The
COMFORT UNIT
developed as part of a Climate Adaptive Skin
Proefschrift
ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,
in het openbaar te verdedigen op dinsdag 4 juni 2013 om 10:00 uur door
Bastiaan Lodewijk Hendrik HASSELAAR
bouwkundig ingenieur, Master of the Built Environment (Sustainable Development) geboren te Gouda, Nederland
Dit proefschrift is goedgekeurd door de promotor: Prof. ir. J.J.M. Cauberg (Em.)
Copromotor: dr. R.M.J. Bokel
Samenstelling van de promotiecommissie:
Rector Magnificus voorzitter
Prof. ir. J.J.M. Cauberg Technische Universiteit Delft, promotor
dr. R.M.J. Bokel Technische Universiteit Delft, copromotor
Prof. dr. ing. U. Knaack Technische Universiteit Delft Prof. dr. ir. W. A. Poelman Universiteit Twente
Prof. dr. ir. J.J.N. Lichtenberg Technische Universiteit Eindhoven Prof. R. Di Giulio, PhD, Arch. University of Ferrara (IT)
Prof. dr. ir. A. van Timmeren Technische Universiteit Delft
Copyright © 2013 B.L.H. Hasselaar
All rights reserved by the author. No part of this publication may be used an/or reproduced in any form or by any means without the prior permission in writing from the author.
Cover photo: water (ice), probably the best known phase change material (Antarctica, Bas Hasselaar, 2010)
Printed by: Proefschriftmaken.nl || Uitgeverij BOXPress Published by: Uitgeverij BOXPress, ‘s-Hertogenbosch ISBN: 978-90-8891-633-5
Preface
During the past six years of doing PhD research, besides learning how to do research and how to write a (scientific) book, some of the most notable events in a person’s life took place: I bought my first car, my first house, got married, and became father of two sons.
Doing a PhD research was not always easy: three months after my official start as a PhD candidate, my promoter, out of the blue, quit his job; I learned the value of hav-ing multiple backups (and havhav-ing them at different places) when our faculty buildhav-ing burned down in 2008, destroying my computer and 5 out of 6 of my backups. In the aftermath of the fire we were forced to first work from tents, then temporary work-places in the Faculty of Civil Engineering, before being moved to the current Faculty of Architecture building, where construction work still took place during the first few months of working there. Again the value of backups became apparent when within a year four laptops from which I worked on my PhD on were stolen as security strug-gled to keep the building safe from thieves, and I learned that being dependent on oth-ers for software, hardware, testing facilities, ordering equipment, response on a ques-tion, or approval for something can be a time consuming and frustrating experience. Good memories will always have the upper hand though, as doing a PhD means that you have little responsibility besides your own work, meaning that you often can decide for yourself where and when you work. I cherish the good memories from the old building where I shared a room with Remco Looman and Martin Tenpierik, my fellow PhD candidates, and with whom I shared many a discussion and game of chess when our heads were full and we needed a break. As the chair of Climate Design grew with an increasing number of PhDs, we earned ourselves the moniker ‘Climate Mafia’ from one of the professors at the faculty, a title we are still proud of. Being a PhD also meant being able to visit conferences abroad (especially before the financial crisis), enabling me to visit places I had never been before, such as Japan, Lebanon and Argentina, meeting many people and absorbing new cultures.
The book that lies before you is the result of almost 5 years of work, spread out over 6, during which time I received help from many people that I would like to acknowledge and thank:
Hans Cauberg, my promoter, for his insight and discussions on how to improve the quality of my research; Regina Bokel, my daily supervisor, for her diligent reading of all my work, her critical feedback and the occasional proverbial kick in the butt and Wim van der Spoel for making the simulation model; without his work my research would not have been possible in its current form.
I would like to thank my review committee, Ulrich Knaack, Wim Poelman, Jos Lich-tenberg, Arjan van Timmeren, and especially Roberto Di Giulio, who came all the way from Italy, for their critical review and insight on how to improve the quality of this thesis.
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Part of my research involved of doing tests in a climate chamber. Related to this part I would like to thank Jos Stegeman of Cauberg Huygen Raadgevend Ingenieurs in Zwolle for allowing me to use the climate chamber and provide support, John van der Vliet from JF Engineering b.v. for lending me measuring equipment and Leon Wolters and Ron Inthout from ASW Gevelbouw for providing the casing for the test units.
From the TU Delft, I would like to thank Hans Weber for his help with ICT related issues and Rein van den Oever for his help with Labview software. From my direct colleagues Kees van der Linden for his positive leadership and relentless efforts to extend my contract when my original contract expired, Arjan van Timmeren for his belief in my work and bringing me in contact with ASW Gevelbouw and Dura Ver-meer/Deerns, Martin Tenpierik, Remco Looman and other fellow PhD colleagues for the valuable discussions about both relevant and irrelevant topics and all my other colleagues from Climate Design for the company and pleasant working environment. On a more personal note, I would like to thank my wife Marja for supporting me no matter what and for providing a home where I am always safe and loved, my parents for raising me to be the person I am, my brother for racing me which one of us would actually get the title ‘dr.’ first, Janus for keeping me sane during our weekly climbing sessions, Alan for our friendship and all my other friends for providing the necessary fun, excitement and relaxation that makes life a joy living.
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‘We must begin by taking note of the countries
and climates in which homes are to be built
if our designs for them are to be correct. One
type of house seems appropriate for Egypt,
another for Spain…. One still different for
Rome… It is obvious that design for homes
ought to conform to diversities of climate.’
