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Two Novel Student-Designed Solar Thermal Pumps and a Proposed Steam-Driven Design that Operates Below 100C Abstract

Two student-designed solar thermal pumps are described. One of them uses water as a working fluid, but uses air to lift water from a well. It features a transparent boiler. The other pump uses an inverted water column to lower the pressure in the boiler, reducing the maximum temperature required during operation. This feature reduces demands on the solar collector. An improved design is proposed in which the working fluid is water boiled well below 100 C. It should be capable of lifting water to heights of a few meters, while allowing the effective use of very simple solar collectors.

Introduction

Solar thermal pumps are of interest as 'appropriate technology' because they can be unusually simple, low-cost devices suitable for undeveloped areas. Numerous designs have been proposed and demonstrated1,2. One problem faced by most designs is the need for a working fluid that operates at the low temperatures achievable with simple solar collectors. Two broad approaches have been taken to this problem: Either use water, and design a collector capable of reaching some temperature above 100C, or use some other working fluid that boils at lower temperatures.

Water is the preferred working fluid because it is readily available and non-toxic. Because steam pressure is used in many pump designs to lift water from a well, the pressure of the steam must be above atmospheric, and that implies a boiling point above 100 C. Although this is achievable, it does require some sophistication in solar collector design. Often reflectors must be oriented and used to focus solar energy, or sophisticated flat plate collectors such as the Winston type are needed, but even the best flat plate collectors may not perform well in cold environments. A typical heating curve for water in a crude flat plate collector is shown in Figure 1. The time constant can easily be 10-15 minutes. Heating cycle time can be excessive when the maximum temperature the collector reaches is barely above the boiling point, and most simple collectors fall in this category.

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Post, A. (2006, June), Two Novel Student Designed Solar Thermal Pumps And A Proposed Steam Driven Design That Operates Below 100 C Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--1087