On the Path to a Zero Energy Home: What is Solar Tempering?

You may have heard of a passive house design. Passive house (or, German: Passivhaus) comprises a set of design principles used to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level. It exploits the sun’s energy for heating and uses the thermal mass of the home and its building materials to store that heat in the heating season. Applying these principles to a home can increase its cost by 10% or more. There are techniques you can use when building your home to take advantage of the benefits derived from passive house design without incurring many of the additional costs. It’s called Solar Tempering. 

What is a Passive Solar Home? 

Passive design is practiced throughout the world and has been shown to produce buildings with low energy costs, reduced maintenance, and superior comfort. Most of the literature pertaining to passive solar technology addresses heating concerns. Solar energy is a radiant heat source that causes natural processes upon which all life depends. 

The basic natural processes that are used in passive solar energy are the thermal energy flows associated with radiation, conduction, and natural convection. Additionally, the heat produced by the sun causes air movement that can be predictable in designed spaces. Thermal mass is used extensively in passive solar homes and must be carefully positioned to maximize the amount of energy it absorbs. Room design and layout is affected because of this and many passive solar homes use an open plan design for better air flow and heat transfer. 

A true passive solar home can easily provide between 50% and 80% of a home’s annual heating demand, depending on design, construction, availability of sunlight and the local climate. 

What is a Solar Tempering? 

Solar Tempering means making small changes to a home to maximize its incidental solar gain. This means orienting the long wall to true south (so the home is on an east-west axis) and slightly increasing the window surface area along the south side. This is typically accomplished by taking windows which would have normally been placed on the other sides of the house and placing them on the south facing side thereby adding no additional window costs.  

Using Solar Tempering doesn’t affect the thermal mass inside the building. The mass that exists in a typical home design usually provides enough storage to prevent overheating and make the home comfortable. While it is good to create a tight thermal envelope and increase insulation as economically as possible (to provide extra returns on the sun’s input), excessive insulation isn’t needed in a Solar Tempered home.  

Solar Tempered homes, designed properly and sited correctly on the building lot, rarely cost more than a standard home to build. Here are some design elements to aid with Solar Tempering: 

• Use higher Solar Heat Gain Cooefficient (SHGC) Windows on the south side with a SHGC of .4 or more. 
• Target a 14% window to floor area for the whole house. About 50% of these windows should be on the south side where the common living areas should be located. 
• Design shading to maximize winter sun and summer shade on the south facing windows. 
• Use insulated cellular shades to help keep out unwanted cold or heat, depending on the season.

How Can These Ideas Help My Home? 

Applying Solar Tempering principles is a great way to take advantage of the sun for heating without some of the drawbacks of implementing a fully passive house design. Some of the reasons to shift to Solar Tempering include: 

• variable climate factors 
• the higher cost of low U-value/high SHGC windows 
• the benefits of having fewer windows 
• the high cost of thermal mass 
• the risks of overheating if passive solar is not properly implemented 

Solar tempering provides a cost-effective alternative that involves taking advantage of solar heat gain without increasing window area or cost. It works best when the common living areas and most windows face south.

If you own your lot, use the principles of home placement to take advantage of the sun and/or minimize its negative impacts. If you are still shopping for a building site, it is important to think about how your home will placed on the site for Solar Tempering. There is something called the “10-Degree Rule”. The rule states that, whenever possible, a building should be constructed with the long axis facing within 10 degrees of true south (not magnetic south). The more you deviate from it, the more the east and west sides of the house are exposed to the sun early and late in the day in summer. This means that the home not only gets reduced heat on the southern face in winter, but that the building can be baking hot in summer. The reason for this rule is very simple: south-facing walls get the most sun (in the northern hemisphere). You want as much of a building as possible facing that way to gather as much heat and energy as possible. 

A sun-tempered home is an excellent choice for a prospective homeowner who wants to go for energy efficiency but isn’t ready for – or cannot afford – the full-on passive solar choice. 

MODULAR HOMES: ENERGY EFFICIENCY IS DESIGNED IN 

When it comes to building a home with modular construction, energy efficiency is a natural part of the construction process. Applying the concept of Solar Tempering involves not only the materials you will build with but how your home is sited on your building lot. The design flexibility of modular means it is easily adapted to build your home to take advantage of the principles of Solar Tempering.  

Add to that the benefits of indoor construction, the cost savings that can be associated with volume purchasing, and the health benefits of being built indoors and out of the weather makes the modular construction option one that is hard to beat. 

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