T50 on new install?

[John.g]

So you are thinking that a 17 kw boiler can,t keep up with the combined demand of both CH & DHW even if the Boiler is running continuously?

 

[siricosm]

I suppose in the winter the incoming water temp could be as low as 5C, so at 10 lpm with a 40C rise it would require around 28kW with the hot water running full blast. Add another 7-8kW for CH on a cold day and it could get up to 35kW peak demand.

In the summer, if the incoming water was 18C, 17kW could provide 9lpm at 45C, so it could likely keep up forever.

The winter numbers above are a bit pessimistic, but with a more reasonable 10kW deficit, the tank should last around 40 minutes, or 400 litres if it starts at 65C and drops to 45C.

 

[John.g]

The combination of CH demand + mains water at 5/6C certainly requires a lot of energy especially if running HW demand at 10LPM for 30/40 minutes, the 120 litre cylinder wasn't much use with that sort of use.

What ~ is the DHW temp at 10LPM with cylinder temp at 50C. (current mains temp ~ 7.5C) as I'd like to do another LMTD calc on it.

 

[siricosm]

I will see if I can measure that. I'll have to find a day/time when I can drop the store temperature without the family noticing.

 

[John.g]

No need to drop it, just give as accurately as you can any current readings, the important ones are the store temp, the DHW temp and estimated DHW flow, you can always take a another set of readings sometime when the store temp is at its lowest due to a big demand for both DHW & CH.

 

[siricosm]

I think will I have to drop it, because there is a TMV that I have on its max setting, that appears to be around 48C, and I have no way to get upstream of that. I thought about plumbing the laundry sink direct to the hot from the plate exchanger, since sometimes very hot water is useful, but from what I have read it is not legal to have any hot taps that are not protected by the TMV. So do any calcs, I was thinking I would need to get the temps low enough that the TMV doesn't interfere.

 

[John.g]

Don't know about the legalities but seems to plenty on the net that allow 60C outlet, here's one,

Caleffi Adjustable 1" Thermostatic Mixing Valve 40-60°C

Caleffi Adjustable 1" Thermostatic Mixing Valve 40-60°C

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