Annual Heat Loss Research Articles

Optimizing PCM-integrated walls for potential energy savings in U.S. Buildings

Buildings in the United States account for nearly half of total U.S. energy use. The energy used for space conditioning can be reduced by utilizing thermal energy storage, such as phase change materials (PCMs), into building envelopes; however, the energy savings of PCM-integrated building envelopes reported in the literature vary widely. In the absence of established guidelines, thermophysical requirements of an optimal PCM, its method of application into the building envelope, and the corresponding energy savings under various climates remain unknown. In this study, we perform an extensive numerical investigation on the integration of PCM into building walls to establish the key conditions required for effective utilization of PCM in reducing heat gains in the cooling season and heat losses in the heating season. We also determine the optimal transition temperature, optimal PCM location in the wall, and the energy-saving potential of the PCM-integrated building walls in five U.S. cities located in different International Energy Conservation Code climate zones. Results show that employing PCMs in building walls does not always lead to an improvement; in fact, incorrect applications of PCMs can substantially increase energy use in the buildings. In the climates we studied, PCMs were found effective in reducing heat gains during the cooling season while mostly ineffective in managing heat losses during heating season. Depending on the climate, optimized PCMs in U.S. building walls can provide reduction in the annual heat gain in the range of 3.5%–47.2% and the annual heat loss in the range of −2.8%–8.3%. Future consideration of buildings with substantial solar gains in winter may lead to more reduction in heat losses by PCMs.

EFFECT OF APPLIED INTERIOR THERMAL INSULATION SYSTEMS ON THE ENERGY PERFORMANCE OF A HISTORICAL/CONTEMPORARY MASONRY

The paper is aimed at the investigation of the effect of applied internal thermal insulation system on the energy performance of historical and contemporary masonry. For that reason, sandstone masonry and ceramic brick masonry were selected as representative examples and their energy performance was analyzed using hygrothermal simulations in two states. First, each wall was simulated without being thermally insulated to obtain reference values of energy performance. Then, the walls were thermally insulated – sandstone masonry with mineral wool and ceramic brick masonry with wood fiber insulation – and new performance after wall retrofitting was quantified. All simulations are performed for two different locations to analyze the effect of boundary conditions as well. The paper demonstrates how the computational simulation using advanced moisture-dependent material parameters can be utilized for accurate assessment of thermal and energy performance of building envelopes under dynamic conditions, which is often omitted by national standards or black-box simulation tools. The results clearly indicate that application of thermal insulation on the interior side can significantly contribute to the reduction of annual heat losses varying from 66.7% to 87.2% depending on the material of thermal insulation and the location of the building.

Integration of solar latent heat storage towards optimal small-scale combined heat and power generation by Organic Rankine Cycle

Abstract Thermal energy and distributed electricity demand are continuously increased in areas poorly served by a centralized power grid. In many cases, the deployment of the electricity grid is not economically feasible. Small-scale Organic Rankine Cycle (ORC) appears as a promising technology that can be operated by solar energy, providing combined heat and power (CHP) generation. Additionally, thermal energy storage can ensure stable and continuous operation in case of scarce thermal energy availability. This paper evaluates the potential application of latent heat storage to enhance solar ORC performance at operating temperatures between 80 °C and 140 °C, aiming at improving the efficiency and capacity of ORC for low-cost non-concentrating solar-thermal collectors. Three thermal energy storage scenarios are considered. Scenario 1 and 2 consist of reference cases based on a solar ORC system integrated with a conventional hot water tank and a pressurised water tank. Scenario 3 implements a storage unit based on a phase change material. The simulation was carried out through models developed in TRNSYS for solar energy balance and ASPEN for ORC system performance. The results show that solar latent heat storage tank can provide 54% of useful collector gains with a higher and narrower temperature range in the evaporator, increasing the annual thermal energy capacity by 19%, reducing annual heat losses by 66% and decreasing the investment cost by 50% in comparison with a pressurised water tank. It also allows increasing the efficiency of ORC cycle by approximately 18% (from 8.9% to 10.5%) with a higher net generated power than a conventional water tank integration, scaled up from 498 W to 1628 W. These results highlight the potential benefits that latent heat integration provides to improve the low-cost solar ORC performance for powering electricity and thermal energy supply.

