We at Canetis, now we have seen the post on the Canetis Superflow (CSF) would like to answer the question from David Stanton and correct the misinformation from “Simon G” and “King and Pipes”. CSF can indeed address poor domestic hot water performance and is not magic rather just a logical development of engineering technology. The actual flow rate of domestic hot water (DHW) from the boiler is governed by a restrictor that is installed by the manufacturer and the only way to increase this is to remove this device. However with a CSF installed the 24KW boiler that David seems to have installed should supply adequate hot water for all but the very largest homes.
The CSF works be providing preheated water to the boiler. This allow the combi boiler to deliver water at a greater temperature than without the device thus increasing the energy value. The 25 litre CSF tests show that when heated to a temperature of 80°C it is able to deliver over 100 litres of preheated water benefit that compares well to a typical 75 litre British bath and less water for a shower. The CSF allows a combi boiler to produce hot water at its design temperature (>40oC ) even when the cold input water is lower than the assumed mains water temperature of 10oC.
Canetis suggest the use case of CSF is for multi bathroom properties, where there is low gas pressure and to achieve Silver Standard for heating systems on new build in Scotland. In an ideal world CFS could be used to promote the use of smaller boilers in the UK that are sized for space heating (SH) not DHW which will ensure boilers work efficiently without cycling more of the time. This was a key problem outlined in the paper by George Bennett entitled
“The secret life of boilers: Dynamic performance of residential gas boiler heating systems – a modelling and empirical study”.
We note that David Stanton has a Worcester Bosch (WB) boiler. We provided them with a boiler to install in the house of Neil Schofield (a well known member of the WB team) to address his poor domestic hot water demand. Whilst positive test data was collected the key feedback was from Mrs Schofield who believed the hot water performance had markedly improved. As far as we are aware the system is still operational.
The issue of legionella was raised by Simon G. Many tens of thousands of CSF and the other main Canetis product GasSaver have been sold over many years and there have been no cases of legionella. Legionella is generally considered to be primarily a problem of cooling towers not domestic water systems. In domestic hot water supply it is controlled by the heat range such that cold water is generally kept below 20oC and hot water above 50oC. The water that is pre heated to enter the boiler is mixed to 30oC but then heated in the boiler to 70oC to 80oC. The legionella operating range is:
- Above 70 °C (158 °F) – Legionella dies almost instantly
- At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
- At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain
- 48 to 50 °C (118 to 122 °F) – can survive but do not multiply
- 32 to 42 °C (90 to 108 °F) – ideal growth range
- 25 to 45 °C (77 to 113 °F) – growth range
- Below 20 °C (68 °F) – can survive, even below freezing, but are dormant
In short there is no
evidence we have seen that legionella is an issue with CSF just comment, largely from German manufacturers, about the potential of legionella in what appears to be an attempt to deny consumers the chance to purchase the most appropriate boiler system. There are however potential challenges that will need to be addressed as we move towards lower heating profiles with the likes of heat pumps where the system will generally produce water at much closer to the temperature of use by the consumer thus the water will be often held within the legionella growth range and will unlikely to operate above 50 °C where legionella is killed.
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