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.     

A study on the energy performance of a cooling plant system: Air-conditioning in a semiconductor factory

This paper will focus on the energy performance evaluation of a cooling plant system in a semiconductor factory. Several energy saving technologies namely: integrated cooling towers, free cooling systems, control of the chilled water quantity, etc., have been adopted to improve efficiency of the cooling plant system. We have collected actual operating data for 2 years and evaluated the performance of chillers’ COP and the whole cooling plant system's COP and they showed satisfactory results even if the thermal load of the factory was about half compared with design phase assumption.

We also have verified each effect of the energy saving technologies through model-based simulation analysis. The annual electric power consumption dropped about 35% compared to conventional cooling plant systems in case of design phase thermal load. And the faulty status operation of the chiller's number control miss occurred while we monitored. Electric power consumption increased about 17% compared to normal status operation at the same period.     

Simulation of a VAV air conditioning system in an existing building for the cooling mode

In this study, simulation of a variable air volume (VAV) air conditioning system in an existing office building is presented for the cooling mode. A building simulation package was used for the simulation [DOE, EnergyPlus Engineering Document, Version 1.3., U.S. Department of Energy, Washington, DC, 2005]. The design information of the existing office building, the actual number of the internal load sources such as occupants, lighting, office equipments and the manufacturer's data for the existing rooftop unit (RTU) and the VAV boxes were used in the building simulation package. The simulation results; RTU power consumption, indoor zone temperature and relative humidity, were validated with the data obtained from the on-site measurements performed in the existing office building under the same outdoor conditions. It was found that 71.1% of all simulated power consumption data falls within ±15% range from the experimental data. The reason for the existence of some data out of band is due to the possible errors associated with the difference in the solar data used for the location 40 km away from the experimental location. It was found that 90.6-94.7% of the indoor temperature experimental data fall within ±1.5 °C range from the simulated data, and 88.3-91.3% of the indoor relative humidity data fall within ±18% range from the simulated data.     

Study on simulation methods of atrium building cooling load in hot and humid regions

In recent years, highly glazed atria are popular because of their architectural aesthetics and advantage of introducing daylight into inside. However, cooling load estimation of such atrium buildings is difficult due to complex thermal phenomena that occur in the atrium space. The study aims to find out a simplified method of estimating cooling loads through simulations for various types of atria in hot and humid regions. Atrium buildings are divided into different types. For every type of atrium buildings, both CFD and energy models are developed. A standard method versus the simplified one is proposed to simulate cooling load of atria in EnergyPlus based on different room air temperature patterns as a result from CFD simulation. It incorporates CFD results as input into non-dimensional height room air models in EnergyPlus, and the simulation results are defined as a baseline model in order to compare with the results from the simplified method for every category of atrium buildings. In order to further validate the simplified method an actual atrium office building is tested on site in a typical summer day and measured results are compared with simulation results using the simplified methods. Finally, appropriate methods of simulating different types of atrium buildings are proposed.     

校园建筑节能监测系统的设计与应用

分析高校现有能耗计量系统,以节约型校园建设示范工程——合肥工业大学校园节能监测系统改造项目为背景,对校园建筑节能监测系统的组成及其功能做详细说明,并对系统实施过程中的关键技术进行探讨。     

Effects of utilizing seawater as a cooling source system in a commercial complex

This paper treats energy and cost performance of a cooling source system with indirect seawater utilization for air conditioning in a commercial complex. Seawater utilization has merits as a cooling source, because seawater temperature is lower than outdoor air in summer and it is cost effective because there is no water monetary cost. Actual operating data has been measured for about 2 years and the chiller and system co-efficient of performance (COP) have indicated about 4.77 and 2.93, respectively, even in summer season and the mean efficiency of the thermal storage system was about 89.9% taking into account heat loss of pumps. In addition, we have constructed simulation models for cooling tower systems, air cooling chiller systems and direct seawater utilization systems then compared them to this system. The electric power consumption of the indirect seawater utilization system was almost the same as the other systems except the air cooling chiller system, because using lower seawater temperature made the chiller efficiency higher. In conclusion, our results showed the indirect seawater utilization system was able to improve the system COP compared to air cooling chiller system, and cancel water consumption compared with the cooling tower system, and cut down an initial and maintenance costs compared with the direct seawater utilization system.     

