Categories of indoor environmental quality and building energy demand for heating and cooling

Maintaining suitable indoor climate conditions is a need for the occupants’ well being, while requiring very strictly thermal comfort conditions and very high levels of indoor air quality in buildings represents also a high expense of energy, with its consequence in terms of environmental impact and cost. In fact, it is well known that the indoor environmental quality (IEQ), considering both thermal and indoor air quality aspects, has a primary impact not only on the perceived human comfort, but also on the building energy consumption. This issue is clearly expressed by the European Energy Performance of Buildings Directive 2002/92/EC, together with the most recent 2010/31/EU, which underlines that the expression of a judgment about the energy consumption of a building should be always joint with the corresponding indoor environmental quality level required by occupants. To this aim, the concept of indoor environment categories has been introduced in the EN 15251 standard. These categories range from I to III, where category I refers to the highest level of indoor climate requirement. In the challenge of reducing the environmental impact for air conditioning in buildings, it is essential that IEQ requirements are relaxed in order to widen the variations of the temperature ranges and ventilation air flow rates. In this paper, by means of building energy simulation, the heating and cooling energy demand are calculated for a mechanically controlled office building where different indoor environmental quality levels are required, ranging from category I to category III of EN 15251. The building is located in different European cities (Moscow, Torino and Athens), characterized by significantly different wheatear conditions. The mutual relation between heating and cooling energy demand and the required levels of IEQ is highlighted. The simulations are performed on a typical office room which is adopted as a reference in validation tests of the European Standard EN 15265 to validate calculation procedures of energy use for space heating and cooling.     

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.     

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.     

The study of energy-saving strategy for direct expansion air conditioning system

Most air conditioning, energy-saving research has focused on the chiller system, the most effective energy-saving procedure of its kind would be the use of forced downtime or load shedding control methods. However, the use of forced downtime control methods on direct expansion systems, while saving energy, would be at the expense of increasing room temperature, leading to the discomfort of the inhabitants. This research focused on the direct expansion system and used periodic downtime control methods to execute energy-saving procedures, thus providing reasonable temperature control and saving energy at the same time. According to the results, by reducing the periodic downtime, we can improve unstable temperature problems; i.e. operating for 15 min and downtime for 5 min, provided the optimal energy-saving efficiency, saving 21.66% of energy. However, the percentage of high room temperatures during this downtime period was 40.43%, this meant that if we wanted to save energy, we would have to sacrifice comfort; if we wanted more comfort, then we have to select an operating mode that was secondary to operating for 10 min and downtime for 5 min. We also discovered that if the air conditioner manufacturer modified the embedded program and adjusted the limit for upper temperatures of the settings upward by 1 °C, users would save 7.22% of energy; this was a procedure that was more direct and effective than any other energy-saving requisition.     

Feasibility study of desiccant air-conditioning system in Thailand

The objective of this study was to conduct an experimental analysis to investigate the performance and energy saving of the well-known desiccant air-conditioning system in Thailand. The system was composed of a silica gel bed, a split type air-conditioner (1.5 ton refrigeration) installed in a room of volume 76.8 m³, air ducts and a blower. Its design allows us to adjust the percentages of return air, outdoor air and indoor air mixed to the air leaving the desiccant, and desiccant bed thickness as well. Tests were conducted on several days with relatively similar ambient conditions. Under the test conditions used here, a 5 cm bed thickness is recommended with a maximum adsorption rate of 473 g/h. The optimum percentages of air ratios are as follows: 15% outdoor air, 15% return air (mixed together at the desiccant bed inlet) and 70% of indoor air mixed to the dry air leaving the desiccant. The corresponding electricity saving was about 24%. As expected, simple economic analysis indicated that the desiccant air-conditioning is only viable for large cooling capacities and central air-conditioned buildings. The payback period is about 4 yr.     

Energy-saving strategies with personalized ventilation in cold climates

In this study the influence of the personalized supply air temperature control strategy on energy consumption and the energy-saving potentials of a personalized ventilation system have been investigated by means of simulations with IDA-ICE software. GenOpt software was used to determine the optimal supply air temperature. The simulated office room was located in a cold climate. The results reveal that the supply air temperature control strategy has a marked influence on energy consumption. The energy consumption with personalized ventilation may increase substantially (in the range: 61-268%) compared to mixing ventilation alone if energy-saving strategies are not applied. The results show that the best supply air temperature control strategy is to provide air constantly at 20 °C. The most effective way of saving energy with personalized ventilation is to extend the upper room operative temperature limit (saving up to 60% compared to the reference case). However, this energy-saving strategy can be recommended only in a working environment where the occupants spend most of their time at their workstation. Reducing the airflow rate does not always imply a reduction of energy consumption. Supplying the personalized air only when the occupant is at the desk is not an effective energy-saving strategy.     

