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.     

Collector cum storage solar water heaters with and without transparent insulation material

The integrated collector–storage solar water heaters are less expensive and can offer the best alternative for domestic applications particularly to small families to meet hot water requirements. The top heat losses of such solar water heaters are quite high during the night and the temperature of stored hot water is considerably reduced unless covered with extra insulating cover in the evening which is a cumbersome job. The transparent insulation material widely used in Europe for space heating can also minimize top heat losses, if used in such solar water heaters. For this purpose, two units of solar collector cum storage water heaters have been designed to study the relative effect of TI for retaining solar heated hot water for a night duration. Both units were identical in all respects except one of them was covered with TIM. The theoretical exercise was carried out to evaluate design parameters of ISC which revealed total heat loss factor (U_L) 1.03 W/m² K with TIM glazed against 7.06 W/m² K with glass glazed. The TIM glazed has been found to be quite effective as compared to glass glazed SWH and yielded hot water at higher temperature by 8.5 to 9.5°C the next morning. The storage efficiency of such solar water heaters has been found to be 39.8% with TIM glazed as compared to 15.1% without TIM. The TIM glazing means not having to cover the ISC solar water heater with a separate insulator cover in the evening and thus makes its operation much simpler.     

A numerical study of solar chimney for natural ventilation of buildings with heat recovery

The performance of a glazed solar chimney for heat recovery in naturally-ventilated buildings was investigated using the CFD technique. The CFD program was validated against experimental data from the literature and good agreement between the prediction and measurement was achieved. The predicted ventilation rate increased with the chimney wall temperature. The effects of solar heat gain and glazing type were investigated. It was shown that in order to maximise the ventilation rate in a cold winter, double or even triple glazing should be used. Installing heat pipes in the chimney for heat recovery not only increased the flow resistance but also decreased the thermal buoyancy effect. To achieve the required air flow rates in naturally-ventilated buildings with heat recovery, use should be made of wind forces.     

Thermocirculation characteristics of a Trombe wall passive test cell

Passive heating, using Trombe wall elements for solar energy collection, can be readily integrated into new building structures and can be retrofitted to existing buildings.

Although the basic physical principles underlying the natural operation of such air thermosiphon devices have been well known for many years now, there is still insufficient design information available to allow sensible sizing and installation decisions to be undertaken by architects and thermal system designers. In this experimental investigation, flow visualisation studies have given a deeper insight into the fundamental flow mechanisms; whilst air velocity and temperature measurements have been used to explore the natural convection heat transfer processes involved in the thermocirculation flow. Particular attention has been paid to the effects on operational performance of the wall parameters such as wall/glazing distance and vent size.

Adequate data correlation of the experimental results has been achieved by using expressions derived for natural (free) convection processes occuring between vertical paralled plates; in this case the vertical heated wall surface and the cooler vertical glazing panel. It is felt that this type of fundamental heat transfer information is vital so that the overall performance of Trombe wall systems can be adequately modelled using the large range of simulation techniques currently available for thermal network analysis.     

Thermal balance at heat reflecting windows

The program described in this paper computes the heat loss by convection and radiation from one or two pane windows, glazed with plastic or glass, coated with infra-red reflecting layers, bloomed to reduce reflection of visible radiation, and whose interpane space is filled with various gases. Comprehensive weather measurements from Kew (London) for the years 1959–1969 are read in for each hour. Energy losses at each glazing element are calculated using data concerning the behaviour of the various coatings and glazing materials towards visible and infra-red radiation. the advantages of coated windows for passive solar heating are discussed.     

Solar and thermal energy gain through windows in Jordan

Solar gain and thermal energy transfer through windows is studied for three different sites in Jordan using the TRNSYS computer program. Solar and thermal energy is calculated using the monthly average daily data for the above-mentioned three regions. Calculation of hourly radiation on a vertical plane is presented, and also the method of determination of the amount of radiation transmitted through the glazing layers is given. The effect of window orientation on the total solar gain is analysed. It is found that for all directions, solar gain is season-dependent, and this dependency varies from one direction to another. Calculations are carried out for two cases of glazing location: case 1, glazing flush with the outside of the wall; and case 2, glazing recessed by 15 cm from the outside wall, which represents a window with overhang and sidewalls. The number of glazing layers is taken as 1, 2 and 3 to observe the effect on solar gain as well as on the thermal energy exchange between the inside and outside of the building. During the calculations, the temperature of the inside is fixed at 22°C for the entire year. The results are tabulated to serve as a database for solar and thermal energy in Jordan.     

