CLIMATE-RESPONSIVE DESIGN – MATCHING SUPPLY OF RENEWABLE ENERGY SOURCES AND ENERGY DEMAND PATTERNS IN DWELLINGS FOR IMPROVED COMFORT

Remco LOOMAN 1

Dr. Andy VAN DEN DOBBELSTEEN 2

Prof. Hans CAUBERG 3

Keywords: Climate-responsive design, renewable energy, indoor comfort, energy patterns

Abstract Typical newly-built dwellings in industrialised countries and temperate climates function rather indifferent to dynamic climatic conditions. The indoor environment is controlled by comfort systems that rely heavily on auxiliary fossil energy (e.g. electricity and natural gas). Alternatively, one could benefit from the ubiquitous renewable energy sources in the built environment, such as direct solar radiation, daylight, wind and the earth’s high thermal storage capacity. Implementation of these natural energy sources in building design contributes to lowering the energy consumption of traditional building designs and, in addition, reduces undesired effects of pollution and waste generation. The key in making successful use of their potential is to bridge the discrepancy between patterns in space and time of the natural energy supply and building energy demand. With climate-responsive design the whole building as a system responds to dynamic climatic conditions in order to comply with comfort demands, without the direct need for electricity and natural gas. In the paper patterns in energy supply and demand will be explored from the climate and its sensitivity to climate variations. Different passive climate-responsive concepts will be discussed. Furthermore, the relationship between energy and both architectural form and climate-responsive concepts are analysed to identify initial design principles for climate-responsive building.

1. Introduction Typical newly-built dwellings in industrialised countries and temperate climates function rather indifferent to dynamic climatic conditions. The indoor environment is controlled by comfort systems that rely heavily on electricity and natural gas. As for example in the Netherlands installations such as balanced ventilation with heat recovery and high-efficiency boilers for space heating and hot water production have become the standard set of equipment. Alternatively, climate-responsive design benefits directly from available natural energy sources. The basic idea is that comfort is provided in close interaction with the dynamic conditions in the built environment. Comfort is provided when needed and delivered where needed, while buildings can respond to changes in the internal and external climate and to occupant intervention (IEA, 2006).

2. Climate-Responsive Design With climate-responsive design one benefits from low-grade energy sources in the built environment for passive or low-energy comfort provision. However, sometimes the dynamics of outdoor conditions do not match indoor comfort requirements. In these times, comfort can be guaranteed from an effective energy housekeeping strategy where the harvesting of external energy forces is complemented by principles of energy conservation, distribution, buffering, recovery and storage. Many comfort aspects can be sufficed directly from harvesting or adverting naturally available energy flows. These so-called comfort-from-climate principles include common principles such as passive solar heating, natural ventilation and natural illumination and less common principles such as solar driven ventilation that can be made beneficial as well. There are different strategies of supporting energy deployment that can be

1 Faculty of Architecture, Delft University of Technology, r.h.j.looman@tudelft.nl 2 Faculty of Architecture, Delft University of Technology, a.a.j.f.vandendobbelsteen @tudelft.nl 3 Faculty of Architecture, Delft University of Technology, h.cauberg@chri.nl

called upon to complement comfort-from-climate principles. These energy housekeeping strategies are based on conservation, buffering, distribution, recovery and storage of energy.

Figure 1 Energy balance of a climate-responsive building (see picture) combines both comfort-from-

climate principles (open green arrows; upper part of table) and energy housekeeping principles (solid blue arrows; lower part of table).

Many climate-responsive design solutions are based on these principles or operate from a combination of them. A patchwork of different design solutions will provide a comfortable building from an effective use of energy. While significant energy reduction is the aim of climate-responsive design, passive design measures can be seen as a first step in design optimisation. However, overall performance can be improved with aid of complementing mixed-mode systems and smart control mechanisms. Most principles will function next to one another without compromising individual performance, but some combinations require special attention in the design process in order to prevent conflicts in the final design that would significantly reduce overall performance. Beside possible conflicts, some climate-responsive principles have a great opportunity of improved overall performance through collaboration. Piling up multiple climate-responsive design solutions can boost both energy and comfort performance.