Vitruvius 85 – 20 BC
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Contents
Preface I
Summary XI
Samenvatting XIV
Glossary XVII
1 Introduction
3
1.1 The façade and climate control 4
1.2 Office buildings 5
1.3 Problem definition and research questions 6
1.4 Method 7
1.5 Thesis overview 9
2 Climate and comfort
13
2.1 Outdoor climate 13 2.1.1. Test Reference Year 13 2.1.2. Irradiation on vertical surfaces 14 2.2 Indoor thermal climate 16 2.3 Comfort 18 2.3.1. Thermal comfort 19 2.3.2. Air quality 24 2.3.3. Visual comfort 24 2.3.4. Acoustical comfort 26 2.4 Comfort demands for the new façade concept 27
3 Façades and climate control
31
3.1 A short history of the façade 31
VI • 3.3 Decentralised climate control 35 3.3.1. Building Management System 35 3.3.2. Centralised vs. decentralised climate installations 36 3.3.3. Examples of decentralised climate control systems 38 3.3.4. Conclusion 45
4 Designing the Comfort Unit
49
4.1 The Climate Adaptive Skin 49 4.1.1. Assessment criteria 50 4.2 Materials/technologies 52 4.2.1. Phase Change Materials 53 4.2.2. Evaporative cooling 54 4.2.3. Colour changing glass 54 4.2.4. Polarised foils 56 4.2.5. Dynamic insulation 57 4.3 Initial design stage 59 4.3.1. Creative concepts 59 4.3.2. Types of façades 63 4.3.3. Inspiration for first design 66 4.4 Full façade designs 67 4.4.1. Design 1.0 67 4.4.2. Design 1.1 72 4.4.3. Design 2 75 4.4.4. Design 3 76 4.4.5. Design 4 78 4.4.6. Design 5 79 4.5 The Comfort Unit 80
5 The simulation model
87
5.1 Explanation of the simulation model 87
5.1.1. PCM module 88
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5.1.3. Room model 92 5.1.4. Determination of airflow 95 5.2 Standard office model 96 5.3 Comparison of Simulink model with TRNSYS 98 5.3.1. Simple room without window 99 5.3.2. Simple room with window 101 5.3.3. Conclusion 1056 Experimental testing of the Comfort Unit
109
6.1 Experimental setup 109 6.2 Measuring equipment 113 6.3 Method 117 6.3.1. Calibrating the fans 118 6.3.2. Testing the heat exchanger 120 6.3.3. Testing the PCM 121 6.4 Results 125 6.4.1. Heat exchangers 125 6.4.2. PCM 126 6.4.3. TEC heating 131 6.5 Conclusions 132
7 Comparing climate chamber results with simulation results 137
7.1 Simulation input 137 7.1.1. Dimensions of the PCM plates 138 7.1.2. Thermal behaviour of the PCM 138 7.1.3. Interaction between plates and air 139 7.2 Comparing simulations with measurements 140 7.2.1. Original model comparisons 140 7.2.2. Discussion 140 7.2.3. Improved simulations 143 7.3 Conclusion 144
VIII •
8 Performance of the Comfort Unit
149
8.1 Indoor comfort 149 8.1.1. Standard office 149 8.1.2. Comfort Unit 151 8.1.3. Thermal comfort performance in the Dutch climate 153 8.1.4. Effect of the PCM 155 8.2 Energy consumption 157 8.2.1. Passive technologies 157 8.2.2. Energy consumption through heating 161 8.3 Conclusion 163
9 Application of Comfort Unit to new designs
167
9.1 Prerequisites 167 9.1.1. Thermal mass present in the building volume 170 9.1.2. Energy gain from internal sources 171 9.1.3. (Solar) energy gain from external sources 171 9.1.4. Insulation 172 9.1.5. Ventilation 172 9.2 Case studies 173 9.2.1. Cascade office project 173 9.2.2. Design studies by students 174 9.2.3. The Comfort Unit applied to the new ASW headquarters 179 9.3 Conclusions 182
10 Conclusions
185
10.1 Assessment criteria 185 10.1.1. Autonomous operation 185 10.1.2. Flexible 186 10.1.3. Comfortable 187 10.1.4. Energy neutral 188 10.2 The Comfort Unit compared 189 10.3 SWOT analysis of the Comfort Unit 1900
10.4 Concluding 193
Literature 199
Appendix 207
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Summary
At the base of this research stands the research question: In what way would a façade be able to create a comfortable indoor office environment using only the indoor and outdoor environment as its energy sources?
Taking the Dutch climate as a reference, the diurnal outdoor temperatures are (on average) at maximum 17 °C in summer, which is still too cold for a comfortable in-door temperature (which is around 22 °C), while in winter this temperature drops to approximately 2 °C. Indoors, internal heat loads (people, appliances) in combination with solar irradiation through windows cause a rise in temperature that, especially in summer, is higher than the heat loss through the façade, requiring cooling to keep the indoor climate at a comfortable temperature. The low (average) outdoor temperatures suggest that, providing that there is a way to store the cold, the outdoor climate is cold enough to cool the indoor climate through ventilation with fresh outdoor air without resorting to active climate control, such as through centralised air conditioning. To be able to create a comfortable indoor climate, first a proper understanding of ‘comfortable’ is needed. Unfortunately, comfort is subjective to personal preference and dependent on multiple parameters, being psychological, medical and building physical. Parameters that the building has a direct influence on are the physical pa-rameters temperature, air quality, light and sound. Current regulations regarding thermal comfort are for a large part based on research dating back to the 1970s, that has since been updated with progressive insights into the influence the type of build-ing and climate installations have on the perception of a comfortable temperature, and the ability of people to adjust their comfort perception based on their expecta-tions of climate and ability to adapt their behaviour. The quality of (ventilation) air af-fects both productivity of people and their health, and care should be taken to prevent pollution of indoor air from, among others, building materials, office equipment or people, by providing ample ventilation with fresh air. The effects of light and sound on the comfort experience are less well understood, but in general, visual comfort increases with the presence of a (nice) view and availability of daylight, while the al-lowed amount of background noise is dependent on the level of concentration needed for a task. For an average concentration task, the recommended maximum level of background noise tops at 45 dB(A). The thermal comfort guidelines are taken as assessment criteria for the façade design, while the other requirements are used as boundary conditions.
The modern façade, besides being the separation between indoors and outdoors, more and more acts as a dynamic, adaptable entity, providing comfort and status to the user. The way in which a façade performs its tasks differs, however, there are a number of tasks that every building skin fulfils to some extent: (day)light access, thermal energy loss and gain, (ventilation) air access and removal, reducing sound transmission and provide shelter against (rain) water. For climate control, more emphasis has come on the use of decentralised installations. Using decentralised installations instead of
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centralised, the climate installations have a smaller impact on the building and they provide more user control. Most of the decentralised climate control units, however, only feature decentralised ventilation; they are still dependent on centralised instal-lations to provide hot and cold water for heating and cooling
Instead of designing one specific façade, this research aims to create a solution that can be applied to various designs, so that the outcome is not limited to one specific situation, with the goal to be able to create a comfortable indoor climate while con-suming very little energy for climate control. Assessment criteria for the façade are a high level of autonomous and, if possible, energy neutral operation, the ability to create a comfortable indoor climate and to be useful as a concept, i.e. applicable to multiple different façade designs. By using the stand-alone Comfort Unit (CU), besides the general pros and cons of decentralised climate control vs. centralised cli-mate control, optimal use can be made of both internal and external energy sources, thereby reducing the energy consumption for heating and cooling, while the simplici-ty of the design creates a very robust system, in the sense that it has few moving parts and utilises mostly passive technologies, reducing the likelihood of malfunction. The CU is created using the ‘research by design’ method, evolving from a fully in-tegrated façade design to a stand-alone climate unit in combination with an unde-fined façade and a standard office. The CU is designed within a conceptual frame-work that includes the façade and the indoor space, called the Climate Adaptive Skin (CAS). The CAS consists of more or less standard elements and includes high quality shading, but is climatised using a separate decentralised ventilation unit containing PCM (phase change material) plates to store temperature differences between day and night: the CU. The stored thermal energy is used to create ventilation air at a comfortable temperature so that it can be used both for heating and cooling. This CU differentiates itself from systems already on the market by integrating both an air-to-air heat exchanger and thermal storage through the use of PCM in one device, while potential additional heating is achieved through electric heating rather than through the use of a water-to-air heat exchanger, which limits the degree of decentralisation. To validate the CU, its (theoretical) performance is simulated in a custom model using the simulation program Simulink. Within this model, both the behaviour of the CU and the office space, including internal heat production, thermal exchange through the façade, thermal buffering in the floor and ceiling and solar heat gains through the windows have been simulated. Since the quality of a simulation is only as reliable as its input, the reliability of both the room model and the PCM-ventilation model are validated. The room model without PCM is validated by comparing simulation outcomes of a standardised office environment from the Simulink model with the same office environment simulated using TRNSYS, an internationally used energy simulation tool. After some improvements of the Simulink model, the Simulink and TRNSYS model show good agreement. Therefore it is concluded that the Simulink model is sufficiently accurate to be used to predict the thermal behaviour of an indoor space with thermal mass, ventilation and indoor heating load.
