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All about Ground Source Heat
Pumps
Guy Cashmore, Technical Director
www.kensaheatpumps.com
Overview
Kensa – a brief history!
What is a ground source heat pump and how
do they work?
Anatomy of a Kensa ground source heat pump
Sizing and typical application configuration
Electrical / hydraulic connections
A word about controls
Domestic hot water
Slinky ground collectors
www.kensaheatpumps.com
What is a heat pump?
Highly energy efficient space and water
heating solution
Electrically driven appliance
Moves solar energy from the ground into
the property
Utilises “collector” pipework buried in the
ground
Typically one unit of electricity produces
between 3 and 4 units of heat Borehole
Heat Pump
Hot water cylinder
Radiator system
4
Heat Pump Cycle
www.kensaheatpumps.com
Heat Pump Efficiency
o Heat Pump efficiency is called the Coefficient of Performance (CoP)
o Ratio between electrical energy used and heat delivered
o E.g. 1kWh electrical energy to produce 3-4kWh heat = CoP 3.0 to 4.0
o Or 300 – 400% efficient
www.kensaheatpumps.com
Heat Pump Efficiency
Real-life efficiency is expressed as a SPF (Seasonal Performance Factor) which is a very
complex calculation and is influenced by numerous factors quite distinct from the heat
pump performance.
Kensa’s heat pumps use Copeland scroll compressors, the most advanced available,
and capable of providing the best available performance.
Branding of the heat pump is not the critical factor in determining performance.
Factors linked to the property and the site are far more influential.
Ability to highlight the impact of some of these factors is helpful in gaining credibility
with the client.
6
6
www.kensaheatpumps.com
Anatomy of a Kensa GSHP
7
Compressor
Evaporator H/X
Condenser H/X
Ground Array Water Pump
Heat Distribution Water Pump
Pressure Gauges
Controller
www.kensaheatpumps.com
Specification of Heat Pump
All Kensa units come complete with:
Ground and load side circulation pumps within the
appliance cabinet to simplify installation and
reduce costs.
Advanced control system to permit remote
diagnostics to eliminate the need for unnecessary
maintenance visits.
‘Smart starts’ to spread the starting electrical current
Compact design to allow installation into small
spaces with pipe connections under the unit
8
8
Ground Source Heat Pumps –
The Kensa Approach
www.kensaheatpumps.com Microgeneration Certification
Scheme (MCS)
To access the RHI, installers (and equipment) need to be accredited under MCS
About MCS:
Government backed, industry-led scheme
Aims to promote best practice and provide consumer protection
Certifies installation companies to ensure the microgeneration products have been installed and
commissioned to the highest standard, based on a set of installer standards
www.kensaheatpumps.com Microgeneration Certification
Scheme (MCS)
MCS aims and aspirations are - FULLY SUPPORTED BY KENSA
Important for our industry because:
Ensures all heat pump installations are well designed and
installed
Ensures those selling and installing heat pumps are properly
trained and “competent”
Provides specific design practice on sizing of heat pumps and
use of back up heating
Clear guidance for installers on ground collector sizing
Clear guidance on sizing of heat emitters (rads and UFH)
www.kensaheatpumps.com
12
GSHP Sizing:
GSHP Performance - Output
0
5
10
15
20
25
30
35
B0/W35 B0/W40 B0/W45 B0/W50 B0/W55
He
at
Pu
mp
Th
erm
al O
utp
ut
(kW
)
Kensa Compact Range - Actual
Thermal Outputs
C060-S1H C100-S1H C100-S1H C120-S1H
C160-T1H C200-T1H C240-T1H C300-T3H
Flow temperature has an impact on
thermal output (kW)!
Sizing needs to be considered
accordingly with heat loss
MIS3005
Kensa “Actual Output” sheets
provide all required data
www.kensaheatpumps.com
13
GSHP Sizing:
GSHP Performance - Output
0
5
10
15
20
25
30
35
0 2 4 6 8 10
Kensa 21kW Hybrid - Output vs Inlet
Temperature
W35 W45 W55
Source temperature also has an impact on thermal output (kW)
However, ground “source” temperature remains reasonable stable throughout the year
MCS requires return from ground to be >0ºC
Sizing needs to be considered accordingly with heat loss
MIS3005
Kensa “Actual Output” sheets provide all required data
www.kensaheatpumps.com
ASHP Performance - Output
Ground source heat pumps not
impacted as significantly by source
temperature as an air source heat pump
Temperature stability of the heat “source”
affects:
Heat pump output (kW)
Heat pump efficiency
A larger (more expensive!) ASHP would
be needed in this situation
This is where ground source heat pumps
have a significant benefit!
0
2
4
6
8
10
12
14
16
-7C -2C 2C 7C
Heat Pump Outputs
Ground source heat pump output (kW)
Air source heat pump output (kW)
For a 12kW heat demand, this “12kW” ASHP would be too
small!
www.kensaheatpumps.com
15
GSHP Performance - Efficiency
Flow temperature also has a BIG
impact on efficiency (CoP/SPF)…
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
B0/W35 B0/W40 B0/W45 B0/W50 B0/W55
Ax
is T
itle
Kensa Compact Range - CoP vs
Flow Temperature
C060-S1H C080-S1H C100-S1H C120-S1H
C160-T1H C200-T1H C240-T1H C300-T3H
www.kensaheatpumps.com
Heat Emitters
Heat pumps can provide both space heating and domestic hot water
35-55ºC water temperature
Radiators
Higher flow temperatures required
Compromises heat pump efficiency
Require larger surface area than for conventional boilers
Therefore radiators have to be increased in size
RHI reflects lower efficiency in deeming calculation
www.kensaheatpumps.com
Underfloor Heating
Heat pumps can provide both space heating and domestic hot water
35-55ºC water temperature
Underfloor heating
Underfloor heating is traditionally considered to compliment heat pumps well
Lower temperatures required
Larger surface area, typically 35 – 40ºC
Helps heat pump run more efficiently
Screed can act as thermal store
Pipe spacing important!
