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Heat Pump Basics – Is this System Right for Your HVAC Needs?

Published on: January 1, 2014

In the Southeast U.S., where winters are mild but summers are scorching, a heat pump is a nearly ideal way to keep your home comfortable. These systems perform best in temperatures above 30 degrees, which our area sees plenty of. If you’re considering investing in one of these systems, get to know a little about how they work before you start shopping around.

The Heat Pump: Designed for Efficiency

Heat pumps run on electricity rather than burning fuel the way gas and oil furnaces do. Unlike electric heaters, though, they don’t use electricity to produce heat. Instead, they move or “pump” heat from one location to another. This is what makes them more energy efficient than any other form of electric heating. What’s more, heat pumps can both heat and cool. A heat pump is essentially an air conditioner with an extra component that allows it to work in reverse to both move warm air into your home in winter and out of your home in summer. In cooling mode, a heat pump works much the same way a refrigerator does.

Investing in a heat pump saves you both money and time on installation. Instead of a separate furnace and air conditioner, there’s only one system to install.

How Heat Pumps Do Their Job

The conventional ducted air source heat pump – the most common type – has an outdoor unit and an indoor unit. The outdoor unit contains a fan, refrigerant coil, compressor and reversing valve. The indoor unit also contains a fan and refrigerant coil.

When the system kicks on, liquid refrigerant is pumped through the outdoor coil, which works as the condenser. As the fan draws outdoor air over the coil, the refrigerant absorbs the heat from the air and turns into a vapor. The refrigerant vapor passes through the compressor, further increasing in temperature and pressure, and then passes into the indoor coil, which works as the evaporator.

Once at the indoor coil, the refrigerant loses heat, condenses back into a liquid and flows back to the outdoor unit. The heat the refrigerant brought in is moved by the indoor blower fan into the ductwork so it can be distributed throughout your home.

In summer, your system switches modes and works to cool your home, drawing heat out of the house and releasing that heat outdoors. The component that allows a heat pump to cool as well as heat is the reversing valve. This valve reverses the direction of the refrigerant flow, turning the outdoor coil into the condenser and the indoor coil into the evaporator.

Different Models for Different Needs

Different types of heat pumps are available to suit different home designs and personal preferences. These include ducted air source heat pumps, ductless air source heat pumps and ground source heat pumps.

Ducted vs. Ductless

Ducted air source models are the most common. These models work in the way described previously, transferring heat between the outdoor air and your home, then distributing heated or cooled air through ductwork.

While these systems can be highly efficient, the ductwork itself poses a number of problems. First, installing ductwork in a finished home requires opening the ceilings and walls, which is expensive, time-consuming and messy. If you’re looking to renovate a historical home without destroying its features, construction of that kind may be out of the question. For heating and cooling a garage or a room addition, extending existing ductwork or adding ducts is often impractical.

The solution is a ductless heat pump system. Although these systems are still catching on in the U.S., they’ve long been popular elsewhere. If you’ve traveled in Europe or Southeast Asia, you’ve probably seen one.

They consist of an outdoor unit and one or more indoor air handlers that deliver warmth and cooling directly to the room. The outdoor unit is connected to the indoor unit through a conduit line that requires only a three-inch hole in the wall. There are no ducts to install and therefore no risk of duct leaks or design flaws wasting energy.

Ground Source Systems

The air isn’t the only place a heat pump can transfer heat to and from. The ground also works for this purpose and ground source, or geothermal systems, take advantage of this fact. These systems use the ground or a body of water, such as a lake, as a source of heat (in heating mode) or place to release heat (in cooling mode). The most common type uses a set of refrigerant-filled pipes buried underground to exchange heat with the earth.

While air source systems are efficient, their efficiency depends in part on the air temperature, which varies a lot over the seasons. The ground, on the other hand, remains at a relatively stable temperature year round. Better yet, it’s almost always cooler than the air in summer and warmer than the air in winter. This allows geothermal systems to achieve higher efficiencies than air source ones. Some of the benefits of these systems are:

  • Efficiency – Ground source systems can achieve efficiencies of 300 to 600 percent even in cold weather. Air source systems reach 250 percent efficiency at best, even when the weather isn’t so cold.
  • Durability – The indoor unit should last around 25 years while the ground loop can keep working for 50 years or longer. There’s no above ground outdoor unit, so your components aren’t at risk for vandalism or weather damage.
  • Better humidity control – These systems work to keep your indoor humidity at around 50 percent, which is helpful in the Southeast’s summers.

Efficiency Ratings to Know

When you’re browsing around for heat pumps, one of the first things you’ll need to check on each model is its efficiency. As with other electronics, you can find information about a heat pump’s efficiency on its yellow Energy Guide label and in its documentation. There are two main ratings to consider:

  • Heating seasonal performance factor, HSPF – This rating expresses how efficient the system is at heating over the course of the season. The number is a ratio of heat supplied compared to the energy used to supply that heat. Systems with higher HSPFs are more energy efficient. Because the numbers used in the calculation are averaged out over the season, HSPF gives you a realistic idea of how efficient the system will be on cool fall days as well as on the coldest winter days. The minimum HSPF you’ll find 7.7, but choosing a system with an HSPF of 8 or higher is preferable if you’re looking for energy savings. Although an HSPF of 8.2 or higher is considered high efficiency, systems with HSPFs of 9 and 10 aren’t unheard of.
  • Seasonal energy efficiency ratio, SEER – This rating is an indication of the system’s cooling efficiency. Like HSPF, it’s averaged out over the season to take into account milder as well as hotter days. A higher SEER means a more efficient system. The minimum SEER for heat pumps and A/Cs is 13, but SEERs for heat pumps go up into the mid-20s.

Energy Star

The Energy Star program, managed by the U.S. Environmental Protection Agency (EPA), rates and endorses products that meet certain requirements for energy efficiency. Heat pumps that bear the Energy Star logo are among the more efficient models on the market.

To become Energy Star-qualified, an air source heat pump must have an HSPF of 8.2 or greater, a SEER of 14.5 or greater, and an EER of 12 or greater.

Maintaining Your System

Heat pumps aren’t particularly high maintenance. A little regular care helps keep the system running efficiently and ensures the components reach the life span for which they were designed.

  • Keep your filters clean – Replace or clean your air filters on the schedule recommended by the manufacturer. Dirty filters impair your system’s efficiency and lower your indoor air quality.
  • Clean the outdoor unit – Keep any vegetation around your outdoor unit trimmed back. Periodically use a soft brush to gently remove leaves, grass clippings and other debris from the fins. At least once a year, clean the coil by running a light stream of water through it from the inside out.
  • Schedule an annual tune up – Once a year, call in a professional to verify sufficient air flow, check for refrigerant leaks and electrical faults, inspect and lubricate the motor, and otherwise ensure your system is in top form.

If you could use some professional guidance on choosing the right heating and cooling system for your needs, visit us at AC Southeast. With our Find a Contractor service, you can locate a reliable professional anywhere throughout the Southeast U.S.