In this paper the effects of moisture on the heat transfer from two basic types of building foundations, a slab-on-grade and a basement, are examined. A two-dimensional finite element heat and moisture transfer program is used to show the effects of precipitation, soil type, foundation insulation, water table depth, and freezing on the heat transfer from the building foundation. Comparisons are made with a simple heat conduction model to illustrate the dependency of the soil thermal conductivity on moisture content.

A combination of high energy costs, uniform solar resource, and an active solar industry combine to make Hawaii a good location for cost effective applications of solar water heating. The non-freezing climate allows for simple solar water heating system designs. In the mild climate of Hawaii, solar water heating can displace a large fraction of a home’s electricity use since heating and cooling loads are small. In 1998, sixty-two solar water heaters were installed at Kiai Kai Hale US Coast Guard Housing Area in Honolulu, HI as a pilot project under a grant from the US DOE Federal Energy Management Program (FEMP). The systems are active, open loop systems with a single tank (electric water heater with the bottom element disabled). An assessment of these pilot units will help inform a Coast Guard decision regarding implementing solar water heating on the remaining 256 units in the housing area, and may be useful information for other government and utility programs. On 25 houses with solar water heating and 25 identical houses without solar, instruments were installed to measure on/off cycles of the electric water heaters and the tank outlet temperature. This paper describes the results the monitoring for a six week period From June 11 to July 25, 2002, with a statistical extrapolation to estimate annual savings. Demand savings are estimated at 1.62 kW/house, energy savings at 3,008 kWh/house/year, and annual cost savings per house is estimated at $380/year due to solar. For a system cost of $3,200 ($4,000 minus a $800 utility rebate) and a 25 year present worth factor of 17.1, the savings to investment ratio (SIR) is 2.03, so this solar water heating application is cost effective according to Federal regulation 10CFR436 (which requires SIR>1.0). The annual solar fraction is estimated at 74% and annual solar water heating system efficiency is estimated at 24%. This paper describes the statistical design of the survey; the measured load profiles; the energy, demand, and cost savings; and the observed condition of the systems. The paper includes a discussion of application of the International Performance Measurement and Verification Protocol (IPMVP) applied to renewable energy systems.

Freezing is an important thermal process with solar applications. The Phase Change Material (PCM) undergoes freezing process and the rate of freezing is influenced by natural convection in the melt if it is above the melting point. Experimental study was conducted on two PCMs namely Paraffin wax (m.p 63–65°C) and n-octadecane (m.p 27.7 °C). Steel and copper containers with insulation at both bottom and top by thermocol (1 cm thick) and acrylic plates (1 cm thick) are used to allow only radial heat flux. The PCMs were separately heated in a container to a known superheat and placed in an isothermal bath (± 1°C) containing the Heat Transfer Fluid (HTF). Water is used as HTF in this case. The temperature distributions in the PCM were measured using PT100 sensors with digital indicator to cover 10–16 points in radial and axial locations. In another separate set of experiments, the PCM under identical initial conditions of superheat is placed in the cylindrical metal container without any temperature sensors. Separating the frozen mass and unfrozen liquid at different time intervals and weighing, generate the frozen mass vs. time data following Sparrow et al (International Journal of Heat and Mass Transfer, 24, 273–284,1981). The range of parameters studied are given below: • Container L/D ratio: 0.6–5.4; • Initial Superheat of PCM: 5–35 °C; • Range of water temperature: 5–25 °C; • Volume of PCMs: 35–500 ml. From the experimental data of temperature distributions, frozen mass vs. time data were generated following El Dessouky et al (Journal of Solar Energy Engineering, Transactions of ASME, 121, 98–109, 1999), whose data pertains to melting outside tubes. The data of melt separation and weighing of n-octadecane and paraffin wax are compared with temperature-based data. A tentative correlation of entire data is presented.

Hybrid solar lighting (HSL) has been successfully demonstrated as a means of collecting sunlight and transferring it through optical fibers into a building. The collected solar energy is primarily intended for illumination purposes. However, this technology may have an application in solar water heating. For a traditional solar water heating system, energy is required to pump the water to the roof and collected solar energy is lost to the environment through the collector and plumbing. If such a system is to be used in climates where the temperature falls below freezing, complexity is added resulting in lower system efficiencies. If, rather than pumping water to the roof to absorb solar energy, the solar radiation is “piped” into the hot water store, a solar water heating system may be much less complex and potentially more efficient. HSL technology can be used to collect solar radiation and transport it through optical fibers into a hot water store. Since the water remains in the tank, it is not exposed to freezing temperatures and heat loss through plumbing. The efficiency of the system would not be dependent on the outside temperature or the temperature of the water as traditional systems are, but solely on the efficiency in which solar radiation is transferred into the water. This paper will outline the major advantages of using HSL technology for solar water heating over traditional systems. The approximate efficiencies of a flat-plate collector, 2-axis solar tracking collector, and a system using HSL technology are compared using F-Chart for locations in the Southwestern and Northeastern United States. It is shown that improvements in efficiency are obtained using HSL technology if the system is capable of collecting and transferring the visible and infrared spectrum of solar radiation.