According to the U.S Department of Energy, heating and cooling account for 56% of energy use in a typical U.S. home. To significantly reduce this number, the Stuttio Workshop team began researching alternative methods of heating, including passive solar heating techniques. The two most common passive solar heating systems are direct gain systems and indirect gain systems, both of which rely on similar principles regarding the collection, storage, and distribution of solar energy (heat). The basic idea of thermal storage is that a material such as concrete (or masonry or water) takes a long time to heat up, and an equally long time to cool down. This inherent material property is advantageous for passive heating systems in that the material will slowly heat up during the peak sunlight of the day, and then slowly release (via radiation) this stored heat into the space, well after the sun has set and the heating demand in the house is greatest.
Direct Gain System
A direct gain system, the most simple and cost-effective passive solar heating strategy, is defined by transparent glazing on the south face of the building that allows winter sunlight to penetrate into the space and to strike the floor surface. Typically, this floor surface is of a material with a high thermal storage mass, like concrete. Most often, moveable insulating panels will need to be designed in a direct gain system so that heat loss does not occur through the glazing during evening hours. In both direct and indirect gain systems, an overhang must be designed on the southern façade to limit the solar exposure of the wall during summer months when heating is not required.
Indirect Gain System
An indirect gain system utilizes a thermal storage wall on the south façade of the building. This wall, typically concrete, masonry, or water, is placed directly behind insulated glazing, with a small airspace between the two surfaces that when coupled with a vented storage wall can also utilize convection (in addition to radiation) to distribute heat throughout the interior of the building. These walls are often referred to as Trombe Walls. Conceptually speaking, the main difference between a direct and indirect gain system is simple: occupants reside IN a direct gain system and NEXT TO an indirect gain system.
Thermal Diagrams
Stuttio Workshop ultimately decided to pursue an indirect gain system so that our chosen wall system of Virginia Limeworks EMU could actually be used as a passive solar heating component. If we were to choose to use a direct gain system, the wall type (either the wood HIBs or the ICFs) would be less important as a thermal storage mass since the primary storage medium in a direct gain system would be the floor material. Rather than allow our decision between the three given wall construction products to be an arbitrary one, our goal was to make every component and material selection of the house a deliberate design decision that would contribute to the overall performance and experience of the space.
Thermal Mass Wall Construction
After deciding to incorporate an indirect system into our building, we identified natural daylighting as a potential drawback of a typically constructed masonry Trombe wall. Our research into thermal storage walls revealed that water, in addition to concrete and masonry, has excellent thermal storage qualities and for many years has been used as primary storage medium in thermal wall construction. Seeing a potential opportunity to create an innovative revision to the traditional thermal storage wall of masonry, concrete, or water exclusively, Stuttio Workshop proposed a hybrid EMU/Water wall. In terms of performance, both the EMU blocks and the water tubes(http://www.solar-components.com/tubes.htm) provide similar thermal storage capacity. In terms of design, the transparent qualities of the waterwall tubes would allow us to modulate daylight through the south façade based on the requirements of the interior programs. What results from this strategy is a mosaic pattern aesthetic reminiscent of an aerial view of the agricultural land parceling surrounding Greensburg.
There are so many options of heating systems these days. It’s great that people are taking advantage of the different options in order to save money in the long run.