Cem S. Kayatekin
ICON: Journal of the International Committee for the History of Technology 30, no. 2 (2025): 120–153
https://doi.org/10.11590/icon.2025.2.05
The discourse concerning the work of Steve Baer, while extensive, does not capture the full depth and trajectory of his innovations within the domain of passive solar heating and cooling. The more advanced work that he developed across his career has been broadly overlooked. This paper focuses on one such item from Baer's overlooked portfolio, a water-based thermosiphon passive heating and cooling system, which Baer would refer to as a double-play structure. It was a project that Baer was deeply invested in, starting with its development in the late 1960s, and continuing with refinements to the system that he would pursue well into the last stages of his career. This paper sheds light on how this specific innovation was seeded in the late 1960s, how it was refined across the 1980s–2010s, and where the bleeding edge of the double-play thermosiphon concept lies today.
In the wake of the Second World War, two dominant societal strands emerged within the United States. The first was the shift from the pursuit of "good society" to the pursuit of "good life," as epitomised by rise of high consumerism oriented towards individual comfort. The second was the contrapuntal reaction of the counterculture movement. The New Communalists sought to mobilise change via the reshaping of the material and built world. A significant root of this thread traces back to Buckminster Fuller. Several decades down the line, the American Southwest became a critical experimentative landscape. Steve Baer, who passed away in May 2024 while this manuscript was being developed, was a key figure within this new societal fabric.
In popular circles, Baer is most widely recognised for his work around polyhedral dome structures and The Dome Cookbook. As Drop City began to lose momentum by the late 1960s, Baer formed Zomeworks in Albuquerque to focus on passive solar technology development. The discursive landscape surrounding Baer and his work, while extensive, does not frame the full depth of his innovations. Much of the discourse focuses on thermal mass, passive solar heating, and dome construction. The more advanced work—including the double-play thermosiphon—has been broadly overlooked.
The focus of this paper is one particular piece from Baer's overlooked portfolio: a water-based thermosiphon system that he started developing in the early 1970s, which he referred to as a double-play system. What Baer meant by double-play was a system that could achieve both heating and cooling of an interior space, ideally in a simple, passive manner. The double-play system was one of the concepts that Baer was most invested in, and yet academic articles on this concept are effectively non-existent. The few published sources are either pamphlets and reports from Zomeworks or pieces written by Baer's own hand.
At the 1968 International Solar Energy Conference in Palo Alto, Steve Baer and Harold Hay first crossed paths. Hay had already established a career in low-tech passive heating and cooling, including the Skytherm system (roof ponds and movable insulation). One stepping stone was Hay's experiments with Styrofoam ice chests—filling one with water, opening or closing the lid by day and night to keep the water cool in summer and warm in winter.
In the same period (1967–68) Baer was working on a cattle rancher's problem: breaking ice on stock ponds in winter. Baer created a small closed-loop system with aluminium and rubber piping filled with methyl alcohol, placed in the pond so the bottom sat near the warmer water and the top in the ice. The fluid would warm at the bottom, rise by convection, release heat into the ice, and sink again. After the first night of testing, the loop had melted the ice around the rim. Baer patented this stock pond melter (US Patent 3,618,569, 9 November 1971). It was the seed for the double-play system—though not a single stock pond melter was sold. "I have come to suspect that the cowboys enjoy their winter ice-breaking expeditions," Baer remarked.
While Baer had patented the stock pond melter in 1971, the closed-loop thermosiphon idea re-emerged only in the late 1980s. Telecommunications companies were extending infrastructure to remote sites; battery arrays did not react well to temperature extremes. Zomeworks developed the Cool Cell as a response—a scaled-up, layered version of the stock pond melter concept.
At the heart of the Cool Cell were two interconnected arrays of water (no air bubbles) forming a single loop: a larger array inside as heat sink, and a smaller array on the roof as radiator. The cell was white and well insulated. During the day the interior array absorbed excess heat; at night, night-flush cooling occurred as hotter water rose to the radiator and colder water sank to the interior. By day the radiator was warmer than the interior, so the cycle stopped. On cold nights the radiator water froze, stopping the flush and keeping warmer water in the interior array above frost levels.
The Cool Cell became a critical product for Zomeworks (about 70% of sales for several years). In 1988 Baer built Andy Shack, a 10 ft × 10 ft cabin on Zomeworks grounds, with a sub-ceiling array of 8-in PVC pipes filled with water connected to a rooftop radiator of black pig mats. Below the array were aluminium louvers to control heat transfer. The system was effectively a hybrid of Hay's Skytherm and the stock pond melter thermosiphon.
In 1992–93 Bruce Davis remodelled a former laundromat in Albuquerque (Davis House 2). In a small detached studio (236 sq ft), Baer and Davis collaboratively designed a double-play variation (2003): 12 pig mats on the roof (127 sq ft) as radiator, connected to an interior array of 4" PVC pipes (38 pipes on two walls). The key difference from Andy Shack was that the internal array was vertical (mounted on walls) rather than horizontal under the ceiling. Baer preferred horizontal; Davis needed vertical to avoid leaks over his drawings. Between July–August 2004 the system kept the studio between 73.5°F and 78°F while ambient ranged 58°F–94.5°F.
Baer later reverted to horizontal sub-ceiling arrays at Zomeworks. For Baer, the horizontal array created complications for passive heating; for Davis, working with Karen Terry, the vertical array allowed a simpler path forward.
Davis House 3 and the Sol-Mod (designed with Karen Terry) used the Trombe wall as primary heating—Davis House 3 with infilled concrete block, the Sol-Mod with a vertical water array (as in the Davis House 2 studio). The Sol-Mod demonstrated that a vertical water Trombe wall could solar-heat a lightweight, off-grid building with stable day–night temperatures. Davis then sketched Double Play 2.0: cooling as before (roof radiator + internal PVC array), but with the internal array vertical and placed against south-facing windows so it could act as a Trombe wall for heating. The array could be drained (as in the Sol-Mod) so the roof radiator could be emptied in winter to avoid freezing while the Trombe wall stayed active; in summer the system could be refilled for cooling. Exterior roller shades would shield the array from summer sun by day and open to night sky at night. Double Play 2.0 has not yet been built but represents the current bleeding edge of the concept.
Baer developed the closed-loop thermosiphon with the stock pond melter in the late 1960s; the idea remained dormant until the Cool Cell (late 1980s) brought it to industrial scale and then to building scale (Andy Shack). Davis and Baer collaborated on the Davis House 2 studio in 2003; only after Davis's work with Terry on the Sol-Mod did Davis hybridise the double-play thermosiphon with a Trombe wall in the Double Play 2.0 concept. Baer's insistence on a horizontal sub-ceiling array led him toward complex solar collectors and piping for winter heating; a vertical water Trombe wall was within his reach (his own residence used one) but he did not combine it with the double-play loop. The discursive landscape on the double-play thermosiphon is effectively barren—no academic piece fully explains the system. This paper addresses that gap and points to the value of deeper research into passive solar innovations of the 1950s–1980s before that knowledge is lost.
Source: ICON: Journal of the International Committee for the History of Technology 30, no. 2 (2025). Text extracted from PDF.
PDF: 2025-01-01_steve_baer_double_play_thermosiphon_kayatekin.pdf