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Combating Legionella In Renewable Hot Water (Solar Thermal & Heat Pumps) Seminar Sept 2010 MCS

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Abstract and Figures

Legionella risk assessment for solar thermal water heating systems and heat pump domestic hot water storage tanks discussed in relation to compliance with UK standards. Concludes that safety compromises regarding legionnaire’s disease are being made for renewable energy, compromises that might be unacceptable in other fuel contexts.
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Renewable Heat, Legionella and Hot Water:
Heat Pumps and Solar Water Heating
15 September 2010 presentation, H&V seminar: “Combating Legionella”
By Barry Johnston, Managing Director, Solar Twin Ltd, UK.
Solar PV and solar thermal suppliers / innovators for over a decade.
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Thermodynamic realities:
it saves energy (green or otherwise)
to cut water storage temperatures.
You lose 25% less energy when, domestic hot water is stored at 50C
(instead of 60C), assuming the air is at 20C.
This energy saving happens whether that energy is solar or not.
Similarly, heating a cylinder to 60C once a day, instead of keeping it hot
24 hrs a day cuts storage energy losses by 25-50%.
Installing a solar water heating system saves about as much energy as this
change to 24h heating to evening-only heating.
Solartwin.com innovation in action
zero carbon solar water heating
Moving from 24h heating to evening-only heating.
Polysun simulation, 120 litre cylinder: no solar.
Annual results
24/24 1/24
This saves 37% of energy = 1762 kWh.
(Adding solar water heating saves 600-2000 kWh.)
Solartwin.com innovation in action
zero carbon solar water heating
This green benefit happens - whether the conventional
energy is saved - or replaced by green energy.
So a renewables-only exemption from L8 is not logical.
The foot-in-the-door: is there reason for a wider
energy efficiency exemption?
Solartwin.com innovation in action
zero carbon solar water heating
Introducing Heat Pumps (HP) and
Solar Water Heating (SWH).
Techn
ology
Is is
really
solar?
Under-
floor /
central
heating?
Water
heating?
Energy in-
out ratio?
(COP)
Variants
Typical
energy
storage
media
Performance
limitations
HP
yes
yes
yes
1:6
to1:1.5
Air or
Ground
source
Building
fabric /
water
Best where no
gas grid. Low
COP over 50C.
SWH
yes
usually
no
yes
20 x to
infinite
Mains or
PV
pumped
Water
30-70% solar
fraction only.
Solartwin.com innovation in action
zero carbon solar water heating
Seasonal solarthermal performance
Source: side by side testing of eight solar water heating systems
DTI publication no: URN 01/1292. Research by The Energy Monitoring Company.
Solartwin.com innovation in action
zero carbon solar water heating
6:1 seasonality of solar supply
Source: side by side testing of eight solar water heating systems
DTI publication no: URN 01/1292. Research by The Energy Monitoring Company.
Solartwin.com innovation in action
zero carbon solar water heating
Solarthermal and Heatpumps
examples of hot water applications
Single family installations
Private homes
Social homes
Multi-user installations
Residential: flats, care homes, prisons, hotels
Other: offices, fire stations, public toilets, farm / zoo handwashing
sports: showers and pools, health centres
Solartwin.com innovation in action
zero carbon solar water heating
Three potential plumbing risk areas:
Thermostatic blender valves on stores
(eg avoid upward cold dead legs)
External loop in direct solar systems
(eg avoid organic polymers)
Hot water storage / dedicated pre-heat
(eg heat the full volume daily?)
Solartwin.com innovation in action
zero carbon solar water heating
Today’s focus is
Legionella in
Hot water storage / pre-heat in
HP (scarce data)
SWH (more data)
L8 has the same wording as:
European Guidance
for the prevention and control of
travel associated Legionnaires’ disease
Solartwin.com innovation in action
zero carbon solar water heating
Dedicated solar volume in space
(twin coil solar cylinder)
Does not comply with L8 Guidance Para 158 because:
The UK sun can not ensure heating to 60C every day
And backup heater is not basal
It is part-way up instead.
From:
DEFRA
SAP 2005
(Solar
Appendix)
Most solar
installations
are: Twin coil
cylinders b).
Safety
flagged up
Solartwin.com innovation in action
zero carbon solar water heating
Over 80% of solarthermal
installations in UK are like this.
Vs (- - - - -) is
“dedicated solar volume in space”.