Energy conservation using new structured-core and transparent vacuum insulation panels: Numerical simulation with experimental validation

The rate of heat gain or heat loss from the windows of existing buildings represents a large portion of building energy consumption in harsh hot or cold regions, respectively. Therefore, several thermal insulation technologies have been applied in new buildings. However, these technologies are difficult to implement in existing buildings. Therefore, this study proposes a new, low-cost insulation method using slim, transparent panels with structured cores, for the windows of existing buildings. To do this, five new distinctdesigns of vacuum insulation panels (VIPs) are proposed to retrofit insulation for the windows of existing buildings. The VIPs comprise a hollow-frame structured-core material encapsulated in a transparent multi-layered polymeric envelope. The effective thermal conductivity of VIPs with different spacers, namely, peek, modified peek, mesh, silica aerogel, and frame, are evaluated at different pressure levels. The spacers are 3D-printed and experimentally-examined. A 3D thermal model is developed and validated using the experimental results of the present work and results from the literature. First, the influences of spacer structure and vacuum pressure on the centre-of-panel thermal conductivity, light transparency, and VIP production costs are evaluated. Second, three different trial manufacturing methods for these VIPs are proposed and compared. Finally, the annual building heat gain and heat loss in two different harsh hot and cold regions, respectively, in Japan are estimated while applying these new proposed VIP designs to the existing windows. The results indicate that VIPs with frame and mesh spacers accomplish better insulation performance, with a centre-of-panel thermal conductivity of 7 × 10−3 W/m K at a pressure of 1 Pa. Further, the VIP with the peek spacer accomplishes the highest light transparency (0.88). Furthermore, using a frame-type VIP with a total thickness of 3 mm attached to an existing window as a curtain decreases the space heat loss by approximately 69.5%, whereas the light transparency decreases to 75%. In that regard, using a frame-type VIP attached to 3 mm-glass windows decreases window insulation costs by 72% compared with vacuum glazing thermal insulation.

Heat Balance in the Sharm Obhur and Exchange with the Red Sea

A comprehensive understanding of the balance and exchange of heat is vital to explore the interaction between atmosphere and ocean. Sharm Obhur is one of the most important lagoons along the eastern coast of the Red Sea. In situ observations of current speed and direction, temperature, and salinity along with near surface meteorological parameters are used to investigate monthly variability of heat balance in the Sharm Obhur and the exchange with the Red Sea. The net heat flux in the Sharm shows a notable seasonality with an annual heat loss of 49 W m−2. The heat loss in the region peaked during December while maximum heat gain noticed during August. The entrance of the Sharm is well mixed during winter, while it is stratified by 2–3 °C during summer. Heat exchange between the Sharm and the Red Sea shows significant seasonality associated with the velocity of spring and neap flows. Interestingly, the annual net heat gain of 49.9 W m−2 noticed from the heat exchange is well compensated by the net surface heat loss of 49 W m−2.

The cold accumulative effect of expressway embankment with a combined cooling measure in permafrost zones

The thermal performance of an experimentally built expressway embankment with a combined cooling measure at Beiluhe Basin in the Qinghai-Tibet Plateau was investigated based on long-term field monitoring. Six-year records of soil temperatures showed that the embankment cooled by a measure combining hollow concrete bricks and ventilation ducts had a significant cooling effect on the subgrade soil. Over the investigated time period, the permafrost table beneath the embankment moved upward to the natural ground surface, and the subgrade soil layers down to a depth of −15 m underwent a considerable cooling. Then, the long-term thermal performance of this kind of cooled embankment with different surface widths (13 and 26 m) is comparatively studied using numerical simulations. The simulated results show that both embankments perform well in cooling the subgrade soil. However, the annual heat loss of the subgrade soil beneath the wider cooled embankment is greater than that of the narrow ones. Via the wider cooled embankment, more cold accumulates in the subgrade soil after the embankment's construction, which we term as the “cold accumulative” effect. This cold accumulative effect can ensure the underlying permafrost thermal stability better in the context of climate warming and strength the long-term embankment stability.

