Pool-heater cooling

“There are tens of thousands of candidates for radiant cooling where a big part of the system is already paid for. The designer has a running start. He’s getting something for nothing; he is harvesting a second crop off his solar pool heater.” — Steve Baer, July 2002.

The idea

Inspired by Harold Hay’s Sky Therm designs, Zomeworks had spent over a decade on night-sky radiative cooling — manufacturing thousands of passively cooled battery cabinets for telephone companies and patenting a heating/cooling system (US Patent 6,357,512). But “it has been difficult to get people to understand how effective cooling with night sky radiation is.” Jesse Rodefer suggested the bridge: use the tens of thousands of existing swimming pool solar heaters as night-time building coolers.

Running pool collectors at night is already a familiar technique for cooling pools in hot climates. The leap is to connect them to building thermal storage so the same collectors cool the house.

What’s needed beyond the pool heater

The pool heater itself is already paid for. Additional costs:

Thermal storage — bare PVC pipes in ceiling and walls, or a large insulated tank outside connected to indoor heat exchangers. About 20 lbs H₂O per square foot, roughly matching the radiator in area.
Pump and controls — the pool collector has too much flow resistance for thermosiphon, so a small pump is needed. Control: a sensor measuring sol-air temperature; pump on when below setpoint, off when above.
Intimate thermal coupling — “The success of the cooling system depends very much on the closeness with which the house tracks the storage temperature.” With overhead pipes, coupling can reach 3 BTU/°F·hr·ft². If coupling is weaker, “the house may become too warm even though the storage is cool.”

The economics

A pool collector radiating 150 BTU/ft²/night for 120 nights/year, against an electric system with EER of 10, saves only 1.5 kWh/ft²/year — hard to justify on electricity savings alone. The real value: replacing a conventional A/C unit entirely. 400 ft² of 8″ PVC pipe (suitable thermal mass for 400 ft² of house) costs less than adding a one-ton A/C unit, “and there is no noise, no drafts, and almost no power bill.” 400 ft² of radiator provides the same 60,000 BTU cooling as a one-ton unit running 5 hours/day.

Seasonal reversal

A pool heater used for summer cooling can’t heat the house in winter if it’s heating the pool — but in many climates the pool is only heated in spring and fall. During winter, the collector (designed for drain-down at night to prevent freezing) could heat the space it cooled in summer.

External validation

The DOE’s Energy Saver guide on solar pool heaters (2012) explicitly confirms the night cooling reversal as mainstream practice: “In hot climates, the collector(s) can also be used to cool the pool during peak summer months by circulating the water through the collector(s) at night.” The DOE does not extend this to building cooling — that is Baer’s specific contribution — but the underlying physics is validated by the world’s largest energy agency without qualification.

DOE cost context: solar pool heater systems run $2,500–$4,000 installed with 1–7 year payback for pool heating alone. Baer’s argument is that these already-paid-for collectors can do a second job — cooling the adjacent building — at marginal additional cost.

Why it matters for the archive

This essay is the clearest statement of Baer’s deployment strategy: don’t wait for purpose-built radiators. Piggyback on existing infrastructure. The pool heater is “not the exact radiator we would use in our Cool Cell™ systems,” but it is “an ideal way to interest the public in our patented heating and cooling method.”