Is it a dedicated Legionella
volume x area x time
= risk as well?
The temperature at
the bottom of a
solar cylinder in
Denmark.
Timespan is a year.
Nearly 3 months
elapse without
reaching 50C.
Source CEN Technical
Committee 312 (Solar
Thermal) 06/06/2007
9.2 months
3x
4x
5x
6x
7x
8x
9x
Approx how much less solar is there is there in December vs June?
Solartwin.com innovation in action
zero carbon solar water heating
Vs = risk =
Larger volume to
inhabit
Larger surface
area to inhabit
More time to
grow.
Solartwin.com innovation in action
zero carbon solar water heating
Regarding solar hot water
storage / pre-heat, Legionella
bacteria need several factors
including nutrients, temperatures
under 50C, plus:
Volumes to inhabit
Surface area to inhabit
Time to grow.
Brief BS 8580 context:
1. Contamination: header tank lids!
2. Amplification:
2.1. typically 100 litres “dedicated solar volume”,
2.2. large surfaces, sometimes also limescale,
2.3. time: not heated to 60C for about 3 months
2.4. (often no shunt / destratifier pumps)
3. Transmission & exposure: aerosols from
showers and spray taps.
4. Host susceptibility: retail age median 50y.
Solartwin.com innovation in action
zero carbon solar water heating
Para 158 in L8
“pack of four”
1. heat to 60C
2. for >1 hour
3. every day
4. to the base of store.
Solartwin.com innovation in action
zero carbon solar water heating
TCC’s and L8 para 158’s “pack of four”
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
CEN Solar TC 312 Legionella paper
seeks exemption: to bypass the precautionary principle
Although positioned against heating to the base of the cylinder
TC 312 “understand the precautionary principle of disease
management”.
But then seek to bypass it, asking for “special consideration of
renewable energy pre-heating on the basis of national and European
policies.”
This bypass is sought on a questionable claim that “approx 50%”
less solar energy would be gained if cylinders were heated to the
base.
A recent paper by the author of this TC 312 paper Chris Laughton
aiming to substantiate this 50% turned out to be flawed
methodology. The real figure is in fact under 11% less energy gain
(but potentially better costs-benefits).
Solartwin.com innovation in action
zero carbon solar water heating
CEN Solar TC 312 Legionella paper
claims heating to the base is unnecessary” because...
TC 312 sees no need for any recommendations for additional heating
of the [dedicated] pre-heated part of a solar water heating system [ie
to the base] to certain minimum temperatures.”
They claim that the “solar pre-heated hot water will anyway pass
through the back-up heated zone with the high temperature and be
sterilised within short time [sic] at the correct temperature.”
The above presumes that the heat is on all the time (ie 24 hrs a day)
It also presumes that the hot water draw off rate never exceeds the
heat addition rate.
To achieve this you might need peak hot water flow limiters to be
physically in place. These are often impractical , for example they would
play havoc with most showers.
Solartwin.com innovation in action
zero carbon solar water heating
CEN Solar TC 312 Position
“special consideration” of solar is requested
if solar really deserves “special consideration”,
then perhaps so does energy efficiency in general?
Solartwin.com innovation in action
zero carbon solar water heating
CEN TC 312’s paper on Legionella (06/06/2007)
can be set aside.
Its “Safe Hot Top” concept is not robust.
(High water flow rates / what happens below it etc).
“50% less solar performance” claim for alternatives is exaggerated.
(More like 10% less. Some alternative designs are in fact cheaper.)
So no imperative to ignore the precautionary principle of safety.
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Europe solar thermal
Solartwin.com innovation in action
zero carbon solar water heating
UK: over 80% outside L8 guidance.
Solartwin.com innovation in action
zero carbon solar water heating
Ubiquitous L8-guidance noncompliant
documents in UK: Building regs.
Building Regs part G (water)
Building Regs part L (energy) refer to
Domestic heating compliance guide
Draft domestic Services compliance guide
SAP (DEFRA originated energy calcs).
Solartwin.com innovation in action
zero carbon solar water heating
More L8 guidance noncompliant docs:
UK, other than building regs.
Microgeneration Certification Scheme (MCS) Solar thermal installer
specification MIS 3001
Energy Saving Trust Solar Guide CE 131 (referred to in part L and MCS)
CIBSE Solar Heating Guide (referred to in part L and MCS)
British Plumbing Education Council Solar Installers Manual.