Non-uniform temperature district heating system with decentralized heat storage units, a reliable solution for heat supply

In this work, the novel concept of non-uniform temperature district heating system is proposed and analyzed. This system mainly works on a low-temperature supply mode for space heating, while it goes to high-temperature mode for domestic hot water supply only 4 h a day. The system employs decentralized heat storage units to be charged during the high-temperature mode. In this way, the system operates based on a minimum rate of heat loss and there is no legionella risk due to thermal disinfection. The system is designed for a town in Brazil and a detailed thermodynamic model of the system is presented. The performance of this system is compared with other popular district heating schemes. With a total annual heat loss of 64 MWh, the proposed system outperforms the third generation technology in which the loss is almost double. As such, although the heat loss of the ultralow-temperature system is 28% lower (i.e. around 50 MWh), the non-uniform temperature system is still preferred to this case as well. This is because not only the proposed case supplies both of the hot water and space heating demands of the buildings, but also it does not need any further actions for legionella prevention.

The impact of snow and soil freezing for commonly used foundation types in a subarctic climate

Heat losses from a building foundation are affected by both the surrounding conditions and the surrounding soil properties. These include many factors that complicate the analysis of heat loss, such as thermal storage, snow and soil freezing. The effect of snow and soil freezing was studied with a 3D simulation model in a subarctic climate.The heat losses from the most commonly used foundation types in Sweden were studied. This paper shows that it is possible to achieve a good thermal estimation of the air temperatures in a crawl space, with an average difference of 0.4 °C compared with the validation data over a year. Snow and soil freezing reduce the annual heat losses through the different foundation types by 7–10% and the maximum heat loss rate by 13–25%. In order to describe the heat transfer correctly, snow must be included in the calculations, while soil freezing has only a minor impact. The 3D model implemented in this study shows a significant impact on the soil temperatures when these parameters are included.For a subarctic climate, the commonly used calculation methods based on the European standard ISO 13370 are not thorough enough to calculate the heat transfer through a foundation accurately.

Thermal Performance of Lightweight Aggregate Concrete Containing Expanded Shale Aggregates

Achieving energy efficiency of building in north part of Kazakhstan is very critical due to the large temperature difference during long harsh and severe winter and short hot summer seasons. Energy efficient building shows significant savings to homeowners including costs reduction from energy, water, waste, and lower operations and maintenance costs. In terms of building materials, lightweight aggregate concrete (LWAC) due to its thermal properties is often used to maintain thermal comfort levels in buildings and to reduce building energy consumption. In this paper, the potential of LWAC to improve the energy performance of building was assessed for LWAC with three different mixture proportions and a normal weight concrete (NWC) for comparison purpose. The energy saving effect of LWAC was simulated using OpenStudio software tools with an EnergyPlus engine. Moreover, annual heat loss and amount of heat transfer of construction wall of building were calculated. Results showed that LWAC can improve the energy efficiency of building and thus the use of LWAC can be a good alternative to the traditional NWC.

Heat losses in power boilers caused by thermal bridges

In this article the analysis of heat losses caused by thermal bridges that occur in the steam boiler OP-140 is presented. Identification of these bridges were conducted with use of thermographic camera. Heat losses were evaluated based on methodology of VDI 4610 standard, but instead of its simplified equations, criterial equations based on Nusselt number were used. Obtained values of annual heat losses and heat flux density corresponding to the fully insulated boiler surfaces were compared to heat losses generated by thermal bridges located in the same areas. The emphasis is put on the role of industrial insulation in heat losses reduction.

Decentralized substations for low-temperature district heating with no Legionella risk, and low return temperatures

To improve energy efficiency and give more access to renewable energy sources, low-temperature district heating (LTDH) is a promising concept to be realized in the future. However, concern about Legionella proliferation restricts applying low-temperature district heating in conventional systems with domestic hot water (DHW) circulation. In this study, a system with decentralized substations was analysed as a solution to this problem. Furthermore, a modification for the decentralized substation system were proposed in order to reduce the average return temperature. Models of conventional system with medium-temperature district heating, decentralized substation system with LTDH, and innovative decentralized substation system with LTDH were built based on the information of a case building. The annual distribution heat loss and the operating costs of the three scenarios were calculated and compared. From the results, realizing LTDH by the decentralized substation unit, 30% of the annual distribution heat loss inside the building can be saved compared to a conventional system with medium-temperature district heating. Replacing the bypass pipe with an in-line supply pipe and a heat pump, the innovative decentralized substation system can reduce distribution heat loss by 39% compared to the conventional system and by 12% compared to the normal decentralized substation system with bypass.

