How to Build a Fossil-Free Duluth: Heat Pumps Part 2

Dr. Eric Enberg

 In this article we will explore home and water heating through two different kinds of heat pumps:  Cold climate heat pumps and networked geothermal.

To recap from last time, a heat pump uses a bit of electricity to move a lot of heat from one place to another. Your refrigerator is a heat pump. It moves heat from the inside of the refrigerator box and expels it to the atmosphere of the kitchen.    

A cold climate air-source heat pump (ccASHP) does this in reverse, moving heat from the atmosphere to the inside of the box, your house. Networked geothermal removes heat from the ground and from industrial sources of waste heat to heat homes and businesses through an interconnected grid of tubing in a neighborhood or city.  Each has its advantages and disadvantages.  

The ccASHP can be privately owned and operated, installation is quick and relatively easy. However, the gas network would still be in place (building codes demand a backup source of heat) but with customers demanding far less natural gas. Prices for the remaining customers, usually the poor and renters, will need to rise to cover the costs of maintaining the gas system. The ACEEE estimates that with 25% of households defecting from gas to a ccASHP, costs for the remaining customers will rise 21%. With 50% defection gas prices rise 43%; 75% leads to a price increase of 129%. While this is a death spiral for the gas utility, it does allow for a dramatic reduction in greenhouse gas emissions though the leaky distribution system would still be present and leak methane.  

Networked geothermal is in some ways similar to the ccASHP and in other ways diametrically opposite. A heat pump is still used to extract heat, concentrate it, and use it to provide domestic water and heat but instead of using fluctuating atmospheric temperatures, networked geothermal uses the steady temperature of the earth with the addition of industrial waste heat as the source of heat energy. The result is dramatically greater efficiency, no need for a backup source of heat like a gas furnace and an ability to heat the entire city, including businesses and high-density housing. Along with electrification of the rest of the household’s appliances, networked geothermal allows for the systematic taking down of the natural gas system, a process known as strategic abandonment.   

Building a networked geothermal system involves the drilling of bore holes six inches in diameter and up to 850 feet deep on 10-foot centers under alleyways and sometimes streets. Easy access to bedrock is a plus, which Duluth has in spades. Tubing in the boreholes picks up the heat from the rock which is looped to each building along the route. When you need heat or hot water, the heat pump in the house takes out the needed heat energy and concentrates it as needed.  

As you might have guessed by this point, the start-up costs of such a system is expensive. However, such a system is expected to last more than 100 years (the downtown heat district has lasted nearly that long already). It’s also being done elsewhere in the world. Look up the Everything Electric Show on YouTube titled “THIS is How to Speed Up The Heat Pump Rollout” for a very accessible look at a typical system. Framingham, Massachusetts is moving ahead with a pilot program using networked geothermal and multiple northeastern states are requiring gas utilities to move along these lines.      

There is no way for a single household to build a networked geothermal system so this represents an excellent opportunity for a collectively-owned utility such as Duluth’s Comfort Systems or Duluth Energy Systems to organize and provide the financing for this effort. How we can put all these parts together to take Duluth off all fossil fuels in a cost-effective and equitable manner is the subject of the next article.

Dr. Eric Enberg practices family medicine in West Duluth and is a member of the Duluth Climate and Energy Network (DCEN).