IN
DEGREE PROJECT THE BUILT ENVIRONMENT,
SECOND CYCLE, 30 CREDITS ,
STOCKHOLM SWEDEN 2020
Studying building behaviors by
using the Building Management
System of a new teaching building
A study case of a school building in Stockholm
KAIYING ZHANG
Studying building behaviors by using the
Building Management System of a new
teaching building
A study case of a school building in Stockholm
Kaiying Zhang
Thesis for the degree of Master of Science (MSc) at the Royal Institute of
Technology, Stockholm
Supervisor: Folke Björk
Examiner: Kjartan Gudmundsson
Acknowledgement
I would like to express my deep and sincere gratefulness to my supervisor Professor Folke Björk from KTH Royal Institute of Technology who lead me to such brilliant research and introduce an interesting study case. Thank you for the support, advice, and inspiration throughout the degree project and for introducing me to people who also helped a lot with this thesis.
I also would like to thank Sven Lindahl from Akademiska Hus for providing extensive and valuable information about the building management system of the building. He spent a lot of time on the building and system and gave advice and explanation. The completion of the thesis could not have been accomplished without his help and guidance.
A special thanks to KTH and Akademiska Hus for offering this great study case and platform enabling me to explore the indoor climate and building performance.
Last but not least, I would like to express my gratitude to my family and friends for supporting and loving me all the time. I’m thankful for their care and encouragement throughout my master's program study.
Abstract
Building management system (BMS) offers a wide range of measurements and historical data about the building but few types of researches use these data to analyze the building performance. This study aims to explore the indoor climate and building insulation by taking advantage of the BMS of the study case, which 767 sensors are installed in the room and wall structures and the signal data are available at the online web application. In addition, during the inspection, several error sensors and meters are detected are discussed as feedback for the system.
It is concluded that the building management system is a good tool to study the building performance in different aspects and the measurements from the sensors are helpful but need validation by conducting a further field measurement in the building,
Keywords: Building management system (BMS), Building envelope, Indoor climate, Thermal comfort,
Table of Contents
Acknowledgement ... i Abstract ... ii 1 Introduction ... 1 1.1 Background ... 1 1.1.1 Certification system ... 11.1.2 Building management system ... 2
1.2 Aim of this work... 3
1.3 Scope and boundaries ... 4
1.3.1 Scope and outline ... 4
1.3.2 Assumption and boundaries ... 4
2 Literature review: Terminologies and concepts ... 5
2.1 Building Insulation ... 5
2.2 Indoor climates ... 6
2.2.1 Thermal Climate ... 6
2.2.2 Indoor Air Quality (IAQ) ... 12
2.3 Energy consumption in buildings ... 13
3 The study case... 15
3.1 U-house ... 15
3.2 Platform: Styrportalen ... 16
4 Method ... 17
4.1 Styrportalen ... 17
4.2 Indoor environment assessment ... 19
4.2.1 Data from the sensors in the building envelope and weather station ... 19
4.2.2 CBE Thermal Comfort Tool ... 20
4.2.3 Ventilation systems ... 21
4.3 Energy Analysis ... 21
4.4 Interview, documents from Akademiska Hus ... 22
5.1 The control system ... 23
5.2 Building behavior ... 24
5.2.1 Interesting moments ... 24
5.2.2 Building behavior in Cold days ... 27
5.2.3 Building behavior in warmer days ... 41
5.3 Energy consumption ... 48
6 Discussion ... 50
6.1 Feedback and fault diagnosis ... 50
6.2 Future research and reflection ... 53
7 Conclusion... 55
1
Introduction
1.1 Background
World’s energy consumption in buildings is increasing every year and it occupies a share of 40% in the total primary energy consumption in the US and EU (Cao, Dai, & Liu, 2016) which is above industry and transport figures (Pérez-Lombard, Ortiz, & Pout, 2008). In the past, during the operation of the building, up to 50% of the building energy consumption is consumed by the heating, ventilation, and air-conditioning system. (Meir, Garb, Jiao, & Cicelsky, 2009) Today demand for high thermal comfort with minimal energy consumption is a mission pursued by researchers and designers.
Buildings have different purposes serving human beings and people spend 90% of their time performing activities in some specific indoor environment (USGBC, 2020). In order to maintain a proper building indoor environment for the occupants, researches are concerned about the indoor environment quality (IEQ). IEQ includes indoor air quality(IAQ), thermal comfort, lighting, acoustics, tap water, vibration, and other aspects that affect human life inside a building (Mujeebu, 2019). Therefore, the occupants’ health and productivity are largely affected by IEQ (Fisk, 2002). Occupants exposed in buildings with poor IEQ will lead to having building syndrome symptoms (SBS), such as headache, sore throat, and loss of concentration (Lyles et al., 1991). For educational buildings, people spend years studying and working in these buildings, and hence it is very important to inspect the IEQ of an educational building. 1.1.1 Certification system
To assess the quality of building environment and performance, encourage the design of a more sustainable building, and motivate a future smart building technology, different green building certifications and rating systems come into the building industry. There is a range of sound building certification systems in the industry.
The WELL building standard is a third party performance-based system certified by the Green Business Certification Incorporation (GBCI). It measures, monitors, and certifies the environment quality of the building and sets requirements in terms of air, water, nourishment, light, fitness, comfort, and mind. It focuses exclusively on the connection between building and the health or well-being of its occupants by conducting massive medical researches and it is awarded at three levels, silver, gold, and platinum (USGBC, 2020).
Leadership in Energy and Environment Design (LEED) is one of the international green building certification program developed by the non-profit U.S. Green Building Council for worldwide environmentally sound buildings. The program consists of several rating systems such as Building Design & Construction (BD+C), Interior Design &Construction (ID+C), etc. for different building types and construction phases (USGBC, 2020). To achieve the LEED certification, there are prerequisites and credits to earn for the projects, and the more credits the project gained, the higher level of certification it achieves (USGBC, 2020).
Swedish building certification systems are available such as the Miljöbyggnad. It measures 16 different aspects by independent third parties. The indoor environment is the main area that the assessment focus. The air quality, sufficient daylight according to the performance, Miljöbyggnad with different levels, including bronze, silver, and gold, will be issued by the organization. To achieve a Miljöbyggnad gold, the environment profile should be excellent with low energy cost and high comfort since the gold
standard is extremely high and even a survey about the users’ satisfaction of the building will be conducted after the two-year operation (SGBC, 2020). It is a high demand for the designers and constructors and building certified by this honor not only assure the sustainability of itself but also helps improve the quality of the neighborhood.
There is evidence that a certified green building has a higher asset value because it has lower operational expenses and higher occupants’ productivity (Al Horr et al., 2016). A survey of over 500 tenants who worked in a LEED or Energy Star labeled building shows that green buildings reduce the absence rate, increase occupant productivity and their wellness (Miller, Pogue, Gough, & Davis, 2009).
Overall, adopting a green building certification system is helpful to encourage a better future building performance design that the building works safer, more effective, and economically. Constructors of the certified green buildings can build the trust of their brand and meanwhile benefiting society (Nilsson, 2018).
