Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 1, BIPV/T system and house energy concept

This paper is the first of two papers that describe the modeling, design, and performance assessment based on monitored data of a building-integrated photovoltaic-thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) in a prefabricated, two-storey detached, low energy solar house. This house, with a design goal of near net-zero annual energy consumption, was constructed in 2007 in Eastman, Québec, Canada - a cold climate area. Several novel solar technologies are integrated into the house and with passive solar design to reach this goal. An air-based open-loop BIPV/T system produces electricity and collects heat simultaneously. Building-integrated thermal mass is utilized both in passive and active forms. Distributed thermal mass in the direct gain area and relatively large south facing triple-glazed windows (about 9% of floor area) are employed to collect and store passive solar gains. An active thermal energy storage system (TES) stores part of the collected thermal energy from the BIPV/T system, thus reducing the energy consumption of the house ground source heat pump heating system. This paper focuses on the BIPV/T system and the integrated energy concept of the house. Monitored data indicate that the BIPV/T system has a typical efficiency of about 20% for thermal energy collection, and the annual space heating energy consumption of the house is about 5% of the national average. A thermal model of the BIPV/T system suitable for preliminary design and control of the airflow is developed and verified with monitored data.     

The effect of solar radiation on dynamic thermal performance of floor heating systems

This paper presents a numerical investigation of transient heat transfer in floor heating systems using a three-dimensional explicit finite difference model. The study focused on the influence of the cover layer and incident solar radiation on floor temperature distribution and on energy consumption. Complete and partial (area) carpets were considered as well as hardwood cover layers over concrete or gypcrete thermal storage. Experimental and simulation results for an outdoor testroom reveal that solar beam radiation can cause a local floor surface temperature in the illuminated area 8°C higher than that in the shaded area. Partial carpet cover further increases floor surface temperature differences up to 15°C when solar radiation is absorbed. Solar radiation stored in the floor thermal mass was found to reduce heating energy consumption significantly (30% or more). Increase of thermal mass thickness from 5 cm to 10 cm did not lead to higher energy savings with conventional proportional-integral control. Advanced control algorithms need to be developed to maximize energy savings while maintaining good thermal comfort.     

温控下被动式太阳房辅助热源量的动态分析

减少对辅助热源的依赖是太阳能建筑设计的一个重要目标,利用建筑自身的集热蓄热能力,可以减少辅助热源量.研究了根据一维热网络模型、温控下辅助热源量的计算公式及热平衡方程,计算不同辅助热源的控制常数以及设定温度下室内温度和辅助热源量的变化;分析了不同的热源控制常数取值和设定温度对室内温度和辅助热源量的影响;讨论了设定温度对墙体蓄热利用的影响.     

Passive solar radiant system,SIRASOL. Physical–mathematical modeling and sensitivity analysis

When using passive solar heating systems, it is necessary to have available an Equator-facing facade on which to install them. Rooms without such a facade are not the best option for conventional passive solar heating systems. SIRASOL is a passive solar radiant system that captures solar energy and is to be installed in the ceiling of the room. This room must not necessarily have an Equator-facing facade. Solar energy heats up a metal sheet, which is the radiant panel, which transfers heat by long-wave radiation to the room below it. This paper presents a mathematical model and a sensitivity analysis. The mathematical model was used to analyze radiant panel temperature, radiant mean temperature, operative temperature and panel surface area. Results of the sensitivity study showed that when solar radiation rises (from 200 to 800 W) panel temperature increases from 36 °C to 92 °C, whereas variations in outside and inside air temperature have a negligible impact on the panel temperature. Thus, the use of SIRASOL is possible in locations with clear skies. Moreover, from panel temperature values we calculated mean radiant temperature and thereby the room’s operative temperature, which is proportional to the radiant panel area. When this area is 50% of the room’s floor area, operative temperature grows 3.1 °C higher than inside air temperature when solar radiation is 500 W/m². The analysis shows that a thermal asymmetry appears only when SIRASOL’s surface area to floor area ratio is higher than 32%.     

