I've recently added the hot water kit to my EvoHome, to control an unvented cylinder that has twin coils. The boiler is currently feeding both coils in parallel ( the idea was the twin coil gives me the option of solar-thermal in future without having to replace the cylinder again. ) It's a Worcester Bosch cylinder that has several temperature sensor locations - currently I've put the EvoHome insertion sensor in at the lowest level, fractionally above the primary heating coil, theory being it will "see" the temperature drop quickly and hence all water above will be at or above the temperature band set on the EvoHome ( assuming the water is switched on. )
Several thoughts/questions spring to mind though. The default hot water temperature on the EvoHome was 50°C, and the "eco" ( which is the recommended setting ) on the boiler is 60°C - it obviously makes sense to have the boiler about 10°C higher than the EvoHome so the water is capable of being heated to the set point fairly quickly, so that makes sense and clearly Honeywell and Worcester Bosch have a similar idea of what the setting should be. However, legionella will survive at 50°C, so that seems too cool from that point of view. In fact, with the default differential setting, the water will regularly get to 40°C, a temperature at which the bacteria can actually thrive. On the flip side, if it's such a danger, why do both manufacturers have this as the default or recommended setting? Is it because the tank is sealed so there's less risk? Is that even true?
In my case, stratification I assume will mean the top of the cylinder is hotter than the bottom, and this is a 250L tank which is nearly 2m tall, so maybe by quite a bit. I could obviously check that by measuring with another probe near the top, but I'm still not sure I really want bacteria living happily at the bottom of the cylinder! For now, to feel a bit safer whilst not wasting too much energy, I've set the EvoHome to 55°C ( differential 7°C ) and the boiler to 65°C, but it still seems odd to me that the default settings are as they are if it's such a risk. ( There's a lot of discussion about this in various places on the net, and of course the environmental conditions under which legionella live and grow is well known, but most stuff that I see on this specific topic of unvented cylinders seems to be speculation paraded as fact, with no reason for the defaults being cited that make sense. )
My second thought after the install is, why bother with a hot water schedule at all? My tank loses around 0.4°C an hour when the water isn't used, with the only real significant drops happening when a shower is taken. Given the fact you presumably always want the water heated during a shower, and that's the most common time the boiler will need to fire anyway, having a schedule seems to make no difference, other than add the possibility that if you shower during the day when the water would normally be off, you risk having a nice comfortable environment for the aforementioned bacteria.....
Several thoughts/questions spring to mind though. The default hot water temperature on the EvoHome was 50°C, and the "eco" ( which is the recommended setting ) on the boiler is 60°C - it obviously makes sense to have the boiler about 10°C higher than the EvoHome so the water is capable of being heated to the set point fairly quickly, so that makes sense and clearly Honeywell and Worcester Bosch have a similar idea of what the setting should be. However, legionella will survive at 50°C, so that seems too cool from that point of view. In fact, with the default differential setting, the water will regularly get to 40°C, a temperature at which the bacteria can actually thrive. On the flip side, if it's such a danger, why do both manufacturers have this as the default or recommended setting? Is it because the tank is sealed so there's less risk? Is that even true?
In my case, stratification I assume will mean the top of the cylinder is hotter than the bottom, and this is a 250L tank which is nearly 2m tall, so maybe by quite a bit. I could obviously check that by measuring with another probe near the top, but I'm still not sure I really want bacteria living happily at the bottom of the cylinder! For now, to feel a bit safer whilst not wasting too much energy, I've set the EvoHome to 55°C ( differential 7°C ) and the boiler to 65°C, but it still seems odd to me that the default settings are as they are if it's such a risk. ( There's a lot of discussion about this in various places on the net, and of course the environmental conditions under which legionella live and grow is well known, but most stuff that I see on this specific topic of unvented cylinders seems to be speculation paraded as fact, with no reason for the defaults being cited that make sense. )
My second thought after the install is, why bother with a hot water schedule at all? My tank loses around 0.4°C an hour when the water isn't used, with the only real significant drops happening when a shower is taken. Given the fact you presumably always want the water heated during a shower, and that's the most common time the boiler will need to fire anyway, having a schedule seems to make no difference, other than add the possibility that if you shower during the day when the water would normally be off, you risk having a nice comfortable environment for the aforementioned bacteria.....
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