exp

...

Figure 3.31

Yet another hypothesis for a hot-climate wood-framed greenhouse

...

Figure 3.32

Hypothesis for a hot-climate wood-framed greenhouse (experimenta

...

Figure 3.33

Hypothesis for a hot-climate wood-framed greenhouse (experimenta

...

Figure 3.34

Hypothesis for a hot-climate wood-framed greenhouse (Author: Gia

...

Figure 3.35

Hypotheses of post-and-cable greenhouse frames for hot climates

...

Figure 3.36

Construction scheme of the structure of a hoop greenhouse

Figure 3.37

Assembling criteria for the sides and stake foundation of a low-

...

Figure 3.38

Gable wall of a steel hoop greenhouse. The primary part of the v

...

Figure 3.39

Gable wall of a hoop plastic greenhouse with a wooden framed doo

...

Figure 3.40

Internal view of a multi-bay arched greenhouse

Figure 3.41

A multi-nave arched plastic greenhouse with wide sliding door op

...

Figure 3.42

Drying greenhouse hosting racks for Japanese persimmon. The film

...

Figure 3.43

Main possible ventilation solutions for arched greenhouses, vali

...

Figure 3.44

Bamboo nethouse for tomatoes built with tied connections. Author

...

Guide

Cover Page

Title Page

Copyright Page

Introduction

Table of Contents

Begin Reading

Conclusion

References

Index

Summary of Volume 1

Summary of Volume 2

Summary of Volume 4

Other titles from iSTE in Civil Engineering and Geomechanics

Wiley End User License Agreement

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Series EditorGilles Pijaudier-Cabot

Design and Construction of Bioclimatic Wooden Greenhouses 3

Design of Construction: Envelopes

Gian Luca Brunetti

First published 2022 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK

John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA

www.iste.co.uk

www.wiley.com

© ISTE Ltd 2022The rights of Gian Luca Brunetti to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.

Library of Congress Control Number: 2022941888

British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78630-853-5

Introduction

The topic of this third volume of four is the construction of greenhouse envelopes, transparent envelopes (such as those built with glass panels, plastic panels and plastic films) as well as opaque envelopes. There is a close connection between the second volume – which dealt with structural frames – and this volume; however, of the four volumes that make up this work, there is something that makes this third volume unique: the fact that envelopes are the domain in which most innovations have taken place in the last decades, and are likely to take place in the near future. In the field of greenhouses, only computer-based approaches have undergone advancements of comparable intensity.

Within the domain of greenhouse envelopes, glass panels, rigid plastic panels and transparent films have all seen the introduction of dramatic novelties, but probably no other components have been so revolutionized by innovation as multi-wall translucent plastic panels. In fact, some of the multi-wall plastic panels available on the market today are even perfectly adequate to enclose houses. This extension of the domain of application of rigid plastic panels has contributed to blurring the distinction between construction typologies, as well as that between opaque and transparent enclosures.

However, the components that currently seem the farthest from reaching their full potential of application may not even be multi-wall plastic panels; they are plastic film enclosures. In fact, despite their dominance in the commercial crop-growing sector, an exploration of their possibilities has not yet been accomplished, especially with regard to their multi-layer applications. In this regard, special care has been taken here to explore several experimental framing arrangements suitable for a combination with film layouts. This has been done particularly in the section related to hot-climate greenhouses (section 3.6), given their potential to profit from the thermal transparency of plastic films.

1Prolog – Overview of Types of Transparent Enclosures

The decisions about the types of transparent enclosures to be used in a greenhouse and those related to the kind of frames to which they are connected are highly interrelated. The spans between the members of the frames that hold the transparent panels depend on the bending resistance of the enclosure components, which in turn depends on the type of enclosure material and their installation method.

Transparent enclosures can be obtained from rigid panels or stretched films, and which of the two types of enclosures are used depends on the climate. As a rule of thumb, today, rigid panel enclosures are especially used in climates where snow loads are expected, which are capable of collapsing the plastic films (such as in Central or Northern Europe, or in the northern part of North America), or when greenhouses need to be combined with buildings, and film-enclosed greenhouses are used in most other situations.

The types of materials from which transparent rigid panels can be produced are glass or synthetic materials – mainly plastics. Currently, the main types of glasses used to produce the glass sheets are ordinary clear glass (usually, float glass), toughened glass, tempered glass, laminated glass (multi-layer mutually glued glass layers, usually two or three) and reinforced glass. The main types of synthetic panels currently used are single sheets of polycarbonate, acrylic (polymethylmethacrylate), fiberglass, PVC, or polypropylene, plain or corrugated, and multi-wall (i.e. ribbed, alveolated, containing cells) extruded panels of polycarbonate, acrylic, PVC, or polypropylene, again, plain or corrugated. The properties of the transparent enclosures will be discussed in the section which follows, and are listed in Appendix 3 in Volume 4.

