writer has come to the conclusion that the UK story follows
the classic British pattern viz: in at the beginning, good
theoretical contributions, limited practical deployment by
obsessed individuals with no follow through to widespread
commercial success! We are now fervently trying to address
the last of these, at least in the area of ground-coupled heat
pumps for delivering heating and cooling to buildings.
Clutching at straws, Sumner (1976) notes that the
first mention of a heat multiplier (or heat pump) is
associated with William Thompson (later Lord Kelvin).... As
one of the worlds first conservationists, he therefore outlined
and designed a machine which he called a Heat Multiplier.
This machine would permit a room to be heated to a higher
temperature than the ambient temperature, by using less fuel
in the machine than if such fuel was burned directly in a
furnace. Suffice to say that in a fossil fuel rich Britain, there
was little interest in such a device at the time (i.e., 1852).
Sumner reports that the only interest that was shown was for
the possible cooling of public buildings and British residences
in India. The notion of heat pumps for heating and cooling
buildings was born.
Some readers will know that Cornwall has been
prominent in UK geothermal activity over recent decades
through its Hot Dry Rock programme. It is opportune to offer
a historical plug for the region. Earlier this year, a full-scale
replica of the first steam-powered vehicle, built by the
Cornish engineer Trevithick, ran up Cambrone Hill200
years after its first run. I mention this because the current
interest in Trevithicks prodigious technical innovation
reveals that his thinking ranged right across the steam cycle
and into the refrigeration air cycle (Burton, 2001). Next week
(Oct. 2001), there will be an international conference in
Cornwall discussing the steam and air cycles. While the self-
taught Trevithick was trying to find a cheaper method of
producing ice, the search for replacement refrigerants for heat
pumps is of immediate concern to our technology. There is
active research on the topic in British universitiesunrelated
to ground-source heat pumps per sebut related to heat pump
refrigerants in general (e.g., Butler, 2001).
Moving forward in time, the following is an extract
from a 1981 publication:
Taking heat from the ground by digging a
hole of twice the area of the house and
burying a pipe in it works well, and is
widely used in Germany, Scandinavia and
other places that have very low winter air
GHC BULLETIN, DECEMBER 2001
temperatures. This has been tried in
Britain. It is not significantly more
efficient than an air-source installation
and if you feel like digging a hole that is
twice the size of your house, this may be of
interest. If not, read on....
...none of this is criticism of those who put
forward these proposals, whether in the
media or in experimental housing. They do
an important job, but in this book, we are
concerned with proven pump technology
that is commercially available now, it is
essential to differentiate between the two
approaches......!! (Armor, 1981).
Let us hope that we are now in a position to avoid
digging quite such large holes and that we can now offer
the technology on a commercial basis, or we will not have
moved forward significantly from this somewhat cynical view
of ground-coupled technology.
This was the view of the technology at the time,
despite information printed in a small booklet (Sumner, 1976)
produced by the same publisher in 1976, concerning a closed-
loop ground-source heat pump installed and used by the
earliest known UK champion of the technology John Sumner.
This was installed in 1960 using a horizontal copper coil in
the garden of a small bungalow and ran continuously and
successfully thereafter. A trade journalist recently revealed
that he had the privilege to meeting John Sumner, but that his
house was one of the coldest heat had ever been in? This
probably says more about the appalling low level of insulation
in British houses built in the 50s and 60s, than anything to do
with the ground-coupled heat pump.
Sunmer, a vigorous proponent of heat pump technol-
ogy for buildings, clearly demonstrated the benefits of using
the ground as the ambient energy source in UK climatic con-
ditions. His booklet also hints at research work carried out
30 years ago on ground coils by a Miss Griffiths (Griffiths,
1946). The author has yet to obtain a copy of this paper.
A comprehensive book on Heat Pumps in
Buildings (Sharrat, 1984), which was based on a significant
UK conference on the subject in 1983, has only passing
references to the use of the ground and groundwater as the
energy sources.
In 1995, the writer reported on the evidence found
to-date at that time of ground-coupled heat pumps in the UK
(Curtis, 1995). Apparently in 1948, Sumner had been
commissioned by the philanthropist Lord Nuffield to install
3-kWe ground-source heat pumps in 12 houses. Even in
those days, a seasonal performance factor (SPF) of 3 was
reported.
23 Since 1995, in the light of current interest and
activity in the UK, evidence of a limited number of one off,
open and closed-loop ground-source applications have been
brought to the writers attention. In some cases, the systems
are no longer in use for a variety of reasons. In others, they
have only come to light because, after many years of faultless
operation, a minor problem has forced owners to make
contact. As an example, a Scandinavian resident who had
imported a complete horizontal loop system from Sweden,
had to make a service call for the first time in seven years of
operation. The reason for the fault eventually proved to be
that his plumber, knowing nothing about heat pumps, had
unwittingly released all the refrigerant through attempting to
replenish the ground- loop brine circuit using the wrong set
of valves!
It is thought that in the period 1970 - 1994, perhaps
a dozen or so other horizontal closed-loop systems were
installedall domestic. A number are believed to be in the
south coast area due to the presence of an installer importing
Swedish heat pumps.
It should be mentioned that there is considerable
technical potential for open-loop heat pump systems in the
UK (Day and Kitching, 1981). This arises because accessible
groundwater is present under a very large proportion of the
UK landmass. The barriers are primarily the necessity for
licensing, well testing and proof of resource prior to being
able to confirm availability to any potential user. Again, in
the period 1970 - 1994, there is evidence of a handful of
installations, from small domestic, to larger commercial
build-ings, using open-loop heat pumps. Difficulties with
reinjection and heat exchanger corrosion problems afflict a
number of these. Nonetheless, it is likely that more of these
systems will be installedbut probably in connection with
fairly high profile, high cooling-demand projects, or those
where the groundwater resource has already been proven and
licensed.
UK BACKGROUND AND IMPLICATIONS FOR
GROUND COUPLING
For any country or region involved in the
deployment of ground-coupled heat pumps, several natural
and man-made factors play significant roles in the rate of
adoption of the technology.
Climate
The UK (currently) has a moderate climate,
considerably influenced by the warming effect of the Gulf
Stream. This has positive and negative effectsextremes of
temperature rarely arise; but as a result, we have traditionally
constructed buildings with poor levels of insulation compared
to countries with severe winters.
Geology
A minor nightmare for ground-coupled installers in
the UK, is the extensive range of geology that exists within
such a small regional area. Almost all known geological
sequences exist within the UK. We can be drilling with air
hammers in granite in Cornwall, contending with pure
sandstone in areas of the midlands, and have to case and
operate with drilling mud for running sands in areas of the
southeast. This means that there can be a significant range of
24
drilling and trenching costs across the UK, as well as a wide
range of thermal conductivities and hence, variations in the
required sizes of closed-loop systems to meet given thermal
demands. On the positive , side, a very large proportion of
the UK landmass (probably >75%) has a shallow water table,
most of our boreholes will be in wet or at least damp
conditions. For larger commercial installations, it has already
become established practice to carry out thermal conductivity
testing. As well as obtaining data for sizing, the exercise
confirms the anticipated geology, the appropriate drilling
method, and the quantity of water that might be encountered.
Building and Level of Insulation
Because of the mild climate, and an abundance of
fossil fuel (i.e., coal initially, oil and gas subsequently), a
large proportion of the UK housing stock was built with what
many other northern European countries would regard as
appallingly low levels of thermal insulation. In recent
decades, the building regulations have been slowly tightened
to improve this situation; but, housing stock turnover is slow
and it will take many years to rectify this situation. On the
other hand, the UK climate is generally (some would sa