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Solar Heat Pipe Wall

Computer simulations were performed to compare the thermal performance of several conventional passive solar heating systems, including direct gain, concrete wall indirect gain and water wall indirect gain, with a novel heat pipe augmented passive solar system (Fig. 1). Heat pipes provide one-way heat transfer into the building during sunny days,

chematic of the solar heat pipe wall. The sun passes through the glass cover and strikes the absorber, which heats the evaporator end of the heat pipe. Heat is transfered through the insulated wall of the house by the heat pipe to the thermal storage tanks inside the house. Heat is delivered by natural convection from the tanks to the house.                             Passive Solar Test Facility

Figure 1. Left: Schematic of the solar heat pipe system. Right: Two prototypes installed in the Passive Solar Test Facility.


with little heat loss out of thebuilding during nighttime and cloudy days. In the  evaporator end of the heat pipe, which is attached a an absorber plate, a heat transfer fluid is boiled  and the resulting vapor travels up to the condenser end (Fig. 2). There the fluid condenses, transferring its energy to the interior of the building.


Schematic of a heat pipe showing the two-phase flow of heat transfer fluid inside. Heat added at the lower evaporator end boils the fluid and the vapor rises to the upper condenser end, where it releases energy and condenses. The condensate falls by gravity back to the evaporator end, completing the cycle.


Figure 2. Schematic of a heat pipe.


Simulations were performed for Louisville, KY, Albuquerque, NM, Rock Springs, WY and Madison, WI. Results showed that the direct gain system performed well in cool and sunny Albuquerque, but produced a net loss in cold and cloudy Madison (Fig. 3). The indirect gain systems performed better than direct gain in all locations but Albuquerque. The water wall system provided greater gains than the concrete wall in all climates. The heat pipe system performed significantly better than all other systems in all climates. The heat pipe system was especially advantageous in cold and cloudy Madison. In Louisville, the solar fractions were 22.4%, 30.8%, 38.8% and 50.7% for direct gain, concrete wall indirect gain, water wall indirect gain and heat pipe systems, respectively. These performance values were better than those in Rock Springs, which is sunnier but colder, and considerably better than Madison, which is colder but only slightly cloudier. Though Louisville receives less solar radiation during the winter than Albuquerque and Rock Springs, it remains a favorable climate for solar heating because of its mild winter temperatures.

Bar graph comparing the annual solar fraction of the solar heat pipe system to direct gain and indirect gain concrete and water walls in four climates - Albuquerque, NM, Louisville, KY, Rock Springs, WY, and Madison WI. The heat pipe wall performed better than these conventional passive solar systems in all four climates.

Figure 3. Comparison of the thermal performance of several passive solar heating systems.

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