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  #1   Report Post  
Mr Fizzion
 
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Default Secondary Circulation loop on a combi

Can you have such a thing or is this one of Doctor Evil's fantasies?

If you can...how would you do it?

TIA

Mr F.

  #2   Report Post  
Christian McArdle
 
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Can you have such a thing or is this one of Doctor Evil's fantasies?

If you can...how would you do it?


You'd do it the same as any secondary circulation loop. It doesn't really
matter what the heating appliance is, provided there are no pressure
reducing devices such as TRVs or air breaks (i.e. cold water cisterns)
actually in the loop. These may be before the loop, however.

However, not all combis would be suited to a secondary circulation loop.
They work better on a storage based system as an instantaneous combi will
cycle with much greater rapidity than a system boiler off a storage
cylinder.

Christian.


  #3   Report Post  
Aidan
 
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Mr Fizzion wrote:
Can you have such a thing or is this one of Doctor Evil's fantasies?


Assuming youre referring to a secondary circulation loop on the hot
water supply system, then;

The combi fires on a draw off from the hot water outlets. The only way
I could imagine installing a circulation loop would be to install a
heat exchanger (tube-in-shell, preferably) on the secondary return and
pipe the primary side of the HX as a zone on heating. You'd need the
heating to operate 365 days. You could use an electric heater.

There are also electric trace heating system for hws, which are
installed under thermal insulation to minimize the heat loss from the
pipes. These don't need a circulation loop.

If you're doing that you'd be better off installing an unvented hot
water storage cylinder ( which has got a heat exchanger & has got a
large volume of water, so it won't discharge scalding water if the
controls overshoot the set-point slightly). If you're doing that, you
might as well scrap the combi and put in a conventional hot water
storage system.

You should realise that Drivel is a moron and his rantings should be
treated accordingly.

  #4   Report Post  
John Rumm
 
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Mr Fizzion wrote:

Can you have such a thing or is this one of Doctor Evil's fantasies?


It ought to work on "simple" combis so long as the manufacturer states
it is ok for the "cold" inlet temp to much hotter than it usually would.
You also need a combi that can operate on very low mains pressure (so
that it will work correctly when the flow is being driven by the pump
and not the mains).

However you could potentially run into all sorts of difficulties with a
modern combi that uses a more sophisticated control loop, or one that
includes a small store of tempered water so as to give "instant" hot water.

If you can...how would you do it?


Timer, pipe stat, check valves, secondary circulation pump, loads of
good insulation on the pipe run etc. You would then need to juggle stat
temperatures carefully to get the operation you require without ending
up in a deadlock state with the pipe stat demanding heat and the combi
HW stat satisfied and hence inhibiting the burner (and the result that
the boiler sits in HW mode for extended periods while the house gets cold).

--
Cheers,

John.

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  #5   Report Post  
Ed Sirett
 
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On Wed, 28 Sep 2005 13:43:02 +0100, Mr Fizzion wrote:

Can you have such a thing or is this one of Doctor Evil's fantasies?

If you can...how would you do it?


For me this is just plain nonsense.

1) I doubt very much whether any manufacture would permit the boiler to be
used in this way.
2) The boiler is not designed to take luke warm let alone hot water as
it's input.
3) All the while the 2ndry pump is going the boiler is in DHW mode. When
does the house get heated?
4) The whole system would rely on the boiler shutting down because the
primary is at or over its maximum temperature for DHW mode. This will only
happen when the DHW temperature is very hot. Ergo the heat losses on the
2ndry loop will be huge.
5) Whilst the burner is shutdown the fan will still be going so that the
primary will be losing heat at a rate comparable with the burner rating
i.e. tens of kW. This is going straight out the flue!
6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html




  #6   Report Post  
John Rumm
 
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Ed Sirett wrote:

For me this is just plain nonsense.


I would agree that the concept has serious flaws in many cases.

1) I doubt very much whether any manufacture would permit the boiler to be
used in this way.
2) The boiler is not designed to take luke warm let alone hot water as
it's input.


Those two are likely to be show stoppers anyway...

3) All the while the 2ndry pump is going the boiler is in DHW mode. When
does the house get heated?


That is where the pipe stat and the timer comes in I suppose. Once the
loop is up to temperature it kills the pump and allows it to return to
heating mode. The big problem will be the heat capacity (or more the
lack of it) of the pipework - it will get cold quickly.

