I have a unique situation that I am looking for ideas on.
I grow orchids and have a room (bonus room over garage)in the house dedicated to this activity. It is all fluorescent lighting but also has independent humidification that keeps it 60-80% humidity at all times. The lighting and air exchange with the house is enough to keep the room heated throughout the year...the HVAC vents in this room are blocked to not allow HVAC to enter this room.
There in a 6" inline fan that exhausts air from the room base controlled by a thermostat...when the room gets too warm the exhaust fan kicks on. In summer this exhausts into a very open area of the attic and out through roof vents. In winter the air is redirected into the main portion of the house allowing recapture of both the heat and the humidity from the room. The duct run is 3 feet in summer and adds and additional 7 feet in winter. Both the duct and fan are insulated from the unheated attic space where they reside. Despite this insulation I am experiencing condensation in both the ducts and the fan during cold periods causing both a concern for health (mold) and potential fan problems if it gets wet. No issues of mold/condensation are seen in summer.
I have been unable to find a solution that would allow me to recapture the heat and humidity from this area and return it to the rest of the house without the electrical and health concerns. I do not want to exhaust it directly outdoors as then I would need to open exterior inlet vents in winter which would be damaging to the orchids from the cold air entering the space. I am hoping someone may have some innovative ideas for either a product or approach to help.