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The validation of the PCM model is through building and testing of the CU, devel-oped as part of the CAS concept. Two ventilation units have been built, both contain-ing 30 plates PCM, a heat exchanger, and two fans: one for fresh and one for stale air. The units are identical, save for the heat exchanger, which in one case is 150 mm wide and in the other 250 mm wide. The units are tested in a climate chamber, monitor-ing the (changes in) temperature of the PCM plates and ventilation air. Based on the measurements in the climate chamber, the following conclusions can be made: the design of the ventilation unit itself is not suitable to be applied in real life situations, as the airflow through the unit is sub-optimal. The difference between the wide and narrow heat exchanger is that the wide heat exchanger provides a more even air dis-tribution and less counter pressure, while the thermal efficiency is only slightly lower than the narrow heat exchanger. The latent energy storage in the PCM plates is dis-tributed differently along the phase change temperature range than indicated in the information supplied by the manufacturer, which becomes apparent when comparing test results with simulation results. Once the thermal behaviour of the PCM in the simulation model is adjusted, the model shows good agreement with the test results. The PCM plates are able to condition the ventilation air through thermal exchange. Using the validated simulation model, the optimal settings for the use of a CU in an office environment are determined. In order to make optimal use of the CU, the space it is placed in needs to adhere to a number of prerequisites concerning the amount of thermal mass available as a thermal buffer for the indoor climate, the effectiveness of shading, the amount of thermal mass (PCM) available in the CU, the amount of additional heating, the amount of ventilation and the internal heat load. Once these basic conditions are met, an office room can be kept at a comfortable temperature and provided with ample fresh air all year round using the CU in combination with almost any façade design, while consuming less than 5 kWh/m2 per year for heating.
XIV •
Samenvatting
Aan de basis van dit onderzoek staat de onderzoeksvraag: Op welke manier kan een gevel een comfortabel binnenklimaat realiseren, waarbij slechts gebruik gemaakt wordt van het binnen- en het buitenklimaat als energiebronnen?
In Nederland is de maximale (24-uurs) gemiddelde temperatuur 17 °C in de zomer, wat te laag is als comfortabele binnentemperatuur (rond de 22 °C), terwijl in de win-ter de gemiddelde temperatuur zakt tot ongeveer 2 °C. Binnenshuis zorgt de inwin-terne warmteproductie (mensen, apparatuur) samen met zoninstraling door ramen voor een stijging van de binnentemperatuur die, vooral in de zomer, hoger is dan afkoeling door warmteverlies door de gevel, waardoor er behoefte ontstaat aan koeling om het binnenklimaat op een comfortabele temperatuur te houden. De lage (gemiddelde) buitentemperatuur suggereert dat, zo lang er een manier is om de koelte op te slaan, het buitenklimaat koud genoeg is om het binnenklimaat te koelen door middel van ventilatie met verse buitenlucht zonder dat actieve klimaatbeheersing zoals air con-ditioning nodig is.
Voordat een comfortabel binnenklimaat gecreëerd kan worden is er eerst een goed begrip van ‘comfortabel’ nodig. Helaas is de beleving van comfort afhankelijk van persoonlijke voorkeuren en andere parameters, namelijk psychologische, medische en (bouw)fysische. Parameters die direct door het gebouw beïnvloed worden zijn de fysische parameters temperatuur, lucht kwaliteit, licht en geluid. Huidige regelgeving met betrekking tot comfort is voor een groot deel gebaseerd op onderzoek naar com-fortbeleving uit de 70er jaren, dat sindsdien is aangepast en aangevuld naar aanleiding
van voortschrijdende inzichten in de invloed van een gebouw en klimaatinstallaties op de comfortbeleving, en het vermogen van mensen hun comfortperceptie aan te pas-sen naar verwachtingen en door aanpassing van gedrag. De kwaliteit van (ventilatie) lucht beïnvloedt zowel de productiviteit van mensen als hun gezondheid, en vervuil-ing van binnenlucht door o.a. bouwmaterialen, (kantoor)apparatuur of mensen moet worden vermeden door voldoende te ventileren met verse lucht. De effecten van licht en geluid op de comfortbeleving zijn minder goed bekend, maar over het algemeen neemt het visuele comfort toe bij een (aantrekkelijk) uitzicht en beschikbaarheid van daglicht, terwijl de maximaal geadviseerde hoeveelheid achtergrondgeluid afhanke-lijk is van de mate van concentratie voor een taak. Voor een taak waarbij gemiddelde concentratie nodig is wordt een maximaal aanbevolen achtergrondgeluidsniveau van 45 dB(A) aangehouden. Voor het gevelontwerp in dit onderzoek worden thermische comfortcriteria als leidend aangehouden, waarbij de overige criteria als randvoor-waarden worden meegenomen.
De moderne gevel wordt, behalve als scheiding tussen binnen en buiten, meer en meer ingezet als een dynamisch, aanpasbaar element dat comfort en status levert aan de gebruiker. De manier waarop een gevel gebruikt wordt verschilt, maar er zijn een aantal functies die iedere gevel vervult en beïnvloedt: (dag)lichttoetreding, opwarm-ing en afkoelopwarm-ing, (ventilatie)lucht toe- en afvoer, geluidweropwarm-ing en beschermopwarm-ing tegen
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(regen)water. Voor klimaatbeheersing komt er steeds meer aandacht voor decentrale installaties. Decentrale klimaatinstallaties hebben een kleinere impact op het gebouw waarin ze verwerkt zijn dan centrale installaties, en ze bieden meer controle voor de gebruikers. De meeste van de decentrale klimaatinstallaties bieden echter alleen gedecentraliseerde ventilatie; ze zijn nog steeds afhankelijk van centrale installaties die warm en koud water bieden voor verwarming en koeling.
In plaats van één specifieke gevel te ontwerpen beoogt dit onderzoek een oplossing te creëren voor een verscheidenheid aan gevels - zodat de uitkomst niet gelimiteerd blijft voor één specifieke situatie - met als doel de mogelijkheid om een comfortabel binnenklimaat te realiseren, met een zeer lage energieconsumptie voor klimaatbe-heersing. Beoordelingscriteria voor het ontwikkelde concept zijn een hoge mate van autonomie en, indien mogelijk, energie neutraal functioneren, het vermogen om een comfortabel binnenklimaat te creëren, en inzetbaar als een concept, d.w.z. toepas-baar op verschillende gevelontwerpen. Door gebruik te maken van de Comfort Unit (CU), of comfort kast, kan, afgezien van de voor- en nadelen van decentrale klimaat-beheersing, door gebruik te maken van zowel interne als externe energiebronnen, het energieverbruik voor verwarmen en koelen worden verminderd, terwijl de eenvoud van het ontwerp een zeer robuust systeem oplevert, in de zin dat het weinig beweg-ende delen heeft en voornamelijk gebruik maakt van passieve technologieën waar-door de kans op storing kleiner wordt.
