Performance assessment of low-energy buildings in central Argentina

This paper summarizes the results obtained from the energy and thermal performance assessment of residential and non-residential low-energy buildings that were designed to minimize fossil energy use. They are located in the province of La Pampa, central Argentina, in a temperate continental climate that shows extreme hot and cold records during the summer and winter seasons, respectively. The common applied technologies for saving energy were passive solar heating, natural ventilation for cooling and daylighting. The glazing area in the principal functional spaces facing to the North oscillates between 11 and 17% of the building useful areas. All the studied buildings are massive, with the exception of an auditorium that was designed with a lightweight insulated technology. The mean thermal transmittance of the envelope is 0.45 W/(m² K). Double glazing and hermetic carpentry were used to reduce thermal losses (U-value = 2.8 W/(m² K)). The volumetric heat loss coefficient (G-value) oscillates between 0.90 and 1.00 W/(m³ K). During the design and thermal simulation convective-radiative heat transfer coefficients were estimated through a dimensional equation (h = 5.7 + 3.8 ws, wind speed). On internal surfaces, convective-radiative heat transfer coefficients of 8 and 6 W/(m² °C) (for surfaces with and without solar gain, respectively) were applied. The monitoring process provided information on the energy and thermal behaviour under use and non-use conditions. The measured value of energy consumption was similar to the expected value that was used during the pre-design stage. Building technologies work well during the winter season, allowing 50–80% of energy savings. However, overheating is still an unresolved problem during the summer. Interviews with occupants revealed that they need both, information about functional details, and good-practice guidance to manage thermal issues of the building. In most cases, the annual consumption of energy was lower than those established by the Low Energy Housing German Standards and the Minirgie Switzerland Certificate. Despite their relative cost increase during the last years, the use of insulation technology and the application of passive solar devices involved an extra cost of only 3% in our works. Provided the expected depletion of natural gas production in the coming decade, the importance of applying energy-efficiency guidelines will increase very soon in Argentina in order to match the requirements of a new national energy matrix.     

Estimating the effect of using cool coatings on energy loads and thermal comfort in residential buildings in various climatic conditions

The impact from using cool roof coatings on the cooling and heating loads and the indoor thermal comfort conditions of residential buildings for various climatic conditions is estimated. The energy cooling loads and peak cooling demands are estimated for different values of roof solar reflectance and roof U-value. The results show that increasing the roof solar reflectance reduces cooling loads by 18–93% and peak cooling demand in air-conditioned buildings by 11–27%. The indoor thermal comfort conditions were improved by decreasing the hours of discomfort by 9–100% and the maximum temperatures in non air-conditioned residential buildings by 1.2–3.3 °C. These reductions were found to be more important for poorly or non-insulated buildings. For the locations studied, the heating penalty (0.2–17 kWh/m² year) was less important than the cooling load reduction (9–48 kWh/m² year). The application of cool roof coatings is an effective, minimal cost and easy to use technique that contributes to the energy efficiency and the thermal comfort of buildings.     

Natural ventilation with traditional Korean opening in contemporary house

In this study, a natural ventilation opening was designed based on the traditional Korean opening to improve indoor environment on the contemporary house. The prototype of the opening was composed of three hanji papers and two air layers to improve airflow rate, and also to recovery heat lose. The performance of the heat recovery and airflows of the prototype was measured in laboratory, and the CFD simulation was used to verify its performance in the contemporary house. The airflow rate of the prototype is exponentially increased according to the pressure differences, and it ranges from 12.6 to 39.6 m³/m² h in 3–10 Pa, pressure difference. The total amount of heat recovery ranges from 47.8 to 67.7 W/m² in the prototype, and the heat recovery rate is about 25% at 10 Pa. In the CFD simulation, the prototypes were installed at 25% of the total window areas of the model house. The outside air was totally supplied through the prototypes at 67.2 m³/h in the model house, and it is equivalent to 0.2 h⁻¹ ventilation rate. The results show that the prototype is capable of providing natural ventilation even at low wind pressure, and also that it prevent cold draft in heating period. Further analysis of the ventilation performance including the thermal force is needed to apply the prototype to the contemporary house.     

