Best ideas from the past 50 episodes
By Bristol Stickney, technical director,
Cedar Mountain Solar Systems, Santa Fe, N.M.
Last month this “Solar Solutions” column passed an auspicious milestone — 50 episodes and counting. In these past columns I have presented a wide spectrum related to the design and installation of solar heating systems in whole buildings, a.k.a. solar combisystems. Each article represents a single puzzle-piece of a larger picture puzzle that provides a roadmap for hydronic solar heating system deployment on a larger scale. Just in case you missed some of the earlier articles, I would like to take this occasion to sum up some key topics covered in the last four years, starting with a concept I have recently come to think of as the “Prime Directive” (with apologies to Star Trek).
The Prime Directive (for solar heating)
We cannot expect solar heating to be widely accepted in the larger consumer market today unless it is “at least as reliable and trouble-free” as conventional hot water boiler systems. It will not become a sought-after and desirable upgrade by homeowners and building managers unless it achieves consistent “performance and longevity better than conventional heating,” with the fingertip control that we have come to expect in hybrid cars and PV electric systems.
This defines the Prime Directive: Always design and install solar heating equipment that is at least as reliable and trouble-free as the conventional system it replaces. Whenever possible, provide performance, longevity and controls that surpass the conventional alternatives.
So, for example, we would shy away from a system that requires that the collectors be covered with tarps during the fall season, because a hot water boiler system does not require this; it would be unreasonable if it did. We would also avoid a system that might stagnate and blow steam during a daylight power failure, because a hot water boiler never does this; no one would want one if it did. We do have the technology to make solar heat as good as, or better than, conventional heating technology. To ensure that solar heating is always seen as an advance in technology and an upgrade to the building, follow the Prime Directive. To do this, try starting with the Six Principles of Good Solar Hydronic Design.
The Six Principles
As many of you already know, in this series of articles, I have been making the case that the key ingredients for solar/hydronic design and installation can be divided into six categories, listed below, roughly in order of their importance.
1. Reliability. Make it reliable. There is no “solar payback” and no benefit when it stops working.
2. Effectiveness. Think user satisfaction. The user expects consistent, controllable and comfortable results from their space heating and DHW heating, solar or no solar.
3. Compatibility. Make it compatible in every possible way. Avoid temperatures, pressures, fluids or components that are not compatible with existing systems, the architecture, materials, human skill levels or anything else at each jobsite.
4. Elegance. Use less to do more. Fewer parts mean lower cost and fewer things to go wrong. Think of ways to use a single component to do two or three different functions.
5. Serviceability. Make it easier to install, repair and adjust. Isolation valves, balance valves, air bleeders and unions can save a lot of grief. Data logging and remote control are often worth the savings in service trips.
6. Efficiency. Build in thermal and electrical efficiency. The solar equipment, the electrical components and the controls must all work together to provide high energy performance with some way to verify it. The success of any solar hydronic home heating installation depends on the often-conflicting balance between any of these six principles. Finding the balance between them defines the art of solar heating design.
Top seven design and installation measures
In the past 50 articles, we have presented a lot of discussion about the details of solar combisystem design. Many of my recommendations are in direct response to the incomplete and unreliable installation details found in past solar heating installations. I have repaired, remodeled and dismantled many solar heating systems over the past 30 years. Here is the short list of ideas that appeared in past columns and have withstood the test of time. In recent years, they have proven their worth in many solar installations, both retrofit and new. I now include virtually all of these measures in every combisystem I design these days.
1. Documentation. Make a complete piping, wiring and control diagram.
Solar plumbing design and the controls are two sides of the same coin. The plumbing system will not work without compatible controls and vice versa. This does not happen by accident, and must be planned carefully before construction starts. The time spent documenting a complete piping and wiring plan is rewarded many times over in the time saved during installation, startup and maintenance. It is also invaluable to the future users and service people throughout the considerable decades in the life of the system.
