3.5 Task 1: Model development and validation
3.5.4 Housing stock representation using archetypes
The housing stock is represented in the models through the creation of 12 different archetypes as shown in Table 3-2. The parameters which are used to differentiate between archetypes are: 1) Building construction by built form, and 2) Building size in terms of useable floor area. These two parameters have been chosen as they are considered to be amongst the main heat energy consumption influencing factors associated with the building physical characteristics as discussed in Section 2.5. The built-form and building geometry parameters considered are consistent with the categorisation used by the EHS and other researchers as previously discussed in Section 2.3., and standard house descriptions by Allen and Pinney (1990) (DCLG, 2013; Yeo et al., 2005; Yohanis, et al., 2010; Firth et al., 2010; Taylor et al., 2013).
Table 3-2. Details of the building archetypes considered.
Archetype differentiators
Built forms Floor sizes (m2)
Variables Detached, Semi-detached, Mid- terrace
and purpose built Flat 70, 90 and 150
Total variables 4 3
Total number of archetypes 12
Building typology and the internal living space arrangement
The built forms considered during this research are detached, semi-detached, mid- terrace and purpose built flats. Figure 3-4 shows Google SketchUp screen shots of these dwelling built forms. In this study simplified buildings are considered with straight rectangular or square windows. The models incorporated glazing values ranging from about 16% to 20% of the external wall surface area.
The buildings were arranged to have three thermal zones; Zone 1) Ground Floor (GF), Zone 2) First floor (FF), and Zone 3) Loft, with exception of the flat. The table in Appendix A contains details of the floor area, volume and thermal capacity values used for each of these thermal zones. The GF and the FF zones are living spaces and are connected to the heating system via convector radiators. Zone 3 is not heated, therefore not connected to the heating system. Treating each floor as a single zone is consistent with some of the commonly used steady state models such as BREDEM (Korolija, et al., 2013). There is a 2m2 air hole between the GF and the FF simulating airflow through the stair case. The flat has only one thermal zone and
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connected to the heating system by convector radiators. The FF floor and the GF ceiling are identical with a layer of carpet on the FF side and a layer of plasterboard on the GF side. The internal partitions reflect the ground floor and first floor each having 4, 6 or 8 rooms corresponding to the useful floor area of 70m2, 90m2 and 150m2 respectively.
Shading objects were added to represent adjacent properties (see Figure 3-4). The party-walls between the dwellings are defined as boundaries with identical surface temperature as the inside surface temperature of the external walls, to simulate similar heating characteristics.
a) b)
c) d)
Figure 3-4. Screen shots of Google SketchUp drawings of the buildings illustrating the built forms with adjacent shading blocks: a) Detached – Base Case, b) Semi-detached, c) Mid terrace, and d) Flat.
The sizes of the buildings are identified by the useful occupied floor area that is heated. The size of UK dwellings can vary considerably from around 50m2 for a flat to over 150m2 for a detached building, and have an average value of around 90m2 to be in line with the average floor area of dwellings in the housing stock (DCLG, 2013). In terms of the heating needs, the three sizes of dwellings have been considered in this
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study represent the majority (approximately 85%) of the existing housing stock in terms of the usable floor area. For example, a floor area of 70m2 represents dwellings sizes up to and including 70m2, a floor area of 90m2 represents floor sizes from 70m2 to 90m2, and floor area of 150m2 represents floor sizes from 90m2 to 150m2. The floor area is assumed to be equally split between the Ground Floor (GF) and the First Floor (FF) with the exception of the flat. All building typologies except the flat have loft floor area, though this is not considered as occupied and is not heated.
The thermal characteristics of the housing stock are represented through depicting the thermal insulation levels of the main building fabric components reflecting the recommendations of the 1980, 1990, 2002 and 2010 building regulation standards. This meant that the research focused on investigating the impact of TES in dwellings with thermal insulation levels recommended by these building regulation standards. The reason for this approach is that TES for heat demand management purposes could be more useful in the future where electric heating is wide spread, and when the thermal quality of buildings has improved. It was considered that this approach would provide better insight into how the TES characteristics and its effects could change as lower thermally performing dwellings are brought to the levels required by the later building regulation standards, through retrofits and upgrades of the building components.
Building regulations are used as drivers for improving the thermal performance of the buildings and bringing the dwellings to common levels. This is done by ensuring that the main building fabric components such as the external walls, roof, floor and windows and doors adhere to specific heat transfer rate requirements in terms of the U-value. Research indicated that the U-values of the external walls, external windows & doors, roof, floor and the infiltration level due to air tightness are the main building components which dictate the thermal performance of buildings. The U-values used for these components which correspond to the four building regulation considered are provided in Table 3-3.
