Hygrothermal Comfort Research Articles

Application of Combined Passive Cooling and Passive Heating Techniques to Achieve Thermal Comfort in a Hot Dry Climate

The hot dry regions in Mexico occupy more than seventy-five percentage of total land surface with severe climate conditions for both cooling and heating seasons. The buildings located in these regions present large energy consumption patterns due to their high dependence on air conditioning (AC) for providing comfort to the occupants, which in turns provokes the emission of huge amounts of greenhouse gasses (GHG) to the atmosphere, affecting the environment at regional al global levels. For those people who cannot afford AC in their buildings, the situation is even worse, as it severely affects their health conditions. This research work deals with the investigation of several passive cooling and heating techniques in experimental modules aimed at achieving hygrothermal conditions for building occupants. These cooling techniques involved the four environmental heat sinks and included: Ground cooling, solar control, night ventilation, direct evaporative cooling, night sky infrared radiation and thermal insulation. During the typical underheating season, direct and indirect heating techniques along with infiltration control and thermal insulation were implemented and examined. These systems were built and implemented in experimental cells during the prevailing overheating and underheating periods and the results showed that the combined effect of the strategies provided more promising synergy results than the single influence of any of them. During the underheating period, the indoor minimum temperature was 15° C, and the maximum temperature during the overheating season registered 29° C. Therefore, it is suggested to implement the combined action of the passive cooling and heating techniques in buildings located in representative hot dry regions of Mexico, to improve hygrothermal comfort and to reduce the energy consumption for AC and this would eventually reduce also the emission of pollutants to the atmosphere.

Experimental study of the urban microclimate mitigation potential of green roofs and green walls in street canyons

This paper presents the design and the results of a reduced-scale experimental bench to study the effect of green roofs and green facades on local urban microclimate. An analysis of experimental data was carried out on three street canyons: one reference street, one street between two buildings with green roofs and one with a green wall to the west. The results show a hygrothermal effect of green envelopes on buildings on urban heat island mitigation. In the detailed analysis of these green coating techniques, we highlighted that green facades modify strongly the radiative balance of the street and improve the hygrothermal comfort in urban canyons through reducing the overheating in the street in hot summer days.

Experimental investigation of moisture buffering capacity of sprayed hemp concrete

This study deals with dynamic characterization of hydric behaviour of sprayed hemp concrete. The measurement of moisture buffer value (MBV) is held according to the NORDTEST protocol (Rode, 2005). Specimen are exposed to daily cyclic variation of relative humidity: 8h at 75%RH and 16h at 33%RH the test is held under isothermal conditions (23°C). The experimental set-up is validated by comparison of moisture buffer value measured on cellular concrete with values given in the NORDTEST project for the same kind of material. Results show that sprayed hemp concrete has an excellent moisture buffer capacity (MBV=2.15g/(m2%RH)). So, it is an excellent hydric regulator that improves hygrothermal comfort and reduces energy needs. Moisture effusivity is then calculated from sorption and water vapour permeability value and from dynamic test of MBV. The results (respectively 5.8×10−07 and 4.8×10−07kg/(m2Pas1/2) show a slight discrepancy between values obtained from steady-state and from dynamic conditions. Finally, the penetration depth for daily cyclic variation is estimated about 5.8cm for sprayed hemp concrete. Also, the experimental data set can be used for benchmarking buffering models.

Optimisation of Envelope Insulation for the Retrofit of an Educational Building

This paper presents ongoing work for the definition of an optimal design strategy for retrofitting educational buildings. The term “optimal design” refers to the selection of different retrofitting solutions to ensure an energy efficient building that can be developed which will not compromise hygrothermal comfort, indoor air quality, health and durability. In this paper, a selection model of thermal insulation thickness of envelope elements is developed, aiming the control of surface condensation and upgrade of hygrothermal comfort. The mathematical formulation of this model leads to a nonlinear program with linear objective function. The software Gmas/Minos was chosen to solve the optimization problem and to develop a calculation program to solve this specific application. The software Energy-Plus developed by the US Department of Energy was used to simulate hygrothermal performance of the building, providing results for a comparison with the developed simulation tool. The paper presents an example of an optimal design problem for a specific classroom of a retrofit educational building.

Hygrothermal comfort in Lamu Town (Kenya)

Comfort measurements have been conducted over a period of one week, four times each year, inside several houses of different types in Lamu Town, a traditional Swahili settlement on Lamu Island off the Kenyan North Coast. The house types investigated consisted of the traditional Lamu house (single and double stirey), a 19th century Arab residence, and modified houses. The Hygrothermal (HGT) factor according to Scharlau was applied as comfort indicator. for reasons of comparison an HGT N index was introduced by the author to evaluate the comfort levels at different recording positions and periods against the overall climatic impact as recorded at the meteorological station. The HGT N index contains the following information: the actual comfort stress level (HGT) and N, its duration in time, expressed as a percentage of the measured period. For instance: —6.0 HGT 30 indicates a stress intensity of —6.0 HGT exceeded for 30% of the time. The result of the investigation gives an indication of the actual performance of the buildings under discussion, in respect of their reaction to the prevailing climatic conditions. Hence, detailed conclusions for particular design features can be arrived at.