Feasibility of solar absorption air conditioning in Tunisia

Due to the high cost of fossil fuels and the environmental problems caused by the extensive use of air-conditioning systems for both residential and industrial buildings, the use of solar energy to drive cooling cycles becomes attractive since the cooling load is roughly in phase with solar energy availability particularly in Tunisia. In this paper, we present a research project aiming at assessing the feasibility of solar-powered absorption cooling technology under Tunisian conditions. Simulations using the TRNSYS and EES programs with a meteorological year data file containing the weather parameters of Tunis, the capital of Tunisia, were carried out in order to select and size the different components of the solar system to be installed. The optimized system for a typical building of 150 m² is composed of a water lithium bromide absorption chiller of a capacity of 11 kW, a 30 m² flat plate solar collector area tilted 35° from the horizontal and a 0.8 m³ hot water storage tank.     

Solar integrated energy system for a green building

Shanghai is characteristic of subtropical monsoonal climate with the mean annual temperature of 17.6 °C, and receives annual total radiation above 4470 MJ/m² with approximately 2000 h of sunshine. A solar energy system capable of heating, cooling, natural ventilation and hot water supply has been built in Shanghai Research Institute of Building Science. The system mainly contains 150 m² solar collector arrays, two adsorption chillers, floor radiation heating pipes, finned tube heat exchangers and a hot water storage tank of 2.5 m³ in volume. It is used for heating in winter, cooling in summer, natural ventilation in spring and autumn, hot water supply in all the year for 460 m² building area. The whole system is controlled by an industrial control computer and operates automatically. Under typical weather condition of Shanghai, it is found that the average heating capacity is up to 25.04 kW in winter, the average refrigerating output reaches 15.31 kW in summer and the solar-enhanced natural ventilation air flow rate doubles in transitional seasons. The experimental investigation validated the practical effective operation of the adsorption cooling-based air-conditioning system. After 1-year operation, it is confirmed that the solar system contributes 70% total energy of the involved space for the weather conditions of Shanghai.     

A new type of double-skin façade configuration for the hot and humid climate

The performance of the double-skin façade depends closely on the chosen ventilation means within its intermediate space. The modes of ventilation could be natural (buoyancy driven), forced (mechanically driven) or mixed (both natural and forced). Oesterle et al. has attempted to classify the double-skin constructions into four different types, namely box window façade, shaft-box façade, corridor façade and multi-story façade. A number of interesting investigations and findings are reported in the literature pertaining to passive ventilation in buildings and the thermal performance of double-skin facades. The researches have revealed close link between natural ventilation design and the function of double-skin façade. Most of them are using the idea of stack effect or the solar chimney concept and found that passive ventilation in summer is possible even for multi-storey buildings. It was found that significant energy saving is possible if natural ventilation could be exploited through the use of double-skin façade. In this research, CFD was used to analyse various thermal comfort parameters with different double façade configurations to determine a new type of double-skin façade configurations which will provide a better indoor thermal comfort in the hot and humid climate through natural ventilation strategies for the high-rise buildings.     

Real climate experimental study of two double window systems with preheating of ventilation air

This paper aims to characterize the thermal performance of a window system that consists in doubling an existing window, converting it into a ventilated double window. The air coming from the outside circulates upwards through the channel between windows and enters the building through a vent on the top of the window's case. A series of experimental measurements was conducted in a test cell exposed to real outdoor weather conditions located in a mountain region at Centre of Portugal, during heating season in order to determine how this window system can act as a heat exchanger. It was found that such window system act as an efficient heat exchanger using transmission heat losses and solar radiation to preheat ventilation air, thus reducing the building's operational energy costs. An average of about 19 m³/h of air flow rate was found with an air temperature increment within the air gap of about 6 °C, during night-time, for an indoor/outdoor temperature difference of about 16 °C. Air temperature increment reached up to 12 °C using a plastic shutter. With solar radiation, the average of that increment was about 10 °C. This is a simple and cheap building technology which can be implemented both in new and existing buildings.     