3. Research Context Climate-responsive building design preferably commences from scratch and uses climate and comfort as a context. Redesigning conventional buildings with climate-responsive design solutions is a different way to determine a design strategy. A starting-point is to exclude conventional comfort systems and assess (thermal) comfort when applying different climate-responsive design principles. The reference building model then becomes a typically newly-built dwelling but without its mechanical comfort systems. This means there is no energy input to control the indoor temperature other than from natural gains (e.g. solar irradiation, occupation) and losses (e.g. transmission, ventilation). Building simulations conducted on these so-called free-running buildings provide insight into the building’s initial comfort performance and energy-saving potential. Simulations were performed with the aid of TRNSYS, a transient simulation tool that simulates thermal energy systems, such as buildings. An integrated assessment of results is assured while climate-responsive concepts are implemented into a reference building model. Climate-responsive building design is beneficial regardless of climate and building use, because it takes the dynamics of the climate and required comfort demands as a starting point. In order to assess different solutions, a single-family house situated in The Netherlands was taken as the reference.

3.1 Climate Building simulations are performed with reference climate data for De Bilt, the Netherlands (52˚ 06’ N and 5˚ 11’ E), which contain climatic data from the year 1995. Mean ambient temperatures range from 2.2˚C in winter to 16.9˚C in summer.

3.2. Comfort Comfort knows many facets, including thermal, visual, acoustical and aesthetical aspects. Thermal comfort is an important aspect in building design and often considered as the driving force on which many comfort-related design solutions are made. Traditional thermal comfort standards consist of strict temperature ranges in which the indoor temperature may vary in order to maintain a certain level of comfort. The lower and upper limits of indoor air temperatures are respectively 20˚C and 26˚C for habitable rooms (NEN, 2007). Thermal comfort performance assessment is often done by calculation of the frequency that the comfort limits are exceeded.

3.3 Building model A mid-terraced dwelling is chosen as the reference dwelling. This type of dwelling is the most common in both existing stock and new housing developments in the Netherlands. The building shape and layout is based on the reference dwelling as described by SenterNovem (2006), an agency of the Dutch Ministry of Economic Affairs, and can be seen as a schematic representation of the standard in current and expected building design in the Netherlands. The two-storey building has a flat roof, a gross floor area of 91.0 m2 and a floor height of 2.60 m. The living room has a large transparent opening to the terrace.

Figure 2 Reference building plan (SenterNovem, 2006) with a slightly altered layout. The reference dwelling is constructed from massive building elements (concrete and brickwork) and meets standard thermal and acoustic insulation requirements. All transparent openings are constructed from high-efficiency insulated double glass panels. The properties are gathered in table 1. Ventilation rates are based on minimal demands set by Dutch regulations (VROM, 2003), which are determined by health aspects. A total amount of 160 m3/h of fresh air is delivered to all habitable rooms. The airtightness of the building is relatively high which is typical for this type of construction when special attention is paid to architectural details during construction.

3.4 Design strategy The key in making successful use of climate-responsive design solutions is to bridge the discrepancy between patterns in space and time between natural energy supply and building energy demand; between climate and comfort. Discrepancies in time occur in many time-scales. In this paper the focus is on diurnal and seasonal variations. Both time-scales can be visualised simultaneously by using so-called ‘temperature squares’, which display monthly mean air temperatures per hour of the day. The use of such temperature squares provide a quick preview to what extent certain design solutions harness a specific climate and establish more comfortable indoor temperatures. Moreover, they can assist in decision-making. A selected set of temperature squares is shown in figure 3. It includes the square for ambient air temperature for the specific climate (#01) and indoor air temperature from free-running building simulations with reference building characteristics (#02). The temperature course of the reference calls for a strategy to increase energy gains for heating throughout the day during the colder periods (October to April). At the same time, cooling strategies are needed to prevent overheating during the latter parts of the day in summer (July and August). As shown in figure 1 comfort-from-climate principles include sun and earth as potential sources for heating and energy housekeeping principles include thermal conservation and thermal mass, among others. The proposed design solutions in this research paper focus on simple passive measures, considered as an initial step in climate-responsive design, and do not require human or mechanical intervention during its operation (e.g. sensors, switches). The only ‘responsive’ behaviour may be season-dependent intervention to switch between summer and winter climate-responsive strategies (e.g. placement of shading devices in summer).