In greenhouses, rigid transparent components other than panels – such as glass blocks or glass-channels (U-glass) – are instead rarely used, due to their substantial weight, low (relatively speaking) transparency, substantial overall length of the joints, construction complexity and often weak interruption of thermal bridges.

On references

The source from which the author profited the most in writing this section and the following ones about construction criteria is by far Allen and Iano (1992), a masterpiece of its kind, full of universal detailed advice. The book by Martin (1977) has been an authoritative source of information on the specific topic of joints. Journals providing invaluable information about construction solutions were Detail (since the 1990s), Arketipo (since 2006) and The Plan (since 2002). On the same topic, the following books have in some way influenced this work: Melet (2002), focusing on Dutch architecture; McLeod (2011, 2015), about timber architecture and glass architecture, respectively; Horbostel and Bennet (1952), referred to an earlier modern “age”, but featuring examples of extraordinary and perhaps unrivalled quality; Siegele (1999), Siegele and Linsler (2002) and Braun, Birk and Heilmeyer (2005), reporting the most interesting cases of details published by the German review Deutsche Bauzeitung in their period of construction; Jenkins and Dezart (1989), Blyth (1994) and Dawson (1996), reporting the most interesting cases of details published by the review The Architects’ Journal in their period of construction; the diverse and enticing collections of architectural details from all around the world by The Images Publishing Group (1999, 2000, 2001); and the robust and thorough collections of details by Ballast (1990) and Stitt (1990), both referring to the North-American context. On the side of scientific journals, the articles by Bissolulis et al. (1997a, b), reviewing the mechanical properties of transparent greenhouse enclosures, and Zhang et al. (1996), reviewing the technical options available for greenhouse enclosures, must be cited.

1.1. Risks of condensation on transparent enclosures

Transparent enclosures usually have a lower thermal resistance than opaque ones and, being vapor-proof, in temperate and cold climates, during winter, they are more likely to cause vapor condensation, with a likelihood that is higher, the higher the thermal conductance of the enclosures. In a greenhouse hosting plants, single-panel glazing in the winter will cause condensation in most cold and temperate climates, while double clear glass panels will cause condensation only in the coldest climates.

A superinsulated greenhouse will have the highest likelihood of avoiding condensation in most situations, but it would require at least triple clear glass panels or double low-e panels. The other side of the coin is that the lower the thermal conductance of the transparent enclosures – and therefore the lower the probability of condensation – the higher the absolute water vapor content left uncondensed in the indoor air, and consequently the greater the advantage of providing heat recovery in the air. This is because, when the air is very moist, and no heat recovery is given, the waste air (the air “used” by plants and/or persons) will have to be exchanged with the outdoor environment anyway, causing a substantial heat loss in the exhausts: a heat loss much greater than that which would have been caused from an equal amount of dry air, due to the fact that a volume of dry air can contain much less heat than the same volume of humid air (i.e. air containing a substantial amount of water vapor). A difference in heat capacity that is in the order of three times, for air at a 100% relative humidity.

Moisture in the indoor air sets the basis for causing winter thermal losses in multiple ways. One is that, as we have just seen, exfiltration of moist air produces greater thermal loss than exfiltration of dry air. The other is that a large vapor content in the air favors condensations on the transparent enclosures during winter, which makes the indoor air lose an additional amount of heat towards the transparent enclosure (because the condensation process, as seen, produces heat) and, ultimately, towards the outdoor environment.

The fact that dry air contains less heat than humid air also explains why cold moist air exerts on the human skin a stronger sensation of cold than cold dry air: because moist air has a higher thermal capacity than dry air, it can transmit more heat – as well as more coolth – to our body.

Furthermore, too much condensation is disadvantageous because it speeds up the decay of the timber greenhouse assembly, and because, when it takes place at the intrados of roofs, it causes drops of cold water to drip onto the plants. This can impact negatively on the health of the plants, because it can provoke thermal shocks and promote the growth of fungi.

The increased risk of growth of fungi in greenhouses is accompanied by an increased risk of pests and diseases, which in turn is due to the closed nature of the greenhouse environment, in combination with the fact that the glazing panels filter out the ultraviolet component of solar radiation, which would have a disinfectant effect.

In greenhouses built in the past, when there was no possibility of using double glass panels, condensation could not be prevented, and therefore the frames holding the glazing panels, in order to avoid the dripping of water droplets from the glazed ceiling, often incorporated channels into their glazing profiles, to make the condensed water flow by gravity and be drained in an orderly fashion (see Volume 1, Figure 3.22). In such cases, the condensed water was usually channeled through the rafters, and from there to the sills, from where it was expelled, or collected into the gutters to be expelled. But that solution is far too complicated for today’s standards. Today, condensation is most usually prevented, rather than channeled, and this is obtained by using transparent enclosures of higher thermal resistance (multi-layer panels in place of single-layer ones), or is dealt with by means of an increased slope of the ceiling.

