Flow patterns and thermal comfort in a room with panel,floor and wall heating

Thermal comfort aspects in a room vary with different space heating methods. The main focus in this study was how different heating systems and their position affect the indoor climate in an exhaust-ventilated office under Swedish winter conditions. The heat emitters used were a high and a medium–high temperature radiator, a floor heating system and large wall heating surfaces at low temperature. Computational fluid dynamics (CFD) simulations were used to investigate possible cold draught problems, differences in vertical temperature gradients, air speed levels and energy consumption. Two office rooms with different ventilation systems and heating needs were evaluated. Both systems had high air exchange rates and cold infiltration air.     

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6 m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3 h during each session of the experiment. Nominal vertical air temperature gradients between 0.1 and 1.1 m heights were 1, 3 and 5 K/m while nominal room air temperatures at 0.6 m height were 20, 23 and 26 °C. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative humidity at 0.6 m height was maintained at 50%. It was found that temperature gradient had different influences on thermal comfort at different overall thermal sensations. At overall thermal sensation close to neutral, only when room air temperature was substantially low, such as 20 °C, percentage dissatisfied of overall body increased with the increase of temperature gradient. At overall cold and slightly warm sensations, percentage dissatisfied of overall body was non-significantly affected by temperature gradient. Overall thermal sensation had significant impact on overall thermal comfort. Local thermal comfort of body segment was affected by both overall and local thermal sensations.     

Thermal evaluation of a chair with fans as an individually controlled system

It is difficult for a total air-conditioning system to satisfy the thermal comfort of all workers in an office. Therefore, an individually controlled system that can create a comfortable thermal environment for each worker is needed. In the present study, two chairs incorporating two fans each, one under the seat and one behind the backrest, were developed to provide isothermal forced airflow to the chair occupant. The chairs differed in the size of the fans. Experiments were conducted in a climate chamber during the summer. Seven subjects, who were healthy male college students, were allowed to freely control the two built-in fans by adjusting dials on the accompanying desk. The room air temperatures were set at 26 °C, 28 °C, 30 °C and 32 °C. The following findings were obtained. At a room air temperature of 28 °C, the whole-body thermal sensations were almost thermally neutral, regardless of the type of chair. At a room air temperature of 30 °C, the occupants were able to create acceptable thermal environments from the viewpoints of whole-body thermal sensation and comfort by using the chairs with fans. Their local discomfort rates at the back and lower back, which were affected by the isothermal airflows, were greatly improved at this room air temperature. However, at a room air temperature of 32 °C, the chairs tested in the present study were not able to provide acceptable thermal environments. In order to provide a more comfortable environment to the chair occupants, additional local systems to cool the head, arms, and hands are needed.     

Local thermal sensation and comfort study in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of local thermal sensation (LTS) and comfort in a field environmental chamber (FEC) served by displacement ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 tropically acclimatized subjects, 30 male and 30 female, were engaged in sedentary office work for 3 h. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures of 20, 23 and 26 °C at 0.6 m height. The objective of this study is to investigate the mutual effect of local and overall thermal sensation (OTS) and comfort in DV environment. The results show that in a space served by DV system, at OTS close to neutral, local thermal discomfort decreased with the increase of room air temperature. The OTS of occupants was mainly affected by LTS at the arm, calf, foot, back and hand. Local thermal discomfort was affected by both LTS and OTS. At overall cold thermal sensation, all body segments prefer slightly warm sensation. At overall slightly warm thermal sensation, all body segments prefer slightly cool sensation.     

