Comprehensive Guide to Heat Pumps: Operation, Types, & Benefits

Enbridge Thermostat Rebate

Heat pumps are an energy-efficient alternative to traditional heating and cooling systems. This in-depth guide will provide you with everything you need to know about heat pump technology, types, components, operations, and more.

What is a Heat Pump?

A heat pump is a system that transfers heat energy from a source of heat to a destination called a heat sink. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

In heating mode, a heat pump absorbs heat from the cold outdoor air and pumps it into a warm indoor space. In cooling mode, the indoor space is cooled as a heat pump absorbs heat from the indoor air and discharges it outdoors. Heat pumps can provide year-round climate control with greater efficiency than furnaces and air conditioners.

How Heat Pumps Differ from Air Conditioners

While heat pumps and air conditioners are similar systems, a key difference is that air conditioners only provide cooling, while heat pumps can provide both heating and cooling.

Air conditioners use the refrigeration cycle to remove heat from the indoor space. They discharge the absorbed heat outdoors, leaving the indoor air cooler. However, an air conditioner requires supplemental heat from a furnace or heating system in winter.

Heat pumps are able to reverse the refrigeration cycle to provide heating or cooling as needed. The same heat pump system can extract heat from outdoor air in winter and act as an air conditioner by rejecting heat outdoors in summer.

Advantages of Heat Pumps

There are several benefits that make heat pumps an attractive home heating and cooling solution:

  • Energy efficiency: Heat pumps provide home heating and cooling using as little as one-third the electricity of conventional air conditioner and furnace systems. This saves homeowners money on utility bills.
  • Environmentally friendly: Since they don't burn fossil fuels, heat pumps produce lower greenhouse gas emissions than furnaces and boilers. Heat extracted from outdoor air is renewable.
  • Versatile heating and cooling: One system provides heating, air conditioning, and supplemental water heating. Some units can operate efficiently down to below-freezing temperatures.
  • Zoned comfort: Ductless mini-split heat pumps allow different temperatures to be maintained in different rooms.
  • Quiet operation: No noisy outdoor units or fans.
  • Long lifespan: Quality heat pump systems can provide reliable service for over 20 years.

Types of Heat Pumps

There are two main types of heat pumps used in homes: air-source heat pumps and ground-source (geothermal) heat pumps.

Air-Source Heat Pumps

An air-source heat pump transfers heat between the inside of a building and the outside air. It works like a reversible air conditioner, with an indoor unit mounted on a wall or ceiling and an outdoor unit.

During winter, an air-source heat pump takes heat from the outdoor air and pumps it indoors. The refrigeration system allows heat transfer to take place even when the outdoor air is colder than the temperature inside the home.

In summer, the system reverses to cool indoor air by transferring heat from inside to outside. Air-source heat pumps work best in milder climates but can also provide effective heating at sub-zero temperatures with a backup heating system.

Air-source heat pump system with indoor and outdoor units

Ground-Source (Geothermal) Heat Pumps

Ground-source, or geothermal, heat pumps tap into the stored solar energy in the ground to provide heating, cooling, and hot water. These systems transfer heat between a building and the ground instead of outdoor air.

Pipes buried in the shallow ground or submerged in an underground pond absorb heat from the soil/water. The heat pump compressor then raises the temperature of the heat absorbed by the refrigerant as it passes through the system.

In summer, the process reverses as heat is extracted from the indoor space and transferred to the ground through the buried pipes. While geothermal systems have higher installation costs, they can provide greater efficiency than air-source heat pumps.

Geothermal heat pumps use buried pipe loops to exchange heat with the ground

How Do Heat Pumps Work?

Heat pumps operate on a refrigeration cycle that allows them to absorb heat at one place and release it another. Here is an overview of the basic heat pump operation:

  • A compressor increases the pressure and temperature of the refrigerant vapor, concentrating heat energy.
  • The hot refrigerant passes through a heat exchanger, releasing heat to the indoor air stream of the home.
  • The refrigerant condenses back to a liquid state while giving up its heat indoors.
  • An expansion valve reduces the pressure of the cooled refrigerant liquid before it enters another heat exchanger.
  • The refrigerant absorbs heat from the outdoors as it evaporates into a gas in the cold coil.
  • The refrigerant returns to the compressor to repeat the cycle and transfer more heat.

A reversing valve switches the direction of refrigerant flow between heating and cooling modes. This allows the indoor and outdoor heat exchangers to alternate roles as evaporators or condensers when their function needs to reverse for heating or cooling.

Comparison of Heat Pumps, Furnaces, and Air Conditioners

While heat pumps, furnaces, and air conditioners all control indoor comfort, they differ in how they generate and distribute heated or cooled air:

  • Heat pumps move heat between indoor and outdoor environments by using the refrigeration cycle. Electrical energy powers the compressor and fan motors.
  • Furnaces burn fuel such as natural gas, propane, or heating oil to directly generate heat that’s circulated by fans. No refrigeration cycle is involved.
  • Air conditioners use the refrigeration cycle to cool indoor air but lack a heating function. Separate systems like a furnace provide winter heating.

Choosing a Heat Pump System

Important factors in choosing an appropriate heat pump system include:

  • Home size: Required heating and cooling capacities are determined by the home's square footage and insulation.
  • Climate: The local climate helps determine which heat pump is most suitable. Geothermal and dual-fuel heat pumps offer greater efficiency in colder regions.
  • Expertise: Consulting Simply Smart Home's heating and cooling specialists ensures proper sizing, selection, and installation of equipment.
  • Combination heating: In cold climates, heat pumps can be combined with propane or natural gas furnaces in dual-fuel systems for optimal efficiency and performance.

