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How Do Heat Pumps Work in Cold Weather?

February 24th, 2017

Heat pumps can be used to both heat and cool your home. They use a similar process that your refrigerator uses to keep your food cold and fresh. Have you ever noticed the hot coils on the back of your fridge? They are releasing heat from the inside your fridge. “How does it do this?,” you may ask.

Continue reading to learn how heat pumps transfer heat energy to both heat and cool enclosed spaces.

How Heat Pumps Work

Heat pumps work by using refrigerant to absorb and release heat energy through a process that pressurizes the gas to heat it up and depressurizes it to cool it down. There are several different types of heat pumps, such as geothermal and air-to-water, however, air-source heat pumps are the most common.

Think of an aerosol can or a bicycle pump. When you release air (a.k.a. pressure) the released gas feels cold. If you add pressure, you will notice that the bicycle tire heats up.

When the refrigerant changes states, from a liquid to a gas, the temperature changes. The refrigerant is designed to reach certain temperatures at specific pressures for optimum efficiency (the common R-22 coolant, or HCFC-22, is being phased out and replaced by a new, more environmentally friendly coolant, R-410A).

Heat Pump for Cooling

In spring and summer, the heat pump absorbs heat from the inside of your home (using the evaporator in your indoor unit) and then releases it outdoors via the outdoor unit.

The liquid coolant moves to the evaporator where it gets depressurized and turns into a gas. This gas gets very cold and absorbs all the heat it can from the inside of your home before traveling to the outdoor compressor and changing into a hot liquid.

The hot coolant then goes through your condenser coils while a high-powered fan kicks on. The air flows over all of the condenser coils to aid the release of heat energy. After the refrigerant’s heat is dispersed outdoors, the refrigerant cools down and gets sent back to the evaporator to start the process all over again. In your car, the same process occurs, but the condenser coils are called a “radiator.”

how does a heat pump work - diagram

Source: Popular Mechanics

Heat Pump for Heating

The closed loop coolant system operates much the same way in the fall and winter, but in reverse. Instead of the refrigerant picking up heat from inside the home, the refrigerant now gets to gather heat from the outdoor environment.

When the refrigerant loses pressure and turns into a vapor, it gets much colder than the temperature outside. Since heat energy flows from hot to cold ((2nd Law of Thermodynamics), the refrigerant picks up heat from the outdoor environment. After the refrigerant absorbs all the heat it can, the outdoor compressor pressurizes the gas into a hot liquid. The extremely hot refrigerant travels to your indoor coils and your blower helps release the heat from the refrigerant into your duct system.

You may think that when it’s cold outside, there is no heat to absorb. Fortunately, there is still plenty of heat to be harvested, even when temperatures are as low as -15° C/5° F (Energy Savings Trust).

Unfortunately, when temperatures dip below freezing, the effectiveness of your heat pump goes down significantly. This is why people who live in more extreme climates tend to use furnaces or another type of heating system. There are also hybrid heating systems available that give you the best of both worlds. When temperatures are mild, the heat pump keeps your operating costs low. During extreme cold, the backup gas-fired heater kicks on to maintain high energy-efficiency levels.

Since heat pumps move heat rather than generate it, they are much more efficient in temperate climate zones.

Heat Pump Defrost Cycle

When it gets very cold outside, you may notice that your outdoor heat pump unit gathers a layer of ice and frost. This is normal. Your heat pump actually has a defrost cycle that pumps hot refrigerant back to your heat pump to melt the frost and ice (similar to how the heat pump works in summer mode). Cool air may temporarily come out of your vents and registers at this time. Wait around 15 minutes for the defrost cycle to complete.

If you have a big chunk of ice or lots of snow, however, your defrost cycle may not be working properly. If this happens, turn on your “emergency heat” or “auxiliary heat” and call a professional HVAC technician right away.

The emergency heat turns on the electric heating system. This will keep you comfortable in the meantime, but will significantly raise your heating costs. Schedule professional heat pump service as soon as possible to avoid running up your electrical bills.

Heat Pump Maintenance

In order to keep your heat pump operating efficiently, proper maintenance is necessary:

  1. Replace air filters every 30-60 days.
  2. Schedule professional HVAC maintenance twice a year (once in the fall and once in the spring)
  3. Periodically check your outdoor unit and clear away grass clippings, leaves, dirt, snow, and other debris (you can use your garden hose).
  4. The heat pump should be completely level, supported by a concrete support pad.
  5. Never stack anything on top of the unit.
  6. Maintain a minimum 2-foot clearance around the entire unit.
  7. You can improve heat pump efficiency with shade from trees, trellises, and awnings.
  8. Sign up for a Home Maintenance Plan.

If your heat pump gets interrupted by a power outage or tripped breaker, do not operate the unit for at least 6 hours, especially if it is cold out. Instead, turn on the emergency heat and wait 6-8 hours before turning the pump on.

If you have any problems with your heat pump, whatever season it may be, contact the professional team of technicians at Service Champions.

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