Effect of warm air supplied facially on occupants’ comfort

Human response to air movement supplied locally towards the face was studied in a room with an air temperature of 20 °C and a relative humidity of 30%. Thirty-two human subjects were exposed to three conditions: calm environment and facially supplied airflow at 21 °C and at 26 °C. The air was supplied with a constant velocity of 0.4 m/s by means of personalized ventilation towards the face of the subjects. The airflow at 21 °C decreased the subjects' thermal sensation and increased draught discomfort, but improved slightly the perceived air quality. Heating of the supplied air by 6 K (temperature increase by 4 K at the target area) above the room air temperature decreased the draught discomfort, improved subjects' thermal comfort and only slightly decreased the perceived air quality. Elevated velocity and temperature of the localized airflow caused an increase of nose dryness intensity and number of eye irritation reports. Results suggest that increasing the temperature of the air locally supplied to the breathing zone by only a few degrees above the room air temperature will improve occupants' thermal comfort and will diminish draught discomfort. This strategy will extend the applicability of personalized ventilation aiming to supply clean air for breathing at the lower end of the temperature range recommended in the standards. Providing individual control is essential in order to avoid discomfort for the most sensitive occupants.     

Performance of “ductless” personalized ventilation in conjunction with displacement ventilation: Impact of intake height

The importance of the intake positioning height above the floor level on the performance of “ductless” personalized ventilation (“ductless” PV) in conjunction with displacement ventilation (DV) was examined with regard to the quality of inhaled air and of the thermal comfort provided. A typical office room with two workstations positioned one behind the other was arranged in a full-scale room. Each workstation consisted of a table with an installed “ductless” PV system, PC, desk lamp and seated breathing thermal manikin. The “ductless” PV system sucked the clean and cool displacement air supplied over the floor at four different heights, i.e. 2, 5, 10 and 20 cm and transported it direct to the breathing level. Moreover, two displacement airflow rates were used with a supply temperature adjusted in order to maintain an exhaust air temperature of 26 °C. Two pollution sources, namely air exhaled by one of the manikins and passive pollution on the table in front of the same manikin were simulated by constant dosing of tracer gases. The results show that the positioning of a “ductless” PV intake height up to 0.2 m above the floor will not significantly influence the quality of inhaled air and thermal comfort.     

Room air temperature affects occupants’ physiology,perceptions and mental alertness

Thermal environment that causes thermal discomfort may affect office work performance. However, the mechanisms through which occupants are affected are not well understood. This study explores the plausible mechanism linking room air temperature and mental alertness through perceptual and physiological responses in the tropics. Ninety-six young adults participated as voluntary subjects in a series of experiment conducted in the simulated office settings. Three room air temperatures, i.e. 20.0, 23.0 and 26.0 °C were selected as the experimental conditions. Both thermal comfort and thermal sensation changed significantly with time under all exposures (P < 0.0001). Longer exposure at 20.0 °C led to cooling sensations due to lower skin temperatures (P < 0.0001) and was perceived as the least comfortable. Nevertheless, this moderate cold exposure induced nervous system activation as demonstrated by the increase of α-Amylase level (P < 0.0001) and the Tsai–partington test (P < 0.0001). A mechanism linking thermal environment, occupants' responses and performance is proposed.     

Application of radiant cooling as a passive cooling option in hot humid climate

In hot and humid region, air-conditioning is increasingly used to attain thermal comfort. Air-conditioning is highly energy intensive and it is desirable to develop alternative low-energy means to achieve comfort. In a previous experimental investigation using a room equipped with radiant cooling panel, it was found that cooling water kept to 25 °C could be used to attain thermal comfort under some situations, while water at such temperature would not cause condensation of moisture from air on the panel. This paper reports results of a series of whole-year simulations using TRNSYS computer code on applications of radiant cooling to a room model that represents the actual experimental room. Admitting the inability of radiant cooling to accept latent load, chilled water at 10 °C was supplied to cooling coil to precool ventilation air while water cooled by cooling tower was used for radiant cooling in daytime application. For night-time, cooling water from cooling tower supplied for radiant cooling was found to be sufficient to achieve thermal comfort. Such applications are considered to be more amenable to residential houses.     

