Framework for optimising daylighting and passive indoor thermal comfort in single-banked office buildings in the temperate dry climate of Nigeria

Cite this article
Musa, M.A., Salisu, A.S., Salihu, M.M. (2024) ‘Framework for optimising daylighting and passive indoor thermal comfort in single-banked office buildings in the temperate dry climate of Nigeria’, Architecture Papers of the Faculty of Architecture and Design STU, 29(2), pp. 15-23. https://www.doi.org/10.2478/alfa-2024-0008

SUMMARY

Achieving adequate passive indoor environmental comfort determines whether a sustainable building design succeeds or fails. The relationship between daylighting and passive thermal comfort is crucial in tropical countries like Nigeria in order to prevent environmental disorder. Maximisation of sunshine during periods of strong solar radiation, for instance, would result in an increase in indoor temperature and discomfort from heat. This is an example of a single comfort element taken out of context. As observed, comfort increases performance, which is a function of three factors acting together: ability; motivation; and opportunity. Many researchers have differed on the optimum values of Daylighting and Passive Indoor Thermal Comfort (DPITC) determinants in tropical climates. For example, one researcher recommended the best orientation of office spaces in a temperate dry climate with the windows north- and south-oriented, while another proposed a compromise position of 22.5° (south-southwest) for thermal and visual comfort. However, a different researcher proposed 15° west of south and 15° south of west as the compromised value for DPITC. ASHRAE 90.1 recommends a window-to-wall ratio (WWR) of 20% for mid-rise buildings while the International Energy Conservation Code (ICC) recommends a different value of 30%. Another study carried out in the temperate dry climate of Singapore suggested the use of 24% WWR, whereas one scholar found a range of 20% to 30% as the recommended values of WWR in the temperate dry climate of Lahore Pakistan for PITVC. For R-values, ASHRAE 90.1 recommends a minimum range of 1m²K/W to 2.68m²K/W, while International Energy Conservation Code (ICC) suggests 2.64m²K/W to 3.52 m²K/W, and Energy Conservation Building Code (ECBC) recommends a value of 3.7 m2K/W.

The study is aimed at developing a framework for optimising DPITC in singled-banked mid-rise office buildings, during the activity period (8 a.m. to 5 p.m.), in the temperate dry climate of Nigeria. It was achieved by evaluating the effects of Orientation, WWR, R-values, and shading devices on DPITC. A quantitative research design using an explorative design approach was employed in the study as well as an experimental research strategy using a simulation method to enhance DPITC. The study used the Federal Secretariat building as a prototype of a single-banked office building. The criteria used in the selection of this building were based on the building type, number of storeys, access to buildings, and its passive method of achieving indoor comfort. The Google SketchUp 2022, Radiance, and OpenStudio simulation tools were used to evaluate the prototype building of the Federal Secretariat in the temperate dry climate of Nigeria from January to December 2023. Six (6) sets of offices (48) were selected for the simulation and the data generated was analysed using relevant statistical tools (MANOVA, ANOVA, column charts, graphs, and tables).

The findings revealed that the best orientation for daylighting and thermal comfort was found to be 0⁰ and 11.5⁰ respectively, while the compromise value was found to be 11.5⁰. For WWR, the optimum for daylight and thermal comfort were found to be 20% and 15% respectively while the compromise value was 20%. The result has also revealed that 0.6 was the most appropriate projection factor for better operative temperature as well as relative humidity, and 0.35 for daylighting and the compromised value for DPITC was found to be 0.5. It was also noted that the R-value of the external wall insulation material does not affect the daylighting of the office building but affects operative temperature as well as relative humidity; the optimum value was found to be 3.26 m2·K/W. These were all done using parametric optimisation due to its easy use and vivid logical procedure. A framework was developed and used to obtain four more optimised DPITC values for single-banked buildings. The multiple regression was then carried out to investigate whether the optimised values of WWR, projection factor, and R-value of external wall material could significantly predict different enhanced azimuth angles for DPITC in single-banked office buildings in a temperate dry climate of Nigeria. The results of the regression indicated that the model explained 99.9% of the variance and that the model was a significant predictor of azimuths, F(3,1) = 4700.848, p = .010721.

The WWR, projection factor (PF), and R-value of external wall materials (R) contributed significantly to the model (B = -1254.84, p=0.010872), (B = 102.8743, p=0.017526), and (B = -4.10695, p=0.044915), respectively.

Y = C + M1X1 + M2X2 + M3X3 … … .4.1

The 4.1 formula was used to develop the model from regression results as follows:

The framework was then validated using the examination of framework output for reasonableness under a variety of settings of the input parameters. The values given by the Building Code of Australia (BCA), Australia’s guide to environmentally sustainable homes (AGESH), ASHRAE standards as well as International Energy Conservation Code (IECC) were tested, and the results were complied with A= 224.58 – 1254.84WWR + 102.87PF – 4.11R.