F u t u r e E n e r g y D e m a n d i n U K H o u s i n g
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The building is provided with airtightness, durable and visually pleasing external cladding.
It has been adapted with solar thermal system to provide hot water source throughout
the year and was designed to meet Code Level 3 standard in the Code for Sustainable
Homes.
Data Acquisition
The construction detail of building fabric for the case study home is shown in Table 2.
The construction input data is based on three different scenarios as ‘Uninsulated’, ‘2006
Building Regulation’ and ‘Best Practice’, and also the study investigates the comparison
in energy consumption/demand between heavy-weight and light-weight structures.
Table 2. Adapted building standards (U-value and ac/h).
Uninsulated*
2006 Building Regulation
Best Practice
Case Study
Home
Wall
2.071
0.35
0.25
0.23
Floor
1.463
0.25
0.15
0.1
Roof
1.54 (flat)
2.93 (pitch)
0.25 (flat)
0.16 (pitch)
0.15
0.14
Window/Door
6.121
1.978
1.978
2.26
Air Infiltration
1
0.5
0.3
0.5
* Sourced from DesignBuilder building construction database.
If the UK climate warms up, it is reasonable to assume widespread adoption of cooling
systems in UK homes similar to that of warmer present day European countries. The fan
coil unit system was chosen to represent cooling systems in the study. A relatively poor
efficiency with a nominal energy efficiency ratio (EER) of 2.5
was used to show the
worst case electricity consumption of domestic cooling units. It is assumed that although
the building is naturally ventilated, the occupier will turn on the cooling system and close
the windows when the dwelling becomes too hot.
The weather data from the IPCC TAR A2 has a low confidence level for the wind data
and therefore the natural ventilation method was used by schedule rather than the
calculation. A minimum level of 0.8 ac/h and maximum level of 2.5 ac/h was chosen to
establish the effect of ventilation on energy use. The infiltration rate is affected by each
construction method and the input data is based on the three different building standards
as described. A large survey of houses by BRE (Uglow 1989) has shown that most
dwellings in the UK vary between 10 to 20 ac/h air leakage of 50@ Pa, and it is
equivalent to 0.5 to 1 ac/h at atmospheric pressure. Natural ventilation by operating
windows is assumed that between 0.5 and 1.5 ac/h. Therefore in this study, this gives an
overall combined value for infiltration and natural ventilation of 0.8 (‘Best Practice’ level)
ac/h to 2.5 (‘Uninsulated’ with poor airtightness level) ac/h.
Heating and cooling operation, internal gains and ventilation with infiltration were all
controlled by on/off mechanisms or profiles. Occupancy was set through these profiles to
represent a typical working family and a household with 9 to 5 working week day hours
was used. Internal gains from lighting, domestic appliances, number of people occupying
the dwelling and activity of the people, all affect the dynamic simulation results. These
gains are all essentially behaviour related parameters and as such are difficult to model.
Internal gains have been shown to vary widely even in identical properties (Socolow
1997, Summerfield 2007). The internal gains have been used by the UK National
Calculation Method (NCM) in the DesignBuilder database. This study focuses on
circumstantial rather than behaviour-related input variation. All other inputs other than
those detailed here are fixed with DesignBuilder default values and assumed to obtain
2
This was found to be suitable in compassion with a recent market survey on energy efficiency, by the
European Commission; ECODESIGN project.
