Performance evaluation of an integrated solar water heater as an option for building energy conservation

Since a majority of residential and industrial building hot water needs are around 50 °C, an integrated solar water heater could provide a bulk source that blends collection and storage into one unit. This paper describes the design, construction and performance test results of one such water-heating device. The test unit has an absorber area of 1.3 m² and can hold 170 l of water, of which extractable volume per day is 100 l. Its performance was evaluated under various typical operating conditions. Every morning at about 7:00 a.m., 100 l of hot water were drawn from the sump and replaced with cold water from the mains. Although, during most of the days, the peak temperatures of water obtained are between 50 and 60 °C, the next morning temperatures were lower at 45–50 °C. Daytime collection efficiencies of about 60% and overall efficiencies of about 40% were obtained. Tests were conducted with and without stratification. Night radiation losses were reduced by use of a screen insulation.     

Behavior of FRP-confined concrete after high temperature exposure

This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase experimental program was conducted. In the first phase, 42 standard 100 × 200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high temperature exposure, specimens were tested under uniaxial compression till failure. The test results demonstrated that at a temperature of 100 °C (a little more than the glass transition temperature (T_g) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100 × 100 × 650 mm concrete prisms were prepared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens.     

Development and experimental validation of a novel indirect-expansion solar-assisted multifunctional heat pump

This paper proposes a novel indirect-expansion solar-assisted multifunctional heat pump (IX-SAMHP) which integrates a domestic heat pump with a solar water heater. The IX-SAMHP can not only work in operation modes included in the two household appliances, but also operate in four new energy-saving operation modes for the space cooling, space heating and water heating. All operation modes have functioned successfully and can be switched to each other smoothly on a purpose-built experimental setup. Experiments of the heat pump water heating mode at outdoor air temperatures of 8 °C and 15 °C and the solar-assisted space heating mode at indoor air temperatures of 20 °C have been investigated in detail. Electric heaters were used to simulate solar radiation intensity in different weather conditions. The experimental results show that the IX-SAMHP can produce hot water with much less electric consumption in cloudy days compared with a solar water heater and can operate in much higher coefficient of performance than a domestic heat pump in cold winter. The IX-SAMHP is especially suitable for the regions abundant in solar radiation where the space heating, space cooling and water heating are required all the year round.     

Buttock responses to contact with finishing materials over the ONDOL floor heating system in Korea

The ONDOL is a conventional floor heating system in Korea. Eight healthy college students volunteered as the subjects to investigate the buttock responses to contact with 10 types of the ONDOL covering materials: mortar, plywood, artificial marble, PVC, rubber foam, tempered glass, steel, insulation mortar, carpet, and aluminum. The temperature of water supply flowing into the floor coil underneath the floor surface was altered from 15 to 40 °C at 5 °C intervals. Floor surface temperature, skin temperature including buttock and subjective thermal sensation were monitored. The study revealed that the lower the contact coefficient of covering material, the more stable the temperature fluctuations in the floor surface and the buttock skin were. The floor finishing material should be chosen by the heat flux based on the heating load, and the friendship to human body. Using regression analysis, the neutral temperature of the buttock was determined at 32.6 °C.     

Effects of elevated water temperatures on interfacial delaminations,failure modes and shear strength in externally-bonded CFRP-concrete beams using infrared thermography,gray-scale images and direct shear test

This paper reports the results of a durability study of the effects of exposing externally-bonded CFRP-concrete beams to three elevated water temperatures (25 °C, 40 °C and 60 °C). The effects of the heated water environments on the adhesive bonding layer between the CFRP and concrete beams were evaluated by quantifying: (1) the changes of delaminations within the adhesive bonding layer, (2) the changes in resistance to direct shear force and (3) the changes of failure mode distribution. Before the exposure, the condition of the adhesive bonding layer was inspected by infrared thermography (IRT). After exposure, the deterioration of the same bonding layer and failure mode distributions were measured by analyzing the visual photos on the failed CFRP strips. The failure modes were found to be affected largely by the combined effect of elevated temperature and moisture ingress, in which three types were identified: failure at concrete beams, at adhesive bonding layer and interface between CFRP strip and concrete. With these methods, results of 54 specimens show that the adhesive bonding layers of all the specimens had gradually deteriorated in the 40 °C and 60 °C water baths. This deterioration was due to the weakening of the adhesive bonding layers when the glass transition temperature (T_g) or the heat distortion temperature (HDT) was approached or even exceeded, and gradual development of delaminations at adhesive bonding layer.     

