Heat Pumps: 3-to-1 Energy Winners
Electric heat pumps are now so efficient, even at low temperatures, that fuel-burning heating systems are unnecessary.
Before cold climate heat pumps were invented, people would get excited about increasing the annual utilization efficiency of their fuel-burning heating systems from 0.8 to 0.95. Now, we can get systems with a coefficient of performance of 3 or more.
Electric heat pumps have been the standard technology for refrigerators, freezers, and air conditioners since 1913, cooling enclosed spaces and heating up ambient air. Recently, this technology has been applied in reverse, pumping hot refrigerant gas through tubes to heat enclosed spaces and pumping very cold refrigerant liquid through tubes to cool ambient (outdoor) air. Now, we can heat very efficiently with electricity and no longer need furnaces, boilers, or hot water heaters that burn fuel.
To benefit the most from energy-saving electric heat pump technology, we can take the following sustainable steps:
For refrigeration, replace older refrigerators and freezers that fail Energy Star standards with new appliances that meet standards.
For domestic hot water (supplying sinks, showers, etc.), replace gas-burning or resistance electric hot water heaters with heat pump hot water heaters.
For space heating, control ventilation, super insulate, and then install heat pumps.
Weekly Poll: Enjoying Heat Pumps?
Help! What’s the difference between “ductless mini-splits” and “ducted heat pumps”?
A “ductless mini-split” heat pump is a system that provides heating and cooling using two pieces of equipment connected by a “line set” (flexible tubes for refrigerant).
In its cooling cycle, a ductless mini-split works just like a window air conditioner. The main difference is that a window unit is “unitary” (all of its components are together in one piece of equipment), whereas a mini-split splits the equipment into an outdoor unit (called a “compressor” or “condenser”) and an indoor unit (called a “head”).
Another difference from an AC unit is that a heat pump has a reversing valve that can change modes to pump heat into a building.
A “ducted heat pump” is essentially central air conditioning but with a reversing valve so you can use it for heating as well as cooling.
You didn’t ask, but “ground source heat pumps” are another option that pumps heat to and from groundwater.
Help! How do I know when to replace my old refrigerator with a more energy-efficient model?
Most electric refrigerators and freezers use heat pumps for cooling, but poor designs waste energy. You can buy a 12.8 cubic-foot refrigerator with a freezer that is rated to use 370-kilowatt hours of electricity per year, an energy parsimony of about 23.7 hours of operation per kWh of electricity. Older refrigerators have an energy parsimony below 6 hours per kWh (1,700 kWh per year). In other words, powered by a 12 kWh home battery, an efficient refrigerator and freezer could keep running for almost six days, but an older, inefficient one would only work for a day and a half.
To compare how much energy your old refrigerator uses compared to a new one, you can do an online search for the EnergyGuide label for your refrigerator make and model. This will show you the estimated yearly electricity use in kWh.
You can also get a general sense of the efficiency of a refrigerator from its rating plate (also called a “compliance plate” or “serial plate”).
A 20.7 cubic foot Bosch refrigerator model #B21CL81SNS/01 draws 2.7 amps at 115 volts. An older refrigerator might draw 3 or 4 amps. The higher the amps, the less efficient the appliance. To really determine how efficient your refrigerator is, borrow or buy a Kill A Watt electric monitor. Plug that into the wall output, then plug your refrigerator into the device to record electricity usage over a week.
Your refrigerator’s energy efficiency depends not only on its design but also on how you use it. Here are some steps to help your refrigerator work more efficiently for you:
Keep your refrigerator out of direct sun. Move it to a north wall or shade windows so sunlight does not heat up your refrigerator every day.
Put space between your refrigerator and your oven or dishwasher. Refrigerators and freezers should not be directly next to any appliance that produces heat.
Regularly vacuum the back and bottom of your refrigerator and freezer to remove dust and debris from clogging vents so that air can flow through the condenser, which gives off heat during a cooling cycle. Make sure hot air can flow up and out rather than being trapped around your refrigerator.
Turn down the heat in your kitchen overnight; don’t waste energy heating up your refrigerator when you’re not in your kitchen.
Help! Can our home use a heat pump hot water heater?
Most homes can install an electric heat pump hot water heater (also called a “hybrid” water heater), but there are a few things to know before jumping into this project.
First, there are two types of hybrid electric heat pump water heaters:
High-power heat pump water heaters take a “regular” (high-power, low-efficiency) electric water heater with one or two resistance heating elements and add a low-power, high-efficiency heat pump on top. You’ll need a dedicated 240-volt circuit to supply enough power for the resistance heating elements.
Low-power heat pump water heaters are designed to be powered from a 120-volt circuit and can often simply be plugged into a wall outlet.
Second, when the heat pump is running to produce hot water for your tank, it also cools and condenses water out of the air around the water heater. Ensure the following for proper operation:
Supply the heat pump with enough warm air. If you put it in a closed closet, you’ll create an ice box. An unfinished basement is the ideal location, but if you can provide vents for airflow you can put these units in utility rooms.
Provide a drain for the condensate that dribbles out of the unit during normal operation rather than collecting it in the drain pan or creating a puddle.
Check, clean, and replace the air filter periodically. These units run a fan to suck in air through an intake port and blow it out through an exhaust port.
Compared to a gas-burning water heater, an electric heat pump water heater is much safer and more energy efficient. It cools and dries the air around it but not does not produce carbon monoxide or other poisonous gases, and it operates on electricity only.
Compared to a “regular” water heater, an electric heat pump water heater is about three times more energy efficient but can be less reliable because more parts can break. Resistance heating elements are only 100% efficient but have no moving parts. Heat pumps are 250% to 300% efficient but require two motors (a fan and a compressor) and fancy electronic controls to operate properly.
Check with your state or local power utility for rebates on heat pump water heaters.
What’s Still Ahead on the Pathway…
Earlier this year, we explored the pathway to sustainable movement; now, we’re exploring the related pathway to sustainable energy. What are the best ways to save, use, and make energy? Stay with us on the journey to sustainability as we take action to have a positive impact on the world.
References and Further Reading
DOE Announces Breakthrough in Residential Cold Climate Heat Pump Technology, United States Department of Energy
What is a condensing boiler and why are they so efficient?, mass save
Achieve Comfort and Reliable Performance with Cold-Climate Heat Pumps, Zero Energy Project
Energy Saver History Timeline: Refrigeration and Refrigerators, US Department of Energy