Solar stations (thermal solar pump modules)

By Bob "Hot Rod" Rohr,

Radiant expert

The latest wave of interest in thermal solar has brought some interesting products to this shore. By now you have probably seen or used the pre-plumbed and pre-wired radiant zone panels and circulator stations available from most of the radiant manufacturers. Well, a number of Euro-manufacturers and solar manufacturers are offering a pre-packaged solar module.

These nicely constructed and well- engineered solar modules offer an interesting array of components. These components are specific to the solar application and provide for a quick, simple and correct installation. The various brands I have installed all provide fill and purge ports, check valves, gauges for supply and return temperature, as well as system pressure. In addition, solar-specific relief valves are provided, along with an expansion tank connection port, flow meter, air eliminator and iso-valves. That’s a lot of components in a well-insulated box measuring approximately 20 inches in height and 10 inches in width.

The first one I received from Schuco Solar. (www.schuco-usa.com) I completely disassembled the module and all the various components to see the internals so I could understand the operation.

I particularly like the triple duty gauge/valve/ checks. This clever component offers a dry well for the temperature gauge, a low psi pop, plastic, spring check, also know as a gravity gate, or gravity brakes in Euro-speak,  and a positive shut-off ball valve feature. In addition the valve can be rotated 1/4-turn to lock open the check valve feature for fast fill and purging. Pretty clever -- a real space-saving component. No reason this triple duty valve couldn’t be adapted to hydronic applications! Just downstream of the circulator discharge, for example.

The air eliminator was another interesting piece I had not come across before. While it looks to be just a wide spot in the fluid path, it does have some engineering inside. A perforated cylinder helps to separate the air, and a dip tube -- for lack of a better name -- moves the air to the high point in the eliminator. There, either a coin-operated or small square keyed valve allows the release of the captured air. (Don’t lose the special key!)

The components are connected to one another with a gasketed union connection, or directly threaded to one another. On the Oventrop Solar Module (www.oventrop.com), the connections between the various components were some version of a press fitting.

The pressure relief valve and expansion tank connections are above the isolation valve so they can not be inadvertently isolated from the collector piping, which could risk an un-checked high pressure condition. The components all seemed to have a higher temperature rating than those found in the hydronics industry, generally around 266 - 300 F.

The Caleffi (www.caleffi.us) brand module used a Grundfos circulator with a yellow solar label. In addition to the complete solar module, Caleffi has an assortment of yellow labeled solar components available separately in their 2007 solar catalog. Included are relief valves, air vents and air purgers, expansion tanks and thermostatic mixing valves. The solar components differ from the similar hydronic components by the operating temperature. Some, in the case of their relief valves, list 320 F as the maximum operating temperature! Caleffi has the best looking insulation jacket, in my opinion. Leave it to the Italians to add some pizzazz.

There were some differences from brand to brand. The Oventrop module, for example, had a spot in the insulation jacket for the solar differential controller. A nice touch from an aesthetic viewpoint, but it did involve snaking wiring alongside the piping and union connections. The piping connections on the Oventrop were Americanized NPT threads.

The Caleffi and Schuco had nice solid mounting plates that the components were fastened to and it also provided a sturdy wall bracket to ease wall or tank mounting. The Caleffi required you to pull the temperature gauges to remove the insulated foam jacket. Not a big deal as the gauges fit into dry wells. The Schuco had an odd thread on the expansion tank connection. I found a way around it, but would suggest you order the optional stainless expansion tank connection pipe, which is also insulated.

I believe there is an insulation standard or code in Europe, as all the Euro components come in EPP hard foam jackets. They look real pretty but also keep all those solar-collected Btus inside and working hard, not escaping to the surrounding space.

I see several of the manufacturers also offer modules with plate heat exchangers. These dual circ modules allow you to use a basic insulated storage tank, instead of a tank with a coil inside. Pommerening Armaturenwerk (PAW) offers a Solar Separation module with a flat plate heat exchanger built in. The preliminary info sheet indicates a variable speed circulator on the primary side of that module. Paw builds solar and radiant modules and individual components for a number of solar suppliers. www.solarnetix.com. 

Solar modules are not brand new to the solar industry. Recently I removed a 20-year-old Lennox module. The newer Euro versions seem to be engineered more specific to the task.

I recall Taco offering a pre-packaged solar module, during the last solar “heyday.” Possibly this will be revived and updated. I see a few other domestic built modules offered. Heliodyne out of California offers a pump module if you purchase their panels.

I’m curious to see which, if any, of the manufacturers offer an ECM circulator to lower the electrical consumption. In the case of a single or dual panel array, a 25- 30W ECM could possibly supply the flow rates required. All the modules I tested had 80W circulators on board. No reason not to look at the wire-to-water consumption side of the module also.

Once you see the price of these ready-to-go modules, I think you would be hard pressed to build your own. You just can‘t get the same quality of the insulation package for anywhere near the selling price. I can see these modules being a great fit for the newbie solar installer, as well as the old school solar gurus. This is another way to leverage your time and let your installers do the work and you go out and sell more systems.                    

Bob “Hot Rod” Rohr is particularly interested in “hybrid” radiant systems -- systems that utilize solar and wood energy in addition to, or in place of, fossil fuel. He also is interested in systems that incorporate different methods of heat delivery. He owns and operates Show Me Radiant Heat and Solar Inc in southwest Missouri.

 

He has been knee deep in plumbing, heating and solar work since he was a kid. He’s learned a lot of simple ways to install, repair and update hydronic systems. Check out his new, download-able “Cool Tips from Hot Rod” at www.showmeradiant.com.

 

Questions or comments? Reach Hot Rod at hotrodradiant@aol.com.