When it comes to geothermal residential or commercial installations, two things make good business sense.
Selecting the right sized equipment and loop systems to maximize heating and cooling efficiency, and installing loop systems designed to meet not only today’s needs but those in the future as well.
It’s not rocket science. Regardless of the size or type of heat pump they feed into, geothermal loop systems are made to last. The sturdy high density polyethylene (HDPE) pipe that winds through the open and closed loop systems used in our industry carries warranties of up to 55 years.
That means thirty or forty years from now, when a home or business owner wants to upgrade to a newer heat pump, they should be able to do so with the confidence that their existing loop system will be able to support what will surely be a more efficient pump given our ever evolving technology.
As contractors, drillers and installers, we should all take pride in making sure we’re designing the right system for the business or homeowner from the outset. And that includes not only ensuring the systems we design heat the entire home or business, but that they also take into consideration future heating and cooling needs.
Consider the open and closed loop systems used in geothermal installations. Regardless of where someone lives or works in Canada, the average home or business experiences a heat loss of about 60,000 BTUs and therefore requires a 5-tonne geothermal system to heat or cool the entire building. The size of the equipment and the characteristics of the property help determine whether or not an open or closed loop system is used.
Open Loop System
Open loop systems are often the loop system of choice on properties that have an existing water well. The key determining factor is quantity. It’s important that the water well has the capacity to support the geothermal system beyond the existing domestic requirements of the building (eg. the water used for drinking, flushing toilets, showers, washing clothes, etc.). Open loop systems need two gallons per minute of water per nominal tonne; therefore a 5-tonne geothermal system would need ten US gallons per minute over and above domestic water requirements at peak times. If the average household uses eight gallons of water per minute for domestic use, then the well would need to supply 18 gallons of water per minute to be effective.
It’s not unusual with the installation of open loop systems to have to upgrade the building’s existing pump and pressure systems to accommodate the additional load generated by the geothermal system. This type of loop system generally calls for hiring a licensed groundwater specialist to drill a second well. Groundwater is drawn from an aquifer through the supply well and pumped into the heat pump, while discharged water from the heat pump is redirected into the second well and back into the same aquifer.
Closed Loop System
In cases where an open loop system isn’t feasible, a closed loop system can be used instead. In closed loop systems, a continuous geothermal loop is placed in the ground either horizontally or vertically, depending on the expanse of the property. Heat transfer fluid re-circulates through the loop with both ends connected to the heat pump in the building and absorbs the natural heating and cooling properties from the earth.
A 5-tonne geothermal system would require a minimum of 5,000 square feet of ground space for a horizontal loop. In this case, a continuous loop of pipe is buried five to six feet below the ground. This is an ideal system from a cost and simplicity standpoint.
When the land space isn’t available, a vertical loop system can be used instead. Given the type of drilling equipment needed to install a vertical loop system, this approach is more expensive than the horizontal loop system. Depending on the property conditions and available equipment, a 5-tonne geothermal system would require between 900 – 1200 feet of drilling to accommodate about 1800 feet of continuously looped HDPE pipe. The ideal approach is to drill two 455 foot holes to maximize heat transferability from the ground to the pipe (allow five feet for hook-up). Generally speaking this would have more heat transfer value than drilling 10-90 foot holes and is less invasive to the property.
I prefer to install 1¼” pipe in vertical loops because it provides greater heat exchange. However, I also appreciate that our GeoSmart DeltaBase 95GT drill rig is one of the few in the country capable of drilling 450 foot holes (900 feet of drilling). If the capacity of the drilling equipment available is limited or the terrain affects how deep you can drill, it may be necessary to drill as many as twelve 100 foot holes (1200 feet of drilling) and use the smaller ¾” pipe to obtain the same heat exchange as the larger pipe.
The trend is moving towards longer loops to support the higher efficiency heat pumps hitting the market. And as efficient as our geothermal systems are today, we know they’ll be even more so in 30 to 40 years. So be generous when installing loop systems today.
The right heat pump, the right loop system and the right-sized pipe will meet the heating and cooling needs of the entire house or business both now and in the future, ultimately generating proud and satisfied customers and reflecting well on the industry.
Stan Marco is a well-respected and highly sought after geothermal knowledge expert and educator. He is an active member within the ground water community, is a board member with the Canadian GeoExchange Coalition and is Co-founder and CEO of GeoSmart Energy & GeoSmart Drilling Services.