4) The whole system would rely on the boiler shutting down because the
primary is at or over its maximum temperature for DHW mode. This will only
happen when the DHW temperature is very hot. Ergo the heat losses on the
2ndry loop will be huge.


Where do most boilers sample the DHW output temperature. in the DHW flow
on on the return of the primary for example?

5) Whilst the burner is shutdown the fan will still be going so that the
primary will be losing heat at a rate comparable with the burner rating
i.e. tens of kW. This is going straight out the flue!
6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.


Circumventable with a doublecheck valve?

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).


Indeed ;-)

--
Cheers,

John.

/================================================== ===============\
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\================================================= ================/
  #7   Report Post  
Doctor Drivel
 
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"Aidan" wrote in message
oups.com...

Mr Fizzion wrote:
Can you have such a thing or is this one of Doctor Evil's fantasies?


Assuming youre referring to a secondary circulation loop on the hot
water supply system, then;

The combi fires on a draw off from the hot water outlets. The only way
I could imagine installing a circulation loop would be to install a
heat exchanger (tube-in-shell, preferably) on the secondary return


Boy are you confused.

  #8   Report Post  
Doctor Drivel
 
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"John Rumm" wrote in message
...
Mr Fizzion wrote:

Can you have such a thing or is this one of Doctor Evil's fantasies?


It ought to work on "simple" combis so long as the manufacturer states
it is ok for the "cold" inlet temp to much hotter than it usually would.
You also need a combi that can operate on very low mains pressure (so
that it will work correctly when the flow is being driven by the pump
and not the mains).

However you could potentially run into all sorts of difficulties with a
modern combi that uses a more sophisticated control loop, or one that
includes a small store of tempered water so as to give "instant" hot

water.

What difficulties might these be? Or did you make that up?

If you can...how would you do it?


Timer, pipe stat, check valves, secondary circulation pump,


Can be booster pump to achieve the pressure to operate the combi.
http://www.heatweb.com/products/pumps/homebooster.html
Plumb Center also sell them. You also need a time clock to switch off
during the night.

loads of good insulation on the pipe run etc. You would then need to

juggle stat
temperatures carefully to get the operation you require without ending
up in a deadlock state with the pipe stat demanding heat and the combi
HW stat satisfied and hence inhibiting the burner (and the result that
the boiler sits in HW mode for extended periods while the house gets

cold).

Set the pipe stat to 40C


  #9   Report Post  
Christian McArdle
 
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2) The boiler is not designed to take luke warm let alone hot water as
it's input.


But I suspect most boilers would cope for the minute or two operation
period.

That is where the pipe stat and the timer comes in I suppose. Once the
loop is up to temperature it kills the pump and allows it to return to
heating mode. The big problem will be the heat capacity (or more the
lack of it) of the pipework - it will get cold quickly.


It only needs to be on for about one minute to heat the loop. Then the loop
will stay hot for many minutes with a high hysterysis thermostat satisfied.
Obviously any secondary circulation system would have to be very well
insulated. This applies to all types.

It will still cycle the boiler much more than a storage based system,
though. However, I don't see this as a show stopper, just a disadvantage.

6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.


I can't see how this applies to secondary circulation loops. They aren't
really closed loops.

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).


Indeed ;-)


Whilst I'm no fan of permanently on secondary circulation loops in most
cases due to energy efficiency reasons, I can see the benefit of a manually
operated (i.e. 2 minute timed) system in a domestic property, as it would be
very effective at water conservation. A manually operated system would also
actually save energy, as the reheated water will start at a higher
temperature than fresh mains.

Christian.



  #10   Report Post  
Doctor Drivel
 
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"Ed Sirett" wrote in message
news
On Wed, 28 Sep 2005 13:43:02 +0100, Mr Fizzion wrote:

Can you have such a thing or is this one of Doctor Evil's fantasies?

If you can...how would you do it?


For me this is just plain nonsense.


On what does he base this wild claim on....we shall see....

1) I doubt very much whether any manufacture would permit the boiler to be
used in this way.


The boiler is not being monkied about with.

2) The boiler is not designed to take luke warm let alone hot water as
it's input.


Some are and most are really. See makers. Many accept very hot water from
solar preheated water. Eco-Hometec for e.g. The cold inlet to most combi's
is just a pipe to a plate heat exchanger and a flow switch. Nothing there
to say 40C water will screw the system up.

3) All the while the 2ndry pump is going the boiler is in DHW mode. When
does the house get heated?