Are Heat Pumps Right for You?

Heat pumps are well suited for heating and cooling needs in mild to moderate climates. Colder regions may require a dual-fuel system with supplemental heating.

Heat Pumps in Cold Climates

While heat pumps work optimally in temperatures above freezing, advances in cold climate heat pump technology allow them to operate efficiently in sub-zero weather.

  • Variable speed compressors adjust capacity based on demand. This maintains efficiency as outdoor temperatures drop.
  • Specialized outdoor coils promote defrosting.
  • Backup electric resistance heat or a dual-fuel system with a furnace provides extra heat on the coldest days.

Dual-Fuel Heat Pump Systems

Rather than choosing either a furnace or heat pump, dual-fuel systems integrate the two technologies for maximum comfort and efficiency:

  • The heat pump provides heating down to a certain outdoor temperature, typically around 35°F depending on climate.
  • Below this “balance point”, the system switches over to the gas or propane furnace for heating.
  • The dual-fuel approach utilizes the high-efficiency heat pump for most of the heating season but can operate economically even in sub-zero weather.

Heat Pump System Components

Complete heat pump systems are comprised of an outdoor unit, indoor air handling unit, distribution network, controls, and a supplemental heat source.

Outdoor Unit

This exterior component has:

  • Coil: Acts as the refrigerant evaporator in heating mode, condenser in cooling. Has fins to transfer heat.
  • Fan: Pulls air across coil fins to aid heat transfer.
  • Compressor: Increases refrigerant pressure and temperature. Reciprocating, scroll, or variable-speed compressors are common.
  • Expansion valve: Lowers pressure of cooled refrigerant before it enters the evaporator.

Indoor Air Handler Unit

The indoor components include:

  • Coil: Serves as the evaporator in cooling mode and condenser during heating.
  • Blower: Circulates air from home’s ductwork across the coil and back into rooms.
  • Filter: Removes airborne particles to protect coils and indoor air quality. Should be cleaned or replaced regularly.

Refrigerant Lines and Reversing Valve

Refrigerant fluid transports heat between the indoor and outdoor heat exchangers. Insulated refrigerant lines connect the external condenser/evaporator unit with the indoor evaporator/condenser coil.

A reversing valve alternates the direction of refrigerant flow between heating and cooling modes.

Heat Pump Controls

Smart thermostats like the Ecobee SmartThermostat monitor indoor and outdoor temperatures, stage multiple heat pumps, and switch between heating and cooling modes. Zoning systems allow different temperatures in different rooms.

Supplemental Heat Sources

Dual-fuel heat pumps combine a heat pump with a propane or natural gas furnace. Electric resistance heat modules provide backup heat for cold climates.

Heat Pump Operation Modes

Heat pumps operate in reverse cycles for heating and cooling:

Heating Mode

  1. At low pressure, the refrigerant absorbs heat from outdoor air at the exterior coil, turning from a liquid to a gas.
  2. The compressor raises the pressure and temperature of the hot refrigerant gas.
  3. The reversing valve directs the refrigerant to the indoor coil where it condenses back to a liquid state while releasing heat.
  4. An expansion valve reduces the pressure before the refrigerant flows back outside to absorb more heat.

Cooling Mode

The heating mode process essentially runs in reverse:

  1. The refrigerant absorbs heat from room air at the indoor coil, evaporating from a liquid to a gas.
  2. The compressor increases the temperature and pressure of the refrigerant vapor.
  3. At the outdoor coil, the hot gas condenses to a liquid while transferring heat to the outside air.
  4. Passing through an expansion valve reduces the pressure before re-entering the indoor coil to absorb more heat.

Professional Heat Pump Installation

Given the complexity of heat pump systems, installation is best performed by qualified HVAC technicians like those at Simply Smart Home. Our heat pump expertise includes:

  • Sizing: Heat loss/gain calculations based on home size, insulation, and local climate. Ensures right-sized system.
  • Efficiency: Selection of highest-SEER, Energy Star heat pumps available.
  • Zoning: Design of optional zoning system for individual room control.
  • Ductwork: Integration of heat pump with existing or new ductwork.
  • Electrical: Proper hookup to electrical supply by licensed technicians.
  • Permits: Obtaining necessary permits and meeting local code requirements.

Heat Pump Systems Review and Summary

  1. Heat pumps provide home heating and cooling by absorbing heat from one place and transferring it another using the refrigeration cycle.
  2. Reversing valves switch the direction of refrigerant flow between heating and cooling modes.
  3. Outdoor units exchange heat between refrigerant and outside air or ground. Indoor units exchange heat with home's air.
  4. Heat is absorbed from the heat source as the refrigerant evaporates into a gas. Heat is released at the destination as the refrigerant condenses back to a liquid.
  5. Expansion valves and compressors enable the pressure changes needed in the refrigeration cycle.
  6. Air-source heat pumps exchange heat with outdoor air. Geothermal heat pumps exchange heat with the ground.
  7. Dual-fuel heat pumps combine heat pump and gas furnace systems for efficiency across heating seasons.
  8. Qualified technicians properly size and install heat pump systems matched to local climate and homes.

By understanding how these high-efficiency heating and cooling systems operate, you can make an informed heat pump purchase and installation decision. Contact the experts at Simply Smart Home to determine if a new heat pump is the right choice for your home comfort and energy savings.

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