A novel on-off TRV adjustment model and simulation of its thermal dynamic performance

Field test results show that about 15% to 40% of building heat loss in China is attributable to poor heating systems regulation. The current method for addressing this problem is to install thermostatic radiator valves (TRVs) to the ends of radiators, a method adapted from northern Europe. However, this method has resulted in poor performance from delayed controlling action due to thermal inertia as well as insufficient system control accuracy. This is further compounded by incorrect operation by system users and a lack of financial incentives to regulate the system if users are not billed for their heat consumption. We present a new method for simultaneously heat controlling and metering. The core challenge is to design a control strategy that will maintain the room’s temperature. Thus, we established dynamic heat transfer models for water flow, the radiator and the building so as to obtain the optimal heating strategy. We also simulated the indoor thermal dynamic performance of the heating system with different heating loads, supply water temperatures, and supply water flow rates using three methods: a continuously changing flow rate (Method 1), a step-change flow rate based on temperature deviation (Method 2) and an intelligent step-change flow rate (Method 3) which predicts the duty cycle of the valve in the proceeding period and controls the valve’s on-time. The simulation results indicate the performance of these three methods. For Method 1, as the room temperature is above the set point, the flow rate can be automatically reduced to a level which is proportional to the room temperature deviation. Further, the scale factor of the flow rate is designed according to the +2°C deviation, so it is accepted that the room temperature is higher than the set point by +2°C using this method. However, this low control precision is unsatisfactory. The mean temperature is higher than the set point and greatly affected by the heating load and supply water’s temperature and flow rate. For Method 2, the controlling action is delayed by thermal inertia, the room temperature fluctuates between the highest and lowest levels, and the temperature deviation can be greater than the set value. For Method 3, both the simulation and field test results showed that room temperature deviation was maintained within a ±0.5°C range under the various conditions. This method appears relatively robust and adaptable, and was the best control strategy of the three methods.     

户内水平单管跨越式系统的设计计算

通过对能够实现分室控温,分户计量的户内水平单管跨越式系统的散热器数量的设计计算及分析,认为采用自力式两 恒温阀加跨越管的做法不妥,而应采用每组散热器前设置手动三通调节阀或自力式三通恒温阀的单管跨越式系统.     

北京新康小区供暖系统设计及分析

作为示范工程，该住宅小区供暖系统采用了节能设计和设备，在户内设置空阀和热表，在锅炉房供水总管上设总热表；供暖水系统为二级泵系统，二级泵配备变频调速装置，控制管网始端压差，系统采用变频调速泵定压。测试了冬季运行工况，并对测试结果进行了经济分析。     

散热器恒温阀控制有效性的模拟分析研究

本文以实际建筑及安装恒温阀的供热系统为研究对象,建立了热力水力综合仿真模型,进行了多工况模拟,分析了恒温阀对不同原因(流量分配不均、散热器面积过大和供水温度过高)引起的过热现象的改善程度,进而探讨了适合新型供热系统的运行调节方式。主要结论为:当恒温阀设置档位为2~3时,恒温阀改善过热的有效性与过热原因及过热程度有关;对流量偏大引起的过热损失的控制有效性小于0.6,对供水温度偏高及散热器面积偏大引起的过热损失的控制有效性约为0.8;过热损失越大,应用恒温阀后的节能潜力越大,但仍有约20%~40%的过热损失需要从改善不合理的运行调节和设计角度去解决。基于上述分析,本文提出水泵定压差变频运行、并以系统流量变化为反馈量分日调节供水温度的策略,从而适应系统负荷变化,并可将系统流量控制在较合理范围内。     

太阳能热泵-地板辐射供热系统实验研究

实验研究了太阳能热泵-地板辐射供热系统的性能,并与燃油、燃气锅炉集中供热系统进行了经济性分析比较。实验结果表明,热管真空管集热器的集热效率为64·4%,U形管真空管集热器的集热效率为59%,热泵机组的能效比为3·08;室内温度变化相对机组供热时间滞后3h,有利于采用间歇运行方式降低运行费用。经济性分析结果表明,在青岛地区为节能型建筑供热时,该系统的单位面积费用年值介于燃气、燃油锅炉集中供热之间。     

预测控制在二次网供暖控制系统中的应用

建立了燃气热水锅炉系统模型,分析了二次网供暖控制系统的特性,提出了采用动态矩阵控制算法,介绍了该算法的原理、实现方案及算法应用的过程。进行了半实物仿真实验,验证该算法的控制效果。     

供热工业锅炉计算机控制系统的设计与应用

本文在分析我国工业锅炉运行水平的基础上，介绍了计算机系统在工业锅炉控制领域的应用状况，并以10t／h燃煤供热工业蒸汽锅炉计算机控制系统的开发为例，详细阐述了一种采用上业PC作为主体的简化分散控制系统的设计思想。     

