LCA-based environmental assessment of the use and maintenance of heating and ventilation systems in Dutch dwellings

Buildings contribute significantly to the human-induced environmental burden. This comes not only from construction and demolition but also from activities throughout the operational phase – building maintenance and energy use for climate control. This paper describes how life cycle assessment (LCA) methodology can be applied to quantitatively assess the environmental performance of the use and maintenance of heating and ventilation systems. The studied climate systems include individual non-condensing boilers, condensing boilers and heat pumps on exhaust air for heating and hot tap water combined with either collective mechanical exhaust ventilation or individual balanced ventilation with heat recovery. This study shows that a heat pump causes the highest environmental burden of all the assessed climate systems due to the electricity needed for operation, high material content of the system and the refrigerant used. If the electricity used by the heat pump is generated fully by local photovoltaic cells, environmental performance will improve, but not for all environmental impact categories. Climate systems that reduce energy demand for heating, such as ventilation with heat recovery, will reduce the environmental impact related to energy use for space heating. However, if the electricity used to operate the system increases, along with the material content of the systems and distribution networks, other environmental impact categories than those related to space heating will also increase. Finally, maintenance frequency and related transportation of maintenance workers have a marginal effect on total environmental impact.     

Performance assessment of fuel cell micro-cogeneration systems for residential buildings

The reduction of greenhouse gas emissions in the building sector to a sustainable level will require tremendous efforts to increase both energy efficiency and the share of renewable energies. Apart from the lowering of energy demand through better insulation and fenestration, small combined heat and power (micro-cogeneration) systems may help improve the situation on the supply side by cutting both the non-renewable energy demand for residential buildings and peak loads in the electric grid. Though still on the brink of market entry, fuel cells are the focus of interest as the prime technology for such systems. In this study, a methodology for assessing the performance of such systems in terms of primary energy demand and the CO₂ emissions by transient computer simulations is established, and demonstrated for a natural gas driven solid oxide fuel cell (SOFC) and, to a lesser extend, a polymer electrolyte fuel cell (PEFC) home fuel cell cogeneration system. The systems were evaluated for different grid electricity generation mix types and compared to traditional gas boiler systems. The interaction with hot water storage and solar thermal collectors, and the impact of storage size and predictive control was analyzed. Typical heat and electricity demand load profiles for different types of residential buildings and occupancy were considered, and the sizing of the fuel cell system in relation to the heat demand of the building was analyzed. Primary energy savings decline for cases with lower heat demand and for cases with solar thermal systems, and peak for fuel cell systems sized in accordance with the heat demand of the building. Future assessments of fuel cell systems will need a refined methodology, and depend on realistic performance characteristics and models that accurately consider dynamic conditions.     

The duck curve in a drying pond: The impact of rooftop PV on the Western Australian electricity market transition

Rooftop solar photovoltaics (PV) are significantly influencing the electricity market and system operability in Western Australia. Qualitative methods are used to determine likely impacts and solutions to associated technical and market challenges in this islanded electricity system. Solutions focus on flattening the load curve and addressing minimum system load issues, including via; tariff reform, new ancillary services, automation, storage and energy productivity; targeted markets to match energy supply to the new demand curve; together with enabling technologies such as; improved inverter functionality and control systems. A parsimonious model demonstrates the impacts of rooftop PV on the local mid-day wholesale energy prices.     

空调专用循环泵的选择

分析了空调循环泵系统的系统特性和泵的特性，比较了空调专用循环泵与非专用循环泵的区别，指出了选择空调循环泵应注意的问题。     

Fuzzy and feedforward control of an hybrid thermal energy storage system

A control model for operating a system that stores simultaneously sensible heat from solar and electric energy is proposed. The hybrid thermal energy storage system accumulates solar energy during sunny days and releases it later at night or during cloudy days. It also stores heat from an electric heater during off-peak periods so as to release it later during peak periods. The control model, which makes use of 24-h weather forecasts, comprises two types of controllers: a fuzzy logic controller for estimating the daily amount of thermal electric energy to be stored and a feedforward controller for determining the electricity consumption profile of the heating element during off-peak hours. Results indicate that the proposed control system is far superior to traditional control systems. It maintains a comfortable thermal environment at all times, i.e. the temperature fluctuations are kept within the imposed margins and overheating of the room never occurs. Furthermore, compared to a traditional electric base board heating system, it reduces the electricity consumption for the winter season by 24% and 94% of this electricity is consumed during off-peak hours.     

