Ceiling Surface Temperature Research Articles

Green roof retrofitting of a lightweight security booth under subtropical conditions

The thermal performance of a vegetated roof system was tested for a lightweight, fiberglass security booth during a spring-summer period in subtropical Curitiba, Brazil. An experimental and a control booth, commercially available and widely used in Brazil, were compared for three roof configurations (only substrate; substrate and vegetation; substrate, vegetation and shading mesh) and for two window conditions (shaded and unshaded). Comfort and thermal stress analyses followed normative parameters of wet-bulb globe temperature (WBGT) and effective temperature (ET). The non-insulated lightweight enclosure reduced advantageous effects from thermal stabilization of indoor air temperatures with the addition of the green roof. Benefits were otherwise observed in ceiling surface temperatures, which reached a peak reduction of 12 K at the experimental booth relative to the control booth. Infra-red images further confirmed spot measurements of surface temperatures in both booths.

Indoor thermal environment and air distribution in a floor-ceiling heating room with mixing or displacement ventilation

A hybrid system with a floor-ceiling heating system (FCH) and a mixing or displacement ventilation system (MV or DV) is a potential advanced heating, ventilation, and air conditioning system in the modern buildings. To date, very few studies focused on the indoor thermal environment and air distribution for FCH + MV or FCH + DV. Therefore, in this article, the effect of double heated surface temperature on indoor thermal environment and air distribution in a simulated office room with FCH + MV or FCH + DV were studied. Vertical distributions of air temperature and velocity and globe temperature in the occupied zone and horizontal distributions of contaminant concentration in the breathing zone were measured when floor and ceiling surface temperatures ranged from 25.0 °C to 29.5 °C. Vertical air temperature difference, turbulence intensity, difference between operative temperature and air temperature, and air distribution effectiveness were calculated and compared for all test conditions. The results showed that the vertical air temperature differences were all less than 0.5 °C with both positions for FCH + MV and were 4.0 °C to 4.9 °C with sitting position and 4.3 °C to 5.3 °C with standing position for FCH + DV. The turbulence intensities were from 12.5% to 17.5% with sitting position and from 12.8% to 17.1% with standing position for FCH + MV and were all within the range of 10% for FCH + DV. The differences between operative temperature and air temperature were all no more than 0.5 °C with both positions for FCH + MV and FCH + DV. The air distribution effectiveness was close to 1.0 with FCH + MV and between 1.04 and 1.21 with FCH + DV. The results in this article are relevant to the design and operation of an FCH integrated with an MV or DV.

Indoor thermal environment due to non-steady-state radiation heat transfer of a capillary ceiling radiation cooling system

The capillary ceiling radiation cooling panel (C-CRCP) is a newly developed terminal device for air conditioning to provide indoor thermal comfort for occupants and to save energy. In this paper, numerical modelling of a room with a C-CRCP system was used to analyze radiant heat transfer under non-steady-state conditions. Experiments were conducted in an environmental chamber to verify simulation results. The chamber was equipped with a C-CRCP, which was covered with gypsumboard. The results showed that the inlet water temperature had a significant influence on ceiling surface temperature. The ceiling surface temperature and the steady-state time were increased with higher inlet water temperature. A vertical gradient in indoor air temperature was found. Ceiling surface temperature and indoor air temperature were increased with an increase in inlet air temperature. The energy supply rate of the radiant panel had a positive correlation with chilled water velocity. The amount of radiation was double the amount of convection, and the thickness of the gypsumboard had virtually no effect on the proportions of radiation and convection. The model was considered validated since the maximum relative errors between experimental data and simulation results of inlet water temperature and supply air conditions were within 10%.