2. Primary loop configuration. Standardize the solar/hydronic piping.
A primary loop “flow center” piping configuration allows multiple heat sources to be connected to multiple heat loads and to provide heat directly, to bypass any source or any load or to allow simultaneous operation of any source or load. In past articles, I used a simple primary loop combisystem called “Combi 101” to illustrate these features on a system that includes a bank of solar heat panels, a boiler, a domestic hot water tank and warm floor space heating. Larger primary loop systems may also include swimming pools, baseboard zones, wood boilers and heat storage water tanks attached together on the same loop (just to mention some examples from recent installations). Here at my company, Solarlogic, we have developed a software design tool that speeds the design process of the standard primary loop system. We call it the “Slash-D,” and it is available (free) through our website.
3. Direct in-floor solar heat storage. Use concrete floors instead of water tanks.
By using two-stage heating room thermostats integrated into the solar control system, the considerable thermal storage capacity of concrete radiant heated floors can be used directly as solar heat storage. In many cases, this will downsize, or even eliminate, the need for large heat-storage water tanks. (The “Slash-D” design software will help make that determination.) The same principal has been used successfully to heat swimming pools and hot tubs when radiant heat tubing is embedded in the concrete shell of a pool or spa.
4. Controlled overheat dissipation. Prevent collector overheat by heat dumping.
Solar heat collectors can cause a lot of trouble if the liquid inside them is allowed to overheat. We now employ control systems that can dissipate extra heat safely into an existing garage floor, ice melt sidewalk or other normal masonry heating zone to cool the collectors in a controlled way. When controlled properly, human comfort is not compromised, and steam is prevented in the collectors, using existing in-floor or in-ground zone loops. This can eliminate the need for more complex cooling system add-ons.
5. Passive self-cooling. Some self-cooling methods work during a power failure.
Thermosyphon self-cooling fins can be added to any bank of flat plate solar heat collectors, as long as the piping inside and outside the collectors meets some simple prerequisites. Most of our recent solar combisystem installations include this cooling option to reduce the need for service over the long term. Drain-back solar heating systems will also survive power failures just fine, because they empty themselves when the solar pump loses power.
6. Night sky radiant cooling. Flat plate panels can be used at night for cooling.
NSRC cooling can be accomplished using glazed flat-plate solar “heat” panels or (even better) using unglazed flat panels (often used to heat swimming pools). In many recent installations, we have included control settings that allow the “warm floors” to be cooled at night in summer by running the solar collectors backwards at night. Similar control systems can be programmed to dissipate heat at night from overheating water tanks when the stored heat is not being consumed.
7. Performance verification. Data-loggers, remote display and remote control.
One of the chronic problems that have plagued the solar heating professional in the past is the difficulty in verifying that a complex solar control system is working properly from season to season. This usually requires a site visit, with hours spent in the mechanical room meditating over a slew of manual control settings. More hours can be spent on-site trying to observe proper system response, which varies with the weather conditions. Some installers have added data-loggers to record temperatures and system status, so that a long-term record of performance can be used to make better informed adjustments. “HOBO” data loggers, for example, from Onset Corporation have been used this way. Some conventional solar controls now come with a built-in data card that can be removed and downloaded to your computer. These kinds of data-loggers still require a trip to the site to gather the data.
Here at SolarLogic we have overcome this problem by developing the SLIC system. This is an integrated control system for solar home heating that includes data logging that can be downloaded over the Internet. The SLIC also provides remote monitoring and remote adjustment and control over the Internet. As an added bonus, it provides all the control functions and capabilities mentioned in items 2 through 7 above in a single control box.
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 recommendation or endorsement. n
Bristol Stickney has been designing, manufacturing, 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 in Santa Fe, N.M., where he is involved in development of solar heating control systems and design tools for solar heating professionals. Visit www.solarlogicllc.com for more information.
Bristol Stickney has been designing, manufacturing, 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 in Santa Fe, N.M., where he is involved in development of solar heating control systems and design tools for solar heating professionals. Visit www.solarlogicllc.com for more information.