A. H. Taki

An investigation into thermal comfort in the summer season of Ghadames, Libya

Abstract This paper reviews the results from a field survey of thermal comfort within two types of buildings; old (traditional) and new (contemporary), in Ghadames oasis in Libya. The survey was undertaken in the summer seasons 1997 and 1998, which were typical of the hot–dry climate of North Africa. It shows how the 237 residents responded to the environmental conditions. Questionnaires were collected from the residents of 51 buildings: 24 old buildings that employ natural ventilation systems with courtyards and 27 new buildings that employ air-conditioning systems. In addition the environmental parameters were measured in 11 buildings (5 old, 6 new) representing 50 subjects, to calculate the predicted mean vote value of the subject using Fanger’s model as presented in ISO 7730 standard 1995. The survey has shown that the measurements of predicted mean vote (PMV) in new air-conditioned buildings provide satisfactory comfort conditions according to ISO 7730 and the occupants agree by indicating a satisfactory actual mean vote (AMV). The equivalent measurements and survey results in old traditional buildings indicated that although the PMV, based on measurements and ISO 7730, implied discomfort (hot), the occupants expressed their thermal satisfaction with the indoor comfort conditions. The field study also investigated occupants’ overall impression of the indoor thermal environments; the results suggest that people have an overall impression of higher standard of thermal comfort in old buildings than in new buildings.

Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

Abstract The current design standard BS EN ISO7730 [Moderate thermal environments—determination of the PMV and PPD indices and specification of the conditions for thermal comfort, International Standards Organisation (1995)] is based upon the work of Fanger, and essentially comprises a steady-state human heat balance model that leads to a prediction of the sensation of human thermal comfort for a given set of thermal conditions. The model was derived from laboratory-based measurements conducted in the mid-1960s in relatively ‘conventional’ environments. However, a chilled ceiling operated in combination with displacement ventilation represents a more sophisticated environment as compared with the original conditions in which the Fanger model was derived. This raised a question about the applicability of the current standard when designing for thermal comfort in offices equipped with chilled ceiling/displacement ventilation systems. This paper presents findings from an EPSRC-funded study that sought to answer the above question. Human test subjects (184 in total) carried out sedentary office-type work in a well-controlled environmental test room that simulated an office fitted with the above system. Measurements of environmental variables were taken at a number of locations near the subjects, each of whom wore a typical office clothing ensemble. The reported thermal comfort sensations were compared with values predicted from BS EN ISO7730 over a range of system operating conditions. It was shown that the current standard BS EN ISO7730 may be used, without modification, when designing for the thermal comfort of sedentary workers in offices equipped with chilled ceiling/displacement ventilation systems. These findings are interpreted within the context of a proposed modification to thermal comfort design standards that includes adaptive effects, and the influence of BS EN ISO7730 on the development of other radiant surface/displacement ventilation configurations is discussed.

Thermal comfort in chilled ceiling and displacement ventilation environments: vertical radiant temperature asymmetry effects

Abstract The paper presents some of the findings from a broader investigation aimed at determining thermal comfort design conditions for combined chilled ceiling/displacement ventilation environments. A typical chilled ceiling/displacement ventilation office has been created within a laboratory test room, in which the ceiling temperature can be varied over a range of typical operating values; the thermal comfort of eight female test subjects was then measured in the test room over the range of ceiling temperatures. Vertical radiant temperature asymmetry was found to have an insignificant effect on the overall thermal comfort of the seated occupants for the typical range of ceiling temperatures that would be encountered in practice in such combination environments. There was a slight trend for the reported sensation of ‘freshness’ to increase as ceiling temperature was reduced though this requires further study. It is concluded that existing guidance regarding toleration of radiant asymmetry is valid for thermal comfort design of chilled ceiling/displacement ventilation environments

Assessing thermal comfort in Ghadames, Libya: Application of the adaptive model

This survey measures human thermal comfort and assesses the validity of the adaptive thermal comfort model when applied to the climatic extreme (hot dry) condition of Ghadames. This paper reviews the results from two field surveys of thermal comfort within two types of buildings, old (free running) and new (climate control), in Ghadames oasis in Libya in the summer seasons of August 1997 and July 1998. Questionnaires were collected from 19 buildings representing 88 subjects: nine old buildings that employ a natural ventilation system with a courtyard and ten new buildings that employ an air conditioning system. The results from the present study show that the neutral temperatures in old and new buildings are 31.6°C and 29.4°C respectively. The adaptive model is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants in such environments.

Surface convection coefficients for building facades with vertical mullion-type protrusions

Accurate knowledge of the heat transfer processes that take place at the external surfaces of a building is necessary for thermal modelling and for design purposes. Using a heated test plate fixed at the sixth-floor level to the wall of an eight-storey building, correlations are presented for the external convection coefficient, hc, as a function of wind speeds measured 1 metre from the test surface and 11 metres above the roof in the free stream. The effects of vertical mullion-type protrusions on the value of hc are measured for a range of protrusion heights separated by a fixed spacing, the geometries tested relating to facade configurations which are commonly found in British commercial high-rise buildings. Regression correlations are derived which may be used by designers and thermal modellers for the prediction of hc values for a range of typical building facades with vertical mullion-type protrusions.

Bioclimatic housing design to desert architecture: A case study of Ghadames, Libya

This article assesses the most common architectural and environmental strategies in Ghadames housing in Libya. Preliminary data were collected through field surveys undertaken in July 2013, the hottest and driest season in Ghadames. The surveys investigated the indoor thermal environment and efficiency of energy use in Ghadames housing. The actual mean vote scale was used to investigate occupants’ thermal feeling coupled with recording physical environment and also actual measurements of a number of existing houses. Additionally, objective surveys were conducted to (a) verify the subjective data, (b) provide an overall view of the residents’ life style in the old town, and (c) understand the most significant techniques employed in old dwellings. The subjective survey “questionnaire” distributed among nine new and eight old houses shows that the majority of respondents is satisfied with the number of architectural issues in modern housing design. This general satisfaction excludes the inherited identity of the traditional architecture embedded within the society. On the other hand, occupants are more satisfied with old buildings in regard to indoor environmental conditions, energy consumption, and construction materials. The occupants of old houses expressed their thermal satisfaction with the indoor comfort conditions, but the predicted mean vote, based on measurements and ISO 7730, implied discomfort (hot).The survey also carried out interviews with a number of locals, underlining their personal impressions and preference toward the change of the existing built environment. Findings indicate that, occupants’ satisfaction and perception toward the built environment have not been achieved in new housing developments of Ghadames owing to the lack of understanding of the sociocultural needs of the local community. In addition, a 3D digital model was created for the old town and imparted a full understanding of the building dynamics and physics, explicating the complexity of the compactness of its urban morphologies. The results also showed subjects were feeling neutral to slightly warm in old buildings even when indoor air temperatures reached 32°C.