We have a five bedroom farmhouse with about 15 radiators. The boiler is in
an outbuilding whulst the pump is in the house. There is about thirty-five
metres (times two) of pipe between the two. It isn't possible to move the
boiler nearer.

The old pump and LPG boiler were having problems so I have installed an
90,000 BTU oil boiler with a Grundfos Alpha pump. However I'm still not
sure the water is being circulated fast enough due to the resistance of the
piping. The oil boiler isn't commisioned yet but the LPG certainly
struggled big time.

Is there any definition of what the minimum acceptable water velocity is ?

And if it is too low, is it possible to install a second pump by the boiler
just to pump water through the long legs, presumably with an automatic
bypass valve in the house, and then use the Alpha just to pump the water
around the house ?

"G&M" wrote in message
...
We have a five bedroom farmhouse with about 15 radiators. The boiler is
in
an outbuilding whulst the pump is in the house. There is about
thirty-five
metres (times two) of pipe between the two. It isn't possible to move the
boiler nearer.

The old pump and LPG boiler were having problems so I have installed an
90,000 BTU oil boiler with a Grundfos Alpha pump. However I'm still not
sure the water is being circulated fast enough due to the resistance of
the
piping. The oil boiler isn't commisioned yet but the LPG certainly
struggled big time.

Is there any definition of what the minimum acceptable water velocity is ?

And if it is too low, is it possible to install a second pump by the
boiler
just to pump water through the long legs, presumably with an automatic
bypass valve in the house, and then use the Alpha just to pump the water
around the house ?


If the water velocity is too high, you'll get noise in the pipes. If it's
too low, you'll have too big a temperature drop across your radiators.

Start by getting yourself a decent non-contact thermometer (like the 30 quid
IR one from CPC) and balance your system to get an equal drop across all
radiators. Ideally, this should be about 11 degC. If it's substantially more
than this, water isn't getting to your radiators fast enough to balance the
heat loss to the room - and you need to increase the velocity. If your pump
is running flat out, but is still not enough, I'd be tempted to install
another one very close to the existing one but in the other pipe - so that
one is in the flow and the other in the return. [Make sure they're the right
way way round so as not to fight each other!] Connect them together
electrically so that they both go on and off at the same time. In effect,
one will be circulating water between the house and the boiler and the other
will be circulating it round the radiators - but they will just be working
in series, so there's no need for any additional by-pass circuits.

[I hope that the long pipes between the house and out-house are well
lagged!]

HTH.

Cheers,
Set Square

"Set Square" wrote in message
...
If your pump
is running flat out, but is still not enough, I'd be tempted to install
another one very close to the existing one but in the other pipe - so that
one is in the flow and the other in the return. [Make sure they're the
right
way way round so as not to fight each other!] Connect them together
electrically so that they both go on and off at the same time. In effect,
one will be circulating water between the house and the boiler and the
other
will be circulating it round the radiators - but they will just be working
in series, so there's no need for any additional by-pass circuits.

Thanks - that's even easier to do.


[I hope that the long pipes between the house and out-house are well
lagged!]

In the process of doing so. This farm building had the original warm roof
concept - hot water pipes right under the tiles.

"G&M" wrote in message
...

"Set Square" wrote in message
...
If your pump
is running flat out, but is still not enough, I'd be tempted to install
another one very close to the existing one but in the other pipe - so
that
one is in the flow and the other in the return. [Make sure they're the
right
way way round so as not to fight each other!]

Thanks - that's even easier to do.

One thing you'll have to watch - if it's a vented system - is that the
addition of a second pump doesn't cause it to pump over. If it does, you may
either have to change where the feed and expansion pipes are connected or
turn both pumps round so that the circulation is in the opposite direction.
If you *do* reverse the flow, make sure that any TRVs fitted to radiators
are bi-directional.

Cheers,
Set Square

"G&M" wrote in message
...

We have a five bedroom farmhouse with about 15 radiators. The boiler is
in
an outbuilding whulst the pump is in the house. There is about
thirty-five
metres (times two) of pipe between the two. It isn't possible to move the
boiler nearer.

The old pump and LPG boiler were having problems so I have installed an
90,000 BTU oil boiler with a Grundfos Alpha pump. However I'm still not
sure the water is being circulated fast enough due to the resistance of
the
piping. The oil boiler isn't commisioned yet but the LPG certainly
struggled big time.

Is there any definition of what the minimum acceptable water velocity is ?

And if it is too low, is it possible to install a second pump by the
boiler
just to pump water through the long legs, presumably with an automatic
bypass valve in the house, and then use the Alpha just to pump the water
around the house ?

When calculating the rad/pipe sizes of a system the pump size is also
determined. You may have is far too many elbows giving too much resistance
fooling the Alpha which then drops its speed.

Two practical ways around this:

1. Fix a high head fixed speed pump at least the same head as the replaced
pump.

2. Instead of installing loops with one pump to assist the other, just split
the system into two zones with a time clock on each. Then you could have
say the upstairs off during mid day. Divide and rule and save fuel too,
which is a good thing with a oil boiler in price and storage longevity.

"IMM" wrote in message
...

When calculating the rad/pipe sizes of a system the pump size is also
determined. You may have is far too many elbows giving too much
resistance
fooling the Alpha which then drops its speed.