Energy Saving Trust / Building Research Establishment-drafted “solar best
practice” series documents which said that the larger the dedicated solar
volume the better the practice. (Now abandoned.)
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Are consumers kept informed?
European Standards: A member of CEN solar TC 312 seeks to repeat
a procedurally-based boycott of new ideas in the Legionella debate In
April 2010.
(fat-finger TC 312 member in an email to several other members).
“To my opinion we should not react directly to Johnston’s email, but
stick to our previous position that we do not enter in dialog with
people that bypass their national mirror committee.
“I do not want to be involved in discussions that are not seriously
based on physical and biological arguments, with people that only
want to promote their own system. What do you mean?
“Does anybody know why ESTIF delegated to Johnston the task of
dealing with this sensible issue? Does ESTIF know what could
happen on this sensitive issue if Johnston’s proposal would be
agreed to by CEN/TC164/WG2?”
Solartwin.com innovation in action
zero carbon solar water heating
Are consumers kept informed?
Solar grants / DTI / DECC / Building Research Establishment (BRE)
BRE administered DTI grant approval of tens of thousands of grant
aided installations for twin coil cylinders which are out of compliance
with L8 guidance para 158.
When BRE were the the sole solar installer accreditation body for
Low Carbon Buildings solar grants:
We requested the “pack of four” ie heating to the base of a hot
water cylinder to be allowed for grants but BRE refused to
contract to accredit Solar Twin Ltd as a Microgeneration Scheme
solar thermal installer when we requested performance
assessment to be made in the context of safety, including
Legionella.
Solartwin.com innovation in action
zero carbon solar water heating
Are consumers kept informed?
Solar Trade Association, February 2007 warns (and threatens):
“The legionella issue is best left alone (for all members) as any
mention of legionella and solar brings customer concerns out that
are unjustified.
“...any mention of legionella will reduce total sales.
“Any mention of potentially negative perceptions that are
unjustified such as electrical safety or legionella that is just not
happening and I will take action.”
Solartwin.com innovation in action
zero carbon solar water heating
Are consumers being kept well informed
of the extent of the Legionella debate?
By subsidy / grant awarding bodies? - No.
By the Solar Trade Association? - No.
By the Consumer’s Association? - No.
(Which’s Magazine’s Solarthermal and Legionella article
was pulled from publication in Spring 2009, apparently
following industry pressure.)
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Small European Study
Found Legionella 6 x more common in solar homes.
A Danish study found 50% of solar homes had Legionella.
Non-solar homes had six times less, at 8%.
Only 24 homes were studied, so a relatively small study.
Ref: Undersøgelse af legionella i solvarmebeholdere og i traditionelle beholdere. Civ.ing. Klaus Ellehauge,
SolEnergiCentret, Energidivisionen. Civ.ing. Ph.D. Lene Bagh, Miljødivisionen. 1. udgave, 1. oplag 2001. Tryk og
indbinding: Teknologisk Institut. Miljø- og Energiministeriet, Energistyrelsen. Amaliegade 44, 1256 København K,
Danmark. J.nr.: 51181/00-0040. ISBN: 87-7756-650-5.
Like UK, Denmark is a Northern European state.
Other sampling studies have reported no increase with solar.
Solartwin.com innovation in action
zero carbon solar water heating
http://www.q-net.net.au/~legion/
Legionnaires_Disease_England_Wales_1996.htm
"Outbreak III The first outbreak of legionnaires’ disease
ever associated with the Caribbean island of Antigua
was detected in October 1996.
Two cases occurred in September and one in October
1996. All had stayed at a hotel complex in Mamora
Bay. The PHLS and the Caribbean Epidemiology
Centre (CAREC) were invited by the Ministry of Health
of Antigua and Barbuda to carry out environmental and
epidemiological investigations into the source and
extent of the outbreak.
The hotel’s sickness records showed that the incidence
of respiratory illness was higher than expected among
staff in August and among guests in September,
suggesting that the outbreak had been triggered by a
single event.
This event was found to be the installation in
August of a solar powered hot water system
at the hotel.
Thirty-one out of 54 hot and cold water samples
from the hotel’s water systems were positive for
legionella and 19 of these contained L.
pneumophila sg 1....