Numerical model of a building with transparent insulation

An explicit finite difference simulation model is developed to study the thermal performance of an outdoor test-room with one transparently insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device and for air flow through the TI wall to the room. Simulation results indicate significant energy savings with practically no auxiliary heating required on cold sunny days in Montreal. However, appropriate control strategies are required to prevent overheating of the room and discomfort. Air flow through the TI wall and then into the room succeeds in lowering its room surface temperature to less than 31°C and reducing to zero the auxiliary heating required on any clear day. Blind control is based on several criteria, including outside temperature, room-facing surface temperature of TI wall (not to exceed 29°C) and room air temperature not to exceed a certain maximum.     

Optimal heating control in a passive solar commercial building

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building response, it has to anticipate internal and external disturbances. In the case of a passive solar commercial building, the need for anticipation is reinforced by important solar and internal gains. Indeed, large solar gains increase the energy savings potential but also the overheating risk. Optimal control theory presents an ideal formalism to solve this problem: its principle is to anticipate the building behaviour using a model and a forecasting of the disturbances in order to compute the control sequence that minimises a given cost function over the optimisation horizon. This cost function can combine comfort level and energy consumption. This paper presents the application of optimal control to auxiliary heating of a passive solar commercial building. Simulation-based and experimental results show that it can lead to significant energy savings while maintaining or improving the comfort level in this type of building.     

Performances of the Barra–Costantini passive heating system under Algerian climate conditions

The present work studies the Barra–Costantini passive solar heating system, with particular emphasis on the aspect of economics. The system which is studied is developed by Barra and Constantini. This system seems to be well adapted to the climatic and economic conditions in Algeria. In the first part of this work, an ideal model representing the thermal behavior of a room provided with the heating device is elaborated. The results of this model are compared with the results of an experimental study carried out on an Italian site. Initially, the model was used to determine the temperature variation for the different elements of a room with the Barra–Costantini (B-C) system. The model is then used for conditions corresponding to several Algerian sites. This study makes it possible to quantify the energy savings obtained by the addition of the B-C system to a traditional gas heating system. The introduction of a ratio between the cost of energy and the cost of equipment makes it possible to conclude that only the intervention of the authorities can make the passive solar system economically viable.     

Review of passive systems and passive strategies for natural heating and cooling of buildings in Libya

By proper passive design concepts which essentially consist of collection, storage, distribution, and control of thermal energy flow, an energy saving of 2.35% of the world energy output is possible. The basic methods of heating and cooling of buildings are solar radiation, outgoing longwave radiation, water evaporation, and nocturnal radiation cooling. A Trombe-Michel wall consists of a large concrete mass, exposed to sunlight through large, south-facing windows; it is used for heating buildings. Solar absorption cooling and solar dehumidification and evaporative cooling are two approaches that utilize solar energy for the generation of the working fluid and the cooling of dwellings. Outgoing longwave radiation is the most practical way of cooling buildings in desert climates and is effective on roof surfaces, emitting the radiations from the surface of earth to the atmosphere and to outer space. Water evaporation in desert coolers is the usual method of cooling in arid regions. Nocturnal radiation both heats in winter and cools in summer, in suitable climates, and does so with no nonrenewable energy other than a negligible amount required to move the insulation twice a day. The study of 24 different locations in Libya divides the country into regions with distinct passive strategies. The northern region and the Mediterranean coast need passive heating. The buildings in this region should restrict conductive heat flow, prevent infiltration and promote solar heat gains. The southern region, a part of the Sahara desert, needs passive cooling. The buildings in this region need high thermal mass and should promote natural ventilation, restrict solar heat gains and encourage evaporative and radiant cooling. The difficulties encountered in passive solar design are the large exposed area required with suitable orientation for the collection of energy and the large space requirement for the storage of thermal energy. This paper reviews these passive systems and discusses suitable strategies to be adopted for Libya.     

