Passive cooling in a low-energy office building

In office buildings, the use of passive cooling techniques combined with a reduced cooling load may result in a good thermal summer comfort and therefore save cooling energy consumption. This is shown in the low-energy office building ‘SD Worx’ in Kortrijk (Belgium), in which natural night ventilation and an earth-to-air heat exchanger are applied. In winter, the supply air is successively heated by the earth-to-air heat exchanger and the regenerative heat exchanger, which recovers the heat from the exhaust air. In summer, the earth-to-air heat exchanger cools the ventilation air by day. In addition, natural night ventilation cools down the exposed structure which has accumulated the heat of the previous day. In this article the overall thermal comfort in the office building is evaluated by means of measuring and simulation results. Measurements of summer 2002 are discussed and compared to simulations with a coupled thermal and ventilation simulation model TRNSYS-COMIS. The simulations are used to estimate the relative importance of the different techniques. The evaluation shows that passive cooling has an important impact on the thermal summer comfort in the building. Furthermore, natural night ventilation appears to be much more effective than an earth-to-air heat exchanger to improve comfort.     

Innovative economic options for low-energy housing in northern climates

In a joint project, the authors have investigated several possible options to reduce the heating energy demand in residential dwellings in northern climates. The single measures investigated include improved thermal insulation of walls, doors, and windows, heat recovery systems and transparent insulation (TI). The investigations were carried out using the simulation programme TRNSYS by Klein et ea. (1990) with the TI extension for the building model treated in Sick and Kummer (1992). Climate data basis are hourly irradiation and temperature values from Jyväskylä, Finland (latitude: 62.16° North). The results show that (a) even during the winter months with very few hours of sunlight per day, the irradiation gains through the TI walls can compensate the heat transmission losses to a large extent. The average night U-value of the TI wall may be twice as high as an opaque wall U-value to lead to the same heating demand in November, December, and January; (b) the efficiency of a south-facing TI facade may exceed 60% in the winter months and still reach more than 15% in July and August; and (c) seasonal shading is sufficient to prevent overheating in the summer months. An analysis of the TI behaviour is given in the paper. The economics of the TI solution are compared to conventional measures for reducing the heating energy demand. Due to the simple seasonal shading control, it will be competitive when the building is optimized for TI use and the TI material production volumes increase to a realistic extent.     

Transient numerical and physical modelling of temperature profile evolution in stabilised rammed earth walls

Three established stabilised rammed earth (SRE) mix types (433, 613, 703) were identified for analysis, in the form of 300-mm thick test walls, by being subjected to different static air temperature and relative humidity differentials. The predictive numerical model outputs from WUFI Pro v4.1 hygrothermal simulations displayed good accuracy when validated against experimental data from physical modelling conducted using test walls in a climatic simulation chamber. The wall temperature profile evolution and resultant steady state gradients were very similar regardless of mix type indicating that the majority of the wall remained relatively dry. Unless liquid water is present, the thermal resistance and heat capacity of these materials does not change sufficiently to make significant differences to temperature profile evolution regardless of soil mix type. Little scope exists to intelligently modify the ability of SRE walls to absorb and store heat energy simply by manipulation of particle size distribution (PSD) and the resultant bulk density/void ratio relationships, under these conditions. Only the outer layers of the walls appear to interact with moisture in the air, and the predicted transient responses indicate that significant potential exists to intelligently modify the ability of SRE walls to absorb, store and release moisture vapour from the surrounding air simply by manipulation of PSD and the resultant bulk density/void ratio relationships.     

Energy performance of a hybrid space-cooling system in an office building using SSPCM thermal storage and night ventilation

Thermal performance of a hybrid space-cooling system with night ventilation and thermal storage using shape-stabilized phase change material (SSPCM) is investigated numerically. A south-facing room of an office building in Beijing is analyzed, which includes SSPCM plates as the inner linings of walls and the ceiling. Natural cool energy is charged to SSPCM plates by night ventilation with air change per hour (ACH) of 40 h⁻¹ and is discharged to room environment during daytime. Additional cool-supply is provided by an active system during office hours (8:00-18:00) necessary to keep the maximum indoor air temperature below 28 °C. Unsteady simulation is carried out using a verified enthalpy model, with a time period covering the whole summer season. The results indicate that the thermal-storage effect of SSPCM plates combined with night ventilation could improve the indoor thermal-comfort level and save 76% of daytime cooling energy consumption (compared with the case without SSPCM and night ventilation) in summer in Beijing. The electrical COPs of night ventilation (the reduced cooling energy divided by fan power) are 7.5 and 6.5 for cases with and without SSPCM, respectively.     

