First we observed the changes of solar volumes as a result of a single 6m high pole at various durations of solar exposure on the latitude 46.03N (Ljubljana, Slovenia). The1-3-5 hours duration (1 hour on the 21st of December, 3 hours on the 21st of March and 5 hours on the 21st of June) is the duration of solar exposure according to the legal requirement in Slovenia. Winter duration of solar exposure is only 1 hour, which is too short for any serious consideration of collecting solar energy. The incidence angle is 20°. The periods during spring and autumn are considerably longer (3 hours) compared to winter, but during that time the most of solar energy for heating can be used (at least 5 hours), so objective are long winter and spring/autumn solar exposures. The interest for summer solar exposure is oriented mostly on active solar features (solar collectors and PV), otherwise sun can present problem due to overheating. If we observe Figure 4: Distances bettween buildings obtained with the shape of the solar volumes for the sun-on-ground method the considered durations, we notice that summer solar envelope is almost “contained” within the spring one. With the solar volume method we have to combine two or more solar pyramids to satisfy the requirement (Fig. 2).The 1-3-5 hours shadows were taken as reference (they are the minimum requirement which protects the user from receiving no solar radiation at all).

The reference situation was changed in the way that the solar durations were increased in equal steps of 1 hour — from 1-3-5 hours to 2-4-6 hours. The 2-4-6 hours duration (2 hours on the 21st of December, 4 hours on the 21st of March and 6 hours on the 21st of June) represents a slightly improved basic situation. Due to that measure the solar envelope spreads its influence to the north for a minimum 1%, but the east and west influences double their size. As a consequence the maximum building density on the site decreases (when organizing the same size buildings) — but on the other hand the feasible building volume increases (Fig.2).

The 3-5-7 hours duration (3 hours on the 21st of December, 5 hours on the 21st of March and 7 hours on the 21st of June) (Fig.3) is a situation where winter and spring/autumn solar exposures are substantially prolonged. We can observe a change in the solar envelope pattern. The spring and summer solar volumes are contained within the winter volume.

The solar envelope influence increases toward north for 10% and towards east and west for a factor of 3.3 comparing to the reference situation 1-3-5 hours. Compared to the iso­shadows method the site size is much larger. This is a model for further investigation.

The 4-6-8 hours duration (4 hours on the 21st of December,

6 hours on the 21st of March and 8 hours on the 21st of June)

(Fig.3) is the maximum duration that can be achieved in the given circumstances. The winter elevation angle in this model is 16° (close to the 15° which are recommended in the literature).

As a consequence the summer azimuth angle is almost 90° declined from the direction South and spring azimuth is 56 declained from South. The summer and spring/autumn azimuths during early and late hours are too large to gain any reasonable benefit from solar incidence. The adjustments of summer and spring/autumn solar exposures could be made in the sense of diminishing the duration time.

Solar volume method works well only for longer exposures, which contain the year-round shadowing in the winter solar volume — then we can say the volume is easy to understand and design. When the spring and summer envelopes »stick out« of the winter envelope we have two possibilities: combine several solar volumes or diminish the spring and summer solar exposures. One of the possible approaches would be to increase the winter and the spring/autumn durations of solar exposure and keep the summer duration at 5 hours (summer overheating of passive solar features) The 5 hour summer solar exposure would be contained in the adjusted 2-4-5 hours variant, the combination of the 2-4-6 hours variation and the 1-3-5 hours variation.

The solar volume method was compared to the sun-on ground and the iso-shadow method. The comparission was carried out on the simulaton model described previously in the text. Shadows calculated with the sun-on-ground method have almost rectangular shape (Fig.4). We can notice a distinctive longitudinal shape of the shadows running north, the east and west shadows are much shorter than the north ones. Laterally we can put the buildings very close together.

When we observe the results of the simulations obtained with the iso­shadow method we see that the shapes of the shadows are more complex and more evenly arranged around the building than in the previous method. It is evident that shadows over a long period of time were taken into consideration.

The shadows at the east and west side of the building have more influence (the consequence of the Figure 7: Distances between buildings obtained with

morning and afternoon sun, when the solar envelope method for the 3-5-7 hours solar

the incidence angles are low) duration (floor plan)

(Fig. 5). We can see on the picture that

the buildings have longer southern as well as east and west solar exposures during the year.

The distances between the buildings obtained with the solar volume method depend on the solar exposure duration. The results of the reference 1-3-5 hours duration resemble
the results of the sun-on-ground metho (Fig.6). With the increase of the solar exposure duration, the results become similar to the iso-shadow method, where we can certaily say, that 80% of insulation during the year will be available on the building envelope (Fig.8).

The results of the calculations show that the area of the shadowing is larger when calculated with the iso-shadow and the solar volume method. Figure 8: Distances between buildings obtained with

The shadowed area is more the solar envelope method for the 4-6-8 hours solar

evenly disposed around the duration (floor plan)

building than in the sun-on-ground method, where the shadows have a distinct north-south axes. Large shadows appear at the east and west sides of the buildings calculated with the iso-shadow and solar volume method. The lateral distances between the buildings have to be larger when defined with those methods, too. The shadow length and shape toward north are similar if calculated with all the methods.