Using multi-layer transparent enclosures (i.e. transparent enclosures containing cavities in their layers) does a lot to decrease the risks of condensation in winter, but only when the cavities within a transparent enclosure are vapor-tight. If they are not, the presence of the cavities actually increases the likelihood of condensation: only, in this case, the condensation “frontier” shifts towards the inner face of the external transparent layer (panel or film). This happens because the external transparent layer remains colder than it would be if it faced the indoor space directly, and because that layer, in that situation, is not spared the level of moisture of the air within the space.

In the described case, the higher the non-sealed thermal resistance of the layers before the exterior glass is, the higher the likelihood of condensation. A typical situation related to a high probability of condensation is a single-glass enclosure protected from the inside by a non-air-tight (and therefore non-vapor-tight) bubble wrap cover. That said, it should also be considered that placing a bubble wrap cover is the most inexpensive way to improve the thermal performance of a single-layer glass (and suitable to bring its thermal conductance from about 5 to about 4 W/mK). Another situation related to a high probability of condensation is that of movable insulation applied in a non-air-tight and non-vapor-tight fashion (a very likely circumstance) to the inside face of single glazing.

The easiest solution to avoid condensation on a transparent enclosure is to use air-tight multi-layer glazing panels, such as sealed-perimeter double or triple glass panels, or alveolated multi-wall synthetic panels. An alternative solution is treating the inside face of the glazing with antisurfactants, which are suitable for decreasing the surface tension of water, so as to make the likelihood of the appearance of water droplets on the transparent surfaces enclosing the indoor space less likely. (However, it should be noted that antisurfactants have the drawback that their efficacy decreases with time, at such a speed that it can be considered virtually lost after about 18 months, after which the surfaces have to be re-treated to bring the antisurfactant property back.)

A third option, which will be explored further on in this work (see section 1.5.1.2.2), is based on accepting that the condensation between non-air-tight multiple glazing panels will take place, and letting that water out on the spot.

A problematic outcome of the condensation is the fall of water droplets on the crops. This is most likely during the temperature inversions in the early mornings. The problem is exacerbated in tunnel greenhouses enclosed with polyethylene films, due to the fact that they produce large thermal losses, and is particularly evident at the top zone of the vaults, where the intrados is nearly horizontal and less suitable for letting the water flow downwards by sticking to the plastic films. The detachment of the droplets, in those cases, occurs most frequently on the longitudinal wires coupled with the hoops. To make this occurrence less likely, IR-resistant films may be used to decrease thermal losses and therefore condensation; or pointed-arch-framed frames can be used to reduce the quantity of intrados that is nearly horizontal, or, finally, to encourage the water droplets to stick to the intrados, longitudinal wires connecting the parallel hoops may be avoided.

On references

In Pollet and Pieters (1999), the results of measurements of the PAR transmittance of wet and dry greenhouse cladding materials are reported. In Pieters et al. (1997), the light transmission through glass panels and polyethylene enclosures in situations of condensation is quantified. In Geoola et al. (2004), the effectiveness of anti-waterdrop cladding materials is investigated.

1.2. Essentials on glass panel enclosures

The simplest possible type of glass panel used in greenhouses is the single clear one, which is prevalently produced through the so-called float process (Pilkington patent, filed in the 1950s), or, alternatively, by hot rolling. Float glass is cast by making the molten glass float on a pool of molten tin, then letting the glass cool down and solidify on the melted tin, profiting from the fact that the melting temperature of tin – about 230°C – is substantially lower than that of glass (approximately 1,500°C). Usually, the float glass panels employed in greenhouses are annealed – that is, cooled slowly after subsequent re-heating, so as to redistribute the internal tensions arising in them during the first cooling process.

The choice between single-sheet panels and multi-sheet panels (mainly double-sheet, in the case of glass) depends on the climate and greenhouse usage. When the difference in temperature between the inside and the outside is considerable, multi-sheet enclosures are usually preferred. This situation occurs commonly during winter in cold and temperate climates. When that difference is not great, single-sheet enclosures are usually preferred instead (at least as regards the return on investment). This commonly takes place in hot and warm climates, particularly in the case of a greenhouse which is not actively cooled.

Glass units, and expecially multi-layer glass units, can be low-emissivity or clear (non-low-emissivity). For inhabited greenhouses, the choice between low-e glass panels and clear ones is common, while in high-end greenhouses attached to buildings and primarily aimed to plant growing, double clear glass panels (single or double) are usually preferred, due to the substantial reduction in light transparency entailed by low-emissivity panels. Low-e transparent enclosures – double low-e glass panels included – improve the greenhouse effect (because they increase the temperatures derived from solar gains), but they do that at the expense of the amount of daylight admitted.

