Boston Apartment Complex Showcases Energy Efficiency

As it currently stands, the seven-story brick box apartment complex in Boston’s South End hardly strikes the onlooker as an example to be replicated. But this is set to change as the 192-unit Castle Square Apartments receive a deep energy retrofit to elevate the city block’s attractiveness, comfort conditions and energy performance.

The building owners – Castle Square Tenants Organization and WinnCompanies – intend this energy efficiency overhaul to be an example that can be replicated among similar multifamily dwellings. The Northeast hosts one -third of all buildings with 50 or more housing units, and many of these share similar needs and opportunities with Castle Square Apartments. Energy efficiency retrofits are a priority in this region, where buildings are usually older, winters are cold and long, and energy prices are high. Needless to say, lessons learned from this project also would apply to plenty of buildings in other regions, such as the Midwest or Mid-Atlantic.

To be replicable, the project must be economically feasible and enhance the living space. The prospects for the Castle Square retrofit look good on both accounts. And the over 60% expected energy cost savings are something to write home about. We’re not talking incremental here!

Making it Happen

How did the owners of Castle Square find the resources for this dramatic improvement? Financing is certainly at issue because 60% of the residents are below medium income.

For this project, timing is everything. A building like Castle Square Apartments tends to be renovated every 20 years to keep it in good shape. While energy efficiency is not the primary reason for a building overhaul, adding energy efficiency upgrades during renovation is far more affordable and less disruptive than implementing them individually at separate times. Since Castle Square was scheduled for renovation anyway, combining this with a deep energy retrofit simply made sense.

As an affordable housing complex, Castle Square is eligible for a federal Low Income Housing Tax Credit. This credit is available for new construction and needed rehabilitation, including measures such as window replacement. In addition, the project is taking advantage of funds from the Commonwealth of Massachusetts, utility programs, and $4.4 million dollars of federal stimulus funding. Although similar projects may not receive the same level of assistance – the stimulus funding is gone and state and utility resources vary – crucial support for affordable housing renovations often is available. The owners of Castle Square were also able to stretch the project budget by taking on debt, which will be repaid from the substantial energy cost savings.

The residents of Castle Square are the key drivers for the deep energy retrofit approach, making sure that thermal comfort, health and environmental sustainability considerations are addressed and that the expected energy savings materialize. The residents’ input is important as the apartments remain occupied during the retrofit process.

Energy Savings

Energy costs for the 192 housing units of Castle Square Apartments are expected to drop from about $590,000 per year to about $230,000 per year. The most substantial savings stem from the reduced use of natural gas for water heating (by 78%) and space heating (by 71%). Electricity use for air conditioners, lighting, refrigerators and plug loads is anticipated to drop by 60%.

Wall, Roof and Window Upgrades

Most of the heating and cooling savings will be achieved with building enclosure enhancements, which will also help attain occupant comfort levels. The overall insulation value of the building enclosure will be increased about tenfold. This insulation boost is accompanied by air sealing, which contributes 40% of the projected heating savings.

An air and water control membrane and mineral wool insulation, protected by durable insulating metal panels, are being added to the outside of the main apartment building’s uninsulated brick  walls. This boosts the wall R-value from R-3 to R-40; roof insulation will be doubled from R-20 to R-40.

Castle Square’s windows are the weakest links in the old building envelope. The current aluminum double pane sliders with a U-factor of around 0.75 were poorly installed, allowing substantial air
leakage around the frames. These are being replaced with fiberglass-framed casement windows with a U-factor of around 0.2. To ensure air tightness, the installation practices for the windows along with the wall insulation measures have already been tested in model units. The potential for thermal bridging due to the window installation was also carefully assessed and minimized. As an additional check for quality, 15% of the renovated units will be sampled with blower-door tests.

The new casement windows were chosen for their air tightness and ease of egress. Though relatively expensive, fiberglass was selected as frame material for being a well-insulating, dimensionally-stable
and environmentally-friendly option. This choice concurred with the residents’ preference for comfort and sustainability. The windows have low-solar-gain triple glazing. A higher solar heat gain coefficient (SHGC) was suggested by modeling of annual energy use, but models that took into account the
comfort impacts of potential overheating advised for a low SHGC.

As a result of the substantial building shell improvements, much smaller equipment will satisfy the apartments’ heating needs, substantially cutting the retrofit’s overall cost.

Heating and Cooling Equipment

Old central boilers with 70% efficiency needed to be replaced. Due to the substantial shell improvements, tiny, 94.5 percent efficient boilers can supply the needed heat, with each boiler serving
16 apartments. Right-sizing the boilers based on a careful assessment of the heating needs will further improve system efficiency.

For cooling, Castle Square will continue to rely on through-the-wall air conditioners in order to leave individual residents with the ability to determine their own air conditioning intensity and costs.

Looking Ahead

The Castle Square deep energy retrofit started in December 2010 and is expected to finish in March 2012. Most of the building shell measures are being performed over this summer.

To communicate the lessons learned from this retrofit and encourage similar projects across the country, the Castle Square deep energy retrofit team shares its experiences at www.castledeepenergy.com.

For More on Windows

This article was adapted from the Summer 2011 Word on Windows, which is the Efficient Windows Collaborative's newsletter. The Efficient Windows Collaborative is the Alliance’s consortium dedicated to increasing the market share of high-efficiency windows in both the residential and commercial sectors.