Cool roofs: High tech low cost solution for energy efficiency and thermal comfort in low rise low income houses in high solar radiation countries

Cool roofs are most effective in reducing cooling loads and alleviating overheating in locations with high solar radiation and external air temperature. This paper presents results of an experimental study of a low income house in Jamaica and a computational study in three countries around the equator: Jamaica, Northeast Brazil (Recife) and Ghana. A case-study typical of single storey houses in Jamaica was monitored before and after the installation of a cool paint on the roof; on days with average solar radiation intensity of ∼420 W/m2 and ambient air temperature of ∼28 °C, internal ceiling surface temperature is reduced by an average of 6.8 °C and internal air temperature by 2.3 °C. Monitoring results were used to calibrate successfully an EnergyPlus model; similar models were developed for Ghana and Brazil differing in size and/or construction to reflect country specific practices. Annual simulations indicate that internal ceiling surface temperatures are reduced on average by 3.2–5.5 oC and internal air temperatures by 0.75–1.2 °C. Cooling demand simulations (setpoint 24 °C) indicate similar annual potential savings in the three locations (∼190 kWh/m2/year) although estimated CO2 emissions reduction differ reflecting electricity generation fuels. Aging of the cool roof has an impact reducing load savings by 22–26 kWh/m2/year.

Validation of dynamic building energy simulation tools based on a real test-box with thermally activated building systems (TABS)

Empirical validation and code-to-code comparison of more than one building simulation tool has seldom been done in literature. Therefore this paper presents the first detailed comparison of 1D building energy simulation tools with 3D CFD simulation and measurement data from a test bed (Test-Box), exposed to natural environmental conditions. Dymola (library: IDEAS), EnergyPlus, IDA ICE and TRNSYS –four commonly used tools– were selected for comparison against highly accurate real measurement data and dynamic CFD results. This paper evaluates the performance of mentioned above 1D simulation tools and in particular their implemented Thermally Activated Building Systems (TABS) models. The mean error, RMSE, standard deviation and maximal error for the room air, the ceiling surface and concrete temperature of the Test-Box model results are acceptable for all tools. The time course of the room air temperature follows the measurement data relatively well for all four tools. However, the negative bias (Dymola -0.92 K, EnergyPlus -2.18 K, IDA ICE -0.37 K and TRNSYS -1.13 K) indicates a general overestimation for all tools. Furthermore, the paper reflects the properties of simulation tools regarding the modelling language, GUIs, co-simulation capabilities and their recommended field of application.

Experimental and numerical study of the effects of acoustic sound absorbers on the cooling performance of Thermally Active Building Systems

Free-hanging horizontal and vertical sound absorbers are commonly used in buildings for room acoustic control; however, when these sound absorbers are used in combination with Thermally Active Building Systems, they will decrease the cooling performance of Thermally Active Building Systems and this will affect the thermal indoor environment in that space. Therefore, it is crucial to be able to quantify and model these effects in the design phase.This study quantifies experimentally the effects of horizontal and vertical free-hanging sound absorbers on the cooling performance of Thermally Active Building Systems and on the thermal indoor environment. The experiments were carried out in a climate chamber configured as a two-person office room. Different ceiling coverage ratios were tested. In addition, a commercially available dynamic building simulation software was used with a recently developed plug-in for acoustic elements, which allows modeling free-hanging horizontal sound absorbers that partially cover the ceiling.With horizontal sound absorbers, the cooling performance of the Thermally Active Building System decreased by 11%, 23% and 36% for ceiling coverage ratios of 43%, 60% and 80%, respectively. With vertical sound absorbers, the decrease in cooling performance was 8%, 12%, and 14% for the corresponding cases, respectively. The numerical model predicted closely the cooling performance reduction, air temperatures and ceiling surface temperatures in most cases, while there were differences in mean radiant temperatures and cooling capacity coefficients, indicating that the model can be improved in certain aspects.

Investigation and Simulation on Indoor Thermal Environment of a Passive Residential Building in Severe Cold Area of China

The indoor thermal environment of the first passive house in Harbin in the severe cold region of China was investigated, which applied heating system coupled ceiling radiant with displacement ventilation. The field investigation results indicated an overheating problem during heating period. To reduce the indoor air temperature, the effect of ceiling heating combined with displacement ventilation on thermal indoor environments was studied by means of CFD. A model of a living room in the passive house was established and validated by the field measured data. Based on the validated model, five cases with different ceiling surface temperatures (CSTs) and supply air temperatures (SATs) were simulated. When the CST was set at 24℃ combined with the SAT of 20℃, the indoor temperature was close to the lower comfort limit temperature of 20℃ to achieve a more comfortable environment with less energy consumption.

