THE DAY IS COMING IN WHICH CITIES will no longer allow combustion heating (NYC 80X50; #ONENYC). Cities and governments throughout the world have already, and continue to make similar commitments. There is only one power alternative to combustion heating; electric power. Consider the increasingly renewables-powered electrical grid and we find that there are only two non-combustion choices available; electrical resistance heating and heat pump technology.
Electrical resistance heating is most easily identified as the same technology that produces warm forced air in a common hair blow-dryer, or the red-hot elements in a toaster. When electrical elements are placed in a heating appliance (such as a water-heater) or ductwork, then we have an electrical resistance heater. The coefficient of performance (COP) for electrical resistance heating is 1.0 COP. That is the same as saying that electrical resistance is 100% efficient. All of the energy consumed by the heater goes into the space. This probably sounds pretty good; 100% efficiency is nothing to sneeze at.
A heat pump uses electricity to power a pump (also called a “compressor”) instead of heat strips. This pump (compressor) takes the available heat outside of the space, and concentrates it to a higher temperature so that it can be used to heat the structure. Usually, when the air outside the space drops to below 25F, the process of pumping heat out of the air is greatly diminished. The number of hours in which heating is needed while the temperature outside is below 25F is high, making it necessary for typical “air-sourced” heat pumps to require "back-up" or "emergency-heating". This can cause high energy use during cold weather. That’s when ‘Geothermal Heat Pumps” (GHPs) become the reasonable answer.
GHPs use the warmer temperature of the earth (45F to 75F in most of the US) as a source temperature for the heat pump. Geothermal heat pumps work effectively with these temperatures, providing a COP of 4.0 to 6.0. Efficiency ratings of 400% to 600% (4.0 to 6.0 COP) mean that for each unit of electricity, between 4 and 6 units of heat are delivered to the building space.
GHPs are clearly the answer to heating and cooling our buildings. There is no question of whether GHPs will be the main source of heating and cooling in the world; the only question is, “how soon”? One challenge remains, and that is placing the loops into the earth. There are situations, especially in concentrated urban areas where it is impractical to place loops adjacent to each building.
In my consulting work with various cities, governments and organizations, the challenges center on getting the geothermal piping into the ground without disrupting traffic and business-as-usual. If there were a way to use utility infrastructure that is already in place, it would be a big win for tight urban areas and beyond.
One of the ideas that I’ve been following is the use of city-water mains (domestic water distribution lines) for urban geothermal distribution piping. I’m pleased to say we have just such a project, and I think this is going to be a big part of the solution. American Water Works Comany, Inc, or “American Water” reported in July, 2015 that they had installed a water-main sourced system for the William L. Buck Elementary School in Valley Stream, N.Y. to feed the school’s geothermal heat pumps (GHPs). You’ll notice in the illustration that the test case uses a consumptive water use scenario, meaning that the water is used in a “one-pass” configuration. The next stage will involve a decoupled secondary circuit configuration which will facilitate zero water use. Dr. William M. Varley, President of American Water is a keynote speaker at the International Ground Source Heat Pump Association (IGSHPA) Expo in Kansas City, MO on October 7, 2015.
To expand upon this idea, we may attach several buildings to the same water main. A couple of modifications to the main are required. First, there can only be a certain amount of thermal load on a system before additional energy will need to be added or removed to the water in the pipe. Strategically placed geothermal loop-fields would be added to the water main in public parks and recreational fields providing the necessary energy exchange. Then, in some cases a loop and circulator pumps will have to be added to keep the water moving through the pipeline so that the energy can be “moved” to wherever it is needed.
City water mains may be the key to providing geothermal heating and cooling where it was not possible before. This will likely require some legislation of varying kinds. Construction codes will need to be clear to keep our drinking water safe. Second, the water utility would become essentially sellers of energy or a type or "power company", requiring the typical public service commission (PSC) approvals and regulation.
Water mains are often laid out in grids. On any given grid, it’s likely that office buildings which need cooling even on the coldest of days (this scenario is called “cooling dominant”) will be connected with residential buildings that need heating (called “heating dominant”). In effect, the waste heat from the office buildings can be shared with, or “given” to the residential buildings that are in need of heating. This scenario creates a "site sourced renewable-energy mini-grid", and is ultra efficient in utilizing thermal energy that is presently being wasted as cooling towers "vent" thermal energy to the atmosphere.
Geothermal heating and cooling systems have many additional benefits, offering a multitude of advantages to our communities. Industry Stakeholders have created a website with vast resources to educate the public on geothermal heat pumps. The “Geothermal Day” Website http://www.geothermalday.com/ aims to raise awareness about environmental and economic benefits of geothermal energy and its vital role in building a clean and secure energy future. The US Department of Energy (DOE) is on board with this effort; we are inviting industry partners, communities, businesses and educators to join efforts to advance further understanding and acceptance of geothermal technology as an unlimited, renewable form of energy. Join us by co-creating and sharing educational resources and participating in interactive activities in local communities and on-line.
Jay Egg is a geothermal consultant, writer, and the owner of EggGeothermal. He has co-authored two textbooks on geothermal HVAC systems published by McGraw-Hill Professional. He can be reached at firstname.lastname@example.org