Natural ventilation in a double-skin facade

Double-skin facades are assuming an ever-greater importance in modern building practice. There is an increasing demand for higher quality office buildings. Occupants and developers of office buildings ask for a healthy and stimulating working environment.Double-skin facades are appropriate when buildings are subject to great external noise and wind loads. A further area of application is in rehabilitation work, when existing facades cannot be renewed, or where this is not desirable. Double-skin facades have a special aesthetic of their own, and this can be exploited architecturally to great advantage.However, there are still relatively few buildings in which double-skin facades have actually been realized, and there is still too little experience of their behavior in operation.In this matter, we choose to study the natural ventilation in multi-storey double-skin facades. Simulations where realized with TAS software on a building proposed in the frame of the subtask A of the Task 27 (performance of solar facade components) of the International Energy Agency, Solar Heating and Cooling Program.We decide to study a sunny summer day; and we analyze the double-skin facade behavior for various conditions: impact of the double-skin orientation and impact of the wind orientation and the degree of wind protection.     

Optimal operation of a south double-skin facade

There is an increasing demand for higher quality office buildings. Occupants and developers of office buildings ask for a healthy and stimulating working environment. Double-skin facades are appropriate when buildings are subject to great external noise and wind loads. A further area of application is in rehabilitation work, when existing facades cannot be renewed, or where this is not desirable. Double-skin facades have a special esthetic of their own, and this can be exploited architecturally to great advantage. However there are still relatively few buildings in which double-skin facades have actually been realized, and there is still too little experience of their behaviour in operation. In this matter, we choose to study a multistory double-skin facades behaviour. Simulations were realized with TAS software on the building proposed in the frame of the subtask A of the Task 27 (performance of solar facade components) of the International Energy Agency. Simulations were performed on the chosen building with and without double-skin facades. We decide to study eight types of days; and we analyze the double-skin facade behaviour for various operations. The thermal behaviours of the building with and without double-skin are compared. The study of these eight cases showed the importance of the dynamic use of the double-skin. The operation of this one must be obligatorily related to the climatic conditions as well external as interior and a bad operation of the double-skin could lead to catastrophic results.     

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m² a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m²a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.     

Application range of thermally activated building systems tabs

This paper presents application range and functionality of thermally activated building systems (tabs). Tabs are increasingly used for energy efficient and economical cooling and heating of commercial buildings. Thereby, the building structure is used as thermal storage allowing the use of renewable energy sources. Based on a simulation study for a typical office building the aspects of thermal comfort, maximum permissible heat gains in the room and the re-cooling of the building mass are analysed. It is shown that depending on the maximum permissible daily room temperature amplitude with tabs typical heat gain profiles with peak loads up to around 50 W/m² floor area can be managed. However, the transitional (mid-season) periods with already high solar gains and still restricted comfort range, in most cases will be decisive for the dimensioning of tabs, thus limiting maximum loads to lower values. The results also show that processes on the room side are almost unaffected from the processes on the supply side. In the cooling case, this allows for the re-cooling period of the fabric being extended to 24 h a day with accordingly “high” supply temperatures and peak load reductions of up to 50%. The results given may serve as orientation guide whether a tabs may be applicable in a specific building, and provides relevant parameters for the dimensioning of tabs.     

Passive cooling for air-conditioning energy savings with new radiative low-cost coatings

Passive cooling is considered as an alternative technology to avoid unwanted heat gains, to reduce urban heat islands and to generate cooling potential for buildings (limiting air-conditioning energy). According to materials and surface treatments, the roof can represent to be a major heat gain source from opaque elements of the building fabric, heating up the outer surface and increasing heat flow by conduction. This paper presents low-cost new radiative materials (1 ∉/m²) allowing to limit heat gains during diurnal cycle for hot seasons. To evaluate the relevance of these new substrates, their reflective UV-VIS-IR behavior are studied and compared to classical roofed materials available in industrial and developing countries. A 48 m² experimental roof having different surfaces (plate steel sheets, fiber cement, terra cotta tiles and corrugated sheets) allows to determine the temperature ratio δ between uncoated and coated materials. Up to 34% surface temperature gains are obtained for white coated CS, 25% for FC and ∼18% for TCT and PSS. According to uncoated materials for a surface temperature T₀ = 60 °C, simulations showed that the low-cost white opaque reflective roofs (50 m²) presented in this study would reduce cooling energy consumption by 26-49%.     

