"Convection Loop" Passive Solar Home
Site characteristics or focus during construction or remodel: Direct south orientation, treeless lot
Construction Type: Wood frame, classic “envelope” design from the prototypic “Smith House,” 2 Stories, 3-4 bd/3 ba
Envelope design employs a “convection loop”; an attached solarium is continuous to airflow over the living space ceiling, down an airspace in the north wall and in contact with the crawlspace/basement, then back to the solarium. This involves a double wall on the north and ceiling dropped from the roof. The interior foundation is insulated with rigid foam.
With so many sunny winter days, especially when temperatures are very cold., solar radiation heats and expands the solarium air, driving it over the ceiling and down the north wall plenum space (aided by contracting, cooler, crawlspace air) and then returns to the sunspace after loosing heat to the native soil under the house. A continuous, barely perceptible airflow is established that brings heated air all the way over and around in the envelope space. The concept is counter-intuitive, but it really works!
The most “active” part of this home’s design involves the occupants having to manage opening and closing windows, doors, and skylights at the most advantageous times for optimal heating or cooling.
Passive Solar System: 39 panes of 4x 6.5 glass on south wall. Convection loop (envelope) passes heated air over and around the ceiling through north “plenum” to thermal storage mass (foot print of foundation) also serves as super insulated double wall. East & west walls are thermally “broken” (staggered studs) and are not connected to convection loop.
- There is a 80 gal “breadbox” domestic hot water pre-heater supplying 80-120F water to 2 conventional electric water heaters
- Minimal north windows, few strategically placed east & west windows
- Convection cooling by four ventilating skylights in sunspace.
- Indoor sunspace provides approx 1000 sq ft of indoor decks.
Auxiliary Heating System: Upstairs woodstove – one cord lasts 6 YEARS! Three bathroom electric wall heaters. Thermal storage mass within living area and under house keeps living space 60-80F while convection loop experiences temperature swings of 40-120F. Woodstove is used only on 3rd consecutive cloudy day.
Conservation Features: Abundant day lighting from south glass reduces use of electricity for lighting. Airlock entry pre vents excess heat loss. House is insulated and all windows & doors have thermal seals, but it is not “super tight”, so indoor air quality is excellent with naturally occurring air exchange with outdoors does occur.
Subjective Evaluation/ design considerations: So much is accomplished with site orientation and strategically placed windows and thermal mass storage. It is a very comfortable house to live in!
- This designed could be improved by: More strategically designed mass and “tighter” construction.
- Active systems to consider to add performance would be:
- Hydronic system with differential thermostat controls for moving excess heat from sunspace to mass storage or living room, as needed.
- Insulate window wall at night to reduce conduction and convection heat loss.