Harold Hay

Harold Hay (1909–2009) was an American chemist and inventor who developed the Skytherm roof pond passive cooling system — the earliest documented large-scale application of night-sky radiation to building cooling, predating Baer’s Cool Cell by more than two decades. Hay was among the first to articulate the principle that Baer later built an entire product line on: buildings can be cooled without electricity by exposing water to the night sky.

Steve Baer acknowledged the influence directly, writing the chapter “Harold Hay’s influence and the Zomeworks Corporation” in Activism in Architecture (Routledge, 2018) — placing Hay as a named upstream figure in the Zomeworks thermal work.

Biography

Born 1909 in Spokane, Washington. Career in chemistry: pentachlorophenol wood preservation at Monsanto, municipal water purification methods. Government of India adviser on low-cost housing (1952), where he developed the “Growing House” concept using manual movable insulation to manage heat transfer seasonally. Further assignments in Latin America applied movable insulation to solar desalination.

Hay was characteristically difficult. Solar architect Ken Haggard: “He’s a caricature of the mad inventor. He’s a genius. But he’s also impossible. And he has not mellowed one iota.” He died in 2009, around age 99–100.

The Skytherm system

The core principle: a roof covered with water bags absorbs heat through the day and radiates it to the night sky. Movable insulating panels reverse this — covering the water during summer days (keeping the building cool) and exposing it during winter days (warming the building). No pumps, compressors, piping, or ducts required.

Hay’s formulation: “You don’t need electricity to cool! You don’t need an air conditioner! You do it with the sky.”

Phoenix prototype (1967)

Built on John I. Yellott’s property; Yellott contributed instrumentation, property, and thermal comfort expertise from Arizona State University.

Specification	Value
Area	120 sq ft
Roof panels	Three 4×8 ft polyurethane foam, 1.5” thick, 125 lbs each
Water depth	6–7 inches in black polyethylene bags
Operation	Manual — nylon clothesline, hand winch, pulleys
Wall construction	Vermiculite-filled lightweight concrete block

Performance: Interior 70–80°F during 91% of annual hours. Daily swing 4–8°F. Fan cooling required only when outdoor temperatures exceeded 110°F.

Atascadero house (1973)

Full-scale, 1,100 sq ft. Plastic waterbed-like bags. Indoor 68°F–72°F vs 32°F–68°F outdoor range. The building operated for approximately 40 years. Hay later donated the house and $1 million to Cal Poly for research.

Recognition: 1974 — Congressional testimony. 1976 — American Revolution Bicentennial Commission, one of America’s 200 most promising inventions.

Hay’s quote in his last years: “My house was one of the unique things, and it’s gone nowhere.”

Why, despite the recognition: a 1975 federal evaluation report called Skytherm “a unique and invaluable national and worldwide asset” — yet even congressional testimony, national recognition, and that evaluation weren’t enough to scale it commercially. Two concrete causes: the late-1970s return of cheap fossil fuels killed the economic urgency, and real, unglamorous engineering problems went unresolved — leaky bladders, deflection of the movable insulation panels, edge-seal thermal leaks, and the structural cost of a roof built to carry a load of water. Publicity and government recognition proved necessary but not sufficient.

Technical principles

Water as thermal medium: “Water is the cheapest and most efficient heat storage material for buildings. Its fluid convection provides an outstanding advantage over the heat lag of solar materials.” This argument — water over mass — runs continuously through Baer’s own 1999–2004 thermal engineering documents.

“Cool black and warm white”: Surface thermal behavior depends on insulation context. Tropical animals have dark coats because they need to radiate heat outward; polar bears are white to absorb heat. The same logic governs roof surface design.

Nocturnal radiation underutilized: Hay argued for decades that night-sky cooling was the most overlooked resource in building physics. Baer’s “Night and Day” essay (2002) makes the same argument from scratch, reaching the same conclusions independently.

Hay and Baer

Hay called Baer, Harry Thomason, and similar figures “creative activists” — people who “took their own time and money and worked with their own hands to develop solar energy systems that work.” The description fits both men equally.

Both shared key positions:

Against centralized solar — satellites and large desert collector farms with transmission lines are polluting and economically irrational; distributed roof-level systems are the answer
Against government subsidy — NSF and DOE grants crowd out genuine innovation (Baer’s “solar insecticide” metaphor in Sunspots; Hay’s independent funding of Atascadero)
For passive systems over active — no pumps, no electricity, no moving parts beyond simple mechanical covers

The architectural difference between their solutions is structural, not philosophical:

	Hay’s Skytherm	Baer’s Cool Cell
Water location	On the roof	In the ceiling
Radiator	The water itself (exposed at night)	Separate roof panel (connected by thermosiphon)
Insulation	Movable panels over roof water	Thermosiphon flow control
Control mechanism	Manual panel operation	Passive thermosiphon (density-driven)
Earliest prototype	1967	Battery cabinet series, 1990; Cool Cell, 2002

Baer’s separation of the thermal mass (ceiling water) from the radiator (roof panel), connected by a thermosiphon, allowed the Cool Cell to work in conventionally roofed buildings rather than requiring a flat, waterproof, structurally reinforced roof. This is the key engineering advance over Hay’s design.

Scientific predecessors (pre-Hay)

Daniels’ Direct Use of the Sun’s Energy (Yale, 1964) documents that Bliss had already built and tested a nocturnal radiation cooling system in Arizona by 1961: “a black cloth radiator 280 ft² in area. The ‘cold’ amounting to 120,000 BTU was stored in a 10-ton pile of rocks buried in the ground. The cooling was equivalent to about 2 tons of refrigeration.” (§13.3) Bliss presented this at the 1961 UN Conference on New Sources of Energy, Rome.

Also from 1958: Yanagimachi proposed combining solar energy, nocturnal radiation cooling, radiant panel systems, and heat pumps as a complete year-round system. Whether Hay knew these references is not confirmed in the archive; his Phoenix prototype (1967) appears to be independently developed.

Daniels also documents the quantitative physics: “10 to 35 BTU ft⁻²hr⁻¹” for nocturnal radiation cooling (§13.3).

In the archive

Hay appears in the archive as an upstream acknowledged peer rather than a cited source. The connection is documented by Baer’s own chapter in Activism in Architecture (Routledge, 2018, eds. McDonald & Dayer) — a formal academic acknowledgment that Hay’s roof pond was an influence on the Zomeworks thermal work. The book also contains a chapter on “Untapped potentials in Harold Hay’s roof pond system for passive heating in cold climate regions” (Daniel Overbey) and the Google Books preview confirms Sunbenders are discussed as still available from Zomeworks.

The NSRC field study (2006) that validated Baer’s Cool Cell approach — pool collectors as night-sky radiators — is a modern metered test of the same physical principle Hay demonstrated in Atascadero in 1973.