It is useful to know the implications for energy conservation of the designer's early decisions. The plan form, the facade design, and the proportion of internal areas all play a crutial role.

Any calculation method employed must be quick and easy to use, in order to allow the designer to explore a number of options. Secondly, it must be able to respond to the main design parameters under consideration. Energy consumption will also depend upon other parameters such are artificial lighting levels and plant efficiencies. However, these can be regarded as engineering parameters and to some extent can be considered independently.

1. local climatic conditions
2. orientation of facade
3. area and type of glazing
4. obstructions due to adjacent buildings(or parts of the same building)
5. the inclusion of an atrium(optional)
6. occupancy and vacation patterns
7. lighting levels
8. internal gains

The basis of the design tool is a set of graphs, the LT Curves, giving annaul primary energy consumption per square metre for North, East/West and South orientations of the facade, plus one for horizontal glazing(rooflights). Curves are presented for lighting, heating, ventilation and cooling, and total energy, for two climatic zones, northern UK and southern UK. (Curves are also available for all European climatic zones but not illustrated here.)

The model used to dervive the curves takes account of the energy flows associated with inputs for heating, cooling, and ventilation, and lighting, and ambient energy flows due to fabric and ventilation heat losses, solar gains and useful daylight as illustrated below:

Amongst the considerations early in the development of a building design, the designer is concerned with two issues:

• The form of the building - its plan depth, section orientation etc. and;
• design of the facades; in particular the area and distribution of glazing

It is useful to know the implications for energy conservation of the designer's early decisions. The plan form, the facade design, and the proportion of internal areas all play a crutial role.

Any calculation method employed must be quick and easy to use, in order to allow the designer to explore a number of options. Secondly, it must be able to respond to the main design parameters under consideration. Energy consumption will also depend upon other parameters such are artificial lighting levels and plant efficiencies. However, these can be regarded as engineering parameters and to some extent can be considered independently.

The LT Method (LT standing for Lighting and Thermal) is an energy design tool which has been developed expressly for this purpose. A computer-based model has been used to predict annual primary energy consumption per square metre of floor area as a function of:

1. local climatic conditions
2. orientation of facade
3. area and type of glazing
4. obstructions due to adjacent buildings(or parts of the same building)
5. the inclusion of an atrium(optional)
6. occupancy and vacation patterns
7. lighting levels
8. internal gains

The basis of the design tool is a set of graphs, the LT Curves, giving annaul primary energy consumption per square metre for North, East/West and South orientations of the facade, plus one for horizontal glazing(rooflights). Curves are presented for lighting, heating, ventilation and cooling, and total energy, for two climatic zones, northern UK and southern UK. (Curves are also available for all European climatic zones but not illustrated here.)

The model used to dervive the curves takes account of the energy flows associated with inputs for heating, cooling, and ventilation, and lighting, and ambient energy flows due to fabric and ventilation heat losses, solar gains and useful daylight as illustrated below:

The Climatic Zones

• Zone 1 - Jan less than 6^oC July less than 24^oC
• Zone 2 - Jan greater than 6^oC July greater than 24^oC

About 2/3 of sites in Southern Europe fall into one of these categories. A substantial number of sites experience the higher winter temperature with the lower summer temperature and vice versa. This can be allowed for by using the appropriate curves from both zones.

It must be stressed that the LT Method only responds to relatively few of the many designparameters of a building. It is beyond the scope of simplified methods to deal with the full range of these parameters and their interactions quantitatively.

The LT Method is available both as a manual and computer based tool. The manual method requires only the use of pencil and calculator, entering values taken from the architectural drawings and the LT curves, on to the LT Worksheet. The computer method is provided as an Excel (Microsoft) spreadsheet application which is available for both the PC and the Macintosh.

Two totals are shown, heating + cooling + lighting (total), and heating + lighting (h + l). The cooling curve includes an allowance for fan power as well as refrigeration. The total without cooling can be used to indicate the energy use of a non air conditioned, naturally ventilated building. However, a fixed allowance for fresh air mechanical ventilation must be added for all non-passive zones. This value is given at the bottom of each set of four graphs. For buildings with high internal gains, these non-passive areas would be air conditioned and the cooling and fan power should be read off from the LT Curves at the zero % glazing intercept.

Using The LT Method involves the following sequentially addressed concepts and issues:

• The passive zone
• The LT curve
• Glazing & Orientation
• Shading
• Using A/C ?
• CO₂emissions