Warm season cooling requirements for passive buildings in Southeastern Europe (Romania)

The first Romanian passive office building has been constructed by the AMVIC Company in Bragadiru, 10 km south of Bucharest. The overheating rate and the cooling load are higher for a passive building than for a standard building. The internal heat sources and the maximum allowed indoor temperature do markedly affect the cooling load. A time-dependent model shows that cooling is necessary during April-September. The ground heat exchanger is an effective system for cooling-down the fresh air inlet temperature. Also, the Venetian blinds prove to be efficient in diminishing the building heat input. However, these two systems are not able to ensure a controlled thermal comfort during summer. This suggests that an active cooling system should be used when passive buildings are implemented in the Romanian climate. The standard configuration of the passive buildings ventilation system (which is usually designed for heating purposes), must be changed in case cooling becomes necessary during the warm season. The results are of interest for other countries in Southeastern Europe.     

Solar thermal modelling of a non-airconditioned building: Evaluation of overall heat flux

This paper presents an investigation of the thermal behaviour of a non-airconditioned building with walls/roof being exposed to periodic solar radiation and atmospheric air while the inside air temperature is controlled by an isothermal mass, window and door in the walls of the room. The effects of air ventilation and infiltration, the heat capacities of the isothermal storage mass inside air and walls/roof, heat loss into the ground, and the presence/absence of the window/door have been incorporated in the realistic time dependent periodic heat transfer analysis to evaluate the overall heat flux coming into the room and the inside air temperature. A numerical computer model using typical weather data for Delhi has been made to appreciate the analytical results quantitatively. It is found that the heat fluxes through different walls have different magnitudes and phase lags w.r.t. the corresponding solair temperatures. The overall heat flux coming into the room as well as the room air temperature are sensitive functions of the number of air changes per hour, closing/opening of the window and the door ventilation. The effects of the heat capacity of the isothermal mass and the basement ground are found to reduce the inside air temperature swing and the presence of a window is found to increase the inside air temperature even when the window area is much smaller than the wall/roof area. The model presented would be an aid to a building architect for good thermal design of non-airconditioned buildings.     

Numerical investigation of the performance and soil temperature recovery of an EATHE system under intermittent operations

One of the problems in operating earth air tunnel heat exchangers (EATHE) for cooling in summer, with soil having high specific heat and low moisture content is accumulation of heat around the pipe. The low rate of heat dissipation due to conduction restricts the performance of EATHE over subsequent years. In the present paper, numerical simulations have been performed to investigate the thermal performance and soil temperature during summer operation in Jaipur to estimate extent of soil degradation. The simulation result indicates that by the end of summer, the soil leads to thermal saturation which in turn, may render it unusable for next summer. This scenario demands for heat removal through force convection. Three strategies namely, night purging during summer operation, day operation during winter and night operation during winter were attempted to estimate extent of soil recovery. Simulation results show that the average COPs for summer, summer with night purging, winter day and winter night operation mode are 4.23, 3.68, 5.01, and 6.65 respectively. It was found that advantage of night purging is less than energy required to run blower for night purging. However, winter day/night operation offers space heating and better soil for next summer.     

A building unit decomposition model for energy leakage by infrared thermography image analysis

A quantitative energy leakage model was developed based on the thermography image data measured for both external and internal building surfaces. The infrared thermography images of both surfaces of doors, windows, and walls of an office building in the Hengqin Campus of University of Macao were taken at various times in a day for four seasons. The transient heat flux for sample units were obtained based on measurements of the seasonal transient local temperature differences and calculations of the effective thermal conductivity from the multiple-layer porous medium conduction model. Effects of construction unit types, orientations, and seasons were quantitatively investigated with unit transient orientation index factors. The corresponding electric energy consumption was calculated based on the air conditioning system coefficient of performance of heat pump and refrigerator cycles for different seasons. The model was validated by comparing to the electric meter records of energy consumption of the air conditioning system. The uncertainties of the predicted total building energy leakage are about 14.7%, 12.8%, 12.4%, and 15.8% for the four seasons, respectively. The differences between the predicted electric consumption and meter values are less than 13.4% and 5.4% for summer and winter, respectively. The typical daily thermal energy leakage value in winter is the highest among the four seasons. However, the daily electric energy consumption by the air conditioning system in summer and autumn is higher than that in winter. The present decomposition model for energy leakage is expected to provide a practical tool for quantitative analysis of energy leakage of buildings.     

