What does In-Situ (in place) Testing Provide?
In-Situ Testing of Thermal Conductivity, Pressure Testing and Systems Operations:
In-situ Thermal Conductivity:
The first discussions to directly measure the thermal conductivity of the earth between the Professors Claesson and Bose is interesting to read as follows: click here .
Thermal Conductivity is the most important factor in ground heat exchanger sizing for the facility loads. The testing and reporting quantifies the thermal conductivity of the earth at the borehole. Ewbank pioneered direct measurement of the earth thermal conductivity. Ewbank's method, available since 1994, has been adopted by IGSHPA and ASHRAE. An overview of the specifications for direct measurement of the the earth thermal conductivity is available: click here . To learn more about in-situ thermal conductivity with the IGSHPA/AEE training click here (will open a new browser).
Also, the undisturbed deep earth temperature is measured during in-situ testing. To learn more please click here
Thermal resistivity is the reciprocal of the thermal conductivity and, therefore, is also known with this method.
Also, during the first ten (10) hours of testing the conductivity (and resistivity) of the grout in the borehole can be seen. Low grout conductivity causes inefficient operation of the ground heat exchanger. This DOES NOT change the earth's thermal conductivity. It simply requires a larger temperature differential to move heat causing a loss of efficiency. The ability of a heat pump to move heat to or from the earth is affected and therefore the delivered capacity for the facility is lower. To learn more about borehole resistance click here .
However, the thermal diffusivity is a property that requires other measurement methods to determine and can not be measured during only in-situ thermal conductivity testing since only one borehole is used.
To determine and measure the thermal diffusivity two boreholes are required; one to transfer heat to the earth (which could be during an in-situ thermal conductivity test) and a second parallel and certain distance observation borehole to record the effects of the heat of rejection through the earth. A piezometer borehole used to observe the effects of a pumping water well is a good comparison. The thermal resistance of any and all grouting and piping, in both boreholes, must be known and minimized, particularly within the observation borehole. No testing standards are in place at this time to perform this test.
Thermal diffusivity is not the major factor in ground heat exchanger sizing and it can only be estimated. To overcome not being able to measure it, in situ, well spacing is increased. This is the common practice in designing a GHEX to the facilities (design) load.
HDPE Pressure Testing:
The testing and reports are used to determine the structural integrity of the plastic piping of a ground heat exchanger after installation and before commissioning to the facility. The tests follow the ASTM methodology for testing.
Ground Source Systems Operations:
In-situ measurement and verification of the entering and leaving water temperatures of an installed ground source heat pump confirms the proper operations of a system. Issues can be identified to the heat pump or the ground heat exchanger. If the space is not being properly conditioned it is straight forward to find the cause and take action. Ewbank's data loggers and charting of the results give real time information of the system. Therefore the manufacturer's published capacity and operation of a unit can be compared to the actual operation of the unit.
Just the facts are what you get with Ewbank testing therefore:
Don't base your ground source heat exchanger on speculation and estimation.
You need the facts. Here are some facts.
1. Thermal conductivity is the key variable in system design.
2. Ewbank and Associates is the only test service that has verified its testing results through research.
3. Any representation of diffusivity from test data is speculation and estimation.
4. Ewbank pioneered thermal conductivity testing and it has been adopted by IGSHPA and ASHRAE.
5. Ewbank reports the facts you need for a reliable system design. We let others do the speculation.
Ewbank gets the facts right