1.1.2 Building management system
The development of the building automation system and cloud technology give a brand new method to optimize the indoor building environment while saving the operation cost. A building management system is a computer-based controller network installed in buildings for regulating and monitoring the mechanical and electrical equipment of the building which is known as Building Automation Systems (BAS) and Building Control System as well (Gjoko K., 2019). Most major buildings or facilities implement BMS linked to the HVAC system, water circulation system, sprinkler system, and electrical power, aiming to guarantee the safety operation while optimizing the building performance (Jagschies, Lindskog, Lacki, & Galliher, 2018). Figure 1.1 shows an example of components controlled within a BMS. BMS subsystems link the functionality of different equipment and hence they can work within the integrated system (Gjoko K., 2019).
The prime functionality of the BMS should be retained within the building environment, offering malfunction alarms to the operator of the building, monitoring device disfunction, and performing building-wide. Adapting BMS to the design of a building is necessary for achieving sustainability (Hossain, 2018).
The study of BMS is prevalent in designing and controlling the building but researchers barely take advantage of the wealth of data logged by the BMS (O’Sullivan, Keane, Kelliher, & Hitchcock, 2004). As a result, BMS is not only an essential part of the building maintenance but also a tool for studying the building performance by measuring the output of the control system. The study result can guide a further improved operation of the building.
1.2 Aim of this work
Undervisningshuset (The U-house) which was built in 2017 is a relatively new building applied with advanced technologies and it is well-known for its popularity among students and its unique design. Its monitoring system is designed as a tool to explore the building and it is feasible for students in KTH to access. Though there are some research studies done about this building, few researchers adopting the system, using sensors installed in the building, accessing the data from these signals as a tool to acquire information and measurements of the building condition. Therefore, this thesis aims to focus on the building management system of the U-house, describing the sensors, the operating system, and through this, investigating the building indoor climate by using the data from the sensor signals.
To be more specific, the thesis explains the detailed approach of using the online application Styrportalen where the information in the BMS is available, to investigate the building and find useful data, and demonstrates how it can be such a useful and unique tool for studying the building.
The energy consumption of a building has a connection with its envelope. It is necessary to check the performance of the building envelope by using the BMS system of the building when designing new buildings. (Hossain, 2018). Commonly the sensors in the structures are limited by the requirements, discontinuous signals, and high cost(Hung, Chang, Hsu, & Chen, 2012) but the U-house has sensors installed in the different layers in the building envelope and connected the signals to the BMS. Therefore, the insulation inspection is available through Styrportalen.
The building environment responds to factors e.g. climates, occupants, etc. and is controlled by the building management system, providing a dynamic environment for users to perform their daily work, such as teaching, studying, and communicating with each other. This thesis also investigated the thermal comfort, the indoor air quality, and the energy use of this building through the historical data from the BMS.
There are 767 sensors installed in the buildings and the BMS keeps receiving and recording data from the sensors and it is inevitable to have errors in some sensors and signals. In the thesis, the faults and errors found through the historical data were reported and discussed. It is a feedback for the constructors and designers, to make further improvement for the U-house and other construction.
Furthermore, most of the documents and drawings of this building are in Swedish and this thesis can be a useful reference and guide for people who want to use the Styrportalen to study the building environment.
1.3 Scope and boundaries
1.3.1 Scope and outline
First, a literature review was done for a basic overview of the terminology and theories about the building insulation, building indoor environment, including the thermal comfort, indoor air quality (IAQ), and energy consumption or office buildings.
The second part specifically introduced the study case, which is the U-house of KTH, the use of the monitoring system, and its overview performance in terms of certification and energy declaration). The platform that makes the building management system visible and accessible was introduced.
The methodology part showed the approach of using Styrportalen to access to the data from the sensors with pictures illustration. It also described what kind of data and its source used to understand the behavior of the building.
The result part showed the understanding of the building behavior and the assessment its performance. Detailed inspections and measurements are provided by the sensors through Styrportalen and a range of findings are demonstrated in this part, followed by the discussion, further analysis of some errors, problems, and giving feedback to the control system of the building. At last, a conclusion was presented with a summary of findings, measurements, and assessment.
1.3.2 Assumption and boundaries
The measurements of the building only came from the sensors visible in the system Styrportalen. There are three levels of authority to access Styrportalen. In this thesis, it’s the KTH student level that can check all the historical data of the building but cannot edit or control it through the system. The building includes lecture rooms, group rooms which are fairly private spaces for studying and on the other hand, in the open studying area, some sensors are not available because it is difficult to define the area and to measure. Therefore in this thesis, only the rooms with clear boundaries are studied. The open area can be measured by devices in the field in further study and applied the data in the system as assistance. The study focuses on the most recent time period during the operation of the building, which is 2019 and 2020.
There are diverse data in many aspects of the building and therefore it is impossible to check and study all of them. In the thesis, only part of the data was used to study the temperature changes in the building façade, the thermal comfort, and IAQ of the related rooms. Some remaining sensors have not been checked and used.
Some unpublished construction documents are obtained from Sven, the engineer of the Akademiska Hus who was in charge of the control system of Undervisningshuset. All the documents available are in Swedish since the building is constructed in Swede by Akademiska Hus. The translation of the documents was helped by google translate.
The study only focuses on U-house and using its building management system and weather information in Sweden, the Stockholm region. Only the operating time of the building, which excludes the summer and winter holidays was taken into consideration and for occupants in the building, the KTH academic schedule was applied. There are no field measurements in this thesis.
2
Literature review: Terminologies and concepts
2.1 Building Insulation
Thermal insulation is the process that the rate of heat transfer between objects in thermal contact is reduced. This process involves a combination of materials with low thermal conductivity (Thermal engineering, 2020). Proper thickness of insulation in the building envelope helps to reduce the heating and cooling load of the building (Kaynakli, 2012). In addition, it can help cut down the CO2 and SO2 emissions into the atmosphere. A study shows that when the building applies an optimum insulation thickness, the energy consumption was decreased by 46.6% and the emissions of CO2 and SO2 were reduced by 41.53% (Dombaycı, 2007). As a result, the performance of the external façades of the building is the key to the green building.
Thermal conductivity is the time rate of steady-state heat flow (W) through a unit area of 1m thick homogeneous material in a direction perpendicular to isothermal planes, induced by one Kelvin temperature difference across the sample. It measures the ability of a material to conduct heat (Al-Homoud, 2005). The thermal conductivity of a type of material is uncertain and it is sensitive to the density, porosity, moisture content, and operating temperature of the material. Studies show that the thermal conductivity of the material becomes higher when its moisture content rises or when it is at a higher operating mean temperature. The relative level of sensitivity to operating temperature for a group of materials will vary regarding the considered density of the material (Abdou & Budaiwi, 2005). As references, the thermal conductivity of air is 0.024 W/m-1 k-1 at 0 ℃ and 0.026 W/ m-1 k-1 at 25 ℃
(Thomas, 1993).
The most commonly used materials for building insulation are made from mineral wool such as glass wool or rock wool and plastic foam such as polystyrene, which has the best performance per unit cost. Therefore, these materials have the largest commerce potential for insulation material (Pavel & Blagoeva, 2018). Figure 2.1 shows different types of materials used for building insulation in the market.
