Big Changes for New York Buildings to Address Renewable Energy and Resiliency


New York is preparing for the potential closure of the Indian Point nuclear power plant by investing in demand reduction, on-site energy production, and energy storage. The Combined Heat and Power (CHP) Acceleration Program from NYSERDA is part of this effort.

CHP provides resiliency in case of power outage. Because the equipment runs 24/7, it is likely to continue operating during an emergency, as long as natural gas supply is not disrupted. Backup generators, on the other hand, risk not starting when they are needed and generally do not have the fuel to operate for days at a time. For commercial buildings over 50,000 square feet (5000 square meters), multifamily buildings with more than 200 units, and buildings that have a high hot water demand, CHP is economical, especially with state incentives. In smaller buildings with Passive House levels of efficiency, however, it may make more sense to disconnect from the natural gas connection to avoid fossil fuel use. Providing hot water using direct electricity is more efficient within a renewable structure.  [2014 PHI Conference Proceedings P. 651] Domestic hot water tanks heated by air source heat pumps can act as energy storage for a renewable smart grid infrastructure.

More information about installing CHP microturbines in NYC buildings.

Currently CHP relies on natural gas supplied by utility companies. However, there is a potential synergy with a new technology called Power-to-Gas (P2G). P2G is useful for seasonal storage of surplus renewable energy. With P2G the amount of methane gas required for a typical house would be about 3.5% of the amount of natural gas equivalent (fossil energy) currently consumed. [2014 PHI Conference Proceedings p.641] Why not use biogas? Biogas is problematic because it requires a lot of agricultural and forest land that could otherwise be used for food, raw material, and transportation fuel.

Renewable energy is likely to continue its fast growth. In fact, the investment bank UBS sees residential PV as a huge growth market in the near future, even though utility-scale PV is less expensive per installed peak watt. As onsite PV energy production becomes more common, there will be a challenge with overproduction on sunny days and the need to use energy from storage at night, especially during cold winters. A change to New York State’s utility structure may be needed to address the cost of renewable energy storage and transmission. In addition to energy storage, one solution is to use onsite PV energy as much as possible before exporting it to the grid. This has been called—a little inelegantly—self consumption. German architect Kay Künzel presented his self-consumption strategies at a New York Passive House presentation on February 27, 2014. His home automation system timed certain appliances to run during the day to take advantage of direct PV energy. Another self-consumption strategy is to use DC power as much as possible to avoid the DC-to-AC inverter losses.

Solar panels on vegetated roof of Etrium Passive House office building near Cologne. Photo by Greg Duncan

Solar panels on vegetated roof of Etrium Passive House office building near Cologne. Photo by Greg Duncan

New York City recently passed the Zone Green amendments which make installation of solar panels easier, although in order to qualify for New York property tax rebates for installation of solar panels, you will need to have a registered architect or engineer file with the Department of Buildings. To calculate the photovoltaic potential in your location and to get information about incentives, use the PV Watts calculator.

Duncan Architect can help you create buildings that are energy-efficient and resilient with onsite renewable energy where feasible. Email for more information.


Passive House Institute to Include Renewable Energy in New Ratings

The Passive House Institute has announced [PDF] that it will start rating buildings that produce renewable energy while meeting the clearly defined Passive House Standard. In order to do this, PHI had to reexamine the calculations for primary energy. PHI uses the term primary energy to refer to what the US EPA calls source energy which you may be familiar with for Energy Star ratings. I’ll use PHI’s terminology in this post. See the Energy Star Portfolio Manager Technical Reference [PDF] for national source energy ratios for the US and Canada. These ratios depend on the mix of electricity generation. EPA chose to use national averages instead of local or electrical grid ratios. The choice of a “correct” primary energy ratio is complicated and not apolitical. For example, some people may disagree that burning coal on site is equivalent to onsite PV (both have primary energy ratios of 1.0 per EPA).  And the ratios are constantly changing. When designing buildings that will last decades, should we use past primary energy ratios or future forecasts? These choices only get more complicated as renewable energy becomes a larger fraction of the electric grid because wind and sunlight are intermittent, requiring energy storage.