The Influence of Central Regulation Methods upon Annual Heat Loss in Heating Network

For directly buried hot water heating network, heat loss per unit length can be calculated by the thermal theory of heating network, then the calculating method of annual heat loss would be deduced. By comparing the heat loss of three different regulation schemes, it is detected that different regulation scheme has different supply and return water temperature, resulting in different heat loss. The heat loss of variable flow regulation of equivalent temperature difference is the largest, while the heat loss of constant flow regulation is the smallest, which has significant guiding to the operation of district heating system. Finally, based on the calculation of the annual heat loss of the heating network in Jiu Tai, Ji Lin Province, it is found that the distribution heat losses take up 2.4%~2.7% of the total supplying heat, which are equivalent to the heat consumptions of the heating area from 30.7×10 4 m 2 to 34.4×10 4 m 2 . Therefore reducing the heat losses of large scale heating networks is imminent.

Pipe Internal Recirculation in Storage Connections – An Unseen Efficiency Barrier

Abstract Basically, pipe internal recirculation (PIR) at storage connections is a known phenomenon. However, it is not sufficiently considered by storage manufacturers and installers. There is still a lack of awareness and quantification of the PIR effect in typical installations and practice-oriented solutions. Within this paper, the final results of a research project aiming at the detailed qualitative description and quantification of the effect including extrapolation of the results regarding the PIR impact on storage heat losses are presented. This includes the results regarding the influence of the pipe's material (copper, stainless steel, plastic), diameter, insulation and connection type (direct to storage, indirect via immersed or external heat exchanger) on PIR including their effects on the overall heat losses of ready installed storage tanks. Derived from generalized measurements, a calculation method has been developed, which enables to determine the annual heat losses caused by PIR in domestic hot water storages using dynamic system simulations (TRNSYS). In conclusion, different measures for the reduction of PIR induced heat losses and their effectiveness may be presented.

Observations of Water Mass Transformation and Eddies in the Lofoten Basin of the Nordic Seas

AbstractThe Lofoten basin of the Nordic Seas is recognized as a crucial component of the meridional overturning circulation in the North Atlantic because of the large horizontal extent of Atlantic Water and winter surface buoyancy loss. In this study, hydrographic and current measurements collected from a mooring deployed in the Lofoten basin from July 2010 to September 2012 are used to describe water mass transformation and the mesoscale eddy field. Winter mixed layer depths (MLDs) are observed to reach approximately 400 m, with larger MLDs and denser properties resulting from the colder 2010 winter. A heat budget of the upper water column requires lateral input, which balances the net annual heat loss of ~80 W m−2. The lateral flux is a result of mesoscale eddies, which dominate the velocity variability. Eddy velocities are enhanced in the upper 1000 m, with a barotropic component that reaches the bottom. Detailed examination of two eddies, from April and August 2012, highlights the variability of the eddy field and eddy properties. Temperature and salinity properties of the April eddy suggest that it originated from the slope current but was ventilated by surface fluxes. The properties within the eddy were similar to those of the mode water, indicating that convection within the eddies may make an important contribution to water mass transformation. A rough estimate of eddy flux per unit boundary current length suggests that fluxes in the Lofoten basin are larger than in the Labrador Sea because of the enhanced boundary current–interior density difference.