Comparative case analysis on some commercial thermal insulation including Polyisocyanurate, Polyurethane, stone wool, XPS, etc. concluded that the polyisocyanurate performs the best in aspects of thermal transmittance with the thermal conductivity of 0.022 W/m-1 k-1. It has the most suitable material
for a cold climate while in warmer time, it is not the best choice due to its low density (Schiavoni, Bianchi, & Asdrubali, 2016). Though the commercial materials are economical and effective, significant environmental damage is caused by these materials during the production phase since the production uses a large amount of fossil energy and non-renewable and they are also problematic in the disposal phase that the material cannot be recycled (Asdrubali, D'Alessandro, & Schiavoni, 2015). There are sustainable insulation materials made from renewable materials such as biopolymers but the price of the new materials is high (Pavel & Blagoeva, 2018) and even some of them are not available in the market. Therefore the insulation materials are still under development.
Generally, the building envelope is made up of different layers including the insulation and the structural components such as the concrete junction, steel in openings (windows, doors), painting, and plaster. The structure components may have high thermal conductivity, resulting in a heat loss and thermal bridges and in the end, weaker insulation and larger energy consumption. Thermal bridge means an area in the building envelope that has higher thermal transmission than the surrounding area of the walls, overall leading to reduced performance of the thermal insulation of the building (Gorse, Johnston, & Pritchard, 2012). There are various types of thermal bridge occurred caused by different reasons such as the geometric thermal bridges and structure thermal bridges and they exist in different types of building (Nagy, 2014). To detect thermal bridges, either on-site with thermographic techniques or the numerical simulation can be used and it is important for a high-insulation building to evaluate and avoid thermal bridges for sustainability (Asdrubali, Baldinelli, & Bianchi, 2012).
2.2 Indoor climates
2.2.1 Thermal Climate
2.2.1.1 Heat exchange between body and environment
The heat transfers between the body and environment by means of conduction, convection, radiation, evaporation. The process can be described by the heat balance equation,
𝑆 = 𝑀 − (±𝑊𝑘) ± (𝑅 + 𝐶) − 𝐸
[𝑊 ∙ 𝑚−2] S is the rate of storage of body heat (+ for net gain); M is the rate of metabolic energy production (always +); E is the rate of evaporative heat transfer (− for net loss); Wk is the rate of work (+ for work
against external forces, − for work eccentric or negative work); R is the rate of radiant heat exchange (+ for a gain); C is the rate of convective heat transfer (+ for gain). (Gagge & Gonzalez, 2010)
2.2.1.2 Thermal Comfort
Thermal comfort means the state of mind that expresses satisfaction with the surrounding environment and assessed by subjective evaluation (ASHRAE Standard 55, ISO 7730). The human body has different sensations, cold, hot, or neutral in different indoor environments. Researches on thermal preference concluded four types of thermal preferences for users, consistent directional preference, fluctuating preference, high tolerance and sensitive to thermal changes, and high tolerance, not sensitive to thermal
changes (Shahzad, Calautit, Hughes, Satish, & Rijal, 2019). To maintain a comfortable thermal climate for occupants, a well-designed HVAC (heating, ventilation, and air conditioning) system in the building is required. As a result, enormous researches about thermal comfort are done to help design an ideal indoor thermal climate for occupants.
There are six factors that affect the thermal comfort perceived by the human body.
Influencing factors
1. Air temperature
The air temperature, also known as dry-bulb temperature, is the average temperature of the air around the human body with respect to location and time. It is measured by a dry-bulb thermometer which is freely exposed to the air but shielded from radiation and moisture (Shah, Krueger, & Strand, 1994). When measuring the air temperature, it should be careful to avoid the radiation of the heat source (Standard & ISO, 1998).
2. Radiant temperature
Mean radiant temperature (MRT) is the uniform temperature of an imaginary enclosure in which the radiant heat transfer from the human body (Standard & ISO, 1998). It is associated with the human body and significantly influence the thermal comfort indexes such as predicted mean vote (PMV) (Poul O Fanger, 1970) and therefore this factor is the most popular in human thermal comfort study (Chaudhuri, Soh, Bose, Xie, & Li, 2016). It can be measured by a black globe thermometer or calculated according to the measured values of the temperature, the sizes, and the distance to a person of the surrounding surfaces (Standard & ISO, 1998).
3. Relative humidity
The relative humidity is the ratio between the actual amount of water vapor in humid air and the amount of water vapor saturated in the air at the same temperature and pressure, usually expressed in percentage (Standard & ISO, 1998).
People perceive hot or cold through the skin and the relative humidity can be detected as well. The relative humidity affects the evaporation from the skin because the rate of evaporation is determined by the ability to hold water vapor by the surrounding air and therefore has an influence on the thermal comfort. High relative humidity decreases the effect of evaporation but an extremely dry environment is harmful to the body as well (Balaras, Dascalaki, & Gaglia, 2007).
The recommendation of the relative humidity in the air-conditioned house is around 30% to 50% depending on the times and seasons of the year (Housh, 2017).
4. Metabolic rate
The human body generates heat and it can be measure in the amount of energy and expressed by metabolic rate. The metabolic rate depends on the activity level and the environmental conditions and the unit of it is met which,
1 𝑚𝑒𝑡 = 58.2 𝑊/𝑚2
1 met energy is equal to the produced per unit surface area of an average person (1.8 m2) seated at rest
(ANSI/ASHRAE Standard 55-2010, 2013).
Table 2.1 Metabolic Rates for typical tasks (ANSI/ASHRAE Standard 55-2010, 2013)
5. Clothing insulation
The clothes that people wear can provide an effect of thermal insulation and protect the human body from cold and outdoor pollutants. The insulation effect can be expressed in clo (Icl) units (ASHRAE,
2005)
1 clo amount of clothes can maintain thermal equilibrium for one person at rest in an environment at 21°C in a normally ventilated room (0.1 m/s air speed). Clothing insulation values for some typical clothes are shown in Table 2.2.
Table 2.2 Clothing Insulation Values for Typical Ensemblesa (ANSI/ASHRAE Standard 55-2010,
2013)
6. Air movements
The rate of air movements at a point can be defined as the air speed or air velocity without considering the direction. It affects the thermal sensation of the human body, slightly cooler, slightly warmer, or neutral (Toftum, Melikov, Tynel, Bruzda, & Fanger, 2003). A high air speed may cause draught, an undesired cooling of the human body caused by air movement (ASHRAE, 2005). It not only causes discomfort but also implicated the indoor air quality and energy consumption (Povl Ole Fanger, Melikov, Hanzawa, & Ring, 1988). Figure 2.2 shows the estimation of the air velocity required to offset the temperature based on a theoretical calculation.
Figure 2.2 Air speed required to offset increased air and radiant temperature (ANSI/ASHRAE Standard 55-2010, 2013)
The combined effect of the air velocity and temperature results in heat loss from the skin and to avoid discomfort, ASHRAE Standard 55-2010 requires that for operative temperature above 25.5 ℃, the upper limit of air velocity shall be 0.8m/s for an office building and for operative temperature below 22.5 ℃, the limit shall be 0.15 m/s to prevent discomfort from draught. The recommended air velocity is below 0.25 m/s during the hot season and below 0.15 m/s during the cold season (ANSI/ASHRAE Standard 55-2010, 2013).