You really can't figure this out can you. A highly insulated loop from the
outlet to the inlet with pipe stat set to 40C means that the loop will be
warm within a minute or so and then be switched off, amd stay off for a long
time. There are keep warm boilers around. The same thing but extended to
outside the boiler casing.

4) The whole system would rely on the boiler shutting down because the
primary is at or over its maximum temperature for DHW mode.


What are you on about?

This will only
happen when the DHW temperature is very hot. Ergo the heat losses on the
2ndry loop will be huge.


Again. What are you on about?

5) Whilst the burner is shutdown the fan will still be going so that the
primary will be losing heat at a rate comparable with the burner rating
i.e. tens of kW. This is going straight out the flue!


More confusion.

6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.


Not so. Thermal store are done this way. Here are The DPS Heat bank makers
giving advice on uk.d-i-y on how to connect up a heat bank using "exactly"
this method.
http://tinyurl.com/cfet8

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).


What tripe. The basin and washroom may be way off from the combi, so
looping the DHW makes sense. In fact a secondary circulation loop saves a
hell of a lot of water and gives instant DHW at the taps, which is a great
convenience.

Have a look at the one box AVC Heatmaster for a system in your view is not
grown up.

...and you are a professional? Struth.



  #11   Report Post  
Doctor Drivel
 
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"John Rumm" wrote in message
...
Ed Sirett wrote:

For me this is just plain nonsense.


I would agree that the concept has serious flaws in many cases.


What serious flaws might these be?

1) I doubt very much whether any manufacture would permit the boiler to

be
used in this way.
2) The boiler is not designed to take luke warm let alone hot water as
it's input.


Those two are likely to be show stoppers anyway...


Any evidence of this? Or just making it up again.

3) All the while the 2ndry pump is going the boiler is in DHW mode. When
does the house get heated?


That is where the pipe stat and the timer comes in I suppose. Once the
loop is up to temperature it kills the pump and allows it to return to
heating mode. The big problem will be the heat capacity (or more the
lack of it) of the pipework - it will get cold quickly.


Not it heavily lagged.

4) The whole system would rely on the boiler shutting down because the
primary is at or over its maximum temperature for DHW mode. This will

only
happen when the DHW temperature is very hot. Ergo the heat losses on the
2ndry loop will be huge.


Where do most boilers sample the DHW output temperature. in the DHW flow
on on the return of the primary for example?


DHW outlet

5) Whilst the burner is shutdown the fan will still be going so that the
primary will be losing heat at a rate comparable with the burner rating
i.e. tens of kW. This is going straight out the flue!
6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.


Circumventable with a doublecheck valve?


A rank DIYer and confused professional agreeing with each other. My, oh,
my!

If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or thermal
store).


Indeed ;-)


A rank DIYer and confused professional agreeing with each other. My, oh,
my! The professional should stick to Vaillants.


  #12   Report Post  
Doctor Drivel
 
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Default


"Christian McArdle" wrote in message
. net...
2) The boiler is not designed to take luke warm let alone hot water as
it's input.


But I suspect most boilers would cope for the minute or two operation
period.

That is where the pipe stat and the timer comes in I suppose. Once the
loop is up to temperature it kills the pump and allows it to return to
heating mode. The big problem will be the heat capacity (or more the
lack of it) of the pipework - it will get cold quickly.


It only needs to be on for about one minute to heat the loop. Then the

loop
will stay hot for many minutes with a high hysterysis thermostat

satisfied.
Obviously any secondary circulation system would have to be very well
insulated. This applies to all types.

It will still cycle the boiler much more than a storage based system,


On what do you base this article of faith?

though. However, I don't see this as a show stopper, just a disadvantage.

6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.


I can't see how this applies to secondary circulation loops. They aren't
really closed loops.


Yep, you are right.

If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or thermal
store).


Indeed ;-)


Whilst I'm no fan of permanently on secondary circulation loops in most
cases due to energy efficiency reasons,


6 of 1/2 dozen of the other. You save a hell of a lot in water wastage
which on a meter you pay for. Then the convenience. Most people who use
the front door toilet (cloakroom) very rarely wash their hands in hot water,
because of the long lag.

I can see the benefit of a manually
operated (i.e. 2 minute timed) system in a domestic property, as it would

be
very effective at water conservation. A manually operated system would

also
actually save energy, as the reheated water will start at a higher
temperature than fresh mains.


