Solar Engineering of Thermal Processes, 4th Edition

Chapter 10

System Thermal Calculations

In Chapters 6 through 9 we have developed mathematical models for two of the key components in solar energy systems: collectors and storage units. In this chapter we show how other components can be modeled and how the component models can be combined into system models. With information on the magnitude and time distribution of the system loads and the weather, it is possible to simultaneously solve the set of equations to estimate the thermal performance of a solar process over any time period. These estimates (simulations) are usually done numerically and provide information on the expected dynamic behavior of the system and long-term integrated performance.

The collector performance is a function of the temperature of the fluid entering the collector. This temperature, neglecting (for the moment) heat losses from the connecting pipes, is the same as the temperature in the exit portion of the storage unit. The outlet temperature from the collector becomes the inlet temperature to the storage unit. In these equations, time is the independent variable and the solution is in the form of temperature as a function of time. Meteorological data (radiation, temperature, and possibly other variables such as wind speed and humidity) are forcing functions that are applied hourly (or at other time steps) to obtain numerical solutions through time.

Once the temperatures are known, energy rates can be determined. It is then possible to integrate the ...