all about ground source heat pumps · all about ground source heat pumps guy cashmore, ... w35 w45...

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


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


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


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


Anatomy of a Kensa GSHP

7

Compressor

Evaporator H/X

Condenser H/X

Ground Array Water Pump

Heat Distribution Water Pump

Pressure Gauges

Controller


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)


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


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


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!


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


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


Underfloor Heating



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!


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


Domestic Hot Water



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


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


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


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


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.


Ground arrays - Boreholes

Twin probe

borehole

ready for TRT: 27


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


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


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


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".


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


Electrical Connections


Sounds confusing?

Don’t worry – it doesn’t need to be!

Kensa is here to help….


Questions?

all about ground source heat pumps · all about ground source heat pumps guy cashmore, ... w35 w45...

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