De CU is tot stand gekomen middels de ‘research by design’ methode, waarbij het ontwerp is geëvolueerd van een volledig geïntegreerd gevelontwerp naar een opzich-zelfstaande klimaatbeheersingsbox in combinatie met een ongedefinieerde gevel en een standaard kantoor. De CU is ontworpen binnen een conceptueel raamwerk dat de gevel en de binnenruimte omvat, genaamd de Climate Adaptive Skin (CAS), of klimaat adaptieve gevel. De CAS bestaat uit min of meer standaard elementen en bevat hoge kwaliteit zonwering; maar regelt klimaatbeheersing middels een aparte, gedecentraliseerde ventilatiekast met platen Phase Change Material (PCM, fase ver-anderingsmateriaal) om temperatuurverschillen tussen dag en nacht op te slaan: de CU. De opgeslagen thermische energie wordt ingezet om ventilatielucht van buiten op een comfortabele temperatuur te krijgen zodat deze binnen kan worden gebruikt voor zowel verwarming als koeling. De CU onderscheidt zich van reeds bestaande syste-men door zowel een lucht/lucht warmtewisselaar als thermische opslag met PCM in een apparaat te combineren, waarbij eventuele aanvullende verwarming wordt ver-zorgd door elektrische verwarming in plaats van door middel van een water/lucht warmtewisselaar, wat de mate van decentralisatie beperkt.
Om de CU te valideren wordt het (theoretische) gedrag gesimuleerd met een op maat gemaakt simulatiemodel in het programma Simulink. Met dit model zijn het gedrag van de CU en van de kantoorruimte, inclusief interne warmteproductie, thermische uitwisseling door de gevel, thermische opslag in vloer en plafond en warmtewinst uit zontoetreding door ramen gesimuleerd. Aangezien de betrouwbaarheid van simula-tieresultaten slechts zo hoog is als de betrouwbaarheid van de input, worden zowel het kamermodel als het PCM-ventilatiemodel gevalideerd. Het kamermodel zonder
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PCM is gevalideerd door een standaard kantoor te simuleren in zowel Simulink als in TRNSYS, een internationaal bekend energie-simulatieprogramma, en vervol-gens de resultaten te vergelijken. Na enige verbeteringen aan het Simulink model geven het Simulink model en het TRNSYS model vergelijkbare overeenkomsten. Er wordt daarom geconcludeerd dat het Simulink model voldoende accuraat is om voor-spellingen te doen over het thermisch gedrag van een binnenruimte met thermische massa, ventilatie en interne warmteproductie.
De validatie van het PCM-ventilatiemodel gebeurt middels het bouwen en testen van de CU die ontwikkeld is als onderdeel van het CAS-concept. Twee ventilatiekasten zijn gebouwd, beide met 30 PCM-platen, een warmtewisselaar en twee ventilatoren: een voor toevoer- en een voor afvoerlucht. De kasten zijn identiek, op de warmtewis-selaar na, welke in het ene geval 150 mm en in het andere geval 250 mm breed is. De kasten worden getest in een klimaatkamer, waarbij de (veranderingen in) temper-atuur van de PCM-platen en de ventilatielucht wordt geregistreerd. Op basis van de metingen kunnen de volgende conclusies worden getrokken: het huidige ontwerp van de ventilatiekast is niet geschikt om daadwerkelijk toegepast te worden in gebouwen aangezien de luchtstromingen door het apparaat suboptimaal zijn. Het verschil tussen de brede en de smalle warmtewisselaar is dat de brede wisselaar een meer gelijk-matige luchtstroom en minder tegendruk oplevert, terwijl de thermische efficiëntie slechts marginaal lager is dan bij de smalle warmtewisselaar. Uit de vergelijking van meetresultaten met simulatieresultaten blijkt ook dat de latente warmteopslag in de PCM-platen anders is verdeeld over het temperatuurstraject waarin faseverander-ing optreedt dan de documentatie geleverd door de fabrikant suggereert. Wanneer het thermische gedrag van de PCM in het simulatiemodel is aangepast vertoont het model goede overeenstemming met de testresultaten. De tests zijn succesvol in het aantonen dat de PCM-platen in staat zijn de ventilatielucht te conditioneren door mid-del van thermische uitwisseling.
Middels het gevalideerde simulatiemodel zijn de optimale instellingen voor het ge-bruik van een CU in een kantoorklimaat bepaald. Om optimaal gege-bruik te kunnen maken van een CU moet de ruimte waarin de kast geplaatst wordt aan een aantal eisen voldoen die betrekking hebben op de hoeveelheid thermische massa bereikbaar voor het binnenklimaat, de effectiviteit van zonwering, de hoeveelheid thermische massa (PCM) beschikbaar in de CU, de hoeveelheid aanvullende verwarming, de hoeveelheid ventilatie en de interne warmtelast. Indien aan deze basisvoorwaarden is voldaan kan met de CU het hele jaar door een comfortabel binnenklimaat worden gerealiseerd met ruim voldoende ventilatie, in combinatie met bijna elk gevelontwerp, waarbij minder dan 5 kWh per m2 wordt geconsumeerd voor verwarming.
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Glossary
Abbreviations
ATM active thermal mass
BMS building management system
CAS climate adaptive skin
CU comfort unit
DI dynamic insulation
DSC differential scanning calorimetry
GBA governmental building agency (rijksgebouwendienst)
GTO weighted temp. exceeding hour (gewogen temp.overschrijding)
HE heat exchanger
HVAC heating ventilation air conditioning IR infrared
PCM phase change material
PMV predicted mean vote
PPD predicted percentage dissatisfied PV photovoltaic
RH relative humidity
RMOT running mean outdoor temperature
SBS sick building syndrome
TC thermocouple
TEC Peltier element (thermal electric cooling)
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Dimension Symbol Unit
light intensity I cd
sound pressure level L dB(A)
pressure p hPa mass m kg distance l m surface A m2 volume V m3 litre l dm3 time t s temperature T °C temperature (absolute) T K energy J heat flux W J/s thermal energy transfer coefficient α W/m2K specific heat capacity c J/kgK thermal conductivity λ W/mK (air flow) velocity v m/s density ρ kg/m3
thermal resistance R-value m2K/W
overall heat transfer coefficient U-value W/m2K
average of daily max. and min. temp. Tavg °C
angle of incidence θ °
azimuth of the sun az °
azimuth of the (building) face av °
total (solar) energy transmission factor g-value
-difference quotient d
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Introduction
The simulation model
Analysis of the performance
Climate and comfort
Testing the Comfort Unit
Application to new designs
Façades and climate control
Conclusions
Designing the Comfort Unit
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Introduction
Indoor comfort
Most people spend the largest part of their life indoors. In general this is because the indoor climate is better suited to our needs; indoors we can live and work more com-fortably, meaning that we can be at a state of physical ease without having the desire to be warmer, colder, dryer or better sheltered against wind. Indoors we are protected from the ever changing and unpredictable weather conditions.
Throughout the ages, more and more effort is put into improving the indoor climate. From a fire in a cave, through tents, huts, stone buildings and the first glazed win-dows, we have now reached a state where we can create any climate that is desired, as long as sufficient means such as air conditioning and other building services are available.
Energy demand
Currently, more and more emphasis is put on reducing the energy consumption of buildings, both commercial and residential. Most of these efforts are aimed at reduc-ing the energy consumed by the climate installations: installations that are used to create a comfortable indoor climate through heating, cooling and ventilation. The cli-mate installations are necessary to provide heating/cooling, lighting and ventilation in case the building itself is unable to adequately provide these. All these services are directly related to the outdoor environment, while interacting through the building shell, the façade: heating because it is too cold outside, lighting because not enough daylight is available and ventilation because the outside air is fresher than the inside air.
