Solar In Seattle
The 2015 Seattle Energy Code mandates the use of on-site solar infrastructure for buildings or additions over 5,000 square feet of gross conditioned floor area. This mandate can be found in code section C411 - Renewable Energy. The code allows for either photovoltaic systems, i.e. electrical generation, or water heating systems. The most commonly applied solution to this mandate on multifamily buildings is the use of photovoltaic panels assembled in an array on the roof. There are a number of companies that will design, permit, and install these light weight systems. The project electrician provides conduit to the roof and a termination point in the electrical room. The solar panel subcontractor does the rest.
There are three exceptions to this mandate written into the same code section C411. The first exception is for mechanical equipment that is 10% more efficient than code minimum. This allows one to take into consideration all types of HVAC systems whether they are wet or dry, gas or electric. This exception seems best fitted to commercial or office spaces that may use large central plants and that require both heating and cooling.
The second exception allows for the use of heat recovery systems on either air exhaust systems or water based systems in lieu of solar panels, as long as one can show that the annual energy saved by these heat recovery systems meets or exceeds the mandated amount of renewable energy production from the solar panels. This exception, you will note, does not require any increased equipment efficiency, rather it seeks to capture waste heat which is the same as capturing energy from the sun. This exception is commonly used in multifamily buildings that don’t have large central plants and whose major mechanical systems are air exhaust systems using Heat Recovery Ventilators (HRV’s) or Energy Recovery Ventilators (ERV’s). Another clever means of achieving this exception is through a reverse cycle chiller integrated into the garage exhaust system.
The third and final exception is to improve the energy efficiency of the exterior skin of the building and can be met by designing a skin that has a target UA value that is 15% less than code mandated. This works well for buildings heated primarily by electrical resistance heating and do not have large central plants. Multifamily buildings are a good example of this type of building.
Why mandate solar then allow exceptions? It is the opinion of the author that the code, as written, is meant to get us thinking about ways to save energy either through more efficient equipment or the recovery of waste energy. If one does not want to think much about it, the easy path is to install the solar. But an analysis of the costs of the alternates may prove to be more cost effective than putting in solar. This has been found to be true in multi family buildings through the use of HRV’s in lieu of solar. Not so much by improving the UA by 15%.
In conclusion, solar is mandated in Seattle Energy Code section C411, but you may be able to save money by employing one of the exceptions allowed in that same section. This analysis can be done very early in the project design by a mechanical engineer in tandem with the contractor and mechanical subcontractor (though we have also seen it done well after permitting of the project). These exceptions may allow you to skip the solar panels required by code section C411, but remember that code C412 still mandates that you provide a solar zone on the roof for future solar panels.