PV panels on vegetated roof of Etrium Passive House office building near Cologne. Photo by Greg Duncan

Solar panels on vegetated roof of Etrium Passive House office building near Cologne. Photo: Greg Duncan

Current definitions of Net Zero Energy Buildings—there are at least four—ignore the energy storage and transmission requirements due to renewable energy produced on site. Different uses of energy have different requirements for storage and transmission. Because of these problems, PHI is replacing the primary energy ratio with a new concept, Primary Energy Renewable (PER), that takes into account storage losses as well as production and distribution losses. For example, onsite PV can power air conditioners during summer days when there is plenty of sun, so there is no need for storage and the PER is lower. Conversely, PV systems are not particularly ideal for heating. The PER for heating with electricity—ideally with an air source heat pump instead of direct resistance—is therefore higher. In the future, it will be much more environmentally sound and cost-effective to use renewable energy to cover energy demand for any cooling that may be needed than for heating. These new application-specific PER ratios are also climate specific, dependent on seasonal solar and wind production potential. [Proceedings of the 18thInternational Passive House Conference, pp 648-9. Aachen, Germany 2014. ISBN 978-3-00-045216-1.]

USAF - 070731-F-8831R-001

Utility-scale solar at Nellis Air Force Base USAF – 070731-F-8831R-001

As you can see just from the examples of heating and cooling, calculation of a Net Zero Energy building is complicated. All of them rely on the building itself as the boundary condition for renewable energy production, although sometimes including parking lots and public rights of way. The Net Zero concept discriminates against tall buildings because it is not feasible to install enough PV or wind turbines to meet the energy demands of a 4+ story building. WNYC has an article on the challenges of going solar in an urban environment and why Passive House should be the basis for the design, in order to reduce energy consumption. The article uses the example of a Net Zero Energy school on Staten Island with the luxury of a more suburban location than most of New York City that will open in 2015. This building uses the “trick” of including PV panels over a parking lot.

P.S. 62, being built on Staten Island's South Shore, will have 2,000 solar panels to generate as much energy as the building uses. (Chris Mossa/WNYC)

P.S. 62, being built on Staten Island’s South Shore, will have 2,000 solar panels to generate as much energy as the building uses. (Chris Mossa/WNYC)


To address the discrimination against tall buildings that Net Zero definitions perpetuate, PHI is proposing new classifications based on renewable energy produced on site per lot area rather than floor area:

  • Passive House Classic: unchanged except for the new definition of Primary Energy Renewable. No onsite renewable energy required.
  • Passive House Plus: for a single family house, about as much energy is produced as is consumed.
  • Passive House Premium: for a single family house, produces an energy surplus.

Without changing the Passive House definition, PHI will also start recognizing “Energy Conservation Buildings” that meet a certain threshold for energy efficiency but fall short of meeting the Passive House standard.

Thermal Bridging

At Gregory Duncan Architect we use THERM 6.3 software—a 2-D building heat-transfer modeling tool developed by Lawrence Berkeley National Laboratory—to analyze thermal bridges.

Thermal bridges are areas in a building envelope that have higher than normal heat loss. The color infrared analysis in THERM pictured above shows a thermal bridge at the footing of a heated basement. Adding a small strip of insulation at the base of the foundation wall eliminates the thermal bridge. In this example we reduced the heat loss from a U-Factor of 0.41 W/m²K to 0.30 W/m²K by adding a 100 mm wide by 450 mm high strip of Foamglas insulation.

The next step is to calculate the U-Values for the foundation wall and the floor slab separately.

Here you can see that the concrete foundation at the right provides almost no resistance to heat loss, while the Foamglas insulation at the left prevents most of the heat transfer from the basement to the ground. The U-Value per THERM is 0.196 W/m²K.

Here a 100 mm layer of Foamglas over the existing concrete slab provides a U-Value of 0.382 W/m²K.

Then we input the U-Factor of the footing detail and the U-Values of the wall and floor into a Psi-Value calculator to determine ?, a linear heat-loss value. In this case we get 0.005 W/mK.

Using PHPP energy-modeling software we can then calculate the difference in annual heat demand for the two footing details. Multiply ? by the length of the thermal bridge to get the heat loss in watts per degree temperature difference between inside and outside. In our example, this is 0.005 W/mK * 60 m = 0.3 W/K. From PHPP we get the SI equivalent for heating degree days for heat loss through the ground for our particular climate, in this case New Haven, Connecticut. This value is 28 kKh/a, or 28,000 degrees Celsius * hours annually. So 28 kKh/a * 0.3 W/K = 8.4 kWh/a. So this detail results in extra energy use of about 8 kWh per year more than if the detail were completely thermal-bridge free. And the detail without the extra insulation results in a Psi-Value of 0.184 W/mK. Doing the math again: 0.184 W/mK * 60 m * 28 kKh/a = 309.1 kWh/a. So the extra insulation saves 309.1 kWh – 8.4 kWh = about 300 kWh per year. If heat is provided by a heat pump with a coefficient of performance (COP) of 3, that means it takes 100 kWh of electricity to make up for the extra heat loss every year. That’s the amount of energy consumed by a 100-watt incandescent lightbulb left on for 1000 hours.

