The PG&E Test 2010

The real-world energy study that inspired E. Jess Tudor of Coverplay, Inc. to create Airframe.

The first big clue came in 2008.

PG&E and the Association of Pool & Spa Professionals (APSP) worked with Cal Poly University, San Luis Obispo to test the standby energy use of 27 No. American portable spas for the California Energy Commission. The standout performer was entry ‘V’ equipped with the Coverplay single-hinge, angle of compression spa cover invented by E. Jess Tudor (U.S. Pat. # 7752685).  Docket # 12-AAER-2G on May 14th 2014 for Analysis of Standards Proposal for  Portable Electric Spas 

But Tudor believed there was still an important question the indoor control test didn’t observe:

What happens to efficiency when you take the spa outside?

Therapy spas don't spend much time inside temperature-controlled rooms.

They’re in open backyards.

They experience ambient weather conditions like cold, wind, humidity, changing temperatures and evaporation.

So from December 2009 through February 2010, Tudor conducted a second outdoor energy study authorized by P.G. & E. and submitted those results to that energy giant for its continuing energy study . The report was later presented to the California Energy Commission. P G & E Ambient Report

This time, the spas were exposed to practical world environment conditions.

The Second Test Was Different

The original Cal Poly study gave researchers an excellent controlled comparison.

The follow-up PG&E ambient study asked a different question:

How would these spas perform in actual weather conditions?

Testing took place outdoors in Medford, Oregon over approximately ten weeks.

Temperatures ranged from 23°F to 64°F , averaging in the low-to-mid 40s.

Each spa was maintained at or above 102°F and tested over 96-hour periods.

The study compared spas fitted with dual-hinged foam covers to a Coverplay Airframe physics based, beveled-angle of compression design. P G & E Ambient Report 2010.

As the spas were tested outdoors, a natural phenomenon became more evident as observed with laser thermometers.

The “Chimney Effect”

Jess Tudor coined the term “chimney effect” to describe what he observed happening the length of those dual hinged spa covers provided by spa manufacturers.  

Spa manufacturers seem content to provide bi-folding Styrofoam spa covers to allow cover lifters a space to rest their lifting bar to the detriment of energy efficiency.  

That dual hinge design allows convection heat to escape unimpeded making spa heaters work more often to keep up with increasing demand.  

Using laser thermometers, the ambient study found significant heat loss at the vinyl gap hinge of dual-hinged covers. Tudor described warm vapor escaping through this area like heat rising through a chimney. P G & E Ambient Report 2010.

At sunset, the effect became especially interesting.

During one observation in October, the outdoor air temperature was approximately:

60°F measured with a laser thermometer

Yet the surface of the cover measured only:

33°F

That unusual experience defies logic until you consider deep space is -455F. Few have witnessed this event, but NASA has named the phenomenon ‘Radiative Cooling’.

The report included this observation and cited evaporation and accelerated heat loss from the cover surface of a heated outdoor spa. P G & E Ambient Report 2010

 Why Nighttime Matters

During the day, outdoor surfaces absorb energy from sunlight radiation.

After sunset, that extra source of warmth gives way to deep space and the ambient atmosphere cools.

Meanwhile, the water beneath the spa cover is still +/- 102°F.

Cold dense convection air naturally moves toward warm radiant objects.

The dual hinge provides a path of least resistance; convection heat is continuously lost there.

Spa heaters routinely replace the wasted heat at the expense of higher energy bills and shortened life spans of heaters and pumps.

Colder conditions can expose weaknesses in the temporary cover that aren't as obvious during the day.

What About the Fill “Wedgie”?

The temporary spa-cover industry has tried to obscure the hinge gap by using fill pads or wedgies between the two halves of a temporary spa cover.

That idea defies logic as it trades convection heat loss for conduction heat loss without the integrity of verifiable efficacy.

Stuffing conductive material into that gap doesn't solve the inherent problem with that gap.

It will impact air movement but will not have an efficient barrier between the separate foam cores.

The PG&E ambient report continued to identify the dual hinge gap as an area of significant heat loss despite these wedgies. P G & E Ambient Report

Tudor's solution was supported by the science of heat energy transfer.