夏热冬暖地区办公建筑围护结构改造节能经济性分析

对夏热冬暖地区某办公建筑进行能耗测试,利用能耗模拟软件TRNSYS对该建筑空调能耗进行模拟,分析空调冷负荷对于各围护结构的敏感性,对影响能耗显著的外墙、遮阳系数及建筑渗透率进行改造。利用NPV动态经济评价体系,在建筑运行时间内对26种改造方案进行节能经济性分析。结果表明,外墙中度强化、建筑渗透率高度强化及遮阳系数高度强化方案的经济收益值最大,改造成本回收年限较短,为经济性最优改造方案。     

Year round experimental study on a constant temperature and humidity air-conditioning system driven by ground source heat pump

Numerous studies about the ground source heat pump building heating and cooling systems have been constructed in office building, hotel, residential building and school et al. However, few researches about the constant temperature and humidity air-conditioning system driven by ground-coupled heat pumps were carried out. In this paper, a constant temperature and humidity air-conditioning system driven by ground source heat pump was designed and constructed in an archives building in Shanghai, China. During the operation in the cooling mode, the heat extraction from the condenser of the heat pump was divided: part was rejected to the soil while another was used to reheat the air in AHUs. According to the experimental results, the indoor temperature and relative humidity fulfilled the “Archives Design Code”. In summer, the heat rejected to the soil was reduced by 32%, which was helpful for the earth energy conservation. The soil temperature increased only 0.5 °C after the GSHP system operating for a year. The energy cost of the air-conditioning system was 56.1 kWh/m². Compared with air source heat pump system and water cooled unit with boiler system, the operating cost of ground source heat pump was reduced by 55.8% and 48.4%, respectively.     

基于熵权法的光热耦合综合能耗的百叶外遮阳控制策略

为探究百叶外遮阳控制策略对室内光环境、热环境及综合能耗3个方面的综合影响,采用熵权法建立光热耦合综合能耗的评价模型,利用EnergyPlus软件模拟青岛某办公建筑夏季不同百叶外遮阳角度下的光热环境及能耗,利用评价模型对光环境、热环境及综合能耗进行综合评分,最终确定最合适的百叶外遮阳角度.研究结果表明,该百叶外遮阳控制策...     

Comparative study of room temperature control in buildings with and without the use of PCM in walls

The concept of thermal energy storage in building gains a specific importance in the present energy scenario related to energy consumption and indoor thermal comfort. The material used to store the thermal energy which undergoes a phase change referred as PCM and it is considered as a possible solution for reducing energy consumption in the building by storing and releasing heat within a certain temperature range; it raises the building inertia and also stabilizes indoor air temperature fluctuations. The room temperature is controlled by imposing PCM inside the walls. An attempt has been made to compare room air temperature with and without the use of PCM inside the walls of constructed modular building unit. The PCM imposed modular building shows the reduced temperature fluctuations in room, the PCM absorbs and liberates excess heat which is gained from the outer side of the room and maintains constant inner room temperature. The PCM imposed walls of modular building unit have an ability to reduce 10–30% of heat load in comparison with the plain wall. The results showed that reduction in room temperature is about 2–4°C and it has been concluded that the PCM imposed modular building unit has more energy saving opportunities than normal modular building unit.     

Trombe wall management in summer conditions: An experimental study

The application of Trombe walls in temperate climates is problematic due to undesired heat gains and overheating phenomena in summer. A proper shading and ventilation of this system can reduce such drawbacks, but the impact of these strategies on the wall’s thermal parameters is yet not widely investigated in quantitative terms.This paper presents an experimental study on the thermal behavior of Trombe walls in summer under Mediterranean climate conditions. The aim of the study is to determine experimentally the thermal parameters of a Trombe wall in summer conditions through the changing of shading, ventilation and operational conditions.In order to do that a series of experimental campaigns were carried out on a case study. A detailed simultaneous monitoring of two Trombe walls made it possible to compare the thermal behavior by varying the screening, ventilation and internal gains conditions. Furthermore, monitoring of indoor thermal comfort conditions and energy simulation using a model in dynamic state were carried out. The results showed that shading, ventilation and occupancy conditions affect significantly the thermal parameters of Trombe wall in summer: screening with roller shutters determines a decrease in internal surface temperature of the wall of 1.4 °C and a decrease in daily heat gains of about 0.5 MJ/m²; the combined use of overhangs, roller shutters and cross ventilation for the Trombe wall can assure a satisfactory thermal comfort level in summer and a reduction of the cooling energy needs respectively of ?72.9% and ?63.0% for a dwelling with low or highly insulated building envelope in comparison with the case of an unvented Trombe wall without solar protections.     

Comportement thermique de differents types d'habitation soumis a un ensoleillement et à une température extérieure périodiques

This paper presents the response of different kinds of schematic dwellings under daily periodic variations of the solar flux and the external temperature. The influence of the parameters which are characteristic of coupled heat transfer is studied (thermal diffusion and heat storage in external and internal walls, heat loses or solar heat supply by windows or airing).Calculations show that for an idealised regulation: (i) The energetical consumption depends only on mean variations of external temperature and solar flux and does not depend on the insulation location. (ii) For a building with a regulated internal temperature, the thermal inertia for the internal walls does not play a role. (iii) For an unregulated building, the internal temperature variations depends of the insulation location. The best location is the external one. (iv) There is an optimal thickness of walls corresponding to the daily periodic variations.     

