Energy performance evaluation of a novel evaporative cooling technique

High summer conditioning consumption is becoming a tough and critical issue and consequently there is a need to provide buildings with new technologies for energy saving. Current European and Italian legislation is also working in this direction. We present a preliminary experimental evaluation of the energy performance of a new technology which is capable of canceling conduction gains through walls: “water-evaporative walls”, which are not only able to prevent the entrance of energy fluxes from the exterior to the interior, but also to reduce wall temperatures to below the values found indoors. This solution basically suggests equipping standard ventilated façades with a proper water-evaporative system, which exploits the latent heat of water evaporation, in order to absorb summer cooling loads. From the technological point of view, it requires the insertion of a water spraying system and a proper insulating layer in the ventilated air chamber. The insulation will act not only as a standard insulating material, but also as a porous surface to store water sprayed by the system and then gradually release it when needed for cooling. The experimental analyses showed the effectiveness of this technology, which decreases the overall summer energy load in buildings by canceling conduction loads.     

Energy savings in Danish residential building stock

A large potential for energy savings exists in the Danish residential building stock due to the fact that 75% of the buildings were constructed before 1979 when the first important demands for energy performance of building were introduced. It is also a fact that many buildings in Denmark face comprehensive renovations in the coming years and in connection with this renovation process energy-saving measures can be implemented relatively inexpensive and cost effective. This opportunity should be used to insure the buildings in the future as far as energy consumption is concerned. This paper gives a short account of the technical energy-saving possibilities that are present in existing dwellings and presents a financial methodology used for assessing energy-saving measures. In order to estimate the total savings potential detailed calculations have been performed in a case with two typical buildings representing the residential building stock and based on these calculations an assessment of the energy-saving potential is performed. A profitable savings potential of energy used for space heating of about 80% is identified over 45 years (until 2050) within the residential building stock if the energy performances are upgraded when buildings are renovated.     

Study on a novel thermally driven air conditioning system with desiccant dehumidification and regenerative evaporative cooling

Existing desiccant cooling systems reduce the temperature of process air either by adopting evaporative coolers or incorporating vapor compression systems. While the former is restricted by inaccurate control, the latter still consumes certain quantity of electric power. To solve this problem, a thermally driven air conditioning system, which combines the technologies of rotary desiccant dehumidification and regenerative evaporative cooling, has been proposed and investigated. In addition to dehumidification, the system is capable of producing chilled water, thereby realizing separate temperature and humidity control without increasing electrical load. To find out the characteristics of produced chilled water and evaluate the feasibility and energy saving potential of this novel system, a mathematical model has been developed. Case studies have been conducted under Air conditioning and Refrigeration Institute (ARI) summer, ARI humid and Shanghai summer conditions. It is found that the system can achieve a thermal COP higher than 1.0 and an electric COP about 8.0. The temperature of chilled water produced by the system is around 14–20 °C. This chilled water can be used with capillary tube mats for radiant cooling. It is suggested that the system can also be designed as a standalone chilled water plant. As a desiccant dehumidification-based chilled water producing technology, this would expand desiccant cooling to a boarder niche application. The effects of chilled water flow rate, air distribution ratio, inlet air conditions and regeneration temperature have been analyzed in detail. Reachable handling regions, which will be helpful to system design and optimization, have been obtained.     

Space conditioning using evaporative cooling for summers in Delhi

The article examines the possibility of space conditioning the interiors of a multistorey office building in Delhi using evaporative cooling in the summer months of April, May and June. The temperature and humidity conditions obtained in a room of the building with direct evaporative cooling are studied by simulation. In this case study, the room is assumed to have a south-facing wall with a window and all other walls, ceiling and floor are interior partitions. The effect of number of air-changes per hour (ACH) from 1 to 40 and fresh-air bypass factor (BPF) 0% to 100% on performance is studied by simulation. The aim is to find whether some combination of ACH and BPF succeeds in keeping room conditions below 80% RH and temperatures between 27 and 31°C, depending on RH. It is found that the desired results are achieved by keeping the ACH and the BPF within certain limits depending on weather conditions. If the temperature and relative humidity of the ambient air are too high then a direct evaporative cooler cannot achieve comfort in the room. Appropriate combinations of ACH and BPF have to be selected to obtain the best results.     

Energy performance of a cooling plant system using the inverter chiller for industrial building

The purpose of this paper is to clarify energy performance of the cooling plant system in the industrial building using actual measured operating data and numerical simulation analysis. One aspect of industrial buildings is that they have large energy consumption for manufacturing and air-conditioning compared with office and commercial buildings. Some examples of high-efficiency technologies installed in this particular cooling plant system are inverter chillers, integrated cooling towers and a free-cooling system. The inverter chiller which has been put on the market recently is state-of-the-art technology. The maximum COP of the inverter chiller reaches about 18 under certain conditions and integrated cooling towers make lower temperature cooling water as the whole capacity is large. Actual operating data indicates satisfied values for chiller and system COP during the running period and the simulation results show that the cooling plant system can cut down annual electric power consumption by about 48% compared with conventional cooling system.     

