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.     

Heat requirements and energy use in British houses

Housing data likely ranges of insulation levels are combined to give estimates of the heating requirements for conventional houses and small flats to be built in Britain in 1977–1987. After allowance for non-solar heat gains, requirements of 65–120 kWh/day for 4–6 person houses and of 8–47 kWh/day for small flats are predicted. The 65 kWh/day lower limit for houses will be improved on in the case of very well insulated houses using modified construction techniques.Data are collated showing average incidental heat gains from appliances, water heating, and other sources. The effects of these on annual heating energy use and on mean power requirements are assessed, and annual heating energy use per kW of design heat loss is calculated for a range of levels of incidental gains at three British locations; Pembroke, Croydon and Edinburgh. The typical solar contribution to this heating energy is also calculated.Mean-to-peak power variations are considered, showing that on average a heating system operates at 20–30% of the house design heat loss; this is the level at which energy use efficiency is most significant.The theoretical predictions of heating energy use are shown to give reasonable agreement with actual use as measured in field trials, despite the wide variability of the latter. The variation of total solar heating with orientation of a house with windows on two opposite sides is studied in the Appendix, showing a variation of ±15% in winter and ±6% in spring and summer for a particular house design.     

加拿大卡尔加里市Okotoks小镇太阳能小区建设

简要介绍了北美目前最大的跨季太阳能储存项目——加拿大0kotoks小镇的太阳能小区建设，对其太阳能供热系统的工作原理及利用土壤床作为储能体进行大规模跨季节太阳能储存的方法进行了分析。该项目根据不同季节可利用太阳能数量的不同，分别设置了短期（临时）太阳能储箱（STTS）及跨季节太阳能储存箱（BTES），以提高太阳能的利用率。其中，BTES的效率可达50％以上。小区太阳能家用热水系统（DWH）可满足住户60％的热水需求，而太阳能采暖系统则可满足90％采暖要求；建成后每幢住宅每年可减排5t温室气体，整个小区可减排260t／年。     

低温地板辐射供暖的动态仿真

建立了低温地板辐射供暖系统传热过程的数学模型,通过数值模拟,用有限差分法计算了地板内的温度场。利用动态仿真程序预测了不同的供回水温度,埋管层厚度,盘管间距对地板传热过程,地板表面温度的影响,并在典型工况下,通过对理论值与实验值进行分析,验证了本模拟程序是正确的,该研究为地板辐射供暖系统的推广应用奠定了基础。     

地表装饰材料和保温层性能对辐射地板热量损失影响的数值研究

建立了辐射地板供暖的传热模型，利用SIMPLER计算程序模拟计算了地表装饰材料和埋管保温层性能对辐射地板换热和地表温度分布的影响，得出了地板内部的温度场分布规律。研究结果表明，地表装饰材料对地板换热有很大的影响，埋管保温层对减少地板下层热量损失有十分重要的作用。     

Energy-efficient terrace houses in Sweden: Simulations and measurements

Reducing energy use in buildings is essential to decrease the environmental impact. Outside Gothenburg in Sweden, 20 terrace houses were built according to the passive house standard and completed in 2001. The goal was to show that it is possible to build passive houses in a Scandinavian climate with very low energy use and to normal costs. The houses are the result of a project including research, design, construction, monitoring and evaluation. The passive house standard means that the space heating peak load should not exceed 10 W/m² living area in order to use supply air heating. This requires low transmission and ventilation losses and the building envelope is therefore highly insulated and very airtight. A mechanical ventilation system with approximately 80% heat recovery is used. The electric resistance heating in the supply air is 900 W per living unit. Solar collectors on the roof provide 40% of the energy needed for the domestic hot water. The monitored delivered energy demand is 68 kWh/m² a. Energy simulations show that main differences between predicted and monitored energy performance concern the household electricity and the space heating demand. Total delivered energy is approximately 40% compared with normal standard in Sweden.     