冰蓄冷系统中卤水泵的合理配置和选型

按板式换热器的数量对并联蓄冰系统、按泵的数量对串联蓄冰系统进行了分类，并对常见的蓄冰系统水泵设计方法进行了分析和评价。针对并联单板式换热器系统传统设计方法存在的问题，提出了泵的改进设计方法；对于串联系统，则提出采用制冷机旁通、多级泵和变频泵的方法使系统配置更加合理。     

Energy efficient control of variable speed pumps in complex building central air-conditioning systems

This paper presents the optimal control strategies for variable speed pumps with different configurations in complex building air-conditioning systems to enhance their energy efficiencies. Through a detailed analysis of the system characteristics, the pressure drop models for different water networks in complex air-conditioning systems are developed and then used to formulate an optimal pump sequence control strategy. This sequence control strategy determines the optimal number of pumps in operation taking into account their power consumptions and maintenance costs. The variable speed pumps in complex air-conditioning systems can be classified into two groups: the pumps distributing water to terminal units and pumps distributing water to heat exchanges. The speeds of pumps distributing water to terminal units are controlled by resetting the pressure differential set-point using the online opening signals of water control valves. The speeds of pumps distributing water to heat exchanges are controlled using a water flow controller. The performances of these strategies are tested and evaluated in a simulated virtual environment representing the complex air-conditioning system in a super high-rise building by comparing with that of other reference strategies. The results showed that about 12-32% of pump energy could be saved by using these optimal control strategies.     

Economic benefits of optimal control for water-cooled chiller systems serving hotels in a subtropical climate

A water-cooled chiller system in an air-conditioned hotel can take up about one-quarter of the total electricity consumption and considerable amounts of water in the heat rejection process. This paper evaluates operating cost savings of a chiller system integrated with optimal control of cooling towers and condenser water pumps. A sophisticated chiller system model was used to ascertain how different control methods influence the annual electricity and water consumption of chillers operating for the cooling load profile of a reference hotel. It is estimated that applying load-based speed control to the cooling tower fans and condenser water pumps could reduce the annual system electricity use by 8.6% and operating cost by 9.9% relative to the equivalent system using constant speed fans and pumps with a fixed set point of 29.4 °C for cooling water temperature control. The ways to implement this advanced control for system optimization are discussed.     

Comparison of natural gas driven heat pumps and electrically driven heat pumps with conventional systems for building heating purposes

Electrically driven heat pumps achieve good efficiencies for space heating. If heat pumps are driven directly by a combustion engine instead of an electric motor, losses attributed to the production and transport of electricity are eliminated. Additionally, the use of the combustion engine's heat leads to a reduced temperature difference across the heat pump. This article presents annual efficiencies of these systems and compares internal combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO₂ emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems in two cases of maximum flow temperatures (40 °C and 60 °C). These temperature levels represent typical modern buildings with large heating surfaces and older buildings with high-temperature radiators, respectively. In addition to the different heat pump setups, conventional space heating systems are included in the comparison. The calculations show that natural gas-driven heat pumps achieve about the same efficiency and CO₂ emissions as electrically driven heat pumps powered with electricity from the most modern natural gas-fired combined cycle power plants. The efficiency of such systems is about twice that of conventional boiler technologies.     

大温差水蓄冷空调系统的模拟研究

对水蓄冷系统的动态模拟计算及能耗分析的结果表明：大温差水蓄冷系统的冷水泵耗电量较一般温差水蓄冷系统可减少9％；大温差水蓄冷系统中空气源热泵的COP值有所提高；与非蓄冷空调系统及一般温差水蓄冷系统相比，大温差水蓄冷运行费最少。     

A simulation of an underground heat storage system using midnight electric power

The purpose of this study is to investigate how much the peak daytime demand for electricity is reduced by an underground heat storage system that uses surplus electricity during the nighttime. In this paper, we report on a numerical simulation method and the results from an energy performance simulation of this system at Park Dome Kumamoto, a Kumamoto Prefectural indoor athletic facility. The simulation results were in good agreement with the measurements, and that shows that this simulation method is applicable for the prediction and optimization of an underground heat storage system for other conditions.     

An optimal control algorithm for borehole thermal energy storage systems

The aim of this paper is to present an optimal control algorithm to manage borehole thermal energy storage systems (BTES). Such a system gets exhausted, if it is employed intensively, i.e. outlet fluid is outside acceptable temperature ranges, and can no longer provide the desired heat or cold. To avoid this problem a control algorithm is proposed, which simultaneously optimizes the operation costs. This algorithm is based on a dynamic programming technique and results in an array which provides the optimal heat flux for a given field temperature, date and demand. The controller is illustrated on a simulation of an existing building. Several weather scenarios have been examined and the system remained robust under all situations.     

相变换热系统对室内温度影响的探究

相变换热系统利用相变材料的蓄热特性,在夜间谷电时段使用廉价电能蓄热,并在白天释放热量,控制室内温度。试验表明相变换热系统在夜间蓄热之后,实现连续30小时出风温度在20℃以上,将空间体积为50 m3的试验房维持在10℃以上的效果,实现电力的移峰填谷,提高室内的舒适性。     

Influence of building parameters and HVAC systems coupling on building energy performance

The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan.The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%.     