Determination of annual heat losses from heat and steam pipeline networks and economic analysis of their thermomodernisation

The paper presents a method of evaluation and selective thermomodernisation of overhead thermal pipeline networks. The expression “thermomodernisation” is used for determination of all those activities that deal with improvement of heat insulation features of the pipelines under consideration. The method is particularly useful for extensive and complex heat or steam pipelines. A novel method for the determination of annual heat losses from overhead pipelines into the environment has been developed in the work. The heat losses from the pipelines are generated during the whole year. The proposed method is based on the concept of one-off examination of the pipeline under consideration by means of a thermovision camera, performed in existing weather conditions. An example of an analysis has been carried out and results are presented for an existing industrial pipeline network. In this analysis the whole pipeline network was divided into segments characterised by identical technical features. To determine the annual heat loss, the operation of the considered pipeline during the whole year in different meteorological conditions was simulated numerically. Next, economic factors were calculated for each pipeline segment. Generally, the selection of line segments recommended for thermomodernisation was done on the basis of heat losses and SPBT (simple pay-back time) calculations.

Energy Efficiency Analysis of Internally and Externally Insulated Apartment Buildings

Apartment buildings are the most common type of residential buildings in Korea, where hot water heating pipes are installed in the floor structures. An internal insulation system (IIS) has been applied to the outside walls of most Korean apartment buildings, so there are many cases in which the layer of insulation is disconnected by structural components at the wall-slab joints. These joints become thermal bridges where heat transfer increases. An external insulation and finish system (EIFS) is a possible solution to this problem. In this study, the surface temperature distributions of actual apartment buildings with an IIS and an EIFS were investigated with an infrared thermal imaging camera. Annual heat losses and gains through the wall-slab joints with an IIS and an EIFS were calculated by three-dimensional transient heat transfer simulations in which hot water heating was excluded and included, respectively, in order to evaluate not only the heating and cooling loads, but also the heating efficiency when the building is actually heated. The results show that the amount of heat transfer through the wall-slab joints with an IIS is considerable, even though additional insulation is installed under the slab, and the EIFS significantly reduces the heating and cooling loads and improves the heating efficiency.

Persistent unstable atmospheric boundary layer enhances sensible and latent heat loss in a tropical great lake: Lake Tanganyika

Energy fluxes across the surface of lakes regulate heat storage and affect the water balance. Sensible and latent heat fluxes are affected by atmospheric stability, especially for large lakes. We examined the effect of atmospheric stability on the heat fluxes on seasonal time scales at Lake Tanganyika, East Africa, by estimating hourly sensible and latent heat fluxes and net radiation using thermistor chains and meteorological stations. The atmosphere was almost always unstable, in contrast to the atmosphere above North American Great Lakes which is unstable in winter and stable in summer. Persistent atmospheric instability resulted in a 13% and 18% increase in the annual mean heat loss by latent and sensible heat fluxes, respectively, relative to conditions of neutral stability. The persistent unstable atmosphere is caused by a higher water surface temperature compared with air temperature, which we argue is the case in general in (sub)tropical lakes. Low humidity further enhanced the frequency of unstable conditions and enhanced the exchange of heat and vapor from the lake to the atmosphere. The estimated heat fluxes were sensitive to the temporal scale of data inputs and to the local values of parameters such as air density. To our knowledge this is the first paper that demonstrates and quantifies the effect of atmospheric stability on latent and sensible heat fluxes from a lake on an annual basis, using data collected from the lake surface.

Precipitation rates and atmospheric heat transport during the Cenomanian greenhouse warming in North America: Estimates from a stable isotope mass-balance model

