GREEN BUILDING DESIGN: PASSIVE HEATING AND COOLING STRATEGIES

The first step in designing a “green” or “sustainable” home is to design it in a way that reduces energy use through passive instead of active heating and cooling methods. Heating & cooling accounts for 43% of total energy used in a home, The goal is to eliminate the need to use your AC or heater to reduce utility costs, help save the planet’s natural resources, and reduce our carbon footprint. In Santa Barbara’s mild climate, if a house is designed utilizing the techniques I’m going to discuss, air conditioning wouldn’t be necessary at all, and even the use of your heater would be very minimal. However, some of these techniques here can only be implemented on a new ground-up house, although many can be implemented on remodels as well. Many of the concepts presented here were invented and used hundreds or even thousands of years ago, and they are still useful today.

House Orientation

House orientation refers to how the house is placed on the site, and can only be accomplished with new ground-up homes versus a remodel. The first thing architect’s do when they are proposing how to place a house on the site is a Site Analysis which takes into account the sun’s angle in the winter and summer, the wind patterns, views, and other site features and limitations. For the purpose of passive heating and cooling, it’s best to orient a building so the largest side of the building, as well as the majority of the windows, are located on the South and North sides. This is because the afternoon sun from the West causes the most amount of heat gain in the house, so we want to limit the wall area and window area that faces West. However, this is not always practical when you might want to orient the house for certain views, or because of the property’s limitations. In Santa Barbara, our ocean views are actually to the South, so it works out great. If the views are to the West however, there are some creative strategies to blocking the low-angled sun without blocking views such as retractable screens. High-tech windows with a reflective coating can also significantly reduce heat gain on West facing windows. In addition to knowing the sun’s path and angle, it’s important to know the direction of the wind patterns at the location of the house. In Santa Barbara, cold winter winds, which we want to block, tend to blow from the north, while summer winds are typically from the west, bringing ocean breezes that can cool the house and its outdoor areas. These winds must be considered when orienting the house on the site as well as in where to plant trees, hedges, or build walls that can block the winter winds while facilitating cool summer breezes. The wind patterns at any given location are highly dependent on local topography and other factors, and wind speed and direction can vary widely based upon the way a house and its landscaping are designed. Orienting the house on the East-West axis is something that can only be accomplished with new ground-up homes. Adding wind screens with walls or landscaping, as well as adding shading devices, are easy to accomplish with a remodel.

Ventilation

Doors, windows, and skylights provide ventilation. They let fresh air in and remove moisture and pollutants from inside the house. But ventilation also helps keep a house cool during the summer. Stack ventilation and cross ventilation are two methods that work differently. Stack ventilation uses warm air rising to create a draft and draw in fresh air from lower levels, while cross ventilation uses the outside wind to create a current of air across a building from one side to the other. Cross ventilation creates air inlets on opposite sides of a building to allow fresh air to flow through. It can be achieved with well-placed operable windows which can cool down the house both in the day and at night. It relies on wind so is suitable for buildings oriented in a way to take advantage of prevailing winds. Every location’s wind directions are different so it’s important for the architect to know the summer and winter wind directions in the location for which they’re designing. An architect needs to also consider the room placement within the house for functional purposes and find a good compromise between window placement for functional purposes and window placement for passive cooling. Cross ventilation can provide a more direct and efficient exchange of air compared to stack ventilation, particularly in buildings with regular wind patterns, but is not as effective in still, hot conditions. Stack ventilation uses both low operable windows near the floor, and high operable windows near the ceiling to allow hot air to escape. The hot air rising reduces pressure in the lower portion of the building thereby drawing cool air in at the lower levels. The next level of stack ventilation expands on these same principles in order to provide ventilation by way of extract vents within the wet rooms of your property such as bathrooms and kitchens which are routed vertically to the outlet vents at the ridge of your roof. But this can allow for a lot of air leakage, air infiltration, and heat loss. An intelligent version of this includes the addition of humidity sensing vents in the inlets and extracts. These detect humidity in the air and react by expanding or contracting which opens (increasing ventilation) and closes the vents (decreasing ventilation) depending on the humidity levels within the property. These “smart” vents and trickle vents don’t require any electricity to operate as they tend to use nylon filaments within the vents that expand and contract relative to the humidity levels in the individual rooms within the property and should therefore be maintenance free. The main advantage of this system is that it will self regulate the ventilation. To facilitate achieving good ventilation, it’s relatively inexpensive now to have automated windows, as well as window shades, operated through an app on your phone through which you can automate the opening and closing on a schedule. Adding windows, doors, and skylights for ventilation can be easily accomplished with a remodel.