An experiment-oriented simulation method for cooling capacity determination of cooling ceiling radiant panel system

The correct evaluation of the heat transfer process is important to the radiant cooling/heating system's design and operation. For different types of radiant systems, the cooled/heated surface and indoor environments are actually subject to the same heat transfer process. Thus some basic rules can be revealed to simplify the research or the design for the radiant systems. The purpose of this research is to establish a basic characteristic curve for cooling ceiling radiant panel system and provide a simple approach to determine its cooling capacity. Considering the limitations to conduct exhaustive experiments, this research applies an experiment-oriented simulation method to determine the cooling capacity of cooling ceiling radiant panel systems. A model for capillary tube mats is first developed and then validated by available experimental data. Based on the validated model, more conditions are simulated and more data are generated to investigate the relationship between the specific cooling capacity and temperature difference. The model treats the cooling capacity as a function of cooled ceiling surface's temperature and the air temperature at the third-boundary condition. Results show that the key variables, for example, the total heat flux density and the cooled ceiling surface's temperature, agree well with the experimental data, thus it is feasible for the model to be used in the simulation. The coefficients for the simplified cooling capacity model are obtained by fitting the data generated from the model. In addition, it is found that the total heat transfer coefficient can also be expressed similarly to the correlation reported in a literature for the natural convective coefficient, but with different coefficients so as to include the effects of radiation indirectly. The experimental and simulation results reported in this study can provide guidance for engineering applications.

Implementation of a simple and reliable human model to evaluate thermal cabin comfort using CFD methods

The optimization of thermal comfort in buildings and passenger cabins has become one of the major aspects during the conception phase of HVAC systems. The static PMV model is among the most recognized thermal comfort models and depends besides the dry air temperature, radiant temperature, humidity and air velocity also on the activity level and the clothing of the human. The aim of this investigation is the application of a simple and reliable model of human metabolism based on Olesen combined with CFD simulations to attain a sufficiently accurate reflection of the human heat exchange to evaluate the PMV index and predict thermal comfort in a fast and cost-effective way by CFD simulations. Basis of the CFD model developed in the current investigations are measurement results obtained during experimental investigations inside a cabin mock-up model placed in a controlled climatic chamber under various pre-defined steady-state environmental conditions. The cabin mock-up model is equipped with a radial-flow fan for influencing convective flow inside the cabin and a temperature control system for adjusting the ceiling surface temperature to obtain mainly the impact of radiant temperature on the thermal comfort. Depending on the activity level, the local clothing and ambient conditions such as the flow structure inside the cabin, the local human heat flux due to convection and radiation is examined within a steady-state, two-way-coupled CFD simulation coupling human and environment with one continuous fluid phase (dry air) and the usage of the discrete transfer radiation model.

Analysis on combinations of indoor thermal microclimate parameters in radiant cooled residential buildings and drawing of new thermal comfort charts