So, is it worth it to add the extra strip of insulation? Depends on the incremental cost of installing it and how much value we place on reducing the energy use of the building. Assuming $0.20/kWh, 5% discount rate, period of 30 years, and 2% electricity inflation means that an investment of $392 is cost neutral, that is, Net Present Value = $0. Now, the homeowner can determine if spending more than that amount is worth it for the non-monetary benefits of reduced energy use.

Thermal-bridge analysis should be integrated into the architectural design workflow so that all major construction details can be analyzed with increased productivity.

Gregory Duncan Architect provides thermal-bridge consulting to architects, engineers, and contractors. Please contact Greg Duncan at for more information.

Net Zero Energy and the Passive House Standard

What does net zero energy really mean?

For a grid-tied net-zero-energy building, this is about offsetting the energy consumed with energy produced by renewable, emissions-free means. Why not offset by purchasing renewable energy or just buying carbon offsets? This could be called a Net-Zero Off-Site Energy Building. While there is no standard or third-party verification system for net zero energy, the four most common definitions do not allow offsets for off-site renewable energy. A 2006 paper (PDF) by the National Renewable Energy Laboratory explains these definitions in detail.

  • Net Zero Site Energy: A site ZEB produces at least as much energy as it uses in a year, when accounted for at the site.
  • Net Zero Source Energy: A source ZEB produces at least as much energy as it uses in a year, when accounted for at the source. Source energy refers to the primary energy used to generate and deliver the energy to the site. To calculate a building’s total source energy, imported and exported energy is multiplied by the appropriate site-to-source conversion multipliers.
  • Net Zero Energy Costs: In a cost ZEB, the amount of money the utility pays the building owner for the energy the building exports to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year.
  • Net Zero Energy Emissions: A net-zero emissions building produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources.

One design implication of a site ZEB is that this definition favors electric equipment that is more efficient at the site than its gas counterpart. Using the site ZEB definition, a 95% efficient gas boiler consumes 1053 kWh to produce 1000 kWh [3412 BTU] of heat, while an air-source heat pump with a coefficient of performance of 2.85 only consumes 351 kWh to produce the same amount of heat. However, using the source ZEB definition, the two are equivalent. 1000 kWh of heat requires 1158 kWh of source energy in both cases, assuming a source-energy factor of 3.3 for electric and 1.1 for natural gas.

The NREL paper ignores the embodied energy required to produce photovoltaic and solar thermal equipment. The source energy factor for PV including embodied energy is 0.7 according to the standards used by the Passive House Institute. Additional source energy factors per PHI are 2.7 for electric, 1.1 for gas, and 0.2 for wood. The PHI factor for electric is lower than the US average because it is based on the average for Europe, which uses less coal than the US. Determining the correct source energy factor can be difficult. For instance, in New York, should the factor be based on a state-wide average or on average for the entire Eastern US/Canada power grid?

HOK and The Weidt Group designed the Net Zero Court project to be Net Zero Energy Emissions and therefore carbon neutral. The office building still has an estimated energy bill of $0.01/SF so it is not Net Zero Energy Cost. In St. Louis, where the project is located, 81% of electricity comes from coal, so a carbon-neutral building would have a large impact. Their design methodology parallels that of Passive House.

  • Start with optimizing the building orientation and thermal envelope to improve energy efficiency.
  • Then use efficient mechanical systems.
  • Finally, offset the remaining emissions with on-site renewable energy. In this case, with a large four-story structure, they had to rely on PV panels in the parking lot as well as on the roof in order to produce enough electricity to balance that used by the building.

See their PDF report here.

Off-grid buildings—also called energy autarkic buildings—use more total energy over 80 years because of the embodied energy for the PV and batteries which must be replaced every 30 years on average.  [source]

A building constructed to Passive House standards can be a Net Zero Energy Emissions building by adding photovoltaic arrays or a wind turbine. The Passive House Planning Package (PHPP) software provides a tool to calculate what is required for carbon neutrality. All other things being equal, the Passive House building will cost less to operate.