Solar heat gain factors and heat loss coefficients for passive heating concepts

The concept of solar heat gain factor has been introduced for calculating the net energy gain of passive heating elements and other components of a building as a result of incident solar radiation. For passive heating concepts (namely, the direct gain, mass wall, water wall, Trombe wall, and solarium), exact analytical expressions have been obtained for the solar heat gain factors and the corresponding overall heat loss coefficients. These will allow a building designer to calculate immediately the overall heat gain/loss in a building. Numerical calculations have been done for typical values of solar radiation and ambient temperature of typical climatic conditions in India. The method has been compared with the other methods reported in the literature so far. A good comparison is found between the earlier methods and the method of using solar gain factors and the corresponding heat transfer values.     

Application of U and g values for sizing passive heating concepts

The concept of solar gain factor and the overall heat loss coefficient, obtained for solar passive heating concepts, has been extended to size these as building elements for different climatic conditions. As an example, India's four climatic zones where winter heating is required have been selected and the required area of passive heating concepts calculated by a steady-state analysis applied to a single zone building. The size of various concepts expressed as percentages of the south wall area are independent of the building size as confirmed for the case of army shelters in cold and sunny conditions of Laddakh in northern India. For a building with capacity effects in walls and roof, the dynamic simulation confirms the values of room temperature at a comfortable level assumed to be 18.3°C in the steady-state analysis.     

Novel glazing technologies to mitigate energy consumption in low‐carbon buildings: a comparative experimental investigation

Buildings play a key role in total world energy consumption as a consequence of poor thermal insulation characteristics of facade materials. Among the elements of a typical building envelope, windows are responsible for the greatest energy loss because of their notably high overall heat transfer coefficients. About 60% of heat loss through the building fabric can be attributed to the glazed areas. In this respect, novel cost‐effective glazing technologies are needed to mitigate energy consumption, and thus to achieve the latest targets toward low/zero carbon buildings. Therefore in this study, three unique glazing products called vacuum tube window, heat insulation solar glass and solar pond window which have recently been developed at the University of Nottingham are introduced, and thermal performance analysis of each glazing technology is done through a comparative experimental investigation for the first time in literature. Standardized co‐heating test methodology is performed, and overall heat transfer coefficient (U‐value) is determined for each glazing product following the tests carried out in a calibrated environmental chamber. The research essentially aims at developing cost‐effective solutions to mitigate energy consumption because of windows. The results indicate that each glazing technology provides very promising U‐values which are incomparable with conventional commercial glazing products. Among the samples tested, the lowest U‐value is obtained from the vacuum tube window by 0.40 W/m²K, which corresponds to five times better thermal insulation ability compared to standard air filled double glazed windows. Copyright © 2015 John Wiley & Sons, Ltd.     

Solar heat gains through train windows: a non-negligible contribution to the energy balance

The sector of transportation accounts for about one third of the total energy consumption in Switzerland. A monitoring campaign of the energy consumption of a regional train revealed the critical energy-consuming systems. Heating, cooling and ventilation were identified as major consumers. Windows are a source of non-controlled heat transfer. In summer, it may result in overheating leading to larger cooling loads while in winter, it is an important source of thermal losses. Selective double glazing and solar protection coatings can reduce these effects. Angular-dependent optical properties of a selective double glazing have been measured, and the solar heat gain coefficient (g value) was determined. An estimation of the solar gains received by a panoramic waggon was performed using the monitored solar irradiation and the measured properties of the glazing. These data were compared to the heating and cooling energy consumption monitored in this waggon. Solar gains were found to be in the same order of magnitude that the heating energy during some sunny days. They were also compared to the estimated thermal losses through the glazing and the entire envelope. These results show that the solar gains play a non-negligible role in the energy balance of the waggon. Furthermore, thermal simulations were performed to evaluate the solar gains in different conditions. It showed that 7 to 13% of energy can be saved using the glazing adapted to the climatic conditions. In addition, improving the thermal insulation of the train envelope or equipping the train with an efficient heat recovery system can lead to significant energy savings.     

