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Thermal response tests

Measuring ground conductivity in boreholes

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A thermal response test measures the thermal conductivity of the ground
 
They are often undertaken prior to installing a closed loop ground source heat pump system using vertical boreholes.  In order to accurately predict the capacity of the ground to deliver and or store the required amount of heat or cooling energy to match the needs of a building over a long life cycle it is advisable to undertake a thermal response test in a borehole to assess the ground conditions and measure the reaction of flows through ground loops inserted in the bore hole.  This is done as a continuous process over a period of around 3-4 days using Geowarmth’s purpose built thermal tesponse test rig.  Thermal conductivity is arrived at by applying heat to water circulating in the closed loop pipework.  Data is collected on site by our technicians and then analysed and reported on by our thermogeologist to arrive at the average thermal conductivity for the bore hole.  Our rig is self contained with its own on board power supply.
 
For a proposed ground source heat pump installation a thermal response test can then be used to establish the number of boreholes required to service the heating and cooling demands of the building.  Moreoever the holes used for the thermal response test can be incorporated into the borefield for the heat pump installation so they can subsequently become ‘production’ holes, not just trial holes.
 
In order to size and design a borefield for a proposed ground source heat pump development, the value of thermal conductivity derived from the thermal reponse test can be used in conjunction with a borehole array design software package.  The heat extraction or rejection rate per metre of borehole is approximately proportional to the ground thermal conductivity.  Other factors are simulated by the design package including the thermal resistance of the borehole, the geometry and spacing of boreholes in the array (thermal interference), the thermal storage effects in the ground and the distribution of heating and cooling loads throughout the year. Together with the thermal response test, Geowarmth are able to provide the complete borefield design service. Please contact us to discuss your requirements.
 
A separate technique - thermal needle probe measurement -  is available for measuring conductivity at shallow depths where horizontal ground collectors are proposed.  For an explanation please see our thermal needle probe measurement page.
 
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