4. Performance Assessment of Climate-Responsive Concepts

4.1 Benefit from the heating potential of the sun Careful tuning of solar radiation collection, thermal conservation and diurnal storage determines to what extent passive solar heating can contribute to annual space heating. The collection of solar radiation is set by three design parameters: building orientation, window size and reflective characteristics of transparent openings. It is commonly known that for maximum solar radiation collection, a building should face the sun (i.e. south in the Northern Hemisphere) (Brown & DeKay, 2001; Roaf et al., 2007). Small deviations up to 30 degrees have a slight affect on total collection but can shift the collection more towards the early or late hours of the day, if desired. The obvious design solution for thermal conservation is to increase insulation levels. Special attention is needed when using both passive solar heating and thermal conservation techniques while windows are ‘weak’ elements in a thermal conservation strategy. Typical insulation capability of windows is in general worse than that of non-transparent building elements. Furthermore, insulation properties of non-transparent elements can be improved at much lower costs. It is therefore important to find a balance between solar radiation collection and heat loss through windows. Thermal mass spreads diurnal variations in solar radiation, reducing both cooling needs during daytime and heating needs during night-time. At direct gains, surfaces of thermal mass should be both large and thick enough and should be well-exposed to direct solar radiation. A point of concern is the cumulative accumulation effect during longer hot periods in summer. Further extension of the concept of passive solar heating can be done through a sunspace. A sunspace is an adjacent room to the building, not necessarily a living space, which specifically collects solar heat in order to heat other rooms. Therefore the sunspace itself suffers large temperature swings. The climate-responsive capability of a sunspace consists of three functions: thermal buffer of rooms attached, direct solar air heating of rooms attached and preheating of fresh air. In this paper the sunspace is considered in one design and two different configurations, as thermal buffer and to preheat fresh air.

Table 1 Design parameters selected for passive heating strategies.

Strategy Abbreviation* Properties Passive solar heating Orientation OR _REF South Window size on ground floor WS_GF _REF 73 % (= 9,7 m2; Effective glass fraction = 62 %) _90% 90 % (= 12,0 m2; Effective glass fraction = 77 %) Thermal conservation Insulation INS _REF Wall and floor = 3.0 m2K/W; Roof = 4.0 m2K/W _+ Wall and floor = 4.0 m2K/W; Roof = 5.0 m2K/W _++ Wall and floor = 8.0 m2K/W; Roof = 10.0 m2K/W Window configuration WC _REF Uglass = 1.27 W/m2K; g-value = 0.591 Thermal mass Thermal mass of ground floor TM_GF _REF ~ 160 kJ/m3K _+ ~ 410 kJ/m3K Additional measures Solar space +SS1 Sunspace used as thermal buffer

+SS2 Sunspace used both as thermal

buffer and to preheat fresh air

* All parameters are marked with an abbreviation which generates a quick reference of assessed parameters.

The results of the simulations are listed in table 2. The simulations are ranked to the frequency of exceeding the lower comfort limit (T < 20˚C), represented by index numbers. The frequency of the reference (REF) is set as index 100.

Table 2 Results – impact of passive heating strategies. R

anki

ng

WS_

GF_

90%

TM_G

F_+

INS_

+

INS_

++

+SS1

+SS2

Inde

x - T

< 2

0˚C

1 SIM036 ■ ■ ■ ■ 72 2 SIM034 ■ ■ ■ 72 3 SIM035 ■ ■ ■ 73 4 SIM033 ■ ■ 73 5 SIM024 ■ ■ ■ ■ 76 6 SIM022 ■ ■ ■ 76 7 SIM023 ■ ■ ■ 77 8 SIM021 ■ ■ 77 9 SIM020 ■ ■ ■ 78 10 SIM018 ■ ■ 78 11 SIM019 ■ ■ 79 12 SIM017 ■ 79 13 SIM028 ■ ■ ■ 88 14 SIM026 ■ ■ 88 15 SIM025 ■ 92 16 SIM008 ■ ■ ■ 93 17 SIM032 ■ ■ ■ ■ 93 18 SIM006 ■ ■ 93

