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Axis Directional Drilling services and job suitability...

Our main service is for heat pump installers/companies who contract out the ground works of a job.

Traditionally we have used the HDD construction method to install pipelines beneath areas where conventional open trench or other construction techniques may cause undesirable surface disturbance. Thus HDD is a proven technology which can be easily transferred to the GSHP industry for the instillation of the ground loop in many varied applications.

We are a crew of experienced directional drillers whose aim is to introduce and establish horizontal directional drilling in the ground loop construction method. We operate a Vermeer 7x11 drill rig which is one of the smallest HDD rigs on the market. The advantage of using this setup means we have access through alley ways and garden gates. The rig also has a specially modified drill head which is able to match the pipe diameter and create a smoother path.

Wayne on rig
Wayne on rig

Suitability for Directional Drilling

Every job site is different and all will have to be physically examined for suitability. However, as a general rule horizontal drilling can be used as an alternative to nearly all trenching and many vertical jobs. There are some basic prerequisites that need to be met, which are:

The drilling rig requires an area of 12ft x 3ft for setup and a total distance 18ft from the back of the rig to entry pit at a depth of 70-80cm

The Pipes are bored in typically at a depth of 700 to 1500 mm (3 to 5 feet). Bore lengths can range from 15 to 100m (30 to 160 feet), depending on soil texture and moisture content, and available area. Bores are typically spaced 1 to 4 m (3 to 12) feet apart.

So for an average 4 bed detached an area of 50x20m of garden would be suitable, though this is an approximation and nearly every situation is different.

The finished drilling results in an undisturbed surface and the ground loop pipes neatly spaced ready for electrofusion or chemical jointing to complete the loop.

Once all the connections are finished the loop is flushed to remove any debris and pressure tested to make sure the joints are good.

Other features of GSHP ground loop instillation to be considered are:

Site Geology: Soil texture
The thermal conductivity of dry soils tends to increase as their texture becomes increasingly fine. This simply is a consequence of the fact that the thermal conductivity of air is about one hundred times less than that of solid soil particles. Finer soils have more particle-to-particle contact and smaller insulating air gaps between particles than coarse soils, hence increased conductivity. The opposite is true for soils saturated with water, when the pore spaces between particles is filled with water rather than air, since the thermal conductivity of water is about two to three times greater

Groundwater level
As already noted above, the extent to which the soil is routinely saturated with water greatly influence a soil's thermal properties and the selection and design of an appropriate ground loop.

Soil Thermal Properties
Heat capacity (also known as specific heat) indicates the ability of a substance to store heat energy; the greater its heat capacity, the more heat it can gain (or lose) per unit rise (or fall) in temperature. The heat capacity of dry soil is about 0.20 BTU per pound per ºF of temperature change, which is only one-fifth the heat capacity of water. Therefore, moist or saturated soils have greater heat capacities, typically in the range of 0.23 to 0.25 BTU/lb/ºF. light dry soils experience greater seasonal temperature swings at a given depth than wet soils. This is because their lower heat capacity causes their temperature to rise or fall more than wet soils for a given amount of heat energy gained in the summer or lost in the winter.

Thermal conductivity is another soil property that must be known in order to design a closed-loop or direct expansion GSHP system. This indicates the rate at which heat will be transferred between the ground loop and the surrounding soil for a given temperature gradient. The thermal conductivity of the soil and rock is the critical value that determines the length of pipe required, which in turn affects the installation cost as well as the energy requirements for pumping working fluid through the ground loop. Soil-Btu

Figure 1 indicates the thermal conductivity of different soil types. Heat transfer capability tends to increase as soil texture becomes increasingly fine, with loam mixtures having an intermediate value between sand and clay. As also shown in this figure, the thermal conductivity of any soil greatly improves if the soil is saturated with water. This effect is much greater for sandy soils than for clay or silts, since coarse soils are more porous and therefore hold more water when wet. Therefore, groundwater level is another important site factor in evaluating a potential GSHP project and optimizing the depth at which horizontal and spiral ground loops should be installed.

If you’ve read everything and think your GSHP project is viable for HDD then call Wayne 07876028079 or contact us online.

More information about Heat Pump Ground Loop installation