FOUNDATION HEAT EXCHANGER RESEARCH · “FOUNDATION HEAT EXCHANGER DESIGN TOOL DEVELOPMENT AND...
Transcript of FOUNDATION HEAT EXCHANGER RESEARCH · “FOUNDATION HEAT EXCHANGER DESIGN TOOL DEVELOPMENT AND...
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FOUNDATION HEAT
EXCHANGER RESEARCH
Institute of Energy and Sustainable Development
Simon Rees, Denis FanGSHPA Research Seminar
21 January 2010
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What is a Foundation Heat
Exchanger?
• A novel horizontal closed loop heat exchanger for residential buildings
• Minimises cost by making the most use of foundation/basement excavations and service trenches
• Horizontal loops are fixed to the outside of the excavations before they are backfilled.
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FIRST PHASE FHX DEVELOPMENT
• Trials were successful but questions remain:
– Long term performance?
– Sensitivity to building form and occupancy patterns?
– Feasibility in other climates?
– Design and simulation methods need to be development
• Early trials in Tennessee monitored
by Oak Ridge National lab
• Trial designs were dictated by site
conditions and building form – no
design tools were available and no
optimisation was possible
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THE CURRENT PROJECT“FOUNDATION HEAT EXCHANGER DESIGN TOOL
DEVELOPMENT AND VALIDATION”
• US Department of Energy funded project in partnership with Oklahoma State University and Oak Ridge National Lab
• The novel heat exchanger has been installed in two experimental low energy houses in Tennessee
• Oklahoma State University is working on design tool development
• DMU is working on implementation of a numerical model in the building simulation tool EnergyPlus
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EXPERIMENTAL HOUSING
• Two Low Energy houses have been
instrumented in Oak Ridge
Tennessee – SIPS and advanced
framed construction
• FHX is installed around two sides of
the basements and in the service
trenches
• Soil thermal conductivity and
undisturbed temperatures have been
measured
• Wall heat fluxes and system, wall and
soil temperatures are being collected
over a 2 year period for model
validation
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FHX INSTRUMENTATION
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DESIGN TOOL DEVELOPMENT
• OSU are studying two
approaches to design tool
development:
– Superposition of responses
calculated using an analytical
“line-source” solutions
– A course-grid 2D finite
difference model
Mirror line sources
Here, ground surface is approximated as isothermal (mirror source has opposite sign; building wall is approximated as adiabatic surface (mirror source has same sign.)
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NUMERICAL MODEL
DEVELOPMENT• A detailed FHX model is being developed using
the GEMS3D Finite Volume Method code and will
be used to:
– Model the system in the experimental buildings in 3D
– Form a reference for comparison with simpler models
– Incorporate a component model in the building
simulation program EnergyPlus (probably 2D)
• The code has been validated using the IEA Annex
43 BESTEST analytical and inter-model test suite
for ground coupled buildings
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2D OR NOT 2D: THAT IS THE
QUESTION?• A tool has been developed to
generate 2D computational meshes
from basic design parameters. This is
essential for a robust model suitable
for routine building simulation tasks.
• A 2D representation may be good
enough but three-dimensional
effects (e.g. corners) are known to be
significant in predicting slab and
basement heat transfer
• Currently a 3D model is probably too
slow for annual simulation tools
• The limitations of 2D models are
being explored – a 2 ½ D model is
conceivable
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RESEARCH QUESTIONS
• Coupling between the FHX and building zone
models
• Interactions between the FHX and the basement
• System feasibility and scalability:
– Building form
– Fabric design
– Internal heat gains
– More extreme climates
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QUESTIONS
?