Thermal network predictions of the daily temperature fluctuations in a direct gain room

This paper studies the daily temperature fluctuations in a direct gain room measuring 6.1 × 4.57 × 2.44 m³ (20 ft × 15 ft × 8 ft). The room is assumed to have losses on three faces and 8.36 m² (90 ft²) of south glazing. Let r denote the ratio of the surface area of the mass wall to the area of the south facing glazing. The effect of r on mass walls 10.16, 20.32 and 30.48 cm (4, 8 and 12 in.) thick was determined for values of r equal to 1, 2, 4, 8 and 11.1. The temperature and solar insolation values for a typical January day in Nebraska were duplicated thirty consecutive times and were used for the weather data input to the modeling program. Using thirty consecutive like days has the advantage of damping out the transient solution to the point where it is negligible. It was found that for each thickness of wall, the temperature fluctuations over a day decrease as r increases, and it was also found that for a fixed value of r, the daily temperature fluctuations decrease as the wall thickness is increased. These results are consistent with those reported by Mazria.In addition cloudy day storage was considered for both the 10.16 and 20.32 cm (4 and 8 in.) walls, with r fixed at 4, runs were made with 20, 33, 50 and 100 per cent cloudy days. The results are presented in graphical form and indicate a rapid recovery of the system in most cases.     

The passive solar heated school in wallasey. I foreword and introduction

St. George's School, Wallasey, situated in the U.K. at latitude 53.4° N was designed so that equitable thermal conditions should be achieved within it using solar gains, heat from the lighting system and body heat from the children without the use of a conventional heating system. The building opened in 1962 and evoked considerable comment, both favourable and unfavourable, in the mid-sixties. This article briefly notes some of the comments and provides an account of some of the features which the architect incorporated to control the solar gains that enter through the large south-facing solar wall. Later articles in this series describe the findings of observational surveys carried out in the building.     

Wind effect on the performance of a solar organic Rankine cycle

The effects of wind, ambient temperature and solar radiation on the simultaneous productions of mechanical work and heat by a solar Rankine cycle are studied. The on site experimental study uses the pentafluorobutane R365mfc as working fluid in a system consisting of a small-scale single glazed flat plate collector, a micro turbine, a condenser and a pump. The theoretical study focuses on the prediction of the optimum operating temperature of the collector according to the solar radiation, the temperature of air and the wind speed. Then, the total production of mechanical and thermal energy is calculated during a sunny day for which various wind speeds are simulated. The results highlight the effect of wind on the corresponding production and they also establish the value of the recommended evaporating temperature according to weather conditions.     

Highly insulating aerogel glazing for solar energy usage

Granular silica aerogels have been integrated into highly-insulating translucent glazing. This work was performed within the large R&D project ISOTEG pursued by the ZAE Bayern. To avoid settlement of the granules, which often occurred in earlier glazing concepts and even caused destruction of the glazing, the granules were sandwiched between a double skin sheet made of PMMA. The sheet was mounted between two low-e coated glass panes. To optimize the thermal insulation, krypton was used as filling gas. This construction allows to achieve heat transfer coefficients of less than 0.4 W/(m² K). Optimized granular layers provide high solar transmittance of 65% for a thickness of 20 mm. Thus a total solar energy transmittance of 35% for the whole glazing unit is achieved. The glazing has a thickness of less than 50 mm. Such aerogel glazings can be integrated into solar wall systems or used as lightscattering daylighting elements with vanishing energy losses over the heating period even for north facade integration. Optical and thermal properties of the developed granular aerogels as well as the thermal properties of the whole glazing unit are reported.     

Influence of thermal emittance on the performance of laminated solar control glazing

Influence of thermal emittance on the performance of laminated solar control glazing is presented. A transient one-dimensional mathematical model allowing the prediction of conductive heat transfer within the glazing and convective and radiative heat transfer from the glazing towards the interior and exterior are considered separately. A constant normal incidence of air mass 2 solar radiation of 750 W/m² was assumed. The redistribution of the component of the solar radiation absorbed by the laminated glass and the shading coefficient (SC) were calculated for solar transmittance, 0.05 to 0.35; thermal emittance of the inner surface of the glazing, 0.15 to 0.85; convective heat transfer coefficient for the exterior surface, 10–100 W/m² K and exterior ambient temperatures of 15°C, 32°C and 45°C. The results indicate that as the emittance decreases, the SC decreases by 10–20% for all cases of ambient temperatures considered. The contribution from the convective mechanisms to the heat transfer to the interior is always higher than that from radiative process in the range of ambient temperatures considered. The results presented in this paper would help to decide whether for a given location of interest, the incorporation of a heat mirror glazing would make a meaningful reduction in the cooling load in enclosures with single glazed windows.     

Non-convective roof pond for passive space heating

This paper reports on an investigation of a passive system comprising a non-convective pond placed on the roof of a building in order to heat the building. Periodic analysis of the solar heat transfer process in the system, which is exposed to solar radiation and atmospheric temperature on one side and is in contact with room air at constant temperature (corresponding to an air-conditioned room) on the other, indicates that this system provides better thermal storage than a thick concrete roof or the convective roof pond system. In sunny winter climates, such a system can provide 100% of all heating needs. A viscosity stabilised non-convective pond of shallow depth (10–15 cm) is envisaged to be the most suitable for the present application.     