Numerical and experimental analysis of convection heat transfer in passive solar heating room with greenhouse and heat storage

In this paper, heat transfer and air flow in passive solar heating room with greenhouse and heat storage are studied. Thermal insulation of solar heating room has significant effects on temperature distribution and airflow in the heating chamber of this solar system. Heat transfer and air flow in a rock bed, which is used as solar absorber and storage layer, are also studied. If porosity is kept within certain range, increasing the rock size causes an increase of the capability of thermal storage and heating effects; increasing the porosity of thermal storage materials results in an increase of the bed temperature but a decrease of the rock mass. The specific heat capacity and thermal conductivity have a remarkable effect on the average temperature of rock bed. All these factors should be taken into account when designing a solar heating system.     

On eliminating peak load auxiliary energy consumption in passive solar residences during winter

This paper uses simulation analysis with Albuquerque, NM and Madison, WI weather data to address the following four questions:

1. Assuming a properly designed and controlled passive house, how does total electrical auxiliary energy consumption depend on the choice of peak load blackout periods?

2. What comfort penalties arise from properly coping with a variety of peak load blackout periods?

3. Where should off-peak energy be introduced into the thermal masses of the house?

4. What are the effects of imprecise information on short term future weather?

Using a combination of linear programming and gradient techniques, the following conclusions are obtained:During the worst days of the heating season, passive solar houses built above ground use a substantial amount of peak backup energy even if they are well designed. Even relatively crude off-peak controls provide reasonable comfort provided the energy is introduced in thermal masses well coupled to the room [e.g. 0.05 m (2 inches) beneath the inside face of the Trombe wall or 0.05 m (2 inches) below the top of the slab floor]. Introducing off-peak energy in thermal masses poorly coupled to the room (e.g. deep in the floor slab) makes proper control very difficult without very accurate weather prediction.Reducing backup use to zero from 7 am to 10 pm requires a doubling of daily backup use in Albuquerque and Madison. Excluding backup for shorter periods (e.g. 5 pm to 9 pm) requires an increase of about 25% in daily backup consumption.Even if off-peak energy is stored at points reasonably well coupled to the room, significant backup and comfort penalties are incurred with erroneous weather forecasts. Even in two adjacent days in Madison, reversing the weather patterns while maintaining the same off peak control strategies resulted in either wasting half the backup energy or severely under heating the house. The effects of faulty weather forecasts are more severe when poorly coupled storage sites are used.     

Discrete fourier series models for building auxiliary energy loads based on network formulation techniques

This paper presents a discrete Fourier series methodology for determining auxiliary energy loads in buildings. By applying network theory, flexible and efficient computer formulation techniques for the nodal frequency domain equations are developed. Two types of auxiliary sources are modelled; in the first one the room air temperature profile is specified, while in the second one an auxiliary heating/cooling source is modelled as a proportional control heat source. Unlike analytical frequency domain approaches such as those based on the Fourier transform, the discrete frequency domain methodology employed allows complex heat transfer mechanisms such as longwave radiant exchanges between room surfaces to be directly included in the formulation, and time-varying conductances such as that for a window with night insulation are also modelled. Thus, the methodology is particularly suitable for passive solar analysis.     

Solar-energy harnessing performances of direct-gain and non-vented Trombe walls under yemeni weather conditions

The presented design method shows how the monthly average auxiliary energy demand (which is required in a building incorporating direct-gain and non-vented Trombe walls as passive heating aids) in a hot climate, depends upon the building's characteristic parameters and average monthly meteorological data. For this purpose, a direct-gain ambient-energy recuperation factor has been defined and correlated with the difference between the ‘indoor’ thermostat setting and the ambient environment's air temperature, divided by the total amount of solar radiation transmitted per day into the living space through the glazing. An expression for this factor is obtained by solving a one-dimensional energy-balance equation which involves (i) the total amount of solar and ‘internal’ energy gains, (ii) the average thermal conductance of the house's envelope, and (iii) the storage properties of the constructional materials employed in this envelope. The method facilitates the estimation of the following: the solar contribution to the building's heating requirements; the amount of solar energy captured per day that exceeds the house's daily heating load, and which must therefore be vented to prevent overheating; as well as the variation with time of the temperature within the building. Finally the effects of altering (i) the thermostat set-temperature, (ii) the properties of the thermal-store, and (iii) the collector-to-store areas ratio upon the direct-gain ambient-energy recuperation factor (and consequently on the amount of auxiliary energy needed for heating or cooling) have been investigated.     

