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String Theory

As summer temperatures blaze, WarmSpring makes the heat flow!

WarmSpring attic heat recovery system takes a practical approach to exploiting low-grade heat from a seasonally hot attic. Working with the combination of an attic ventilation fan with a compact air-to-water heat exchanger, designer Chris Roseberry of Garland, Texas uses Alibre Design Professional to improve access to a valuable source of heat.


Since 1989, Chris has been producing the WarmSpring attic heat recovery system, which utilizes attic space heat for warming water in swimming pools & spas. During the warm seasons across the northern hemisphere, this product allows the roof and attic portion of a house to function as an effective solar collector. WarmSpring uses the effect of surface solar adsorption and the resulting heated air within the attic space.


Using Alibre Design Professional's 3D design tools to combine an air-to-water heat exchanger with a attic ventilation fan, Chris creates the RTU (Roof Top Unit) that heats the water from the heated air in the attic. By simply turning off the water flow to the heat exchangers, a WarmSpring unit can also engage ventilation only to moderate the attic temperature during the portion of summer when no pool heating is required. To prevent the possibility of water damage, the entire water piping system is external to the house. WarmSpring also departs from convention by not routing the entire filter pump flow to the heat exchangers. Instead 3 to 12 gallons per minute flow through a heat exchanger loop that is in parallel with the primary pool pump flow.


This small flow rate allows the use of very inexpensive ¾ PVC fittings and tubing for the heat exchanger loop. Moreover, a small 140 W pump is thermostatically engaged to drive the flow in the heat exchanger loop rather than a power-actuated valve which costs twice as much. The visual impact of WarmSpring is about the same as an ordinary attic fan. The small-diameter water lines attract little notice when painted to blend with the roof.


Being a low-tech product with a small number of parts, WarmSpring can be manufactured with long-established sheet metal and coil fabrication techniques. Several seasons of testing in Dallas have indicated that a single unit will routinely produce 250,000 BTU/day. Many of the owners of the eight million pools and four million hot tubs in the US will soon have a new lower-cost option for dramatically reducing their reliance on hydrocarbon-derived heating with its inherent cost and impact on the climate. WarmSpring was a contestant in the NASA Tech Briefs - Create the Future Design Contest 2010. The 2010 contest is now closed for entries. You can vote on entries through August 31st. at http://contest.techbriefs.com/


WARMSPRING Technical Specifications

    Diameter: 30"
    Width: 30"
    Mount to Roof Attic Vent Opening
    Volume = 9.255964297E2 in³
    Mass = 1.469107565E4 kg
    Surface Area = 8.008567371E3 in²

Design summary:

    Sheet Metal Frame
    Parts : 34
    Faces : 1436
    Edges : 3449
    Vertices : 2285
    Unique parts : 12

3D model and manufacturing drawings: Alibre Design Professional

About Alibre, Inc.
Alibre is the leading global provider of cost effective professional grade mechanical CAD, CAM, and PDM solutions. Founded in 1997 and based in Richardson, Texas, Alibre develops Alibre Design™ and Alibre CAM™, the fastest growing parametric CAD/CAM solution on the market. One fifth the cost of comparable software, Alibre Design offers the same core features of SolidWorks, Pro/E, Inventor, and other mid-range solid modeling packages at a cost that is affordable to any business or individual. Alibre CAM extends Alibre Design to provide integrated 2½ to 5 axis CNC machining. Used by an immensely diverse user base, Alibre Design and Alibre CAM provide design and manufacturing solutions to Fortune 500 companies, small businesses, consulting firms, machine shops, start-ups, hobbyists, inventors, teachers and students. Alibre products are distributed in 50 countries and in 15 languages.