Geothermal Heat Pump: How It Works

By: Max Alexander, This Old House magazine (Page 3 of 3)

illustration of how geothermal pump works

Enlarge this image Illustration:

An electrically powered, geothermal heating and cooling system transfers heat between your house and the earth using fluid circulated through long loops of underground pipe.

Enlarge this image Illustration:

Heat Pump Parts

As with ordinary heat pumps, the refrigerant in a geothermal heat pump runs in a loop through a compressor, condenser, expansion valve, and evaporator, collecting heat at one end and giving it up at the other. The direction of refrigerant flow, which is controlled by the reversing valve, determines whether heat is moving into the house in winter (shown) or being pulled out of it in summer. With the addition of a desuperheater, residual warmth from the system can also supplement a conventional water heater, further reducing energy bills.

Browse Images

How-To Video

Browse More

How to Install Radiant Heat

In this how-to video This Old House plumbing and heating contractor Richard Trethewey shows the basics of retrofitting radiant-floor heating system to a bathroom

Watch The Video

On Newsstands Now

In the Magazine

Reinvent your rooms with color

What You'll Learn:

The Basics

What it is

An electrically powered heating and cooling system that transfers heat between your house and the earth using fluid circulated through long loops of underground pipes.

How it works

An indoor heat pump uses a basic refrigeration cycle—evaporation, compression, condensation, and expansion—to capture and disburse heat from and to the ground to warm the house in winter and cool it in summer.

Why you’d want one

Cuts home heating and cooling bills by 30 to 70 percent. Eliminates noisy outdoor compressors and fans. Reduces greenhouse gas emissions by the equivalent of planting 750 trees or taking two cars off the road.

What to look for

For federal tax credits, pumps must meet Energy Star efficiency standards. For closed-loop systems, you need an EER of 14.1 and a COP (coefficient of performance) of 3.3.

Where to get it

To find manufacturers, visit the Geothermal Heat Pump Consortium website. To find trained installers and designers who know the local geology and how to size systems for maximum efficiency, go to the International Ground Source Heat Pump Association’s website.

What it costs

$15,000–$20,000 installed for the system, including ground loops, heat pump, and controls. The Database of State Incentives for Renewable Energy (dsireusa.org) provides up-to-date information on state incentive programs.

Can I Retrofit One?

Retrofitting a ground-source system is not difficult, as long as burying the ground loop is feasible. A house will need ducts to distribute cool air on hot days. Those same ducts can provide warm air in winter. Some geothermal heat pumps can hook up to an existing air handler, other units come with their own integral air handler. Houses with hot-water heating can use geothermal systems, too, although additional radiators may be needed because these systems do not reach the higher temperatures of fuel-fired boilers. (That’s not a problem for radiant floor heat, which operates at lower temperatures.)