A façade separates two different environments: the outdoor environment, where in The Netherlands the average temperature during a full day (24 hours) ranges between 3 °C in winter and 17 °C in summer (See also Figure 2.1 on page 14) and the air is considered to be fresh, and the indoor environment, where the average desired tem-perature is 22 °C, a little lower in winter, a little higher in summer, and where the air needs to be refreshed. Indoor heat sources, such as people and appliances (equipment and lighting), but also incoming solar radiation cause a rise in temperature, while heat loss through the building skin, i.e. either windows or the walls themselves, usually causes a drop in temperature, its magnitude being dependent on the outdoor tempera-ture and the insulating properties of the walls and windows (Figure 1.1).
The creation of a comfortable indoor climate is one of the major sources of energy consumption: lighting, mechanical ventilation, heating and cooling, all are dependent on a steady supply of energy. Based on a reference lifespan of 75 years, more than 77 % of the annual environmental load of an office building is caused by energy con-sumption. The three main sources of energy consumption are heating, cooling, and
4 • Chapter 1
lighting and equipment (mainly computers), which almost equally divided constitute 86 % of the environmental load of energy consumption (Dobbelsteen, 2004).
1.1
The façade and climate control
The modern façade no longer acts as a non-changing, two dimensional separator of the in- and outside, but as a dynamic, adaptable entity, providing comfort and status for the user. The way in which this is done varies; there are many different types of façades that take different approaches towards controlling the indoor climate, some with some sort of intelligent, computer controlled system (a building management system, or BMS), and most with the help of centralised climate installations. The cen-tralised installations are active systems: they work through mechanical actions, such as moving a fan to force ventilation or compressing a gas in a heat pump to create cold. Active technologies therefore require more maintenance and/or are more prone to failure, compared to passive technologies that use technologies and materials with properties that can be used beneficially directly, utilising the material properties such as thermal mass to store heat or cold instead of mechanical action. Passive technolo-gies utilise the indoor climate and locally available sources, such as indoor heating loads and available thermal mass in floors and ceilings to control the indoor climate. Considering the important role the façade plays in the separation of indoor and out-door, it would be a logical place to locate the climate installations at the façade: directly mediating between both climates instead of separating, taking over the func-tions of a centralised HVAC (Heating Ventilation Air Conditioning) installation. Since the mean daily outdoor temperature generally is low enough to cool the indoor environment in summer, while the indoor heating load is almost high enough to heat
1
the building in winter (providing there is sufficient insulation), it should be possible to completely condition the indoor environment for the largest part of the year using only natural resources.
Locating the climate installations at or near the façade has more benefits: if each room has its own climate installation that is able to operate autonomously, there is no longer a need to transport conditioned media such as air or water from one point in the building to each individual room, which saves a considerable amount of space since there is no longer a need for ducts, pipes and lowered ceilings. The absence of ducts may also reduce SBS (sick building syndrome) symptoms, as SBS related com-plaints often have to do with ventilation air coming from air ducts that are contami-nated with mould or dust (Brager and de Dear, 1998). By providing each office with its individual installations, building services can be provided where and when they are required, giving the user a more central role. In addition, in case of malfunction-ing, only a single room is affected instead of the full building and installation during the building phase can be a lot easier since prefabrication is possible.
Combining the arguments of a user centred approach with the benefits of decentral-ised installations and the principle that a simple system is more robust, i.e. less prone to failure, than a complex one, the basis is formed to create a new façade concept that relies on simple technologies and is able to autonomously create a comfortable indoor climate while consuming less energy for climate control than current solutions.
1.2
Office buildings
This research focuses on office environments in the Dutch (temperate maritime) cli-mate, because of familiarity with the climatic circumstances at the fact that the re-search takes place in The Netherlands. When looking at the built environment, the largest diversity in façade types occurs in office buildings. This has various reasons: the appearance and quality of a building face reflects the company housed in the building itself and, because of the commercial nature of the building, usually more money, compared to dwellings or factory buildings, is available for the building, and therefore the façade, resulting in increased building quality with possibly improved indoor environment quality and employee productivity. Office façades generally con-tain the largest amount of technical features and play a potentially significant role because of high demands regarding the indoor climate, which is (at least) partially dependent on the façade performance. The office façade therefore offers the largest initial opportunity for innovation, from where it can ‘trickle down’ to other building functions.
6 • Chapter 1
1.3
Problem definition and research
questions
From the introduction above, the problem definition, or main research question, for the research becomes apparent:
In what way would a façade be able to create a comfortable indoor office environ-ment, using only the indoor and outdoor environments as its energy sources?
This question reasons from the presumption that the key to creating a comfortable indoor climate, while consuming as little energy as possible, lies in the improvement of the building shell that separates indoor from outdoor, i.e. the façade. As a working title, this new façade idea or concept is called the Climate Adaptive Skin, or CAS, derived from the principle that the building skin needs to adapt its characteristics to better mediate between different climatic circumstances in order to be optimally suited to create a comfortable indoor climate.
The answer to the main research question lies embedded in a whole field of related questions that together determine the research area. Many different issues, which range from the perception of comfort to the use of HVAC installations in buildings, play a role in determining the research area and should be addressed to determine the research area boundary conditions.
What is comfort and how can it be defined?
Elements that determine boundary conditions for comfort can be found in many sci-entific fields, such as psychological, biological and chemical (airborne pollutants) and building physical fields.
Scientific research into thermal comfort has been going on for at least 50 years (Fanger, 1972, Koch, 1962), with more recent insights indicating that the sensation of comfort of a person is not only dependent on the temperature and air quality, but also on the outdoor weather conditions and the type of building the person is in (Linden et al., 2004, Kurvers et al., 2005).
Key questions about the sensation of comfort that need answering are: • what conditions are regarded as comfortable for the indoor climate; • by what and how is the indoor climate influenced;
• how should the façade react to changing climatic circumstances to ensure a comfortable indoor climate?
The requirements for a comfortable indoor climate are used as guidelines for the creation of the new façade concept. More about comfort can be found in paragraph 2.3 Comfort. How a façade should react to ensure a comfortable indoor climate is a more complicated question, that is answered at the end of the research in Chapter 8 Performance of the Comfort Unit.
1
What is missing from the current status quo in façade design?
A lot is happening in the improvement of façades. The building industry is a large one, and as such, much development is put into the improvement of the performance of the façade in terms of insulation, appearance, structural characteristics, but also into the possibility of making the façade responsible for climate control. Many of these initiatives concentrate on integrating small-scale HVAC installations into the façade, or placing small-scale HVAC installations near or at the façade. More infor-mation on façades can be found in Chapter 3 Façades and climate control.
Why is it important to use only the indoor and outdoor environments as an energy source?
This research takes the approach of using passive technologies, such as heat exchang-ers and thermal storage in the façade in combination with a simple temperature ori-ented control system, to let the façade mediate between indoor and outdoor environ-ments, thereby resulting in a comfortable indoor climate. This approach is different from the prevalent status quo, in the way that it focuses on passive instead of active, aiming to be low-tech instead of high-tech. The presumed benefits of this approach are that the façade consumes very little energy, and that the chance of malfunction-ing is very small: few movmalfunction-ing parts mean that few parts can break down, resultmalfunction-ing in a façade that is reliable in operation. By limiting the available energy sources to the indoor and outdoor environments, discarding sources that are tied to a site or building, such as the use of aquifers or centralised HVAC, the consequence for the façade is that it must be able to function autonomously, meaning that it must be able to deliver the conditions that are needed to create a comfortable office environment by itself. This in turn has its consequences on both the façade itself, but also on the building it is part of.
