Rahmah Design Feb 11, 2011

Band drawbacks associated with a potential design change from the current Solar Hot Water design to a Forced Convection Solar Hot Air system.

PROS:
-Maintenance of this kind of system would be much easier than SHW, since it has only one moving part: a small 14 watt fan that is powered by an onboard PV panel on most models. This is probably a big pro since maintenance was an issue with the previous project in Ramah because as of now (particularily because there is no heater) the building is not always used on a daily basis.
-Installation could be significantly easier for us than with the SHW system.
-SHA systems start providing warm air more quickly in the morning.
-The simplicity, passivity and replicability of the system puts it more in line with the general ethos of EWB than did the SHW system.
-This simplicity also makes the education initiative much easier, both in terms of explaining the system to the community and kids and in creating a user manual.
-Overall, the system is likely to be much cheaper than the SHW system, lessening our fund-raising requirements and getting us toward our real goals much faster
-Although the system we have been looking at is made in Canada it is available through several distributors in Albuquerque alone and has a 5 year warranty.

http://www.yoursolarhome.com/solarsheat.com/dealers/northamerica/index.html

CONS:
-There is no thermal storage so use at night is pretty much not an option.
-Installation actually may be an issue: if we mount directly on a south facing wall we would need to remove trees at the site. If we mount on the roof we run into some of the issues we were grappling with in the SHW design (although this panel weighs only about 100lbs).
-Overall, it seems the biggest issue would be capacity, could we actually heat the Hoogan with these and how many would we need?
-This area probably requires the most research on our part. According to the numbers given by Solar Sheat, a double-wide unit on a sunny day is capable of providing 40,800 BTU/day. Our initial heat load calculations (which were generous over-estimations) by Adam and the guys at Bridgers and Paxton put our need at about 9,682 BTU/Hr. So were forced to consider things like purchasing and installing more panels (3 would get us close) and may loose some of the advantages in cost and installation ease. According to one dealer I looked at the double units were about $3,000 and the single units about $2,000.

One of the side benefits of this limited capacity however may be that we would have to put even more thought into increasing efficiency elsewhere in the building with insulation etc. Being forced to work around various expected and unexpected constraints while still resolving the initial problem... sounds like engineering!