Case Study

The Towers


Oldest US multifamily co-op transforms wastewater into clean energy

In Bronx, NY, the Amalgamated Housing Cooperative (AHC) embarked on a pioneering low carbon retrofit project at ‘The Towers,’ two 20-story buildings containing 316 affordable apartments across 425,000 square feet. Established in 1927, AHC is the oldest limited equity multifamily co-operative in the country. 

The retrofit focuses on upgrading the heating and cooling infrastructure to enable simultaneous operation, diverging from the existing seasonal limitation. By introducing cutting-edge solutions including wastewater heat recovery and geothermal systems, AHC aims to harness energy from domestic water sources, thereby phasing out its reliance on cooling towers and decreasing fossil fuel consumption. This initiative not only promises enhanced thermal comfort and sustained affordability for its residents but also sets a benchmark for energy efficiency and climate resilience. The project’s success could potentially revolutionize energy management across similar multifamily complexes in New York State, demonstrating a scalable model for other buildings with similar heating and cooling system configurations– a total market estimated at 200 million square feet. 

AHC’s commitment to its low-to-moderate income community underscores this ambitious venture, reinforcing its legacy and leadership in sustainable development.

The Towers buildings

Project Status


Under Construction

Monitoring & Evaluation

Emissions Reductions


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.


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

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 improvefments
  • 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
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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. 

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





Building System Affected

  • heating
  • cooling
  • ventilation
The Towers Before Illustration
The Towers After Illustration
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
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
Take advantage of rooftop space to install solar PV system for clean electricity generation
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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

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.

Retrofit Costs

Decarbonization Costs


Capital costs of decarbonization.

Avoided Risks

Business-as-Usual Costs

$29.5M + $35k / YR

BAU cost of system replacement.

Repairs & maintenance.

Avoided Risks

Business-as-Usual Risks


LL97 fines do not apply at this property.

Added Value

Decarbonization Value



Net Present Value


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

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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.

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.
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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.

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