Solar collectors with colored absorbers

The integration of solar collectors in buildings should be compatible with the architectural design, and solar collectors with colored absorbers would be aesthetically preferable. In our laboratory we constructed and tested flat plate solar collectors with colored absorbers for water heating applications. The study includes collectors in their typical form with the protective glazing, and also collectors without glazing. Unglazed solar collectors are not widely used, although they are cost effective solar devices, suitable for low temperature thermal applications. We tested outdoors the constructed models, glazed and unglazed, with black, blue and red brown absorbers. In order to overcome the high thermal losses of the unglazed collectors and the low optical efficiency of the colored absorbers, we used flat booster reflectors. The additional solar radiation input from the reflectors increases the thermal energy output of the collectors, improving their performance. Theoretical steady state efficiency curves are also given for collectors with or without glazing. The presented experimental and theoretical results determine the range of the effective operation of the proposed solar collector types, which can be used in a variety of applications, instead of glazed or unglazed solar collectors with a black absorber.     

Solar assisted biogas plants IV: Optimum area for blackening and double glazing over a fixed-dome biogas plant

The paper presents the economic analysis of a fixed-dome biogas plant of rated capacity 8 m³, above which a part of the ground is blackened and doubly glazed in the cold climate of Srinagar. Blackening and glazing of the ground cannot alone maintain the slurry temperature at 35°C, which is the optimum temperature in the mesophilic range for the anaerobic digestion of cattle dung, and so a part of the biogas must be burnt. The electrical simulation experiments have been performed to determine the loss or gain of heat from the underground biodigestor to the ambient atmosphere through the ground if a part of the ground above is blackened and double glazed. Economic analysis of the system shows that the optimum area to be blackened and glazed would have a radius 1.5 times that of the biodigestor.     

Determination of glazing area in direct gain systems for three different climatic zones

This study determines the glazing area in direct gain passive systems needed to ensure thermal comfort inside a building (room air temperature 20 ± 2°C). A 4 m × 4 m × 3 m single zone isolated house is analyzed in three different types of climates namely composite (8°C to 20°C, New Delhi), cold-cloudy (−2°C to 5°C, Srinagar), and cold-sunny (−14°C to −3°C, Leh). The analysis is based on the periodic solution of the heat conduction equations describing heat transmission in the building components, floor, walls, and roof, and the Fourier representation of the ambient temperature vnd the total solar radiation intercepted by the building envelope. Two types of construction are analyzed: the first type is a traditional construction with 22-cm-thick brick wall, plastered 15 mm on both the sides (U = 2.0 W m⁻² K⁻¹); and the second one is of the same type but with 10 cm of expanded polystyrene insulation on all the four walls and the roof (U = 0.31 W m⁻² K⁻¹). It is found that for traditional construction with U = 2.0 W m⁻² K⁻¹, the glazing U value has almost no effect on the room temperature even for large variation of the glazing area (10% to 40%, expressed in terms of percentage of floor area). For a well-insulated house (U = 0.31 W m⁻² K⁻¹), the glazing U value has no effect upon the room air temperature if the glazing area is small (less than 10%). The position of the insulation on the external surfaces is more effective in reducing large inroom air temperature. Finally, for an insulated house, we recommended glazing is 30%, 20%, and 10% for cold-sunny, cold-cloudy, and composite climates, respectively.     

CFD analysis of the thermal losses on the upper part of a flat solar collector

To investigate the reduction of heat losses on the upper part of a flat solar collector, a two‐dimensional study was carried out by CFD analysis using Fluent. For this purpose, the heat transfer behavior in the air gap over a wide range of thicknesses of the latter (1‐20 mm) and the addition of a second glass cover fixed at midheight of the air gap spacing have been investigated. For small thicknesses of the air gap (1‐8 mm), the heat transfer is essentially conductive. An increase in the thickness leads to the intensification of the natural convection which induces high thermal losses. The simulation results have shown that the addition of a second cover glazing leads to the weakening of the natural convection and thus to an average enhancement of the solar collector temperature over the range of thicknesses studied of approximately 17%. The overall thermal losses coefficient is then reduced by an average of 26% compared with the single‐glazed solar collector. They have also shown that the thickness of the air gaps resulting in the minimum overall heat losses is 8 mm and that the thickness of the second glass cover has no significant effect on these results. In addition, this study has highlighted the importance of taking into account the radiation heat transfer in establishing the thermal balance of a flat solar collector. Indeed, this consideration leads to an average decrease of the absorber temperature of about 30%.