ABSTRACT
The biggest challenge in the utilization of energy
micropiles in underpinning projects is related to the through holes for
geothermal energy collector pipes in the load transfer structures. In the FIN-C2M project (Case 2 Micropile Research Project in ISM
collaboration) several technical solutions were studied and the most
suitable load transfer structure cases for the use of energy micropiles were
defined. There are thirteen known load transfer structure cases and energy
micropiles can be used with nine of them. In five of the cases, the through
holes for collector pipes can be made as found in new buildings. In the other
four cases, where pretensioning is achieved by jacking directly above the
micropile, the construction of through holes needs further development . There
are already some possible solutions and the challenge is to bypass the jack.
USING DEEP FOUNDATIONS AS GROUND HEAT COLLECTORS
The first projects
where openings in pile casing were used to install heat exchange piping are
from the early 21st century. The research for energy piles started the late
1990’s. All the cases have been large new construction projects where the load
bearing soil layer has been several metres beneath the surface.
These projects
include Zurich Airport terminal E and Main Tower in Frankfurt.
In this article the recovery of ground heat in
underpinning projects is studied.
The focus is on load
transfer structures transferring the load from old to new foundations,
the through holes of ground heat collector piping and their technical
implementation in these load transfer structures.
This study is part
of FIN-C2M project. FINC2M project is part of Case 2 Micropile Research Project
in International Society for Micropiles collaboration.
Current technology
and research results make the use of energy piles possible in certain cases.
There are altough limitations and possibilities related to energy piles that
need to be taken into account when estimating the energy production investments
and life cycle of buildings. Two such limitations are
mean distance
between the piles and the length of piles. This is vital for ensuring the ground
thermal balance. If the underpinning project will be carried out in any
case, it might be reasonable to consider energy piles. Also hybrid energy
micropiles are one possibility as well. Any piles large enough for the
ground heat collector piping are suitable as energy piles.
These include steel pipe piles and concrete piles
with holes. Of
these two only steel pipe piles have been used in underpinning projects in
Finland.
ENERGY PILES AND LOAD TRANSFER STRUCTURES
One of the
challenges using energy piles in underpinning projects is the load transfer
structures, specifically the through holes for ground heat collector pipes. In
the FIN-C2M project this is studied on the basis of load transfer cases by
examining which types of load transfer structures are suitable for energy piles.
There are
thirteen recognized load transfer cases and
according to the studies nine of these are suitable for use with energy piles.
[...]
INSTALLATION OF GROUND HEAT COLLECTOR PIPES INTO
PILE
When the heat
collector pipes are fed into the energy pile, the procedure and techniques is a
combination of installing pipes into heat wells and installing piles. In
regarding the filling material, in Finland piles are typically filled with concrete.
The use of concrete is supported by its good thermal conductivity and
the way it bonds with steel pile to form a load-bearing composite structure.
The selection of
filling material has a great significance in the long run as the increased
thermal conductivity affects the energy gain positively throughout its life
cycle. Then why is concrete not used always although it has better thermal conductivity
than water? Water filling has its own advantages as the pipes can
be replaced more
easily if they break or reach the end of their life cycle.
As pipe
installations performed alongside underpinning projects are usually done in
cramped basements, the chance of breaking the pipes is much higher when
compared with the usual piping of heat wells outside the actual building.
Pipes can also break
due to other causes than weakening by age. During transportation, moving at the
construction site, storage or installation, precision is important as plastic
pipes scratch easily and are then unusable.
Nowdays constructions are generally designed with
100-200 year service life and the heat collectior pipes may well need
replacement during that period.
CONCLUSIONS
As a result of this research
it was found possible to find technical solutions to combine energy micropiles
and groud heat collector pipes with nine load transfer structure cases. In five
cases the work can be done as in new building.
There is also a
special solution if steel beams have to used. In four cases the pipes have to
be led out trough the side of the pile before the pile cap or alternatively to
use special jack system. The system allows installing collector pipes right after piling
phase and jacking after piping without breaking the pipes.
There are certain
challenges and questions, especially concerning the installing process, that
have to be researched and tested. The energy micropiles are one solution to
produce heat from the ground and furthermore one way to reduce the greenhouse
gas emissions in energy production.