Ran

king

WS_

GF_

90%

TM_G

F_+

INS_

+

INS_

++

+SS1

+SS2

Inde

x - T

< 2

0˚C

19 SIM027 ■ ■ 93 20 SIM030 ■ ■ ■ 93 21 SIM029 ■ ■ 95 22 SIM031 ■ ■ ■ 95 23 SIM004 ■ ■ 96 24 SIM002 ■ 96 25 SIM014 ■ ■ ■ 97 26 SIM016 ■ ■ ■ ■ 97 27 SIM007 ■ ■ 97 28 SIM005 ■ 98 29 SIM012 ■ ■ ■ 99 30 SIM010 ■ ■ 99 31 SIM013 ■ ■ 99 32 SIM015 ■ ■ ■ 99 33 REF 100 34 SIM003 ■ 100 35 SIM011 ■ ■ 101 36 SIM009 ■ 101

The results clearly show diversity in overall performance as the result of the interaction between multiple design solutions. For example, the use of a sunspace which also preheats fresh air (+SS2) avails in any configuration but the sunspace used solely as a thermal buffer (+SS1) does not necessarily. In any comparable setup, increased insulation levels lead to better performance, just like increased transparent openings facing the sun. As shown, simple passive changes already prove to be beneficial. Furthermore, the frequency of crossing the upper comfort limit increases significantly due to the use of the sunspace (+SS2). The application of sunspaces clearly calls for the need of cooling strategies to prevent discomfort due to overheating.

4.2 Cooling strategies External solar shading is an effective way to harness high solar radiation levels in summer. Different scenarios, such as assuring comfortable natural illumination levels or to be able to still benefit from passive heat gains during the early hours, recall measures that completely avert the sun. To suffice different needs, transparent elements can be partially accommodated with solar shading or supplied with shading devices that allow sufficient daylight to pass. Placement of temporary solar shading on the upper glazing of the sunspace during the hot summer period can decrease problems of overheating. The shading is mounted at the beginning of the summer and is demounted afterwards. While the lower part of the sunspace is not shaded, comfortable illumination levels should be guaranteed. Ambient temperatures hardly exceed the upper limits of human comfort perception (see figure 3, #01). Ambient air therefore has a large potential to cool down a building. A potential scenario is to ventilate the habitable rooms with ambient air in the hot summer months instead of warm air from the sunspace. Point of concern is to avoid undesired effects of draught when flushing the room with large air volumes.

Table 3 Design parameters selected for cooling strategies.

Parameter Abbreviation Properties Solar shading +SHAD External solar shading fixed to the upper glazing of the solar space during

May to September; shading reflects 70% of solar radiation. Natural air cooling +AIRCOOL The habitable rooms attached to the sunspace are directly ventilated with

ambient air during May to September. The impact of different cooling strategies is analysed using the best performance configuration, SIM036, which accommodates a sunspace to preheat fresh air (+SS2). The results are listed in table 4, and indicate the frequency of exceeding the upper comfort limit (T > 26˚C), represented by an index number. The frequency of the reference (REF) is set as index 100.

Table 4 Results – impact of cooling strategies.

Index - T > 26˚C REF 100 SIM036 221 SIM036 +SHAD 180 SIM036 +AIRCOOL 149 SIM036 +SHAD +AIRCOOL 93

The implementation of design solutions for passive heating provision will cause serious overheating during the summer if no cooling strategy is applied. Both cooling strategies have significant impact on cutting back high temperatures, with an improved performance when combined. Overall performance can be further improved by alteration of the cooling strategy through extension of the shading or natural air cooling period and by changing shading and air cooling properties (e.g. shading area, air flow rate), among others. Figure 3 shows the combined diurnal and seasonal variation for different configurations. These temperature squares indicate ambient air temperatures (#01) or indoor air temperature (#02 to #04) in the living room, located on the ground floor on the sunny side, which is taken as the representative zone. Highlighted values show discomfort; either temperatures too low (blue) or too high (red). The non-highlighted values show comfortable indoor temperatures between 20˚C and 26˚C.

Figure 3 Temperature squares: monthly average air temperature per hour of the day – ambient

temperature (#01); indoor air temperature for the reference building (#02); indoor air temperature for SIM036 (#03) and indoor air temperature for SIM036 including cooling strategies (#04).

