DHW Head question

[robgraham]

I've been looking into using a venturi shower and was kindly sent a large amount of data by Trevi. One thing that does puzzle me is that their diagrams show the DHW head to be to the *bottom* of the cold water tank and not the internal water level as I would expect.

Surely the head is the effective weight of the total cold water column and therefore should be measured to the water level in the cold water tank. I appreciate that most tanks aren't that deep to make a significant difference but am I wrong or are they wrong ?

Rob

[John Rumm]

No you are right.

The only thing that possibly changes it is if the shower can draw water faster than the tank can refill, then you may end up with the water level at the bottom of the tank!

[Roger]

The message from robgraham contains these words:

I have long since lost the Trevi paperwork but ISTR that the head in question is the minimum head which is the level the tank can be drawn down to.

[robgraham]

Interesting point, John, which I hadn't thought of. It would be in the manufacturer's interest to make sure that the system has a bit of buffer in the head and as you say the cold tank level could fall

So I'm right and the manufacturer is building in a margin - ie could be said that both are right in their own way!!

Rob

[David Hansen]

On Wed, 28 Nov 2007 15:58:56 -0800 (PST) someone who may be robgraham wrote this:-

Neither of you are wrong.

It is common practice to consider the head to be from the outlet. This allows for other appliances having drawn off a considerable amount of water and a slow supply. It gives a worst case.

[Dave Plowman (News)]

And a cold one? ;-)