Reducing unwanted thermal gains during the cooling season for a solar heat pipe system

Comparative Performance of Two Prototypes of a Passive Solar Heat Pipe System

Volume 2: Economic, Environmental, and Policy Aspects of Alternate Energy; Fuels and Infrastructure, Biofuels and Energy Storage; High Performance Buildings; Solar Buildings, Including Solar Climate Control/Heating/Cooling; Sustainable Cities and Communities, Including Transportation; Thermofluid Analysis of Energy Systems, Including Exergy and Thermoeconomics ◽

10.1115/es2014-6346 ◽

2014 ◽

Author(s):

Brian S. Robinson ◽

M. Keith Sharp

Keyword(s):

Heat Pipe ◽

Test Facility ◽

Reverse Direction ◽

Storage Tanks ◽

New Model ◽

Solar Heat ◽

Pipe System ◽

Evaporator Section ◽

Passive Solar ◽

New System

Thermal performance of an improved passive solar heat pipe system was directly compared to that of a previous prototype. Simulated and experimental results for the first prototype established baseline performance. Subsequently, potential improvements were simulated, and a second prototype was built and tested along side the first. The system uses heat pipes for high rates of heat transfer into the building, and limited losses in the reverse direction. The evaporator section of each heat pipe is attached to a glass-covered absorber on the outside of a south wall, and the slightly elevated condenser section is either immersed in water in a thermal storage tank or exposed to air in the room. Two-phase flow occurs in the heat pipe only when the evaporator is warmer than the condenser, creating a thermal diode effect. Computer simulations showed that system performance could be improved by using thicker insulation between the absorber and the storage tanks, and by switching from a copper to a rubber adiabatic section, which both reduced heat losses to ambient from the storage tanks. Early morning heating was improved by exposing one of five condensers directly to room air, which also improved overall system efficiency. A copper solar absorber soldered to the copper evaporator section improved heat conduction compared to the previous aluminum absorber bonded to the copper evaporator. Together these modifications improved simulated annual solar fraction by 20.8%. The new prototype incorporating these changes was tested along side the previous prototype in a two-room passive solar test facility during January through February of 2013. Temperatures were monitored with thermocouples at multiple locations throughout the systems, in each room and outdoors. Insolation was measured by four pyranometers attached to the building. Results showed that the design modifications implemented for the new model increased thermal gains to storage and to the room, and decreased thermal losses to ambient. The load-to-collector ratio for the experiments was 2.7 times lower than for the simulations, which decreased the potential for experimental improvements compared to the simulated improvements. However, average daily peak efficiency for the new system was 85.0%, compared to 80.7% for the previous system. Furthermore, the average storage temperature over the entire testing period for the new model was 13.4% higher than that of the previous model, while the average room temperature over the same period was 24.6% greater for the new system.

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Solar Load Ratio Parameters for a Passive Solar Heat Pipe System

Volume 1: Advances in Solar Buildings and Conservation; Climate Control and the Environment; Alternate Fuels and Infrastructure; ARPA-E; Combined Energy Cycles, CHP, CCHP, and Smart Grids; Concentrating Solar Power; Economic, Environmental, and Policy Aspects of Alternate Energy; Geothermal Energy, Harvesting, Ocean Energy and Other Emerging Technologies; Hydrogen Energy Technologies; Low/Zero Emission Power Plants and Carbon Sequestration; Micro and Nano Technology Applications and Materials ◽

10.1115/es2015-49136 ◽

2015 ◽

Author(s):

Logan S. Poteat ◽

M. Keith Sharp

Keyword(s):

Heat Pipe ◽

Load Ratio ◽

Building Design ◽

Weather Data ◽

Prediction Algorithm ◽

Solar Heat ◽

Pipe System ◽

Thermal Network ◽

Pipe Systems ◽

Passive Solar

The Solar Load Ratio (SLR) method is a performance prediction algorithm for passive solar space heating systems developed at Los Alamos National Laboratory. Based on curve fits of detailed thermal simulations of buildings, the algorithm provides fast estimation of monthly solar savings fraction for direct gain, indirect gain (water wall and concrete wall) and sunspace systems of a range of designs. Parameters are not available for passive solar heat pipe systems, which are of the isolated gain type. While modern computers have increased the speed with which detailed simulations can be performed, the quick estimates generated by the SLR method are still useful for early building design comparisons and for educational purposes. With this in mind, the objective of this project was to develop SLR predictions for heat pipe systems, which use heat pipes for one-way transport of heat into the building. A previous thermal network was used to simulate the heat pipe system with Typical Meteorological Year (TMY3) weather data for 13 locations across the US, representing ranges of winter temperature and available sunshine. A range of (nonsolar) load-to-collector ratio LCR = 1–15 W/m2K was tested for each location. The thermal network, along with TMY3 data, provided monthly-average-daily absorbed solar radiation and building load to calculate SLR. Losses from the solar aperture in a heat pipe system are very low compared to conventional passive solar systems, thus the load-to-collector ratio of the solar aperture was neglected in these preliminary calculations. Likewise, nighttime insulation is unnecessary for a heat pipe system, and was not considered. An optimization routine was used to determine an exponential fit (the heart of the SLR method) to simulated monthly solar savings fraction (SSF) across all locations and LCR values. Accuracy of SSF predicted by SLR compared to the thermal network results was evaluated. The largest errors (up to 50%) occurred for months with small heating loads (< 80 K days), which inflated SSF. Limiting the optimization to the heating season (October to March), reduced the error in SSF to an average of 4.24% and a standard deviation of 5.87%. These results expand the applications of the SLR method to heat pipe systems, and allow building designers to use this method to estimate the thermal benefits of heat pipe systems along with conventional direct gain, indirect gain and sunspace systems.

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Technical-Economic Analysis of Steam Double Effect Absorption Chiller-Heaters Equipped with Solar Heat Pipe System

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.465-466.327 ◽

2013 ◽

Vol 465-466 ◽

pp. 327-334

Author(s):

Morteza Khalaji Assadi ◽

Hamidreza Akhavan Armaki ◽

Mahmoud Zendeh Del

Keyword(s):

Economic Analysis ◽

Heat Pipe ◽

Cooling System ◽

Double Effect ◽

Coefficient Of Performance ◽

Absorption Chiller ◽

Solar Heat ◽

Pipe System ◽

Break Even Point ◽

Solar Cooling System

The aim of this research is to indicate a steam double effect chiller-heater equipped with solar heat pipe in a certain space with the area of 975 m2 located in Tehran, which is currently equipped with a direct-fired single effect absorption chiller-heater. Thereafter , the most obvious differences of the two chiller-heater systems are compared: the solar cooling system increases coefficient of performance as high as 0.54, decreases CO2 dissemination by 829 tons in each year, and reduces energy consumption by 1552.42 MWh/Yr. Economic analysis of the two systems using break-even-point showed that the use of solar system is attractive in applications that have excess thermal energy, and the conversion of this energy to higher value energy markets is to be more profitable than absorption gas-fired system from 13th year on. Keywords: Technical-economic analysis, energy optimization, solar chiller, absorption chiller-heater, solar heat pipe.

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