Top 5 Strategies for a Net Zero Ready Building Design: In Hot and Humid Climates

For a building to be Net Zero Ready, the estimated overall energy use must be reduced as far as possible before adding renewable energy sources.  A Net Zero Ready Building can be constructed and be fully functional without relying on the immediate availability of renewable energy sources, but it is important to understand and efficiently utilize the available conventional energy sources at a site, and offer cost effective ways of converting to renewable sources when they become available.  Converting services to take advantage of available renewables (i.e. solar and/or wind power) and phasing out the dependency on conventional energy sources would then take the building to Net Zero.   First costs for renewable energy systems can be very expensive and often cost prohibitive under most project budgets, so incorporating more cost effective strategies to reduce energy use are logical first steps.

The energy use of the building can be expressed in Energy Usage Intensity, or EUI, which is the amount of energy used per square foot per year.  Early in the design phase, it is best to target a goal which is called the predicted EUI, or pEUI.  Building designs with pEUI’s below 20 are excellent candidates for Net Zero, however pEUI’s below 35 are reasonable targets.

1. Find the optimal orientation for the building on the site. This is a simple and low cost strategy to lower energy use.  Generally an East-West orientation works best to take advantage of solar orientations in the summer and winter.  It allows the lower sun angles along the south façade in the winter into the building for heat gain, while minimizing heat gain in the summer with proper sun shading devices.   Typically a 15 degree rotation of the building in either direction from the true East-West axis will work just as well.  In addition to this long standing traditional understanding of building orientation, there is software that can help further test strategies early in design to help make these decisions, such as Sefaira.
2. Build a great envelope. A great envelope should have an improved thermal value over the code requirements and a continuous air barrier.  Thermal bridging should be minimized everywhere possible to keep heat transfer from occurring either into or out of the building.  This requires attention to details such as continuous insulation, attachment methods of materials, thermal breaks at door and window frames, and transitions from wall to roof, wall to floor, etc.  An analysis of wall, roof, and slab assembly is important to determine the best system, best thermal value, and best fit for the project, while also comparing cost and constructability issues of each assembly.   This can go a long way to help determine the most cost effective system with the most optimal R-value for the envelope.
3. Study window-to-wall ratios. This is the percentage of window area to the overall wall area.  First, it is best to select a high performing window glazing that has high thermal values and lower solar heat gain properties.  The window area will always be a lower thermal value than a solid wall system, so it is important to balance the overall area of windows with the HVAC system and with desired daylighting and views goals.  Working with the mechanical engineers, using software such as Sefaira for early analysis, and referencing guidelines such as ASHRAE’s Advanced Energy Design Guide are all great strategies to help determine the optimal percentage.
4. Selection of building systems. HVAC and lighting systems have the highest impact on energy use in the building, so selecting the best fit for the project is important to reduce the overall pEUI.  The project budget and life cycle cost analysis will have an influence on selection, so balancing those factors with energy usage goals can sometimes be challenging.  Lighting types will also contribute to overall energy usage.  LED fixtures have rapidly come down in cost, so this is becoming a preferred solution since the energy usage is lower than fluorescents.  Including daylighting sensors is another great way to further reduce artificial light use.
5. Manage plug loads. Most items that are plugged into the building are consuming energy even when not in use, so making informed selections on equipment type (such as Energy Star rated) can contribute to energy savings.  Encouraging building occupants to reduce plug load usage, and informing them of the impact through building performance dashboards can be an effective way to lower energy usage.  This requires sub-metering of the building systems that would need to be incorporated during design.

These are just some of the ways that design can transform a project into an energy efficient Net Zero Ready building.  From the big picture down to the details, it all adds up to contribute to the overall energy usage of the building.