I have seen a pump on the DHW draw-off pipe activated by a flow switch.
This pumps out water from a cylinder pronto reducing the lag



  #13   Report Post  
Christian McArdle
 
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It will still cycle the boiler much more than a storage based system,

On what do you base this article of faith?


It is based on the fact that a storage based solution will be able to
perform a considerable amount of secondary loop heating service before this
activates the vessel thermostat, allowing the boiler to perform a slightly
longer more efficient burn.

With an instantaneous combi, the combi must fire every time the secondary
loop pump activates, and in the worst case, if the loop circulation is slow,
it might even be below the modulation threshold, so it might even have to
cycle to maintain primary temperature, although careful design can eliminate
this.

Therefore, even in a best case scenario, the instantaneous combi fires every
time the loop thermostat calls for heat, whilst the storage based system
could service for hours without boiler assistance, with sufficient capacity
and thermostat hysterysis/double thermostat.

Christian.


  #14   Report Post  
Doctor Drivel
 
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"Christian McArdle" wrote in message
. net...
It will still cycle the boiler much more than a storage based system,


On what do you base this article of faith?


It is based on the fact that a storage based solution will be able to
perform a considerable amount of secondary loop heating service before

this
activates the vessel thermostat, allowing the boiler to perform a slightly
longer more efficient burn.

With an instantaneous combi, the combi must fire every time the secondary
loop pump activates, and in the worst case, if the loop circulation is

slow,
it might even be below the modulation threshold, so it might even have to
cycle to maintain primary temperature, although careful design can

eliminate
this.

Therefore, even in a best case scenario, the instantaneous combi fires

every
time the loop thermostat calls for heat, whilst the storage based system
could service for hours without boiler assistance, with sufficient

capacity
and thermostat hysterysis/double thermostat.


A secondary circulation loop is well, a secondary circulation loop. Whether
there is a large cylinder on the loop or an instant water heat makes no
difference. The loop will cool no quicker on any of them.

You could have a few small DHW vessels on the loop, in series, like under
sink units, have a pressure vessel too. So when you draw off small volumes
of water at the local point, the combi does not kick in as there will be no
flow through the boiler until the pressure has dropped - avoids nuisance
firing. There could be a thermostat on each small vessel to fire the combi
to replenish the vessel of DHW. A Dutch/Belgian company did somthing
similar to this - distributed storage giving instant water at the taps. The
total volume of all the vessels is enough to fill a bath.



  #15   Report Post  
Aidan
 
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Doctor Drivel wrote:

You could have a few small DHW vessels


snip.

Thanks for clarifying that for us all, Dr. Drivel, I'm sure that's all
crystal clear now.


Is it just me, or can anyone else detect the tiniest soupcon of utter
********?



  #16   Report Post  
Mr Fizzion
 
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On Thu, 29 Sep 2005 00:21:22 +0100, Ed Sirett
wrote:

2) The boiler is not designed to take luke warm let alone hot water as
it's input.

One would hope the boiler can handle lukewarm water at least for a
couple of minutes. My loft sometimes reaches 50 celsius in the summer
and there will be a few litres of water in the pipe at possibly over
20 celsius.

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).

Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!

Mr F.

  #17   Report Post  
Doctor Drivel
 
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"Aidan" through a wall of brainache wrote in message
oups.com...

Doctor Drivel wrote:

You could have a few small DHW vessels


snip.

Thanks for clarifying that for us all, Dr. Drivel, I'm sure that's all
crystal clear now.


To normal people it would be....but....

Is it just me,


It is you for sure.

or can anyone else detect the tiniest soupcon of utter
********?


Those with brains can't detect any at all, so precluding you. Sad but true.


  #18   Report Post  
Doctor Drivel
 
Posts: n/a
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"Mr Fizzion" wrote in message
...
On Thu, 29 Sep 2005 00:21:22 +0100, Ed Sirett
wrote:

2) The boiler is not designed to take luke warm let alone hot water as
it's input.

One would hope the boiler can handle lukewarm water at least for a
couple of minutes. My loft sometimes reaches 50 celsius in the summer
and there will be a few litres of water in the pipe at possibly over
20 celsius.


More like 30 to 35C My mains temperature is 19C right now

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).


Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!


It does save on water too.


  #19   Report Post  
Christian McArdle
 
Posts: n/a
Default

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).


Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!


Actually, there is some environmental benefit as well as a convenience one,
due to the reduced wastage of water. I would suggest that a secondary loop
that has a boost button that you can press before have a bath, or before
sitting on the toilet (so it is ready when you finish) means that energy is
actually saved as well as water. However, a secondary loop constantly on
connected to a combi is likely to be somewhat wasteful of energy.

