Does it matter which way water circulates in an indirect hot water cylinder coil
Tim Snell
I hope that title gave the right impression.
Over the past week I have had to replace an old indirect HW cylinder
due to a number of leaks.
I have replaced the old (900x450 - 120L) with a larger one (1200x450 -
162L). It was pretty much a straight swap apart from changing the
shower pump connection from an essex flange to a surrey flange.
Certainly I have not changed the layout of pipes to the coil from the
boiler.
The system is a 1992 vintage Johnson Starley warm air unit 'J50' or
something like that with a built in Eljan water heater. The water
heater is used exclusively for indirect heating of the water
cylinder. The system is 'gravity fed' with the cylinder directly
above the bolier displaced by about 2m horizontally. unlagged 22mm
copper throughout
There were some fun and games along the way, most notably a stubborn
airlock in the coil which I cleared using mains pressure via a hose
into the vent pipe in the loft. The system is now 'working' in that I
have hot water. However I had never really examined the old system
prior to the last week but since giving my undivided attention in the
evenings I have noticed something, I think, is wrong.
Flow comes from the bolier into the coil/heat exchanger at the bottom
of the cylinder and exits at the top before returning to the boiler.
I think this seems wrong (detrimental to gravity feed, heat exchanger
ideally should be hottest at top, flow pipework from boiler needs to
be very hot), the diagram here suggests it is wrong.
http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm
I have a few questions
Q1 Is there any way the flow in a gravity fed system can get reversed?
Sounds stupid I know but how is the flow normally encouraged in one
direction - any valves or just position and layout of pipes and heat
exchanger
Q2 Bearing in mind the system seems to work now (and I have *not*
changed the setup) how bad is it to have it plumbed like this?
Inefficient, slower to heat tank, dangerous.
Q3 Is this 'mistake' common, are there any legitimate reasons for
doing it this way and should I change it or am I worrying about
nothing
Thanks
Tim
Grimly Curmudgeon
drugs began to take hold. I remember Tim Snell
<tim.a...@googlemail.com> saying something like:
>Q2 Bearing in mind the system seems to work now (and I have *not*
>changed the setup) how bad is it to have it plumbed like this?
>Inefficient, slower to heat tank, dangerous.
Inefficient, certainly; slower to heat the tank, yes; dangerous,
probably not.
I've seen a couple of cack-handed installations that worked, but
depended on a great roaring fire to get flow going and were always on
the verge of kettling in the back boiler. One of them was as you
described and the other, while plumbed in correctly as regards flow, was
damn near defiant of the law of gravity.
If it were me, I'd re-plumb the coil connections.
TheScullster
"Grimly Curmudgeon" wrote
>
> If it were me, I'd re-plumb the coil connections.
If you do, add a bleed at the highest point to get rid of air in the coil
(if your system doesn't have one already)
Phil
d...@gglz.com
use:
RobertL
> Right... long time no posting,
>
> I hope that title gave the right impression.
>
> Over the past week I have had to replace an old indirect HW cylinder
> due to a number of leaks.
>
> I have replaced the old (900x450 - 120L) with a larger one (1200x450 -
> 162L). It was pretty much a straight swap apart from changing the
> shower pump connection from an essex flange to a surrey flange.
> Certainly I have not changed the layout of pipes to the coil from the
> boiler.
>
> The system is a 1992 vintage Johnson Starley warm air unit 'J50' or
> something like that with a built in Eljan water heater. The water
> heater is used exclusively for indirect heating of the water
> cylinder. The system is 'gravity fed' with the cylinder directly
> above the bolier displaced by about 2m horizontally. unlagged 22mm
> copper throughout
Why not lag the upgoing pipe, especially right near the boiler. That
should help get the flow going more quickly (and in he right
direction).
Robert
Tim Snell
wrote:
> Inefficient, certainly; slower to heat the tank, yes; dangerous,
> probably not.
> I've seen a couple of cack-handed installations that worked, but
> depended on a great roaring fire to get flow going and were always on
> the verge of kettling in the back boiler. One of them was as you
> described and the other, while plumbed in correctly as regards flow, was
> damn near defiant of the law of gravity.