间接连接区域热水供暖系统特性及控制策略仿真

应用质量和能量守恒定律,创建间接连接热水区域供暖系统动态模型。通过仿真,分析系统补水率、散热器及换热器面积、室外温度、太阳辐射、室内得热、散热器循环流量和供水温度对系统和用户运行的影响。根据燃料控制器及温度控制器不同配置,仿真及分析了6种控制策略运行和能耗情况。控制仿真显示,基于用户侧的控制策略可实现系统节能及用户热舒适性双赢目标。     

Response of conventional and energy-saving buildings to design and human dependent factors

During the year 2000, energy-efficient buildings for low-income students at La Pampa University were designed and constructed. Buildings are located at the centre of La Pampa province, in a temperate semi-arid region of central Argentina Socio-economic, educational and environmental reasons have driven the design. Energy conservation devices, passive solar heating, natural ventilation and solar protection were the main strategies. The resulting design comprises two blocks of apartments with a useful floor area of 700 m² and main spaces. Two bedrooms, a dining room and essential services make up each apartment. Solar windows are provided for all main spaces. Northern shading devices and metallic pergolas protect all windows in summer. Once the building was finished, a monitoring plan started on December 2000. This paper shows the results of the thermal and energy behavior of apartments. The evolution of internal temperature was different in each apartment. The consumption of natural gas varied among dwellers, but the volume consumed was lower than that of conventional dwellings. Without extra building cost dwellers live under good higrothermal conditions at 50% of the auxiliary energy consumed by conventional dwellings.     

Overheating caused by passive solar elements in Tunis. Effectiveness of some ways to prevent it

Although Tunisian winters are mild compared with northern regions, there are heating requirements; their limited level suggests that passive solar energy would probably be able to meet them. However, the summer is hot enough, and one may wonder whether a solar design oriented toward the cold season would not induce severe overheating. Numerous studies have dealt with the heating performance of passive solar elements, but very little has been done to analyze their behavior in hot climatic conditions. The National School for Engineers of Tunis has built a passive solar pavilion which has been carefully instrumented. Special care has been devoted to the summer behavior of the pavilion. In this paper we describe some of the actions taken to prevent overheating, and we investigate their efficacy both by analysis of recorded measurements and by simulation. It is found that night ventilation is the most responsible action in decreasing room temperature, and that Trombe wall screening is more efficient than operating the walls as a solar chimney; overhangs are of valuable aid, and shuttering of the direct gain element also helps against overheating. The high thermal capacity results in a very stable room temperature, and plays an essential role for cooling when coupled with night ventilation. Finally, it is found that if appropriate action is taken in the hot season, a house equipped with passive solar heating elements can reach a very acceptable level of comfort in summer time.     

Definition, test and simulation of a thermochemical storage process adapted to solar thermal systems

The increase in the use of solar energy closely depends on the development of efficient storage processes. Solid–gas sorption processes are a promising option as they offer a high storage capacity and their specific working mode. In this paper, the integration of a sorption process based on the use of bromide strontium as the reactant and water as the refrigerant fluid is investigated. Combined with flat plate solar collectors and direct floor heating and cooling, the system makes it possible to provide a heating and a cooling storage function. Experimental tests have been conducted in the temperature ranges used in the solar heating and cooling systems. A simple model is proposed which allows an estimation of the performances in line with the heat and mass transfer characteristics of the reactive solid.     