This paper proposed to discuss some issues about indoor microclimate parameters design in radiant cooled residential buildings. Based on the thermal comfort model, the relationships between low mean radiant temperature and other thermal microclimate parameters such as indoor air temperature, air velocity, and relative humidity were analyzed. The improved and reasonable combinations of four thermal microclimate parameters including radiant cooling surface temperature, air temperature, air velocity, and relative humidity were further derived. Furthermore, a number of new thermal comfort charts using radiant cooling surface temperature and air temperature as dominant parameters were drawn. The results show that the air temperature can be increased 1–3℃ within the recommended thermal comfort range when the mean radiant temperature is reduced 3℃. Under the design goal of thermal neutral, when the chilled ceiling surface temperature is in the range of 16–26℃, the air temperature should be set at 25.3–29.3℃; when the chilled floor surface temperature is in the range of 19–26℃, the air temperature should be set at 25.8–29.2℃. The design values of air velocity and relative humidity are not recommended to be changed, and still can follow the design standards for conventional all-air systems. Practical application : In this paper, some issues about indoor microclimate parameters design in radiant cooled buildings were discussed. A number of new thermal comfort charts using radiant cooling surface temperature and air temperature as dominant parameters were provided, and the design values of indoor air temperature, mean radiant temperature, air velocity, and relative humidity for radiant cooling system in residential buildings were also suggested. The research results can provide a more intuitive reference for the design of radiant cooling systems in residential buildings.

Simple Method to Predict Downward Heat Flux from Flame to Floor

This work presents a simple model to predict the radiation heat flux from a flame to a floor surrounding it. This heat flux was measured both in an unconfined space (open air) and under a ceiling. Flame lengths, flame temperatures, and ceiling surface temperatures, all of which are necessary to predict radiation heat flux, were also measured. Flame shapes were modeled by two cylinders and two disks representing the impinging flame's continuous and intermittent flame regions. The emissivity of the cylinders was calculated from the heat balance at the flame surface, and the radiation heat flux to the floor was predicted well by the model.

An experimental study of air flow and temperature distribution in a room with displacement ventilation and a chilled ceiling

Displacement ventilation and chilled ceiling panel systems are potentially more energy efficient than conventional air conditioning systems and are characterized by the presence of vertical temperature gradients and significant radiant asymmetry. The characteristics of this type of system have been studied by making temperature and air flow measurements in a test chamber over a range of operating parameters typical of office applications. Results from the displacement ventilation study are consistent with other studies and show that normalized temperature profiles are independent of internal heat gain. Linear temperature gradients in the lower part of the room were found, in all cases, to be driven by convection from the adjacent walls. Significant mixing, indicated by reduced temperature gradients, was evident in the upper part of the room in the chilled ceiling results at higher levels of heat gain. Visualization experiments, velocity measurements and related numerical studies indicated that with greater heat gains the plumes have sufficient momentum to drive flow across the ceiling surface and down the walls. The significance of forced, as opposed to natural convection, is also suggested by relatively low Richardson Number (Ri) values found near the ceiling. Furthermore, in cases with moderately high internal gains, comparison of the temperature gradients indicated that the effect of ceiling surface temperature on the degree of mixing and the magnitude of the temperature gradient were of secondary importance. These findings are in contrast to the view that it is natural convection at the ceiling that causes enhanced mixing.

Performance of desiccant dehumidification with hydronic radiant cooling system in hot humid climates

Experimental investigations were carried out to determine the performance of a rotating desiccant wheel with chilled ceiling panels for humid climates in Malaysia. Dehumidification capacity was in the range of 0.89–2.673kg/h. Relative humidity reduction to 40% with high dehumidification capacity of 2.673kg/h was achieved within 10min with air flow rate of 243kg/h. Chilled ceiling surface temperature between 14 and 18°C was achieved by varying the chilled water inlet temperature from 6°C to 10°C at steady state. Condensation was absent on the chilled ceiling surface panels below 70% relative humidity. Thermal comfort room temperature for this investigation was 24–24.5°C for chilled ceiling height of 2m.

Room air stratification in combined chilled ceiling and displacement ventilation systems

