Office design software

Devised by National Energy Services (NES) and funded by the Department of the Environment, Transport and the Regions, the Windows-based program can provide a rapid and accurate analysis of different ventilation and air conditioning strategies. Results from design iterations are expressed in simple, easy to understand, computer graphics (figure 1).

The effectiveness of the strategies are assessed in relation to building type, location, and internal and external loads. The user selects a typical ventilation scheme, sets the physical parameters of the building – location, loads, U-values, glazed area etc – and the program gives predicted values of internal temperature, daylight factors, noise and air quality.

Other screens provide predictions of overheating exceedance hours, benchmark data for energy consumption, capital and maintenance costs.

Users can either select the program's default values, which cover structure, glazed area, air change rates etc, or create a specific building profile. Hence, if a client wants a naturally ventilated, lightweight office block in an urban location, the known details can be entered and any thermal or acoustic problems quickly identified.

Conversely, if a client wishes air conditioning for a rural location, the program should enable the services engineer to demonstrate the comfort, energy and cost benefits of a more energy efficient solution.

Using the program

After loading the program into Windows, users are presented with an introductory screen which gives access to 44 building case studies.

There are various ways to use the database, the custom search being the most useful for finding a building close to the one under design. The user can search for location, structure type and ventilation/air conditioning system.

The case studies provide details on spatial layout, U-values and thermal mass, with information given about energy consumption when it is available, which is rarely.

Once the user has located a building close to the one being planned, they can model a variation on the theme. This can be done in two ways: via a "model" dialogue box, which goes straight to a modelling program, or for novice users, indirectly through an electronic version of the AM10 ventilation strategy decision tree.

If following the AM10 route, the user must answer a series of questions about the proposed building, such as: "Is space heat gain more than 35-40 W/m²?" While these questions demand yes/no answers, clues are given about lighting, occupancy levels and small power loads to guide the user to the most appropriate answer.

Depending on the users' responses, the program will select a ventilation strategy, from natural ventilation to full air conditioning (figure 2).

Selecting the highlighted strategy allows the user to return to the case studies or carry out a design exercise on the generic building type chosen in the AM10 tree. Users can either use the default settings for design heat gains, glazing ratio etc, or key in values.

Dynamic modelling

The ODT program provides users with a list of the default characteristics of a typical building. They can then choose a particular ventilation and cooling strategy and see the effect this has on dry resultant temperature, air quality, daylighting and internal acoustics.

Active dialogue boxes enable users to change structural characteristics of the building, its window heights and glazed areas, and floor to ceiling heights. By clicking on a plan view of the building the internal structure can also be modified.

Four generic office types – from lightweight to heavyweight – can be chosen, or the user can manually select structural elements; suspended ceilings and floors with heavyweight internal and external walls, for example.

Finally, the user can change the type of glazing, the sky angle and endow the building with a range of shading devices, from mid-pane blinds to external sunbreakers (figure 1). They can then modify metabolic, equipment and lighting gains, and change hours of occupancy to examine what effect this will have on comfort conditions.

All of this will have either a negative or positive effect on the building's comfort parameters. These are displayed for the 23 July design day, the day generally used in modelling for overheating calculations (see figure 1).

Different ventilation and air conditioning strategies can also be applied to the customised building to see which offers the best internal conditions. The program asks the user if the air change rate should be set to the design recommendation. If yes is selected the system defaults to loaded settings. If no is chosen the air change rate can be modified.

At all stages in the process the program allows the user to takes "snapshots" of the building profile. Multiple profiles can then be compared on the basis of dry resultant temperature, noise, air quality etc.

Usability

The program is eminently useful for lay clients and specialists alike, and allows quick and accurate iterations. The snapshot feature is ultimately the most helpful function, enabling the user to keep track of changes to the default settings.

Indeed, the industry steering groups governed by project manager ECD Energy and Environment, concluded that developers and other clients would find the program very useful for understanding the technical implications of concept designs. If clients get this program, then designers should too, even if it can't do full thermal simulation.

The program is riddled with warnings not to adjust default settings unless the user has the required knowledge. Each step has a dialogue box which the user must click to acknowledge the consequences of a choice before moving on. Irritating but defensible, and after a while easy to do without thinking.

The energy and cost information is currently passive, showing only typical and good practice benchmark figures for the default settings. Any changes made to equipment gains, ventilation rates and lighting will affect dry resultant temperature but not the building energy consumption.

This was regarded as too difficult to set up for the first version of the Office Design Tool, but NES intends to include this vital function in a later version. The same is true for the capital and running costs, although it would have been useful to enable users to attach their own cost database in the way that a glazing catalogue can be added in the windows section.

It is worth noting that ECON Guide 19 does not recognise advanced natural ventilation, so the programmers broke down the subsets in ECON Guide 19 and generated a unique profile.

The daylighting side is not as sophisticated as some might expect. For example, if the daylight factor falls below a certain level it is reasonable to assume that the electric lighting gains will be higher, which will affect internal temperature. However, the program does allow the office decor to be lightened or darkened, which does affect the daylight factor.

The program has been extensively tested by designers and developers. Although the thermal calculation program is not a full dynamic thermal simulation, the BRE ran it against the SERI-RES program and got almost identical results.

The case studies are useful as far as they go, but there is a distinct paucity of performance and measured energy consumption data. What design data there is relies on BRECSU reports and BREEAM assessments. There is also very little information on occupancy satisfaction beyond anecdotal reporting. This would be a very useful addition in latter versions of the program, as would a more user-friendly front end.

The tool is not wholly intuitive to use. It is not clear, for example, whether one should start by browsing case studies or go through the AM10 ventilation decision tree. The program would certainly benefit from an installation wizard to guide people on how to use it.

Nevertheless, as a tool for advising clients, the program is extremely useful, and it can only get better as information is added and the passive elements like energy and cost data are made more dynamic.

Cost and availability

National Energy Services will be selling and maintaining the program on behalf of the DETR. It ran happily in this test on a 233 mHz pc with 64 mB ram under Windows 98, but it should run on slower machines.

Nearly 200 mB of hard disk space is required, about 181 mB of which is for the case-study images, so ram is important.

The price has been set at £500 per copy or per computer, but National Energy Services will negotiate special rates for multiple users. A normal site licence to enable the program to run on every pc at one location will cost £1250.