Solar panels legionella. Solar water heating systems = Solar panels + solar energy. Solar thermal: solar power & solar hot water. L8 HSE. Solartwin review solar safety and find competitors may have problems.
Solartwin review old style solar water heating systems with conventional twin coil solar cylinders.
To use, but without attributing them, the words of another professional with an interest in solar and legionella:
Solar Twin Ltd believes that the drive for renewable energy sources should be balanced with due consideration given to the potential risks to the users’ health and safety. In solar heated water systems, these risks are likely to include risks from exposure to Legionella bacteria. Solar systems comprise a range of design and operational configurations, some of which appear to pay little heed to established parameters to control Legionella growth. With the anticipated growth of the renewable energy market it is essential that proper consideration is given to the safe design of such systems.
Of course, not all hot water systems require elaborate legionella assessment and control measures. Indeed our simple risk assessment validates the position given in HSE Legionellosis guidance L8 para that the legionella risks of conventional small, domestic-type hot water systems where temperatures and turnover are high, are, indeed low risks.
However in the hot water stores of some twin coil solar water heating systems, the very same simple risk assessment shows that their specific legionella risks may be up to ten times higher because the installers of these systems pay little heed to established parameters to control Legionella growth, in particular that of heating daily to the base to 60C, something which usually does not happen for months at a time each year. Hence our concerns.
Legionellosis infection requires a chain of five events, A-E:
A – contamination (most domestic water systems end up contaminated with low levels of Legionella bacteria)
B – amplification (conditions to grow, such as a slimy surface biofilm containing protozoa such as amoebae, tepid water, certain nutrients and space – plus a lack of lethal factors like regular heating, toxic radiation or chemicals)
C – transmission (they need to get from where they grow best into out into a person’s lungs)
D – exposure (usually people are exposed via a contaminated spray)
E – susceptibility (for example, smokers, men and most of all, immunosuppressed people are most susceptible)
We are sometimes asked how to reduce Legionella risk if you already have twin coil solar cylinders fitted.
Here are five approaches to consider with brief reasons, costs, pros and cons for each. We hope this Legionella safety guidance is useful. I have ranked them in terms of approximate costs. The first is the cheapest to do…
1 – Zero cost and immediate:
The simplest is to stay clear of hot water spray. Take baths, not showers. This is an essential and immediate action for very high risk people who are immunosuppressed (eg with HIV or organ transplants)
Contemplate while you are in the bath what you plan to do next: of 2-4 below.
Why? This is because Legionella infects by being inhaled into your lungs. Taking baths instead of showers will stop you inhaling water droplets which might be contaminated. If you actually disconnect all hot or warm sprays, then the home may well comply with L8.
2 – Lower cost. (Usually under £100 if you already have an immersion heater in place)
Buy and fit a long immersion heater which is the full length of the cylinder and which will reach to the bottom.
Time this to come on at the end of the day to heat the whole cylinder to 60C.
Why? This will heat the cylinder daily to the bottom and complies with HSE Legionellosis L8 guidance para 158. This guidance actually is for installations which are covered by the Heath and Safety at Work Act. Owner occupied homes are not covered by this Act. But in the absence of other guidance it obviously makes sense to treat L8 as a starting point for all domestic installations, not just those which are already covered by L8, such as social homes.
- Pros: Good if you can buy cheap rate + green tariff electricity.
- Cons: Not all cylinders will have a suitable top entry hole in the cylinder for the immersion heater. I am not sure if long immersion heaters are available for solar cylinders since these tend to be taller. Heaters may not fit – they may touch or get stuck on the heat exchangers inside. If they touch they may “spot-overheat” and fail too soon. Peak rate electricity is costly and is 2-3 times as carbon intensive per unit of energy than mains gas. So your net carbon savings from having solar may fall, possibly even to zero. So it is not a very sustainable solution unless – you are a green / renewable energy electricity tariff, of course.
3 – Medium cost. Requiring a plumber and electrician and keeping the cylinder: (£300-500)
Have the twin coil cylinder fitted with a mains powered destratification pump which comes on:
- Every day so that it holds the water at 60C all the way down for one hour.
- At the same time as the water heating is turned on, whether immersion or other type of water heater.
Why? This will heat the cylinder daily to the bottom and complies with L8 guidance para 158.
- Pros: medium cost.
- Cons: cost money to run. Uses electricity. Reduces carbon savings.
4 – Higher cost. Requires a plumber only: replacing the cylinder with a safer one: (£500-£1000)
Replace the twin coil cylinder with another twin coil cylinder which has BOTH heat exchangers (solar and backup) at the bottom. Also time the backup heating to come on in the evening.
Why? Again this will heat the cylinder daily to the bottom and complies with L8 guidance para 158.
- Pros: operationally greener in that you don’t need to run an extra mains pump.
- Cons: arguably less green in that you are recycling / throwing stuff away. More costly to fit than any other option so far. But Solartwin is no longer recommended with twin coil cylinders even those which heat to the base because they limit its heat export function.
5 – Highest cost. Requires a plumber only: replacing the cylinder with a supersafe thermal store: (£1000-£1500)
Replace the twin coil cylinder with a thermal store. With a Solartwin installation, this has one heat exchanger to take heat out only. With conventional solar, some have a second heat-in heat exchanger thus reducing efficiency a bit. You may want to time the backup heating to come on in the evening.
Why? Having fast flowing, frequently replaced water of low heated volume at any one time super-complies with L8.
- Pros: operationally greener than a shunt pump. in that you don’t need to run an extra mains shunt pump. A thermal store can give you high pressure hot water throughout the house.
- Cons: arguably less green in that you are again recycling / throwing stuff away. Most costly to fit. If moving to high pressure hot water some of your low pressure plumbing fittings, showers etc may need replacing as well, pushing up the cost even more.
Should I bring an umbrella? Prevention by good design is much better than any cure after the event…
At Solartwin you can be sure that today’s installations, which were invented in Edinburgh, comply as close as possible with HSE’s code of practice L8’s guidance to heat the stored hot water in the cylinder to the bottom. We do this by: either having the backup heating positioned at the bottom of the cylinder and ideally it coming on at sunset (dedicated solar volume in space) or by using thermal stores which have a low volume of stored water in the heat-out heat exchanger.
Solartwin have been advising Which? magazine (The Consumers’ Association) on how to make solar water heating installations safer. To date Which? have not taken our advice. “Don’t mention the L-word!” seems to be their motto.
