TPi October 2010

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October 2010 Tube Products International 55
pipesPVC, PE & XLPE
An advanced ground source heat pump
system that harnesses free energy from
boreholes sunk beneath a rugby pitch is
providing low cost, low carbon energy
to heat and cool Wyke College, in
Hull, England. The green initiative is
part of a £20mn development at the
college, culminating in the construction
of a state-of-the-art new wing, the Oak
Building.
The pioneering ground source heat
pump system uses 50 boreholes, each
112m deep, sunk into the college’s
playing fields. It provides all-year-round
indoor comfort conditions for students
using the new college facilities, which
include a library, theatre, sports hall,
recording studio and lecture rooms.
A low carbon strategy for the building
was developed by consultant Beverley
Clifton Morris, using detailed Dynamic
Simulation option appraisals. The
solution selected has ground source
heat pumps at the heart of the building’s
services. The heat pump system was
designed and installed by Ecovision
Systems Ltd, working with Neville
Tucker Heating Ltd. More than 1km of
HDPE ground pipe work required for the
project was supplied by Pipe Center.
The main contractor was Hobson and
Porter.
The project had to take into account
the unique thermal conductivity and
properties of the rock and soil at the site.
From this came the design specification
for the heat pump system, which
determined the number and depth of
boreholes required. Most of the energy
needed to heat and cool the building
will be provided by the boreholes and
heat pump system – even in the depths
of the harshest winter and the hottest
summer.
Some 75% of total energy required
comes from the ground, with the
remaining 25% being contributed by
electricity used to drive the four Glen
Dimplex heat pumps. The 50 boreholes,
each spaced 10m apart, are arranged in
an array about the size of a rugby pitch,
and took between one and two days
Harnessing ground energy
from boreholes to cool
and heat
Drilling the boreholes:
the project used 1km of
HDPE pipe in 50 boreholes
Wyke College has installed a ground source
heat pump system
each to drill. Each borehole has a 40mm
diameter HDPE input and return pipe,
joined with a fusion-bonded u-bend
connecting flow and return at the base.
The head of each borehole is linked
to its neighbour by 75mm HDPE pipe
set into a sub-surface trench. Finally,
flow and return for the entire array to
the plant room is laid in larger 180mm
HDPE pipe.
The boreholes are used in three ways:
to supply energy for upgrading by the
heat pumps for heating the building; to
provide ‘free cooling’ via an under-floor
system, with heat from the building
being transferred back into the ground
during summer; and as an energy
source to drive reversible heat pumps to
provide refrigerant-based cooling via air
handling units. The normal temperature
of the ground 100m beneath the surface
is a steady 10ºC throughout the year. As
a result of the boreholes and operation
of the heat transfer system, this can fall
to as low as -1ºC in winter. In summer,
energy is returned to the ground as the
free cooling potential is tapped, with
temperatures below ground rising at the
end of the season to as high as 20ºC.
The ground pipe work is designed as a
closed-loop system. It contains 5,000
litres of glycol solution, which is passed
through a brazed plate heat exchanger
to extract and receive energy from the
building. A 3kW pump on each heat
pump keeps the loop circulating. The
entire heating and cooling system is
under the control of a sophisticated
building management system (BMS)
that constantly monitors and ensures
optimum use of energy sources at all
times.
Ecovision’s technical manager, Mark
Witzenberger, who designed the system,
said: “It is a superb installation and a
great example of what can be achieved.
The savings over the lifetime of the
building will be substantial. With the
cost of energy rising all the time, the
investment will pay for itself many times
over.” He added, “People are waking up
to the fact that natural energy sources
can be harnessed to provide much of
the needs of our buildings. Heat pumps
have been around for some time, but
their full potential is only now being
realised. All it takes is a little imagination
and a willingness to invest, and projects
can pay for themselves quickly – with
savings accruing over the lifetime of the
building. We believe it is the future for
heating and cooling buildings.”
Pipe Center – UK
Ecovision – UK