The operative temperature(t0) mentioned above, is “the uniform temperature of an enclosure in which
an occupant would exchange the same amount of heat by radiation plus convection as in the existing non-uniform environment” (ANSI/ASHRAE Standard 55-2010, 2013). The calculation of operative temperature is based on air temperature, mean radiant temperature (MRT), and air velocity (Dave, 2014). In most practical cases where the relative air velocity no larger than 0.2 m/s or where the difference between MRT and air temperature is smaller than 4 ℃, the operative temperature can be calculated with sufficient approximation as the mean value of air and MRT (Standard & ISO, 1998).
The range of acceptable thermal comfort is according to the operative temperature instead of the dry-bulb air temperature, which is shown in Figure 2.3.
Thermal Comfort model
When analyzing the thermal comfort, two main thermal comfort models are applied according to different scenarios.
1. PMV/PPD
Based on the heat balance of the human body and empirical studies, P.O Fanger developed the PMV/PPD method that is widely used as a tool to evaluate thermal comfort.
PMV is an index that predicts the mean value of votes of a larger group of persons on the thermal sensation scale shown in Figure 2.4.
Figure 2.4 Seven-point thermal sensation scale (International Organization for Standardization, 2005) It can be calculated with different inputs of the six influencing factors of thermal comfort but within conditions should be satisfied where metabolic rate range from 0.8 met to 4 met, clothing insulation from 0 clo to 2 clo, air temperature from 10 ℃ to 30 ℃, radiant temperature from 10℃ to 40 ℃, air velocity from 0 m/s to 1m/s, water vapor partial pressure from 0 Pa to 2700 Pa (Poul O Fanger, 1970).
𝑃𝑀𝑉 = 𝑓(𝑇, 𝑀𝑅𝑇, 𝑅𝐻, 𝑣, 𝑐𝑙𝑜, 𝑚𝑒𝑡)
The PPD is an index that establishes a quantitative prediction of the percentage of thermal dissatisfied people who feel too cool or too warm. The relationship between PMV and PPD is shown in Figure 2.5 and can be expressed by the following function according to ISO 7730: 2005.
𝑃𝑃𝐷 = 100 − 95 exp(−0.03353 ∙ 𝑃𝑀𝑉4− 0.2179 ∙ 𝑃𝑀𝑉2)
As Figure 2.5 shows, the PPD value ranges from 5% to 100% and it is affected by the occupants’ position in the room. According to ASHRAE Standard 55-2017, no occupied spots in the room could be over 20% PPD (Guenther, 2019).
Nevertheless, the PMV/PPD model has not taken the adaptation mechanisms and outdoor environment thermal conditions into consideration (Humphreys, Nicol, & Raja, 2007) and proved to has a low prediction accuracy. As a result, the accuracy of PMV/PPD values is significantly influenced by the ventilation, building types, and the climates (Cheung, Schiavon, Parkinson, Li, & Brager, 2019).
2. Adaptive comfort model
People are adaptive to different outdoor climate conditions during different times of the year and this can affect the perception of indoor comfort. Differences in recent thermal experiences can change people's thermal responses (ANSI/ASHRAE Standard 55-2010, 2013). The adaptive hypothesis predicts that the thermal expectations and preferences of occupants in the building are affected by contextual factors such as their recent thermal exposure history (de Dear & Brager, 1998). According to different causes of adaption, there are basically three types of thermal adaptation, behavioral, physiological, and psychological adaption.
The prevailing mean outdoor temperature as the input variable for the adaptive model was introduced in the ASHRAE-55 2010 Standard and it only applies to the condition where outdoor climate conditions can influence the indoor condition and the comfort. To be specific, buildings without mechanical cooling can apply the adaptive model (ANSI/ASHRAE Standard 55-2010, 2013).
Thermal load
Thermal load is the heating or cooling energy demand to maintain the indoor temperature in the range of setpoints. It depends on factors such as the ambient climate, the properties of the building envelope, and the building’s relationship. As a result, the good performance of the building envelop can reduce the thermal load and save energy costs (Widström, 2018).
2.2.2 Indoor Air Quality (IAQ)
The air in the building contains different chemicals and the quality of the indoor air has a significant impact on occupants’ health and performance and hence it is an important indicator for the indoor environment quality. Various contaminants in the air from a range of sources such as the outdoor, building materials, and occupants themselves, release into the air and accumulate to a certain concentration. The concentration of the pollutants is associated with the total volume of air in the room, the rate of production, the rate of removal, the rate of air exchange with the outdoor environment, and the outdoor pollutant concentration (Maroni, Seifert, & Lindvall, 1995).
Pollutants in the indoor air exist in different forms, gaseous pollutants, aerosols, odors, particles, and radioactive matters. Gaseous pollutants such as carbon dioxide, nitrogen oxides, and ozone, volatile organic compounds (VOCs) (Maroni et al., 1995). These pollutants are produced by the occupants or from the outdoor environment, causing unpleasant feelings, irritants. It is worth to mention that the radon gas and radon daughters generated by radioactive decay from water, some type of concrete or rocks in the building can cause serious problems such as lung cancer (Jones, 1999). As a result, the contaminants
in the air should not exceed a certain level otherwise it may cause health problems which is known as sick building syndrome (SBS), for example, headache, dizziness, asthma (Lyles et al., 1991). Requirements are introduced and standards are set for insuring a livable and workable indoor environment. Insufficient ventilation in the room may lead to a high concentration of pollutants and therefore, the requirement worked as guidance for the HVAC system design and a standard for IAQ assessment. The assessment of indoor air quality is necessary to avoid discomfort and health problem. IAQ assessments normally can be conducted by measurements, calculation, or subjective votes. Moreover, numerical simulation is more and more commonly used for IAQ assessment due to the development of computer models (Sarbu & Sebarchievici, 2013).
When people have activities indoor, the oxygen is consumed and the carbon dioxide is produced by occupants making the concentration of CO2 become higher. Therefore, the carbon dioxide concentration
is widely used as a surrogate indicator for assessing IAQ and ventilation efficiency(Hui, Wong, & Mui, 2008), according to the fact that people emit CO2 at a rate that depends on their body size and metabolic
level as well as the fact that the indoor CO2 can be used as a tracer gas when its concentration exceeds
the outdoor level(Persily, 1997). A certain amount of CO2 in indoor air can cause discomfort or even
health problems. Researchers used generalized estimating equation models and concluded that workers exposed to indoor CO2 concentrations higher than 800 ppm were likely to report more eye irritation or
upper respiratory symptoms (Tsai, Lin, & Chan, 2012). CO2 concentrations in acceptable outdoor air
typically range from 300 to 500 ppm. The upper limit of carbon dioxide is 1000ppm for continuous exposure and classrooms and conference rooms 15 cfm (about 7.1 L/s) per individual defined by ASHRAE (ASHRAE, 2016)
Table 2.3 The effects of carbon dioxide on the human body (Engineering toolbox, 2020)
Normal outdoor level 350 - 450 ppm
Acceptable levels < 600 ppm
Complaints of stiffness and odors 600 - 1000 ppm
ASHRAE standards 1000 ppm
General drowsiness 1000 - 2500 ppm
Related health problems 2500 - 5000 ppm
Permissible exposure limit for daily workplace exposures
5000 - 10000 ppm
The air in new constructions may contain harmful chemicals from the paints, glues, furniture, etc. and the old buildings should be careful as well on the fungi, molds, spores, and dust hiding and spreading in the building. It is necessary to assess the IAQ of the building from time to time.
