ZEMCH 2019 International Conference Proceedings April.2020 | Page 288
Figure 2, (L) 400m U-tube used in 2017 simulation. 2(C) Ground Temperature vs depth 2(R) Proposed 200m Heat pipe.
Economics.
However, it is now determined that drilling may cost about AUD150 per meter and the 400m
VGHE would cost AUD60,000 as compared to a ground source heat pump of about AUD5,000.
Figure 2(R) shows a proposed heat pipe that is only half as deep as the 400m VGHE. The bottom 6
meter of this 200m‐deep 100mm diameter HDPE tube is a closed‐end metallic pipe, where the
temperature is expected to be a stable 23°C. The top 15m of the HDPE is insulated so that the water
heated at the bottom could still be 21‐22°C when it rises naturally to the surface. The power extracted
from the ground for the hydronic radiator is expected to be above 1 KW, thus sufficient for a small
house. The drilling cost would thus be halved but is still more expensive than other renewable sources
e.g. solar or biomass as reviewed below.
2.2a. Hot water for RC by solar radiation?
Ooi et al [12] showed by simulations that with by 30 evacuated tubes, the temperature of water in
a two cubic meter indoor tank heated to 50°C by the end of summer, and circulated to a wall‐ HR would
not be colder than 20°C during winter, and could maintain a daytime indoor temperature of 20°C.
However, based on the May 2019 experimental results with the floor‐HR, it appears that this 20°C
indoor temperature may not be achievable.
This doubt is supported by Figure 3 which shows that in the winter months of April to September
the Global Horizontal Solar Radiation drops to below half of the 6KWh/m2 available in summer. The
blue line shows that during winter, the sky is 70% covered. This low availability of solar radiation in
winter is verified by a 5‐year data obtained with a 1.5 KW photovoltaic connected to the grid; the net
electricity bill in summer is nearly zero, but practically unchanged in winter.
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ZEMCH 2019 International Conference l Seoul, Korea