The implementation of passive heating design measures results in elevated indoor temperatures during the heating period, which is significantly shortened (#03). In contrast, indoor air temperatures will become too high during the summer without a proper cooling strategy. A simple strategy of solar shading and air cooling during the hottest period reduces the change of overheating significantly (#04). Figure 4 shows a 3D representation of the final building design; summer situation with shading devices on the left and winter situation without shading on the right.

Figure 4 3D representations of the final building design.

5. Sensitivity to Climate Variations and Occupancy Patterns

5.1 Climate Variations Building design and system performance calculations require detailed weather data. Nowadays, the Test Reference Year used (CD_NL_1995) falls short while it does not take current trends in climate change into account. Within the scope of European standardisation work, a new set of representative weather data for the Netherlands was determined (NEN, 2008). The new reference year (CD_NL_2008*) is based on actual weather data spanning a 20 year period. Figure 5 shows the average ambient temperatures and global solar radiation for both sets of weather data. The average ambient temperature of the new reference year is 10.9˚C, which is 1.6˚C higher than the ‘old’ reference year. Solar radiation levels are on average 9% higher.

Figure 5 Monthly average ambient temperature (left) and solar radiation (right) for both ‘traditional’

reference year (CD_NL_1995) and the new reference year (CD_NL_2008*). The analysis results of the sensitivity to climate variations are listed in table 5.

Table 5 Results - impact of climate variation

Climate Index - T < 20˚C Index - T > 26˚C REF CD_NL_1995 100 100 REF CD_NL_2008* 84 145

The increased average ambient temperature and solar radiation levels clearly lead to a performance shift. The lower limits of thermal comfort are exceeded less while the upper limits are exceeded much more.

5.2 Occupancy Patterns Variations in occupancy patterns lead to a change in the supply of internal heat gains, an important source of energy in passive building design. The impact of occupancy variation is calculated for different time-dependent gains for all habitable rooms. The reference assumes an average value of 6 W/m2 and is compared to lower rates, typical for the PassivHaus standard. The results are listed in table 6.

Table 6 Results - impact of occupancy patterns

Internal heat gain Index - T < 20˚C Index - T > 26˚C REF ~ 6 W/m2 100 100 REF ~ 4.1 W/m2 109 73 REF ~ 2.1 W/m2 120 46

As can be seen, a lower internal heat gain causes a performance shift and puts more emphasis on heating rather than cooling. Beside changes in energy supply, occupancy patterns also define comfort demands in time. Strict comfort demands can be eased during the night or when the building is unoccupied. In addition, a more recent study (Brager & De Dear, 1998) notes downsides of traditional comfort standards (based on Fanger’s work) for non-air-conditioned buildings. New guidelines (Van der Linden et al., 2006) opt for a swing towards adaptive comfort standards, where thermal comfort depends more on the adaptability of humans and their environment. This especially exerts influence on the upper limits of thermal comfort in lasting warm periods, when higher indoor temperatures are allowed.

6. Conclusions From the starting point of analysing free-running building performance of a conventionally designed dwelling in the Netherlands, the impact of different passive climate-responsive concepts on both diurnal and seasonal comfort performance are theoretically studied in this paper. Many simple climate-responsive design concepts already prove to be beneficial. Moreover, their combined use often increases overall performance. Passive measures are considered to be a first step in climate-responsive design. More energy reduction can be achieved through supplementing mixed-mode solutions and smart control strategies. Dynamic outdoor conditions have a large impact on performance behaviour. Increased temperatures and solar radiation levels clearly cause a shift in performance with more emphasis towards cooling needs. Therefore, sensitivity to climate variations becomes an important aspect to building design. Another important aspect is human behaviour. Variations in occupancy not only determine internal heat gains, but also decide on comfort demands. Moreover, when humans are able to adjust their environment they accept larger temperatures swings which are more in tune with outdoor conditions. The results presented in this paper show the need for careful planning and tuning of implemented climate-responsive design concepts in order to benefit from them to the most. More profit can be yielded by using detailed climate and occupancy patterns to shape architectural form and layout.

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