Two practical ways around this:

1. Fix a high head fixed speed pump at least the same head as the replaced
pump.

2. Instead of installing loops with one pump to assist the other, just
split
the system into two zones with a time clock on each. Then you could have
say the upstairs off during mid day. Divide and rule and save fuel too,
which is a good thing with a oil boiler in price and storage longevity.

Now the second IS a good idea. Saves on zone valves which cost about the
same as pumps anyway.
Is there a minimum distance feed to each pump from the T point, or can they
both be connected closely together ? I'm thinking of the case where both
come on and if one is sucking stronger than the other the other gives up and
sulks.

"G&M" wrote in message
...

"IMM" wrote in message
...

When calculating the rad/pipe sizes of a system the pump size is also
determined. You may have is far too many elbows giving too much
resistance
fooling the Alpha which then drops its speed.

Two practical ways around this:

1. Fix a high head fixed speed pump at least the same head as the
replaced
pump.

2. Instead of installing loops with one pump to assist the other, just
split
the system into two zones with a time clock on each. Then you could
have
say the upstairs off during mid day. Divide and rule and save fuel too,
which is a good thing with a oil boiler in price and storage longevity.

Now the second IS a good idea. Saves on zone valves which cost about the
same as pumps anyway.
Is there a minimum distance feed to each pump from the T point, or can
they
both be connected closely together ? I'm thinking of the case where both
come on and if one is sucking stronger than the other the other gives up
and
sulks.


Flow from boiler - then a tee - then a non-return valve for each pump and
then the pump for each zone. The DHW can be regarded as a zone too, so
another tee and non-return valve for the DHW pump.

On Tue, 2 Mar 2004 19:49:19 -0000, "G&M" wrote:

We have a five bedroom farmhouse with about 15 radiators. The boiler is in
an outbuilding whulst the pump is in the house. There is about thirty-five
metres (times two) of pipe between the two. It isn't possible to move the
boiler nearer.

The old pump and LPG boiler were having problems so I have installed an
90,000 BTU oil boiler with a Grundfos Alpha pump. However I'm still not
sure the water is being circulated fast enough due to the resistance of the
piping. The oil boiler isn't commisioned yet but the LPG certainly
struggled big time.

Is there any definition of what the minimum acceptable water velocity is ?

And if it is too low, is it possible to install a second pump by the boiler
just to pump water through the long legs, presumably with an automatic
bypass valve in the house, and then use the Alpha just to pump the water
around the house ?

I'm usng an Alpha on a 20 rad system, 5 beds mostly at ground floor
level.

It has no problem even at the normal setting.
The system is pressurised and TRV's on most rads.

Robert

royall at which dot net

royall at which net

wrote in message
...
On Tue, 2 Mar 2004 19:49:19 -0000, "G&M" wrote:

We have a five bedroom farmhouse with about 15 radiators. The boiler is
in
an outbuilding whulst the pump is in the house. There is about
thirty-five
metres (times two) of pipe between the two. It isn't possible to move
the
boiler nearer.

The old pump and LPG boiler were having problems so I have installed an
90,000 BTU oil boiler with a Grundfos Alpha pump. However I'm still not
sure the water is being circulated fast enough due to the resistance of
the
piping. The oil boiler isn't commisioned yet but the LPG certainly
struggled big time.

Is there any definition of what the minimum acceptable water velocity is
?

And if it is too low, is it possible to install a second pump by the
boiler
just to pump water through the long legs, presumably with an automatic
bypass valve in the house, and then use the Alpha just to pump the water
around the house ?

I'm usng an Alpha on a 20 rad system, 5 beds mostly at ground floor
level.

It has no problem even at the normal setting.
The system is pressurised and TRV's on most rads.


35m -yikes! As a "quick" trial you could try getting a second pump, and
adding it in parallel to the existing one (wherever it is), with an extra
bit of pipe. For the purposes of the test you could turn it on and off by
hand. This "should" double the pressure. Should it prove useful a permanent
installation might require a relay box, as the boiler/controller might not
like the starting current of two pumps, and isolation valves etc. , for
removal and in case one fails


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

"IMM" wrote in message
...

"G&M" wrote in message
...

2. Instead of installing loops with one pump to assist the other, just
split
the system into two zones with a time clock on each. Then you could
have
say the upstairs off during mid day. Divide and rule and save fuel
too,
which is a good thing with a oil boiler in price and storage
longevity.

Now the second IS a good idea. Saves on zone valves which cost about
the
same as pumps anyway.
Is there a minimum distance feed to each pump from the T point, or can
they
both be connected closely together ? I'm thinking of the case where
both
come on and if one is sucking stronger than the other the other gives up
and
sulks.


Flow from boiler - then a tee - then a non-return valve for each pump
and
then the pump for each zone. The DHW can be regarded as a zone too, so
another tee and non-return valve for the DHW pump.


You'll have to find a way of controlling the boiler so that it only comes on
when one or more zones are calling for heat. Zone valves may be easiest
option, because they have volt-free contacts which close when the valve
opens and which can be used to switch the pump. You won't need non-return
valves if you use zone valves. Otherwise you'll have to keep the non-return
valves *and* add relays to do the boiler switching.

Does your boiler need to keep the pump running for a bit after it stops
firing? If so, that will be an interesting problem to solve - if you have 3
pumps, all controlled independently!!

Cheers,
Set Square