Simulation and analysis on control effectiveness of TRVs in district heating systems

Based upon an existing building and heating system with thermostatic radiator valves (TRVs), an integrated model is developed for simulating the thermal and hydraulic behavior of the heating system under various operation cases. According to the simulation results, the effectiveness of TRVs in reducing overheating has been studied. The results indicate that when the set value of the TRV is kept at 2-3, its effectiveness in reducing the overheating phenomena caused by an excessive water flow rate is less than 60%. If the overheating phenomena is caused by an excessive supply water temperature and radiator area, the effectiveness of the TRV can reach about 80%; the TRV's effect becomes more obvious with increasing overheating degree; however, about 20%-40% of overheating loss still needs to be resolved by improving improper operation adjustment and design. Considering these results, a control strategy is proposed, in which the supply water temperature is adjusted daily according to the flow performance of the system, and the pump is operated with frequency conversion and constant pressure difference. Further simulation indicates that, under the new control strategy, the variation of the heat supply quantity of the system can match the heat load change, and the flow rate of the system can be controlled at an appropriate range.     

Analysis of retrofit air source heat pump performance: Results from detailed simulations and comparison to field trial data

In the UK, gas boilers are the predominant energy source for heating in housing, due primarily to the ready availability of natural gas. The take-up of heat pumps has lagged far behind Europe and North America. However, with the development of standards for low and zero-carbon housing, gas price rises and the depletion of the UK's natural gas reserves, interest in heat pump technology is growing. Heat pumps, particularly air source heat pumps (ASHPs), have the potential to be a direct, low-carbon replacement for gas boiler systems in housing.In this paper, monitored data and simulations were used to assess the performance of an ASHP when retrofitted into a dwelling. This required the development and calibration of a model of an ASHP device and its integration into a whole-building, dynamic simulation tool. The predictions of the whole-building model were compared to field trial data, indicating that it provided a suitable test bed for energy performance assessment. Annual simulations indicated that the ASHP produced 12% less carbon that an equivalent condensing gas boiler system, but was around 10% more expensive to run. However, the proposed UK renewable heat incentive transforms this situation, with income from ASHP heat generation exceeding the fuel costs.     

Enabling the hybrid use of air conditioning: A prototype on sustainable housing in tropical regions

This paper demonstrates how the use of active or passive means only does not give the appropriate answers to a tropical design when considering housing. The author discusses about the idea of both modes of operation being used simultaneously or in parallel, and how this concept has been developed for one experimental building prototype in tropical areas of Brazil (Northeast region). Quantification is given through extensive parametric simulations which have been conducted using different environmental simulation programmes—TAS (EDSL, UK), ESP-r (ESRU, UK) and photovoltaic (PV)-Design PRO-G (Sandia Labs, USA). Thermal comfort levels along with energy use were assessed and compared, in terms of degree hours of overheating/under heating and cooling energy use. The prototype design has also taken into account the appropriate use of resources through sustainable design features: efficient use of energy, water and materials. The results have demonstrated that for regions such as the warm-humid tropics, the use of a mixed running strategy have optimized energy performance and provided better levels of thermal comfort in a much more effective way. For some cases, cooling energy savings up to 80% were feasible on a hybrid mode, where thermal comfort was improved up to 65%. It has also demonstrated the integration of energy efficiency and a PV grid-connected system, while enabling those daytime electrical needs to be accomplished by the photovoltaic component.     

Improvement of intermittent central heating system of university building

Most universities in Korea use intermittent central heating system which operates according to a preset intermittent schedule that is determined based on outdoor air temperature. This system is popular for university buildings due to its low initial cost and simple operation. But since it is not based on feedback control, the indoor thermal comfort is unsatisfactory. In this research, problem with the current control system is studied by experiment and dynamic simulation. The measurement shows that the indoor temperature rises to an uncomfortable range during heating and falls below comfortable range when heating is off. To solve this situation, an on-off control is implemented and simulated using a dynamic simulation program. Since there is a good agreement between experiment and dynamic simulation results, dynamic simulation is used to predict other results with different conditions of interest. The simulation shows that by implementing on-off control, the indoor space can be maintained within comfortable range, moreover using less energy. By reinforcing insulation to the walls that are exposed to the outdoor environment, heating energy can be saved further.     