Experimental investigation of an innovative low electricity consumption air cooling system for small building application

This paper investigates the development of a low cost air cooling system used for small scale applications. Its operation is based on the rational and efficient use of energy available in conventional freezers, used for other purposes than air conditioning, to cool small areas. In this paper, the proposed air cooling system is applied to small kiosk prototype (called “periptero”), found very often in the streets of Greek cities and villages, used to sell goods to people. The proposed air cooling system is using the low temperature air inside the freezers to cool the air inside the kiosk and provide a better living environment for the owner, particularly during summer period. The basic principle of the system operation and the experimental installation will be described and the experimental results will be presented and discussed.     

Atmospheric-temperature-based cooling system control for electronic devices using internet of things

ABSTRACT

The operating temperature of electronic devices plays a vital role in its durability of operation. When the electronic chip surface temperature increases beyond threshold limit, it undergoes breakdown and starts to malfunction; upon continuous operation, it gets melt down. Generally, cooling arrangements such as fan or A/C are provided to maintain the temperature. The low operating temperature also leads to problems such as excessive energy consumption and noisy operation. The surface temperature must be maintained in accordance with the surrounding temperature and the control should be independent of the operator, such an intelligent system can be developed by internet of things (IOT). IOT with smart gateways can provide the possible solution; this paper deals with one such intelligent system implementation and its performance. The proposed system considers the atmospheric temperature to control the cooling system. The smart system is estimated to save 6% of power consumption and also simultaneously reduces the noisy operation.     

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.     

Experience on the application of a ground source heat pump system in an archives building

A ground source heat pump (GSHP) system was designed and constructed in Minhang archives of Shanghai. As a demonstration project, it is the first archives to use a GSHP system in China. The system consists of two heat pumps with the rated cooling capacity of 500 kW for each and 280 boreholes with 80 m in depth. In the cooling mode, the heat extraction from the condenser of the heat pump was divided: part of it was rejected to the soil while the rest was used to reheat the air in air handling units. The GSHP system has continuously run for nearly two years. It was shown that the indoor thermal environment met the “Archives Design Code” issued by China national archives. Compared with an air source heat pump system which is widely used in archives buildings, the operating cost of the GSHP system is reduced by 55.8% and the payback time is about two years. Owing to its great potential in energy conservation, such kind of GSHP system is testified to be applicable to the air-conditioning systems of the archives buildings. Besides, the applications of GSHP systems corresponding to different climatic zones of China were analyzed.     

Investigation of the ageing effect on chiller plant maximum cooling capacity using Bayesian Markov Chain Monte Carlo method

Ageing inevitably leads to capacity degradation in a chiller plant. Hence in the life-cycle performance analysis of a chiller plant, ageing always represents a crucial consideration for designers. Ageing is normally quantified using maintenance factor. A conventional analysis recommends that the maintenance factor should be 0.01 for systems that undergo annual professional maintenance, and 0.02 for those that are seldom maintained. However, this recommendation is mainly based on a rule of thumb, and may not be accurate enough to describe the ageing for a given chiller plant. This research therefore proposes a method of identifying the chiller maintenance factor using a Bayesian Markov Chain Monte Carlo method, which can take account of the uncertainties that exist in the estimation of the ageing. Details of the identification will be provided by applying the proposed method to a real chiller plant, and results will be compared with that of the conventional analysis.     

Eawag Forum Chriesbach—Simulation and measurement of energy performance and comfort in a sustainable office building

The Eawag's new headquarters “Forum Chriesbach” is an exemplary illustration of a ‘sustainable’ construction design for office buildings. With a unique combination of architectural and technical elements the building reaches a very low 88 kWh/m² overall primary energy consumption, which is significantly lower than the Swiss Passive House standard, Minergie-P. A monitoring and evaluation project shows that the building is heated mainly by using the sun and internal heat gains from lighting, electrical appliances and occupants, resulting in an extremely low space heating demand. Cooling is provided by natural night time ventilation and the earth-coupled air intake, which pre-cools supply air and provides free cooling for computer servers. However, values for embodied energy and electricity consumption remain significant, even with partial on-site electricity production using photovoltaics. TRNSYS computer simulations show the contributions of individual building services to the overall energy balance and indicate that the building is resilient towards changes in parameters such as climate or occupancy density. Measurements confirm comfortable room temperatures below 26 °C, even during an extremely hot summer period, and 20-23 °C in the winter season. An economic analysis reveals additional costs of only 5% compared to a conventionally constructed building and a payback-time of 13 years.     

