Solar Air Heater Update

     Well, I guess that it's about time for a solar air heater update. I've actually made time in the last week to work on them, so, after 7 hours of work, there is visible progress. It's always exciting to see the images in my head becoming reality in the shop (1-car garage that I'd never park a car it but it will never fall down so I can replace it either...)
     To start, I attached a 0.25"x4'x8' piece of moisture resistant plywood to a 1"x4'x8' piece of R-tech insulation foam board with 2x2s on the opposite side. The plywood is for strength and structure to attach fans and ducting to. The foam is to insulate the warmed air from the exterior air temperature.     The next step was adding double foil, double bubble on top of the R-tech insulation. There are two reasons for this - one, added insulation with minimal thickness - I'm using metal studs to "encase" the outer edges and they're a finite depth of 3.625", and two, I'm not sure if the R-tech insulation boards can handle the heat that I hope will be inside these heaters - I suspect that they won't melt, but just in case...     After that, I installed the 2x2s that channel the air in a serpentine fashion so that it can collect enough energy to overcome any heat loss in the ducting and still feel warm as it blows in to the house.     I've actually already cut the holes for the air intake and exhaust but don't have a photo of that.
     This may all look a little haphazard, but it's actually sort of well thought out. There are calculations that need to be done based on the square footage of the collector and the altitude (to compensate for air density differences) to determine the channel's cross sectional area for optimal heat transfer. Based on Logan's altitude and a collector that is 4'x8', I needed a cross section of 15.22 square inches. With the 2x2s around the outside and creating the channel, the air-gap between them is 10.25". 2x2s are 1.5"x1.5" so the channels' cross sectional area is 10.25" * 1.5" = 15.375 square inches - close enough.
     I'll post a detailed list of the costs later, but so far it looks like each will cost around $175 to make - significantly less than smaller units I've seen during my research that sell for over $1,700. By the way, there are three of these, so I won't be able to recover my costs this winter since my heating bills for November 15th through May 15th total around $510 and that includes water. But I think they will accomplish one thing that will make it all worth it - Jeri Dawn shouldn't freeze this winter - the past three years, the thermostat has been set at 66°F during the day and between 57 and 61°F at night. We should be able to keep the temperature just above Travis and Crystal's subarctic apartment and do it without spending more than last year. After all, the goal wasn't just to save a little money, it was a fun project (that is being funded by a bonus from my awesome job) that will make us more comfortable without giving all our money to Questar Gas! I'll keep you posted.