Stable isotope mass-balance modeling results of meteoric δ 18O values from the Cenomanian Stage of the Cretaceous Western Interior Basin (KWIB) suggest that precipitation and evaporation fluxes were greater than that of the present and significantly different from simulations of Albian KWIB paleohydrology. Sphaerosiderite meteoric δ 18O values have been compiled from the Lower Tuscaloosa Formation of southwestern Mississippi (25°N paleolatitude), The Dakota Formation Rose Creek Pit, Fairbury Nebraska (35°N) and the Dunvegan Formation of eastern British Columbia (55°N paleolatitude). These paleosol siderite δ 18O values define a paleolatitudinal gradient ranging from − 4.2‰ VPDB at 25°N to − 12.5‰ VPDB at 55°N. This trend is significantly steeper and more depleted than a modern theoretical siderite gradient (25°N: − 1.7‰; 65°N: − 5.6‰ VPDB ), and a Holocene meteoric calcite trend (27°N: − 3.6‰; 67°N: − 7.4‰ VPDB). The Cenomanian gradient is also comparatively steeper than the Albian trend determined for the KWIB in the mid- to high latitudes. The steep latitudinal trend in meteoric δ 18O values may be the result of increased precipitation and evaporation fluxes (amount effects) under a more vigorous greenhouse-world hydrologic cycle. A stable-isotope mass-balance model has been used to generate estimates of precipitation and evaporation fluxes and precipitation rates. Estimates of Cenomanian precipitation rates based upon the mass-balance modeling of the KWIB range from 1400 mm/yr at 25°N paleolatitude to 3600 mm/yr at 45°N paleolatitude. The precipitation–evaporation ( P– E) flux values were used to delineate zones of moisture surplus and moisture deficit. Comparisons between Cenomanian P– E and modern theoretical siderite, and Holocene calcite latitudinal trends shows an amplification of low-latitude moisture deficits between 5–25°N paleolatitude and moisture surpluses between 40–60°N paleolatitude. The low-latitude moisture deficits correlate with a mean annual average heat loss of 48 W/m 2 at 10°N paleolatitude (present, 8 W/m 2 at 15°N). The increased precipitation flux and moisture surplus in the mid-latitudes corresponds to a mean average annual heat gain of 180 W/m 2 at 50°N paleolatitude (present, 17 W/m 2 at 50°N). The Cenomanian low-latitude moisture deficit is similar to that of the Albian, however the mid-latitude (40–60°N) precipitation flux values and precipitation rates are significantly higher (Albian: 2200 mm/yr at 45°N; Cenomanian: 3600 mm/yr at 45°N). Furthermore, the heat transferred to the atmosphere via latent heat of condensation was approximately 10.6× that of the present at 50°N. The intensified hydrologic cycle of the mid-Cretaceous greenhouse warming may have played a significant role in the poleward transfer of heat and more equable global conditions. Paleoclimatological reconstructions from multiple time periods during the mid-Cretaceous will aid in a better understanding of the dynamics of the hydrologic cycle and latent heat flux during greenhouse world conditions.

DETERMINATION OF ANNUAL HEAT LOSS AND REQUIREMENT OF ENERGY IN A REİNFORCED CONCRETE BUILDING BY ARTIFICIAL NEURAL NETWORKS

In this study, annual heat loss and requirement of energy in building in third region have been determined by artificial neural network. In application, height, width, length of building and thickness of insulation material used building components have been considered. A backpropagation neural network has been preferred and the normalized data have been presented to network. Different values have been used for the training and test data set. The result obtained from the output of network has been compared with the TS 825 result and the suitability of the results have been discussed and it was seen that the results were satisfactory enough.

Investigation of embankment with temperature-controlled ventilation along the Qinghai–Tibet Railway

Abstract The temperature-controlled ventilated embankment (TCVE) is an improved engineering measure developed based on the duct-ventilated embankment (DVE). The improved cooling effect of the TCVE is a result of enhanced heat exchange through controlling air convection in the ventilated ducts of the DVE. The field observational data from a TCVE testing section at Beiluhe, about midway in the Qinghai–Tibet Railway permafrost zone, indicates that restricting the air convection in the ducts during warm season can reduce the embankment heat absorption in the embankment. The results also indicate that the temperature in the wells of the ducts of the TCVE was about 1.0 °C lower than the temperature in the walls of the ducts of DVE. Especially it was found that in the seasonal ground temperature-decreasing period, the temperature of the permafrost at a depth of 3.5 m below the base of the embankment in TCVE decreased faster than at the same depth below the DVE. Two years after the TCVE was implemented, the temperature at a depth of 3.5 m below the embankment base was found 0.45 °C lower than at the same location below the DVE. Thermal modeling of the embankments shows that the mean annual heat loss of a TCVE is about twice that with the DVE, which means a doubled cooling effect of TCVE over DVE if think in this way. In addition, the cooling period with a TCVE is about 40 days longer than with a DVE, which contributes to its cooling effects.