Christian.


  #20   Report Post  
Matt
 
Posts: n/a
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"Doctor Drivel" wrote:

You could have a few small DHW vessels on the loop, in series, like under
sink units, have a pressure vessel too. So when you draw off small volumes
of water at the local point, the combi does not kick in as there will be no
flow through the boiler until the pressure has dropped - avoids nuisance
firing.


All combi firing unless it is in a high velocity trajectory towards
the sun is a waste of time

There could be a thermostat on each small vessel to fire the combi
to replenish the vessel of DHW. A Dutch/Belgian company did somthing
similar to this - distributed storage giving instant water at the taps.


You've been eating them funny mushrooms again haven't you?

The total volume of all the vessels is enough to fill a bath.


Yes of course it is.

Get back to that counter Dribble. Copper sales are going through the
roof but a few more sales won't go amiss.


--


  #21   Report Post  
Matt
 
Posts: n/a
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"Doctor Drivel" wrote:

My mains temperature is 19C right now


That's the output from the combi you fool.

It does save on water too.


No it doesn't, you have much to learn and so little time before you
get locked up again.



--
  #22   Report Post  
Doctor Drivel
 
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"Christian McArdle" wrote in message
. net...
If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or thermal
store).


Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!


Actually, there is some environmental benefit as well as a convenience

one,
due to the reduced wastage of water. I would suggest that a secondary loop
that has a boost button that you can press before have a bath, or before
sitting on the toilet (so it is ready when you finish) means that energy

is
actually saved as well as water. However, a secondary loop constantly on
connected to a combi is likely to be somewhat wasteful of energy.


Have a flow switch on the lines to the toilets. When a flush the pump comes
on. Or have an infra red sensor in the kitchen too. When occupied the pump
runs. People in the kitchen tend to use water. Still have pipe stat when
it reaches 40-45C.

Using a pipe stat in a well insuated loop would mean the pump would not
cycle too often anyhow.


  #23   Report Post  
Doctor Drivel
 
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"Matt" the resident space cadet wrote in
message ...
"Doctor Drivel" wrote:

You could have a few small DHW vessels on the loop, in series, like under
sink units, have a pressure vessel too. So when you draw off small

volumes
of water at the local point, the combi does not kick in as there will be

no
flow through the boiler until the pressure has dropped - avoids nuisance
firing.


All combi firing unless it is in a high velocity trajectory towards
the sun is a waste of time


Our space cadet is into the sun again. I wonder how much that Treki uniform
cost him.


  #24   Report Post  
Doctor Drivel
 
Posts: n/a
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"Matt" our resident space cadet wrote in
message ...
"Doctor Drivel" wrote:

My mains temperature is 19C right now


That's the output from the combi you fool.


Must an intergalactical combi.

It does save on water too.


No it doesn't,


...confusion has set in.


  #25   Report Post  
Doctor Drivel
 
Posts: n/a
Default


"Christian McArdle" wrote in message
. net...
If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or thermal
store).


Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!


Actually, there is some environmental benefit as well as a convenience

one,
due to the reduced wastage of water.


If using a mains pressure system having hot water within 1 second at the tap
mean that kettles can be filled with hot water reducing electricity
consumption quite a bit. It pays for itself in more ways than one.




  #26   Report Post  
Matt
 
Posts: n/a
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"Doctor Drivel" wrote:


"Christian McArdle" wrote in message
.net...
If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or thermal
store).

Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do it.
Since it seems not to be I shall be content with waiting 30 seconds!


Actually, there is some environmental benefit as well as a convenience

one,
due to the reduced wastage of water.


If using a mains pressure system having hot water within 1 second at the tap
mean that kettles can be filled with hot water reducing electricity
consumption quite a bit. It pays for itself in more ways than one.


But the figures simply don't stack up and you can't prove it "pays for
itself" True but sad.


--
  #27   Report Post  
Doctor Drivel
 
Posts: n/a
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"Matt" from where the clouds are blue and
birds say cuckoo wrote in message
...
"Doctor Drivel" wrote:


"Christian McArdle" wrote in message
.net...
If a house needs a secondary loop it also needs a grown up heating

system
that will include a stored HW of some type (vented, unvented or

thermal
store).

Having hot water in less than a second is a luxury rather than a
necessity. If it were easily possible with my new combi I would do

it.
Since it seems not to be I shall be content with waiting 30 seconds!