Concrete cover effect on reinforced concrete bars exposed to high temperatures

The mechanical properties of structural reinforcement steel have been investigated after the exposure to high temperatures. Plain steel, reinforcing steel bars embedded into mortar and plain mortar specimens were prepared and exposed to 20, 100, 200, 300, 500, 800 and 950 °C temperature for 3 h individually. The S420 deformed steel bars with diameters of ∅10, ∅16 and ∅20 were used. The mortar was prepared with CEM I 42.5 N cement and fly ash. The tension tests on reinforcements taken from cooled specimens were performed, and the variations in yield strength, ultimate strength and in resilience of three different dimensioned reinforcements were determined. A cover of 25 mm provides protection against high temperatures up to 400 °C. The high temperature exposed plain steel and the steel with 25-mm cover has the same characteristics when the reinforcing steel is exposed to a temperature 250 °C above the exposure temperature of plain steel.     

Performance of thermally damaged fibre reinforced concretes

Mechanical characteristics of Fibre Reinforced High Performance Concrete (FR-HPC) subjected to high temperatures were experimentally investigated in this paper. Three different concretes were prepared: a normal strength concrete (NSC) and two High Performance Concretes (HPC1 and HPC2). Fibre reinforced concretes were produced by addition of steel or polypropylene fibres in the above mixtures at dosages of 40 kg/m³ and 5 kg/m³, respectively. A total of nine concrete mixtures were produced and fibres were added in six of them. At the age of 120 days specimens were heated to maximum temperatures of 100, 300, 500 and 700 °C. Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. Reference tests were also performed at air temperature (20 °C). Residual strength of NSC and HPC1 was reduced almost linearly up to 700 °C and 500 °C, respectively whereas the residual strength of HPC2 was sharply reduced up to 300 °C. Explosive spalling was observed on both HPC. Addition of steel fibres increased the residual strength up to 300 °C, but spalling still occurred in HPC1 and HPC2. Such an explosive behavior was not observed when polypropylene fibres were added in the mixtures; however, in this case the residual mechanical characteristics of all concretes were significantly reduced.     

Study on thermal effects on fatigue behavior of cracked steel plates strengthened by CFRP sheets

Carbon fiber reinforced polymer (CFRP) sheets have been used to strengthen steel structures to enhance fatigue life. However there is very limited information on the influence of temperatures on the fatigue strengthening efficiency. This paper describes an investigation on the behavior of cracked steel plates strengthened with CFRP at different temperatures. Firstly, through cylinder coupon tests, mechanical properties of the resin were found to vary at different temperatures, especially when the temperature exceeds the glass transition temperature T_g. Secondly, three cracked bare steel plates and five cracked steel plates strengthened with high modulus CFRP sheets were tested under fatigue loading at different temperatures. The results prove the effectiveness of CFRP strengthening technology to increase fatigue life when the temperature ranges from −40 °C up to 60 °C. It is concluded that the variation of temperature has an obvious influence on properties of the resin, leading to influence on fatigue life. Finally, the existing analytical method to predict fatigue lives of CFRP strengthened steel plates at ambient temperature was modified by considering the temperature effect. Experimental and theoretical results are compared and reasonable agreement is achieved. The influence of the number of CFRP layers and CFRP modulus is also found based on the proposed analytical method.     

Effects of thermal cycles on mechanical properties of an optimized polymer concrete

The aim of this study is the design, fabrication and experimentally characterization of an optimized polymer concrete (PC). To this end, three factors, namely: the aggregate size, epoxy resin weight percentage, and chopped glass fiber percentage; are considered as the influencing factors on the compressive strength, bending strengths and interfacial shear strength between the PC and steel. The number of tests which are necessary to simultaneously optimize three above strengths of the PC are reduced based on the design of experiment using the orthogonal array technique or so-called Taguchi method. Comparison of the predicted strengths based on the Taguchi approach with the measured experimental results shows a good correlation between them. Afterward, the effect of three freeze/thaw thermal cycles; 25 °C to ?30 °C (cycle-A), 25 °C to 70 °C (cycle-B) and ?30 °C to 70 °C (cycle-C) for 7 days; on the strengths of the optimized PC is experimentally investigated. Comparison of the experimental results for the mechanical strengths measured at room temperature (RT) and above thermal cycles shows that the compressive strength of the optimally designed PC is not affected by heating and cooling cycles. On the other hand, the bending strength is more affected by exposing PC to the thermal cycle-B. The interfacial shear strength becomes affected by exposing the PC to cycles-A and -B, whereas no changes are observed on this strength by exposing to the thermal cycle-C. In general, among the three thermal cycles, cycle-B exerted the most deteriorating effect on the strengths.     