2.3 Energy consumption in buildings
There are different types of energy sources in the building energy consumption which can be divided into renewable energy such as solar energy, wind, waste heat, and non-renewable energy such as gas,
coal. Over half of the energy in Sweden generated by renewable energy sources. Hydropower and bioenergy are the top renewable sources in Sweden which the hydropower is mostly for electricity production and bioenergy is for heating (Sweden, 2020).
In Sweden, most of the buildings are required to meet a building code in terms of its energy performance, which are the HVAC system, hot water, and building’s property electricity. Measurements and monitoring system for energy use in buildings is mandatory so that how much actual energy consumption can be read, calculated and checked if the building meets the requirements and the buildings can maintain high energy efficiency. Sweden’s building code’s energy requirements are extremely rigorous for both new builds and building renovations (GBPN, 2020). According to the Swedish building regulation, the energy performance of the building (spacing heating, air conditioning, hot tap water, and property energy) is expressed as a primary energy number which the total energy consumption is aggregated and divided by the heated area of the building (non-heating area such as interior walls, openings for stairs, etc. is excluded) and is in the unit of kWh/m2 per year. For premises
with a heated area of over 50 m2, the requirement of primary energy number is lower than 80 kWh/m2
per year (Boverket, 2018).
When Miljöbyggnad assessing the building, both the amount of energy use and type and energy are included in the rating aspects (Swegon Air Academy, 2013). The expert group of Miljöbyggnad divided the energy resources into three categories, renewable flowing energy, renewable fund energy, and non-renewable energy according to how much resource withdrawal from nature they cause (Johansson, Bagge, & Wahlström, 2018). Energy performances in one year for heating, domestic hot water, comfort cooling, and non-domestic power use (excluding the business appliances) are calculated and 35% lower than the building regulations can be certified Miljöbyggnad gold.
In a comparative study of energy uses in 20 office buildings in Poland, the average total energy consumption of green-building certified buildings was 142 kWh/m2 and 144 kWh/m2 for uncertified buildings but the heating consumption in certified buildings was 26% lower than the consumption in uncertified buildings. The conclusion of the study is that designing a building applying the certification requirements can save operational energy cost of more than 30% and has greater energy saving potential during the operation phase due to the energy-efficient strategies in the designing phase (SKANSKA, 2020).
The energy for artificial lighting, IT equipment, and the HVAC system have steadily risen in office buildings and count for 85% of the total energy use (Pérez-Lombard et al., 2008). In order to save the energy costs during the operation stage, some energy saving strategies are proposed. For example, designing a smart lighting system and a layout with efficient daylight, understanding the occupants’ energy use pattern, and applying automatic shading. A study on the energy consumption of office buildings in London using a simulation model found that the night cooling using natural ventilation lower the cooling demand both in rural areas and city and therefore is beneficial to the environment (Kolokotroni, Ren, Davies, & Mavrogianni, 2012). Studying building behaviors can help to find efficient energy saving methods to further improve the building and its sustainability.
3
The study case
3.1 U-house
Undervisningshuset (the U-house) is a multi-functional educational building of KTH on Brinellvägen in Stockholm, Sweden. The climate of Stockholm is the oceanic climate with an average of over 1800 hours of sunshine per year. The winter seasons are long and cold but still remains above 0 ℃ for most of the time and the summer times are mild (Klima-der-erde, 2020). The length of the day time varies throughout the year, from more than 18 hours daytime in midsummer to merely around 6 hours in December. The average winter temperatures are generally from −3 to −1 °C while the average temperatures in summer range from 20–25 °C and up to 30 °C in midsummer from June to August. The temperatures between winter and summer seasons are cool and mild (Wikipedia, 2020).
The building is designed for teaching and learning and is covered approximately 3500 m2 with 7 floors.
The appearance of the building is a brown beaver tail brick envelop which is energy-efficient whilst kept with the almost 100-year-old tradition of KTH, with a slope roof, serving a unique artistic sensation (Archdaily, 2018). There are various rooms for different study purpose and even the building could be a tool for studying.
The design of Undervisningshuset has 7 floors with various spaces including lecture rooms, group study rooms and open areas for a range of study uses. The spiral layout of the building, showing the space of the building, is very clear to see the construction and installation (Archdaily, 2018). The building has a high transparency with large glass walls, central stairs and a unique slope design. Meanwhile, there are some dark and invisible function rooms and a weather station installed on the roof. The building achieved features of both open and private, quiet, and transparent, serving diverse study demands. The building is designed with a high focus on low energy use and is certified with Miljöbyggnad Guld (Swedish Green building Gold) certified (Akademiska Hus, 2020) This certification has 16 index that measures the performance and sustainability of a building. Karitikou evaluated the building in the aspects of thermal, acoustic and visual perception of users in the building and checked that the building meets the requirement of Miljöbyggnad Gold and it is in function properly (Kritikou, 2018). The building also has an energy declaration that reported by Boverket on how much energy the building use and for the U-house, the information is shown in Figure 3.1. The energy performance includes the energy consumed by heating, air-conditioning, hot tap water and building’s property, and divided by the heated surface of the building (Boverket, 2020).
3.2 Platform: Styrportalen
Collaborated with KTH live-in-lab, the building is a testbed for innovation in the building environment and energy use. The building applied technology for studying how the building works including 767 sensors installed in the whole building and real-time monitoring system, and all the measurements can be achieved by accessing the online application, Styrportalen (KTH//).
With the web-based application, today the plant information stored in the building management system can be assessed from anywhere around the world. By using this application, it is possible to control the building automation system without major investments.
Powered by Nordomatic, Styrportalen as a web-based system, enables the building management system visible on any device. HTML5 gives you full choices of browser and hardware that the web-based portal where all features of the building are accessible from web interfaces on Mac OS, Windows, iOS, Android and WIN-mobile. Moreover, it’s open to all users around the world and is never limited to a technology standard. It can fast access to the data with no place and time limit.
The measurement collection system is designed to be used by students, researchers with several to study the properties of the building over time. It is uncommon that we get access to the signal system of a building and it is rare that sensors are applied to the inner fabric of the building envelope, where is the inner structure of the walls and roof. By adopting the system, an understanding of the buildings behaviors and about how control systems might be improved can be obtained. The sensors include temperature, humidity, CO2 level, power meters, etc. which enable users to analyze in different fields of the building such as thermal comfort, IAQ. Therefore, the system for measurement collection should meet high demands on reliability, stability and accuracy of the measurements. It is important to check the function of the sensors and system from time to time.