The use of floor panel energy storage in a heat pump heated dwelling

A method of improving the performance of heat pumps for domestic space heating has been investigated. The study focuses on the short-term storage of heat pump output energy in concrete floor panels. This paper describes the dynamic computer simulation of an air to water heat pump, a floor panel energy store and energy flowpaths in a dwelling. The heating plant, controls and building thermal behaviour, were simulated as a complete energy system to enable the study of interactions between the subsystems. The model heating system comprised a number of under floor water heated panels installed in ground floor rooms of a two storey dwelling. Supplementary energy was supplied by direct electric heaters situated in most rooms. Heat pump operating periods were controlled as a function of the external air temperature within two prescribed occupancy intervals per day. Results of the investigation indicate that a heat pump system using floor panel storage and emission may be efficiently managed to provide nearly continuous heating with little supplementary energy input. The short-term storage of energy in thick floor panels allowed the heat pump to be operated for extended periods without cycling. Because of this, the seasonal loss in heat pump performance resulting from intermittent operation was less than 1 per cent. Attempting to supply the total space heating load with the heat pump and floor panel system resulted in severe overheating during periods of high solar or casual gain. Under these conditions the simple control strategy based on the measurement of external air temperature was ineffective. This problem was eliminated by reducing the heat pump energy input to the dwelling and supplying about 10 per cent of the seasonal energy demand by direct electric heaters. The influence of floor panel energy storage capacity on the performance of the heating system was investigated. Concrete panel depths of between 25 and 150 mm were considered. The seasonal system efficiency was found to increase with floor panel thickness, although not significantly with panel depths beyond 100 mm. The extensive use of floor slabs to store energy caused mean floor temperatures to be higher than when using direct electric air heaters only. However, with the depth of under floor insulation considered in the study (75 mm), heating the floor slab increased the seasonal energy loss of the building by only 4 per cent.     

A method for the direct generation of comprehensive numerical solar building transfer functions

This paper describes a method for the direct generation of comprehensive numerical room transfer functions with any derived parameters as output, such as operative temperature or thermal load. Complex conductive, convective and radiant heat transfer processes, or any derived thermal parameters in buildings can be explicitly and precisely described by a generalized thermal network. This allows the s-transfer and z-transfer functions to be directly generated, using semi-symbolic analysis techniques, Cayley’s expansion of determinant and Heaviside’s expansion theorem. A simple algorithm is developed for finding the roots of the denominator in the inverse transform of the s-transfer functions, which ensures that no single root is missing. The techniques have been applied to generating the transfer functions of a passive solar room with floor heating. The example calculation demonstrates the high efficiency of the computational method.     

Thermal performance of phase change material energy storage floor for active solar water-heating system

The conventional active solar water-heating floor system contains a big water tank to store energy in the day time for heating at night, which takes much building space and is very heavy. In order to reduce the water tank volume or even cancel the tank, a novel structure of an integrated water pipe floor heating system using shape-stabilized phase change materials (SSPCM) for thermal energy storage was developed and experimentally studied in this paper. The thermal performances of the floors with and without the SSPCM were compared under the intermittent heating condition. The results show that the Energy Storage Ratio (ESR) of the SSPCM floor is much higher than that of the non-SSPCM floor; the SSPCM floor heating system can provide stable heat flux and prevent a large attenuation of the floor surface temperature. Also, the SSPCM floor heating system dampens the indoor temperature swing by about 50% and increases the minimum indoor air temperature by 2°C–3°C under experimental conditions. The SSPCM floor heating system has a potential of making use of the daytime solar energy for heating at night efficiently.     

Performance simulation of a solar- and pellet-based thermal system with low temperature heating solutions

The low energy consumption of new housing, together with low temperature space heating solutions, provides a great deal of potential for an improvement to the thermal and environmental performance of heat-generating technologies and heat loss reduction in heating systems. The objective of this work is to evaluate the performance of a pellet and solar combisystem at different temperature ranges in a space heating (SH) system. The dynamic system simulation was performed in TRNSYS. Four SH temperature ranges will be assessed through different cases. For every SH temperature range, two cases were simulated—with and without an electric auxiliary heater. A system without solar collectors was used for the reference cases. The study will show that in the different cases, the reduction of the SH temperature allows for the reduction of temperature setpoints for the pellet boiler. A higher thermal performance of heat-generating technologies, lower heat losses and lower CO emissions can then be reached as a result. A further reduction of SH temperature will lead to slightly higher solar gains and a lower amount of total CO emissions. At the same time, higher heat losses from some components and lower or similar fractional thermal energy savings were observed.