Thermostatic mixing valve on hot water cylinder

[Little Clanger]

I've just installed a new 160 litre vented Economy 7 hot water cylinder (twin immersions) for our domestic hot water.

 

My plan has been to run it with the immersion thermostats as maximum (65⁰  to 70⁰) to store as much overnight energy as possible, and to avoid any Legionella risk.

 

I assume this would mean that the temperature at the top of the tank could be up to 85⁰ or more. Since we don't have mixer taps in the kitchen or bathroom, I would be concerned about scalding risk when the grandchildren are visiting. 

 

As a result, I have bought a thermostatic mixing valve to mount on the hot water outlet of the cylinder to deliver all our hot water at a safe temperature. It would be easiest to connect the cold inlet of the valve to the supply from the loft tank, although mains would be possible.

 

Am I making the whole system too complicated? Would it be preferable to simply set my immersion heater thermostats lower?

[marshian]

I get that heating the water to a higher temp on E7 maximises the energy used on cheaper rate but heating to a higher temp also maximises the losses so higher levels of waste

 

I'd be looking at it differently

 

How much of the water do you use daily ie is tank same size as previous and did you run out of water in the day

 

The risk of legionaires is very small if you use all the water daily

 

As far as legionaires goes I do a hot cycle once a week to coincide with "her bath night"

 

Rest of the time I'd be heating the water to a temp that meant the tank lasted all day under normal circumstances

 

I only heat HW (114 Litre vented tank to 48 - 52 deg max) and that lasts the two of us all day (showers morning and evening)

 

Having temp logging on the top and bottom of the tank the accelerated heat loss is very obvious when I heat HW to higher temperature

[John Carroll]

53 minutes ago, Little Clanger said:

I've just installed a new 160 litre vented Economy 7 hot water cylinder (twin immersions) for our domestic hot water.

 

My plan has been to run it with the immersion thermostats as maximum (65⁰  to 70⁰) to store as much overnight energy as possible, and to avoid any Legionella risk.

 

I assume this would mean that the temperature at the top of the tank could be up to 85⁰ or more. Since we don't have mixer taps in the kitchen or bathroom, I would be concerned about scalding risk when the grandchildren are visiting. 

 

As a result, I have bought a thermostatic mixing valve to mount on the hot water outlet of the cylinder to deliver all our hot water at a safe temperature. It would be easiest to connect the cold inlet of the valve to the supply from the loft tank, although mains would be possible.

 

Am I making the whole system too complicated? Would it be preferable to simply set my immersion heater thermostats lower?

No, IMO, because the immersion elements are inserted horizontally (presumably) then they will heat the water from the bottom up. If you drew off say 20L of HW from a fully heated cylinder then the element will only reheat this 20L to 60/65C. 

[Little Clanger]

Thank you both for your replies, which will feed into my decision-making. My apologies for a delayed response - been a bit busy