There have been a number of posting recently about gravity HW systems which
I have read with interest, having put off the job of upgrading the current
layout year after year. After doing a good search on google I think I have
all the concepts, and think that the way to go is just to stick a valve on
the cylinder.

Can anyone help me out, and let me know if there is a
simpler/easier/better/more efficient etc etc option before I buy the bits.

I have stuck details on my system on a webpage, so you can see how it is all
plumbed together, any thoughts, comments, recommendations would be
gratefully recieved. I rather be 110% clear on what I am doing, and get it
right first time, than fiddle and have no heating at all!

Details at:

http://www.freewebs.com/jase12345/Fu...%20Heating.doc

In an earlier contribution to this discussion,
Jason wrote:

There have been a number of posting recently about gravity HW systems
which I have read with interest, having put off the job of upgrading
the current layout year after year. After doing a good search on
google I think I have all the concepts, and think that the way to go
is just to stick a valve on the cylinder.

Can anyone help me out, and let me know if there is a
simpler/easier/better/more efficient etc etc option before I buy the
bits.

I have stuck details on my system on a webpage, so you can see how it
is all plumbed together, any thoughts, comments, recommendations
would be gratefully recieved. I rather be 110% clear on what I am
doing, and get it right first time, than fiddle and have no heating
at all!

Details at:

http://www.freewebs.com/jase12345/Fu...%20Heating.doc

If this were my system, my first priority would be to add boiler/pump
interlocks to prevent the boiler from cycling when neither CH nor HW require
it.

I would thus be looking at either a C-Plan system or an S-Plan system. I
would *not* go for a Y-Plan because it would greatly complicate the venting,
and 3-port valves are best avoided anyway.

The choice really hinges on whether or not the HW performance is currently
adequate. If it is, go for a C-Plan - it's a lot easier. You will need a
2-port valve in the HW circuit right next to the cylinder, *after* the vent
pipe tee - so as to maintain an un-interrupted path from the boiler to the
vent pipe. You will, of course also need a cylinder stat and a room stat.
The radiator nearest to the room stat *shouldn't* have a TRV on it. I
presume that you don't get any unwanted gravity circulation in the CH
circuit when the pump is not running? If you *do*, you will need an
anti-gravity valve - which only opens when the pump generates a bit of urge.

If the hot water takes too long to heat with gravity, you need a fully
pumped system - so I would go for an S-Plan. Put a 2-port valve in the HW
circuit next to the cyliner, as for C-Plan. Put another one in the CH
circuit. The current pump location may be a convenient position. Move the
pump to a position in the common bit of pipe before the circuits split. In
order to prevent pumping over, move the fill pipe connection into the HW
flow pipe - very close to where the vent pipe connects.

I would go for a programmable room stat for several reasons:
* It gives you completely independent control over the timing of HW and CH -
which most ordinary programmers don't. [Set your main programmer to HW timed
and CH constant - so that the room stat conrols the CH]
* It adapts to the characteristics of your system/house - and maintains the
set temperature with less overshoot
* With 'Optimum Start' it decides when to turn the heating on in order to
achieve the set temperature by the required time
* In the 'Off' position, it acts as an automatic frost stat - and still
turns on the heating if needed to prevent freezing

I doubt whether you need a by-pass circuit - even if you go for an S-Plan
system. These are needed when you have a boiler which only holds a small
quantity of water and which will overheat due to the residual heat in the
metal bits if the water isn't carried away quickly enough. Such boilers are
only used in fully pumped setups - and have pump over-run stats which keep
the pump running after the boiler stops firing until it has cooled down a
bit. The bypass circuit provides somewhere for the water to go if all the
valves are closed.

If a boiler works ok on gravity without the pump being on at all (when
operating on HW only), it can pretty certainly take care of itself.

Not sure whether I have answered *all* of the questions. HTH, anyway!

--
Cheers,
Set Square
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Please reply to newsgroup. Reply address is invalid.

Thanks for the comprehensive reply, you have given me a couple of things to
think about.

The choice really hinges on whether or not the HW performance is currently
adequate. If it is, go for a C-Plan - it's a lot easier. You will need a
2-port valve in the HW circuit right next to the cylinder, *after* the
vent
pipe tee - so as to maintain an un-interrupted path from the boiler to the
vent pipe. You will, of course also need a cylinder stat and a room stat.
The radiator nearest to the room stat *shouldn't* have a TRV on it. I
presume that you don't get any unwanted gravity circulation in the CH
circuit when the pump is not running?

Not exactly sure on how long it takes to heat HW from cold at the moment- my
guess is that we have a a resonable amount of hot water within about 40 mins
from cold - certainly within an hour. Up to now we have not had a problem
with having hot water (if we have a bath we might stick on the immersion to
"help" the heating) if someone wants a bath straight after. This makes me
inclined to stick with c-plan as you suggest. See below re stats.

.. In order to prevent pumping over, move the fill pipe connection into the
HW
flow pipe - very close to where the vent pipe connects.