北京天创世缘工程空调设计

该工程空调系统采用冰蓄冷与水源热泵相结合的方式，选用6台三工况水源热泵，夏季水源热泵夜间按制冰工况运行、白天按空调工况运行，冬季利用地下水供暖。比较了常规空调系统与该系统的投资与运行费用，并分别对该工程的冬夏工况进行了调试，结果表明系统节能效果显著。     

毛细管网复合水蓄冷空调系统的应用前景

本文提出了毛细管显热末端和水蓄冷相复合的空调系统形式,并阐述了复合系统的特点.以某工程为例,比较分析了毛细管网复合水蓄冷空调系统与常规空调系统在设备选型、设备初投资、耗电量以及运行费用上的差别.结果表明,复合空调系统能够起到移峰填谷、降低能耗和运行费用的作用.     

A general methodology for optimal load management with distributed renewable energy generation and storage in residential housing

In the US, buildings represent around 40% of the primary energy consumption and 74% of the electrical energy consumption [U.S. Department of Energy (DOE). 2012. 2011 Buildings Energy Data Book. Energy Efficiency & Renewable Energy]. Incentives to promote the installation of on-site renewable energy sources have emerged in different states, including net metering programmes. The fast spread of such distributed power generation represents additional challenges for the management of the electricity grid and has led to increased interest in smart control of building loads and demand response programmes. This paper presents a general methodology for assessing opportunities associated with optimal load management in response to evolving utility incentives for residential buildings that employ renewable energy sources and energy storage. An optimal control problem is formulated for manipulating thermostatically controlled domestic loads and energy storage in response to the availability of renewable energy generation and utility net metering incentives. The methodology is demonstrated for a typical American house built in the 1990s and equipped with a single-speed air-to-air heat pump, an electric water heater and photovoltaic (PV) collectors. The additional potential associated with utilizing electrical batteries is also considered. Load matching performance for on-site renewable energy generation is characterized in terms of percentage of the electricity production consumed on-site and the proportion of the demand covered. For the purpose of assessing potential, simulations were performed assuming perfect predictions of the electrical load profiles. The method also allows determination of the optimal size of PV systems for a given net metering programme. Results of the case study showed significant benefits associated with control optimization including an increase of load matching between 3% and 28%, with the improvement dependent on the net metering tariff and available storage capacity. The estimated cost savings for the consumer ranged from 6.4% to 27.5% compared to no optimization with a unitary buy-back ratio, depending on the available storage capacity. Related reduction in CO₂ emissions were between 11% and 46%. Optimal load management of the home thermal systems allowed an increase in the optimal size of the PV system in the range of 13–21%.     

Power grid balancing of energy systems with high renewable energy penetration by demand response

It is generally accepted that the integration of intermittent energy resources like wind energy and photovoltaics into an electricity system cannot exceed a limit of around 20% or 25%, see, e.g. [EWEA, 2005. Large-scale integration of wind energy in the European power supply: analysis, issues and recommendations. The European Wind Energy Association]. However, the decoupling of electricity generation and consumption cannot be implemented only by use of electricity storage. In the end, electricity is converted into many different energy services – quite often into thermal energy – which is better suited for storage. This article presents the results of investigations which studied the potential of those demand response activities for Germany. The investigations are based on both modelling of thermal storage devices and laboratory tests.     

Evaluation of commercial building demand response potential using optimal short-term curtailment of heating,ventilation, and air-conditioning loads

Mismatches in power supply and demand due to infrastructure design and commercial development result in negative economic impacts and societal disruption. These impacts are exacerbated by unusually hot weather as well as energy infrastructure failures. Demand reductions by large commercial and industrial customers are increasingly sought by electrical utilities as a means to control severe supply–demand mismatches. Large electricity consumers have used thermal storage systems, on-site electricity generation, shifting of production processes, and short-term curtailment as means to manage and control their demand during peak demand times. Utility notification may be sent to request a reduction of load for a given duration when demand reaches a specified percent of available supply. This paper examines the interconnected nature of the building heating, ventilation, and air-conditioning systems as they apply to short-term demand response (DR) by conducting a reference case investigation into optimal control of building cooling systems for DR.     

An aquifer thermal storage system in a Belgian hospital: Long-term experimental evaluation of energy and cost savings

Over a three years period, an aquifer thermal energy storage system was monitored in combination with a heat pump for heating and cooling of the ventilation air in a Belgian hospital. The installation was one of the first and largest ground source heat pump systems in Belgium. Groundwater flows and temperatures were monitored as well as the energy flows of the heat pumps and the energy demand of the building. The resulting energy balance of the building showed that the primary energy consumption of the heat pump system is 71% lower in comparison with a reference installation based on common gas-fired boilers and water cooling machines. This corresponds to a CO₂-reduction of 1280 ton over the whole measuring period. The overall seasonal performance factor (SPF) for heating was 5.9 while the ATES system delivered cooling at an efficiency factor of 26.1. Furthermore, the economic analysis showed an annual cost reduction of k€ 54 as compared to the reference installation, resulting in a simple payback time of 8.4 years, excluding subsidies.