Another approach for reducing operational carbon is to ensure regular building electricity is delivered from a specific renewable source under a long-term contract rather than from general grid energy. Care should also be taken to watch some smaller energy uses, like landscaping, and refrigerant would need to be selected carefully or be handled through a small carbon offset.
As mentioned, operational carbon is used in the Standard 228 calculations at the moment. ASHRAE currently is looking into a total-life approach to carbon for the future, incorporating materials and other embedded energy at the front end and the disposal of materials at the end of life.
STANDARD 228 EXAMPLES
The previous page and this page provide an example calculation, using Standard 228. Although the standard typically requires two years’ worth of annual calculations, in this example one year is used.
A 3-story, 66,700-square-foot office building near Atlanta was built in 1978 on an 11-acre site. It had a very extensive remodel with a large emphasis on energy efficiency in 2020. Changes during the 2020 remodel included adding insulation to walls and the roof; decreasing the window-to-wall ratio; and changing the mechanical system to four pipe, using one large and six smaller heat pumps. These and other changes have resulted in a very low energy use of 18.5 kBtu per square foot per year (5.42 kWh per square foot per year). Rooftop photovoltaic panels also were added. A ground-mounted PV system is now in place. The building is all-electric and net-metered. Example Calculations 1 and 2 show the process of determining zero net status.
Note that even with approximately 140 kW of rooftop PV, the building required additional renewable energy to be considered zero net energy per Standard 228. It also would not meet the zero net carbon goal. However, the additional 120 kW onsite ground-based PV system was added, allowing the building to meet the zero net energy and zero net carbon goals. Example Calculation 2 shows the effect of the additional onsite energy generation in the carbon calculation.
THE FUTURE
In a number of Canadian provinces, all electric generation is by hydroelectricity. Any renewable energy exported just offsets this renewable hydropower. In situations like this, any all-electric building connected to that grid would be considered zero net energy, no matter how much electricity it consumes for its energy services. This surplus of renewable power is a situation that the U.S. is just starting to face in certain locations and at certain times of day.
Possibly ANSI/ASHRAE Standard 228 will sunset when renewable and carbon-free energy become our new normal. It will be interesting to see what happens when using energy has a significant cost but limited or no environmental consequences.
Until that time, there is still work to be done. ASHRAE has continued the Standard 228 development committee as Standing Special Project Committee (SSPC) 228, meaning that changes can be suggested at any time. You may send any thoughts for future work to ASHRAE. Call (800) 527- 4723 for information about how to submit suggestions to the committee.
IMAGES: courtesy ASHRAE