Historical collection of data can be logged and used in trending applications to further improve plant processes. as well as create mandated record-keeping for some of the industries out there. Moreover, the system provides logically constructed address, and hence through Styrportalen the BMS of the building can be programmed and combined with other software to further develop its usage.
4
Method
This part introduces the approach of using Styrportalen, accessing to the data of the U-house to explore how this system can help to study the building. One of the features of the system is that trend analysis is possible for different sensors and historical data. It is possible to either using the statistics to have a quantitative analysis or look into the trend to have a qualitative analysis. Both of these methods can contribute to studies about the building.
The study has features of a qualitative that collect the evidence and find the characteristics from the trend. The system has three-year historical data to analyze and the quantitative calculation suits the study of a shorter period. Besides, the thermal comfort index calculation for some extreme situations and energy consumption comparisons are included in the study.
4.1 Styrportalen
To gain data, first of all, an account and the permission from Styrportalen should be set to access the building information. In this case, entering the building with the building’s code KTH A0043032, the overview, which is the shape of the building, and the placement of the rooms are demonstrated with a function toolbox on the side, shown in Figure 4.1. By clicking different room button, the data from the sensors are shown with a simple system drawing as an explanation, shown in Figure 4.2.
Figure 4.2 RU435 room illustration in Styrportalen
Using the toolbox on the side, the system could work as an alarm, an analysis tool, and storing different documents and notes about the building. In “Anläggningar”, it is shown that the building can be explored by different categories, such as the heating system, cooling and water circulation. The whole floor plan with conditions of the room is visible from the sensors mounted in the room. The details of the sensors’ placements are shown along with the plan drawing as well. For example, in Figure 4.3, the 2nd floor plan
with different rooms and the meters with real-time data are demonstrated in this interface.
Figure 4.3 The plan of Floor 2 in Styrportalen
In the plan view, sensors are shown in the drawings with real-time data and alarm. The alarm system can report the unusual situation automatically with warnings with red highlights in the system. The sensors and meters can be viewed in the form of lists as well. It’s convenient for the operators to check and maintain the building.
The main tool used by the thesis is the “Analys” where different sensors and meters can be selected and added and making trend analyses of different periods. Therefore it is not only a real-time monitoring system but also a system that can check the historical data within the system.
The sensor data can be simply selected by clicking it and there are two choices to see the “data trend” of the sensors. One is directly clicking “Visa”, which means seeing in trend analysis and the other is “Lägg till” which means “add to”. By adding the sensor, a list of different sensors can be selected and shown in one diagram in trend analysis by clicking “Lägg till och visa”. The list of sensors can be edited as well by using “Redigera valda”. In that case, the analysis of the combination of sensor data within the system is easy and fast. The diagram that the tool generates could be saved and marked. The selected group of sensors information can be stored in the cloud service of the system as well for using it at another time but the time interval of the diagram cannot be memorized and would be reset to the last 24 hours. Moreover, the data can be downloaded in different picture forms and the statistics can be exported in excel files to have further analysis. Overall, through Styrportalen the building measurements can be acquired and analyzed and it’s the core of this study.
4.2 Indoor environment assessment
4.2.1 Data from the sensors in the building envelope and weather station
The building as a study tool, its uniqueness is that there are sensors mounted in different layers of the building envelope, enabling people to look into the fabric of the wall to see the process of the temperature changes. In addition, the building has its own weather station located on the roof and its data is accessible on Styrportalen as well. Therefore the real-time climate information of the surrounding area could be gained.
Figure 4.4 Weather station of the U-house Figure 4.5 Weather station data in Styrportalen Applying the data from sensors of the weather station when the condition is extreme in one way or another: a very warm day, an extremely cold winter day. To be specific, selecting sensor “Temperatur” in AM101 weather station, checking in a large period, and locating the extreme point. Nevertheless, the precipitation information in the Stockholm region is acquired from the weather website SLB analysis because it’s not available in the weather station.
The sensors are mounted in the façades on the 4th and 5th floor, and the roof, which completely show all
directions of the building. Through the trend analysis tool, diagrams are generated with temperatures in different layers of the wall and different sides of the façade can be compared to see how the directions
affected the wall and room temperature.
In classroom U41 (room code RU420 in Styrportalen), sensor GT 47 is installed to measure the operative temperature of the room as Figure 4.7 shown, which can be a useful reference for evaluating the thermal comfort level of the room. There is no other room with this kind of sensor installed. Therefore, U41 is selected to assess the thermal comfort of the lecture room.
A manual control system is installed in the lecture room and occupants can adjust the temperature themselves to achieve a customized comfort level. This attempt is also visible in the system and through this signal how occupants actually feel about the indoor environment can be inferred.
4.2.2 CBE Thermal Comfort Tool
For the thermal comfort prediction of the lecture room, the study applied the CBE Thermal Comfort Tool (v2.0.0) developed by UC Berkeley. By applying the PMD method in the comfort tool, six thermal comfort influencing factors can be input and according to the combination of the inputs, the PMD/PPD is calculated complying with ASHRAE Standard 55 and displayed a visualization of comfort boundaries within psychrometric or temperature-humidity charts, indicating the ranges of acceptable temperature and relative humidity with the given inputs (Hoyt, Schiavon, Piccioli, Moon, & Steinfeld, 2019). According to ASHRAE 55, the metabolic level input in the tool is 1.1 met during lectures and 1.3 met before the lectures due to the fact that during the lecture people are seated and typing, reading and before the lecture people tend to stand relaxed and chatting. The clothing insulation value is 0.8 clo in winter between wearing long-sleeves, sweaters, jackets and trousers. In warmer days, the study applied a 0.5 clo value with typical summer clothes (ANSI/ASHRAE Standard 55-2010, 2013).
There are no air velocity sensors in the system and therefore using an average value of 0.08 m/s in the warmer season and 0.09m/s in cold season according to the field measurement results from the previous studies on the U-house by Kritikou (Kritikou, 2018).
Figure 4.7 Operative temperature sensor in U41 (Akademiska Hus, 2015)
Figure 4.6 Sensors in the structure of the wall
4.2.3 Ventilation systems
The ventilation system in the room plays an extremely essential role in the building system since it has functions of maintaining the thermal comfort of the room while removing or diluting harmful pollutants in the air. As it is a subsystem of the building management system, the control and the output effects of the ventilation system should be a key point to study.
Lecture rooms are installed with carbon dioxide sensors and airflow controls and hence the correlation between the airflows and carbon dioxide level can be analyzed. Occupants in the indoor environment are generally assumed to follow deterministic schedules in building performance simulation study (Tekler, Low, Gunay, Andersen, & Blessing, 2020). Classrooms in the U-house are only for the lectures and seminars and the schedules are available on the KTH website. It clearly shows when the room will have or had lectures and events and it is reasonable to assume that there should be people present in the room. However, the group room and open study place are not available on the schedule. For the open study area, neither the schedules nor the sensors of carbon dioxide level are available since the open area is difficult to define and measure the properties. Therefore this study focus on the indoor environment in the room where it is predictable from the schedule and is data-available. U41 and U51 are two rooms chosen to explore the ventilation system. These two classrooms are on the opposite directions of the building, the south side and the north side, and hence they can represent most of the classrooms in this building.
