11.4 Data Analysis and Discussion
11.4.5 Bioclimatic Interpretation for Minna
Minna displays a wider range of spread in the positions of the climatic points plot- ted in Fig. 11.3, with some points falling into either of the upper extremes of the climatic types, while others are dispersed in between. However, all the points are located above the shading line and mostly outside the comfort zone, indicating the need for corrective measures. The zone thus offers more flexibility in the mode of corrective measures that can be adopted to restore comfort. The bioclimatic needs for this region can therefore be tackled in one of three ways, depending on the need that is paramount at that particular time:
• By addition of the required air movement, by this mode winds ranging from 100 to 500 fpm can help restore comfort during months of high temperature and high humidity
• Through evaporative cooling, by adding 5–10 gr moisture of air during months of high temperature and low humidity as are usually associated with the dry sea- son months
• By a combination of both measures as may be necessary
Housing design requirements for the three zones, summarised in Table 11.6, are thus specified in relation to this thermal diagnosis.
MRT MRT 120 110 100 90
80
70
60 50 40 30
0 10 20 30 40 50 60 70 80
50 100 150 200 250 300 45 40 35 2530 20 15
50 100 150 200 50
45 40
35 30
25 20
0 5 10 15
COMFORT ZONE PROBABLE SUNSTROKE
PROBABLE HEATSTROKE
DRY BULB TEMPERATURE
250 300
BTU/HOUR RADIATION
100 90
Relative humidity
LIMIT OF WIND OF MODER
ATE INTENSITY LIMIT OF W
IND .MOIS TURE GRAINS OF MOIST
URE/ P OUND OF AIR
Fig. 11.3 Bioclimatic chart for Minna
The available local meteorological data on the climatic elements has thus been used for the purpose of bioclimatic design. The difference between observation height used for data collection by the meteorological agency and living level is small enough to be disregarded, although other localised site features will play out in more specific designs. A further post hoc evaluation of the surveyed houses shows their respective degree of adherence to the identified thermal requirements in each zone.
Table 11.7 and Fig. 11.4 show that a greater percentage of external building design elements, which can be adapted to fulfil indoor thermal comfort, is not bio- climatically aligned.
The types of materials used for cladding and the roof pitch appear to be the most consistent design factors across the zones that display adherence to climate control, with a visible congruence of the radar chart for these features. The composite level of bioclimatic adherence to passive design features amongst the regions varies, with the least level of regional character evidenced in the dry-hot climate of Northern Nigeria. The middle belt with a more flexibility in climatic considerations is shown to have the highest level of design adherence, with 39% of passive design features present in the sampled houses.
Table 11.6 Housing design requirement for the climatic zones Adaptive mechanism
Design requirement Design requirement Design requirement
Warm humid Dry subhumid Dry hot
Cladding
• Material Blocks Blocks/bricks Bricks/concrete walls
• Finishing Light colour Light colour White colour
Roof
• Material Light reflective Light reflective Heavy weight
• Pitch High> 300 Low< 300 Flat/curved
• Overhang Wide Wide Parapet
Windows
• Type Pivot/louvre Pivot/casement Sliding/casement
• Sizing Large Large Small
• Glazing Single reflective Single reflective Double reflective
• Shading Hoods Hoods Hoods
• Height above GL 0.5–1.5 m 0.5–1.5 m Above 1.5 m
Externals/layout
• Building form Elongated Elongated Compact
• Orientation East–west East–west North–south
• Elevation High Low Low
• Courtyard External External Internal
• Fencing Low Low High
• Windbreaks NA NA Trees
• Landscaping Needed Needed Needed
Table 11.7 Post hoc evaluation of surveyed houses in relation to zonal thermal requirements Adaptive
mechanism
Humid Dry subhumid Dry hot
Design
requirement (%)
Design
requirement (%)
Design
requirement (%) Cladding
• Material Sandcrete blocks 72 Sandcrete blocks
51.1 Bricks 19.9
Bricks 40 Concrete 12.3
• Finishing Light colour 27.3 Light colour 37 White colour 15.5 Roof
• Material Light reflective 31.3 Light reflective 40.7 Heavy weight 33.1
• Pitch High > 300 52 Low < 300 69.5 Flat 57.9
• Overhang Wide 31.8 Wide 51.1 Parapet 27.3
Windows
• Type Pivot 29 Pivot 39 Sliding 15
Louvre 26 Casement 5.6 Casement 3
• Sizing Large 42.9 Medium 52.5 Small 31.8
• Glazing Single reflective 12.4 Single reflective
12.1 Double reflective
13.1
• Shading Hoods 27.1 Hoods 24.9 Hoods 27.3
• HAGL 0.5 to 1.5 m 30.7 0.5 to 1.5 m 40.3 Above 1.5 m 18.4 Externals/layout
• Building form Elongated 53.1 Elongated 46.6 Compact 39.2
• Orientation East–west I7.0 East–west 14.8 North–south 13.9
• Elevation High 32.2 Low 38.4 Low 50.2
• Courtyard External 52 Internal 7.5 Internal 6.9
• Fencing Low 17.6 Low 22.6 High 47.8
• Windbreaks NA – NA – Trees 13.1
• Landscaping Needed 19.8 Needed 28.5 Needed 23.3
Regional trend 32.4 39 27.6
0 20 40 60 80
Cladding Material100
Cladding Finishing, Roof Material
Roof Pitch Roof Overhang
Window Type Window Sizing, Window Glazing, Window Shading, Window HAGL
§ Building Form
§ Orientation
§ Elevation
§ Courtyard
§ Fencing
§ Wind breaks
§ Landscaping
HUMID DRY-HUMID HOT-DRY
Fig. 11.4 Regional passive design trend for external housing features in Nigeria