Ecotect in Design

The use of thermal modelling tools in the design process needs to be informative rather than prescriptive. Modelling is a practice which requires a disciplined procedural approach and may not fit in well with everyones approach to design. The incorporation of environmental modelling techniques will therefore demand a degree of flexibility not conventionally applied to modelling. However, some understanding of procedure is necessary before adopting ones own methods.

By considering main priorities and influences we can determine a methodology for using Square One/Ecotect tools. The flexibility of the tool should help in personalising a methodology. However any methodology needs to be flexible and defined by the aims of the project in which it is to be used.

A procedure for using modelling in design may involve some of the following steps

Listing of those aspects which are largely pre-determined: site landscape, terrain, approximate location on the site, climate,...

An assessment of climate can help us to determine priorities:

1. Orientation

Is orientation to be determined by heating or cooling performance or a combination of both? Is there sufficient radiation to make passive heating an option or should effort be concentrated on reduction of heat loss? What type of cooling techniques are appropriate: should we build heavyweight or lightweight? will we be making much use of ventilation and thus (perhaps) have glazing partially determined by ventilation aims?

1.1 Orientation for Passive Solar Heating

These assessments can be made with Weatool, however Weatool examines data which is not modified by the local terrain/geometry of built environment. This omission will be of particular significance where passive solar heating may be useful. Thus, if the result of your analysis is that Passive Solar Heating potential is OK for the climate, can Ecotect itself be used to describe the surrounding environment and perform an analysis which will produce a more realistic assessment of winter solar availability?

1.2 Orientation for cooling: shading design and building form

With regard to orientation for cooling, this may be determined by maximum radiation or say, the most prevalent wind direction. Where it is determined by solar radiation then it might be expected to be roughly due South. If east of south then this will suggest clearer mornings than afternoons and the opposite for west of south. With the correct orientation we can design sunshades to reduce radiation at problem times. The shades do not have to be an add-on to the building but can be used to determine building form, such that major windows are recessed behind the main wall, or the floor above overhangs the floor below etc.

2 Daylight design

Orientation, glazing ratios and building form are likely to be the most influencial thermal factors in your design. Glazing ratios are determined largely by:

  • larger window, greater daylight available
  • larger window, greater ventilation available
  • larger window, greater heat loss in winter
  • larger window, greater heat gain in summer

Choice of glazing ratio will inevitably be made by best compromise of all 4 factors. Initial daylight availability studies will enable decisions on whether this is to be a factor in the choice of glazing ratios. If good daylight is available, then it can be assumed that the glazing ratio will be representative of an average daylight factor between 2 and 5% on the southernmost face. The relative importance of the other factors will help determine if the glazing ratio should be closer to that representing 2% or 5% daylight factor. Identifying

2.1 Daylight planning

The assessment of sky component at the building face is the first step in daylight design. Determining No-sky lines and thus window positioning and thence glazing ratios to achieve given daylight factors are subsequent steps. Ecotect uses the split-flux method (BRE Digest 309) to determine daylight distribution. This involves assessing three components: Sky Component, Externally Reflected Component, Internally Reflected Component. Can Ecotect be used to assess the daylighting potential of a site in a way compatable to that of Paul Littlefair,described in ...? Can it be used in the other steps, if so how. If not how might you use it for daylight glazing specification?

2.2 Shading and Daylight

If we are using the building form to provide shading then the shading will be fixed, thus reducing diffuse solar gains in the winter and daylighting all year. We can design shading for the month requiring maximum cooling (or a representative day in that month), this will have less of an effect in other months but these months will require less shading. To counteract the effect of a shading device providing 100% shading of direct light in the hottest month, will require a large glazing ratio on that wall. A smaller shade, whilst allowing a portion of the direct light through the windows will not need such large windows to achieve the same daylighting levels. The determination of an optimum shade and window size will require a careful procedure of runs with different shade/glazing configurations. For these you will need to make some assumptions about other parameters. For example building fabric and internal gains. These can be determined using known details of the building use together with benchmark figures. Glazing on other faces must be assumed, these could all be minimal or, say, with the North face with the same glazing specification.

3 Building Fabric

Once glazing ratio, orientation and building form have been determined the building fabric may be considered. In determining building fabric we will need to consider the make up of the different layers and the external surface properties. Rather than a trial and error approach of testing a multitude of different constructions one approach is to base your analyses on effectively one type of construction for each element. Each construction can be defined using 3 layers which differ only in their thicknesses. You will need to consider a systematic method of trying different constructions for different components. You will need to consider carefully how your assessments will be made, what period to model and what format output(s) presents best indicator of performances. This kind of study requires careful approach to developing material database and organising the use of it.

4 Further assessments

Further assessments will require closer examination of heating and particularly cooling strategies as suggested by WeaTool. These will depend upon Weatool climate evaluation. External surface properties will be involved in the determination of radiative properties between the building, landscape and the sky. The alternate material property used to specify constructions may be used to alter radiative characteristics for day and night. It appears that evaporative cooling cannot be modelled by ecotect. However, by modifying the temperature and humidity of the climate to the wet bulb temperature with 100% humidity, the potential of indirect evaporative cooling may be assessed.


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Ecotect In Design

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