Design and performance of solar powered absorption cooling systems in office buildings

The paper contributes to the system design of solar thermal absorption chillers. A full simulation model was developed for absorption cooling systems, combined with a stratified storage tank, steady-state or dynamic collector model and hourly resolved building loads. The model was validated with experimental data from various solar cooling plants.As the absorption chillers can be operated at reduced generator temperatures under partial load conditions, the control strategy has a strong influence on the solar thermal system design and performance. It could be shown that buildings with the same maximum cooling load, but very different load time series, require collector areas varying by more than a factor 2 to achieve the same solar fraction. Depending on control strategy, recooling temperature levels, location and cooling load time series, between 1.7 and 3.6 m² vacuum tube collectors per kW cooling load are required to cover 80% of the cooling load.The cost analysis shows that Southern European locations with higher cooling energy demand lead to significantly lower costs. For long operation hours, cooling costs are around 200 € MWh⁻¹ and about 280 € MWh⁻¹ for buildings with lower internal gains and shorter cooling periods. For a Southern German climate, the costs are more than double.     

Field performance of a Japanese low energy home relying on renewable energy

This paper describes the construction and evaluation of an experimental low energy home assisted by a hybrid system using natural energy resources and unused energy. The home, for which a ground source heat pump (GSHP) system has been installed, was built on the campus of Hokkaido University, Japan in March 1997. The total floor area of the home is 192 m². This home is super insulated and airtight; the calculated coefficient of heat loss is 0.97 W/m² K. It has various passive strategies including direct solar heat gain and a ventilation system with an exhaust stack. Photovoltaic (PV) modules, wind power and solar collectors are adopted in order to achieve self-sufficiency in electric power and domestic hot water (DHW) supply. A GSHP is used for space heating and cooling. Two vertical steel wells are used as vertical earth heat exchangers (VHE). In summer, there is a floor cooling system using piped cold water from the VHE.Approximately 80% of the home’s total energy was provided by PV modules, solar collectors, as well as underground and exhaust heat. The annual amount of purchased energy during the test period was 12.5% that of a typical home in Hokkaido.     

Spatial distribution of air temperature as a measure of ventilation efficiency in large uninsulated cowshed

Ventilation in the building is to assure a microclimate suitable for humans and animals as well as the durability of structures. Based on the data from literature theoretical heat and moisture balancing ventilation rate calculations for uninsulated cowshed are presented. At an indoor temperature of −6.7 °C and indoor–outdoor temperature difference of 1 °C, the theoretical ventilation rate of 2300 m³/h per cow is necessary to remove the water vapour produced by the cows from the building. At a difference of 2 °C the ventilation rate of 1200 m³/h per cow and at 5 °C 530 m³/h per cow is needed. But these calculated ventilation rates are probably unrealistic. Traditional methods are unreliable for uninsulated cowsheds and instead of that an alternative method for evaluating the ventilation rate is needed.     

Impact of adaptive thermal comfort criteria on building energy use and cooling equipment size using a multi-objective optimization scheme

Recently adaptive thermal-comfort criteria have been introduced in the international indoor-climate standards to reduce the heating/cooling energy requirements. In 2008, the Finnish Society of Indoor Air Quality (FiSIAQ) developed the national adaptive thermal-comfort criteria of Finland. The current study evaluates the impact of the Finnish Criteria on energy performance in an office building. Two fully mechanically air-conditioned single offices are taken as representative zones. A simulation-based optimization scheme (a combination of IDA-ICE 4.0 and a multi-objective genetic-algorithm from MATLAB-2008a) is employed to determine the minimum primary energy use and the minimum room cooling-equipment size required for different thermal comfort levels. The applicability of implementing energy-saving measures such as night ventilation, night set-back temperature, day lighting as well as optimal building envelope and optimal HVAC settings are addressed by investigating 24 design variables. The results show that, on average, an additional 10 kWh/(m² a) primary energy demand and a larger 10 W/m² room cooling-equipment size are required to improve the thermal comfort from medium (S2) to high-quality (S1) class; higher thermal comfort levels limit the use of night ventilation and water radiator night-set back options. Compared with the ISO EN 7730-2005 standard, the Finnish criterion could slightly decrease the heating/cooling equipment size. However, it significantly increases both the heating and cooling energy demand; the results show 32.8% increase in the primary energy demand. It is concluded that the Finnish criterion-2008 is strict and does not allow for energy-efficient solutions in standard office buildings.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.     