供暖系统恒温阀控制特性分析

恒温阀由恒温控制器(核心元件为感温包)与流量调节阀组成。建立恒温阀控制室内温度的数学模型,对恒温阀的控制特性进行了分析。恒温阀的控制为比例控制,其控制精度由感温包特性、流量调节阀的机械特性、供暖系统计算参数及恒温阀控制环路的滞后性决定。     

散热器恒温控制阀实际应用效果检测分析

通过对两栋相同建筑物进行同期动态检测,分析了散热器恒温控制阀的实际应用效果。分析结果表明散热器恒温控制阀可以有效调控室内温度和节约供暖能耗;恒温控制阀初投资低和投资回收期短,在实际应用中可以产生良好的经济效益。     

三通恒温混水阀在地暖系统中的应用

介绍了三通恒温混水阀的基本原理与性能特点,探讨了其在地板辐射采暖系统中的实际应用,分析了带三通恒温混水阀型地暖系统的技术优势,以推广三通恒温混水阀的应用。     

Development of a radiant heating and cooling model for building energy simulation software

Efficient radiant heating and cooling systems are promising technologies in slashing energy bills and improving occupant thermal comfort in buildings with low-energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modeling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit-tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.     

A method for fully automatic operation of domestic heating

Complex, inconvenient and badly arranged push buttons and menus on domestic heating controls often cause users to enter unsuitable settings that result in impaired comfort and poor operating efficiency. This paper proposes a novel approach to the human interface of home heating systems that greatly simplifies the input required from the user. Time settings are derived automatically from electricity consumption and hot water use, also a temperature set point is provided that adapts to user activity levels and external temperature. Practical results from a prototype control system incorporating these methods are reported, showing useful energy savings. It is argued that this increased automation of control allows the benefits of low carbon technologies such as micro-combined heat and power, and solar hot water heating, to be fully exploited.     

Optimization of air-conditioning system operating strategies for hot and humid climates

This paper describes research into the optimal operation of building heating, ventilation, and air-conditioning (HVAC) systems focusing on both temperature and humidity control. While most previous work on HVAC optimization has been limited to evaluation of conventional temperature-based control systems, this study emphasizes the humidity control issue in meeting both sensible and latent building loads. The analysis is based on a combination of a realistic simulation of a direct expansion (DX) air-conditioning system and a direct-search numerical optimization technique. The simulation models have been validated through comparisons with field data. Optimization was performed on five different system control variables to minimize system power consumption while meeting building loads and maintaining comfort. Indoor temperature and humidity are also optimized within standard comfort constraints. Building loads were modeled using an extended bin method that allows consideration of the interactions between loads and indoor conditions. Results indicate that minimum energy use typically occurs at low airflow rates, with indoor humidity levels below the upper comfort limit. Results also show that coil air bypass and evaporator circuiting control are typically not necessary unless operation would otherwise result in overcooling. The optimization results also translate to relatively simple strategies for system control. Significant savings are demonstrated over conventional control strategies used in packaged DX equipment.     

Performance and control of domestic ground-source heat pumps in retrofit installations

Heat pumps are an essential technology for decarbonisation of domestic heating in the UK. This paper reports on the performance in use of a group of ground-source heat pumps, and in common with other UK studies finds that the seasonal performance is not as good as that reported in trials from continental Europe and that the system controls are unsatisfactory. Control improvements are investigated via a model of the dwelling and heat pump as a combined system, from which the thermal time constant of the building is identified as a critical factor that needs to be considered in retrofit projects incorporating heat pumps. The validity of the conventional practice (and advice from installers to users) of allowing heat pumps to run continuously is tested and bounded. Techniques for improving control are outlined and reasons for the poorer performance in the UK examined with the conclusion that heat pumps need to be better matched in capacity and control to the size and thermal characteristics of UK dwellings. Implementation of these findings by heat pump manufacturers and installers could promote a more rapid transition to renewable heat both in the UK and internationally wherever similar housing stocks and climates exist.     

A simplified physical model for estimating the average air temperature in multi-zone heating systems

A simplified model for estimating the average air temperature in multi-zone heating systems has been developed for use in an inferential boiler control scheme (Building Services Eng. Res. Technol. 24(4) (2003) 245), which can significantly improve the overall performance of heating systems. The model can maintain the long-term accuracy required by the control scheme as well as the simplicity in configuration and commissioning. This paper also presents the method for commissioning the model, the validation of the model using experimental data obtained from different resources, and the application of the model in the control of boilers in multi-zone heating systems.     

蓄热型空气式太阳能集热-空气源热泵复合供暖系统在寒冷地区的应用研究

设计了一种蓄热型空气式太阳能集热-空气源热泵复合供暖系统.该系统具有太阳能供热、太阳能辅助热泵供热和热泵供热3种运行模式,可根据环境工况及供暖负荷的变化自动切换运行模式,保证室内供暖的稳定性.在通辽市的实验研究结果表明:在整个供暖季内,该系统可持续提供42.6 ℃的热水,维持室内温度在21.3?24.1 ℃之间;平均C...