A passive house isn’t only energy-efficient but also comfortable. However, designing and building a passive house requires meticulous planning and careful selection of its site and building materials.
Although rising fuel prices and increased environmental awareness have renewed interest in passive homes, many homeowners are still unsure if the energy savings warrant the extra effort needed to design and build such a house.
This article will provide you with a few statistics to better understand how energy-efficient passive houses are. We’ll also explain some of the most fundamental passive house design elements to help you plan your home.
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How Energy-Efficient Is a Passive House Exactly?
A passive house can be up to 90% more energy-efficient than buildings that do not incorporate any passive solar heating or cooling design. In addition, passive homes are 75% more energy-efficient than newer traditional houses.
Learning more about the potential energy savings you can make through passive houses can encourage you to consider building one or retrofitting your existing home to implement one or more passive design standards.
Energy Savings in Passive Houses
As the temperature of the earth rises and more and more people become environmentally conscious, there’s an increased focus on the performance of passive houses.
As a result, several studies have been conducted worldwide in varied climates to evaluate the energy efficiency of passive homes.
The findings from these studies were published in this paper, including the following:
- A study in Germany found that passive houses can reduce 80% of total energy consumption compared to traditional new buildings. The same study also found that passive houses had 50% lower primary energy consumption (including domestic electricity) than newer traditional buildings.
- In New Delhi, India, a region with brutally hot summers and cold winters, a study found that annual energy consumption for heating and cooling in passive houses were 1481 kWh/a and 1814 kWh/a lower than those in homes that did not employ passive solar designs.
- According to a study in London, passive houses had one of the lowest energy consumption rates for small family homes in the UK.
- And according to a study in Portland, OR, double-decker villas with passive solar design achieved net-zero energy consumption in conjunction with solar panels, which are ideal for the climate in the Pacific Northwest region.
- One study conducted in the Qivli District of Australia found that passive houses had 64% lower energy consumption than traditional houses in the same city.
- A study carried out in Belgium found that a passive house’s per capita energy consumption is 19.6% lower than that of buildings that don’t incorporate passive design standards.
- Finally, according to studies carried out in some severely cold regions across the world, passive houses use 33% less energy to heat and cool indoor spaces than traditional buildings and don’t need mechanical heating and cooling in winter and summer.
Passive solar heating can reduce heating costs by 25%, even in homes not fitted with solar panels.
A 25% reduction in heating needs translates to a 25% reduction in the size of solar panels you need for your home. For example, you’ll only need to install a 4.5 kW system instead of a 6 kW system, saving about $4,500 in upfront costs.
The Five Principles of a Passive House
Passive houses use a building’s location, climate, architectural design, and construction materials to minimize energy use. Minimizing energy use refers to using little or no mechanical heating or cooling.
Besides the emphasis on energy efficiency, passive design standards also strive to create a comfortable indoor environment for the inhabitants of a building.
The following are the five principles of a passive house:
- High Thermal Insulation: Thermal insulation ensures that the heat gained from solar radiation does not escape out of the house.
- Highly-Insulated Windows: According to the Environmental Protection Agency (EPA), heat loss and heat gain through windows accounts for 25-30% of domestic heating and cooling costs. Highly-insulated windows reduce heat loss and allow for solar heat gain.
- Natural Heat Recovery Ventilation: This ensures a steady fresh air flow while significantly reducing heat loss without using any mechanical equipment.
- No Air Leaks: Air leaks let warm air escape from the building or admit cold drafts from the outside and cause living spaces to become frigid.
- No Thermal Bridges: Thermal bridges can cause heat loss of up to 30%. These are areas where the heat transfer rate is very high, resulting in condensation, high humidity levels, and mold growth.
You must remember that while the basic principles of passive house design are general and can be applied to all regions of the world, they must be modified to suit specific climatic conditions.
For instance, too much insulation can overheat homes in warm climates and may create a stifling indoor environment.
Therefore, the following passive strategies are implemented to better design buildings in warm climates:
- Natural nighttime ventilation to let the internal heat escape
- High thermal inertia to prevent overheating
- Use of shades to control solar heat gain
How To Design a Passive House
Benefits of designing a passive house by climate include:
- Passive solar heating if you live in a cold climate
- Passive solar cooling if you live in a warm climate
- Both passive solar heating and cooling if you live in a region with hot summers and cold winters
Passive Solar Heating
Passive solar heating is suitable for regions with cold winters. The goal is to capture the heat from the sun’s rays, store it, and release it throughout periods when the sun isn’t shining, including the evening and night.
The following are the principal design elements that can help you achieve passive solar heating:
In the northern hemisphere, a south-facing window lets the sun’s rays enter the house, where it is stored to be radiated back out into the living space when the sun goes down. South-facing glass should fulfill the following criteria:
- Oriented within 30 degrees of true South
- Trees or other buildings should not shade it from 9 a.m. to 3 p.m.
- It should not have any exterior coating that reflects the sun’s rays into the outside air and prevents them from entering the building.
The sun’s rays that enter a building are absorbed by the exposed hard and dark surface of the storage element. The absorber can be a masonry wall, the floor, or a water-filled container that should be placed such that the sun rays hit it directly.