A naturally ventilated cavity roof as potential benefits for improving thermal environment and cooling load of a factory building

The impact of natural ventilation of a roof cavity on improvement of the thermal environment and reduction of cooling load of a factory building is discussed. A computer program was developed with the logic in a companion paper [1] to observe the effect of cavity ventilation on the operative temperature of the occupied zone in the factory. Comparisons were made between factories with a cavity roof and a single roof in the Japanese climate. Results showed that the cavity roof was superior to the single roof in lowering the operative temperature by about 4.4 °C. When the factory was air conditioned, the cooling load reduction reached approximately 50% during the summer to maintain an operative temperature of 26 °C. Results showed that a naturally ventilated cavity roof has excellent potential for improving the indoor thermal environment and energy savings of factory buildings without complicated cooling installations and life time power consumption.     

Energy simulation in the variable refrigerant flow air-conditioning system under cooling conditions

As a high-efficiency air-conditioning scheme, the variable refrigerant flow (VRF) air-conditioning system is finding its way in office buildings. However, there is no well-known energy simulation software available so far which can be used for the energy analysis of VRF. Based on the generic dynamic building energy simulation environment, EnergyPlus, a new VRF module is developed and the energy usage of the VRF system is investigated. This paper compares the energy consumption of the VRF system with that of two conventional air-conditioning systems, namely, variable air volume (VAV) system as well as fan-coil plus fresh air (FPFA) system. A generic office building is used to accommodate the different types of heating, ventilating, and air-conditioning (HVAC) systems. The work focuses on the energy consumption of the VRF system in the office buildings and helps the designer's evaluation and decision-making on the HVAC systems in the early stages of building design. Simulation results show that the energy-saving potentials of the VRF system are expected to achieve 22.2% and 11.7%, compared with the VAV system and the FPFA system, respectively. Energy-usage breakdown for the end-users in various systems is also presented.     

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.     

Double cooling coil model for non-linear HVAC system using RLF method

The purpose of heating, ventilating and air conditioning (HVAC) system is to provide and maintain a comfortable indoor temperature and humidity. The objective of this work is to model building structure, including equipments of HVAC system. The hybrid HVAC model is built with physical and empirical functions of thermal inertia quantity. Physical laws are used to build the sub-model for subsystems that have low thermal inertia while the empirical method is used to build the sub-model for subsystems with high thermal inertia. The residential load factor (RLF) is modeled by residential heat balance (RHB). RLF is required to calculate a cooling/heating load depending upon the indoor/outdoor temperature. The transparency, functionality of indoor/outdoor temperatures and simplicity of RLF makes it suitable for modeling. Furthermore, the parameters of the model can be calculated differently from room to room and are appropriate for variable air volume (VAV) factor. Nowadays, a VAV system is universally accepted as means of achieving both energy efficiency and comfortable building environment. In this research work, a pre-cooling coil is added to humidify the incoming air, which controls the humidity more efficiently inside conditioned space. The model presented here is verified with both theoretical and numerical methods.     

Thermal performance of a cool-pool system for passive cooling of a non-conditioned building

The thermal performance of a cool-pool system for passive cooling of a non-conditioned building is presented. The system consists of a water pond over the roof which is shaded in such a way that incident solar radiation does not reach the roof surface and the pond loses heat by convection and evaporation to its surroundings. Using periodic analysis, explicit expressions have been obtained for various performance parameters, namely room air temperature and water temperature and the amount of water evaporated from the system. Numerical calculations carried out for a typical day at New Delhi (28.6°N) show that the cool-pool system is more effective than the conventional evaporative cooling techniques such as water film and roof pond; the system also consumes less water in comparison with other evaporative cooling techniques.     

Optimum insulation thicknesses for building walls with respect to cooling and heating degree-hours in the warmest zone of Turkey

Thermal insulation is one of the most effective energy conservation measures for cooling and heating in buildings. Therefore, determining and selecting the optimum thickness of insulation is the main subject of many engineering investigations. In this study, the determination of optimum insulation thickness on external walls of buildings is comparatively analyzed based on annual heating and cooling loads. The transmission loads, calculated by using measured long-term meteorological data for selected cities, are fed into an economic model (P₁−P₂ method) in order to determine the optimum insulation thickness. The degree-hours method that is the simplest and most intuitive way of estimating the annual energy consumption of a building is used in this study. The results show that the use of insulation in building walls with respect to cooling degree-hours is more significant for energy savings compared to heating degree-hours in Turkey's warmest zone. The optimum insulation thickness varies between 3.2 and 3.8 cm; the energy savings varies between 8.47 and 12.19 $/m²; and the payback period varies between 3.39 and 3.81 years depending on the cooling degree-hours. On the other hand, for heating load, insulation thickness varies between 1.6 and 2.7 cm, energy savings varies between 2.2 and 6.6 $/m², and payback periods vary between 4.15 and 5.47 years.     

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.     

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.