The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
G.n. Tiwari - One of the best experts on this subject based on the ideXlab platform.
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Effect of water flow on building integrated semitransparent photovoltaic thermal system with heat capacity
Sustainable Cities and Society, 2018Co-Authors: Neha Gupta, G.n. TiwariAbstract:Abstract In this paper, the simultaneous effect of heat capacity and water flow (evaporative cooling) over Semitransparent Photovoltaic modules have been studied. Analytical expressions for Room Air Temperature, floor Temperature, solar cell Temperature, water Temperature (in the tank), tank Temperature, water Temperature (over the roof), solar cell efficiency, daylight savings and electrical energy have been derived. A comparative analysis has been done with and without the water flow of the proposed system to understand the cooling power offered by water flow over the roof. The computations have been carried for a typical day for the month of June, in New Delhi, India. The effect on different water mass and mass flow rate has also been studied. It was found that there is a drop of 27.88 °C in the peak Room Air Temperature due to the cooling offered by the water flowing over the photovoltaic modules with an increase in the solar cell efficiency by 23.7%.
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Performance evaluation of a building integrated semitransparent photovoltaic thermal system for roof and façade
Energy and Buildings, 2012Co-Authors: Kanchan Vats, G.n. TiwariAbstract:Abstract In this paper, analytical expressions have been derived for Room Air Temperature of building integrated semitransparent photovoltaic thermal (BISPVT) and building integrated opaque photovoltaic thermal (BIOPVT) systems each integrated to the roof of a Room with and without Air duct. Comparative studies have also been carried out between BISPVT and BIOPVT system each integrated to the facade and roof of a Room with and without Air duct for the cold climatic conditions of Srinagar, India. However, the present thermal model is also valid for different climatic conditions. It is observed that there are maximum (18.0 °C) and minimum (2.3 °C) rise in Room Air Temperature for semitransparent photovoltaic thermal (SPVT) roof without Air duct and opaque photovoltaic thermal (OPVT) facade with Air duct respectively. Further, on the basis of sensitive analysis, it is also observed that increase of Air mass flow rate (0.85–10 kg/s) through duct increases the Room Air Temperature from 9.4 to 15.2 °C for SPVT roof for a given climatic and design parameters.
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Modelling of a greenhouse with integrated solar collector for thermal heating
International journal of ambient energy, 2006Co-Authors: Nisha Kumari, G.n. Tiwari, Mahendra Singh SodhaAbstract:SYNOPSIS This study presents the thermal modelling of solar flat plate collectors, installed outside for heating an agricultural greenhouse. The effect of depth of the water tank and area of collectors on plant, Room Air and water Temperature has been studied in detail. The plant and Room Air Temperature have been evaluated with and without north wall and with collector area. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of Numerical results, it is inferred that the plant Temperature, Room Air Temperature and water Temperature of the greenhouse increase significantly with an increase in collector area and decrease with increase of water mass and plant mass.
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Effect of greenhouse on crop drying under natural and forced convection II. Thermal modeling and experimental validation
Energy Conversion and Management, 2004Co-Authors: Dilip Jain, G.n. TiwariAbstract:In this paper, mathematical models are presented to study the thermal behavior of crops (cabbage and peas) for open sun drying (natural convection) and inside the greenhouse under both natural and forced convection. The predictions of crop Temperature, greenhouse Room Air Temperature and rate of moisture evaporation (crop mass during drying) have been computed in Matlab software on the basis of solar intensity and ambient Temperature. The models have been experimentally validated. The predicted crop Temperature and crop mass during drying showed fAir agreement with experimental values within the root mean square of percent error of 2.98 and 16.55, respectively.
