A heat pump is a device that moves heat from one medium (such as air or water) to another using a pair of heat exchangers. One example is a refrigerator, which uses a heat pump to move heat from the air inside the refrigerator to the air outside it. Another example is a reverse cycle air conditioner. In the summer, it uses a heat pump to move heat from the air inside your home to the outside. In the winter, the cycle reverses to move heat from the outside air into your home. There is heat present in a medium even if it is below freezing. Ground source (or geothermal) heat pumps extract heat from earth or water below ground where the temperature is fairly constant throughout the year. A Heat pump water heater uses the same principle, but the first heat exchanger extracts heat from the surrounding air and the second heat exchanger moves heat into a water tank to heat water.

A heat pump works by using a refrigerant, a special fluid that easily changes between liquid and gas states. The SANCO₂ uses carbon dioxide (CO2), a naturally occurring gas, as a refrigerant rather than a synthetic chemical. The SANCO₂ moves heat from one medium (air) to another (water) by continually circulating this CO2 refrigerant through a closed loop system, where it is completely contained in a circuit and never comes in contact with the water or the environment. Unlike other refrigerants, CO2 rarely achieves its liquid state. After being compressed and heated, the CO₂ refrigerant becomes as dense as liquid, while still remaining as a gas (trans-critical state), substantially increasing the transfer of heat between itself and the water, especially in low ambient temperatures. The basic components of such a system typically include 2 heat exchangers (the evaporator and condenser), a compressor, and an expansion valve. The CO2 refrigerant enters the evaporator, where it absorbs heat from the ambient air. The CO2 then loops to the compressor where the CO2 is heated through compression. The high-pressure, high-temperature CO2 refrigerant then transfers its heat to the cold water through a double wall heat exchanger. The heated water is then sent to the stainless steel holding tank while the high pressure CO2 refrigerant passes through the expansion valve which reduces its pressure and causes it to rapidly cool and expand. The CO2 refrigerant, now at low pressure and low temperature, returns to the evaporator to begin the cycle again. This closed-loop process continues as long as the refrigeration system is running, allowing for continuous transfer of heat. For a more in-depth explanation of how heat pumps work, refer to these articles here and here.

Heat pumps require a refrigerant gas in order to effect heat transfer. Historically, many of these refrigerants have been toxic, flammable, harmful to the ozone layer, or potent greenhouse gases in their own right. While ozone-depleting refrigerants have largely been phased out, some of the most popular refrigerants still in use have a global warming potential when released of 1,000 or 2,000 times that of CO2. Although these refrigerants are sealed in the heat pump, they do occasionally leak out during manufacture, when the heat pump is first “charged” with refrigerant, or at the heat pump’s end of life. CO2, by contrast, is a naturally occurring gas which is extracted from the environment, and is eventually returned to the environment from where it came. The operation of a CO2 heat pump, when powered with renewable electricity, produces no carbon emissions at all. For more information on the move to safer, greener refrigerants, see here.

Even when the air outside is below freezing, it still contains some amount of heat energy. When the compressed refrigerant gas is released through an expansion valve, it cools rapidly. As long as the refrigerant gas is colder than the surrounding air, heat will move from the relatively warmer air through the heat exchanger to the relatively colder refrigerant, which absorbs this heat and allows it to be transferred to the water in a second heat exchanger. Although the efficiency of the system does decrease at very low temperatures, the Sanco2 is tested and certified to operate in a range of -26°F to 114°F. For more information on heat pump effectiveness in cold climates, see here and here.

By extracting and moving heat rather than generating it from scratch, a heat pump can be significantly more energy-efficient than a traditional system which generates heat. A Uniform Energy Factor (UEF) value of 1 would indicate that the heat pump water heater is 100% efficient, meaning all the input energy is effectively converted into useful heat energy for heating the water. Water heaters that create heat will always have a UEF lower than 1, whereas heat pump water heaters may have a UEF between 3 and 4 or sometimes even higher, indicating that they are 3 or 4 times as efficient as a resistance electric water heater, for example.

The Uniform Energy Factor (UEF) is a measurement used to evaluate and compare the energy efficiency of residential water heaters, particularly those that use storage tanks. It is a standardized metric introduced in the United States in 2015 by the U.S. Department of Energy (DOE). The UEF takes into account multiple factors to determine the overall efficiency of a water heater, including standby heat loss, cycling losses, and heat input efficiency. It provides a single numerical value that represents the energy efficiency of a water heater, expressed as a ratio of heat created to energy input. A higher UEF indicates greater energy efficiency, meaning the water heater can heat water more effectively while using less energy. A perfectly efficient traditional gas or electric water heater can have a UEF of at most 1, because it cannot create more heat than the energy it uses. However, heat pump water heaters do not create heat, they move it from ambient air to the storage tank, and thus they are currently able to achieve UEFs in the 3-4 range.

The SANCO2 can be used in a wide variety of applications with different capacity needs. Heat pumps can be stacked together and storage tanks can be sized up to provide as much DHW as needed. An array of SANCO2 units is not only more cost-effective than a larger industrial heat pump system, but having multiple independent heat pumps results in a resilient, fault-tolerant system with built-in redundancy. The Arthaus Ithaca is an example of a multi-family development, in a cold climate, employing an array of 16 SANCO2 heat pumps. See https://www.taitem.com/arthaus/

The Department of Energy defines a measure called the Uniform First Hour Rating (UFHR), which measures the volume of hot water that a system can deliver in 1 hour at a temperature of 125°F and at a 3GPM flow rate when starting with a tank full of hot water. This rating is designed to measure the performance of a water heating system using a metric that is relevant to real-world use. The higher the UFHR, the higher the performance the system is able to deliver. The SANCO₂ unit has the highest UFHR rating of any comparably sized Storage Electric or Heat Pump Water Heater.