含湿多孔介质应用于建筑墙体的制冷性能分析

在建立多孔介质墙体热湿平衡的基础上,采用描述非饱和多孔介质热质迁移的数学模型,分析了多孔介质墙体方位及结构、多孔介质层的材料及孔隙率对床层制冷特性的影响,为多孔介质蒸发制冷墙体的推广和应用提供理论依据.     

Validated air handling unit model using indirect evaporative cooling

This paper presents the validated Modelica model of a Menerga? Adsolair? type 58 Air Handling Unit. The unit consists of two fans, four dampers, three air filters and further allows heat recovery (including free cooling), indirect evaporative cooling and active cooling. The first principles model uses manufacturer data sheet information and optionally also measurement data to calibrate some parameters for increased accuracy. Model validation is based on measurement data and results in an average normalized absolute error for the electrical power consumption of approximately 1%. A custom developed control strategy is compared with the measured performance of a proprietary controller. The model is available open source as part of the IDEAS Modelica library.     

Energy performance optimization of radiant slab cooling using building simulation and field measurements

Few field studies of energy performance of radiant cooling systems have been undertaken. A recently constructed 17,500 m² building with a multi-floor radiant slab cooling system in the tower was investigated through simulation calibrated with measured building energy use and meteorological data. For the very cold, dry region where the building was located, it was found that a typical floor of the tower would have had 30% lower annual energy use with a conventional variable air volume system than with the as-built radiant cooling-variable air volume combination. This was due to (1) simultaneous heating and cooling by the existing radiant cooling and air systems, (2) the large amount of free cooling possible in this climate, and (3) suboptimal control settings. If these issues were remedied and combined with improved envelope and a dedicated outdoor air system with exhaust air heat recovery, a typical floor could achieve annual energy use 80% lower than a typical floor of the existing building HVAC system. This shows that radiant thermal control can make a significant contribution to energy-efficiency, but only if the building design and operating practices complement the strengths of the radiant system.     

用人工神经网络方法预测分析直接蒸发冷却空调机的性能参数

针对填料表面不规则造成的数学模型无法求解的情况,利用人工神经网络优良的非线性映射能力和GLASdek填料直接蒸发冷却空调机实验测试数据,建立了三层前馈式神经网络来预测直接蒸发冷却空调机在不同工况下处理空气的能力,预测结果与实测结果吻合较好。     

Estimating energy savings from behaviours using building performance simulations

Occupants’ behaviours are a major determinant of energy use in buildings. The related savings potential has been insufficiently exploited. Although research has addressed behavioural savings through real-world interventions and quantitative modelling approaches, it has not yet explored the full variety of household activities. This work proposes an integrative modelling approach of energy behaviours in the residential setting as a tool to estimate the behavioural impact of households on energy consumption. It uses building energy performance simulation (BEPS) tools to exploit the behavioural savings potential associated with usage and investment energy behaviours when using different energy services in daily household activities. Simulations have estimated significant behavioural savings potential associated with energy behaviours, which may be materialized if some forms of behaviour are induced. Investment behaviours have higher savings potential than usage behaviours, and the behavioural savings potential per energy service is proportional to the energy consumption breakdown. BEPS tools enable a quantitative estimate of the behavioural impact on energy consumption, but further improvements to these tools are needed to incorporate the complexity of behavioural dimensions. Estimating the behavioural savings potential is important for a more effective design of behaviour change interventions, which in turn will support more effective energy efficiency policies.     

Energy and peak power savings potential of radiant cooling systems in US commercial buildings

The paper describes a parametric study developed to estimate the energy and peak power savings potential of radiant cooling systems in commercial buildings in the US. The study is based on the numerical modeling of a radiant cooling system and an all-air system at different locations in the US. The results show that a building equipped with a radiant cooling system can be operated in any US climate with low risk of condensation. For the office space examined in the study, employing a radiant cooling system instead of a traditional all-air system can save on average 30% of the energy consumption and 27% of the peak power demand due to space conditioning. The savings potential is climate-dependent, and is larger in retrofitted buildings than in new construction.     

Energy saving potential of an indirect evaporative cooler as a pre-cooling unit for mechanical cooling systems in Iran

The performance of indirect evaporative cooling system (IEC) to pre-cool air for a conventional mechanical cooling system has been investigated for four cities of Iran. For this purpose, a combined experimental setup consisting of an IEC unit followed by a packaged unit air conditioner (PUA) was designed, constructed and tested. Two air simulators were designed and used to simulate indoor heating load and outdoor design conditions. Using of experimental data and an appropriate analytical method, the performance and energy reduction capability of combined system has been evaluated through the cooling season. The results indicate IEC can reduce cooling load up to 75% during cooling seasons. Also, 55% reduction in electrical energy consumption of PUA can be obtained.     

