April 2007 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was edited by Executive Editor Harry Hutchinson.

Technology Focus part 2:
Fluid Handling
and Fluid Power

Cooled by the Sun

When someone mentions solar-powered air conditioning, laymen—and perhaps some technical people, too—may think first of photovoltaic panels generating electricity for a box in the window. Or maybe lots of panels powering a central-air system.

With an efficiency of about 15 percent in converting sunlight into electricity, it would take quite an array of panels to run the cooling system for a five-story office building or a dry-goods store. Unlike a solar collector, for example, which turns about 40 percent of sunlight into heat.

That's why a group of energy consultants have looked into the feasibility of cooling building space by combining a solar collector with an absorption chiller. Instead of converting the solar flux into electricity, the system will use the sun's energy to heat the absorption chiller. The heat can also be used for a building's hot water supply. It's not a brand-new idea, but there are only a few systems of the sort installed anywhere in the world. One is at the Audubon Society's Nature Center in Los Angeles.

The prospect of collecting sunlight to run a chiller is looking good to several independent researchers.

The consultants say that, although a solar-thermal absorption chiller costs much more to install than a conventional cooling system does, it may make economic sense for commercial installations, at least in some parts of the United States. According to the group's calculations, payback for capital outlay could be reached in about eight years in some cities in the American Southwest.

The consultants, representatives of Sentech Inc. in Bethesda, Md., have written a paper in which they say that rising natural gas prices, an investment tax credit under the Energy Policy Act of 2005, and recent technological advances, particularly in solar thermal collectors, are combining to make the system feasible.

There is also a green incentive. A solar-powered absorption chiller system would use very little electricity—probably only that needed to run a few internal pumps and external air-circulation fans—and so would take a load off the grid and reduce (or at least not add to) power plant emissions. The cooling system, moreover, contains no fluorocarbons, which can leak into the atmosphere and have been deemed harmful to the Earth's protective ozone layer. The fluids involved are solutions consisting chiefly of water.

According to Sentech, the main parts of the system are an array of solar collectors and an absorption chiller. Douglas Hinrichs, clean energy project manager at Sentech who was one of the authors of the paper, said most of the expense of installation is in the solar array. The economic calculations of the paper include a 30 percent investment tax credit under the federal Energy Policy Act.

The scenario put forward by the Sentech paper assumes a solar-thermal chiller setup supporting much of the cooling load for a building in the Southwest. The building would have a conventional electric-powered cooling system as a backup, which would be used part of the time to supplement the solar-powered chiller. The solar system would operate at peak output at the time when cooling and electricity demands are greatest and most expensive—that is, when the sun is bearing down on a roof.

The group considered hypothetical systems that would provide interior cooling and water heating for five-story buildings in San Diego and Albuquerque, each with 20,000 square feet of roof space. Both models allowed for an installed cost of $326,814 for the solar-thermal chiller system. In Albuquerque, the calculated annual cost saving for electricity was more than $21,000 and for water heating more than $20,000, for a payback period of 7.9 years. Annual savings in the San Diego model exceeded $17,000 for electricity and $25,000 for hot water, for a payback of 7.6 years.

In a project unrelated to the DOE's research, Carnegie Mellon University in Pittsburgh is setting up just such a system in a building called the Robert L. Preger Intelligent Workplace, which houses a research entity known as the Center for Building Performance and Diagnostics. According to David Archer, a faculty member who is one of the center's researchers, the system has a cooling potential of 16 kW for a space of about 600 square meters. The system is currently being commissioned for use under the supervision of Ming Qu, a Ph.D. graduate student.

The absorption chiller at the university begins with water under pressure low enough that it will evaporate at 4¡C. That would be a pressure of less than 1 kilopascal. A standard atmosphere is about 101 kPa. As it evaporates at the low temperature, the water absorbs heat. It takes heat from a second, closed system of water, which circulates to cool the air in the building.

The chiller, the solar collector, and a control system were donated to the university by a Chinese manufacturer, Broad Air Conditioning Co.

The solar-powered cooling setup is part of a larger system that will integrate biodiesel-fueled electric generators so the Center for Building Performance and Diagnostics can study their effectiveness year-round, not only in cooling, but also in heating and ventilation, Archer said. It is the purpose of the Intelligent Workplace, which is under Carnegie Mellon's architecture department, to research and demonstrate advancements in building design.

Grease Where It Belongs
by Peter Easton

Whether bearings, or other components, require regular lubrication or have the lubrication sealed in at the factory, the objective is the same: to make certain that the lubricant reaches its proper destination.

Now, a Swedish company located in Åtvidaberg, 200 kilometers south of Stockholm, has come up with a way to solve the problem of knowing where the lubrication is going.

The LubeMon, which comes in aluminum or steel, can monitor grease at a few key points or cover a whole lubrication system.

Assalub AB, a company with 40 employees, has a monitoring system known as the LubeMon. It is composed of one or several accurate grease meters that are installed directly on the grease points. The meters are connected to a control unit that monitors the system continuously. The control unit can monitor up to 10 greasing points, and works with any type of automatic lubrication system. It also operates on manually greased points. It can be used to monitor a few vital points or an entire lubrication system.

"The LubeMon is our newest product, and we only have a few systems running so far," Assalub managing director Pär-Olof Funck said. "We are about to install one system with almost 200 [greasing] points for a paper mill in Sweden," he added.

For larger systems, the grease meters are connected over a data bus to a computer that offers advanced statistical and logging functions. Meters also can be monitored by the programmable logic controller of the lubricated equipment.

The meter comes in two versions, aluminum or acid-proof steel. The aluminum unit weighs 4 pounds, while the steel one weighs 10.