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modeling and experimental validation of a greenhouse with evaporative cooling by moving water film over external shade cloth
Energy and Buildings, 2003Co-Authors: M K Ghosal, G.n. Tiwari, N S L SrivastavaAbstract:Abstract A mathematical model through flowing water film on shade cloth, stretched over the roofs and south wall of an even span greenhouse has been developed to study the effectiveness of cooling in greenhouse. The model was validated experimentally for the climate of Delhi during summer period, out of the data collected in the experiments conducted under three conditions, i.e. shaded with water flow, shaded and unshaded conditions of greenhouse. Parametric studies involving the effects of flow rate of water, length of roof, relative humidity of ambient Air and absorptivity of shading material on the cooling performance of greenhouse Room Air Temperature have been made with the help of the model. From the results it was found that the Room Air Temperature was reduced by 6 and 2 °C in shaded with water flow and shaded conditions, respectively, as compared to unshaded conditions. Also the predicted Room Air Temperatures were in fAir agreement with the experimental values.
Zhang Lin - One of the best experts on this subject based on the ideXlab platform.
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Equivalent Room Air Temperature based cooling load estimation method for stratum ventilation and displacement ventilation
Building and Environment, 2019Co-Authors: Sheng Zhang, Chao Huan, Yong Cheng, Zhang LinAbstract:Abstract Cooling load estimation is the base for the design and control of the Air conditioning system. The indoor Air Temperature stratification of stratum ventilation and displacement ventilation contributes to the energy saving, but challenges the cooling load estimation. The existing building simulation tools are generally equipped with only the fully mixed Air model and ignore the indoor Air Temperature stratification. This study proposes an equivalent Room Air Temperature based cooling load estimation method to enable the fully mixed Air model to accurately estimate the cooling load of stratum ventilation and displacement ventilation. The equivalent Room Air Temperature is the Air Temperature with which the fully mixed Air model can produce the same cooling load as that of stratum ventilation/displacement ventilation. The equivalent Room Air Temperature is modelled as a function of the supply Air Temperature, supply Airflow rate and Room Air Temperature of stratum ventilation/displacement ventilation using response surface methodology. Case studies using the experimentally validated multi-node models are conducted to demonstrate the effectiveness of the proposed method. The mean absolute errors in the cooling load estimation by the proposed method for the constant-Air-volume system and the variable-Air-volume system are 0.02% and 5.78% respectively under stratum ventilation, and 0.07% and 4.78% respectively under displacement ventilation. Compared with the conventional method, the proposed method improves the accuracy in the cooling load estimation by 70.92%–99.94%.
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Dynamic control of Room Air Temperature for stratum ventilation based on heat removal efficiency: Method and experimental validations
Building and Environment, 2018Co-Authors: Sheng Zhang, Zhaosong Fang, Yong Cheng, Zhang LinAbstract:Abstract Stratum ventilation can energy-efficiently provide quality indoor Air and thermal comfort. The Room Air Temperature in the occupied zone is a dominant parameter for thermal comfort. The non-uniform thermal environment of stratum ventilation challenges the dynamic control of the Room Air Temperature. This study proposes a dynamic control method of the Room Air Temperature for stratum ventilation based on heat removal efficiency. The proposed method requires inputs of only supply Air Temperature, supply Airflow rate and exit Air Temperature, and can be readily employed by the building management system in practice. Dynamic experiments, with a wide variation range (i.e., from 24.5 °C to 30 °C), different variation rates (i.e., from 0 °C/min to 0.088 °C/min) and different variation trends (i.e., increase, decrease and steady) of the Room Air Temperature, are conducted to validate the proposed method. The time interval of the dynamic experiments is 1 min. Furthermore, the effects of the cooling load and Room occupancy are also analyzed to demonstrate the robustness of the proposed method. The differences between the predicted Room Air Temperatures by the proposed method and measurements are no more than 0.33 °C, and the root mean square errors are no more than 0.18 °C. Compared with the conventional method, which assumes that the Room Air Temperature equals to the exit Air Temperature at the Air terminals, the proposed method improves the accuracy in the Room Air Temperature prediction by 79.3%–93.3%. The proposed method can be applied to dynamically control the Room Air Temperature to meet the requirement of thermal comfort.
