There are two main ways modern civil engineering achieves solar energy-based buildings: it builds / retrofits and designs homes using solar heating systems or it builds passive solar gathering homes.
In a passive solar building, all elements – walls, roofs, windows and floors – are designed to gather, store and evenly distribute solar energy in the form of heat during the cold months and reject solar heat during the hot season. Everything lies on the shoulders of the design itself and on a few other features we will take a look at next.
The Main Conditions to Build a Passive Solar Home
The passive solar home represents a holistic approach and it is interdependent of the regional climate you live in and the actual site you build on. You can build a passive solar home in an area where the sun doesn’t shine 24/7 all year long, but you should choose the land wisely:
- Look for a patch of land that is deep north to south and build the house on the northern end of the lot having as much view of the sun as possible on the south-side of the building.
When designing a passive solar home you need to have solid knowledge of the house’s thermal mass. This is defined by the material’s ability to retain or store the heat produced by sunlight.
- The most common thermal mass materials are concrete, brick, stone, and tile. They absorb heat from the sun during the warm season and also absorb heat from the warm air inside the house during cold months.
- Water and phase change products are more efficient at storing heat and releasing it during cold seasons.
- Wood and masonry work both as thermal mass materials and finishing products.
Building a passive solar home might seem hard at first, but with the proper team of experts you can benefit from energy efficiency and lower bills on the long run. There are a few basic rules to follow when it comes to the structure:
- Aperture (or collector) – this is a large window or glass wall which allows sunlight to enter the entire building. Traditionally the aperture faces the south within 30° and shouldn’t be obstructed by other buildings, trees and objects from 9 a.m. to 3 p.m. daily during the warm season.
- Properly oriented windows – Just like the aperture, most house windows should face the true south within 30°.
- Windows glazing – the amount of glazing depends on the building type and climate
- The Absorber – this is a darkened surface used in the storage of heat process, which sits in the path of sunlight and then absorbs it as heat.
Heat Distribution and Control
After sunlight is absorbed and transformed into heat, it is distributed through all the rooms in the house.
- Distribution: heat can be distributed through conduction, convection and radiation. This is why you should install fans and blowers, ventilation systems, etc. Create a sunspace and use darker colors for indoor finishing. To further ensure your living environment is healthy and sustainable, use eco-friendly paints and coloring materials as an environmental friendly, non toxic solution.
- Control: among the most common heat control methods, specialists mention roof overhangs to create shade to vertical south windows, programmable and differential thermostats to control fans and ventilation, operable vents and dampers, etc.
We should ensure that the structural integrity and stability are set in place. To do so, we need to have knowledge on how passive solar homes work.
If there are solar panels on the roofs of the home, structural analysis is needed to determine the solar racking system and the type of connections of the panels to the roof structure. We also should be familiar with the load path of the solar panels to the main structure, such as rain ponding on the panels and at the points of connections that will incur stresses at the location of rails and support.
Since passive solar homes have increased windows area ratio at the southern walls, this leads to the decrease of structural shear walls at the south wall. This will cause unequal distribution of lateral resisting support, which can induce torsion of the overall structure and can create cracking at the windows. To prevent torsion, we can design special trimming beams around the windows to reduce cracking at window seals. We can also place windows at locations that can prevent torsional effects.
Structural engineers should also ensure that the structure and its exterior walls are designed for air tightness for insulation effect. Efforts should be made in detailing air tightness connections at joint locations and envelope penetrations. Besides air tightness detailing, we can also consider using prefabrication to cut and join the membrane to structural beams under controlled conditions to ensure that no gaps are present in the insulation. Structural damages can be done when air or moisture penetrates the gaps.
Roof overhangs for solar shading can create additional loading and cantilever moment from the external canopies. Analysis should be made to ensure those members are able to support flexure and buckling.
Moreover, we need to work and communicate closely with different disciplines in the design team. We cannot consider each component separately since this is an integrated system of the building. By understanding the basic principles of passive solar housing and simplifying its details, we can make the project more simple and cost effective.
Guest Blogger: Andrew Patterson
Mr. Patterson is one of the original founders of Paint inspection Ltd, a Surveying and Coat inspection company that maintains eco-friendly and ethical paint inspections.