The use of a heavy internal wall with a ventilated air gap to store solar energy and improve summer comfort in timber frame houses

This paper considers supplementary heating and cooling within timber frame houses. The transmission of solar energy to an internal concrete cavity wall by air is analyzed. The objective of this work was initially to study the dynamic insulation in timber frame houses. The initial studies showed that it is more efficient to recover solar energy rather than heat losses, which is the principle of dynamic insulation. Clearly, the thermal regulations lead to lower heat losses through walls by conduction. Due to these factors we have decided to study a wall with an integrated solar air collector and a heavy ventilated internal wall. This internal wall, which is used to store solar energy will allow the reduction of heat demand in winter and will improve thermal comfort in summer because thermal mass increases and ventilation during the night will cool the internal wall. We have selected a closed loop air circulation system because, with an air to air heat exchanger, it can be proved to be more effective and the risk of unhealthy air pollution is reduced because the flow of fresh air will not pass through the ventilated air gap. We are constructing an integrated air collector prototype.     

Building leakage,infiltration, and energy performance analyses for Finnish detached houses

This study focuses on the relation between the airtightness of a building envelope, infiltration, and energy use of a typical modern Finnish detached house in the cold climate of Finland. The study is conducted with an empirically tested dynamic IDA-ICE simulation model of a detached house. The effect of several factors, such as Finnish climate and wind conditions, balance of ventilation system and leakage distribution, on infiltration was studied and a simple adapted model for the rough estimation of annual infiltration in Finnish detached houses was determined from the numerical simulation results. The energy impact of infiltration is also studied, taking into account the infiltration heat recovery effect. According to the results, infiltration causes about 15–30% of the energy use of space heating including ventilation in the typical Finnish detached house. The average infiltration rate and heat energy use increase almost linearly with the building leakage rate n₅₀. Finland can be roughly divided into two zones based on the average infiltration rate of detached houses, for which stack-induced infiltration is typically dominant, regardless of the climate zone. The infiltration heat recovery effect is minor in the studied detached house.     

A combined low temperature water heating system consisting of radiators and floor heating

Space heating load is decreasing in modern Finnish apartments due to lower U-values of the construction, tight envelopes and heat recovery from exhaust ventilation air. This makes it possible to develop a new combined low temperature water heating system with nominal supply/return water temperatures of 45 °C/35 °C. Such a system includes radiators in rooms and floor heating in bathrooms.In this study, the performance of an apartment building is determined by using dynamic simulation. The simulation results for the combined low temperature water heating system are compared with those for three conventional radiator and floor heating systems. The results show that the combined low temperature water heating system performs well and is able to maintain the zones within the required temperature levels. The thermal comfort analysis indicates that the drifts and ramps in operative temperature using the four studied heating systems are within the limits of Ashrae Standard 55-2004.Temperature measurements in a test room are carried out to find the vertical difference of air temperature using two methods: radiator heating and floor heating. These measurements indicate that there is only a small vertical temperature difference that would not produce any significant thermal discomfort.     

相变储能石膏板应用于地板供暖系统的节能效果及热舒适性分析

本文针对一种电加热相变地板供暖系统,通过模拟计算分析了其稳定性和热舒适性,并通过实验进行了验证.模拟计算结果表明相变地板供暖系统储热能力好,与普通地板供暖系统相比,室内空气温度变化平缓,人体舒适度更高.相变地板利用相变材料储存廉价低谷电热能,系统的节能性和经济性较好.     

Simulation of the heating performance of the Kang system in one Chinese detached house using biomass

A traditional Chinese heating system, the Chinese Kang, is used by 175 million people in detached houses in the rural regions of China, especially in Northeast China. This system utilizes biomass such as corn stalks, straw, corncob and energy plants as the heat sources. The objective of this paper is to establish a set of models to simulate the energy performance of the Kang heating system in one Chinese detached house. An experimental field study was carried out to collect practical parameters in a newly constructed Chinese detached house. The dynamic performance of the Kang heating system was simulated by using IDA-ICE 4.0 embedded with an empirical model built in the field study. The results show that the simulation can obtain good overall agreement with the field measurement results. It was confirmed that the Kang model created by IDA-ICE 4.0 is capable of simulating the performance of the Kang system and of calculating energy consumption in the detached house. Moreover, the result reveals that the thermal environment in the present Chinese detached house is still poor during the severe cold season if only the Kang system is used to heat the whole house.     

