Passive Design Assessment

Passive Design Assessment

To investigate the impact of different passive design measures on the building’s energy demand, we need to model the building using commercial energy modelling software. In Australia, the use of energy modelling software is already well-established since the industry is familiar with Performance Solutions for energy compliance, such as JV3 modelling, VURB, Daylight modelling, and energy modelling for Green Star rating. Using commercial modelling tools, like DesignBuilder that we use at Energy Compliance Consultants, we can undertake a simulation of year-round energy use to find out what solution works best in terms of energy demand reduction and thermal comfort enhancement. We rate the solutions based on their initial cost and impact and choose those that work best for the proposed building under assessment. We then provide a short report outlining different solutions and their impact on reducing space heating, cooling, ventilation and lighting demand. It is then up to the client to decide which solution works best for them and their building design.

What Measures Help with a Passive Design?

In the following, we outline measures we take in our passive design assessments:

Zoning and layout

Buildings are better to be oriented in a way to be able to utilize useful solar gain in winter and to have minimum solar gain in summer. Therefore, it is better to orient living rooms and daytime-conditioned spaces towards the north and bedrooms and other night-time-conditioned spaces towards the south. Also, it is best to orient non-habitable and unconditioned spaces towards the east and west. Through energy modelling, we can assess how much energy could be saved by having an optimum zoning for a specific building.

Insulation

Proper insulation keeps the indoor air relatively mild against the outdoor air fluctuations. It reduces the need for artificial cooling and heating. In our VURB assessments, slab edge insulation has been shown to work very well as it reduces the cold air drafts into the building. However, installing more insulation than necessary may not have much effect in reducing the energy of the building. Energy modelling helps us understand the mechanics of heat transfer for specific buildings and propose proper insulation for them. For example, in many cases, it is shown that the addition of insulation under a concrete slab of a commercial building does not always have a major effect. Through JV3 modelling, we can assess the need for underslab insulation, remove it, or compensate for it by adding more insulation to the ceiling.

Glazing

It is a good practice to have a lower glazing U-value (heat transfer coefficient) to save energy throughout the year. Low-E and thermally-broken windows present good opportunities to enhance energy saving and thermal comfort. However, window solar gain or SHGC is a bit tricky as the solar gain could be both useful or unwanted depending on the location and layout of the building. In our energy modelling endeavours, we find the optimum SHGC for the entire house and then adjust it for northern windows and eastern/western windows. We also present benefits in reducing oversized windows while maintaining daylight access.

Airtightness

One of the main sources of heat loss in buildings is through infiltration. It is worth noting that reducing the infiltration is not a matter of computer modelling and design, but rather, care for the building sealing during construction. However, using computer modelling, we can assess the benefit of adding airlocks or sealing out the transitory corridors/foyers from the habitable rooms. We often offer these insights to our clients, especially while undertaking Performance Solutions for energy compliance.

Ventilation

Passive cooling is the product of a good naturally-vented home. Natural ventilation has the potential to reduce cooling demand and energy bills by a significant amount. By defining enough openings at the right locations, you can enjoy a natural breezeway even on the hot days of summer. Passive design helps to allocate openings at the right locations to maximize the benefits of passive cooling. Natural ventilation analysis using commercial software also helps with the passive design based on prevailing wind pathway inside the house.

Solar access

Allocation, size and tint of a window impact the useful heat gain in winter, reduction of heat gain in summer, daylight access and glare. These combined traits could not be confidently accounted for based on the experience alone. The use of energy modelling could be beneficial to make sure that the sun is on your side throughout the year. Orientation of living rooms towards the north is a good practice to achieve maximum amount of useful solar energy during the winter.

Shading

The impact of shading and shading devices is perhaps the most you can get out of passive design modelling. Window shading height and projection should be calculated with care, as it has the potential to negatively cause an increase in energy use or reduce daylight access while presenting no benefits for cooling purposes. Passive design modelling ensures the best possible solutions in terms of deciding the location of shading, shading projection, shading height or shading type. This is especially the case for Green Star buildings that must both have good passive traits and also high level of daylight access and glare control.

Innovation

Each year, the industry is faced with new ways to make a house more passive with innovative ideas and inventions. Among those, Trombe walls, green roofs, green facades, earth tubes, solar-assisted stack ventilation and PCMs are well-known.

Note that these innovations could be expensive and not cost-effective compared to the other measures discussed earlier. We encourage architects to learn about these already established innovative ideas and the mechanisms of thermal mass and thermal bridging. Using our commercial software, we can investigate the benefits of different solutions and report the most cost-effective and energy-efficient ones.

We will discuss them in our future articles.

What Does a Passive Design Assessment Look Like?

First, our client lists their wishes and concerns regarding their building design. Then we analyse the current situation and come up with the most cost-effective ideas there are. We then undertake energy modelling to assess the impact of each cost-effective solution on energy use and thermal comfort of the occupants. As an example, here is a summary report of our passive design assessment presented to one of our clients. This summary report outlined the supplied building design and examined solutions best suited for the proposed building. Note that we only included some of our recommendations for the sake of this article.

Current Design Assessment

The proposed building is located in Climate Zone 6, where the primary goal is to improve energy efficiency by reducing both heating and cooling demands throughout the year. To achieve this, it is best to orient living and daytime-conditioned areas towards the north to take advantage of beneficial winter solar gain.

Except for the gym, which is oriented towards the west, other living areas have highly glazed external walls facing north, maximizing daylight access and useful solar gain during the winter.

Western habitable rooms experience unwanted solar gains during summer, which leads to an increased need for space cooling. This impact is particularly significant for daytime-conditioned spaces. To mitigate this, we advise to avoid west-facing windows in bedrooms and other night-time-conditioned spaces. Also, installing fixed shadings with long projections or adjustable/retractable shading devices can help minimize unwanted solar gain during the summer.

Although the impact of southern windows on heating or cooling demand in colder climates is mild, it is better not to leave any southern windows unshaded, especially if you aim to passively reduce the cooling demand.

Solution A1 – seal off transitory areas from habitable rooms

Sealing off transitory areas like corridors from habitable spaces offers improved energy efficiency, comfort, noise reduction, air quality control, and privacy. To achieve these benefits, we implemented the installation of two solid-core or sliding doors to separate the Dining/Kitchen area from the Foyer area and the Retreat room from the Landing area.

This solution resulted in a significant reduction in heating demand by 19% and cooling demand by 6%. Consequently, we were able to achieve compliance using low-cost windows, as detailed in our energy summary report.

Solution B1 – Fixed shading over Bed 5’s W-F23 and Ensuite’s W-F22

Installing a fixed shading device with a horizontal projection of 1 meter directly above W-F23, extending to either side, reduces the building’s thermal demand by 0.5%.

Retractable shading devices, such as Venetian blinds, are very effective in reducing cooling demand, particularly when installed on eastern or western facades. According to the BCA, these devices must:

• Restrict at least 80% of summer solar radiation; and
• Be easily operated manually, mechanically, or electronically by the building occupants.

In our modelling, we ensure that the shading devices fully cover the designated windows from the beginning of December to the end of February, allowing only 20% of solar gain to penetrate. This approach effectively minimizes unwanted solar gain during the summer months while still permitting daylight into habitable rooms.

Solution C1 – Add a retractable shading device over Kitchen’s W-G09

This solution reduces the cooling demand by 11%.

Solution C2 – Add a retractable shading device over the Gym’s W-G10

This solution reduces the cooling demand by 7%.

Solution C3 – Add a retractable shading device over Bed 4’s W-F21

This solution reduces the cooling demand by 9%.