Suppression of sodium fires with liquid nitrogen

Sodium has unusual fire hazards, including autoignition when heated in air or exposed to liquid water. Owing to limitations of existing suppression agents for sodium pool fires, suppression using liquid nitrogen (LN₂) is examined here. Sodium pools of 5–80 g were heated in stainless steel beakers. At about 290 °C, pool surface autoignition occurred and caused a rapid pool temperature increase. Vapor phase combustion occurred when the pools reached 320–450 °C, ultimately leading to pool temperatures up to 700 °C. For suppression tests, LN₂ delivery (at 2.7 g/s) began when the fires became fully-developed, near a pool temperature of 600 °C. Liquid nitrogen was found to be an effective suppression agent. The minimum amount of LN₂ required to suppress a fully-developed sodium pool fire was found to be about three times the initial sodium pool mass.     

A mobile solar water heater for rural housing in Southern Africa

One of the day-to-day problems for the low-income rural population of Southern Africa is collecting and transporting sufficient water for domestic use from communal water sources. In addition, the traditional sources of energy used for heating domestic water, such as firewood and charcoal, have become scarce and expensive. Inevitably, hygiene practices are compromised, which has a detrimental effect on the health of the people.An affordable device was envisaged that could assist in rural areas with the transportation and heating of water. Southern Africa is blessed with abundant sunshine, thus making it appropriate to select solar heating for this purpose. The device must have the ability to store the hot water until the evening. An ICS type solar water heater, with insulation and glazing, was selected therefore. Because the mobility of the device was modelled on the wheelbarrow, the device was named the Solar Heat Barrow. Prototypes were designed, manufactured and tested and it was demonstrated that water could be heated to an average of 60 °C by mid-afternoon. Water at 40 °C was still available at 20:00. Problems experienced during both the manufacture and testing of the device will be solved as development continues.     

Effect of high temperature and cooling conditions on aerated concrete properties

In this study, effect of elevated temperatures and various cooling regimes on the properties of aerated concrete is investigated. Air cooled materials are tested at room temperature and in hot condition right after the fire. Water quenching effect is determined by testing the material in wet condition right after the quenching and in dry condition at room temperature. Unstressed strength of the material tested hot is relatively higher than air cooled unstressed residual strength up to 600 °C. On the other hand, water quenching decreases the percentage of the strength particularly when the material is wet right after the quenching; strength is lost gradually as the temperature rises. As a result, if the quenching effect is disregarded, temperature rise does not have a considerable effect on the strength of the aerated concrete approximately up to 700–800 °C. It is able to maintain its volumetric stability as well. However, more care needs to be taken in terms of its use above 800 °C for fire safety.     

Long-term bond performance of GFRP bars in concrete under temperature ranging from 20 °C to 80 °C

Eighty pull-out specimens were used to study the effect of temperature ranging from 20 °C to 80 °C in dry environment on bond properties between Glass Fiber Reinforced Polymer (GFRP) bars and concrete. The pullout-test specimens were subjected during 4 and 8 months to high temperatures up to 80 °C and then compared to untreated specimens (20 °C). Experimental results showed no significant reduction on bond strength for temperatures up to 60 °C. However, a maximum of 14% reduction of the bond strength was observed for 80 °C temperature after 8 months of thermal loading. For treated specimens, the coefficient β in the CMR model, which predicts the bond–stress–displacement behavior, seems to be dependant with the temperature.     

Shear strength of RC beams subjected to cyclic thermal loading

The experiments were performed for assessing the influence of cyclic thermal loading on the shear strength of reinforced concrete (RC) beam specimens. One hundred eleven RC beams of 100 × 150 × 1200 mm size reinforced in tension zone with two bars of 8, 10 and 12 mm diameters were tested under four point loading. The beams were subjected to a number of thermal cycles varying from 7 to 28 cycles with peak temperature taken as 100, 200 and 300 °C. The effects of thermal cycles on the crack pattern, failure mechanism, first crack load and the shear strength of beams have been discussed. The shear strength of the beams has been found to increase by up to 10% at lower temperature cycles of 100 and 200 °C but reduces by up to 14% at higher temperature (300 °C) depending on the severity of thermal loading. The results of study emphasize the need for developing appropriate guidelines for the design of RC structural elements used in comparatively high temperature environment with cyclic thermal loading conditions.     

Modeling mechanical performance of lightweight concrete containing silica fume exposed to high temperature using genetic programming

In this study, the mechanical performance of lightweight concrete exposed to high temperature has been modeled using genetic programming. The mixes incorporating 0%, 10%, 20% and 30% silica fumes were prepared. Two different cement contents (400 and 500 kg/m³) were used in this study. After being heated to temperatures of 20 °C, 200 °C, 400 °C and 800 °C, respectively, the compressive and splitting tensile strength of lightweight concrete was tested. Empirical genetic programming based equations for compressive and splitting tensile strength were obtained in terms of temperature (T), cement content (C), silica fume content (SF), pumice aggregate content (A), water/cement ratio (W/C) and super plasticizer content (SP). Proposed genetic programming based equations are observed to be quite accurate as compared to experimental results.     