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Optimization of Room Air Temperature in stratum-ventilated Rooms for both thermal comfort and energy saving
Applied Energy, 2017Co-Authors: Sheng Zhang, Zhaosong Fang, Chao Huan, Yong Cheng, Zhang LinAbstract:Elevated Room Air Temperature is normally accompanied by elevated Room Air velocity to provide thermal comfort and save energy. One problem is that an excessively high Room Air Temperature would deteriorate the energy performance of the Air conditioning system due to the increased energy consumption of the ventilation fans. Another problem is that existing thermal comfort evaluation models in the field of building energy performance may fail because most of the building simulation tools/building management systems cannot provide accurate information on the elevated Room Air velocity. This study proposes a Room Air Temperature optimization method to achieve intended thermal condition and to minimize energy consumption of the Air conditioning system with stratum ventilation simultaneously. Firstly, the PMV model for thermal condition evaluation is modified by representing the Room Air velocity in the original PMV model given in ASHRAE 55-2013 using the Room Air Temperature and supply Airflow rate. Secondly, with the modified PMV, one supply Airflow rate is quantified for one Room Air Temperature to achieve the intended thermal condition (i.e., the intended PMV value); and the energy consumptions of different Room Air Temperatures are evaluated using building energy simulations. Objective measurements and subjective surveys in a typical classRoom in Hong Kong validate the modified PMV with a mean discrepancy of 0.14 scale from the thermal sensation vote. TRNSYS simulations demonstrate the effectiveness of the proposed method that the energy consumption of the Air conditioning system is reduced by 7.8% while satisfying the intended thermal comfort.
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Effect of neutral Temperature on energy saving of centralized Air-conditioning systems in subtropical Hong Kong
Applied Thermal Engineering, 2010Co-Authors: K.f. Fong, Zhang Lin, Tin-tai Chow, L.s. ChanAbstract:Higher Room Temperature can still let the occupants have a neutral thermal sensation if higher Air speed is provided. With a suitable scheme of neutral Temperature and comfort Air speed, reduction of energy consumption of the central chiller plant may surpass the additional energy requirement of the Air side equipment, then both energy saving and thermal comfort can be achieved for the entire Air-conditioning system. To evaluate this, the energy consumptions of a centralized Air-conditioning system using the common Air side alternatives were studied for the subtropical Hong Kong. The alternatives are variable Air volume (VAV) system, constant Air volume (CAV) system and fan coil (FC) system. Each of them was associated to a central chiller plant to serve a high-rise office building. The studying range of the Room Air Temperature was from 23 °C to 30 °C. It is found that the VAV and FC systems can provide both thermal comfort and energy saving for higher Room Temperature, but CAV system is not feasible when the Room Air Temperature is above 27 °C. If the indoor Air speed threshold is considered, the neutral Temperature can be brought up to 26.5 °C, and the energy saving potentials of VAV and FC systems would be 12.9% and 9.3% respectively.
Mahendra Singh Sodha - One of the best experts on this subject based on the ideXlab platform.
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Modelling of a greenhouse with integrated solar collector for thermal heating
International journal of ambient energy, 2006Co-Authors: Nisha Kumari, G.n. Tiwari, Mahendra Singh SodhaAbstract:SYNOPSIS This study presents the thermal modelling of solar flat plate collectors, installed outside for heating an agricultural greenhouse. The effect of depth of the water tank and area of collectors on plant, Room Air and water Temperature has been studied in detail. The plant and Room Air Temperature have been evaluated with and without north wall and with collector area. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of Numerical results, it is inferred that the plant Temperature, Room Air Temperature and water Temperature of the greenhouse increase significantly with an increase in collector area and decrease with increase of water mass and plant mass.
