– Of course at Solar Twin Ltd we know that the HSE Legionellosis document L8 does not apply to domestic householders and I am not trying to push margins: I am merely trying to made good decisions and to offer good practice to my customers, in compliance with our quality policy of continuous improvement. In the absence of any other more suitable code of practice or guidance it is surely not wrong for anyone to refer to L8 as a good place to start to look for safe practice guidance. Indeed it is surely appropriate to start with the principles behind L8 and also with its guidance, even if they are designed only to protect people at work. Despite the un-biological boundaries imposed on HSE by the H&S@WA, Legionella bacteria do not have any capability to distinguish between the roles, whether work or domestic, which individuals may play, before infecting them. So there is no biological (or medical) reason to treat L8 as not being a suitable place to start from, only perhaps reasons of law and technical complexity.
– In any case the MCS solar thermal standard MIS 3001, specifically refers to “non-domestic” installations in its clause 4.4. So the scope of MCS is in fact, within the remit of HSE ‘s L8 and not outside it. It seems inaccurate for anyone to claim that domestic installations in, for example, social homes, are not an area which HSE regulate, given their inclusion in HSE document INDG 375 / 05/30. In the context of the anticipated growth of the renewable energy market the inclusion of social homes under L8 m has at least particular relevance to the Microgeneration Certification Scheme, MCS.
– Of course I agree that in general, in non-solar domestic-style hot water systems, the risks of legionella bacteria growing are indeed low, as stated in L8, para 20, which you helpfully quote. However in the much more specific case of most solar hot water storage tanks installed in domestic premises, and in some non-domestic premises, these are usually subject to a slower turnover of water by being rather larger than normal. In addition by being not heated to the base daily to 60C and by usually only being heated daily at the top intermittently to 60C they are likely to allow more legionella to grow on its considerably larger and long-unpasteurised internal surfaces.
– The lack of any properly functioning “hot top” disinfection system is likely to allow the bacteria which enter the water also to be distributed without thermal disinfection on the way out. Thus there is a higher risk to those who use such hot water installations, a risk which we calculate to be up to 10 times higher. Solar systems comprise a range of design and operational configurations and we intend to use only installations which already exist within this range and which use well validated or established parameters such as thermal control to control Legionella growth. We think that only one or two of UK’s numerous installation types should just be modified (note: not necessarily avoided!) to make them safer.
– Of course I have also always recognised that no single paragraph of any guidance is necessarily a standalone compulsory requirement. However with reference to para 158 (in particular heating to the base daily for 60C to one hour), this particular practice of basal heating is found to be virtually ubiquitous in non-solar domestic systems and so it seems reasonable to expect any industry to offer proper justification for any departure from this established parameter whether the kit which they install is “green” or not.
– However the solar thermal industry’s claims of a “safe hot top” and, more generically, a safe installation does not actually happen in practice for several reasons, such as the top sometimes being hot and at 60C only for a few hours a day rather than for 24 hours. This then begs the question of whether a large tepid base which is left unpasteurised for months at a time is a proper increase in risk to impose on consumers, without asking them (or at least telling them) first. Regulators supporting twin coil cylinders (in their current form and mode of operation) in effect by being seen to be publicly turning a blind eye to them is getting close to licensing anyone, whether they use solar heating or not to store water at 45C for as long as they want. Is this what UK’s safety regulators want?
– One might as well also encourage (by omission) green customers to strip the insulation off the header tank in the attic in the summer as way of further increasing the solar gain to be had. There is really very little difference: such a header tank is just another a tepid solar pre-feed, another of which already exists in the lower half (solar pre-heat zone) of the cylinder. There is already an intellectually soggy green exemption from commonsense, so let’s now go the whole hog, would be the logical extension of this scary myth-supported-by-myth approach.
– Our having given proper consideration to the safe design of the range of solar thermal plumbing systems, having taken due consideration given to the potential risks to the users’ health and safety, we have concluded that regarding only two solar hot water storage designs, historically we have been in error: a difficult and expensive conclusion to reach (as it will be to implement). We have not taken this decision lightly. However we have announced a product recall and free upgrade service, starting in November because those two solar water heating water storage systems appear to pay little heed to established parameters to control Legionella growth.
– I hope that today’s immense political pressure on regulators to conceal what are now discreetly called L-word matters, will not downgrade this important topic to a technically marginal status or non-statutory status before examining the validity of the alternative parameters which are being claimed to supposedly operate in twin coil cylinders, bogus parameters which on close examination, in fact fail to operate effectively.