....A serological survey of 11 of the 35 hotel staff
who reported a respiratory illness between
August and November revealed two people who
were retrospectively diagnosed as presumptive
cases of legionnaires’ disease with single high
titres of antibody against legionella....
...Several national and international tour
operators stopped sending guests to the hotel
when the outbreak was identified in November
and did not return to the hotel until December
when all investigations and control measures
were completed."
Legionella apparently linked to solarthermal outside Europe
Solartwin.com innovation in action
zero carbon solar water heating
Simple risk index
Relative risk example
calcs:
Hard water: 250 ppm
CaCO3
Simple risk index:
Vol x Area x time
Try your own figures or
methodology.
Notes:
Wetted area (sq m)
not reliably heated to 50C daily.
Vol ume not reliably heated to
50C every day. (litres)
Usual max
time between
100% water
volume
replacement
(days) when in
daily use.
Tot a l
risk
index
assuming:
Risk =
surfaces x
Time x
Volume
Percent of
non-solar
existing
cylinder risk
Assume there is typically an
unheated volume at base of cyl of
15 litres (not thermal stores)
Cylinder
wall, floor
and heater /
solar coils.
Limescale
interstices.
Total
area.
Control /
reference:
Non solar
existing
150 l cylinder.
0.3
1.5
1.8
100%
(reference
case)
Twi n c oi l
conventional solar
cylinder,
200 l.
1
1
2
+ =
+ =
Relative risk example
calcs:
Hard water: 250 ppm
CaCO3
Simple risk index:
Vol x Area x time
Try your own figures or
methodology.
Notes:
Wetted area (sq m)
not reliably heated to 50C
daily.
Vol ume not reliably
heated to 50C every
day. (litres)
Usual max
time
between
100% water
volume
replacement
(days) when
in daily use.
Tot a l
risk
index
assuming:
Risk =
surfaces x
Time x
Volume
Percent of
non-solar
existing
cylinder risk
Assume there is typically
an unheated volume at
base of cyl of 15 litres
(not thermal stores)
Cylinder wall,
floor and
heater / solar
coils.
Limescale
interstices.
Total
area.
Control /
reference:
Non solar
existing
150 l cylinder.
heat almost to base
apart from 0.3
sqm / 15 litres
0.3
1.5
1.8
15
1.2
32
100%
(reference
case)
Twi n c oi l
conventional solar
cylinder,
200 l.
1/0
Base case. Internal
surface 2 sqm
1
1
2
100
1.6
320
988%
X X =
X X =
Relative risk example
calcs:
Hard water: 250 ppm
CaCO3
Simple risk index:
Vol x Area x time
Try your own figures or
methodology.
Notes:
Wetted area (sq m)
not reliably heated to 50C
daily.
Vol um e not reliably
heated to 50C every day.
(litres)
Usual max
time between
100% water
volume
replacement
(days) when
in daily use.
Tot a l
risk
index
assuming:
Risk =
surfaces x
Time x
Volume
Percent of
non-solar
existing
cylinder risk
Assume there is typically
an unheated volume at
base of cyl of 15 litres
(not thermal stores)
Cylinder wall,
floor and
heater / solar
coils.
Limescale
interstices.
Total
area.
Control /
reference:
Non solar
existing
150 l cylinder.
heat almost to base
apart from 0.3
sqm / 15 litres
0.3
1.5
1.8
15
1.2
32
100%
(reference
case)
2 series cylinders
with solar in the
first,
2 x 100 litre.
1/0
Sizing assumes all
cyls 0.6 m dia.
1.5
1
2.5
115
1.6
460
1,420%
Twi n c oi l
conventional solar
cylinder,
200 l.
1/0
Base case. Internal
surface 2 sqm
1
1
2
100
1.6
320
988%
Indirect solar
retrofit
to existing
150 l cylinder.
1/0
Retrofits heat
almost to base
apart from 0.3
sqm / 10 litres. Has
a surface of 2.5
sqm
2.8
1.5
4.3
10
1.15
49
153%
Direct solar
retrofit to existing
150 l cylinder.
(Direct more often needs a
softener)
0/0
with 1 sqm wetted
ext loop surface,
vol is 3 litres.
1.3
0.2
1.5
18
1.2
32
100%
Solar in thermal
store, 200 litre.
0/1
0.5
0.1
0.6
5
0.5
2
5%
X X =
Solartwin.com innovation in action
zero carbon solar water heating
Major plumbers insurance
broker may not cover
conventional solar
cylinders
Courtprice Ltd
Broker to IPHE: Institute of
Plumbing and Heating
Engineering.
