NREL: Passive Solar Home Design for 20-60% Energy Savings

This NREL guideline details passive solar strategies for homes, achieving 20-60% energy reductions via conservation, suntempering (7% south glazing), and full passive solar (direct gain, sunspace, thermal storage wall) with enhanced insulation. Essential elements are south-facing glass for collection and thermal mass (brick, concrete, water) for storage/release. Key concepts cover orientation (within 30° south), site planning to avoid shading, interior planning for heat distribution via open plans, and integrated systems. Conservation improves via super-insulated envelopes (R-40 ceilings, R-19 walls), reduced infiltration (blower-door tested), efficient windows (double-glazing, low-e), and downsized mechanicals. Direct gain systems use 10-15% floor area glazing with 4-8" mass slabs adjacent; sunspaces add buffer zones with vents/mass; thermal storage walls (Trombe) employ dark absorbers, vents, and insulation. Sizing rules: glass/mass ratios of 1:7-12 sq ft concrete, adjusted for climate. Mechanical integration includes night purging, adjustable vents, and backup sizing at 10-20% load. Examples from Great Falls, Montana, illustrate implementations yielding high comfort. Process: site solar access, orient long axis east-west, plan mass under glass, shade summer sun with overhangs (calculated via solar angles), ensure distribution paths. Holistic approach treats house as system, with checklists for performance verification[5].