4.3 Energy Analysis
The system includes meters to record the energy consumption of the building. The building is designed to be low energy cost and real-time monitoring makes it possible to check the energy costs in different periods, no matter warm days or cold seasons.
The total energy consumption of the building consists of heating, cooling, property use electricity and tenant use electricity, which are measured by different meters visible in Styrportalen. The property total energy includes the energy used by warming cable, air handling units, elevator and the building structures. The tenant energy is for lighting, microwave oven, and other energy used by tenants such as the office appliance which are measured separately on floor 1, 2, 4, 6, 7 in the technology room.
There are independent energy meters in the heating system, district cooling and water system. For cooling energy, it only has one meter KP101-MF401 to measure total cooling power. The real-time power of total heating energy is measured by the meter VP101-MF401 and so are its subsystems in terms of radiators (VS101-MF41), air door (VS101-MF42), ventilation (VS101-MF43, VS101-MF44), hot tap water (VV101-MF401) and water circulation (VC101-MF41). By clicking the dialog of the meters, the total energy use from the beginning of the operation till now can be checked. The thesis focus on investigating the energy used in different seasons as well as a whole year consumption in different categories.
4.4 Interview, documents from Akademiska Hus
The information and explanation of the system are all from exclusive documents and construction drawings of the building which are owned by Akademiska Hus. The documents range from the control system, automation system, structure drawings and the energy consumption report. These documents are in Swedish and to fully understand it, google translate is used. The result and conclusion of the thesis are drawn not only through the data from Styrportalen but also with the help of the explanation and field inspection by Sven Lindahl, the engineer from Akademiska Hus.
5
Result
The building reacts to the factors such as the outdoor temperature, the occupants in many aspects and at the same time, controlled by the control system of the building. The building behavior is the output of the interaction with the climate, occupants and the control system. U-house has a complicated automatic control system that maintaining the a safe and proper indoor environment under disturbance with accurate instructions (Widström, 2018). Therefore understanding the components of the control system such as the setpoints and the control signals help explain the response of the building and these subjects and values are visible in Styrportalen.
Using the system sensors and meters, the building behaviors and the total energy consumption of the building can be obtained and evaluated. The result is presented in such outline shown in Figure 5.1.
Figure 5.1 Outline of the result
5.1 The control system
In this part, the information about the control system is described.
For the classrooms in the building, the temperature setpoint is 22 ℃. There are two control mode, comfort operation within and economy operation . Under the comfort modes, operation for a good indoor comforts, the temperature are controlled within ±0.5 ℃. On the other hand, under economy mode, it’s within ± 2 ℃. The classrooms only run in the comfort mode in daytime from Monday to Friday, 7:00 – 22:00 and this can be defined as the operation time of the building. At night and during weekends, it runs in the economy mode.
Figure 5.2 shows how the sensors display in a lecture room in Styrportalen. During operation time, temperature control via GT101 is switched on for comfort mode when the presence sensor GN501 perceives presence for 1 minute and returns to economy operation when there is no presence for 5 minutes. The supply air flow operates in the same way. The minimum flow occurs when there is no presence or the sensors haven’t noticed the presence for 5 minutes, but when the sensor detected
presence for 1 minute, the ventilation runs according to the “presence flow”, which is a default value in the control system. The values of the airflows are shown in ST401-GF and ST402-GF.
Users of the room can customize the temperature if they feel uncomfortable with the current room temperature. Through sensor OS101 “Börvärde offset” which means setpoint offset, the users can adjust the room temperature to reach their demand.
The carbon dioxide sensor GQ101 has an automatic control system linked to the airflow sensors with the actual setpoint of 800 ppm instead of 900 ppm which is recorded in the document.
Figure 5.2 Sensors in RU420
The building operates a default night cooling of 15 ℃ in hot days as the Swedish building regulation recommend to reduce the demand for cooling load in warmer days (Boverket, 2018). That explains why there is some time that the temperature setpoint offset OS101 shows 15 ℃ instead of 22 ℃ in Styrportalen.
Classroom U41 has a sensor for measuring operative temperature and therefore the thermal comfort in this room is studied.
5.2 Building behavior
5.2.1 Interesting moments
The occupants in the building is a control point for facilities to operate (Kayo, 2018) and the main users of the U-house are the students who have lectures or work on their own in the building. Therefore, the indoor environment when there are users in the building should be focused and that is during the academic period of KTH. In this part, the analysis chose the most recent study period, from 2019 to 2020. This includes the spring term of academic year 2018 – 2019, from 15 January to 4 June, 2019 and academic year 2019 – 2020, till 30 April, excluding weekends and holidays (KTH, 2020). These periods consist of the summer of 2019 and cold time from 2019 – 2020.
Figure 5.3 Timetable of Academic Year 19-20 (KTH, 2020)
Through the weather station the temperature around the building for a whole year can be obtained.
Figure 5.4 shows an overview of the temperature around the U-house in a whole year. The warm season is from May to August and most of these time are holidays when nobody will appear in the building. Excluding the holidays of school, clearly the hot season is from the mid of May to the early June and the cold season are throughout December to the end of March.
A comparison can be done between data from the weather station at the U-house and the data from SLB analysis (Stockholm Air and Noise Analysis) which is a department at the Swedish Environmental Administration provided by the web link slb.nu shows that the data from the weather station are reliable and so some interesting moment for inspection can be decided. The building are inspected in two periods, the warmer period from Monday, 13 May to Tuesday, 4 June, 2019, and the cold days from Monday 20 Jan to Monday 17 Feb, 2020. The following analysis are based on these period though some extension were still made for analyzing.
Figure 5.5 Temperature at weather station (Warmer period)
Figure 5.6 Temperature at weather station (Cold period)
Figure 5.7 Temperature at warmer period (SLB, 2020)
Figure 5.8 Temperature at cold period (SLB, 2020)
5.2.2 Building behavior in Cold days
5.2.2.1 Building envelope: The Roof
A weather station and 7 sensor spots are installed on the roof, shown in Figure 5.10. Sensors GT41 to GT44 are placed in between three 100 mm thick insulation boards “PIR TR20”, a high performance rigid thermoset plastic insulation which are illustrated by a triangle patten in Figure 5.9. This material is moisture resistant and suitable for a flat roof insulation (Kingspan, 2013). The rest of the sensors are placed in the structure components (the trapezoid sheets, the sound absorbents and concrete) of the roof.
Using trend analysis to check how temperature changed in different parts of the roof. GT41 to GT46 and the outdoor temperature are added and south and north sides of the roof are compared.
Figure 5.12 Temperatures at Roof-RU560 (South) Figure 5.13 Temperatures at Roof-RU620 (North) Figure 5.10 Sensors placement on the roof
Figure 5.9 Sensors in the roof structure for index 1-5
Figure 5.14 Temperatures at Roof-RU750 (South) Figure 5.15 Temperatures at Roof-RU632 (North) From the figures, the insulation prevent the heat loss layer by layer. The thermal conductivity of 100mm PIR insulation is merely 0.026 W/mk (Kingspan, 2013) and it performed a good thermal insulation that between GT41 (blue lines), GT42 (red lines), GT43 (yellow line) and GT44 (green line), there are three large gaps. On the other hand, the temperature between the trapezoid sheet or the concrete are very close, indicating the materials have a high heat conductivity. Exceptions happened in GT43 of RU560 while it shows an unnormal high temperature. This will be discussed in Chapter 7 Discussion.
