Examining the effect of Geometric index of Street (H / W) on the thermal performance of housing (Case Study: Hamedan residential buildings)

The relationship between building density and energy consumption involves a complex interaction between climate factors, location patterns, the way urban open spaces are located, and the adjacency of the buildings of which they are composed. Therefore, this study investigated the thermal performance of residential buildings based on the patterns of residential blocks in Hamadan Province, Iran using the concept of minor climate and thermal islands influenced by density regulations. It aimed to evaluate the effect of these regulations on energy consumption. A comprehensive collection of thermal simulations were conducted based on the climate of Hamadan and a statistical analysis for examination of the effect of height on the energy consumption resulting from increased urban density.

 Theoretical Framework

A criterion used for measurement of the energy consumption of buildings is the micro-urban climate resulting from the density regulations (H/W).  These regulations can affect the access of buildings to sunlight and, thus, the energy performance of buildings. Density regulation indices include two categories: middle-scale and micro-scale. The middle-scale category involves an H/W criterion for measurement of the impact of the outdoor environment. The micro-scale category involves criteria for changes in the building volume geometry, including the surface-to-volume ratio (S/V), ratio of surface exposed to direct sunlight to total surface (Ssn/Ssh), shadow area (Ssu/Ssh), substructure (Ssu/A), volume (Ssu/V), and ratio of window surface to the total wall surface (WSR), which changes as height varies. 

The methodology involved a combination of qualitative and quantitative methods. In the simulation stage, two modes were considered to specify the effect of H/W on energy consumption. First, fixed height and variable street width were considered in the modeling for examination of the effect of the street width index, and fixed street width and variable height were then considered for examination of the height index. For analysis of the findings of the statistical methods, correlation, analysis of variance, and multiple regression were used.The relationships between energy consumption and the variable of street width and each of the indicators of the variable of height were investigated with the Pearson correlation coefficient. For investigation of the simultaneous effect of all the indices of the independent variable on the dependent variable (energy consumption), multiple regression analysis was used to specify which geometric factor exhibited the greatest impact on energy consumption. Analysis of variance was used for comparison and evaluation of the mean differences between the groups.
For validation, two methods were used: experimental (involving field measurements) and comparative (involving a comparison of the results of different software).

The results obtained from the correlation analysis revealed that there is a close direct relationship in all residential blocks of northern patterns between H(fix)/W(6m-36m) and annual energy consumption, while there is no correlation in southern patterns. The relationship between H(4f-10f)/W(fix) and annual energy is direct in northern patterns but inverse and slightly effective in southern patterns.As the H(fix)/W(6m-36m) ratio decreases, cooling energy consumption increases sharply (inverse correlation), and heating and total energy consumption decrease sharply (direct correlation). In this analysis, energy savings are greater on a wider street than on a narrower street, and fixed-height buildings exhibit lower annual energy consumption on a wider street.Positive correlation (high intensity) and negative correlation with heating energy (low intensity) is established between the geometric characteristics of residential parts (S/V, Ssu/S, Ssu/V, Ssu/Ssh, and Ssn/A) and cooling energy consumption. Wider streets receive more sunlight than narrower ones, so those with lower geometric indices exhibit better thermal performance and greater reduction of heating energy consumption.

Building density and its indices are influential in northern patterns, and increase in height and pathway width contributes to the reduction of energy consumption. Therefore, the geometric index of an urban street is effective in northern patterns, and a rise in height through an increase  in the horizontal distance between buildings affects the reduction of energy consumption. However, the value of the index (H/W) is lower on the urban passages of the cold climate of Hamadan (deep urban valleys), and the energy consumption of the building decreases as the absorption of solar radiation increases. Multiple regression analysis showed that the most indicative energy consumption factors in the patterns included the geometric index (H/W), the number of sunny surfaces (Ssu), the ratio of shadow (Ssh) to the substructure (A), and total surface area (S) . The proposed model (involving a change in the occupancy level of the initial model) exhibited the most optimal thermal performance with decreases by 42.9% in cooling energy and by 4.73% in total energy.

Acknowledgment

The article has been derived from the Ph.D. thesis entitled "Determination of housing deployment pattern considering the influence of climate factors on the inside thermal comfort whit an energy management approach (case study Hamedan)", which has been defended by the first author under the second author’s supervision and the third author’s advisory at the Qazvin Branch, Islamic Azad University.