How heat pumps double efficiency and transform building electrification
By Kenton Archer
HVAC systems are engineered to respond dynamically to human needs, balancing health, comfort, and infrastructure preservation. Think of them like a household refrigerator: it doesn't magically create coldness; it thermally pumps and extracts heat from the inside and dumps it into your kitchen. Building systems operate on this exact same physics principle; true cooling is simply the absence of heat. Consequently, refrigeration is a deliberate thermodynamic transfer, drawing thermal energy from an enclosed space and rejecting it into an unconditioned zone.
Heat pumps are transformative technologies governed by the vapor compression cycle and anchored by a reversing valve that redirects fluid flow to deliver both heating and cooling. During the summer cooling cycle, the system absorbs indoor heat and rejects it outdoors, making the indoor coil an evaporator (which absorbs heat like boiling liquid) and the outdoor coil a condenser (which releases heat like steam turning back into water). In the winter heating cycle, this dynamic inverts: the system extracts thermal energy from the ambient outdoor air and releases it indoors, transforming the indoor coil into a condenser and the outdoor unit into an evaporator. A heat pump's heating capacity naturally diminishes as outdoor temperatures plummet, and these systems used to require dependable electric resistance or gas backup integrations to reliably handle extreme cold weather. However, newer models can provide enough heat even at very low temperatures.
Frameworks such as ASHRAE 55 define thermal comfort targets aiming for a summer baseline of 78℉ at 60% relative humidity and a winter baseline of 68℉ at 50% to 60% relative humidity, which enable engineering teams to accurately select a heat pump that could provide enough heat for a given space under anticipated temperature range.
Because heat pumps use mechanical work to move existing thermal energy rather than generate heat through direct combustion or electrical resistance, they achieve exceptional operational efficiencies ranging from 200% to over 400%. In consumer terms, this means that for every single unit of electricity you pay for, a heat pump with a Coefficient of Performance (COP) of 3 delivers three units of heat by harvesting free ambient energy from the outside air. System performance is further quantified through standardized metrics: the Energy Efficiency Ratio (EER) measures full-load cooling performance, and the Heating Seasonal Performance Factor (HSPF) evaluates residential heating efficiency for units under 65,000 BTU/h, requiring high-efficiency benchmarks of 8 or greater.
NYCHA's first Clean Heat for All window heat pump electrification project was implemented at Woodside Houses in Queens, New York.
NYCHA’s project at Woodside Houses showcases its first Clean Heat for All window heat pump electrification project and leverages technology that goes beyond the heat pump unit's efficiency alone. Instead, it required engineering and forethought about how the unit would be installed and its impact on the tenant and the agency that manages the building. The units fit dimensionally at the bottom of a double-hung window. Unlike traditional window air conditioning, which takes up a considerable portion of the window space, these units are U-shaped when fully installed and take up only about 8-10 inches at the bottom of the window. A special kit comes with the heat pump unit, enabling air sealing around it to prevent air leakage if the window size is a bit larger. The heat pump unit is built around a hinge, giving it an L-shape before installation, so it can be slid in from the inside quickly, with no scaffolding needed regardless of the height. Once it is slid into the bottom of the window, the hinge is released giving it its ultimate U shape. Hot air can contain more humidity than colder air, meaning that during the cooling season, as you cool the air moisture is released as condensate. Often this condensate is disposed of by a network of interior or exterior plastic or metal tubing. The units in Woodside Houses have a small compartment that accumulates the moisture and every 30 seconds or so releases them as mist into the air where they usually evaporate. Eliminating an unsightly network of piping, dripping water, and a maintenance nightmare. The provided units don’t need to be hardwired, they can be plugged into a regular socket. All these make it possible for the electrification to happen without relocating the residents. This saves an immense amount of expense and basically allows doubling or tripling the number of dwelling units that can be electrified with a given budget.
Ultimately, mastering these foundational principles and metrics bridges the gap between theoretical building science and effective field execution. Whether sizing residential equipment, navigating municipal decarbonization guidelines, or exploring pioneering installations firsthand such as on the upcoming GreenHomeNYC tour of the NYCHA Woodside Houses, understanding how these systems move energy rather than create it is essential for modern high-performance design and equitable urban resilience.
About the Author: Kenton Archer’s journey with GreenHomeNYC, where he has volunteered since 2018, has fundamentally shaped how he views the built environment. He helped lead tours in a variety of venues including explorations of the Brooklyn Greenway and the Navy Graveyard Landscape, 1930 Broadway Carbon capture facilities, SIMS Municipal Recycling Center, and the Arthur Avenue Senior Apartments and solar array. Archer’s academic background is in sustainable management, but to act on his belief in learning beyond the traditional classroom and developing systems of thinking that would enable us as a community to decarbonize, he looks forward to the upcoming Room Heat Pumps in Action Tour and wanted to provide the background to make the tour more insightful.