Eliminate the opening.

The Coverplay beveled-angle hinge was designed so the two insulated sections compressed together eliminating the gap.

The solution was to change how the hinge worked.

Then the Numbers Came In

The outdoor study compared several spas before and after changing from the temporary dual-hinged cover to the Coverplay compression angle hinge system with a uniform cabinet insulation.

The differences were substantial.

Phoenix Spa
Temporary Foam with dual hinge: 13.83 kWh/day
Coverplay chambered air cover with single hinge + cabinet wrap: 8.9 kWh/day

Hot Spring Spa
Temporary Foam dual hinge: 7.72 kWh/day

Coverplay technology (chambered air cover) with single hinge + cabinet wrap: 4.27 kWh/day

Sun West Spa
Temporary dual hinge: 14.57 kWh/day
Coverplay chambered air cover with single hinge + cabinet wrap: 8.17 kWh/day

Clearwater Spa
Temporary dual hinge: 11.36 kWh/day
Coverplay chambered air cover with single hinge + cabinet wrap: 6.93 kWh/day

And one of the most dramatic examples was the Life Spa.

Its temporaryl dual-hinge configuration averaged:

10.83 kWh/day.
After a properly constructed Coverplay single-hinge cover and cabinet insulation were installed, it averaged:

4.4 kWh/day.
The report notes that an earlier Coverplay test cover had accidentally been manufactured with a ½-inch gap between its insulating cores . That improperly constructed cover provided only modest improvement.

Once the gap was corrected and the insulated sections could properly compress together, energy consumption dropped dramatically. P G & E Ambient Report

That accidental manufacturing problem actually helped demonstrate Tudor's innovation:

Gaps matter.

Spa ‘V’ Returns!
There was also an important connection between the two energy studies.

The 350-gallon Coverplay spa tested in the outdoor PG&E study was the same Spa V from the 2008 Cal Poly study.

In the outdoor ambient test, equipped with its single-hinge chambered air design Coverplay technology and cabinet wrap, it averaged just:

3.29 kWh per day. P G & E Ambient Report

So the story wasn't based on a single laboratory result.

The engineering idea that performed exceptionally well in controlled testing was carried into a second study designed specifically to investigate real outdoor conditions, evaporation and the hinge-related heat loss Tudor called the chimney effect.

Two Tests. One Important Lesson.

The 2008 Cal Poly study asked:
How efficiently can a portable spa maintain temperature under controlled test conditions?

The 2009–2010 PG&E continuing-energy ambient study asked:
What happens when we put that spa outside and let weather, cold nights and evaporation become part of the equation?

Together, they pushed E. Jess Tudor toward a much bigger idea.

Why keep trying to improve the same temporary foam-cover architecture?

Why not rethink the spa cover itself?

From Coverplay Prototype to the Airframe

The Coverplay compression hinge cover became part of the engineering journey that eventually led E. Jess Tudor to invent the Airframe Spa Cover.

Airframe challenged the pollution issue head on.

Instead of depending on temporary EPS/XPS foam cores, Airframe was designed using the physics of heat energy transfer:

Conduction — chambered air helps slow heat traveling through the cover.

Convection — the cover and perimeter barriers help limit air movement.

Radiant energy — radiant barriers reflect heat back to the source for maximum efficiency.

And without temporary foam cores to become progressively waterlogged, Airframe was designed to remain lightweight, repairable, and useful for the long term.

The solution remained the same that started Tudor's energy-efficiency work years earlier:

Stop squandering the heat you’re paying for to heat your spa!

Invest in an Airframe

Solutions from critical thinking.
Built using the science of physics.
Engineered to sustainably conserve.

***Every single-hinged cover evaluated in these tests incorporated Coverplay’s foam-free, chambered-air design with single-hinge compression technology, invented by E. Jess Tudor at Coverplay. This design served as the original prototype for the Airframe spa cover. The initial version featured a single air chamber and one fabric-covered, 4-mil fluted top panel, with no radiant barriers. Even in this early configuration, the prototype outperformed every dual-hinged Styrofoam cover included in the testing