Hydronic Heating and the Independent Home: The SETH System™

Please read all of this description of the SETH System before contacting us to inquire about use in your application. This is a specific product developed for off grid homes and is not appropriate for most conventional heating applications.

Radiant heating systems that use hot water to deliver heat are growing quickly in popularity. Whether using baseboard fin-tube radiators or imbedded tubing in the floors, hydronic (hot water) radiant heat is one of the most comfortable and unobtrusive ways to heat a home. It can deliver heat silently and evenly while allowing an exceptional degree of control.

Also growing in popularity are homes that generate all or part of their own electric power from renewable sources, without connection to the utility grid. Whether from photovoltaic (solar electric) modules, wind, or hydroelectric power, living "off-grid" has become a viable option for tens of thousands of homeowners. By designing for maximum efficiency and eliminating wasted energy, most off-grid homeowners live comfortably using a small fraction of the electricity of a conventional home.

Manufacturers of radiant boilers and heating systems have given scant attention to the electrical demands of their equipment. For a home that is served by conventional utility power, the relatively low electrical demand of a conventional hydronic heating system is acceptable. In an off-grid home, however, or a home with both renewable and utility power, a conventional hydronic installation will often lead to disappointing results. When a standard boiler system is installed in an independently powered home, the electrical demand of the heating system alone can exceed the daily output of the renewable power system. The owners have often discovered that the pumps and boiler controls demanded all of the available solar or wind power every day during winter.

The SETH System™ Solutions
The Positive Energy SETH Systems were developed specifically to solve this problem by greatly reducing the electrical demand of a hydronic heating system. Both systems typically reduce electrical demand by 50-90% or more over conventional installations. This reduced load means substantial cost savings for the entire renewable power system. In new construction of an independently-powered home, a SETH System easily pays for itself in power system savings alone!

The systems are intentionally designed to reduce or eliminate the constant and excessive electrical load inherent in the transformers, pumps, controls, and other equipment common to conventional hydronic boiler systems. Neither system requires any internal modifications to existing equipment, so all factory warranties are preserved.

The SETH System Stout is used with a conventional hydronic boiler of any size. The SETH System Light, developed for smaller homes, is teamed with a tank water heater, which may incorporate an internal heat exchanger for solar thermal input. Each is a complete, simple, and reliable package of hydronic control and distribution equipment.

How the SETH System Works
The inverter is the component in an independent electric power system that turns stored low-voltage battery power into high-voltage power that is like conventional utility power. An AC boiler contains transformers and control circuitry that are constantly drawing power through the system inverter. Although the amount of power these transformers require is relatively small, the inverter must always be "awake" in order to provide that power. This amounts to what is called a phantom (or ghost) load - the inverter's wakeful state is also a continuous draw on the system's batteries.

The SETH System Stout achieves its remarkable results via a series of relays and thermostats that control efficient DC circulation pumps. Power flows to the pumps when the thermostats call for heat; no power is consumed when the call for heat is satisfied. The SETH System Stout unit also, through a proprietary control circuit, effectively regulates the home’s main system inverter power to an AC boiler, allowing the inverter to operate only when heat is required. This prevents the boiler (and therefore the inverter) from always being on, and translates to a significant reduction in the amount of energy consumed by the hydronic heating system.

Each standard SETH System Stout and Light can control up to six zones, and we have built custom units to handle 12 and 24 zones. A "Link" terminal allows any number of Light units to also function as an add-on slave unit to a master Stout unit. There is no limit to the number of zones that can be controlled by the unit, provided we anticipate the expected load and design the SETH unit accordingly. Certain zones such as a kitchen or living space will almost always want to be heated, while a guest bedroom only requires heat when there are guests. All zone control rests with the plumber planning the installation, comparable to a conventional installation.

The SETH System Stout and Light controls can handle a variety of specialized control tasks. For example, a sidearm domestic water tank can receive priority status, such that a call for domestic hot water always turns off floor radiant zones until satisfied. Priority switching can allow solar panels to provide all or most heat, with a burner firing only if needed. It can also be used in a complex heating system which combines several different means of heating into one system; for example, solar hot water collectors may be combined with an AC boiler, with heat being drawn from each source as it is available. Controls for such complexity are external to the SETH unit.

