DHW - mains pressure, heat bank or indirect ? Also TMVs?

[alyne]

more questions!

I've had a chance to have a good look around my new house and having decided to keep the oil boiler (installed in 2014) I'm now looking at changing the hot water (and maybe heating design).
It's currently got an old uninsulated indirect cylinder (probably there since the house was built in the 1970's) - with a blanket fitted around it and what looks like S-plan heating.

My main question is around running costs.
Assuming all 3 systems are correctly spec'd for size etc - how do the running costs compare of a new indirect cylinder with S-plan, a mains pressure unvented (with S-plan) or a thermal store with a separate heating pump (prob a modulating one - grundfoss alpha or similar)?
Are they all broadly similar in running cost?

I'm also planning to move the boiler into the garage (which is basically behind the wall where it is now), and put the new DHW cylinder next to it in the garage (removing it from the cupboard in a bedroom).

As far as installation costs go I reckon the replacement indirect is by far the cheapest and can be self installed. Ditto the thermal store, but much more expensive to buy.
Mains pressure cylinder, middling to buy - expensive to get installed and annually serviced.

Temperature

At the moment the hot water is scaldingly hot - I could turn down the tank temp - but I believe it has to be at least 60 for legionella?
If I go with the thermal store, then they generally come with TMV's on the plate heat exchanger ( at least the one in my last house did anyway).
If I go with a replacement indirect or mains pressure then can I put a TMV on the tank outlet -or is it generally better (if more expensive) to have TMV's at each bath / shower / tap etc.

 

[flameport]

Running costs will be very similar. The main factor for cost is how much hot water you use, not the system itself.

Cylinder should be at least 60C. If the temperature at the outlets is too hot, fit TMVs at each outlet where the lower temperature is required (probably not the kitchen sink).
You may want to actually check the temperature of the cylinder rather than rely on the thermostat setting - cylinder thermostats are not accurate devices.

Mains pressure cylinder requires a suitable flow and pressure from the cold mains.
A thermal store adds significant cost and complexity for little or no benefit.

 

[alyne]

Thanks

I appreciate there's a depth of feeling on here about such things but I can't understand the "cost and complexity" of a store vs mains pressure?
I'm guessing the cost is similar if not slightly in favour of the heatbank (based on a self install of the store vs professional install of mains pressure?). Or am I forgetting something. (Quite likely!)

I can see that the indirect vented is the cheapest option by far but I had a heatbank in my last house (albeit with UFH) and loved the almost unlimited mains pressure hot water.

And on that point. Is there an easy way to measure the incoming Mains pressure and flow rate?