Comparison of fibrous insulations – Cellulose and stone wool in terms of moisture properties resulting from condensation and ice formation

Cellulose fibres are often used as thermal insulation in buildings. The organic nature of cellulose fibres, however, makes the insulation sensitive to high moisture content. This study investigates the moisture performance of cellulose insulation when exposed to a subzero environment. The paper is focused on the condensation and freezing in the material and includes comparison with the authors previous studies on stone-wool insulation. While the used stone-wool samples were water-repellent due to resin binders, cellulose is a typical representative for hydrophilic thermal insulation to which any contact with water condensate can be crucial.Test specimens of loose-fill cellulose were placed in a special laboratory device providing high moisture load. During a period of 100 h the specimens were subjected to a continuous load of moisture at atmospheric conditions on one side while the other side of the specimen faced a surrounding temperature of 0, −10 and −20 °C and the laboratory tests were repeated three times for each set of the specific thermal conditions (T_i = +20 °C, T_e = 0, −10 and −20 °C). The results indicate that there are minor changes in the water vapour permeability of the specimens. The experimental data from the investigation is compared with a mathematical model that simulates moisture diffusivity of cellulose together with accumulation due to sorption and freezing, using the actual climatic data.     

Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity

Asphalt binder viscosity is of great importance during the production process of hot mix asphalt mixture as typically asphalt plants will store binders between 149 °C and 177 °C. SHRP guidelines state that asphalt binder viscosity must not exceed 3 Pa s. Therefore, given the documented increases in asphalt viscosity when modified with crumb rubber modifier (CRM) it is necessary to produce asphalt binder that fulfills the SHRP criteria while not exceeding plant mixing and storing requirements. This paper reports the results of an investigation of the importance of CRM properties on viscosity of CRM binder. Two binder sources were modified at four concentration levels using four different crumb rubber sources; the viscosities of the produced binders were evaluated by AASHTO T 316. Crumb rubber properties were evaluated by elemental analysis using a scanning electron microscope (SEM) and by determination of glass transition temperature (T_g) using a differential scanning calorimeter (DSC). In general, results indicate that processing procedure and tire type plays an important role in the determination of CRM binder viscosity.     

Granulated foam glass–ceramic material from zeolitic rocks

The objective of this research work was to investigate the production of granulated foam glass–ceramic material from zeolitic rocks. The investigations have shown that grinding raw materials to particle size less than 0.5 mm and adding 13.8% of alkali content provide production of material with the following properties: particle density – 340 kg/m³, strength – 1.6 MPa and water adsorption – 13% at firing temperature of 850 °C. Expanded zeolite with alkali content is a material of glass–ceramic composition with amorphous part of 38.6% and crystalline part of 61.4% that gives higher strength in comparison with sponge glass.     

Beam test on bond behavior between high-grade rebar and high-strength concrete after elevated temperatures

In this paper, post-heating bond behavior between high-grade rebar and C80 high-strength concrete (hereafter, HSC) is studied. The high-grade rebar is HRBF500 fine grained steel with a yield strength of 500 MPa and the concrete grade C80 denotes compressive strength not lower than 80 MPa. First, the residual mechanical behavior of both high-grade rebar and HSC were tested after fire exposure. Second, the beam bond test was carried out to study the bond behavior between high-grade rebar and HSC after exposed heating at 200 °C, 400 °C, 500 °C and 600 °C, respectively. During the bond test, the influence of temperature, bond length, and some construction measurements on the bond–slip behavior were compared and evaluated. The investigation demonstrates that (1) the bond strength between high-grade rebar and HSC decreases while the peak slip increases with the elevated temperature, especially when the temperature exceeds 400 °C and (2) the confinement effect of steel wire mesh can help to improve rebar׳s bond behavior. Third, the bond–slip model between high-grade rebar and HSC for post-heating is proposed.     

Temperature effects on mechanical behaviour of engineered stones

In this research, three types of artificial or engineered stones were compared against two types of natural stones (a limestone and a granite) in what concerns to temperature, thermal ageing and thermal shock effects on flexural strength and Young’s modulus. Temperatures of the thermal treatments, in the range from 20 to 200 °C, were intentionally chosen to simulate some practical applications of this kind of materials, for example, when they are used as kitchen tops. The results reveal the different characteristics of the materials. When tested at temperatures up to 100 °C, engineered stones show much higher values of flexural strength compared to the natural stones; and when tested at ambient temperature after being submitted to rapid cooling (thermal shock) from 200 °C down to 20 °C, engineered stones continue to show higher values of flexural strength compared to the natural stones. For the temperature range from 20 to 200 °C, thermal shock and thermal ageing effects on Young’s modulus are not very pronounced. Young’s modulus (E) of each of the materials was determined at ambient temperature, and the engineered stones keep almost the same value of E after thermal ageing or thermal shock up to 160 °C.