风机盘管占空比模糊控制试验研究

提出了一类风机盘管节能控制的新方法,将占空比的概念引入风机盘管电动水阀的控制中,在特定的控制周期内充分利用水阀关闭状态下风机盘管的冷却除湿(或供热)能力,利用Mamdani模糊规则与作用模糊子集推理方法,根据室温偏差与偏差变化确定水阀占空比与风机档位。试验结果表明,风机盘管占空比模糊控制方法较传统控制方法的节能量高于30%,同时可达到更好的室温控制效果。     

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.     

Exergetic and sustainability performance comparison of novel and conventional air cooling systems for building applications

This study presents energy and exergy analyses and sustainability assessment of one novel and three conventional types of air cooling systems for building applications. First, effectivenesses of the systems are determined using energy analysis method. Second, exergy aspects of the systems are investigated for twelve different dead state temperatures varying from −5 °C to 50 °C with a temperature interval of 5 °C. The specific exergy flows of humid air, dry air and water, exergy efficiency, and specific exergy destruction are then calculated. Sustainability index is also used to define and discuss the systems’ sustainability aspects. Finally, the results obtained here show that at the dead state temperatures of higher than 23 °C (comfort temperature), exergy efficiency and sustainability of the novel system, which is based on the novel Maisotsenko cycle (M-Cycle), is higher than those of the conventional systems. At a dead state temperature of 50 °C, novel cooling system's exergy efficiency can reach 60.329% as the maximum, while the minimum exergy efficiency of other conventional cooling systems becomes as low as 35.866%, respectively.     

Study of PV-Trombe wall assisted with DC fan

A novel PV-Trombe wall (PV-TW) assisted with DC fan is presented in this paper. Based on the original PV-TW model, theoretical simulations have been conducted for PV-TW with and without assisted DC fan. At the same time, field tests for these two cases have been performed to validate the model, and then the simulated and experimental results are found in considerably good agreement after their comparisons. A significant temperature increase of indoor temperature with a maximum of 14.42 °C, if compared with the reference room, can be obtained by the PV-TW assisted with a relatively small DC fan by testing. Meanwhile, the experimental average electrical efficiency of the PV-TW assisted with DC fan can reach 10–11%, due to the glass cover. Furthermore, the testing results for PV-TW assisted with DC fan show that the average (during 7:00–17:00) temperature of PV cells reduces by 1.28 °C and the average indoor temperature increases by 0.50 °C, if compared with the original PV-TW with similar solar radiation, and more than one degree lower ambient temperature. It indicates that the assisted DC fan can help improving the indoor temperature and cooling the PV cells in some measure. The potential of PV-TW can be exerted by the assisted DC fan.     

不同控制策略下变风量空调系统夏季运行工况

针对变风量空调实际运行中出现的冷热不均问题,通过运行两种变静压、一种定静压控制策略下的变风量系统,对比分析室温、风量、风机频率、最大阀位、设定静压值与风机能耗的关系。结果表明:变风量箱在设计控制阀门的算法中除设定温度之外还需要考虑IAQ、相对湿度等因素;使用变风量空调之前应将室温降至设定温度后再打开自动控制系统,避免受到算法的延迟影响;定静压输送单位冷负荷需要消耗的电量,比测点靠近风机的变静压控制策略多7.8%,且降温效果较差;外界环境几乎相同的情况下,变静压策略中,静压基础点远离风机的控制策略较靠近风机的控制策略降温效果好,速度至少快14%,消耗电量几乎相同。     

Space temperature difference,cooling coil and fan—energy and indoor air quality issues revisited

