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


Stranded heat recovery using software controls


O


ver the past 10 years or so, I have got into the habit of designing hydronic heating systems by linking all my heating sources to all my heating loads


using the principles of primary loop piping to create a “flow center” where everything is connected. This can be accomplished with site-assembled primary-secondary (P/S) components or duplicated using hydraulic flow sep- arators and pump modules pre-fabricated “off the shelf” from manufacturers like Caleffi, PHP or Taco. In these articles I have been focusing on piping dia-


grams showing P/S piping, because this is a generic way to install solar hydronic combisystems where the flow paths are relatively easy to visualize. Figure 30-1 shows a typical piping configuration, simi-


lar to dozens of combi-solar home heating systems that we have installed and commissioned in recent years. We have found that, when the piping is always done in a standard way, the controls can be standardized as well. That way, many different installations can be controlled using the same configurations, making the final result more familiar and reliable. This allows the installers to avoid the per- plexing task of acquiring custom control equipment for every job and then learning how to adjust it properly “from scratch” every time. It is better when experienced installers can focus on using standardized and familiar controls for fine-tuning to optimize the energy efficiency of each installation. For the past two years at SolarLogic we have been developing centralized controls for solar heating combi-


systems that allow the standardization and tuning for ener- gy efficiency to advance to a whole new level. We do this with a control system that is based entirely on software and is completely interactive by remote control over the Internet. We can watch the performance of all the heating system components from day to day (or minute to minute, if needed) and “tweak” the control settings any time we see an opportunity for energy improvement. And we can do all this from the comfort and convenience of our office computer or any Internet computer that happens to be nearby. We call this system the Solar Logic Integrated Control (SLIC).


Figure 30-1 Plumbing Engineer


Case Study: Before and after improved control strategy Figure 30-2 shows an example of an immediate improvement in heating efficiency accomplished with a simple time delay. The data in Figure 30-2 was recorded by our SLIC control system and used to verify the success of this energy efficiency strategy. Here is the situation. When a “hot water baseboard” zone calls for heat, the boiler will typically fire to provide the high temperature fluid required by these fin tubes. The diagram in Figure 30-1 shows the actual piping configuration. The boiler fluid can be preheated, either by the solar collectors directly through the heat exchanger or by the solar heat storage tank. The boiler produces the final temperature required for the baseboards, 175 F. The zone (a small bathroom) heats up quickly, and the room thermostat shuts off the call for heat. In a typical heating system, the boiler flame would stop, the boiler pump would stop and, if the solar collectors were cold, the solar pumps would stop. At this point 175 F boiler fluid is stranded in the primary loop. This situation can occur mul- tiple times per day during the heating season. The top graph in Figure 30-2 shows how this stranded heat cools off over a period of hours. The wasted heat goes into overheating the boiler room; for reference, you can see the Domestic Hot Water (DHW) tank sitting there at 125 F, also losing heat very slowly to the boiler room. When we noticed this situa- Continued on page 40


January 2011/Page 37


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