Get in the loop
Install a loop system today that’s designed to meet tomorrow’s needs.
June 24, 2011 By Stan Marco
When it comes to geothermal installations, there are two things that
just make good business sense. One is to select the right-sized
equipment and loop systems to maximize heating and cooling efficiency.
When it comes to geothermal installations, there are two things that just make good business sense. One is to select the right-sized equipment and loop systems to maximize heating and cooling efficiency. Two is to install 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 30 or 40 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. This includes ensuring that the systems we design heat the entire home or business, and that they also take future heating and cooling needs into consideration.
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 five-tonne geothermal system to heat or cool the entire building. The size of the equipment and the characteristics of the property help determine whether an open or closed loop system is used.
Open loop system
Open loops are often the system of choice on properties that have an existing water well. The key determining factor is quantity. It’s important that the water well have the capacity to support a geothermal system beyond the existing domestic requirements of the building (the water used for drinking, flushing toilets, showering, washing clothes, etc.). Open loop systems need two gallons per minute of water per nominal tonne. That is, a five-tonne geothermal system will need 10 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 uses, then the well would need to supply 18 gallons of water per minute to be effective in an open loop system.
With the installation of an open system, it’s not unusual to have to upgrade the building’s existing pump and pressure systems. This is done to accommodate the additional load generated by the geothermal system. This type of loop system generally calls for a licensed ground water specialist to drill a second well. In this type of two-well system, ground water is drawn from an aquifer through the supply well and then pumped into the heat pump. Discharged water from the heat pump is redirected into the second well and back into the same aquifer.
Closed loop system
Where an open loop system isn’t feasible, a closed loop system can be used instead. In a closed loop system, a continuous geothermal loop is placed in the ground. This may be done either horizontally or vertically, depending on the expanse of the property. Heat transfer fluid recirculates through the loop with both ends connected to the heat pump in the building, absorbing the natural heating and cooling properties from the earth.
A five-tonne horizontal closed loop geothermal system would require a minimum of 5,000 square feet of ground space. 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 that much 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 five-tonne geothermal system would require between 900 and 1,200 feet of drilling to accommodate about 1,800 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 hookup. Generally speaking, this would have more heat transfer value than drilling 10- to 90-foot holes and is less invasive to the property.
I prefer to install one-and-a-quarter-inch 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 a dozen 100-foot holes (1,200 feet of drilling). In this case, use the smaller three-quarter-inch pipe to achieve the same heat exchange as the larger pipe.
The trend is moving towards longer loops that support the higher efficiency heat pumps hitting the market. As efficient as our geothermal systems are now, we know they’ll be even more so in 30 or 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, this generates proud and satisfied customers and reflects well on the industry.
Stan Marco is a well-respected geothermal knowledge expert and educator. He is an active member of the ground water community, a board member with the Canadian GeoExchange Coalition and a co-founder and CEO of GeoSmart Energy and GeoSmart Drilling Services.
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