The following screen shots demonstrate well the specifications of the program in input, simulation and results.

1. Simulation Model and PC-program
2. Simulated Strategies for Natural Ventilation and Lighting
    2.1 Natural ventilation
    2.2 Reference Point of Light Sensor
3. Evaluation of Comfort in Summer with an Adaptive Comfort Model
4. Results
    4.1 Standard Weather
    4.2 Hot Summer Weather (2003)
5. Results produced by Primero-comfort
6. Conclusions

1. Simulation Model and PC-program

Figure 1: shows the initial window of the program which enables the user to provide basic project data.

As shown in Figure 1., the user is able to choose the climatic region of the project in the climate map, as well as, it can be user defined. We regard a south oriented, standard office room 3.95 (width) x 5.93 (depth) x 2.70 (height) with 2 (big) desks 0.8 x 2.0 m, in depth between 0.4 and 2.4 m. The internal heat gain considered for office equipment is 42 Wh/m² d and for persons is 30 Wh/m² d, the artificial light has a maximum power of 14 W/m².

Figure 2: Shows basic layout of the office room which can be done directly on the grids provided on the screen or can also be inserted manually by using “Terminal/Console” from drop down menu bar.

With the simulations we try to investigate the possibilities and limits of only passive methods (i.e. no air conditioning) for reaching a good comfort under summer conditions. The comfort will be evaluated with an adaptive comfort model, the Dutch ISSO 74 (2004).

Construction, facade, shading system, artificial light and their control systems are assumed as optimal for avoiding overheating in summer. Ceiling and floor are massive with solid floor, interior walls are assumed as light, the external wall as massive, insulated outside. The facade has a parapet; the window is shaded by a louver blind. For a maximum of daylight (and a minimum of artificial light and internal heat) when activated, the control system of the blind is shared in 2.1 m height: lower part cut off, upper part horizontal. The luminance level for lighting is set to 500 lx, if daylight is not sufficient, artificial light is dimmed to this value.

Figure 3: Shows the options for providing various kinds of floor, walls and ceiling as per the project type, which can be selected from the pre-defined types by the program. Insulation thickness and u-value can be manually inserted.

Parameters of the simulations are:

  • The width of the window (from 40 to 100% of the area above the parapet)
  • The type of glazing (sun g=0.33 or heat protection g=0.60)
  • The depth of reference point for lighting (light sensor for daylight)
  • The climate data: All simulations for Hamburg, but with standard climate / hot summer of 2003
  • The type of natural Ventilation: Only by windows / cross ventilation / ventilation with height difference >=4m, inside / outside working hours.
Figure 4: Shows the options for providing various kinds of windows as per the project type, which can be selected from the pre-defined types by the program or can be user defined .

2. Simulated Strategies for Natural Ventilation and Lighting

2.1 Natural ventilation

The probability of window opening is in correlation with outside temperature (Pfafferot 2002). Everybody wishes to open the window but if this would be too uncomfortable because of cold temperatures outside (let’s say 5°C), the window remains closed. With increasing temperature the probability increases too. At about 18 to 20°C we reach the maximum air change by natural ventilation – the windows are open.

This user behaviour can be reproduced in Primero-Comfort.

Figure 5: Shows the tab for controlling usage, ventilation and lighting of the installed windows.

The kind of natural ventilation may differ during the period of use and outside of it, depending e.g. on the possibilities of a natural night ventilation (protection against weather and burglary). We differentiate between ventilation only by windows / cross ventilation / a ventilation over a height difference of >= 4m with resulting maximum air changes of 1, 2 and 3 resp. (because of higher temperature differences during night time between 22 and 6 o’clock multiplied by 1.5).

Increased natural ventilation outside the period of use is activated above a set temperature of daily mean value of outside temperature (16 to 17°C, this was deduced as good compromise between overheating by to less night ventilation and heating demand by too much night ventilation).