Key questions about using the environment, both indoor and outdoor to this research are:
• in what way is it possible to use the façade as a buffer between indoor and outdoor climate;
• what materials and/or technologies are suitable to be used;
• how can the energy buffered in the façade be used to condition the indoor climate.
This, and the consequences the above considerations have on the building, are further elaborated in Chapter 4 Designing the Comfort Unit.
1.4
Method
To create a CAS, roughly two different approaches can be taken. One is to list and investigate every option available, determine its consequences, investigate all possi-ble material combinations and evaluate every solution, ultimately resulting in a final, potential façade. The problem with this approach is that the amount of work involved
8 • Chapter 1
quickly becomes infinite, as every new option presents itself with numerous addi-tional consequences and that it becomes increasingly difficult to compare and assess different solutions, as each solution has its own unique characteristics that may not be superior or inferior to other solutions, but just different.
The second approach is letting a façade concept or design evolve, starting with an initial design based on literature research and reason that, at first glance, may seem to fit most requirements set by the designer. This design can then be assessed, short of building it, either by throwing different theoretical scenarios at it, or by computer simulation, revealing its flaws, which in turn can be solved in the second iteration of the façade design. The design thus evolves into a façade that is best suited for all the requirements it is weighed against. This method is called Research by Design, and is the method of choice in this research.
If a design claims to be the result of scientific activity (i.e. research), it should com-ply with general requirements put to the scientific approach. The following criteria should be met if design is a product of science (Jong T.M. de & Voordt D.J.M. van der, 2002):
• novelty compared to state of the art of technique;
• design methodological approach with a subjectivity that is argued; • construction and materialisation in reality, if applicable;
• evaluation of actual performance of the design, compared to the performance intended;
• integration of design, development and study;
• integration of designing on different levels of scale (vertical integration); • integration of partial designs and aspects (horizontal integration);
• a vision on future development of the domain – in terms of design, discipline and science – the programme deals with.
Many scientists and designers agree that a design as a produce of scientific work should be based on a transparent process that may be assessed; a logically valid ar-gumentation and accessible source of documentation. The design process, including the argumentation that lead to specific design choices is described in Chapter 4 De-signing the Comfort Unit, while the other criteria listed above are all met during this research.
In the course of the research, the concept of a full façade that incorporates all ele-ments necessary to create a comfortable indoor climate (the CAS) evolved into re-search of a stand-alone ventilation unit that can be added to any façade design. This Comfort Unit is an element placed within an (office) room that controls heating, cool-ing and ventilation. It, however, is not solely responsible for the indoor climate; ther-mal storage in the building mass, solar irradiance and therther-mal exchange through the façade also have an effect. Before building a full-scale office with a Comfort Unit in real life and monitoring its performance, its performance is predicted by simulating it using a computer simulation program. Since the unit contains several technologies that are linked, simulating its performance basically consists of simulating the
differ-1
ent components and linking them together while placed in a room, using the output of one component as input for the next. More information about the simulation model is given in Chapter 5 The simulation model.
Based on the designs and preliminary simulations, two prototypes, or test units, of the Comfort Unit, have been made, that are tested in the (thermally) controlled envi-ronment of a climate chamber (Chapter 6 Experimental testing of the Comfort Unit). This allowed controlled testing of the performance of the Comfort Unit, which in turn allowed validation of the simulation model by comparing measured test results with simulated test results (Chapter 7 Comparing climate chamber results with simulation results). Chapter 8 Performance of the Comfort Unit, describes the results of the sub-sequent simulated performance of the Comfort Unit.
To demonstrate in what way the Comfort Unit might be applied to different building designs, Chapter 9 Application of Comfort Unit to new designs, gives examples of building designs with the Comfort Unit applied, as well as some prerequisites for the building to make optimal use of the unit.
1.5
Thesis overview
This thesis describes the development and validation of a ventilation unit that enables the creation of a comfortable, energy efficient indoor climate. As such, it contains in-formation about all different steps undertaken in the development and validation pro-cess, some or most of which will not be interesting to all readers. To facilitate reading only the parts that are of interest to a certain reader, the chapters can be grouped into specific topics, which can subsequently be read if the topic seems interesting, while skipping past the parts that may not be of interest.
The layout of the different topics is outlined in the graph on the next page and can be distinguished by the coloured lines:
The yellow line is for the reader interested in learning the topic and conclusions of this thesis, but has no time to read the full book. By reading the introduction the main research question can be learned, which is answered in the conclusions.
The green line indicates chapters that provide information, both about topics that form the theoretical background of the research, and information from current practice that act as the current state-of-the-art with regards to decentralised climate control. The blue line indicates the more creative side of the research, describing the process that has led to the creation of the concept and the design that is both simulated and tested. Examples of the applied concept can also be found here.
For those interested in the scientific basis of the façade concept, the red line describes the simulation process and the climate chamber tests and how these have contributed to the validation of the full façade concept.
10 • Chapter 1
Overview
Information
Design
Validation
1 Introduction
2 Climate and comfort 3 Façades and climate control
4 Designing the Comfort Unit
5 The simulation model 6 Experimental testing of the
Comfort Unit 7 Comparing climate
cham-ber results with simulation results
8 Performance of the Comfort Unit 9 Application of Comfort Unit to
new designs 10 Conclusions
2
1
0
5
2
6
9
3
7
10
4
8
Introduction
Analysis of the performance
Climate and comfort
Testing the Comfort Unit
Application to new designs
Façades and climate control
Conclusions
Designing the Comfort Unit
Comparing results
The simulation model
2
2
Climate and comfort
The façade of a building is where indoor and outdoor climate meet, and its purpose, besides being the ‘face’ of a building, is to shelter the indoor climate from external influences and facilitate a comfortable indoor environment.
2.1
Outdoor climate
The Netherlands have a maritime climate, with average outdoor temperatures be-tween 3 °C in winter and 17 °C in summer (Figure 2.1).
2.1.1. Test Reference Year
For many situations (e.g. simulations) it is necessary to have data about the outdoor climate, such as temperature, solar load, relative humidity etc. The difficulty with the outdoor climate however is that it is ever changing, while at the same time it is not an option to use average values for certain applications, because especially the extremes in a year can determine whether a system, (such as a building façade) per-forms well or not. To this end, standard reference years have been determined. In the Netherlands, since the 1970s the year 1964 is used as a reference year as it leads to representative values for energy consumption for heating and cooling, while it also has sufficient hot days in summer to predict the performance of the building in very warm weather.
However, in recent years it became apparent that the use of climate data from 1964 in simulations may lead to too conservative predictions, especially for the number of hot hours, resulting in a higher number of hours where the indoor temperature is too high for comfort than was originally simulated. For that reason, it is often recommended to also include the year 1995 in calculations, which is a much warmer year than 1964; using 1964 alone can lead to an underestimate of the cooling load hours by up to 25 % (Schijndel and Zeiler, 2006).
In the light of recent climate changes, which trend towards higher temperatures, the need arose for better Test Reference Years (TRY) for the determination of energy consumption. To that end, a new reference year has been defined (Figure 2.1 on the next page), which is described in NEN 5060 (2008).