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Effect of phase change material on passive thermal heating of a greenhouse
International Journal of Energy Research, 2006Co-Authors: Nisha Kumari, Geetam Tiwari, Mahendra Singh SodhaAbstract:In this study, a periodic analysis of a greenhouse with combination of phase change material (PCM) and insulation as a north wall has been developed for thermal heating. The thermal model is based on Fourier analysis. Effect of distribution of PCM thickness on plant and Room Air Temperature has been studied in detail. The plant and Room Air Temperature have been evaluated with and without north wall. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of numerical results, it is inferred that (i) there is a significant effect of PCM north wall and heat capacity of plant Temperature during off-sunshine hour due to storage effect and (ii) the rate of heat flux inside greenhouse from north wall is maximum for least thickness of PCM. Copyright © 2005 John Wiley & Sons, Ltd.
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Effect of ground coupling on Room Air Temperatures
International Journal of Energy Research, 1992Co-Authors: Mahendra Singh Sodha, Jagjit Kaur, R. L. SawhneyAbstract:The effect of ground coupling on the Room Air Temperature has been analysed for the hot-dry climate Jodhpur. The wall, floor and roof structures are taken to accord with prevailing buiding practices in this region. The conductive, convective and radiative gains through all the components of the building are used to calculate the periodic heat flux entering the Room through all these components. A Fourier admittance method that takes into account the storage effect of the building components is used for calculating the conductive heat loss through the walls, roof and floor. The steady-state ground loss is calculated using the shape factor methodfor two conditions. The hourly values of Room Air Temperature are calculated for an average day of May
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Effect of under-floor water storage on the thermal performance of a Room
International Journal of Energy Research, 1992Co-Authors: Mahendra Singh Sodha, Jagjit Kaur, R. L. SawhneyAbstract:The thermal performance of a Room coupled to an evaporatively cooled water storage tank below its floor has been evaluated in terms of the discomfort index for the hot-dry climate of Jodhpur. For a given depth of the storage tank, the effect on the Room Air Temperature of the flow rate with which water is cooled evaporatively has been analysed. It is seen that the storage coupling reduces the mean Room Temperature but does not affect the swing in the Room Temperature.
Sheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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Equivalent Room Air Temperature based cooling load estimation method for stratum ventilation and displacement ventilation
Building and Environment, 2019Co-Authors: Sheng Zhang, Chao Huan, Yong Cheng, Zhang LinAbstract:Abstract Cooling load estimation is the base for the design and control of the Air conditioning system. The indoor Air Temperature stratification of stratum ventilation and displacement ventilation contributes to the energy saving, but challenges the cooling load estimation. The existing building simulation tools are generally equipped with only the fully mixed Air model and ignore the indoor Air Temperature stratification. This study proposes an equivalent Room Air Temperature based cooling load estimation method to enable the fully mixed Air model to accurately estimate the cooling load of stratum ventilation and displacement ventilation. The equivalent Room Air Temperature is the Air Temperature with which the fully mixed Air model can produce the same cooling load as that of stratum ventilation/displacement ventilation. The equivalent Room Air Temperature is modelled as a function of the supply Air Temperature, supply Airflow rate and Room Air Temperature of stratum ventilation/displacement ventilation using response surface methodology. Case studies using the experimentally validated multi-node models are conducted to demonstrate the effectiveness of the proposed method. The mean absolute errors in the cooling load estimation by the proposed method for the constant-Air-volume system and the variable-Air-volume system are 0.02% and 5.78% respectively under stratum ventilation, and 0.07% and 4.78% respectively under displacement ventilation. Compared with the conventional method, the proposed method improves the accuracy in the cooling load estimation by 70.92%–99.94%.