兼具地面装饰与供热的一种轻型干式构造地板采暖的研究

地面供热装饰为一体的轻型干式构造地板采暖系统，是将热水盘管直接置于保温层、地面装饰层与龙骨托架构成的封闭夹层空间内。通过对该地板采暖构造传热性能的分析、模拟计算及实验测试，论证了这种干式地板构造的优势和技术经济可行性。     

EnergyPlus vs. DOE-2.1e: The effect of ground-coupling on energy use of a code house with basement in a hot-humid climate

For low-rise buildings, the heat losses or gains through the ground coupled building envelope can be a significant load component. Studies have shown that current simulation tools give dissimilar results for the ground coupled heat transfer (GCHT) with basements. This paper quantifies and explains the differences between EnergyPlus and DOE-2.1e (DOE-2) basement GCHTs based on their results for an all electric code house in a hot and humid climate zone. The code house was modeled with two basement configurations i.e. a conditioned basement and an unconditioned crawlspace. DOE-2 was used with Winkelmann's basement model and EnergyPlus was used with its GCHT calculator utility, Basement. The results revealed that the ground isolated EnergyPlus houses used 3-23% more cooling, 12-29% less heating and 3-7% lower overall HVAC electricity use when compared to the ground isolated DOE-2 houses. Ground coupling added up to three times more heat loss in EnergyPlus than in DOE-2. This increased the overall energy use difference between these two programs from 3-7% (ground isolated) to 14-25% (ground coupled). These results showed that a truth standard is required for basement heat transfer calculations of low-rise buildings.     

太阳能热泵-低谷电与地板辐射采暖系统联合运营方式探讨

论述了太阳能热泵与低谷电作为地板辐射采暖热源的可行性和必要性,提出了一种利用太阳能和低谷电作为地板辐射热源采暖的方案,讨论了系统在冬季采暖期的运行方式.太阳能是一种无污染、无穷尽的自然能源,但具有不稳定和不可靠性,特别在冬季尤为明显.而低谷电作为太阳能的辅助能源,却可以有效弥补太阳能的不足.这两者结合具有节能、环保等优点.终端利用地板辐射采暖与太阳能热泵-低谷电系统提供热水温度特点一致,能够提高热泵制热性能系数,并且具有良好的舒适性和节能效果.因此,在我国北方地区,太阳能热泵与低谷电联合供暖在建筑领域值得推广和应用.     

Numerical simulation of radiant floor cooling system: The effects of thermal resistance of pipe and water velocity on the performance

Using the existing floor heating system, the radiant floor cooling system can be used as an alternative to the conventional all-air cooling systems. In this paper, a numerical model for the radiant floor cooling system is built using finite volume method. The objective of this study is to research the effects of the thermal resistance of pipe and water velocity on the performance of the radiant floor cooling system. In order to provide better heat transfer simulation in the pipe, composite grids are used in the model. The numerical floor surface temperature and the heat flux are in agreement with the measured results. The results illustrate that the pipe has effect on the performance of the radiant floor cooling system when the thermal conductivity of the pipe is low. However, the effect of the water velocity on the performance of the cooling system is not great. The model is helpful to calculate and design such kind of radiant floor cooling systems.     