In temperate climates, the correct position of the low-e film in a double glass panel is on the external face of the internal glass sheet, while in hot climates, at least in the case of actively-cooled greenhouses, that position is on the internal face of the external glass sheet.

The number of glass sheets used in multi-layer glazing panels for greenhouses can be two, or rarely three, and the cavities between the glass sheets must be sealed towards the outside, due to rainwater, while, towards the inside, they can be sealed or unsealed. Sealing is by far the most usual option; but the unsealed option is also feasible, if measures are adopted to drain the condensed water out of the glazing cavities (again, see section 1.5.1.2.2).

1.2.1. Installation of glass panels

Glass panels are usually installed by pressing their edges with gaskets that seal the joints against water and air. The described configuration – which is typical of the most common type of curtain wall, the so-called stick system (i.e. the mullion-and-transom type) – requires a pressor of some kind. In curtain walls, the pressor is usually made up of a pressure cap. In windows, the pressor is made up of the glass holder (that may be nailed, screwed, bolted or snap-locked to the frames, depending on the material and type of the frame), which is also needed to allow for the substitution of the glass sheets. In curtain walls, the pressure cap can be covered or not by a cover cap, which can have esthetic purposes, or can also function as weather protection. The sealants most usually used against the glass sheets are butylic, or made up of polyurethane foams, or silicones.

Putty and traditional window glues are rarely used today, but were the most common solutions in the past – interestingly, allowing us to fix the glass without holders. The reason why they are now rarely used is that, when they were technically fashionable, their lifetime was rather limited, due to the lack of elasticity of the sealant materials used back then. For this reason, they have been gradually substituted with other solutions (see Figure 1.1).

A modern strategy for fixing glass panels without the aid of pressure caps is that of glueing the glass panels, which is made possible by modern, elastic sealants, like silicones. In this situation, the glass panels are held in position by holders “gripping” the grooves at the edge of the panels, along the position of the spacers (see Figure 1.3). This is a solution typical in curtain walls of buildings, which may even be used for greenhouses; but in practice, it seldom is, due to its high cost, and to the lower transparency of the thick, frameless structural glass panels involved, as well as their heavy weight, which puts high functional demands onto the frames backing them. The large thickness of those glass panels, their consequently reduced transparency and their considerable weight are due to the fact that they have to embody in themselves the rigidity and strength that the frames would have provided.

Figure 1.1Solutions using glazing glue or putty to hold the transparent panels to the frame, while at the same time assuring water safety. This straightforward solution is seldom used in modern contexts, but could be revived by modern sealants

Figure 1.2Typical wooden curtain wall configuration featuring aluminum pressure caps. Legend. 1. wooden profile; 2. screw; 3. inner aluminum profile (not mandatory); 4. inner gasket; 5. inner glass sheet; 6. spacer; 7. outer glass sheet; 8. outer gasket; 9. pressure cap; 10. pressure cap cover (not mandatory)

Another reason why structural glass panels are not frequently adopted in greenhouses is their lack of functional redundancy, deriving from the fact that they do not satisfy the basic constructional requirement for technical robustness in waterproofing, constituted by not relying only on the performativity of seals and gaskets, but also on water drainage and water shielding. The rationale of the criterion is: when a construction solution is already watertight without gaskets and sealants, it will likely work even better, and for a longer time, by adding gaskets and sealants to it (Allen and Iano 1992).

Figure 1.3Connection of a structural glass panel to the frame in a curtain wall (at the mullion or at the transom). Legend. 1. aluminum profile; 2. gasket; 3. laminated glass; 4. holder; 5. spacer; 6. tempered or annealed glass

Silicone seals in transparent roofs are often used without pressure caps across the slope. In fact, in these situations, the pressure caps are usually placed so as to close only the joints running on the joints along the roof slope, and the joints that are transversal to the roof slope are usually sealed flush without pressure caps, and without the need to exert any glueing or anchoring action (see Figure 1.4). When even the pressure caps along the slope are absent, the anchoring action must be performed by some other device, such as punctual connections traversing the glass panels, or the joints.

Figure 1.4Joint perpendicular to a roof slope, solved without a pressure cap, but by means of a seal making the joint flush with the glass panels. The pressure caps run along the slope. Legend. 1. transom; 2. gasket; 3. laminated glass; 4. spacer; 5. annealed or tempered glass; 6. backing rod; 7. silicone seal; 8. pressure cap along the slope (this element in the drawing is viewed, not sectioned)

1.3. Essentials on synthetic panel enclosures