Radiant chilled ceilings with displacement ventilation (DV) represent a promising integrated system design that combines the energy efficiency of both sub-systems with the opportunity for improved ventilation performance resulting from the thermally stratified environment of DV systems. The purpose of this study was to conduct laboratory experiments for a typical U.S. interior zone office to investigate how room air stratification is affected by the ratio of cooling load removed by a chilled ceiling to the total cooling load, η, for two different chilled ceiling configurations. The experiments were carried out in a climatic chamber equipped with radiant panels installed in the suspended ceiling. In the first test configuration representative of thermally activated slab applications, 12 panels covering 73.5% of the ceiling were used. During the second series of tests, 6 panels covering 36.7% of the ceiling were used, representing a typical installation of metal radiant panels. The cooling load removed by the panels varied between 0 and 73 W/m2 (0–23.1 Btu/(h ft2)) (based on radiant panel area) or between 0 and 28 W/m2 (0–8.9 Btu/(h ft2)) (based on room area). The average mean water temperature of the panels varied over a more moderate range of 20°C–24°C (60°F–75.2°F) for the 12-panel tests and over a colder range of 16.5°C–22.6°C (61.7°F–72.7°F) for the 6-panel tests. The displacement ventilation airflow rate varied between 1.65 and 4.03 l/(s m2) (0.32–0.79 cfm/ft2), and the supply air temperature was kept constant at 18°C (64.4°F). The results showed that increasing η, the relative amount of the cooling load removed by the chilled ceiling, reduced the total room stratification. However, a comparison between the colder 6-panel tests and the warmer 12-panel tests indicated that average radiant surface temperature (mean chilled water temperature in panels) was a stronger predictor of stratification performance. When smaller active radiant ceiling areas are used (e.g., for a typical radiant ceiling panel layout), colder radiant surface temperatures are required to remove the same amount of cooling load (as a larger area), which cause more disruption to the room air stratification. Despite the impact that the chilled ceiling has on stratification, the results indicate that a minimum head–ankle temperature difference of 1.5°C (2.7°F) in the occupied zone (seated or standing) will be maintained for all radiant ceiling surface temperatures of 18°C (64.4°F) or higher.

屋上緑化された立体駐車場の屋内温熱環境の解析

The influence of the rooftop greening of the multistory parking garage exerted on the thermal environment of the parking lot space under the roof was analyzed based on the result of the measurement of PMV, WBGT, and the ceiling surface temperature. As a result, in summer, it has been found that the parking lot space under the roof fell the hot thermal environment and the ceiling surface temperature reached 47.6degree C on 10 of July in 2008 at the place where roof greening had not been done, and this may increase the average radiation temperature. Average WBGT was 29.1degree C and average PMV was 2.5 from 11:00 until 17:30 on the same day at the place where roof greening had not been done. On the other hand, the decrease of about 0.6 was observed with average PMV and about 0.9degree C in average PMV during the same period of time at the place where roof greening had not been done. Though the difference was smaller than in summer, the lower thermal environment was also observed in autumn at the place where roof greening had been done.

A new thermal performance index for dwelling roofs in the warm humid tropics

This research aims to find a scientific rating scheme for roof system for the warm humid tropics. The overall air-to-air thermal transmittance ( U-value) or thermal resistance ( R-value) of roof are most widely used properties, but these are based on steady-state heat conduction and do not respond to changing conditions of climate, design and comfort needs. The paper presents a new thermal performance index, which is based on thermal comfort and actual thermal performance of a roof design option. It provides a basis for identifying the optimum roof design for unconditioned and acclimatised regimes. A review of the acceptable limits of ceiling surface temperature is presented. The mathematical modelling for predicting performance of roof based on admittance procedure and derivation of thermal performance index is described. In the proposed scheme the galvanized iron roof is given 0% rating and the roof satisfying the comfort needs for the given climate is rated as 100%. Illustrative examples of built roofs or design options are taken from India and Australia. It clearly shows that the roofs with the highest thermal resistance are not necessarily optimum solutions.

