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concepts · updated 2026-08-01

Radiant cooling design brief

confidence: medium volatility: cold verified: 2026-08-01fresh

An Energy Design Resources design brief (prepared by Financial Times Energy for the California utilities) arguing that radiant cooling is more efficient, more comfortable, more attractive, and more healthful than air-circulating systems — with simulation data, California case studies, and an account of why the idea has been slower to spread in North America.

A design brief prepared for Energy Design Resources by Financial Times Energy, Inc. on behalf of the California utilities (PG&E, SDG&E, SCE, under the CPUC). It argues that radiant cooling is more efficient, more comfortable, more attractive, and more healthful than air-circulating systems — and over their lifetimes less expensive to own and operate. It also explains why the idea has been slower to spread in North America.

Summary claims

ClaimMeaning
Water-based panelsCooling water can run through ceiling, wall, or floor panels.
Comfort advantageRadiant systems separate comfort cooling from ventilation.
Market barriersFamiliarity and old moisture-control failures slow adoption.
Best first marketsHealthcare facilities may lead because they benefit most.

The physics and the numbers

Water has roughly 3,500 times the energy transport capacity of air; a hydronic system can move a given amount of cooling with less than 5% of the energy required to deliver cool air with fans. With comfort cooling handled radiantly, the ventilation system can shrink to roughly one-fifth the size, saving fan power and duct space. First costs are comparable to variable-air-volume (VAV) systems, but lifetime energy savings over VAV are routinely 25% or more.

Corina Stetiu (LBNL) simulated a prototypical office in nine U.S. cities: radiant cooling saves on average 30% of cooling energy and 27% of demand, ranging from 17% in cold, moist areas to 42% in warm, dry ones — the Southwest is where the technology pays best. Helmut Feustel (LBNL) reports hydronic radiant cooling has become “the new standard” in Germany; Franc Sodec (Krantz-TKT) reported up to 20% first-cost savings and 40–55% space savings from reduced ducting at German prices.

The key design constraint: cooled surfaces must stay above the dewpoint to avoid condensation, so buildings must be at least moderately well sealed, and humid climates may need dehumidified ventilation air.

California demonstrations

  • Mini-mart west of Sacramento (3,620 ft²): night-cooled water in sub-slab tubing plus evaporative precooling — 51% cooling-energy and 47% demand savings vs a conventional rooftop unit; payback under a year.
  • Historic San Francisco apartment retrofit (30,000 ft²): tubing in light concrete with a compressor-free cooling tower, installed for $140,000 against a $500,000 chiller quote — projected 84% demand and 61% electric-energy savings.
  • Vacaville manufacturer (70,000 ft², 1998): “NightSky” spray array cooling a 10,000-gallon tank feeding a radiant slab — NightSky supplies 67% of cooling; 70% energy and 87% demand savings; 2.5-year payback.

Structure of the idea

cool water in panels -> radiant exchange -> occupant comfort

The brief frames radiant cooling as a systems problem, not just an equipment choice. Design, controls, moisture handling, and industry habits all matter. That is why it reads like a bridge document: it tries to persuade builders, engineers, and owners that the technology is practical.

The archive’s larger pattern shows up again here: a thermal system wins when it is comfortable, low-maintenance, and easy to explain. Performance alone is not enough; adoption depends on trust and familiarity. Notably, the brief’s Davis Energy Group “natural cooling” projects and NightSky system are the mainstream-engineering cousins of Baer’s pool-heater cooling proposal — water cooled at night, stored, and delivered radiantly through the building mass.

See also