Am I right in thinking that if the fill pipe is moved to the HW flow pipe
close to where the vent pipe connects that the system would then effectivly
be a "combined vent and feed"? i.e both vent and feed sharing a pipe back to
the boiler.

I would go for a programmable room stat for several reasons:
* It gives you completely independent control over the timing of HW and
CH -
which most ordinary programmers don't. [Set your main programmer to HW
timed
and CH constant - so that the room stat conrols the CH]
* It adapts to the characteristics of your system/house - and maintains
the
set temperature with less overshoot
* With 'Optimum Start' it decides when to turn the heating on in order to
achieve the set temperature by the required time
* In the 'Off' position, it acts as an automatic frost stat - and still
turns on the heating if needed to prevent freezing

Was going to stick in a programmable room stat in any case - Not sure if a
programmable cylinder stat (AFAIK only Danfoss make one - the WP75) would
be of any use in saving gas? We have hot water all day (house always
occupied), at the moment heating in the morning (no stat), topping up for an
hour at about 2pm, and then again in the evening say 5pm - 10pm. by using a
prog cylinder stat could use cooler water in day (only use it for washing
hands etc) - and hotter in the evening for a bath?

Using a regular cylinder stat we could heat the water in the morning to the
higher temp, similar to before, and then leave it to cool during the day as
it used up, before reheating the water again to the evening tempreture? The
only disadvantage with this is that if the water was used up in the day it
would not be replaced to the evening - a prog cylinder stat would realise
the water usage and reheat the replaced water to the lower temp.

A prog cylinder stat would realise that the temp of the water had fallen,
and then switch on to "top up"


I doubt whether you need a by-pass circuit - even if you go for an S-Plan
system. These are needed when you have a boiler which only holds a small
quantity of water and which will overheat due to the residual heat in the
metal bits if the water isn't carried away quickly enough. Such boilers
are
only used in fully pumped setups - and have pump over-run stats which keep
the pump running after the boiler stops firing until it has cooled down a
bit. The bypass circuit provides somewhere for the water to go if all the
valves are closed.

AFAIK the boiler does have a switch for "fully pumped" - therefore the
valves could be closed and the pump run. Suggesting again to keep to C-Plan

If a boiler works ok on gravity without the pump being on at all (when
operating on HW only), it can pretty certainly take care of itself.

I see your point. Looks like the boiler would be ok left on gravity (i.e no
overrun) - even on a fully pumped syste,

Not sure whether I have answered *all* of the questions. HTH, anyway!


Great. Thanks a lot for your help. I am pretty sure that C-Plan is the way
to go, unless someone come up with something else.

Now I only need to decide between the Honeywell CM67RF or Danfoss TP7000 -
and if to use a regular cylinder stat or programmable cylinder stat!!

Am temped to stick to danfoss with the TP7000 (optimum start/programmable
etc) and a HW cylinder programmeable therm WP75.

http://www.danfoss-randall.co.uk/site/downloads/560.pdf

http://www.danfoss-randall.co.uk/sit...loads/4457.PDF


Cheers,
Set Square

In an earlier contribution to this discussion,
Jason wrote:


. In order to prevent pumping over, move the fill pipe connection
into the HW
flow pipe - very close to where the vent pipe connects.

Am I right in thinking that if the fill pipe is moved to the HW flow
pipe close to where the vent pipe connects that the system would then
effectivly be a "combined vent and feed"? i.e both vent and feed
sharing a pipe back to the boiler.

Sort of. It's probably best to keep them separate, but connect then both
into the same main pipe fairly close together. Mine are connected in a few
inches apart - the idea being that there should't be an appreciable pressure
drop between the connection points. [This only applies to fully pumped
anyway - and you can ignore it if you go C-Plan]

Was going to stick in a programmable room stat in any case - Not sure
if a programmable cylinder stat (AFAIK only Danfoss make one - the
WP75) would be of any use in saving gas? We have hot water all day
(house always occupied), at the moment heating in the morning (no
stat), topping up for an hour at about 2pm, and then again in the
evening say 5pm - 10pm. by using a prog cylinder stat could use
cooler water in day (only use it for washing hands etc) - and hotter
in the evening for a bath?

Using a regular cylinder stat we could heat the water in the morning
to the higher temp, similar to before, and then leave it to cool
during the day as it used up, before reheating the water again to the
evening tempreture? The only disadvantage with this is that if the
water was used up in the day it would not be replaced to the evening
- a prog cylinder stat would realise the water usage and reheat the
replaced water to the lower temp.

A prog cylinder stat would realise that the temp of the water had
fallen, and then switch on to "top up"


I can't see a lot of point in programmable cylinder stats. I suppose if you
really want different temperatures at different times of day, and want more
on/off cycles than are provided by the ordinary programmer, you could make a
case for one. However, if your tank is well lagged, the heat losses should
be very small anyway - and it does little harm keeping the water slightly
hotter than you actually need for some of the time. Features like optimum
start and the ability to adapt to the system are less likely to be useful on
a water heating system.


Now I only need to decide between the Honeywell CM67RF or Danfoss
TP7000 - and if to use a regular cylinder stat or programmable
cylinder stat!!