Broker to thousands of
plumbers.
Solartwin.com innovation in action
zero carbon solar water heating
Courtprice void insurance:
Solartwin.com innovation in action
zero carbon solar water heating
How is today’s solar tradeoff risk level
described?
About ten times higher risk
Simple risk assessment earlier.
Highly likely to be creating a risk
Dr Tom Makin Liverpool University Hosps report to WRAS.
Conventional twin coil cylinders are a Serious flaw in
design” Legionella Control International. Consultants
report to Solar Twin Ltd.
Concern is “Unjustified.” “There has never been a
case of Legionella anywhere in EU on a system
with storage as low as 50C” Solar Trade Association.
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas of hot water storage fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Hot water storage falling
outside L8 guidance.
a) Twin series cylinders with solar upstream
b) Twin coil cylinders (by far the most common)
c) Some combination boiler pre-feeds
These three are usually only out of compliance if they have no
destratification pump or other means of regular heating to the base.
Until Nov 2009 installers had to ignore L8 para 158 in order to gain
Microgeneration Certification for Low Carbon Buildings grants of 10-50%
project value.
From: DEFRA
SAP 2005
(Solar
Appendix)
0 / 0
d). Direct conventional cylinder.
Retrofit or new cylinder.
(Blender valve not shown).
Backup heater at base.
= Dedicated solar vol. in time.
0 / 1
(not in SAP).
Thermal store.
Usually new installation.
Backup heater options:
base (shown) or raised
(with heat exch. also raised.)
2 probably safer installations: risks
0 / 0
d). Direct base-heat conventional
cylinder. Indirect also used.
Hard water needs ion
exchange softener.
Risk similar to conventional
non-solar plumbing.
0 / 1
Thermal store.
Only about 5% of the risk.
Low surface area
Low volume of water
Rapid water turnover.
2 probably safer installations 0/0 & 0/1
0 / 0
d). Direct conventional
cylinder as a retrofit:
Costs 20% less than TCC
About 10% less energy.
0 / 1
Thermal store.
Costs 20% more than TCC
0% - 30% more energy.
Costs-benefits of safer installations
Solartwin.com innovation in action
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So...
Safer alternatives to conventional twin coil cylinders (TCC’s) include:
Heating to the base in evenings
Includes TCC’s with destratification pumps
Thermal stores with backup heating
Both perform fine in energy and costs-benefits terms.
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas (plumbing & backup heating control) fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
Area x volume x time = simple risk index
Relative risk example
calcs:
Hard water: 250 ppm
CaCO3
Simple risk index:
Vol x Area x time
Try your own figures or
methodology.
Notes:
Wetted area (sq m)
not reliably heated to 50C
daily.
Vol ume not reliably heated to
50C every day. (litres)
Usual max
time between
100% water
volume
replacement
(days) when in
daily use.
Tot a l
risk
index
assuming:
Risk =
surfaces x
Time x
Volume
Percent of
non-solar
existing
cylinder risk
Assume there is typically an
unheated volume at base of cyl of
15 litres (not thermal stores)
Cylinder wall,
floor and
heater / solar
coils.
Limescale
interstices.
Total
area.
Control /
reference:
Non solar
existing
150 l cylinder.
0.3
1.5
1.8
15
1.2
32
100%
(reference
case)
2 series cylinders
with solar in the
first,
2 x 100 litre.
1.5
1
2.5
115
1.6
460
1,420%
Twi n c oi l
conventional solar
cylinder,
200 l.
1
1
2
100
1.6
320
988%
Indirect solar
retrofit
to existing
150 l cylinder.
2.8
1.5
4.3
10
1.15
49
153%
Direct solar
retrofit to existing
150 l cylinder.
(Direct more often needs a
softener)
1.3
0.2
1.5
18
1.2
32
100%
Solar in thermal
store, 200 litre.
0.5
0.1
0.6
5
0.5
2
5%
X X =
Relative risk example
calcs:
Hard water: 250 ppm
CaCO3
Simple risk index:
Vol x Area x time
Try your own figures or
methodology.
Notes:
Wetted area (sq m)
not reliably heated to 50C
daily.
Vol ume not reliably heated to
50C every day. (litres)
Usual max
time between
100% water
volume
replacement
(days) when in
daily use.
