GeoExchange BC

GeoExchange heating/cooling relies on the principle that the earth (or ocean) temperatures remain relatively constant year round (approximately 50F in the Lower Mainland). The earth absorbs about half of the sun's energy and we will, in turn, use this energy to heat your home or building. Two important components of the GeoExchange system are the water source heat pump and the source-side heat exchanger (whether open loop or closed ground loop).

The water source heat pump, also commonly referred to as a geothermal or GeoExchange heat pump is capable of heating/cooling both water and air. This allows options for either forced air or hydronic distribution systems. An important note to consider is that a complete distribution system must be designed with the heat pump parameters in mind to heat and cool the building properly and comfortably. The most common example of a heat pump is a refrigerator, which concentrates and extracts heat from the interior, and rejects it into the surrounding space.

There are two different types of source-side systems. Open loop or closed loop. Open loop systems extract energy from water wells or body of water such a lake or pond. Although quite efficient, the opportunity to use this type of system is relatively rare. The more common and reliable source-side system is a closed loop. Closed loop systems can be installed in vertical boreholes, horizontal trenches or submerged in the ocean, lakes, or rivers. Once installed, closed loop systems require almost no maintenance.

An environmentally friendly solution (80% water / 20% glycol or alcohol) is circulated through the ground loop. This fluid absorbs energy from the earth and carries it to one or more water source heat pumps. The heat pump, using a simple refrigeration cycle, upgrades the heat and then distributes it throughout the building. In the summer, the system reverses and heat is extracted from the building and expelled into the ground through the ground loop.

Most loops for residential GeoExchange systems are installed either horizontally or vertically in the ground, or submersed in water in a pond or lake. In most cases, the fluid runs through the loop in a closed system, but open-loop systems may be used where local codes permit. Each type of loop configuration has its own, unique advantages and disadvantages, as explained below:

Horizontal Ground Closed Loops

Image Courtesy of WFI Inc.

The horizontal configuration is usually the most cost effective when adequate yard space is available and trenches are easy to dig. GeoExchange installers work with excavator operators to dig the trenches four to eight feet below finish grade, then lay a series of parallel plastic pipes. They backfill the trench, taking care not to allow sharp rocks or debris to damage the pipes. Fluid runs through the pipe in a closed system. Horizontal ground loops are usually easiest to install while a home is under construction. Care must be taken to examine the ground and soil conditions to ensure a successful installation.

Vertical Ground Closed Loops

Image Courtesy of WFI Inc.

The vertical type of ground loop configuration is ideal for homes where yard space is insufficient to permit a horizontal ground loop. This is a commonly used type of ground loop in BC. This configuration works well when the Earth is rocky close to the surface, or for applications where minimum land area is available. Drilling contractors bore vertical holes in the ground 200 to 400 feet deep. Each hole usually contains a single loop of pipe with a U-bend at the bottom. After the pipe is inserted, the hole is grouted. Each vertical pipe is then connected to a horizontal pipe, which is also concealed underground. The horizontal pipe then carries fluid in a closed system to and from the indoor GeoExchange heat pump. Vertical loops are generally more expensive to install because of drilling costs, but require less piping than horizontal loops because the Earth deeper down is cooler in summer and warmer in winter.

Pond Closed Loops

Image Courtesy of WFI Inc.

If a home is near a body of surface water, such as a pond, lake, or ocean, this type of loop design may be the most economical. The fluid circulates through polyethylene piping in a closed system, just as it does in the ground loops. Typically, workers run the pipe to the water and then submerge long coiled sections under water. The pipe may be coiled in a slinky shape to fit more of it into a given amount of space. GeoExchange experts recommend using a pond loop only if the water level never drops below six to eight feet at its lowest level to assure sufficient heat-transfer capability. Pond loops used in a closed system result in no adverse impacts on the aquatic system provided the loop is sized correctly and the body of water is a sufficient size to accept the loading of the building. An experienced GeoExchange contractor will take care of any government authorizations regarding public land or body of water.

Open Loop System

Image Courtesy of WFI Inc.

This type of loop configuration is used less frequently, but may be deemed quite cost effective if ground water is plentiful. Open loop systems, in fact, are the simplest to install and have been used successfully for decades in areas where local codes permit. In this type of system, ground water from a well (aquifer) is piped directly from the well to the building, where it transfers its heat to a heat pump. After it leaves the building, the water is pumped back into the same aquifer via a second well, or discharged back into a nearby lake or ocean when permitted. Care must be taken to ensure that the ground water quality is sufficient to avoid potential fouling of heat exchangers and equipment.

Although based on a very simple theory, GeoExchange systems require diverse skill sets for a proper installation. Refrigeration technicians, plumbers, electricians, control technicians, drillers, and CGC certified installers all work together with the GeoExchange designer to install and commission the system.

The design of the system is by and large the foundation for an efficient and cost effective system. A few of the considerations and calculations made by the designer are:

Qualified installation technicians and designers will consider the homeowners comfort needs and budget so that they receive the system they desire.

Geothermal Energy Confusion

Do you know the difference between "geothermal energy" and a "ground source heat pump"? All I know is they both run into the ground. But as this article from Green Building Elements explains how together they can more efficiently heat and cool your home at a dramatically reduced price.

Simply stated, a geothermal energy system uses heat from below the surface of the Earth as an energy source (think: tapping into a geyser or a volcano for power).

A "ground source heat pump," also known as a "geoexchange system," uses the ground's stable year-round temperature to more efficiently heat or cool your home. How it does this is best explained by

this video.

Drawbacks of Geothermal Heating Systems

I'm sold on geothermal heating. Just check out my previous blog post. But being trained as a journalist, I can't help but strive for at least some kind of balance. And so, I've felt it necessary to outline some of the various problems associated with geothermal residential heating.

First, let's start with the very basics – the word geothermal itself. Several helpful readers have noted that there's a bit of confusion about just what it means. So let's get that cleared up.

Geothermal, as the word is traditionally used, refers to harnessing "energy from 'hot spots' in the earth's crust, and can only be employed in locations where these exist,” according to the website Lighthouse.