This design for a light commercial thermal system is effective, simplified

Drainback system with Solar Phoenix

Template for a drainback solar hot water system for light commercial, with three flat-plate collectors and a Solar Phoenix

I’m asked, more and more, to provide a solar hot water system design for light commercial systems. There is, indeed, an effective and simple design template for smaller commercial systems that need to heat up to 330 gallons of water per hour or less. The actual system this template is based on is for a fire station; the solar is designed to cover 80% to 100% of the load in a southern climate.

However, this category of light commercial could also include restaurants and cafes, hair salons and spas, grocery stores, laundromats and car washes. Some of these businesses may require even larger systems, which we’ll discuss in an upcoming blog post.

Why am I recommending this template? Because it’s the most efficient in its design, and it offers greatest simplicity in installation. It has freeze and overheat protection. Also, it requires little or no maintenance.

The virtue of this system is that solar directly heats the water to be used. Too often I’m sent designs that preheat water for some conventional water heater that can’t be heated with the solar directly.

This template includes three 4’x8′ flat-plate solar collectors. The number of panels may be adjusted according to the climate of the location. On that fire station I mentioned, because it’s in Texas, a hotter climate, fewer panels are required. If I were to spec out a similar system for a northern location, I’d possibly use one more panel or use larger panels.

System at Eglin Air Base featuring four 4’x8′ collectors.

Drainback system at Eglin Air Base uses a Solar Phoenix.

Drainback system at Eglin Air Base uses a Solar Phoenix in a simple, elegant design.

This system also allows data logging with web monitoring so that its performance can be checked at any time online.

Following is the components list for this system:

  • 1 ea. Solar Phoenix, 199,000 Btu and 119 gallons (PH199-119S) stainless-steel modulating condensing water heater with solar input. Will produce continuously 335 GPH at 100° rise. If this is more than needed, use the PH130-119S
  • 1 ea. SSU-10DB stainless steel drainback tank for overheat protection (10 gallons)
  • 1 ea. Variable speed solar pump control with 4 sensors (8600-047)
  • 1 ea. Solar rated anti-scalding valve (8600-068)
  • 3 ea. 4’x8′ flat plate collectors (FP-32SC)
  • 3 ea. FP-RM mounts (or select mounts for roof application)
  • 1 ea. Field-supplied pump that will supply 4 GPM and the lift from the DB tank to the panels
  • 1″ copper and insulation to the panels

The photos in this story show a system using this design at Corry Station Bldg 3782 (a GSB support building) at Florida’s Eglin Air Base. The contractor is McDonald Construction of Fort Walton Beach, Fla., and they really know what they are doing (850-862-2151). The engineer was Jimmie Johnson of Johnson-Peaden Engineers, also in Fort Walton Beach. Manufacturers’ rep is Coleman-Russell.

For installation instructions, you’ll need to download “Control Instructions” HERE. The last page of the manual should be followed for a correct installation of the drainback configuration. You will also find the programming instructions for this system on page 4 of the Control Instructions.

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