Floor covering important!
www.kensaheatpumps.com
Heating System Star Rating
Flow temperature has a direct impact on
heat pump efficiency
Also used as a proxy for calculation of
“Renewable Heat” content under RHI
Heat Emitter Guide
Higher efficiency of GSHP at a given flow
temperature recognised
www.kensaheatpumps.com
Domestic Hot Water
Heat pumps can provide both space heating and domestic hot water
35-55ºC water temperature
Domestic Hot Water
Important to use correctly sized cylinder
Heat pump will run at lower CoP
Immersion boost required to achieve storage temperatures over 50ºC
“High temperature” heat pumps now becoming available
www.kensaheatpumps.com
Kensa Compact Hybrid GSHP
Kensa’s newest innovation!
• Twin compressor gshp
• 15 & 21kW, single phase
• 55°C flow temperature in space heating mode, at full
output
• 65°C flow temperature in DHW mode on single
compressor
• Diverter valve for heating and DHW modes
• Integral ground pump
• Integral heating system pump
• Typical CoP (B0/W35): 4.2
www.kensaheatpumps.com
Domestic Hot Water
Range of unvented stainless steel cylinders
available from Kensa
150 – 305 litres
Oversized coils
Twin coil options for solar thermal integration
Flow rate and pressure drop important
Kensa “self commissioning” hot water
temperature control
System Schematic
o Hydraulic schematic is similar to a system boiler
o Familiar to heating installers
o Heat Pump has 2 heating temperature set points
o Space Heating
o Hot Water
o Hot water priority
o 3 port valve switches flow between heating and DHW
o Standard thermostat/programmers
control operation of heating system
www.kensaheatpumps.com
Controls
Heating system controllers
Up to the installer to choose!
Space heating – thermostat and time
clock or programmer
DHW – time clock
Heat Pump Controller
Weather compensation
Heating circuit return temperature
Fault reporting
Heat Sources
Horizontal ground loops
Collector pipework laid horizontally
Requires large land area
Cost effective
Slinkies
Pre coiled pipework laid in trenches
Requires large land area, but less digging
Cost effective
Vertical boreholes
Closed loop pipework inserted into vertical hole
Typically 100-150m deep
Most common in commercial buildings
Space efficient
Surface water (closed loop)
o Ideal solution where surface water (eg lake) is
available
o Extremely efficient and cost effective
Open loop
Extracts ground water from an underground aquifer
Efficient
Costly
o Ground provides a highly
efficient source of heat
o Unaffected by air
temperature
o Recharged by solar energy
and rainfall
o Ground type (thermal
conductivity) needs to be
factored into sizing
calculations
o Important not to over
extract – sizing important
www.kensaheatpumps.com
Slinkies
Myths:
You need less land area – FALSE
You need less pipe – FALSE
They are less efficient – FALSE
They are more likely to freeze the ground than straight pipe – FALSE
Facts:
You need the same land area as a straight pipe collector
There require only a fifth of the digging of a straight pipe collector
Quicker, easier and more cost-effective to install
Slinkies Horizontal Slinky Trenches
• Horizontally installed slinkies should be placed in a 1.2m wide by 1.2m deep trench.
Vertical Slinky Trenches
• Vertically installed slinkies should be placed in a 300-400mm wide by 2m deep trench.
Separation Distances
• Each trench should be separated by a minimum of 5m between centres
Energy Absorption
• For every 10m of slinky 1kW of energy can be absorbed from the ground.
Trench Layout
• Trenches do not have to be straight, they can twist and turn as long as the 5m separation distance is maintained.
www.kensaheatpumps.com
Ground arrays - Boreholes
Twin probe
borehole
ready for TRT: 27
www.kensaheatpumps.com
28
Borehole Sizing
Insufficient ground for slinkies.
Drilling – Specialist area
Need site survey
25metres borehole depth = 1kW
Probe and grouting from Driller
£40/45 L/m Budget pricing
Domestic applications - Costly
Thermal response testing
6m separation
60-100m deep
www.kensaheatpumps.com
Application
• Buildings should be:
– Well insulated
– Old buildings with solid walls can be a problem – High U values & heat loss
• Heat pumps are designed to be energy efficient
– Energy wastage needs to be reduced by insulation
– Best suited to new / well insulated buildings
• Existing buildings
– Ensure energy efficiency is considered first!
– Insulation, double glazing, etc
www.kensaheatpumps.com
Heat Loss Calculation
An accurate heat loss calculation must be
performed to determine the required heating
capacity of the properties heating system
An inaccurate assessment of the heat loss can
mean the system selected cannot meet the
requirements
Avoiding under sizing of the heat pump and the use
of supplementary back up heating is important to
improve overall efficiency and keep running costs
low
www.kensaheatpumps.com
Heat Pump Sizing
The heat pump selected must be capable of
meeting the properties heat loss at the intended
design temperature and design flow temperature
conditions.
This is known as the "100% sizing rule".
www.kensaheatpumps.com
Ground Collector Sizing
The ground collector must be suitably sized to
match:
The heat thermal requirements of the heat pump
at the intended water flow temperature
The thermal conductivity of the ground
Too little pipe will lead to ground freezing and
efficiency problems
www.kensaheatpumps.com
Electrical Connections
www.kensaheatpumps.com
Sounds confusing?
Don’t worry – it doesn’t need to be!
Kensa is here to help….
www.kensaheatpumps.com
Questions?