In designing an energy-efficient air-conditioning system that also simultaneously addresses the needs of adequate ventilation and acceptable indoor air quality, several factors begin to play an important role. Among several others, the cooling coil, the fan and the temperature difference between the space and the supply air (commonly known as the Space ΔT) can be considered to be crucial. For a given space cooling load, the choice of a particular Space ΔT has an implication on the amount of supply air required, which further has an impact on the performance of the cooling and dehumidifying coil as well as the fan. Inherent in these implications are issues related to energy, ventilation and indoor air quality. This paper investigates these implications and quantifies them by considering a hypothetical building in a tropical climate and subjecting the design to several parametric variations involving different Space ΔTs for a given space temperature and humidity condition. The total power requirements, comprising additional cooling, reheating and higher fan power, for a design involving a Space ΔT of 5 °C can be as high as a factor of 2.2 of the total power for a design with a Space ΔT of 8 °C. The implication of higher supply air flow rates on duct design is qualitatively discussed. For a given space cooling load and a given Space ΔT, the implication of increased design ventilation rates to address part-load ventilation requirements can lead to an additional installed cooling capacity of 17.5%. Finally, emerging technologies that are aimed at addressing both energy efficiency and IAQ are discussed.     

Energy conservation in honey storage building using Trombe wall

This paper investigates energy conservation, mitigation of CO₂ emissions and economics of retrofitting for a honey storage building with Trombe wall for winter heating application. The passive heating potential of Trombe wall for a honey storage building was estimated using TRNSYS building simulation software. This honey storage building is located at Gwalior (latitude: 26°14′N) in India. During winter months, the room air temperature of building falls below the required temperature range of 18–27 °C which is suitable for honey storage. So, the room air temperature range is maintained in the building using a 2.3 kW capacity electrical oil filled radiator (or room air heater) which accounts for the major energy consumption of the building on an annual basis. On account of which there are significant CO₂ emissions into the atmosphere from the honey storage building. Hence, this case study was conducted to recommend the passive heating concept to the stakeholders of the building so as to conserve the energy requirement for room air heating. The investigation showed that the room air temperature can be easily maintained in the range suitable for honey storage using a vented Trombe wall. The experimental work was carried out for the existing building on a typical clear day of harsh winter month of January to validate the results of TRNSYS model of the present building. The statistical error analysis showed a good agreement between model and experimental results. This investigation concludes that there is potential of energy conservation up to 3312 kWh/year and associated reduction in CO₂ emissions (∼33 tonne/year) using a Trombe wall. Also, the retrofitting of building is economically viable as the simple payback period is only about 7 months.     

集中空调冷却水变流量问题辨析

指出集中空调冷却水系统为开式系统,一般不适用功率三次方定律,静压头应为冷却塔塔体扬程,并提出了冷却水泵变速时轴功率的计算公式;明确变流量的节能效果与控制方式密切相关,即使机组处于满负荷状态,但只要是在非设计工况,采用冷凝温度控制法,也可能实现变流量节能;指出制定多台冷水机组部分负荷性能指标的意义。     

A study of perceived air quality and sick building syndrome in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of Perceived Air Quality (PAQ) and Sick Building Syndrome (SBS) using tropically acclimatized subjects 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 subjects, 30 males and 30 females, were engaged in sedentary office work for 3 h. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative Humidity (RH) at 0.6 m height and outdoor air provision were maintained at 50% and 10 l/s/p, respectively. 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 20, 23 and 26 °C at 0.6 m height. The main objective of this study is to evaluate the influence of temperature gradient and room air temperature (at 0.6 m height) on PAQ and SBS in DV environment. It was found that temperature gradient had insignificant impact on PAQ and SBS. Dry air sensation, irritations and air freshness decreased with increase of room air temperature.     

Optimization of cooling load for a lecture theatre in a composite climate in India

A lecture theatre with dimension 16 m × 8.4 m × 3.6 m located at Roorkee (28.58°N, 77.20°E) in the northern region of India, is selected to calculate the monthly and annual cooling load (kWh) and cooling capacity of air conditioning system by a computer simulation. The paper also presents the results of a study investigating the effect of different glazing systems on windows and the reduction in building cooling load. DesignBuilder software has been used for the computer simulation for calculating the cooling load. The paper aims to investigate the reduction in thermal gains and cooling load requirements by varying the U-values of different glazing types, insulating the ceiling, providing cool roofs, interior and exterior insulation on walls, and replacing the conventional fluorescent tube lamp (FTL) by energy efficient compact fluorescent lamp (CFL). Installation of false ceiling, wall insulation, different glazing types and lighting systems are cost effective with normalized annual saving ranging from 17% to 19.8% from this retrofitting project. Furthermore, the study also highlights the potential of reducing the emission of CO₂ and equivalent carbon credit. Retrofitting techniques strongly influence the level of energy saving, although the payback period is generally quite long of order 8 years.     

