There are several important considerations when thinking about de-carbonizing building heating and cooling and the electrification of HVAC technology. Providing the most energy efficient technology can help reduce system load and avoid the need for additional power. generation and transmission investments. Similarly, utilizing technology that helps reduce peak electrical demand and smooth energy use can also enhance system load factors and mitigate the need for additional generation and transmission capacity. 

Heat pumps are essentially air conditioners that can be operated in one direction to provide cooling and operated in the opposite direction to provide heating. Heat pumps use refrigerants, which take advantage of the ideal gas law (PV = nRT) and move heat around through 4 steps. 

For cooling, a heat pump works as laid out in this table.



Incoming Refrigerant State



Step 1

Cold, Low Pressure Gas

Heat Exchange with Building System

Heat Refrigerant, Cool Building Air or Water

Step 2

Warm, Low Pressure Gas

Compress Refrigerant (consumes power)

Pressurize/Increase Temp of Refrigerant

Step 3

Hot, High Pressure Gas

Heat Exchange with Outside System

Cool Refrigerant, Heat Outside Air or Geo Loop Water

Step 4

Less Hot, High Pressure Gas

Refrigerant Through Expansion Valve

Depressurize/Decrease Temp of Refrigerant



The system works in reverse when the building needs to be heated.

The geothermal energy that occurs across various parts of the globe, such as Iceland, can offer 2 important and beneficial uses. High temperature geothermal (>360 F) can be used to create steam which in turn can be used to generate electricity. Lower temperature (68 – 302 F) geothermal can be used for direct heating, as the ancient Romans did.

Darcy’s technology utilizes what is really a form of solar energy that is stored in the shallow earth.  Groundwater temperatures are relatively stable year-round, and typically reflect the average annual temperature for the area, ranging from 45 degrees F in the northern part of the continental U.S. to 75 degrees F in the southern part of the country. HVAC equipment, such as a heat pump, is designed to supplement these temperatures to provide the desired level of heating or cooling.

There are two major benefits.  

The first benefit is that a system does not lose efficiency over the course of a season due to the gradual decrease in temperature while heating or a gradual increase in ground temperature while cooling (as happens in traditional geothermal). Maintaining consistent efficiency helps reduce electricity use and cost.

The second benefit is that a system can be designed to deliver cooling only or heating only without concern for gradual increase (or decrease) in underground temperature over years of operation. This flexibility enables the incorporation of creative heating or cooling systems (e.g., a cooling only system with the use of chilled beams, a DOAS, and no heat pump) for which energy savings can be significant, sometimes as much as a 70% reduction vs. conventional systems.