Within the norm NEN 5060 (NEN 5060, 2008), besides the new reference year which is meant to replace the old test reference year, three more reference years are present-ed with climatic conditions that can expectpresent-ed to be excepresent-edpresent-ed with a 5, 2 or 1 percent probability (see also Table 2.1). It is up to the commissioner of a building to decide how strict the demands for the indoor climate are and which climate year should be taken as a reference, which has its influence on how climate installations should be dimensioned.
14 • Chapter 2
2.1.2. Irradiation on vertical surfaces
Solar irradiation on a vertical surface, such as a façade, displays a very different behaviour compared to a horizontal surface: on a horizontal surface, the maximum irradiation level is reached at mid-day, when the sun is at its highest point (assum-ing clear skies), regardless of orientation (there is only one) or season. On vertical façades however, the orientation plays a very important role, as does the season, as is Figure 2.1: New Dutch reference year: temperatures with averages during day (red), night
(blue) and overall (white) of the standard reference year with 20 % probability of being exceeded (NEN 5060, 2008)
Table 2.1: selected years per month for the reference year for exceeding hours for heat/ cold simulations (NEN 5060, 2008)
probability of exceeding 20 % 5 % 2 % 1 % January 2003 2003 1997b 1987 b February 2004 1994 1991b 1986b March 1992 1989 1990 1991 April 2002 1991 1987 2003 May 1986 1988 1989 1992 June 2000 1989 1995 2005 July 2002 2003 2001 1995a August 2000 1995 2003a 2004a September 1992 2004 1999 1991 October 2004 2001 1990 1995 November 2001 2005 1999 1996 December 2003 1989 2002 1996
a contains heat wave
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illustrated by Figure 2.2 and Figure 2.3: as the sun travels along different paths across the sky in summer and winter, the angle of incidence on a vertical surface also varies between seasons. Contrary to horizontal surfaces, this means that the orientation that
Figure 2.2: 24 h average irradiation (both direct and indirect) levels on different orientations during a full reference year
Figure 2.3: Irradiation (both direct and indirect) on vertical faces on different orientations during a clear day close to the longest (top) and shortest (bottom) day of the year
16 • Chapter 2
receives the most irradiation can change through the year, as illustrated by Figure 2.2: in summer, the façade that receives the highest 24 h average irradiation is not auto-matically the southern façade, but may also be the eastern or werstern, depending on the weather, as differences between the three orientations are very small. This can be explained by the fact that the sun rises in the east and sets in the west, and that at sun-rise (or sunset) the sun is perpendicular to the east (or west) façade (at solar equinox), creating maximum exposure, while during midday, the sun is oriented towards the south façade at an angle of approximately 30°. In winter, the number of daylight hours is lower, and the angle of the sun is closer to perpendicular (approximately 75°), caus-ing a much higher irradiation level on the south face compared to the east or west. The effect the time of day has on the amount of irradiation on different orientations is clearly visible in Figure 2.3: the sun rises in the east and sets in the west, travelling along the southern hemisphere (seen from the northern hemisphere). The effect this has is clearly visible in the different orientations: irradiation levels peak in the morn-ing on the eastern face, followed by the southern and finally western face. In summer, the northern face may display small peaks in the morning and afternoon, when the sun rises slightly north of due east, and sets slightly north of due west.
It is also important to realise that, although the northern façade of a building only occasionally receives direct solar irradiation (during a few hours in summer), the in-direct radiation still can provide a significant source of energy, especially on overcast days when there is more indirect light.
2.2
Indoor thermal climate
The indoor climate is influenced by many factors that all together create a climate that can be experienced differently by different people. As such there is no solid defi-nition of a comfortable climate (see also paragraph 2.3), but the factors that create the climate can be distinguished.
When speaking of the indoor climate, most of the time the thermal climate is meant, which is often simplified to the air temperature. The perceived indoor temperature, or the operative temperature, is a combination of the radiative temperature in a room (radiative temperature emitted by the surfaces surrounding the subject) and the air temperature in the room, both of which count for 50 % when determining the opera-tive temperature (e.g. if the air temperature is 22 °C and the radiaopera-tive temperature is 20 °C then the operative is 21 °C).
The indoor thermal climate is the result of heat transmission through the façade through radiation (e.g solar radiation) or conduction (reduced by insulation) and con-vection, indoor heat production (e.g. artificial lighting, people), heat storage (in ther-mal mass) and influences from climate installations (e.g. ventilation or heating). The only source of energy originating from inside is the indoor heat production. Every space that is in use has some amount of internal heat production that originates
2
from the use of artificial lighting, appliances such as computers or printers, and the presence of people.
Typical values for the heat production by persons and artificial lighting are listed in Table 2.2 and Table 2.3 (Schalkoort, 2009); in office settings, appliances such as printers and computers add on average another 10 W/m2 each per person.
In a standard sized office space (5.4 by 3.6 m, based on a grid of 0.9 m) with two people (based on 10 m2 floor area per person) the indoor heat production can be
calcu-lated as follows, for three different scenarios with low, average and high indoor heat production (EU Energy Star, 2009, NEN 5067, 1985):
• A low internal heating load would be if one person would be present (100 W), working on a laptop (12 W) with only half of the room artificially lit (10 W/ m2), amounting to a low average of 11 W/m2.
• An average heat production is 30 W/m2: two people present, each with their
own computer (average desktop computer with a 17 inch LCD screen; 90 W) and the full room artificially lit, the total average heating load per m2
becomes 30 W/m2.
• A high indoor heating load comes from 2 people, each with a high-powered desktop computer (190 W) and a large 30-inch screen (108 W) and a laser printer (13 W standby mode) with ample lighting (12 W/m2), amounting to a
high average of 54 W/m2.
Climate installations (can) have a large influence on the indoor climate, depending on Table 2.2: average heat production of persons
Activity W/person
sitting calmly 80
sedentary office work 100
standing office work 110
sitting light assembly work 115
standing light assembly work 150
laboratory work 110 walking (0.8 m/s) 120 walking (1.2 m/s) 150 gymnastics 160 tennis 240 squash/basketball 300
Table 2.3: average heat production of lighting
Type of lighting W/m2 floor area
workplace lighting 2.5
general lighting 400-500 lux
with air extraction through fittings 5
with fittings without extraction 10
18 • Chapter 2
the size and type of installations they can completely condition the indoor climate. This does not, however, guarantee that the climate is also experienced as comfortable as many factors play a role in the comfort experience of people. More information about this can be found in paragraph 2.3.
2.3
Comfort
A basic measure of the quality of the indoor climate is the degree of satisfaction experienced by people who work in it. Human comfort is clearly influenced by the physical environment: a comfortable temperature, the absence of disturbing odours and other polluting substances, appropriate lighting distribution and low noise levels contribute to a comfortable indoor climate. The perception of the physical factors, however, is strongly influenced by physiological, behavioural and psychological vari-ables.
Systems for indoor climate control (climate installations or services) are designed and dimensioned to maintain the indoor climate within the desired range for most of the time. The range can occasionally be wider and outside the comfort zone, to limit the installation size and save money. However, problems with human comfort, health and productivity can be expected if the parameters fall outside the comfort zone for extended periods of time. Many building related environmental factors are linked to human health, e.g. leading to sick building syndrome (SBS) symptoms, with most attention going to indoor air quality. Other factors may also play important roles in SBS, such as noise, light, thermal climate and psychosocial factors: dissatisfaction with the working atmosphere, a person’s position within a company, problems with the organisation structure or private problems may be expressed through complaints about one’s health. Research has shown that many health complaints are related to building characteristics. Minor problems that are not building related can be trig-gered to become major obstacles through an uncomfortable working environment (Nilsson, 2003).
