As we have been working alongside the International Association of Plumbing and Mechanical Officials, the United Association, the New York State Energy and Research Development Authority and the federal government, it’s clear there is a trifecta of important technological evolutions. Here are the three we’re focusing on:

1. Thermal Energy Networks (TENs): These are utility-scale infrastructure projects connecting multiple buildings into a shared network with sources of thermal energy such as geothermal boreholes, surface water and wastewater.

2. Wastewater Energy Transfer (WET): These systems use energy that normally goes down the sewer pipes. This is done by extracting thermal energy from the wastewater to supply energy to heat pumps that provide the heating and domestic hot water (DHW) in the winter and by rejecting heat to the sewer to provide cooling in the summer.

3. Phase Change Materials (PCMs): Used with geothermal heat pumps, PCMs are substances that absorb and release heat energy when they change phase (known as latent heat). When a material melts or solidifies, it changes from a solid phase to a liquid phase. During the phase transition, PCMs absorb and reject a significant amount of heat energy.

It’s a simple fact of thermodynamics that geothermal heat pumps do not cause a spike in demand, surpassing their summertime air-conditioning counterparts. This is because the electrical demand on a ground-coupled heat pump is directly related to the temperature of the source. 

Thus, the widespread adoption of ground-coupled heat pumps is made possible through the implementation of citywide thermal energy networks that move BTU energy and hydronic pipelines between buildings and a master plan urban retrofit or in new construction.

The challenge now is how to address building electrification and decarbonization without missing any important pieces of the puzzle.

TENs, WETs and PCMs work hand in hand to help geothermal heating and cooling technologies become available to the general public with the least degree of construction possible. As you read through and understand these technologies, look at how well they interconnect to become the basis of a noninvasive, urban-centered, earth-coupled solution. 

You will see why the pipe trade unions, federal and local state governments and individual cities, as well as the investment community, have settled on these technologies as what’s next in energy.

Goal: Install the most heat pumps with the fewest dollars without causing wintertime demand issues on the electric grid.

TENs, WETs, PCMs and DHW

WET has risen to the top as a preferred initial method to begin the decarbonization efforts for commercial buildings and TENs of all types and sizes. 

While decarbonization using heat pumps is the obvious path forward, the struggle has been providing space heating and DHW when the temperature is very cold outside, which causes electrical demand spikes that can be two or three times higher than normal. Air-source heat pumps must necessarily work with very cold outdoor temperatures. 

The solution is to use a heat source and sink that is more stable year-round, such as the earth. Using geothermal boreholes is a marvelous solution, but it requires drill rigs and disruptive construction. While this is a necessary part of progress, perhaps on the front end we could find something less disruptive to decarbonize buildings’ DHW needs to start with. This is where WET has such an attractive draw to potential users.

In many cases, all the energy transfer needed for a building’s DHW load can be met by extracting the energy from the wastewater leaving the building. Using wastewater heat pumps, the building’s DHW needs may often be met without a single borehole.

Think of how our grandparents and great-grandparents have been known to talk about hot and cold running water. At first, the only way you got running water was if you had your own water well on the property. Then, local governments and utilities began putting in water and sewer mains, and eventually natural gas.

TENs are fundamentally no different from water, sewer and natural gas infrastructure — a piped utility that provides energy for heating and cooling buildings, including DHW. The responsibility of the building tenants is the heat pump itself, which connects to the thermal energy network a lot like a washing machine connects to the electrical, drain and water supply. 

There will always be people who live far enough from their nearest neighbor that running certain utility lines doesn’t make sense. We’ve seen this in numerous communities that don’t have natural gas and those homeowners who may still have their own water well and septic tank on their property. In the cases of small communities and individual buildings needing seasonal energy storage, PCMs are the answer.

Closed-loop geothermal heat pump systems are designed to have enough linear feet of pipe in the ground to provide continuous heat transfer throughout the year for the needs of the heat pump supplying the heating and cooling to the building. 

Let me break here and share a lifelong idea of mine from the time I was 10 years old.

I grew up in the high desert in California close to the ski resort Big Bear. It got very cold in the winter and very hot in the summer. My 10-year-old mind concluded with a great degree of certainty that if I could find a way to take the summer heat and save it for the winter and the winter cold and save it for the summer, it would be a marvelous solution for the heating and cooling of buildings. Essentially, that is what PCMs do for geothermal heating and cooling.

PCMs are designed to use the very least underground surface area to provide the most thermal storage for a particular application. The application can be for daily, weekly, monthly or seasonal energy storage. Imagine storing enough waste heat from summer cooling to provide all the thermal energy needed for DHW and space heating in the winter with the lowest volumetric requirements. That’s what PCMs do for us.

You can see where we are going with this trifecta. By providing all the energy needed to decarbonize the DHW needs of a building without drilling a single borehole, connecting the remainder of the building to a TEN, and providing some peak thermal energy storage, these three technologies answer some very important questions in the evolution of geothermal heating and cooling technology for our industry.