Tot a l
risk
index
assuming:
Risk =
surfaces x
Time x
Volume
Percent of
non-solar
existing
cylinder risk
Assume there is typically an
unheated volume at base of cyl of
15 litres (not thermal stores)
Cylinder wall,
floor and
heater / solar
coils.
Limescale
interstices.
Total
area.
Control /
reference:
Non solar
existing
150 l cylinder.
heat almost to base
apart from 0.3
sqm / 15 litres
0.3
1.5
1.8
15
1.2
32
100%
(reference
case)
2 series cylinders
with solar in the
first,
2 x 100 litre.
1/0
Sizing assumes all
cyls 0.6 m dia.
1.5
1
2.5
115
1.6
460
1,420%
Twi n c oi l
conventional solar
cylinder,
200 l.
1/0
Base case. Internal
surface 2 sqm
1
1
2
100
1.6
320
988%
Indirect solar
retrofit
to existing
150 l cylinder.
1/0
Retrofits heat
almost to base
apart from 0.3
sqm / 10 litres. Has
a surface of 2.5
sqm
2.8
1.5
4.3
10
1.15
49
153%
Direct solar
retrofit to existing
150 l cylinder.
(Direct more often needs a
softener)
0/0
with 1 sqm wetted
ext loop surface,
vol is 3 litres.
1.3
0.2
1.5
18
1.2
32
100%
Solar in thermal
store, 200 litre.
0/1
0.5
0.1
0.6
5
0.5
2
5%
X X =
Solartwin.com innovation in action
zero carbon solar water heating
Themes
1. Pressures for reducing water storage temperatures, in all applications, renewable
energy or otherwise, are financial and environmental.
2. A historical “green exemption” from parts of L8 (or equivalents) today applies across
Europe for solarthermal and geothermal water heating systems.
3. Across Europe such “exempt” installations are increasing rapidly.
4. Most renewable heat consumers do not seem aware of any “exemption”.
5. How far (if at all) is it OK to permit a tradeoff between maximising energy
conservation and risk?
6. Today, which areas (plumbing & backup heating control) fall outside L8 guidance?
7. Example numerical risk assessment on installations outside strict L8 guidance.
8. Moving forward: who has the final say? Industry, regulators, consumers...?
Solartwin.com innovation in action
zero carbon solar water heating
The final say?
Please take any decision out of the political arena.
Do we wait until a SWH / HP case happens?
Is there a chance of a Legionella
iceberg?
UK aims to expand from about 100,000 solar thermal homes today
To 7 million by 2020.
This is a 70 x increase.
Other European states are planning similarly.
Are we planning ahead well enough?
We will NEVER have ALL the data.
But do we have enough data to act wisely?
Solartwin.com innovation in action
zero carbon solar water heating
Summary
1. Financial & environmental pressures for reducing water storage temperatures / setting
L8 guidance aside are getting stronger.
2. “Green exemption” from parts of L8 (or their EU equivalents) today applies across
Europe but only for solarthermal and geothermal water heating systems.
3. Across Europe “exempt” installations are increasing rapidly, with industry consent.
4. Most renewable heat consumers are probably unaware of this “exemption”.
5. If today’s tradeoff between maximising energy conservation and risk is OK, then
perhaps this tradeoff should extend much wider than just renewable energy.
6. Over 80% of solarthermal and heatpump installations are outside L8 guidance.
7. Numerical risk assessment suggests risks are 10x higher than if no solar. Heating to
the cylinder base / thermal stores are both viable alternatives.
8. Do we just wait? What next? Decision may need to be removed from industry’s hands.
Solartwin.com innovation in action
zero carbon solar water heating
Thank you for
your interest.
15 September 2010 presentation to “Combating Legionella”
By Barry Johnston, Managing Director, Solar Twin Ltd, UK.
Solar PV and solar thermal suppliers / innovators for over a decade.
ResearchGate has not been able to resolve any citations for this publication.
com innovation in action zero carbon solar water heating Thank you for your interest presentation to Combating Legionella
  • Solartwin
Solartwin.com innovation in action zero carbon solar water heating Thank you for your interest. 15 September 2010 presentation to " Combating Legionella "
Managing Director, Solar Twin Ltd
  • By Barry Johnston
By Barry Johnston, Managing Director, Solar Twin Ltd, UK.