2.2 Reference Point of Light Sensor

In accordance to EN 12464 a luminance of 500 lx should be reached at the whole desk area. This leads to a position of the light sensor at the end of a (big) desk at a depth of 2.4m.

But this assumption is very conservative, because it neglects the higher value of daylight in comparison to artificial light. It is known that 300 lx of daylight are felt as very comfortable for office work – there is no need for additional 200 lx of artificial light.

Because of that, an “I like daylight” situation can be assumed too. This could be realized e.g. by two different ways with similar results:

  • A reference point for daylight near to the window. If there are 300 lx daylight in the centre of the desk (where the user is sitting), than the sensor nearer to the window receives 500 lx – no artificial light! Only if daylight in the centre of the desk falls below 300 lx, artificial light is given additionally. With additional simulations for both cloudy (shading system is open) and clear sky with sun (shading system is closed) was found out, that this is fulfilled with a position of the light sensor in a depth of about 0.9m.
  • The reference point remains at 2.4 m, but the sensor is set to 300 lx. Every user has an individual working place illumination of 200 lx and may decide what he wants.

3. Evaluation of Comfort in Summer with an Adaptive Comfort Model – Dutch ISSO 74

In naturally ventilated buildings users can adapt to the surrounding conditions. They feel well with operative temperatures increasing with outside temperatures. Comfort temperature is significantly higher than in buildings with AC, see van der Linden (2006).

ISSO 74 (2004) differs between three comfort ranges:

  • Class A: More than 90% satisfied (for high expectance)
  • Class B: More than 80% satisfied (standard for new buildings)
  • Class C: More than 65% satisfied (standard for renovated buildings)

From a purist point of view an exceeding of just one hour leads to the next lower class. Practice shows, that this would lead to comfort class insufficient very often. That’s why a moderate exceeding of the limits should be allowed. We assume here an amount of 100 h during the period of use (this is about 10% of working time during summer).

Thus, classification results in classes A, B, C or insufficient with a supplement regarding to the number of exceeding hours, like A (75) or B (23) or C (46) and so on. For our investigations the recommendation for new buildings, comfort Class B is the target, of course. This is in accordance with a high comfort.

4. Results

With the parameters listed in chapters 1 and 2 more than 20 simulations were realised. We show here the main results, e.g. good combinations of equipment and control systems.

4.1 Standard Weather

All equipments without ventilation outside the period of use will result in insufficient comfort. Thus, the first principle is: Create a building that allows (cross) ventilation outside the period of use! This requires overflow openings inside the building and openings in the façade which are safe against weather and burglary.

If there is a sun protection glazing, 100% of window size is possible; for the period of use ventilation just by the windows is sufficient (this could be an advantage, because overflow openings can be linked with acoustic problems from other offices).

With heat protection glazing the solar transmittance is much higher, of course. But this can be compensated with a cross ventilation also during the period of use and a smaller window of 80% size – with nearly no reduction in daylight autonomy because of the higher light transmission of this glazing! In both cases the ventilation outside the period of use should be activated at mean daily temperatures above 17°C.

Table 1. Good combinations of window size, system of natural ventilation and position of reference point for daylight, standard weather

4.2 Hot Summer Weather (2003)

The summer of the year 2003 is hold as a century summer; the temperature level is about 4 degrees higher than in standard weather resulting in higher indoor temperatures and worse comfort classes.

Is it possible to compensate this extreme weather conditions only by passive means in spite of this leading to a good comfort and daylight autonomy? This is a central question for the future – if the answer is no, we would be forced to install AC in each office building!

The simulations give reason to the hope that the answer could be yes, but only if we regard all the aspects simultaneously together and if our buildings allow to do so.

Again ventilation outside the period of use is a first key, of course. Here, ventilation with a height difference outside the period of use would be very helpful (or alternatively mechanical ventilation). And the second key is to use heat protection glazing. But also then comfort is changing to the worse to class C – for new buildings insufficient.

So, the third key may be to think about the too strong requirements of EN 12464 and to allow 300 lx of daylight without additional artificial light.

