Net zero buildings are becoming increasingly popular, and some jurisdictions, such as Washington, DC, are projected to become code within the decade. Massachusetts will also begin development of a net zero building code. Curious if your building is a net zero contender or what it would take to reach net zero targets?
What Does it Mean to be Net Zero?
The term “net zero” commonly refers to zero-energy buildings. In simple terms, a zero-energy building is one that produces as much energy as it consumes on an annual basis. There can be nuances and caveats to this definition, but for now, we want to bring you up to speed on five key net zero energy strategies to consider if you’re interested in developing a net zero building.
1. Maximize space for on-site renewable energy.
How tall is your building?
- Any building over five stories will be challenging, if not impossible, to achieve net zero with on-site renewable energy production alone because building energy demand will likely exceed available site area. Maximize your solar with a smart layout and consider if other renewables, such as geothermal, are possible.
Do you have other spaces available for solar photovoltaics (PV)?
- Your development may have a separate parking garage or parking lot on site. These are great places to install a PV system, which can significantly increase the amount of on-site renewable energy production and help make achieving net zero more of a reality.
Do I have to have all renewables on-site to be net zero?
- If you don’t have enough room for on-site renewables, you can look into purchasing off-site renewable energy options, such as community solar, power purchase agreements, or renewable energy credits.
Now that you’ve considered renewables, let’s move on to net zero building design considerations.
2. FIRST reduce the building’s energy demand.
Design and install a robust thermal envelope.
- A well-insulated building enclosure in addition to high performance windows will help reduce the amount of unwanted heat transfer to and from your building.
- A continuous air-tight enclosure significantly reduces the amount of heat loss through air leaks in your building. It is also critical in ensuring optimal occupant comfort and your building’s long-term durability.
Use heat recovery for your fresh air system.
- By utilizing an energy or heat recovery unit you’ll be able to transfer (i.e., recover) up 90% of the building’s heating or cooling energy into the fresh air stream before it is exhausted to the outdoors.
Limit the amount of unwanted internal heat generation.
- Lights, appliances, and hot water piping all generate a lot of heat creating a greater demand for energy to cool your building. Focus on strategies to limit the amount of energy use by these three energy users. This is especially critical with larger, denser buildings.
Passive House is a great design guideline to achieve a building with significantly reduced energy demand.
3. SECOND select high efficiency heating, cooling, and water heating.
By following Step 2, you have the potential to down size your heating and cooling equipment.
- The goal for all heating and cooling equipment is to right size, and by significantly improving your envelope you’ll likely be able to find significant cost savings in using smaller equipment than on a typical project. Invest this savings in higher efficiency systems.
Higher efficiency units will use less energy to meet the needs of your building.
4. Account for plug loads.
It’s all about how you model.
- Plug loads are from anything we plug into the wall – and modern lifestyles have A LOT of these. TVs, cell phones, laptops, chargers, coffee makers, printers, the list goes on. Getting this estimate correct is imperative for your net zero energy assumptions. Miscellaneous plug loads are often the hardest energy use to quantify due to the high variability amongst occupants. But it’s critical to model these as accurately as possible to ensure plug load energy is being accounted for properly. If you under predict this energy use, you may not achieve net zero with the renewable energy system you have designed.
If your building is residential:
- Stick with conservative assumptions in your energy model. A good place to start would be to use the plug load assumptions set in the RESNET standard.
If your building is commercial or industrial:
- Perform a quick accounting exercise. Count the amount of equipment in the building (i.e., computers, printers, kitchen equipment, etc.). Next track down how much power these pieces of equipment will draw while running. Lastly, make an educated guess as to how long they’ll be running on an annual basis.
Consider controls to reduce run time and cut “phantom” loads.
- Certain pieces of equipment can still draw small amounts of energy even when they are off or in sleep mode. When multiplied over the course of a year, this can amount to a lot of energy. Utilize smart outlets or auto-shut off timers to ensure you don’t have unwanted energy use when your building’s equipment isn’t being used.
5. Establish a building commissioning plan and follow through with it.
Develop a commissioning (Cx) plan.
- Many issues that arise when the building is in operation can be avoided with good planning and adequate design reviews. Work to develop a commissioning plan with your Cx agent to make sure these potential issues are flagged and addressed prior to construction completion.
Follow through on this plan.
- Mechanical Cx – properly test and adjust your mechanical systems to make sure they are running as efficiently and effectively as designed. This is critical not only as your building is in its first year of operation, but also as the building is in operation over its entire lifespan.
- Envelope Cx – develop an inspection plan to ensure that the building’s envelope system is built to the high level to which it was designed. Look for locations where insulation or the air barrier is erroneously discontinuous. This will ensure your building’s low heating and cooling demands are as low as you designed in Step 2.
Ready to take on the net zero challenge? Contact Steven Winter Associates for a feasibility assessment of your building.
By Dylan Martello, Senior Building Systems Consultant
By Andrea Foss, Sustainability Director