Simplifying Solar Thermal: Page 2 of 3

Solar Water Heating Tank
Solar Water Heating Tank
A pump station manufactured by Oventrop.
A pump station manufactured by Oventrop.
The Solarnetix pump station
The Solarnetix pump station. The front insulation is removed to show the components.
EnerWorks integrated system
EnerWorks manufactures integrated pump, control, heat exchanger, and storage tank systems.
Heat exchanger, pump, and control package from Oventrop
Heat exchanger, pump, and control package from Oventrop.
Solar Water Heating Tank
A pump station manufactured by Oventrop.
The Solarnetix pump station
EnerWorks integrated system
Heat exchanger, pump, and control package from Oventrop

Component Packages

To ease the burden of sourcing all of the different components required for an SHW installation, several companies offer packages of unassembled components. This eliminates some sourcing headaches but doesn’t necessarily address the range of complex engineering issues that installers face. For example, as a situation dictates, you may need a larger heat exchanger or a different pump capacity. And, once you have addressed the design issues, you still have to assemble all of the individual components. A typical component package contains:

  • Solar collectors
  • Storage tank with heat exchanger
  • Differential temperature controller
  • Fluid circulation components
  • Circulation pumps
  • Installation manual
  • Mounting hardware

While component packages reduce the time required to source individual system parts from various manufacturers or suppliers, unassembled packages rarely reduce the installation time. With all of the individual components in hand, it will still take an experienced crew of two to three people two full days to assemble and install a system. Knowledgeable do-it-yourselfers will probably require twice that time. Unlike pros, they won’t have a van or truck stocked with extra fittings, and will usually have to make multiple trips to the hardware store for elbows, couplings, and the like that aren’t included in packaged systems but are necessary for site-specific installation. Then comes dry-fitting the pieces, making connections, pressure checking, repairing any leaks, rechecking pressure, and then starting up the system.

While unassembled component packages give the system installer a leg up, solutions with greater pre-integration and preassembly are available that can significantly reduce installation time and complexity.

Pump Stations

Pump stations were relatively common in the U.S. solar thermal industry in the 1980s, but virtually disappeared until several years ago, when companies in Europe began offering integrated pump packages (also referred to as circulation stations) for use with specialty heat-exchange tanks. This approach was a giant step toward reducing the complexity of an installation. With a variety of insulated, pre-plumbed components, these systems reduce the time required for the sourcing, connecting, and pressure-checking steps of an installation.

Pump stations do reduce installation time and complexity, but they don’t cover all of the bases. Some stations include controls; others do not. Most are designed to integrate with specialized storage tanks with an integral heat exchanger. The cost of these specialty tanks alone can run $600 more (plus shipping) than a standard, locally purchased hot water tank.

Pre-Packaged Pump & Heat Exchangers

Pre-packaged systems—which integrate heat exchangers into the pump packages—work with standard hot water tanks. They include heat exchangers, pumps, isolation valves, controls, system drains, pressure relief valves, fill valves, pressure gauges, and check valves, all in a single package. Many are compact in design, which enables easy installation in relatively tight places. Each comes with virtually all of the special plumbing components pre-assembled to facilitate on-site installation.

While all of the available integrated systems work, the buyer still needs to pay careful attention to their suitability for a particular situation, including cost. Every system, integrated or not, has to address the questions of flow through the collectors and the transfer of heat to the storage tank. For example, some systems rely on thermosyphoning, convection that circulates liquid without requiring a pump. In these systems, although the cost and complexity are reduced, the slower flow reduces overall system performance. Different manufacturers also use different-sized heat exchangers. Systems that use smaller-capacity heat exchangers will be cheaper, but those that use larger exchangers will allow pumps to run less for the same amount of heat exchange. The size and type of pumps also influence system performance and cost—smaller pumps keep system costs lower but also reduce the flow and efficiency of the heat transfer. Cast-iron pumps are less expensive, but corrode sooner than bronze pumps when subjected to degraded glycol or dissolved oxygen that is present in the heat-transfer fluid.

Comments (2)

Tom M's picture

to reduce cost and maintenence, use off the shelf plumbing components. Prefabricated systems are often hard to work on and present problems when replacement parts are needed. Keep it simple. Often these boxed components put servicable parts in the wrong place in a system. Drains and fillers should be located at the bottom of the loop, temperature and pressure gages are not located where they should be and pump connections are specialized not to mention the poor quality of piping and valves usually associated with the design.

Scott Russell's picture

Thanks to Home Power reader Eric T. for pointing out some outdated pricing info in this article. It has now been updated to reflect current market values. That kind of input is both welcome and encouraged anywhere on the site.

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