Water-filled containers double as absorbers and storage media. However, they are challenging to install and integrate into the existing framework of a building.
The thermal mass is below and behind the absorber. It retains the heat absorbed and releases it back into the living space at night.
The thermal mass should fulfill the following criteria:
- It should be dark in color to absorb the maximum amount of solar radiation.
- To prevent heat loss, it should not be in direct contact with the cooler outside air or the cold ground.
Thermal mass can be a concrete or masonry wall. A water-filled container can also be a thermal mass, but it requires careful planning and installation.
Passive Solar Cooling
Passive cooling design standards are suitable for warm climates.
The following are the goals of passive cooling:
- Reduce unwanted heat gain during the day and prevent overheating.
- Create ventilation without using any equipment.
- Exchange warm indoor air for cooler air from the outside.
- Prevent cool interior air from escaping at night.
The following design elements help you achieve passive solar cooling:
Windows in warm climates should be shaded by an overhang or other devices like awnings, trellises, or shutters to prevent the scorching midday sun from overheating the indoor spaces during summer.
An awning on a south-facing window should shade half of the window’s height. This ensures the living space is shaded from the midday sun high in the sky in summer, but the winter sun low on the horizon can still warm the building.
The sun is low on the horizon during sunrise and sunset as well. So, awnings on the east and west-facing windows are not very effective. So, while designing your house, you might want to minimize the number of windows on the east and west sides.
Creating ventilation in warm climates lets in the cool breeze from outside into a living space, keeping temperatures low, preventing overheating, and establishing an air movement that cools the skin. The result is a comfortable indoor environment.
Here are some ideas on how you can create indoor ventilation:
- Open Windows To Let In Breeze
If you live in a region with prevailing daytime breezes, ensure that you have one or more windows built on the side of the house from where the wind blows.
During the day, open these windows to let the breeze in to cool your living space.
- Create Cross-Ventilation
Create cross-ventilation by opening the windows facing the breeze and those on the opposite wall. Cross ventilation ensures the indoor environment does not become stifling, so this approach is one of the most efficient ways to cool down a living space and increase air circulation naturally.
- Build Wing Walls To Channel the Breeze
Place a wall or a solid vertical panel perpendicular to the prevailing breeze that blows in through a window on the windward side. There should be another window on the leeward side or the side away from the wind.
The wing wall creates a pressure difference that increases the speed of the wind.
- Let In Cool Nighttime Air
Let in the cool air at night and close all windows during the day. This process ensures the coolness does not escape from your living space.
This passive cooling method is suitable for regions with lower nighttime temperatures than daytime ones.
- Use Convective Cooling
Convective cooling is effective in regions with prevailing nighttime breezes. You can let in the cool nighttime breeze that will push out the warm indoor air.
- Hot air rises and pools near the ceiling.
- A vent high on the wall or opening on the side away from the breeze lets the hot air escape.
- When hot air escapes, a vacuum is created.
- The vacuum draws in cool air from outside through vents placed low on the wall facing toward the wind.
You can also create conditions for convective cooling in regions without nighttime breezes with thermal chimneys. Here’s how:
- You must have a south-facing sunroom with vents near the ceiling attached to the living quarters.
- Shade the thermal mass wall of the sunroom to ensure the air in this space remains cool.
- Close all upper vents in the sunroom that open into the living space.
- Close all operable windows.
- Leave open the vent from the living room to the sunroom and all lower vents connecting the two areas.
- Hot air from the living room is drawn into the sunroom through the connecting lower vents.
- Hot air rises, collecting near the ceiling and escaping through the upper vent.
Here are some tips on how you can plant trees, bushes, shrubs, and vines strategically to cool your home:
- Place trellises with vines to shade east and west-facing windows.
- Plant deciduous trees on the east and west sides of your property to prevent solar heat gain during summer.
- Plant shrubs and bushes to shade paved areas like driveways to prevent these surfaces from heating up and radiating warmth to the nearby walls of your house.
- Plant ground cover to prevent heat absorption.
- Plant shrubs and trees to channel breeze into the building.
- You can plant trees with non-invasive root systems near your house on the south side to prevent solar heat gain.
- You can plant trees that shade the house’s roof if you don’t have solar panels installed.
A passive house is built to conform to strict temperature control standards. The house has to be energy-efficient and comfortable for its inhabitants.
However, designing and building a passive house doesn’t mean blindly following the guiding principles. The design elements you ultimately choose to incorporate will depend on your climate and your home’s location.
- Passipedia: What is a Passive House?
- Solar Reviews: How passive solar home design saves you money on energy
- Energies: Heat Transfer and Energy Consumption of Passive House in a Severely Cold Area: Simulation Analyses
- Energy Procedia (ScienceDirect): Comparison of building performance between Conventional House and Passive House in the UK
- Frontiers of Architectural Research (ScienceDirect): Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in UAE buildings
- Williams College: Passive Solar Design
- ResearchGate: A Survey of Energy-Efficient Passive Solar Houses
- BuildPass: What is Thermal Bridging and How Can I Avoid It?
- Energy Saver: Update or Replace Windows
- Climatebiz: Passive House Windows (Everything you need to know)
- Ventive: What is Passive Ventilation With Heat Recovery?