An air-source or air-to-air heat pump can provide both heating and cooling.
- In the winter, a heat pump extracts heat from outside air and delivers it indoors.
- On hot summer days, it works in reverse, extracting heat from room air and pumping it outdoors to cool the house.
Text description of the Heat Pump image.
The image is divided into two parts. On the left, there is a photograph of an outdoor heat pump unit positioned next to a brick wall, with greenery in the background. The unit is rectangular, featuring a large round fan in a mesh-covered front and is raised slightly above the ground on four black legs.
On the right side of the image, there is a diagram illustrating the refrigeration cycle of a heat pump system. The diagram shows a house with arrows indicating the flow of refrigerant between the outdoor and indoor components, with distinguishing features such as a compressor, fan, outdoor coils, and indoor coils. The components are depicted in a colorful manner, with blue and red lines indicating the flow of gas and liquid along with directional arrows.
Nearly all air-source and air-to-air heat pumps are powered by electricity. They have an outdoor compressor/ condenser unit that is connected with refrigerant-filled tubing to an indoor air handler. As the refrigerant moves through the tubing of the system, it completes a basic refrigeration cycle, warming or cooling the coils inside the air handler. The blower pulls in room air, circulates it across the coils, and pushes the air through ductwork back into rooms.
When extra heat is needed on particularly cold days, supplemental electric-resistance elements kick on inside the air handler to add warmth to the air that is passing through.
The Balance Point
As we have learned, air-source and air-to-air heat pumps work by extracting heat from the outside air. These heat pumps require a backup system to supplement their heating ability when the outdoor temperature gets below a certain temperature.
As the outdoor temperature drops, the heating requirement of the house increases and the output of the heat pump decreases. At some point, the temperature of the home’s heating requirement and the heat pump output match. This temperature is called the balance point and usually falls between 30-45 degrees Fahrenheit. For any temperatures below the balance point, supplemental heat will be required.
To locate the balance point, the heating requirement (BTUs/h) of the house and the heat pump output (BTUs/h) are plotted against the changes in outside temperature. The place where the home heating requirement and heat pump output lines cross is the balance point.
Take a look at the graph of the Balance Point.
Text description of the Balance Point Graph.
The image is a line graph depicting the relationship between temperature and heating requirements, heat pump output, and supplemental heat. The x-axis represents temperature in degrees Fahrenheit, ranging from 0 to 80. The y-axis represents BTUs per hour, ranging from 0 to 70,000. Three lines intersect on the graph:
- A brown dashed line labeled "Heat Pump Output" begins near the bottom right and slopes upwards to the left, indicating increasing BTU output as the temperature decreases.
- A green solid line labeled "Home Heating Requirement" starts at the top left and slopes downwards to the right, showing decreasing BTU requirements as the temperature increases.
- A green shaded area labeled "Supplemental Heat" fills the upper left portion between the green solid line and the y-axis.
The "Balance Point" is marked where the brown and green lines intersect, indicating where the heat pump output meets the home heating requirement.