>
When you say 'as you described' what do you mean? I can not
categorically say that it is plumbed incorrectly as I do not really
know which 22mm pipe coming out of the boiler is the flow and which
the return. One has a draincock attached and the other has a probe
thermocouple phial in it.
So perhaps the water is now stubbornly going the wrong way in which
case I want to address this rather than the 'quick' (anything other
given the access restrictions) fix of replumbing the coil
> If it were me, I'd re-plumb the coil connections.
I am inclined to agree - which is why I posted in the first place
really I just wanted to gauge opinion.
Tim Snell
I have made sure that all pipe is angled up to the vent pipe so
hopefully this will achieve the same result
Tim Snell
Once issues are resolved I intend to lag the bits I can see. As
posted above to be effective it does require very high temp in the
boiler and indirect pipework which is not pleasant in the summer.
Tim
>>
> When you say 'as you described' what do you mean? I can not
> categorically say that it is plumbed incorrectly as I do not really
> know which 22mm pipe coming out of the boiler is the flow and which
> the return. One has a draincock attached and the other has a probe
> thermocouple phial in it.
Given that the boiler is the heat source and that hot water is less dense
than cold, in a gravity system the top pipe on the boiler has pretty much
got to be the "flow" and the bottom the "return".
The reason for the flow being connected to the top of the cylinder coil is
so that there is always a temperature gradient between the coil and the
surrounding water, maximising heat transfer. The water from the bottom of
the coil will be as cold as it can possibly get in such a system which will
improve its return to the boiler and hence gravity flow through the system.
> So perhaps the water is now stubbornly going the wrong way in which
> case I want to address this rather than the 'quick' (anything other
> given the access restrictions) fix of replumbing the coil
>
>> If it were me, I'd re-plumb the coil connections.
>
> I am inclined to agree - which is why I posted in the first place
> really I just wanted to gauge opinion.
You could add a pump whilst you're there. Although gravity systems work, a
fully pumped system works an awful lot better. Depending on your hot water
demands, you could notice a vast improvement in your cylinder's "recovery"
time.
Tim D
Heliotrope Smith
news:339d25cc-c091-4b87...@g29g2000yqe.googlegroups.com:
> On Feb 3, 11:49�am, Grimly Curmudgeon <grimly4REM...@REMOVEgmail.com>
> wrote:
>
>> Inefficient, certainly; slower to heat the tank, yes; dangerous,
>> probably not.
>> I've seen a couple of cack-handed installations that worked, but
>> depended on a great roaring fire to get flow going and were always on
>> the verge of kettling in the back boiler. One of them was as you
>> described and the other, while plumbed in correctly as regards flow,
>> was damn near defiant of the law of gravity.
>>
> When you say 'as you described' what do you mean? I can not
> categorically say that it is plumbed incorrectly as I do not really
> know which 22mm pipe coming out of the boiler is the flow and which
> the return. One has a draincock attached and the other has a probe
> thermocouple phial in it.
>
The pipe with the thermostat pocket is the flow and the lower pipe with
the drain off is the return. You should be able to trace the flow pipe
to the top connection on your cylinder. If this is not teed off to vent
into a feed/expansion tank then you are most likely to have a direct
cylinder.
Are you sure you have an indirect cylinder or do you mean "direct"
which doese not have a coil which is the usual set up for your hot water
circulator type?
Do you have a large and a small tank in the loft or just a large tank?
(It is not unknown to have indirect cylinders on these but is not very
common.)
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
Tim Snell
I am absolutely sure it is indirect! I replaced the cylinder and
plumbed the coil.
Many of the houses on the 'estate' built circa 1970 with warm air
systems have later been converted with a similar heater to mine but
with a primatic cylinder. Mine, however, is definitely indirect.
Tim Snell
> > I am inclined to agree - which is why I posted in the first place
> > really I just wanted to gauge opinion.
>
> You could add a pump whilst you're there. Although gravity systems work, a
> fully pumped system works an awful lot better. Depending on your hot water
> demands, you could notice a vast improvement in your cylinder's "recovery"
> time.
>
> Tim D
I would like to add a pump but I am not sure how I would 'control'
this. In previous CH systems I have owned the boiler took care of the
when to start stop the pump based on feedback from thermocouples etc.
Very crudely I could probably add a pump so that when gas is burned
the pump circulates but normally you would want it to run on for a
bit.