Study on the influence of albedo on building heat environment in a year-round

The research of energy saving is one of the highlights of buildings environment. According to the albedo change of the wall-facing materials of urban buildings, two building models were constructed, of which the internal and external microclimate parameters were measured under certain meteorological conditions in different seasons. The experimental results show that the decrease of indoor air temperature was up to 4.67 °C with the average diurnal temperature decrease up to 3.53 °C in summer, and the increase was up to 2.81 °C in winter when the albedo changed from 0.21 to 0.86. Moreover, Laplace integral transform method was used to analyze building energy saving. The results indicate that the wall-facing materials with high albedo have the function of heat-protection and heat-insulation and could reduce 150.3 W per day of the buildings’ cooling load in summer and 69.5 W per day of heating load in winter. The research results confirm that employing high albedo coatings on the building exterior wall is an active and effective approach to improve the urban buildings’ micro-heat environment.     

Saving energy in the make-up air unit (MAU) for semiconductor clean rooms in subtropical areas

The energy requirements to cool, dehumidify, preheat and/or humidify outdoor air are significant in the make-up air unit (MAU) of clean room air-conditioning systems, and can represent 30% to 65% of the total thermal energy required to maintain a clean room environment. Because of these high-energy requirements, cost-effective means to reduce energy costs can influence unit production costs. Reducing or displacing mechanical cooling or electrical heating requirements can achieve the greatest opportunity for significant energy savings. This paper, therefore, aims to improve the energy performance of the MAU system by properly arranging compositions of components of a typical MAU applied in a semiconductor clean room. Explicitly, we investigated the influence of various factors including the fan location (draft-through type vs. push-through type), chilled water system (single-chilled water temperature system vs. two chilled water temperature system) and reheating scheme (electrical heating vs. hot water provided by heat recovery chiller). The result shows that the draw-through type accompanied by two chilled water temperature system with heat recovery function exhibits the lowest electrical power consumption.     

The effect of heat-pipe air-handling coil on energy consumption in central air-conditioning system

A study was carried out to investigate the effect of heat-pipe air-handling coil on energy consumption in a central air-conditioning system with return air. Taking an office building as an example, the study shows that compared with conventional central air-conditioning system with return air, the heat-pipe air-conditioning system can save cooling and reheating energy. In the usual range of 22–26 °C indoor design temperature and 50% relative humidity, the RES (rate of energy saving) in this office building investigated is 23.5–25.7% for cooling load and 38.1–40.9% for total energy consumption. The RES of the heat-pipe air-conditioning system increases with the increase of indoor design temperature and the decrease of indoor relative humidity. The influence of indoor relative humidity on RES is much greater than the influence of the indoor design temperature. The study indicates that a central air-conditioning system can significantly reduce its energy consumption and improve both the indoor thermal comfort and air quality when a heat-pipe air-handling coil is employed in the air-conditioning process.     

Instrumentation strategies for energy conservation in broiler barns with ventilation air solar pre-heaters

At the present consumption rate, world fossil-fuel reserves are expected to be depleted by 2050 unless their consumption is optimized and supplemented with renewable energy sources. The objective of this project was to evaluate the performance of a simple data acquisition system installed to conduct an energy balance and identify energy saving strategies in two commercial broilers barns with ventilation air solar pre-heaters. Located near Montreal, Canada, the two identical barns were instrumented for inside and outside air conditions, ventilation rate and energy recovery by the solar air pre-heaters. Whereas the temperature, relative humidity and radiation sensors were reliable, inside air temperature stratification complicated energy balance analyses and broiler heat production rate calculations. Lack of room air mixing resulted in the loss of 25 and 15% of the generated heater load and recovered solar energy. The proper monitoring of all environmental conditions required their measurement every 5 rather than 20 min. Instead of using a data transmission service found to be unreliable in rural areas, all data loggers were downloaded onto a portable computer every 45 days during regular instrument maintenance. Accordingly, room air mixing is recommended to facilitate energy balance studies and improve the efficient use of heating energies.