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

robgraham wrote:
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 ?

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!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The message
from robgraham contains these words:

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 ?

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.

--
Roger Chapman

On 29 Nov, 04:27, John Rumm wrote:
robgraham wrote:
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 ?

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!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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

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

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 ?

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.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article ,
John Rumm wrote:
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!

And a cold one? ;-)

--
*The longest recorded flightof a chicken is thirteen seconds *

Dave Plowman London SW
To e-mail, change noise into sound.