In office buildings the productivity of the employees is linked to their sensation of comfort. Depending on the source consulted, the annualised cost for the construction of an (office) building is stated to be between 5 and 10 % of the total annual cost for an enterprise over 20 years, while employee cost varies between 75 and 92 % of total expenditure (Winch, 2005, Ree and Hartjes, 2003). Although productivity (the ability to perform various tasks, both mentally and physically demanding) has been shown to be influenced by the indoor environment, particularly the thermal, acoustic and atmospheric (air quality), measuring productivity is not a straightforward process. In 1991, a brochure published by VROM stated that in all of 61 office buildings studied (occupying 7000 employees) at least 20 % of the employees had complaints about the indoor climate adding up to an estimated one million days of absence from work per year (VROM et al., 1991). Creating a comfortable working environment is therefore likely to pay off as people spend less time thinking about the indoor climate and can
2
focus more on their work. Often, the basis for investigating productivity is a financial one: if the cost for one employee in an office is €50,000 per year, a productivity loss of 0.5 % is more expensive than the cost of a good air conditioning system (Nilsson, 2003).
The physical factors that influence the indoor climate consist of four factors: thermal climate, indoor air quality, sound and light. Within this research, the psychological aspects of comfort are not included as they are user and/or site specific and (currently) cannot be expressed in physical requirements for a façade. No additional research is carried out into comfort perception of users, instead, existing research is used to specify the limiting comfort factors of the physical aspects, as these are directly re-lated to building physical properties.
2.3.1. Thermal comfort
Up until the 1960s, buildings were built without mechanical cooling; the temperature was controlled using architectural or building physical solutions. Measures to prevent uncomfortably high indoor temperatures were an important part of the architectural design and architects realised that a comfortable indoor climate was for a large part dependent on the design choices they made. This situation slowly changed with the introduction of air conditioning, which made conditioning of indoor spaces possible independent of the (building physical) quality of the building. Architects were now able to concentrate more on the shape and visual appearance of a building, while the indoor climate was left for specialised consultants and contractors who, most of the time, were bound by boundaries set by the architect. Through developments of HVAC technologies, a need arose for better-substantiated data concerning comfort-able indoor temperatures. The most well known research into indoor comfort is the research performed by the Danish researcher Fanger (Fanger, 1972), researching the thermal comfort of 1300 students in a climate chamber. People were asked how they felt using a 7-point thermal scale:
+3 Hot +2 Warm +1 Slightly warm 0 Neutral –1 Slightly cool –2 Cool –3 Cold
Using these assessments and data from the climate chamber, the average thermal sen-sation of a theoretical group of people in a homogenous indoor climate could be pre-dicted (Prepre-dicted Mean Vote or PMV) with the corresponding theoretical percentage of people dissatisfied with the climate the Predicted Percentage of Dissatisfied (PPD); a PMV of, for example, 0.5 corresponds with 10 % of the people who are dissatisfied with the indoor climate (Figure 2.4).
20 • Chapter 2
According to Fanger, it is impossible to create one indoor climate condition that pleases every person in the building. Because of differences between people’s per-sonal preferences, at least 5 % of the people will be dissatisfied with the current ambi-ent climate (see also Figure 2.4).
The Fanger method gained interest as it provides an apparent accuracy through the PMV-index and it was the basis for standards and guidelines that define temperature limits for buildings and that are used to this day in large parts of the world, including The Netherlands.
Thermal comfort guidelines
In the 1970s, the Dutch Government Buildings Agency (GBA) determined that a ‘good’ indoor climate should meet -0.5 < PMV < 0.5 (10 % dissatisfied). Exceeding these boundaries was allowed during special circumstances (heat or cold wave, or malfunctioning in the climate installations) within -1.0 < PMV < 1.0 (25 % dissatis-fied) during a maximum of 10 % of the time people are present (100 hours in sum-mer). Later, this evolved into the Exceeding Hour (TO)-method of the GBA stating that an indoor temperature corresponding to a PMV of (+ or -) 0.5 is allowed to be undershot or exceeded for a maximum 5 % (each) of the working hours per year, ef-fectively meaning that a temperature of 20 °C and 25.5 °C is allowed to be undershot resp. exceeded for maximum 100 hours per year (each). On top of that, a minimum temperature of 18 °C and a maximum temperature of 28 °C is allowed to be under-shot/exceeded for a maximum 1 % of the year, i.e. a maximum of 20 hours each. Later, the Weighted Exceeding Hour (GTO)-method was added, weighing the ex-tent of how much a temperature is exceeded with the PPD and the duration of the exceeding hours: the weighting factor is 1 at a PMV of 0.5, so one hour with a PMV of 0.7 has approximately the same impact as 1.5 hours with a PMV of 0.5. For office buildings, the maximum total of weighted exceeding hours per year is 150, based on a class B building (‘good’), which is the normal reference. A class A building is al-lowed a maximum of 100 hours (‘very good’), while a class C building is alal-lowed 250 hours (‘acceptable’). 1964 is used as a reference year for these calculations (Alphen
2
et al., 2008, Linden et al., 2002). This year is, however, in the light of recent climate changes, no longer be valued as representative (see also paragraph 2.1).
Based on the PMV model, limits (temperature, air flow speed, temperature gradient, radiation asymmetry and floor temperature) have been defined for different activities and different indoor climate classes (class A (very good), B (good) and C (accept-able)) (NEN-EN-ISO 7730, 1996). There is an ongoing debate, however, about the reliability of these classes as the bandwidth within the classes seems to be bigger than the bandwidth between the classes and there appear to be hardly any significant dif-ferences in experience between the classes in a real environment (Arens et al., 2010). Halfway the 1990s, criticism concerning the PMV method increased when an in-creasing amount of field studies showed that the comfort experience of people often did not correlate with predictions from the PMV-model. The insight emerged that thermal comfort is not only dependent on thermo-physiological factors, but also that factors, such as the behaviour of people and the circumstances they are in, are impor-tant for the acceptance of and preference for certain temperatures. Figure 2.5 and 2.6 display results from a large research by de Dear, Brager and Cooper (1997) and show that the comfort temperature relates to the average outdoor temperature: the warmer it is outside, the higher the perceived comfort temperature. However, the comfort temperature in naturally ventilated buildings is higher in summer and has a larger correlation to the outdoor temperature than in air conditioned buildings.
There are several forms of adaptation to changing climatic circumstances that are related and influence each other (Brager and de Dear, 1998, Kurvers et al., 2010):
• Behavioural (personal adjustment, technological or environmental adjust-ment and cultural adjustadjust-ment). This concerns noticeable influence on the en-vironment, i.e. people experience that they have influence and not just have the idea that they can influence their environment. Influence can consist of opening doors and/or windows to change the temperature, influence the air-Figure 2.5: Adaptive model for predicting
optimum comfort temperature and acceptable temperature ranges (80 % and 90 % general comfort criteria) in naturally ventilated buildings (de Dear et al., 1997).
Figure 2.6: Adaptive PMV method for predicting optimum comfort temperature and acceptable temperature ranges (80 % and 90 % general comfort criteria) in centrally controlled HVAC buildings (de Dear et al., 1997).