气液分离式热管用于地板辐射供暖的特性分析木

通过热管工作特性的分析,提出了一种地板辐射供暖用的新型热管的设计方案。该新型热管的特点在于实现了蒸气流和凝液流两相分离,几乎不存在携带极限效应;蒸发段和冷凝段的面积可根据需要进行改变。该气液分离式热管应用于地板辐射供暖系统可以提高换热量从而降低供水温度,达到节能的目的,同时,为低品位能源直接应用于供暖系统的研究提供参考。     

低温热管辐射地板采暖性能的实验研究

为将低品位可再生能源直接应用于采暖系统,提出了一种以碳钢／水重力式热管为加热管的低温辐射地板采暖方式,分析了其传热特性并对热工性能进行了实验研究。在不同供水温度（35～45oC）、供水流量（0．12—0．37m。／h）以及地板表面初始温度（26～30℃）下,分别得到了地板表面及热管壁面的温度分布、地板散热量和传热滞后时间等参数。实验结果表明：热管辐射地板可以在较低的供水温度下达到较高的散热量,供水温度可比常规塑料埋管地板降低5℃左右;地板升温快、蓄热好,升温期时间约为降温期时间的1／3;地板表面温度梯度合理,有利于减小热损失。根据实验结果拟合了低温热管辐射地板的散热量计算公式。     

Energy consumption and thermal comfort in dwelling-cells: A zonal-model approach

In this study, we present a simplified model of the thermal behaviour of dwelling-cells, with a view to evaluating the performances of various heating systems that are commonly used in such environments. This model is based on a zonal-method representation of thermal exchanges in enclosed spaces.Following the validation of the model, we carried out a numerical study on two types of heat source, i.e. localized (a hot-water radiator and an electrical convector) and distributed (a hot-water heated floor and an electrical heated ceiling).The models were used to predict the heat losses specific to each system, as well as the indoor thermal ambience that the different systems induced. It was found that, for the configurations studied, the distributed heat sources presented a slight advantage over the localized sources, with regard to the criteria of energy consumption and thermal comfort.     

Indoor climate in low-energy houses—an interdisciplinary investigation

If energy demand in the building sector should be decreased, low-energy buildings, which are built with the aim of decreasing the use of energy, but still provide a good environment for the occupants, ought to be built on a larger scale. Investigations into how experimental houses function provides the opportunity of improving next-generation houses. This paper presents the results of an interdisciplinary investigation of the thermal environment and the space heating in 20 low-energy terraced houses. Qualitative interviews with the occupants as well as measurements of physical parameters have been conducted for this purpose. When the houses are inhabited and household appliances and candles are being used, the temperature can be managed within acceptable limits, even on cold days. However, those living in middle houses are generally more satisfied with their indoor temperature than the households of the gable houses. Results from both interviews and measurements show that there is a temperature difference between the floor levels, which is more pronounced in the gable houses. One outcome of the investigation is that information about the functionality of the heating system given to the households should be improved. Another outcome is that the accuracy of the temperature regulation system could be better.     

Residential air-to-air heat exchangers: Performance energy savings,and economics

Residential energy consumption can be decreased if air infiltration is reduced by constructing houses more tightly. In some cases, however, reduced air infiltration can lead to problems with indoor air quality (e.g., excess humidity and high levels of indoor-generated air contaminants). One solution to this problem is to install a residential air-to-air heat exchanger. The heat exchanger provides a controlled supply of ventilation which counteracts the adverse effects of reduced infiltration. In addition, the heat exchanger recovers much of the energy that would normally be lost when ventilation occurs by air infiltration. Thus, by employing heat exchangers in low-infiltration houses, it is possible to save energy without sacrificing indoor air quality.This paper discusses the performance of residential heat exchangers and summarizes results from tests of several models. It also compares the energy consumed, during the heating season, in low-infiltration houses with heat exchangers, with the energy consumed in typical houses in four cities throughout the United States. For each city, a cost-benefit analysis is performed from the point of view of a home-owner. Houses with natural gas, oil, and electrical heating systems are considered. Our analysis indicates that the energy required to heat ventilation air in homes employing heat exchangers is 5.3 – 18.0 GJ less than the energy required to heat ventilation air in typical homes. In homes with heat exchangers, the heat exchanger's fan system required 2.2 – 3.6 GJ of electrical energy during the heating season. The net present benefit for homes employing heat exchangers, when compared with typical homes, ranged from —$1350 to +$2400 and discounted payback periods ranged from five to over 30 years. The cost-effectiveness of employing heat exchangers was found to be highly affected by climate, type of heating fuel, heat exchanger performance, and ventilation rate.