Impact of adaptive thermal comfort criteria on building energy use and cooling equipment size using a multi-objective optimization scheme

Recently adaptive thermal-comfort criteria have been introduced in the international indoor-climate standards to reduce the heating/cooling energy requirements. In 2008, the Finnish Society of Indoor Air Quality (FiSIAQ) developed the national adaptive thermal-comfort criteria of Finland. The current study evaluates the impact of the Finnish Criteria on energy performance in an office building. Two fully mechanically air-conditioned single offices are taken as representative zones. A simulation-based optimization scheme (a combination of IDA-ICE 4.0 and a multi-objective genetic-algorithm from MATLAB-2008a) is employed to determine the minimum primary energy use and the minimum room cooling-equipment size required for different thermal comfort levels. The applicability of implementing energy-saving measures such as night ventilation, night set-back temperature, day lighting as well as optimal building envelope and optimal HVAC settings are addressed by investigating 24 design variables. The results show that, on average, an additional 10 kWh/(m² a) primary energy demand and a larger 10 W/m² room cooling-equipment size are required to improve the thermal comfort from medium (S2) to high-quality (S1) class; higher thermal comfort levels limit the use of night ventilation and water radiator night-set back options. Compared with the ISO EN 7730-2005 standard, the Finnish criterion could slightly decrease the heating/cooling equipment size. However, it significantly increases both the heating and cooling energy demand; the results show 32.8% increase in the primary energy demand. It is concluded that the Finnish criterion-2008 is strict and does not allow for energy-efficient solutions in standard office buildings.     

Comparison of low-energy office buildings in summer using different thermal comfort criteria

Sustainable low-energy office buildings attempt to harness the buildings architecture and physics to provide a high quality working environment with the least possible primary energy consumption. A promising approach to condition those buildings in summer employs the utilization of the building's thermal storage activated by natural heat sinks (e.g., ambient air, ground water or soil) through night ventilation or thermally activated building systems (TABS). However, a certain room temperature cannot be guaranteed as occupants may influence the room energy balance by window opening, internal heat gains or sun shading control. Between 2001 and 2005, monitoring campaigns were carried out over 2 or 3 years in 12 low-energy office buildings which are located in three different summer climate zones in Germany. These climate zones are defined as summer-cool, moderate and summer-hot. The weather at the building site and the room temperatures in several office rooms were monitored by different scientific teams. The raw data are processed for data evaluation using a sophisticated method to remove errors and outliers from the database and to identify the time of occupancy. The comfort in all office rooms in each building is evaluated separately. For data presentation, these separate comfort votes per office room are averaged using the median instead of the arithmetic mean in order not to overestimate extremely cold or hot room temperatures. A comfort evaluation in these 12 low-energy office buildings indicates clearly, that buildings which use only natural heat sinks for cooling provide good thermal comfort during typical and warm summer periods in Germany. However, long heat waves such as during the extreme European summer of 2003 overstrain passively cooled buildings with air-driven cooling concepts in terms of thermal comfort.     

Low-temperature baseboard heaters with integrated air supply – An analytical and numerical investigation

The functioning of a hydronic baseboard heating system with integrated air supply was analyzed. The aim was to investigate thermal performance of the system when cold outdoor (ventilation) airflow was forced through the baseboard heater. The performance of the system was evaluated for different ventilation rates at typical outdoor temperatures during the Swedish winter season. Three different analytical models and Computational Fluid Dynamics (CFD) were used to predict the temperature rise of the airflow inside the baseboard heater. Good agreement between numerical (CFD) and analytical calculations was obtained. Calculations showed that it was fully possible to pre-heat the incoming airflow to the indoor temperature and to cover transmission losses, using 45 °C supply water flow. The analytical calculations also showed that the airflow per supply opening in the baseboard heater needed to be limited to 7.0 l/s due to pressure losses inside the channel. At this ventilation rate, the integrated system with one air supply gave about 2.1 more heat output than a conventional baseboard heating system. CFD simulations also showed that the integrated system was capable of countering downdraught created by 2.0 m high glazed areas and a cold outdoor environment. Draught discomfort in the case with the conventional system was slightly above the recommended upper limit, but heat distribution across whole analyzed office space was uniform for both heating systems. It was concluded that low-temperature baseboard heating systems with integrated air supply can meet both international comfort requirements, and lead to energy savings in cold climates.     