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Dynamic control of Room Air Temperature for stratum ventilation based on heat removal efficiency: Method and experimental validations
Building and Environment, 2018Co-Authors: Sheng Zhang, Zhaosong Fang, Yong Cheng, Zhang LinAbstract:Abstract Stratum ventilation can energy-efficiently provide quality indoor Air and thermal comfort. The Room Air Temperature in the occupied zone is a dominant parameter for thermal comfort. The non-uniform thermal environment of stratum ventilation challenges the dynamic control of the Room Air Temperature. This study proposes a dynamic control method of the Room Air Temperature for stratum ventilation based on heat removal efficiency. The proposed method requires inputs of only supply Air Temperature, supply Airflow rate and exit Air Temperature, and can be readily employed by the building management system in practice. Dynamic experiments, with a wide variation range (i.e., from 24.5 °C to 30 °C), different variation rates (i.e., from 0 °C/min to 0.088 °C/min) and different variation trends (i.e., increase, decrease and steady) of the Room Air Temperature, are conducted to validate the proposed method. The time interval of the dynamic experiments is 1 min. Furthermore, the effects of the cooling load and Room occupancy are also analyzed to demonstrate the robustness of the proposed method. The differences between the predicted Room Air Temperatures by the proposed method and measurements are no more than 0.33 °C, and the root mean square errors are no more than 0.18 °C. Compared with the conventional method, which assumes that the Room Air Temperature equals to the exit Air Temperature at the Air terminals, the proposed method improves the accuracy in the Room Air Temperature prediction by 79.3%–93.3%. The proposed method can be applied to dynamically control the Room Air Temperature to meet the requirement of thermal comfort.
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Optimization of Room Air Temperature in stratum-ventilated Rooms for both thermal comfort and energy saving
Applied Energy, 2017Co-Authors: Sheng Zhang, Zhaosong Fang, Chao Huan, Yong Cheng, Zhang LinAbstract:Elevated Room Air Temperature is normally accompanied by elevated Room Air velocity to provide thermal comfort and save energy. One problem is that an excessively high Room Air Temperature would deteriorate the energy performance of the Air conditioning system due to the increased energy consumption of the ventilation fans. Another problem is that existing thermal comfort evaluation models in the field of building energy performance may fail because most of the building simulation tools/building management systems cannot provide accurate information on the elevated Room Air velocity. This study proposes a Room Air Temperature optimization method to achieve intended thermal condition and to minimize energy consumption of the Air conditioning system with stratum ventilation simultaneously. Firstly, the PMV model for thermal condition evaluation is modified by representing the Room Air velocity in the original PMV model given in ASHRAE 55-2013 using the Room Air Temperature and supply Airflow rate. Secondly, with the modified PMV, one supply Airflow rate is quantified for one Room Air Temperature to achieve the intended thermal condition (i.e., the intended PMV value); and the energy consumptions of different Room Air Temperatures are evaluated using building energy simulations. Objective measurements and subjective surveys in a typical classRoom in Hong Kong validate the modified PMV with a mean discrepancy of 0.14 scale from the thermal sensation vote. TRNSYS simulations demonstrate the effectiveness of the proposed method that the energy consumption of the Air conditioning system is reduced by 7.8% while satisfying the intended thermal comfort.
Risto Kosonen - One of the best experts on this subject based on the ideXlab platform.
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Modelling of Room Air Temperature profile with displacement ventilation
International Journal of Ventilation, 2019Co-Authors: Natalia Lastovets, Panu Mustakallio, Risto Kosonen, Juha JokisaloAbstract:An accurate Temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of supply Air flow rate. Several simplified n...
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Demand response events in district heating : Results from field tests in a university building
Sustainable Cities and Society, 2019Co-Authors: A.k. Mishra, Juha Jokisalo, Risto Kosonen, Tuomas Kinnunen, Matias Ekkerhaugen, Heikki Ihasalo, Kristian MartinAbstract:Abstract Demand side management will play a major role in future energy systems. However, while they have been explored in some depth for electricity grids, a similar progress has not been made for district heating networks (DHN). To this end, the current work field-tested the effect of demand side management, in the form of price based, demand response (DR) events, in the DHN catering to a university building. Responding to variations in a pricing model, the Temperature of inlet water was varied from the heating water substation. Using combinations of parameters, 11 different DR scenarios were executed. To gauge the effect of the DR interventions, inlet water Temperature, Room Air Temperature, and occupant satisfaction were monitored. Depending on the constraints imposed, significant variations in the inlet water Temperature and peaks and drops in the Room Air Temperature were noted. The different DR scenarios did not greatly alter occupant satisfaction levels. The study was able to provide useful data from field tests of DR events in a DHN. The data also showed that price based DR events may be triggered and executed without significantly impacting occupant satisfaction with thermal comfort of the premises.