Use whatever you're comfortable with. I've got a (non-RF) CM67 with optimum
start (they don't all have it) - which I fitted a few months ago to replace
the original conventional room stat. It seems to meet my needs fairly well.
I've also got a conventional cylinder stat, which I don't intend to change.
[FWIW, I've got a Y-plan system - which was in the house when I bought it -
which works adequately but isn't what I would have chosen].

--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Can anyone help me out, and let me know if there is a
simpler/easier/better/more efficient etc etc option before I buy the bits.

The really important question is whether the boiler you have requires a
fully open gravity circuit as a safety measure. If it does (as many ancient
or solid fuel boilers so require) then your options are far more limited.

What make, model and fuel is your boiler?

Christian.

"Christian McArdle" wrote in message
...
Can anyone help me out, and let me know if there is a
simpler/easier/better/more efficient etc etc option before I buy the
bits.

The really important question is whether the boiler you have requires a
fully open gravity circuit as a safety measure. If it does (as many
ancient
or solid fuel boilers so require) then your options are far more limited.

What make, model and fuel is your boiler?

Thanks for your post.

Boiler is Potterton Netaheat running nat gas. According to the potterton
website the boiler can be be gravity or pumped.

Boiler is Potterton Netaheat running nat gas. According to the potterton
website the boiler can be be gravity or pumped.

You're laughing then. Run in whatever way the plumbing works best. Ensure
there is a direct unvalved path from boiler output to vent and a direct
unvalved path from water inlet to boiler return. Then place pumps and valves
where appropriate. You can share valves or use separate as you wish. You can
run each of the 28mm or 22mm system as your desire. Pumps don't count as
valves if in the water inlet path. A fixed (non automatic i.e. gate) bypass
valve counts as a path for the water inlet. If the boiler has an additional
manual reset overheat cutout, then the water inlet restrictions can be
ignored. The water inlet could even be combined with the vent under these
circumstances, which eliminates pumping over.

Christian.

You're laughing then. Run in whatever way the plumbing works best. Ensure
there is a direct unvalved path from boiler output to vent and a direct
unvalved path from water inlet to boiler return.

I still reckon gravity with control is the way to go. as we do not have a
problem with HW recovery time and it is a lot simpler to fit.

Then place pumps and valves where appropriate. You can share valves or use
separate as you wish. You can run each of the 28mm or 22mm system as your
desire. Pumps don't count as valves if in the water inlet path. A fixed
(non automatic i.e. gate) bypass valve counts as a path for the water inlet
If the boiler has an additional manual reset overheat cutout, then the
water inlet restrictions can be ignored. The water inlet could even be
combined with the vent under these circumstances, which eliminates pumping
over.

The boiler is fitted with a manual reset overheat cutout, does this mean
that the 2port could be fitted in the HW circuit close to the boiler? The
vent would still have an open path - and the feed have the 2 port valve
inline but would still be in the HW circuit and stop circulation.. This
contradicts what set square recommened which was to fit a "2-port valve in
the HW circuit right next to the cylinder, *after* the vent pipe tee - so as
to maintain an un-interrupted path from the boiler to the vent pipe" whilst
this has the benefit of leaving the feed and vent open at all time - the
ability to stick the valve in the feed/HW circuit close to the boiler would
mean that I could use a RF tank stat
(http://www.screwfix.com/app/sfd/cat/...30214&ts=48069) and save
running a cable to the loft making fitting extremly simple.

I still reckon gravity with control is the way to go. as we do not have a
problem with HW recovery time and it is a lot simpler to fit.

Not much in it. Just put the pump right next to the zone valve and wired off
it, set on lowest speed. Check for pumping over, both continuous and at pump
start/stop and increase the length of the vent loop over if it does.

The boiler is fitted with a manual reset overheat cutout, does this mean
that the 2port could be fitted in the HW circuit close to the boiler?

Now you're really laughing. This allows you to close off the old feed pipe
and take the F&E cistern feed to the vent pipe with a T. Guaranteed no
pumping over. Only safe with a manual reset overheat boiler. These don't
require the quenching water flow for safety, so can live with having the
pipework blocked by escaping steam until the thermostat blows.

Yes, with such a boiler, you can place the valve anywhere that doesn't
interfere with the vent path.

____
/ \ vent
F&E | | |
|----| |
+--+-+ |
| |
feed +----+
| /---\
| | |
+------+ |
| | / |
| | \ |
| +-----+ |
| | | |
| | +-----+
+--------+ | |
| +--+ |
| Boiler | |
| w.c/o +---+
+--------+

= pump + zone valve (alternative locations)

Hope the picture makes sense!

Christian.

"Jason" wrote in message
...
You're laughing then. Run in whatever way the plumbing works best.
Ensure
there is a direct unvalved path from boiler output to vent and a direct
unvalved path from water inlet to boiler return.

I still reckon gravity with control is the way to go.

It isn't. You already have a pump. You need zone valves on both CH and DHW,
so pump both. Far more efficient. It is silly not to.