A combined low temperature water heating system consisting of radiators and floor heating

Space heating load is decreasing in modern Finnish apartments due to lower U-values of the construction, tight envelopes and heat recovery from exhaust ventilation air. This makes it possible to develop a new combined low temperature water heating system with nominal supply/return water temperatures of 45 °C/35 °C. Such a system includes radiators in rooms and floor heating in bathrooms.In this study, the performance of an apartment building is determined by using dynamic simulation. The simulation results for the combined low temperature water heating system are compared with those for three conventional radiator and floor heating systems. The results show that the combined low temperature water heating system performs well and is able to maintain the zones within the required temperature levels. The thermal comfort analysis indicates that the drifts and ramps in operative temperature using the four studied heating systems are within the limits of Ashrae Standard 55-2004.Temperature measurements in a test room are carried out to find the vertical difference of air temperature using two methods: radiator heating and floor heating. These measurements indicate that there is only a small vertical temperature difference that would not produce any significant thermal discomfort.     

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m² a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m²a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.     

Different glazing systems and their impact on human thermal comfort—Indian scenario

In the present communication, fifteen different glazing systems ranging from 3 mm single glazed clear glass to double glazed with low-e and solar control coating, have been analysed in terms of their human thermal comfort impact. Thermal comfort is measured in term of PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied). Study encompasses all the six climatic zones of India. By using OPTICS 5.0 and WINDOW 5.0, U-values, solar heat gain coefficient, inside glazing surface temperatures and inside solar radiation have been computed. Depending upon different climatic zones, six sets of different design conditions, in terms of ambient temperatures, solar radiation and wind velocity, have been chosen. Typical values of metabolic rate and clothing insulation taken are 1.2 met and 0.5 clo for summer and 1.0 met and 1.0 clo for winter, respectively. Inside room air velocity is taken as 0.15 m s⁻¹ round the year. Room temperature is taken as 20 °C in winter and 25 °C in summer. It is found that for cold station (e.g. Leh) all glazings except solar control glazings, ensure thermal comfort and total PPD is less than 10% (|PMV|?0.5). For warm and hot climates, solar control glazings are thermally suitable. Results for winter night of Delhi shows that all the 15 glazings are inadequate for thermal comfort and PPD, due to cold feeling, varies between 27% and 33% approximately.     

Monitoring results of an interior sun protection system with integrated latent heat storage

An interior sun protection system consisting of vertical slats filled with phase change material (PCM) was monitored from winter 2008 until summer 2010. While conventional interior sun protection systems often heat up to temperatures of 40 °C or more, the monitoring results show that the surface temperature on the interior side of the PCM-filled slats hardly ever exceeded the PCM melting temperature of 28 °C even in case of long-term intense solar radiation. As long as the PCM is not fully melted, the latent heat storage effect reduces the solar heat gain coefficient (g-value) of the sun protection system to 0.25 for a totally closed blind, and 0.30 for slats set at 45° (the g-values of the same system without PCM are 0.35 and 0.41, respectively). This reduced the maximum air temperature in the offices by up to 2 K in contrast to a reference room with a comparable conventional blind. The sun protection system with PCM therefore considerably improves thermal comfort. In order to discharge the PCM, the stored heat must be dissipated during the night. In climates with sufficiently low outside air temperatures, this is best achieved using a ventilation system in combination with tilted windows.     

Heat emission from thermal skirting boards

The performance of three hydronic skirting heating systems was investigated. The main focus of the study was to ascertain whether thermal skirting boards served by low-temperature supply flow were able to suppress strong downdraught. The evaluation was made for a two-person office room with mechanical ventilation. Computational Fluid Dynamics (CFD) simulations and three different draught rating models were employed to predict the level of thermal discomfort inside the room. CFD results were validated against several analytical calculations and four sets of experimental data presented in previous studies. Numerical simulations showed that all three skirting heating arrangements were able to cover transmission and ventilation thermal losses of the office room. Horizontal and vertical heat distribution inside the room was uniform for all heating systems. CFD simulations also showed that thermal skirting boards served by 40 and 45 °C supply flow had difficulty in reducing the velocity of the downdraught at ankle level. Consequently the draught rating in this region was around or slightly above 15% for these cases. In contrast, heat-emitting skirting boards supplied by 55 °C hot water showed a better ability to suppress downdraught, and the proportion of people sensing draught at 0.1 m above the floor was low. The conclusion of this study was that thermal performance of hydronic skirting heaters with low-temperature water supply must be improved in order to counter strong downdraughts, in particular where such systems may be combined with heat pumps of other low-valued sustainable energy sources.     