Through comparison, the sensors in the south part of the roof displayed distinctly higher outdoor surface temperatures on 2, 3, 13, 14 Feb than what were registered on the north side. This abnormal high temperature was caused by the direct sun radiation given the fact that it happened only on sunny day at around 2 pm (Timeanddate, 2020).
Figure 5.16 Stockholm weather from 10 Fen to 15 Feb
Therefore, it can be concluded that, though it’s in cold season, the roof of the building can have an uneven surface temperature due to the solar radiation.
It is relevant to inspect data from the two rooms under the places where the sensors RU632 and RU742 are placed.
Figure 5.17 Temperatures comparison between RU632 and RU742
Figure 5.17 shows that the two rooms have similar temperature at ceiling surface (GT46) and room air temperatures (GT101) despite that the rooms are located on the opposite side of the building with different outdoor surface temperature (GT41). As a result, the three layers of the roof insulation is sufficient for prevent the heat loss in cold season.
5.2.2.2 Building envelope: The wall
The building has sensors installed in the wall of floor 4 and floor 5 with two sensors in the north, two in the south and each one for west and east, shown in Figure 5.18 and Figure 5.19. It allows to compare the insulation performance in the wall from all the directions.
Figure 5.18 Floor 4 plan with detail illustrations
Figure 5.19 Floor 5 plan with detail illustrations
As the detail illustrations show, there are always five temperature sensors in the same positions of the wall. The structure of the walls are identical to each other but different from the roof. Take spot “RU420-NORR” as example, GT41 is placed in the airgap with battens. Between GT41 and GT42 is a 100 mm
lies GT43. The thin layter between GT43 and GT44 are two layers of plaster. Lastly, there is one more layer of 95 mm insulation with steel girders and GT44 and GT45 are mounted inside this layer. No details about the material of the insulation from the drawings (Akademiska Hus, 2015).
Figure 5.20 Temperatures at Wall-RU560-South Figure 5.21 Temperatures at Wall-RU 420-North
Figure 5.22 Temperatures at Wall-RU550-South Figure 5.23 Temperatures at Wall-RU560-West From the diagrams, the gap between GT42 and GT43 are obvious due to the insulation materials and it keep the heat from leaking. That means the 195mm insulation performed well and its thermal conductivity is low. Assuming the material of the insulation is the same as the insulation in other layers of the wall and in that case it can be concluded that thicker the insulation, the lower the thermal conductivity. In the façade of RU560, the break-out open space, the effect of the 95 mm insulation can be seen clearly through the diagram while in the classroom RU460 and RU550, the 95 mm insulation does not work that well.
The outdoor surface temperature is nearly similar in different facades except some spikes on the south-west wall of RU560. It indicates a mild sun radiation on this direction, making the surface of south-south-west part warmer. Even though, it hasn’t affected the temperature in the next layer.
It can be noticed that in RU420 and RU550, room surface temperature has small fluctuations along with the movement of the outdoor surface temperature. Therefore, the trend of the outer surface temperature still have impact on the indoor environment.
5.2.2.3 Rooms: U41 (RU420) & U51 (RU550)
RU420 and RU550 are two classrooms with multiple sensors in Styrportalen with room number U41 and U51 respectively in the KTH course system. Through sensor data, the indoor climate of two rooms was evaluated.
Thermal Comfort
Temperature sensor GT47 in RU420 is used for measuring the operative temperature. Through this the thermal comfort index, PPM and PPD value can be calculated. The analysis should exclude the non-operating time. Therefore, only the data Monday to Friday from 7:00 – 21:00 is selected and shown in Figure 5.24.
Figure 5.24 Operative temperature and relative humidity of U41
The extreme moments are selected as well as an average value of the room operative temperature and relative humidity is calculated.
Table 5.1 Extreme and average values of operative temperature and RH in U41
maximum minimum average Operative temperature 26.5℃ (28/1 19:00) 21.7℃ (3/2 7:17) 23.8℃
RH 45% (28/1 17:43) 28% (3/2 7:27) 36%
From the schedule of U41, there was no arrangement when the max and min operative temperature occurred but there was a lecture at 17:00-19:00 (KTH, 2020) on 28 Jan with over 25 ℃ operative temperature while at the same time the humidity was 45%. The lowest relative humidity occurred almost at the same time when the temperature dropped to the lowest point. Therefore, two extreme cases were selected to calculate the thermal comfort at that time, 18:00 on 18 Jan and &:30 on 3 Feb. The calculation is by the CBE thermal comfort tool and several inputs were required.
Inside the building the air speed could be slow but there is no sensor in the system that measuring the air velocity. Nevertheless, in previous research regarding to the U-house, Kritikou measured the air
value of the air velocity of 0.08 m/s in the heating session and 0.09m/s in the cooling session (Kritikou, 2018).
Occupants of one room with significantly different activities shall not be averaged to find a single average metabolic rate. As the students in the lecture room are assumed to do uniform activities, having the lecture together, doing things like typing, being seated and talking, therefore the metabolic level is assumed to be 1.1 met. Before the first lecture of the day, however, the situation at this time is the occupants come into the building for lectures in advance and they tend to stand, wait and chatting instead of having lectures. Therefore the input metabolic level before the lecture is assumed to be 1.3 (between standing relaxed 1.2 and filing, standing 1.4) according to the ASHRAE Standard (ANSI/ASHRAE Standard 55-2010, 2013).
Table 5.2 Metabolic Rates for typical light task (ANSI/ASHRAE Standard 55-2010, 2013)
On the other hand, in winter, for the clothing insulation in heating-dominated season, people tend to wear long-sleeve shirts, sweaters and trousers in indoor environment and therefore a 0.8 clo insulation level is assumed (ANSI/ASHRAE Standard 55-2010, 2013).
Overall inputting the required values to the CBE thermal comfort model and the results are automatically shown.
Figure 5.25 Case 3 result in CBE Thermal Comfort Tool (Hoyt, Schiavon, Piccioli, Moon, & Steinfeld, 2019)
Table 5.3 Summary of the three scenarios input and results
Case 1: at 18:00, 28/1 Case 2: at 7:30, 3/2 Case 3: average value
input temp 25.5 22 23.8 input humidity 45 28 36 air speed 0.08 0.08 0.08 metabolic 1.1 1.3 1.1 clothing 0.8 0.8 0.8 PMV 0.40 -0.10 0.00 PPD 8% 5% 5%
Sensation Neutral Neutral Neutral
From the summary, the thermal comfort level of different scenarios can be known. U41 performed an average excellent thermal comfort. However the input is based on various assumptions in air speed, clothing insulation and metabolic level and the precise PMV and PPD value at that time should be further verified using more detailed measurements.
Through setpoint offset sensor OS101 in the room, it can be known that though the room is located in the north side, the setpoints kept the default setpoint 22℃, indicating an overall satisfied thermal comfort