Speculation in the feasibility of evaporative cooling

The use of evaporative air cooling, for residential air conditioning, cannot be taken for granted in all situations. It depends on the climatic conditions and the specific nature of application. This work establishes a general foundation for judging the feasibility of evaporative cooling with different evaporative-system configurations, under different climatic conditions and for different applications. Two feasibility criteria were stipulated; the rate of air supply to space and the indoor relative humidity. Systematic procedures are presented for evaluating the required air-flow rate and predicting the achievable indoor condition. Explicit mathematical expressions are derived to define the limitations on outdoor conditions for any allowable specific air flow. The impacts of various pertinent factors are investigated. These include the required indoor temperature, the quality of space load represented by its SHF and the performance index of the system. Computer programs were devised to automate, hence facilitate, the repetitive computations and to evade the graphical work on the psychrometric chart. Samples of program results are graphically displayed.     

Passive downdraught evaporative cooling: performance in a prototype house

The design and performance of a passive downdraught evaporative cooling (PDEC) system are reported. This is the first application of this technique for housing in Europe. The system was integrated within a house designed and built by University of Nottingham students for the 2010 Solar Decathlon Europe event in Madrid, Spain. Testing of the thermal performance of the house occurred for a limited period during June 2010. Performance data have demonstrated that the combination of a high-performance building envelope and PDEC provided comfortable conditions inside the house over a period of increasingly warm weather. Estimates of the cooling achieved, based on the measured results, were compared with the energy required by the system to derive an indicative range of coefficient of performance (CoP) values under varying ambient conditions. The results suggest that PDEC can deliver significant energy savings and achieve comfortable thermal conditions without the need for additional mechanical cooling. This technique may therefore have wider relevance to housing in central and southern Spain, and other hot, dry regions of the world.

Il est rendu compte de la conception et des performances d'un système de refroidissement passif évaporatif à courant d'air descendant (PDEC). Il s'agit de la première application de cette technique dans le domaine du logement en Europe. Le système a été intégré à une maison conçue et construite par des étudiants de l'Université de Nottingham pour la manifestation Solar Decathlon Europe 2010 qui s'est tenue à Madrid, en Espagne. Les données de performance ont démontré que la combinaison d'une enveloppe de bâtiment haute performance et d'un système PDEC ont assuré des conditions agréables à l'intérieur de la maison sur une période où le temps est devenu de plus en plus chaud. Les estimations quant au refroidissement obtenu, sur la base des résultats mesurés, ont été comparées à l'énergie exigée par le système de façon à déterminer une plage indicative des valeurs du coefficient de performance (CoP) dans différentes conditions ambiantes. Les résultats suggèrent que le PDEC peut assurer d'importantes économies d'énergie et créer des conditions thermiques agréables sans qu'il y ait besoin d'un refroidissement mécanique supplémentaire. Cette technique peut par conséquent présenter un intérêt plus large pour le logement en Espagne centrale et du sud, ainsi que dans les autres régions chaudes et sèches du monde.

Mots clés: performance des bâtiments, refroidissement, courant d'air descendant, évaporatif, logement, innovation, passif     

冷却水制冷在某商业建筑中的应用

作为三大能耗产业之一,建筑能耗受到人们广泛关注。在大型公共建筑中空调用电在建筑能耗中占据很大比例,而在暖通空调能耗中,冷热源设备用能为空调用电中主要能耗。为达到建筑节能的目的,可以在一定范围内尽量减少空调主机运行时间,因此当空调负荷降低到一定程度时,可通过冷却水接入空调末端设备,可以在一定程度上降低空调主机运行时间,以达到节能目的。     

Investigation of a hybrid system of nocturnal radiative cooling and direct evaporative cooling

In this paper, the results of a study on a hybrid system of nocturnal radiative cooling, cooling coil, and direct evaporative cooling in Tehran have been discussed. During a night, the nocturnal radiative cooling provides required chilled water for a cooling coil unit. The cold water is stored in a storage tank. During eight working hours of the next day, hot outdoor air is pre-cooled by means of the cooling coil unit and then it enters a direct evaporative cooling unit. In this period, temperature variation of the conditioned air is investigated. This hybrid system complements direct evaporative cooling as if it consumes low energy to provide cold water and is able to fulfill the comfort condition whereas direct evaporative alone is not able to provide summer comfort condition. The results obtained demonstrate that overall effectiveness of hybrid system is more than 100%. Thus, this environmentally clean and energy efficient system can be considered as an alternative to the mechanical vapor compression systems.     

基于蒸发冷却的辐射供冷/热实验台设计探讨

对基于蒸发冷却的辐射供冷/热半集中式空调系统实验台进行了简要介绍,并对实验台的新风系统和水系统设计进行了详细说明.分析了该实验台在中湿度地区不同季节的运行模式,指明了该实验台的特点.     

蒸发冷却新风空调集成系统

分析了对蒸发冷却技术的一些误解，介绍了新风集成系统，单风道、双风道、三风道集成系统等几种方案，在此基础上提出一种借鉴了独立新风系统设计思想的蒸发冷却新风空调集成系统方案。