Design of an individually controlled system for an optimal thermal microenvironment

Individually controlled microenvironment has potential to satisfy more occupants in a space compared to a total volume uniform environment typically used at present. The performance of an individually controlled system comprising a convection-heated chair, an under-desk radiant heating panel, a floor radiant heating panel, an under-desk air terminal device supplying cool air, and a desk-mounted personalized ventilation as used and identified by 48 human subjects was studied using a thermal manikin at room temperatures of 20 °C, 22 °C and 26 °C. At a room air temperature of 20 °C, the maximum whole-body heating effect of the heating chair, the under-desk heating panel, and the floor heating panel corresponded to the effect of a room temperature increase of 5.2 °C, 2.8 °C, and 2.1 °C, respectively. The effect was 5.9 °C for the combination of the three heating options. The higher the room air temperature, the lower the heating effect of each heating option or heating combination. The maximum whole-body cooling effect of the tested system was only −0.8 °C at a room air temperature of 26 °C. The heating and cooling capacity of the individually controlled system were identified. These results, analyzed together with results obtained from human subject experiments, reveal that both the heating and the cooling capacity of the individually controlled system need to be increased in order to satisfy most occupants in practice.     

Computer modeling of displacement ventilation systems based on plume rise in stratified environment

A model for displacement ventilation system based on plume rise of single point heat source was developed. The errors for temperature gradient ratio were less than 6% in most cases. Errors for temperature gradient and displacement zone height were relatively higher (up to 28.1%) which might be due to the derivation of the parameters from experimental data. Still, the errors were lower than those from design model/method of some other workers (68.5% for the temperature gradient ratio and 15.7% for the temperature difference between the supply air and at 0.1 m above floor level). With a room height of 2.4 m (common for office in Hong Kong) and design room temperature 25.5 °C defined at 1.1 m above floor level under the normal load to air flow ratio of 12,000 W/m³/s (typical values for sub-tropical region) and minimum supply temperature of 18 °C, there existed a zone capacity range from 1000 to 5000 W that stand alone operation displacement ventilation system was feasible and that the displacement zone height (minimum 2.2 m) was above normal breathing level. The feasible zone capacity range diminished with decrease in design room temperature and/or room height. In this case, the load to air flow ratio had to be reduced, resulting in a higher flow rate when compared to a mixing ventilation system, or an auxiliary cooling facility such as a chilled ceiling had to be used.     

Assessing thermal comfort of active people in transitional spaces in presence of air movement

The aim of this study is to develop a modeling methodology to assess thermal comfort and sensation of active people in transitional spaces and consider how comfort can be achieved by air movement while changing upper body clothing properties. The modeling is based on a bioheat model, capable of predicting segmental skin and core temperature from locally ventilated clothed body parts. The bioheat model is integrated with thermal comfort and sensation models to predict comfort in presence of air movement.The model accuracy in predicting comfort was validated by and agreed with the results of a survey administered to subjects wearing typical clothing at different activity levels to record their overall and local thermal sensation and comfort in a transitional space at Beirut summer climate. The transitional space temperature monitored during the experiments ranged between 27 °C and 30 °C.A parametric study is performed to assess thermal comfort in transitional spaces for different air movement levels and for three clothing designs. The high permeable clothing at 1.5 m/s and indoor temperature of 30 °C improved the Predicted Mean Vote to values less than 0.5 compared to 1.01 attained with typical low permeable clothing.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.