With the “I like daylight” strategy a window size of 60% would be sufficient (leading to less solar transmission) to reach a daylight autonomy of 80% and a comfort class of B (21).

Table 2. Good combinations of window size, system of natural ventilation and position of reference point for daylight, hot summer weather (2003)

In both cases the ventilation outside the period of use should be activated at mean daily temperatures above 17°C.

5. Results produced by Primero-comfort

As the results are produced in Primero-comfort, a number of variants are presented graphically and in form of histogram, that allows the user to compare the comfort levels and the suitability of the climatic factors as per the project.

The following screen shots gives an idea of the expected results based on the parameters of the individual office designed by the software.

Figure 6: Shows the results under “Year/selection” tab.

As shown above figure 6. represents graphically the outside and inside temperatures (defined by different colors codes) based on various variants like “without cooling”, “improved shading”, “sun protection glazing” and many more. As the user selects a particular variant, the program enables the comparison of the temperatures which can be further used for a more optimal and comfortable design. 

Similarly, figure 7. showing comparison between variants besides that of the temperature comparison; it also compares the performances of various factors like solar radiation, light, people etc (defined by different color codes).

Figure 7: Shows the results under “comparison of variants” tab.
Figure 8: Shows the results under “energy balance” tab.
Figure 9: Shows the comfort model based on DIN 4108.
Figure 10: Shows psychometric chart as per EN 15251.

In the figure 10. above, the dots represent hourly temperature defining the comfort level of the room according to the climatic conditions.

6. Conclusions

The results shown here should be stabilised with expanded simulations and measurements.

But we hope that the tendency given here will be shown as solid. It is almost a bit astonishing – there seem to be chances to meet a good thermal user comfort under summer conditions also for hot summer weather.

But this requires coordination of all aspects influencing comfort.

Instead of the method cooling to 18 degrees in summer and heating to 26 degrees in winter we should think back to our human behaviour and use adaptive qualities of people. What temperature is really felt as most comfortable? This is described in adaptive comfort models that should be used for valuation of achieved comfort.

We should remember that it is a simple method of adaptation to comfort to add or reduce clothing. If it is possible to work without a jacket in summer the felt comfort temperature is 1 to 2 degrees higher and the building has much better chances to deliver this. A weakened or no dress code is a simple measure of sustainability.

Of course the building itself has to allow that the user has the possibility of personal manipulation of windows, shading system, artificial light etc. Only with this pre-condition human adaptation can be realized. A building with a sealed façade, central air conditioning, and automatically activated shading system don’t allow the adaptation of the users according to their wishes and brakes contact with outdoor climate.

The higher quality of daylight in comparison with artificial light should be taken into account again. Precondition is that the user has the possibility to switch on and off artificial light by himself (e.g. with a basic central artificial light of 300 lx and an individual working place light). This increases the number of daylight hours, reduces hours with artificial light and internal heat gains.

Supplementary aspects are a good shading system; sun protection glazing and a window size what is sufficient for day lighting and the view out of the window instead of a glass front.

In short – we should give men back into the centre of contemplation. We should leave the way of believing only on the abilities of the technical equipment and bring it back to that what it is. Just an auxiliary component if the users operating with windows, shading system, light switch and the building alone can’t deliver comfort.


  • Pfafferot, J. 2002, Bürogebäude Vermessungsbüro Lamparter in Weilheim Thermisches Gebäudeverhalten, Fraunhofer ISE report TOS-EB-JPt-02-04, pp. 43-44
  • ISSO 74, 2004, Thermische Behaaglijkheid, ISSO Publicatie 74
  • Van der Linden, A. C. et al. 2006, Adaptive Temperature Limits: A new Guideline in The Netherlands. A new Approach for the Assessment of Building Performance with Respect to Thermal Indoor Climate, Energy and Buildings, 38, pp. 8-17
  • Primero-Comfort, PC-program developed by HCU Hamburg, promoted by Rud. Otto Meyer-Umwelt-Stiftung, release of first version in 2009.