Montgomery County, Maryland recently passed new green building requirements, including adoption of the 2012 International Green Construction Code. Montgomery County was one of the first jurisdictions in the country to enact a green building law in late 2007. Now, county officials have repealed the original law and replaced it with Executive Regulation 21-15 that will likely reduce requirements for many new buildings.
There are some pretty big changes brought about by the new law, which took effect on December 27, 2017 and includes a six month grace period for projects already under design. New projects permitted after June 27, 2018 will need to comply with the following:
- Projects 5,000 gross square feet and larger must comply, lowered from 10,000 gsf.
- Buildings must meet the 2012 International Green Construction Code (IgCC), replacing the requirement that buildings must meet LEED Certified criteria.
- Residential projects under five stories must use ICC-700/NGBS at the Silver Energy Performance Level.
- R-2 and R-4 portions of Mixed-Use buildings may comply with ICC-700/NGBS and the non-residential portion shall comply with the IgCC or the entire building may comply with IgCC or ASHRAE 189.1
- R-1, non-residential and R-1/Mixed-Use projects may select IgCC, ASHRAE 189.1 or LEED Silver with eight points or more under the Whole Building Energy Simulation path.
- All buildings using the IgCC compliance pathway must achieve a Zero Energy Performance Index (zEPI) score of 50 or lower.
Project teams pursuing Passive House frequently ask, “Where do we locate the HRV/ERV?” The answer is complex when the Passive House concept is scaled to a multifamily program. While there are two primary arrangements for HRV/ERV systems, the trade-off is dynamic and needs to be carefully considered as multifamily Passive House projects begin to scale. A low volume HRV/ERV unit ventilating an individual apartment is a unitized HRV/ERV. High volume HRV/ERV units ventilating multiple apartments and often servicing several floors, is referred to as centralized HRV/ERV.
As Passive House consultants we can attempt to address the system arrangement question with building science; however, in New York City rentable floor space is very valuable, so considering the floor area trade-off is of particular interest to project teams. When a unitized HRV/ERV system cannot be located in a drop-ceiling due to low floor-to-floor height, it is placed in a dedicated mechanical closet. This closet is typically no smaller than 10 ft2 and includes the necessary ductwork connections to the HRV/ERV unit. The alternative solution is to increase the floor-to-floor height to accommodate the HRV/ERV unit and horizontal duct runs in the ceiling. Centralized HRV/ERV systems, however, allow short horizontal duct runs but require floor space to accommodate vertical shafts. With supply and exhaust ducts coupled together the required floor area is about 8-12 ft2. As a result, centralized HRV/ERV systems may actually require more floor area than a unitized system.
Example: In the case of Cornell Tech, vertical supply and exhaust duct work for the centralized HRV/ERV system required 222.5 ft2 per floor, or 13 ft2 per apartment (see image 1 below). Unitized HRV/ERV mechanical closets would have required an estimated 170 ft2 per floor, or 10 ft2 per unit (image 2 on right).
Image 1 & 2: These images compare the amount of floor area required for centralized and unitized HRV/ERV systems. Image 1 on the left, shows the 12ft2 floor area required for vertical shafts servicing the centralized ERV at Cornell Tech. Image 2 on the right is hypothetical, showing the typical location and 10ft2 floor area required for a unitized HRV/ERV mechanical closet.
Steam pressure gets a disproportionate amount of attention. That’s partially due to the common, but not necessarily true idea that higher pressure equals more fuel use. Remember, it’s not the steam’s pressure that heats the building; it’s the steam’s heat energy. In fact, you can heat a building with 0 psig steam. You can even heat a building with a boiler that’s too small and never builds positive pressure. You can’t do it well, but you can do it.
Thanks to the law of conservation of energy, we know that energy cannot be created or destroyed — it can only be altered from one form to another. In a steam heating system, the flow of energy goes like this:
- The boiler transfers Btus from the fuel to the steam (energy input).
- The steam transfers those Btus to the rooms.
- The rooms transfer those Btus to the outdoors (heat loss, aka the load).
It’s important to keep this energy flow in mind because they are linked and self-equalizing. If the energy input exceeds the heat loss, the building temperature will increase, which, in turn, increases the heat loss. And, a building’s heat loss depends on the temperature difference between inside and outside and the amount of air transfer occurring. So, the best way to keep the heat loss down is to keep the indoor temperatures as low as possible, and keep the windows closed. Furthermore, in an apartment building, the coldest room drives the load in any steam-heated building and the Super needs to send enough heat around to satisfy the hardest-to-heat apartment.