AN EXPERIMENTAL STUDY ON THE ACQUIRED THERMAL COGNITION THROUGH DAILY EXPERIENCE IN THE BUILT ENVIRONMENT DURING SUMMER SEASON

The purpose of this research is to find a distinctive but rather qualitative relationship between the thermal cognition acquired through daily experience in the built environment during summer and the indoor thermal conditions. We investigated the relationship between subjective responses and environmental quantities obtained from two experimental small wooden buildings: one has a radiative cooling system on the ceiling and the other has a convective cooling system. The ceiling surface temperature of the radiative cooling was set up to be much higher than the conventional radiative cooling panels in order to find a critical level of thermal condition. We sorted out 35 subjects into two types of lifestyles, namely, those exposed much to convective cooling and those using natural ventilation for long hours. We also sorted out the same subjects into two types, namely, those prefering to convective cooling and those who dislike convective cooling. The percentage of comfort votes tend to decrease as the indoor radiant temperature or air temperature increases, but there is quite a clear difference between those preferring to convective cooling and those who dislike convective cooling. It suggests that there exists such a thermal cognition built up through daily experience in the built environment, which is different from a group of people to the other, depending on what kind of cooling they are exposed to.

A numerical investigation on effects of ceiling and floor surface temperatures and room dimensions on the Nusselt number for a floor heating system

In this study, the effect of ceiling and floor surface temperatures and room dimensions on the Nusselt number over the floor of a floor heating system has been investigated numerically. The variation of the Nusselt number with Rayleigh number has been analyzed under constant wall temperature condition for different ceiling temperatures (10–25 °C) and room dimensions. It has been seen that when the room dimensions and temperature difference between the ceiling and interior air are increased, the Nusselt number over the floor increases as well. The numerical results have been compared with the correlations given in the literature. It has been seen that the correlations available in the literature are valid only for given thermal conditions and room dimensions. The results calculated from the correlations which do not consider the effects of ceiling and floor surface temperatures deviate up to 35% than the results of this numerical study carried out for different ceiling and floor surface temperatures and room dimensions. Therefore, a new correlation for Nusselt number over the floor, which contain the influence of thermal conditions and all of room dimensions must be discovered.

Buttock temperature in a sedentary posture on plywood flooring of varying thickness over the ONDOL heating system

This study investigated the thermophysiological responses of healthy subjects that sat on the plywood covering of the ONDOL floor heating system. Environmental chambers were constructed for this study, wherein ambient temperature, and wall and ceiling surface temperature were controlled at 24°C, and relative humidity was 50%. The temperature of supply water (t sw) flowing into the floor coil was altered from 15°C to 40°C at 5°C intervals. The floor covering materials used in this experiment were mortar and three types of plywood with thicknesses of 2.7, 7.5, and 12 mm. The floor surface temperatures (t f) and the skin temperatures of eight subjects were measured while they were sitting on the floor. Buttock temperature, in particular, was monitored. This experiment yielded the following results: (1) t f was 17.0°–35.2°C on mortar finishing and 19.1°–30.2°C on 12-mm plywood covering; (2) the buttocks skin temperature increased with t sw higher than 30°C on mortar finishing and for t sw higher than 30°, 25°, and 20° on 2.7-, 7.5-, and 12-mm plywood finishing, respectively; (3) the differences of buttock temperature when t sw was varied between 15° and 40°C were 11.4°C on mortar, 7.9°C on 2.7-mm plywood, 6.5°C on 7.5-mm plywood, and 5.0°C on 12-mm plywood; (4) using regression analysis, the neutral point temperature of buttocks was determined to be 32.8°C.

Analysis of parameters affecting the internal environment of a naturally ventilated auditorium

A programme of work involving the measurement of ventilation rates, air velocities and temperatures has been completed within a naturally ventilated auditorium in the Queens Building, De Montfort University. Measurements have been recorded for 'winter', 'mid-season' and 'summer' conditions, and average occupancy levels. Measurements carried out in 'winter' and 'mid-season' indicate that the predominant ventilation driving force is the stack effect. However, current control settings of fresh air inlets allow too great a free area to be produced, which causes high room air velocities with associated low temperatures, resulting in high discomfort levels for occupants seated in line with external openings. Results for 'summer' external conditions on particular dates indicate that ventilation rates are driven largely by wind-induced effects, which can be much higher than buoyancy-driven flows. Internal ceiling and wall surface temperatures show little variations with time, owing to the heavyweight nature of the building structure and its exposed areas.