Our simplest system to date has been a single-zone in-floor radiant system using a tank-type water heater. Our most complex system to date, as shown on the right, was installed at a ranch near Rowe, New Mexico. It includes:
--sixteen infloor radiant zones;
--two indirect-fired domestic hot water tanks;
--a hot tub;
--a snow-melt zone;
--a lap pool (controlled as a dump zone for excess solar heat);
--a two-stage, 325,000-BTU LP boiler, with two Taco primary circulation AC pumps;
--eighteen Heliodyne 4X10 solar thermal collectors;
--two PV-direct Conergy SunCentric solar thermal circulators;
--two Six Rivers 640-gallon thermal storage tanks with three heat exchangers each;
--six Goldline electronic remote-sensor thermostats of various models;
--all powered by 48-volt DC battery power.

The current retail cost of the standard SETH System Stout control unit is $1075, and the standard SETH System Light control unit is $650. Custom units are priced on an individual basis. In addition to the SETH System control unit, one zone pack is required for each heating zone or equivalent function. The retail cost of each zone pack is $380-$475, depending on the circulation pump included. Dealer inquiries are invited. Presently, each SETH control unit is hand-built and tested in the Positive Energy shop.

Applications and Limitations of the SETH System: Read This Section before Contacting Us

The SETH system is at its essence little more than a very intelligently designed set of relays and analog control logic, capable of controlling both AC and DC power operations, so the units have no expected failure paths and indefinitely long life expectancy. With no internal electronic components, it is extremely robust and reliable. Pumps used are generally Ivan Labs or March, with life expectancies as specified by their respective manufacturers. Our empirical experience is that both are extremely long-lived when installed correctly. Earliest and prototype units used an internal dedicated inverter, but this approach was discontinued in 2001 in favor of the current approach. We have had no known failures of any part of the SETH system built since at least 2002.

The SETH system does not produce heat from solar electricity. The system is designed to efficiently control and distribute heat from one or more external sources. The sources could be a LPG (propane) or natural gas boiler, a water heater with or without heat exchanger, solar collectors, or even a wood-fired boiler.

The SETH system is not well suited to retrofit application, although it can be and has been done. Retrofit installation involves removal of all existing AC pumps and zone valves, as well as fundamental reconfiguration of boiler room plumbing to a primary/secondary loop arrangement for all but the simplest applications. In addition, tiny (14-45 watts) DC circulation pumps are used. These pumps are ideal in baseboard applications, and in in-floor applications with multiple parallel tubing runs.

SETH is not listed with any Nationally-Recognized Testing Laboratory such as UL®, and never will be, as it will always be a low-volume product for specialized application: we typically build two or three units to order each year. As far as we know, SETH is the only device of its kind. There are about 40 SETH-based systems currently in use in the U.S. and Canada. There is minimal literature available, and no installation manual. There is no marketing for SETH other than this web page you see.

While we build the SETH system, we are solar electric integrators, not solar heating specialists. We are not able to design your hydronic system for you. You (or your hydronic contractor) must have a comprehensive understanding of hydronic design, such that SETH becomes an integral part of your own overall design. For questions related to hydronic design, specific applications, installation and integration, we refer questions to Cedar Mountain Solar, also of Santa Fe, New Mexico, 505 474-5445 (ask for Boaz); www.cedarmountainsolar.com. Cedar Mountain Solar is a licensed mechanical contractor specializing in high-efficiency boilers and solar thermal systems for water and space heating. The technical developer of the SETH system is on staff at Cedar Mountain Solar, can supply schematic drawings of SETH-based hydronic systems, and can work with you to finalize a design for your unique application. You may also use any good hydronic engineer in your area that is familiar with extremely low-head DC circulators, plumbed typically in a primary/secondary loop configuration.
 
The SETH System was originally designed for the extreme efficiency needs of off-grid homes that have power systems with batteries. The system requires DC battery power to function. It does not work in homes that are served solely by utility power, or homes that have a batteryless grid-tied solar photovoltaic power system. We have two installations in homes with small backup batteries and an on-grid battery charger to supply “uninterruptible heat” during a power outage.

We build the SETH System in 24V and 48V configurations only. Note that we do not offer a 12V version of the SETH System. At 48V we use a custom 48-24V DC-to-DC dual-element converter, in a separate enclosure to step down battery voltage to 24V, to run a standard 24V SETH System. For maximum reliability, this converter is fully redundant, such that failure of a unit will not result in lack of heat. We have not yet seen a failure.

History
The SETH System concept has been in development for over ten years. In 1998, Positive Energy, Inc. developed a production prototype with contract assistance from the Technology Commercialization Office of Los Alamos National Laboratory. In 1999, a second grant provided funding for patent protection and prototype manuals. In May, 2001, the U.S. Patent Office issued Utility Patent No.6,237,855, protecting the fundamental design of the SETH System.

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