Case Study

The Towers

Oldest US multifamily co-op transforms wastewater into clean energy

Project Highlights

Emissions Reductions

93%

carbon emissions reduction on an all-electric site by 2035.

Lessons Learned

This project will make clean energy from dirty water by recapturing heat from sinks, showers, and toilets.

Lessons Learned

The project’s complete building re-piping decrease the future loaded needed for the planned geothermal heat pump system improving performance and comfort.

Scale

200 million SF of multifamily building stock for potential replication across New York State.

Step 1

Step 1: Examine Current Conditions

A baseline assessment is key to understanding current systems and performance, then identifying conditions, requirements or events that will trigger a decarbonization effort. The assessment looks across technical systems, asset strategy and sectoral factors.

Building System Conditions

System Failure
Equipment nearing end-of-life
New heat source potential
Comfort improvements
Indoor air quality improvements
Facade maintenance
Resilience upgrades
Efficiency improvements

Asset Conditions

Recapitalization
Capital event cycles
Carbon emissions limits
Investor sustainability demands
Owner sustainability goals

Market Conditions

Technology improves
Policy changes
Infrastructure transitions
Fuels phase out

The Towers are two of 13 buildings that comprise AHC’s multifamily campus located in the Bronx. Many of the systems at the property, including the piping distribution system, are beyond their useful life and in poor condition, causing leaks and requiring continual repair and maintenance. The campus currently uses a central gas-powered boiler plant to produce steam for heating, cooling, and domestic hot water.

As part of its recapitalization cycle, the property is embarking on a decarbonization journey which will include a comprehensive retrofit of the heating, cooling, and domestic hot water systems, an envelope upgrade, and onsite renewable generation in the form of geothermal and solar PV.

This project will increase thermal comfort and secure utility affordability for its low-and-moderate income residents, as well as enhance the energy efficiency and climate resilience of the property.

Step 2

Step 2: Design Resource Efficient Solutions

Effective engineering integrates measures for reducing energy load, recovering wasted heat, and moving towards partial or full electrification. This increases operational efficiencies, optimizes energy peaks, and avoids oversized heating systems, thus alleviating space constraints and minimizing the cost of retrofits to decarbonize the building over time.

Existing Conditions

This diagram illustrates the building prior to the initiation of Strategic Decarbonization planning by the owners and their teams.

Click through the measures under “Building After” to understand the components of the building’s energy transition.

Sequence of Measures

2024

2026

2028

2030

Building System Affected

heating
cooling
ventilation

The existing distribution system and terminal units are beyond their end of useful life (EUL). Install 2 new hydronic loops supplying both heating hot water and chilled water all year round to new fan coil units (FCUs) in apartments.

Install sewage tank and use Sharc Energy heat pumps to produce heating, cooling and domestic hot water (DHW)

Cleaning and balancing of existing ventilation system

Insulate roofs, replace windows and air seal walls.

Drill geothermal boreholes on property land and install ground source heat pumps to produce heating, cooling and DHW

Take advantage of rooftop space to install solar PV system for clean electricity generation

Reduce Energy Load

New hydronic distribution: Replace the dual temperature hydronic system with new piping supplying both heating hot water and chilled water simultaneously to provide heating or cooling year-round improving tenant comfort. The measure includes new fan coil units with more efficient motors and designed for low temperature heating hot water to reduce the load on the buildings and facilitate heat pump technology integration.
Envelope Improvements: roof insulation, window replacement and air sealing walls
Ventilation Maintenance: balancing and sealing of ventilation system to reduce exhaust air
Controls Upgrades: Install modern control system to automate and optimize new heat pump systems

Recover Wasted Heat

Wastewater Heat Recovery: Recapture heat from wastewater using WSHPs to produce heating, cooling, and domestic hot water (DHW). Use wastewater as heat sink in cooling mode to enable removal of old cooling towers.