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The effect of free cooling and demand-based ventilation on energy consumption of self-regulating and traditional chilled beam systems in cold climate:
Indoor and Built Environment, 2017Co-Authors: Risto Kosonen, Jani PenttinenAbstract:This paper presents the energy-saving potential of free cooling and demand-based ventilation with chilled beam system. In the analysis, four beam concepts were considered: standard, self-regulating, free cooling and demand-based ventilation chilled beam systems. The self-regulating chilled beam system utilizes high Temperature water for cooling and there is no need for regulation valve. The inlet water Temperature is close to Room Air Temperature (20–22℃) and the Room Air Temperature is allowed to vary between 21 and 25℃. The free cooling for the inlet water is provided by the preheat coil of the Air handling unit. The introduction of demand-based ventilation further increases the energy efficiency. Energy consumption of the robust self-regulating system is slightly higher than with traditional chilled beam system: self-regulating system keeps the Room Air Temperature lower than with traditional beam system. With free cooling, it is possible to save about 15% of the delivered energy compared with the stan...
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the effect of typical buoyant flow elements and heat load combinations on Room Air Temperature profile with displacement ventilation
Building and Environment, 2016Co-Authors: Risto Kosonen, Natalia Lastovets, Panu Mustakallio, Guilherme Carrilho Da Graca, Nuno M Mateus, Marko RosenqvistAbstract:Abstract Typically vertical Temperature gradient is modelled to be linear over the Room height. More advanced models consist of several nodes that allow different slopes for the Temperature profile between the nodes. Validation and development of all those models have been based mainly on measurement using low ceiling height (below 3 m). Also, the previous studies have not covered typical flow elements that exist in office buildings. In this study, the performance of a displacement ventilation system is studied using 3.3 m and 5.1 m ceiling heights in a variety of load conditions. Typical buoyant flow elements and heat load combinations were measured in a simulated office Room. The experimental study included Room Air Temperature measurements at different heights and locations over the occupied zone in addition to surface measurement and supply and exhaust Air Temperature measurements. The measurement data was compared with current models. The results show that the major part of the vertical Temperature gradient occurs already at low level. With some typical buoyant flow elements there is no benefit if the ceiling is lower or higher level. Also, measurements depict that modelled non-dimensional Temperature profile using low ceiling height (about 3 m) is not valid for high ceiling applications (more than 4 m). Multi-node models works quite well with several buoyant flow elements. Still, the proposed multi-node models did not give good estimation of the vertical Temperature gradient when warm window surface or heat gains at ceiling level were introduced in the Room space.
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assessment of thermal environment using a thermal manikin in a field environment chamber served by displacement ventilation system
Building and Environment, 2006Co-Authors: K W D Cheong, Kwok, Wai Tham, Risto Kosonen, S C SekharAbstract:Abstract This paper presents a thermal comfort study using a thermal manikin in a field environment chamber served by the Displacement Ventilation (DV) system. The manikin has a female body with 26 individually heated and controlled body segments. The manikin together with subjects was exposed to 3 levels of vertical Air Temperature gradients, nominally 1, 3 & 5 K/m, between 0.1 and 1.1 m heights at 3 Room Air Temperatures of 20, 23 and 26 °C at 0.6 m height. Relative humidity at 0.6 m height and Air velocity near the manikin and the subjects were maintained at 50% and less than 0.2 m/s, respectively. The aims of this study are to assess thermally non-uniform environment served by DV system using the manikin and correlate the subjective responses with measurements from the manikin. The main findings indicate that Room Air Temperature had greater influence on overall and local thermal sensations and comfort than Temperature gradient. Local thermal discomfort decreased with increase of Room Air Temperature at overall thermally neutral state. The local discomfort was affected by overall thermal sensation and was lower at overall thermally neutral state than at overall cold and cool sensations.
