The concept of geogrids (geothermal microgrids) is an innovative approach to decarbonize cities. Geogrids are technically like 5th generation district heating and cooling (5GDHC) networks or what is called anergy network in Germany and Switzerland. There are many different terms for this concept.

What is a geogrid?

A geogrid is a shared water loop with a warm and a cold pipe buried in the ground. It uses vertical collector pipes that go 100 to 200 meters into the ground and collect geothermal heat. The network temperature is below 25 °C and in every building a heat pump is installed which raises the low-temperature heat from the geogrid to the needed supply temperature of the building's heating system. A central advantage of geogrids over conventional heat networks is that geogrids can also provide cooling energy with the same infrastructure. In addition, by reusing excess heat from buildings (with a cooling demand) by buildings with a heating demand, the heating and cooling demands are partially balanced out. From the conceptual point of view, there are some distinct differences between geogrids and conventional district heating. Geogrids come with multiple advantages but also disadvantages compared to individual heating solutions or heat networks that need to be taken into account when deciding which system is more suitable for a neighborhood. One interesting fact is that geogrids can be easily extended and can therefore grow step-by-step over an urban area. Their energy efficiency is very high compared to air-source heat pumps since the decentral heat pumps can use a heat source with a comparatively high temperature.

Are geogrids an economic solution for heating neighborhoods?

Geogrids are economically competitive with conventional heating solutions, like air-source heat pumps or conventional district heating. However, it depends on the local conditions and heat sources available in the district. On the subpages about 5GDHC networks, further details about the profitability and typical costs of geogrid-like systems are provided.

Where are geogrids developed?

The concept of 5GDHC networks is already established and investigated in many countries. However, the term geogrid is especially promoted in Boston, Massachusetts (United States) by the Heet organization. Originally, the Boston's gas grid operators planned to just replace natural gas with hydrogen and biogas. In this way, the gas infrastructure could stay and just the fuel would be replaced. However, due to a lack of green gases this strategy comes with high economic risks. Therefore, the concepts of geogrids are also considered as a green heating solution for the city. If the concept of geogrids spreads, gas utilities would become utilities of thermal energy (basically a thermal utility that supplies heating and cooling energy).
In general, the concept of ambient loops (5GDHC networks) exists for some decades already and a substantial number of ambient loops are installed in Europe as shown on our list of 5GDHC districts.

Why do we need to replace gas grids in the long term?

First of all, burning natural gas must be stopped due to the climate change. However, not only the fuel is a problem but also the infrastructure itself will become more and more expensive: Firstly, gas grids have substantial leakages and the maintenance is very cost intensive. Secondly, as the energy transition continues, the number of buildings connected to natural gas grids will decrease. However, the fixed costs to operate the gas grid stay the same. Thus, the costs for the remaining customers will increase progressively.