Performance of trombe walls and roof pond systems

This paper describes an analysis of the periodic heat transfer through thermal storage walls and roof pond systems subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other. A one-dimensional heat conduction equation for temperature distribution in the walls and roof has been solved using the appropriate boundary conditions at the surfaces; explicit expressions for the periodic heat flux through storage walls and the roof have been derived. Numerical calculations for the periodic heat flux into the room have been made in order to assess the relative thermal performance of storage walls and roof pond systems in both winter and summer. It is found that a thermal storage mass wall is preferable for longer heat storage times while a water wall is suitable for rapid heat dissipation into the living space. For New Delhi, a roof pond system comprised of water-concrete-insulation, in ascending order of thickness, in the summer and in descending order of thickness in the winter, is found to be most desirable, whereas a combination with an ascending order of thickness is more appropriate for a typical cold climate like that of Boulder, Colorado, USA.     

The passive solar heated school in wallasey. IV. An observational study of the thermal response of a passive school building

An observational study on the Wallasey School has demonstrated its ability to maintain in most conditions of climate an equitable indoor climate both in regard to daily mean temperatures and daily variations, through use of solar gain and heat from the lights, and the appropriate control of ventilation. During occupied periods, air temperatures are usually between 17°C in winter and 23°C in sunny summer periods. The room provides a mainly ‘cold wall’ environment. The observational data and a series of model estimates have been compared. The general level of temperature within the building is known to depend strongly on ventilation rate, but since ventilation rate was not measured, steady-state comparisons as such are not possible. The observed and estimated temperature profiles for air and various surfaces including that of the furnishings during a very sunny period are in broad agreement. Analyses of the transient response of the structure in winter conditions has demonstrated a long response time (several days) describing the response of the enclosure, and a shorter response time of about half a day which describes the rate of settlement of internal temperature differences which may be initially present. Evidence is presented indicating low values for the convective heat transfer coefficient. An autocorrelational technique demonstrates that the thermal ‘memory’ of the classroom is much longer in winter than in summer. The response of the room during occupied and unoccupied periods is broadly similar, but conditions are rather more variable during occupation.     

Numerical analysis of effect of shape-stabilized phase change material plates in a building combined with night ventilation

Effect of shape-stabilized phase change material (SSPCM) plates combined with night ventilation in summer is investigated numerically. A building in Beijing without active air-conditioning is considered for analysis, which includes SSPCM plates as inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with time period covering the summer season. Effects of the following factors on room air temperature are investigated: the thermophysical properties of the SSPCM, the thickness of SSPCM plate and air change per hour (ACH) at both nighttime and daytime. The results show that the SSPCM plates could decrease the daily maximum temperature by up to 2 °C due to the cool storage at night. The appropriate values for melting temperature, heat of fusion, thermal conductivity and thickness of SSPCM plates need to be considered and calculated according to the climate conditions and building structure. The ACH at night needs to be as high as possible but the ACH at daytime should be controlled.     

Modeling of a hydronic ceiling system and its environment as energetic auditing tool

As a part of a commissioning study, the chilled ceiling system of a large commercial building located in Belgium is evaluated. A representative office has been instrumented and data on the chilled ceiling system operating in real conditions have been collected. The simulation of the whole system is performed by means of a transient thermal model of the building and its HVAC system. The model considers the hydronic panels as a transient-state finned heat exchanger connected to a simplified lumped transient model of the building. The behavior of the hydronic ceiling system and the interactions with its environment (walls, ventilated facade, internal loads and ventilation system) has been experimentally and numerically evaluated. Commissioning test results show that the influence of surfaces temperatures inside the room, especially the facade, is considerable. Then, it is clear that the hydronic ceiling system must be evaluated together with its designed environment and not as a separate HVAC equipment.     

Passive cooling of buildings by using integrated earth to air heat exchanger and solar chimney

Passive cooling is being employed as a low-energy consuming technique to remove undesirable interior heat from a building in the hot seasons. There are numerous ways to promote this cooling technique, and in the present study the use of solar chimney (SC) together with earth to air heat exchanger (EAHE) is introduced. Consequently, theoretical analyses have been conducted in order to investigate the cooling and ventilation in a solar house through combined solar chimney and underground air channel. The finding shows that the solar chimney can be perfectly used to power the underground cooling system during the daytime, without any need to electricity. Moreover, this system with a proper design may also provide a thermally comfortable indoor environment for a large number of hours in the scorching summer days. Based on the required indoor thermal comfort conditions, the numbers of required SCs and EAHEs are calculated and some features of such a system is presented. It is widely expected that the proposed concept is useful enough to be incorporated with a stand-alone or a cluster of buildings especially in some favorable climates.