Bristol’s six principles for good solar hydronic design

By Bristol Stickney,

contributing writer

Driven by rising energy prices and concerns about global climate change, people everywhere are turning towards renewable energy and asking “why not”? Solar heat collectors have been around in practical applications for many decades and are far more abundant around the world compared to other renewable energy installations, dating back not only decades, but a century and more. If any alternative energy technology deserves “Flagship Status” by now it is solar heating.

Riding the green wave

Still, because of public misconception, every week at Cedar Mountain Solar (my company, which specializes in solar-assisted hydronic heating) we receive calls from potential clients who start by asking about “solar panels” to heat their house. When questioned carefully, it often turns out that they mean photovoltaic (PV) panels. PV panels convert sunlight into electricity, and heating is a terrible application for them! Maybe together we can change this odd state of affairs into a profitable opportunity for the hydronic heating industry. After all, prospects are calling us because they want something solar and they want to heat their house. So far, so good.

I believe that anyone with experience in the hydronic heating industry can ride this wave, and should be doing it, if for no other reason, because it’s the right thing to do. As an added bonus, this is one of those rare opportunities when doing the right thing results in tangible benefits for everyone. The owner saves fuel for the life of the system and reduces their greenhouse gas emissions. The installer sells an upgrade to a heating system job along with the possibility of an enhanced maintenance contract on that system in the years to come.

Currently, it can be very difficult for a contractor to take advantage of this opportunity because there are so many different ways to design and install systems that it’s hard for an installer to know where to begin.

And that is what I will be talking about in this column: the method, the reasoning I use to make solar heating design decisions so that the heating equipment functions smoothly and the savings and benefits are actually realized over the years.

Solar heating then and now

I personally worked on my first solar hydronic home heating system at the University of Maine in 1975. I also lived in the house through an entire Maine winter (1975-76) which was an eye-opening experience. We tried some things that I often hear discussed even today: Drain-back atmospheric collectors; liquid-to-liquid heat pump assist; controlling absorber plate temperature to maximize collector efficiency; the use of huge insulated atmospheric heat storage water tanks for many days of heat storage; and water-to-air heat distribution for lower installation costs. This was my introduction to solar hydronic heating, and as the twig is bent so grows the tree. Since 1975 I have been involved in many hundreds of designs and installations, large and small, and I’ve tried just about everything that’s been suggested.

Not everything I have tried is worth repeating. But I have learned a lot about what works and what doesn’t in solar heating for residential applications and other small buildings. In future issues in this column I will be sharing many of these details with you, in the hope that the coming age of solar hydronic heating will proceed smoothly and profitably for everyone who is interested.

The six principles

Before I get into all the gruesome details, I would like to introduce what I call the Six Principles of Good Solar Hydronic Design. There are so many different ways to approach solar heating, and so many details and choices to make, that an objective filter of sorts is needed. After reviewing the best and worst memories of all the installations, repairs, rebuilds and adjustments I have done over the years, a definite pattern has emerged among the most successful installations. These aspects of successful solar hydronic design and installation can be divided into six categories and I list them roughly in order of their importance:

1. Reliable. Make it reliable (There is no solar “payback” when it’s broken.)
2. Effective. Think user satisfaction (don’t you hate it when they complain?).
3. Compatible. Make it compatible with existing systems (remember roof ponds?).
4. Elegant. Use less to do more (fewer parts mean lower cost and fewer things to go wrong).
5. Serviceable. Make it easier to install, repair and adjust (isolation valves can be a bargain).
6. Efficient. Build in thermal and electrical efficiency (do more with the energy you use).

These six principles address the major causes of consumer reluctance to adopt active solar heating systems today. Public perception of past technology can be a major barrier to acceptance of our current offerings. Would you ask a customer to tinker with their hydronic boiler to keep it working from season to season? This was, at one time, a mainstay of active solar hydronic heating, but it is unacceptable for solar heating to become mainstream today.

Design for the real world

My experience includes over 10 years in the trenches as a solar repairman, after which I realized that so many of the technical problems were not with the components, but how the components were installed and controlled, as well as “real world” issues like hard water and power failures. Making sure the system works is more important than optimizing its efficiency. That is why “efficiency” is the last design principle on my list.

Over the next few months, I will be writing in greater detail about each of these principles. I will explain why they are essential and give examples of how each shows up in good solar hydronic designs (my designs and those of others.) Using these principles you’ll be able to make good design choices and have happy solar heating customers.                   

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.