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