The construction of the key building components which are used in the models to make-up the buildings are shown in Table 3-4. The thermal conductivity, specific heat capacity, density and thickness of the key materials used are illustrated. The thickness of the building fabric components and the combined U-values are shown
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for the four building regulations standards considered. Typical ground floor construction is used with varying material thickness and type. The external walls considered are of cavity wall type, incorporating cavity insulation and internal surface insulation according to the U-value requirements of the building regulation. This is because insulated and uninsulated cavity walls made up a large majority (69% or 15,701,000) of the housing stock in England in 2011 (DCLG, 2013). The window variations included single glazed, double and argon filled triple glazed windows. The roof and the first floor ceiling are separated creating an unheated loft space. The U- value of the first floor ceiling in this study is one that provides the main thermal insulation between the thermal zone and the loft zone, and is comparable to the roof U-values usually referred to in the literature.
The whole building infiltration levels used in the models which correspond with the four building regulation standards considered are shown in Table 3-3. Infiltration results due to inadequate air tightness of the buildings and remains present at all times, and is a source of heat loss from the thermal zones.
Table 3-3. Dominant building fabric U-values and whole building air infiltration and ventilation rates by building regulation standards. Floor
W/m2.K
Ext. Wall W/m2.K
Windows & Doors W/m2.K Loft/Roof W/m2.K Infiltration ACH 1980 Regulation 0.74 0.60 5.70 0.40 2.00 1990 Regulation 0.45 0.45 3.30 0.25 1.75 2002 Regulation 0.25 0.35 2.00 0.16 0.75 2010 Regulation 0.17 0.22 0.96 0.14 0.40
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Table 3-4. Building fabric construction details.
Conductivity (kJ/hm2K) Specific heat capacity (kJ/kgK) Density (kg/m3) Thickness(m) Overall U-Value (W/m2K) Internal/external surface
resistance
Building regulation Building regulation Building regulation Building regulation Building regulation Rsi Rse
Material 1981 1990 2002 2010 1981 1990 2002 2010 1981 1990 2002 2010 1981 1990 2002 2010 1981 1990 2002 2010 m2.K/W m2.K/W
Ground Floor Carpet - - - - - - - - - - - - - - - -
0.74 0.45 0.25 0.17 0.13 0.04 Timber flooring, 0.504 0.504 0.504 0.504 1.20 1.20 1.20 1.20 650 650 650 650 0.300 0.300 0.300 0.300 Air gap, - - - 0.300 0.300 0.300 0.300 Insulation 0.090 0.090 - - 1.25 1.25 - - 15 15 - - 0.014 0.030 - - concrete 7.560 7.560 7.560 7.560 1.00 1.00 1.00 1.00 2400 2400 2400 2400 0.400 0.200 0.300 0.350 Polystyrene - - 0.09 0.09 - - 1.00 1.00 - - 15 15 - - 0.080 0.130 Sand gravel 2.52 2.52 - - 1.00 1.00 - - 1800 1800 - - 0.400 0.200 - -
External Wall Plaster board 1.260 1.260 1.260 1.260 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.015 0.015 0.015 0.030
0.60 0.45 0.35 0.22 0.13 0.04
Block inner skin 1.836 1.836 1.836 1.836 1.00 1.00 1.00 1.00 1400 1400 1400 1400 0.100 0.100 0.100 0.100
Insulation 0.155 0.144 0.144 0.144 0.84 0.84 0.14 0.14 12 12 10 10 0.060 0.060 0.093 0.150
Facing brick outer 4.799 4.799 4.799 4.799 0.92 0.92 0.92 0.92 2002 2002 2002 2002 0.100 0.100 0.100 0.100
Internal Wall Plaster board 1.260 1.260 1.260 1.260 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.015 0.015 0.015 0.015
1.89 1.89 1.89 1.89 0.13 0.04
Air gap - - - 0.200 0.200 0.200 0.200
Plaster board 1.260 1.260 1.260 1.260 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.015 0.015 0.015 0.015
Roof Slate tiles, 3.600 3.600 3.600 3.600 1.00 1.00 1.00 1.00 2000 2000 2000 2000 0.025 0.025 0.025 0.025
4.87 4.87 4.87 4.87 0.13 0.04
Ash-felt 0.610 0.610 0.610 0.610 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.002 0.002 0.002 0.002
External Windows
& Doors SG/DG/TG
~15% of floor area 5.70 3.30 2.00 0.96
FF floor/GF ceiling Carpet - - - -
1.33 1.33 1.33 1.33 0.13 0.04 Timber floor 0.504 0.504 0.504 0.504 1.20 1.20 1.20 1.20 650 650 650 650 0.020 0.020 0.020 0.020 Air gap, - - - 0.300 0.300 0.300 0.300 Plasterboard 1.260 1.260 1.260 1.260 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.015 0.015 0.015 0.015 Loft floor/FF ceiling Insulation 0.144 0.144 0.144 0.144 0.84 0.84 0.84 0.84 12 12 12 12 0.090 0.145 0.240 0.275 0.40 0.25 0.16 0.14 0.13 0.04 Plasterboard 1.260 1.260 1.260 1.260 1.00 1.00 1.00 1.00 1200 1200 1200 1200 0.015 0.015 0.015 0.015
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