Windows & Shading Devices

Window placement is key to passive heating and cooling. Architects must take into account the sun’s path and the angle of the sun during various seasons. In our location where we have the sun rising in the East in the morning, and setting in the West in the afternoon, we want to limit the amount of windows on the West side of a building because the hot afternoon sun is low in the sky and comes into the windows fairly horizontally which makes heat gain much greater. Architects must also consider a fairly horizontal angle of the sun for East-facing windows, although the heat gain into the house isn’t as significant in the morning as in the afternoon. There should be a lot of North windows to let in indirect daylight which is the best quality of daylight since it isn’t too bright and it doesn’t shine directly into your eyes. North-facing windows allow a lot of light into the space without any negative consequence. South-facing windows are also important, but they should have overhangs or other shading devices that allow the sun to hit the window directly in the winter to help heat the house, but not in the summer, so the house stays cooler. To design overhangs that accomplish this, it’s important to know the angles of the sun at various times of the year. Every location is different. In Santa Barbara, during the summer, the sun will be high in the sky, reaching a maximum angle mid-day of approximately 70 degrees. During the winter months, the sun is lower in the sky, reaching a maximum angle of around 30 degrees mid-day. It’s sometimes better to use vertical shade devices, or overhangs with louvers to accomplish the right amount of shading of the windows at various times of the year. Window shades on the interior can provide a small amount of protection against heat gain, but once the heat gets past the glass, the house will heat up. Exterior shading devices or even exterior window coverings are necessary to prevent heat gain, and there are lots of creative ways to accomplish this. Much of this is changeable with a remodel.

Insulation and Air Infiltration

The most important aspect in preventing heat loss and heat gain is high-quality insulation and sealing. Insulation technology has come a long way and sealing potential air leaks through joints in the construction is critical. Spray-in foam insulation provides much better thermal performance than fiberglass batt insulation and reduces air infiltration. Spray foam insulation outperforms fiberglass insulation due to its higher R-value, better air sealing, and moisture resistance. Spray Foam Insulation acts as a vapor barrier and air sealant, reducing drafts and improving energy efficiency. It’s resistant to water damage. Fiberglass insulation can be affected by moisture, potentially leading to mold and mildew growth, but it’s more affordable than spray foam insulation, making it a budget-friendly option. It’s also easy to install, as it can be cut and fitted into place by a homeowner. Spray foam is more expensive and has a more complex installation process than fiberglass. It must be installed by professionals. A hot attic equals a hot house. Most houses use fiberglass batt insulation at the attic floor which is also the ceiling of the room below, and no insulation under the roof at the attic’s ceiling. Even though attics are ventilated, this creates a very hot attic which eventually heats the house. It’s recommended to use spray foam insulation at the attic ceiling to insulate the attic as well which eliminates the need for insulation at the attic floor and also eliminates the need for attic vents which helps with wildfire-resistance. Rim joist insulation, and insulation at the foundation wall can seal up gaps that are often overlooked. Spray-foam insulation is the best way to seal these areas, because it easily fills in and seals all the cracks and openings. Fiberglass insulation for these areas is not recommended. Because fiberglass easily allows air to travel through it, it is a very poor choice for insulating the drafty rim joist area. It is almost impossible to get a proper air seal in this tight space. The recommendation is that fiberglass insulation be removed from these areas and replaced with a more effective insulation and vapor barrier system. Rim joists can leak more than windows. Also a house breathes from the basement up. Typically three quarters of the air infiltration comes from the basement or crawl space. Not only is this a problem for heat loss and gain, the air entering or exiting the rim joist and crawl space areas can contain high levels of moisture, increasing the likelihood of mold growth and rot in this area of the house. Adding insulation and sealing joints is easy to accomplish in a remodel.

Thermal Mass

A thermal mass is a material within the building that can help reduce temperature fluctuations throughout the course of the day and night. It must a material with a high heat capacity and high material density such as a concrete or masonry wall or a concrete floor. These materials absorb direct heat from the sun, and store it due to their high heat capacity and density, and then release the heat very slowly when the surrounding air begins to cool. The best location for a thermal mass is on the West or South exterior wall of a house since those sides are exposed to the most heat gain. It not only absorbs heat from sunlight during the hot season, releasing it slowly overnight, it also absorbs heat from warm air in the house during the winter to help warm the house.

​Roofing

A “cool” roof is one that reflects sunlight and absorbs less heat. A roofing material that is light in color or has a reflective coating applied to roof can accomplish this goal. It's also best for the exterior walls to be light in color. Another option for a cool roof is a "green roof" which has vegetation on it.

Plants act as insulation. During the summer, a green roof reduces heat flow into the building, and during the winter, it helps to retain heat. Plants block sunlight, reducing the amount of heat that reaches the roof surface. They also absorb water and release it as water vapor through transpiration, a process similar to sweating

Building and construction are responsible for approximately 40% of global greenhouse gas emissions, more than transportation, cows, or any other sector. Therefore, designing sustainable buildings is crucial to the long-term health of our planet and our species.