Phase I of Solar Furnace for Low Impact HVAC on Second Floor
The large 2nd floor windows (60ft. x 14ft.) are optimal for winter solar energy collection because it is oriented due south and at the optimal 60o tilt. The windows are all double pane panels with a 3-inch(?) air gap and acrylic glazing to make the windows a super-insulated solar collector with a triple glazing.
This 2nd floor layout was originally an open floorplan with the atrium and office space connected by three large archways. This lead to exceptional daylighting for the upstairs offices, but also constant summer overheating that has driven out several tenants in the past. Preliminary modeling by the Burlington Electric Department (BED) resulted in the recommendation of a 15-tonne air conditioning unit to offset this massive solar gain. This would require an enormous quantity of electricity at peak demand times.
FLOORPLAN PICTURES HERE
The atrium space could have been walled off from the office space using drywall and or rigid insulation to contain the solar gain as was done when it was used for a solar kiln. The wall would also block the abundant natural daylight in the office space and decrease office space desirability and productivity. A PV system installed over the windows was also considered to help block solar gain, but this option was also not selected due to daytime lighting concerns. The system could be installed as an awning, but this option was considered cost prohibitive.
Vermont Green Offices employed a creative solution to thermally isolate the atrium space when desired while preserving the abundant daytime lighting in the office space. A transparent thermal break was installed with an access door. Macrolux paneling was used for the transparent thermal break. This material has an R value of 123. The access door has glass panes and can be either opened or closed depending on the ambient temperature in the solar furnace (atrium) and the 2nd floor office space.
The thermal break collects and contains the heat collected by the windows through solar gain in the atrium space. This heat is distributed throughout the 2nd floor in the winter and dumped outdoors in the summer. An air-handler located at the peak of the atrium was retrofitted with an air handling fan with adjustable control to move extra heat to the exterior of the building via a vent on the north side of the building in summer.
Phase II of the solar furnace will include adding several hydronic loops in the solar furnace to reclaim heat from the atrium and move it to where it can be used (such as preheating the electric water heater on the first floor). Our solar kiln experiment has shown that temperatures of over 140F are possible in this space – perfect for water heating applications.
DIAGRAMS AND PICTURES HERE
A BMS will be used for system monitoring and optimization. More on Phase II in Upcoming Improvements.
Additional information on Vermont Green Offices’ Passive Solar Architecture coming soon.
