Applications that use heat from the Earth without any temperature or energy form conversion are classified as direct use. Temperatures for direct use applications overlap with ground-source heat pump operating temperatures at the low end to electricity generating temperatures at the high end. Examples of direct uses at different temperatures are shown in the diagram below.
Direct use is generally the most efficient use of a geothermal resource as no energy is lost in energy conversion: heat from the ground is used as heat in the application. However, geothermal heat cannot be transported and must be used close to its source. Insulated pipes can convey hot water for a few miles with only a degree or so loss in temperature, but unless the temperature is high and the flow is large, the cost of pipes quickly overcomes the economics of transporting the resource.
Common direct uses include space heating and the provision of domestic hot water on an individual or community scale, such as in Pagosa Springs. Heated swimming pools and spas are popular if demand is sufficient, such as at Glenwood Springs. More commercial direct uses can be very profitable, but, because the resource must be used where it is found generally require more planning. Geothermal resources are used at a number of sites in Colorado for heating greenhouses and a one site for aquaculture. Finding a market for the produce from these ventures is an essential component of their development.
Many of the potential direct uses of geothermal resources have not been realized in Colorado because users and resources have not yet come together, and there has been no exploitation to date of subsurface hot aquifers as has happened, for example, in Germany. If energy prices continue to rise, direct use of geothermal resources could provide an economical, clean, renewable source of low-grade thermal energy.