Full Electrification

Ground Source Heat Pumps: Drill boreholes on property land and install WSHPs to produce heating, cooling and DHW. Use boreholes as heat sink in cooling mode.
Solar PV: Install solar PV system on rooftop
Electrify Appliances: install electric dryers and cooking equipment

Step 3

Step 3: Build the Business Case

Making a business case for strategic decarbonization requires thinking beyond a traditional energy audit approach or simple payback analysis. It assesses business-as-usual costs and risks against the costs and added value of phased decarbonization investments in the long-term.

Decarbonization Costs

$33M

Capital costs of decarbonization.

Business-as-Usual Costs

$29.5M + $35k / YR

BAU cost of system replacement.

Repairs & maintenance.

Business-as-Usual Risks

N/A

LL97 fines do not apply at this property.

Decarbonization Value

$6.7M

Incentives.

Net Present Value

$1.97M

Versus -$1.36M for BAU with difference of $3.33M.

To confirm the viability of The Towers adopting energy efficiency measures, the project team constructed several discounted cash flow financial scenarios utilizing Net Present Value (NPV) or the total cash flow of the measures taken over a period of time by assuming a discount rate for the worth of money over a period. For comparison, they constructed a baseline for forecasted equipment replacement compared to the Roadmap measures. A comparison of investment costs are as follows:

Baseline Costs: $29.5 million
Measure Costs (Alternative 1): $33 million, $26.4 million (after rebates, tax benefits, etc.)

Using a 7% discount rate over 20 years, the discounted cash flows resulted in relative net present values (NPVs) of -$1.36 million for the Baseline and +$1.97 million for the planned ECMs, a difference of $3.33 million. Based on the analysis, the cost of planned ECMs is a more viable financial investment.

Notably, the costs of business-as-usual in these scenarios do not capture what New York State prescribes as the Social Cost of Carbon (SCC). The SCC is a metric used by countries, states, and other authorities having jurisdiction (AHJ) to place a cost on climate change impacts. New York State firmly defines the SCC as $125/ton of CO2 emitted. The alternative energy system for The Towers, though capital intensive, has clear economic benefits. This and many other climate change impacts such as point pollution, land degradation, human health, and others, are known as intangible decarbonization benefits.

Strategic Decarbonization Action Plan

An emissions decarbonization roadmap helps building owners visualize their future emissions reductions by outlining the CO2 reductions from selected energy conservation measures. This roadmap is designed with a phased approach, considering a 20- or 30-year timeline, and incorporates the evolving benefits of grid decarbonization, ensuring a comprehensive view of long-term environmental impact.

Strategic decarbonization roadmap for The Towers.

The measures used in our decarbonization strategy have been strategically planned based on priorities, as well as to optimize energy and carbon reduction. The approach is to reduce loads first to allow for reduced and properly sized new systems. This sequence enables implementation of the measures because it allows thermal loads to be reduced as soon as possible, before electrification of heating and cooling with the ground source heat pump (GSHP) system. Most critical to the success of the plan are the early implementation of the distribution system retrofit and installation of the wastewater energy transfer (WET) system for thermal energy recovery.

Due to the critical nature of the decarbonization work, AHC desires an aggressive implementation timeline for the measures. The work, specifically the piping and fan coil unit (FCU) replacement and WET system installation, is slated to occur 2024-2026. Then in 2026-2028 comes the critical steps of envelope improvements, submetering and control upgrades, and geothermal system installation. The geothermal measure will be a critical step for transitioning The Towers away from fossil fuels because the GSHP system will replace the steam supplied from the gas and oil fed central boiler plant for heating, cooling, and domestic hot water (DHW). This measure will allow the chiller, cooling tower, and steam piping to be fully decommissioned, thereby yielding additional operational and maintenance savings. In 2028-2030, installing the solar PV system will allow for further deep energy savings as it will enable The Towers to have a direct source of clean energy and rely less on the main electricity grid, which needs time to transition to clean energy. Lastly, in 2039-2034, electrifying the appliances will be the last component in completely transitioning The Towers away from on-site fossil fuels while also saving energy by installing high efficiency alternatives and providing health benefits to the residents by eliminating gas stoves.