Knowledge: Ground Source Heat Pumps
Knowledge: Ground Source Heat Pumps
Cracking the ground source
code: A beginners guide
Guy Cashmore,
Technical
Director, Kensa
Heat Pumps
Everyone has to start
somewhere. As a reader of this
magazine you are clearly an
ambassador for the renewables
industry, but for some
renewable installers ground
source heat pumps (GSHP)
remain an enigma.
With ground source heat pumps
attracting 19.64p/kWh under the Domestic
Renewable Heat Incentive (RHI) (versus
7.63p/kWh for air source and 4.28p/kWh
for biomass), and innovative micro-district
ground source heat networks attracting
the non-domestic RHI in retrofit and new
build schemes, there is a huge financial
carrot for the specification of ground
source heat pumps. Add to this their
carbon credentials, efficiency savings,
and the Committee for Climate Change’s
Fourth Carbon Budget calling for 4 million
heat pumps to be installed at residential
properties by 2030, the market for ground
source can only go one way. But to fulfil
this ambition, installers need to be on
board and share the vision.
Of course, as Kensa is the UKs only
dedicated manufacturer of ground source
heat pumps, and the confirmed largest
supplier in the UK (Source: BSRIA 2017),
we are bound to say that. So the aim of
this article is to demystify and briefly
explain in simple terms the typical process
of installing a ground source heat pump,
to demonstrate that ground source is a
technology that can be easily integrated
into your repertoire to great reward for
your business and customer. Everything
discussed (and more) is covered by
26 | www.renewableenergyinstaller.co.uk
Far left: A Kensa Evo heat pump; Left: Borehole drilling and Above: Completing a slinky trench
MCS, which isn’t a legal requirement for
installations, but is necessary to claim
Renewable Heat Incentive (RHI) payments.
Know the Load
Arguably the first part of planning
an installation is the most important -
calculating the heat load. Get this part
wrong and everything that follows
will be wrong. You can’t design a GSHP
system without knowing two vital bits of
information, the peak heating load in kW
and the annual heating load in kWh.
If the building is being upgraded in terms
of insulation at the same time, it is perfectly
fine to factor this upgrade work into the
heat loss calculations, but it is equally
important to ensure that the planned work
actually gets done before the heating
system is used in anger!
Typically an installer will either do this
heat loss calculation work himself, or
subcontract it out to a qualified specialist. If
the heat pump is also supplying domestic
hot water then this load also needs to be
calculated and added to the numbers.
Room by room
While the heat pump itself will most likely
be a single unit with a stated kW output,
each room in the building is going to have
a different heat demand, so needs its heat
emitter (the term emitter covers radiators,
under floor heating and other less
common types) individually calculating to
meet that heat demand.
When using a heat pump instead of
a boiler, the rule is always to size the
emitter so that it is capable of heating
the room using the lowest possible water
temperature as this maximises energy
efficiency. Practical limits for radiator
sizes usually mean getting below 45°C
flow temperature is rare, but UFH can
sometimes work as low as 30°C. The usual
practice is work out which room needs the
highest water temperature due to practical
limits and then size all the other emitters to
the same temperature.
In the ground
Once the peak heating load and heating
flow temperatures are known, then a
suitable heat pump model can be selected.
By referencing the manufacturer’s data,
the efficiency (also called CoP) of that heat
pump at the heating water tempera