Optimized design of floor-based air-conditioners for residential use

The feasibility of locating the air-conditioners at low level (FAC unit) for residential use has been ascertained in previous studies by the authors. In order to optimize the design of the unit for maximum thermal comfort, an FAC unit configured to two different angles of deflection and two installed positions (altogether 4 scenarios) was set-up in a 13 m² bedroom-like chamber for experimental studies. In the experiments, the layout of the chamber was determined by questionnaire surveys, and the characteristics of heat source were determined by heat transfer simulations and cluster analysis. The local air speeds and temperatures at 4 different levels of 8 positions were monitored for the calculation of air diffusion performance index (ADPI) and draft risk. The energy performance was determined based upon the monitored cooling outputs and power consumptions. Using the measured air temperatures and velocities as boundary conditions, three-dimensional computational fluid dynamic (CFD) simulations were performed using AIRPAK to examine the vertical temperature distribution, draft discomfort and ventilation effectiveness. It was concluded that the FAC unit with an angle of deflection at 45° and with a finished level of 1.1 m performs better than the unit with other configurations. No thermal stratification and draft discomfort were observed. Further, by using parametric studies, the influences of space cooling loads, supply air velocities, and jet areas were investigated with 24 CFD cases. Based on the simulation results, for a satisfactory ADPI for the use of FAC unit, the optimum supply air velocity range was identified as 2.2 m/s–3 m/s, whilst the A_r numbers were between 0.033 and 0.243.     

Computer modeling of displacement ventilation systems based on plume rise in stratified environment

A model for displacement ventilation system based on plume rise of single point heat source was developed. The errors for temperature gradient ratio were less than 6% in most cases. Errors for temperature gradient and displacement zone height were relatively higher (up to 28.1%) which might be due to the derivation of the parameters from experimental data. Still, the errors were lower than those from design model/method of some other workers (68.5% for the temperature gradient ratio and 15.7% for the temperature difference between the supply air and at 0.1 m above floor level). With a room height of 2.4 m (common for office in Hong Kong) and design room temperature 25.5 °C defined at 1.1 m above floor level under the normal load to air flow ratio of 12,000 W/m³/s (typical values for sub-tropical region) and minimum supply temperature of 18 °C, there existed a zone capacity range from 1000 to 5000 W that stand alone operation displacement ventilation system was feasible and that the displacement zone height (minimum 2.2 m) was above normal breathing level. The feasible zone capacity range diminished with decrease in design room temperature and/or room height. In this case, the load to air flow ratio had to be reduced, resulting in a higher flow rate when compared to a mixing ventilation system, or an auxiliary cooling facility such as a chilled ceiling had to be used.     

Effect of solar chimney inclination angle on space flow pattern and ventilation rate

The solar chimney is a simple and practical idea that is applied to enhance space natural ventilation. The chimney could be vertical or inclined. The chimney inclination angle is an important parameter that greatly affects space flow pattern and ventilation rate.In the present study, the effect of chimney inclination angle on air change per hour and indoor flow pattern was numerically and analytically investigated. A numerical simulation using Ansys, a FEM-based code, was used to predict flow pattern. Then the results were compared with published experimental measurements. A FORTRAN program was developed to iteratively solve the mathematical model that was obtained through an overall energy balance on the solar chimney.The analytical results showed that an optimum air flow rate value was achieved when the chimney inclination is between 45° and 70° for latitude of 28.4°. The numerically predicted flow pattern inside the space supports this finding. Moreover, in the present study a correlation to predict the air change per hour was developed. The correlation was tested within a solar intensity greater than or equal to 500 W/m², and chimney width from 0.1 m to 0.35 m for different inclination angles with acceptable values.