Solar combi connections with hydraulic separators

By Bristol Stickney, technical director,
Cedar Mountain Solar Systems, Santa Fe, N.M.

A solar combisystem is characterized by multiple heat sources providing heat to multiple loads, each with potentially different temperature characteristics. The most productive approach I have found for designing and installing these systems is to arrange all of this different equipment around a “flow center” that allows any number of heat sources and heat loads to be attached with two pipe connections.
In previous articles I have been illustrating this approach by focusing mostly on primary loop applications using primary/secondary (P/S) piping. The primary loop configuration is a generic way to install solar hydronic combisystems, where the flow paths are relatively easy to visualize and the plumbing components are widely available and easily site-assembled using the familiar “closely spaced tees.”

The primary loop is not the only way to create a flow center, which is basically a large container where all the flow from all the secondary pumps can come together without interfering with each other. The primary loop is a doughnut shaped flow center that acts like a traffic circle for the flow from all the circulators. Today, there are an ever-increasing number of products that offer an alternative to the site-built P/S piping by using hydraulic flow separators, manifolds and pump modules pre-fabricated “off the shelf” from manufacturers such as Caleffi, PHP, Taco or PAW. The potential for labor savings and rapid site installation holds great promise. Following are some examples of combisystem installations where we broke away from our primary loop habit, without sacrificing any of the features and benefits of that proven design.

Combi 101 — Primary loop solar heating advantages

A diagram of the venerable Combi 101 primary check-loop can be seen in Figure 34-1 and has been discussed in more detail in previous columns. This configuration has been duplicated many times in our solar heating installations because (among other reasons) it provides the following eight basic design benefits:

• Multiple heat sources and multiple heat loads are all connected in a standard way, each with two pipes, using a flow center.
• The flow center provides manifold connections where secondary pumps are mounted, allowing flow from all the pumps to converge without interference.
• Pipe connections can be sequenced to allow the separation or stratification of hot and cold temperatures to be enhanced and maintained.
• Any heat source or heat load may be added or deleted at any time and for any reason in a modular way using the two-pipe plug-in design.
• Any heat source may provide heat to any load (or loads) whenever available and deemed appropriate by the controls.
• Heat loads may also act as heat sources, when allowed by the control system.
• Any heat source or any load may be bypassed when it is not wanted or needed.
• All equipment connected to the flow center can be managed by a central control system that can be just as standardized and modular as the plumbing components.

Hydraulic separator installation

Figure 34-2 shows the schematic piping details for a series of installations where a hydraulic separator was used as the flow center instead of a Combi 101-style primary loop. For these jobs, the installers preferred using a Caleffi Hydrolink as the flow center because it eliminates the need to assemble a primary loop piece by piece. In some installations, the Caleffi pump modules that were used “plug” right on to the Hydrolink with two threaded pipe connections.

The Hydrolink 2+2 model, seen at the center of Figure 34-2, was configured to provide the same heating functions and advantages that a primary loop system would have done. The result is a piping system that resembles a Combi 101 system with a very compact flow center with a built-in pump manifold. As a unique variation, this design requires a circulator pump on the water side of the solar heat exchanger to deliver solar heated fluid to the flow center when it is available. It is an unconventional use of the top pipe connections on the Hydrolink, but it works much like the Combi 101, with one additional circulator.

Hydraulic separator installation using PAW modules

Figure 34-3 shows a piping diagram taken from a group of solar heating installations that were all designed around the brass modular equipment manufactured by PAW. This line of equipment provides hydraulic flow separators, pump modules and manifolds that can be joined directly together with integral unions or spaced apart using connective piping. As you can see in the diagram, we did a little of both, so that our solar heat exchanger could be mounted in a series flow path between the cool return manifold and the hydraulic separator. By using this configuration, we were able to maintain the same functions and performance as our standard Combi 101 system, with the same number of pumps, using the same control system and control strategies that have proven most effective over the years.

The three piping configurations described here all provide the same heating functions and the same eight design advantages as a Combi 101 solar heating system. All of these heating designs have been installed in different variations multiple times and exist today in functioning buildings. All of them have been outfitted with the same types of control functions, without much modification of the controls systems from one installation to another. Both the older style controls, using differential thermostats and relays, and our newer SLIC (computer based) control systems have been applied to primary loop and hydraulic separator configurations alike with equal success. This bodes well for more and better modular solar heating systems in the near future.

These articles are targeted toward residential and small commercial buildings smaller than 10,000 square feet. The focus is on pressurized glycol/hydronic systems, since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organizations, suppliers and manufacturers are mentioned only to provide examples for illustration and discussion and do not constitute any recommendation or endorsement.

Bristol Stickney, partner and technical director at Cedar Mountain Solar Systems in Santa Fe, N.M., has been designing, manufacturing, engineering, repairing and installing solar hydronic heating systems for more than 30 years. He holds a Bachelor of Science in Mechanical Engineering and is a licensed Mechanical Contractor in New Mexico. He is the Chief Technical Officer for SolarLogic LLC and is involved in training programs for solar heating professionals (visit www.cedarmountainsolar.com or www.solarlogicllc.com for more information.)