Actually, there is some environmental benefit as well as a convenience

one,
due to the reduced wastage of water.


If using a mains pressure system having hot water within 1 second at the

tap
mean that kettles can be filled with hot water reducing electricity
consumption quite a bit. It pays for itself in more ways than one.


But


Yes, but. Me thinks Matt is not really Matt. Me thinks he is an old poster
from here.


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Default Secondary Circulation loop on a combi

Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).

So secondary loop of any sort would seem to help alleviate this waste.

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Default Secondary Circulation loop on a combi

12L per person per day of waster water with combi on average.
Immense time savings (3s vs 30s).

People can buy combi for 2000 or for 700, Implementing this loop would make 700 boiler surpass 2000 one with convenience at fraction of a cost.

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Default Secondary Circulation loop on a combi

There is many ways to regulate the frequency I reckon e.g. hysteresis, timer).
Nevertheless, adding some buffer close to the outlets could greatly help with cycling - e.g. couple of litres of pipe storage.

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Default Secondary Circulation loop on a combi

In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).


So secondary loop of any sort would seem to help alleviate this waste.


Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

--
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Dave Plowman London SW
To e-mail, change noise into sound.
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Default Secondary Circulation loop on a combi

On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).


So secondary loop of any sort would seem to help alleviate this waste.


Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?


More expensive combis have a setting that keeps firing the
burners occasionally to keep the primary circuit hot. This allows
faster hot water performance but uses more gas.
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Default Secondary Circulation loop on a combi

On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).


So secondary loop of any sort would seem to help alleviate this waste.


Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

DHW circulation is standard in larger buildings, without it there would
be huge water wastage as people wait for hot water to reach the taps. I
control mine with a pipe stat and a timer.
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Default Secondary Circulation loop on a combi

In article ,
wrote:
On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).


So secondary loop of any sort would seem to help alleviate this waste.


Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

DHW circulation is standard in larger buildings, without it there would
be huge water wastage as people wait for hot water to reach the taps. I
control mine with a pipe stat and a timer.


But that will be from a storage system. A combi is connected to mains
water.

--
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Dave Plowman London SW
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Default Secondary Circulation loop on a combi

On 23/10/2020 18:46, Dave Plowman (News) wrote:
In article ,
wrote:
On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).

So secondary loop of any sort would seem to help alleviate this waste.

Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

DHW circulation is standard in larger buildings, without it there would
be huge water wastage as people wait for hot water to reach the taps. I
control mine with a pipe stat and a timer.


But that will be from a storage system. A combi is connected to mains
water.

True, I was responding to your comment and didn't spot that the subject
was about combi boilers.


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Default Secondary Circulation loop on a combi

In article ,
wrote:
On 23/10/2020 18:46, Dave Plowman (News) wrote:
In article ,
wrote:
On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).

So secondary loop of any sort would seem to help alleviate this waste.

Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

DHW circulation is standard in larger buildings, without it there would
be huge water wastage as people wait for hot water to reach the taps. I
control mine with a pipe stat and a timer.


But that will be from a storage system. A combi is connected to mains
water.

True, I was responding to your comment and didn't spot that the subject
was about combi boilers.


Didn't potable water give you a clue?

You can circulate a stored system in a house to give quicker hot from a
tap. Whether it is worth it in cash terms, I doubt it.

--
*The older you get, the better you realize you were.

Dave Plowman London SW
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Default Secondary Circulation loop on a combi

On 24/10/2020 11:14, Dave Plowman (News) wrote:
In article ,
wrote:
On 23/10/2020 18:46, Dave Plowman (News) wrote:
In article ,
wrote:
On 23/10/2020 16:14, Dave Plowman (News) wrote:
In article direct.com,
mafj wrote:
Recent research that in UK households with combis kitchen water use is 2.5 higher than other systems. (18L vs 7.2L per person per day).
And the most likely reason pointed out is time for HW to arrive).

So secondary loop of any sort would seem to help alleviate this waste.

Not sure circulating water within a potable supply is either allowed or a
good idea. And just when were we short of water in the UK?

DHW circulation is standard in larger buildings, without it there would
be huge water wastage as people wait for hot water to reach the taps. I
control mine with a pipe stat and a timer.

But that will be from a storage system. A combi is connected to mains
water.

True, I was responding to your comment and didn't spot that the subject
was about combi boilers.


Didn't potable water give you a clue?

You can circulate a stored system in a house to give quicker hot from a
tap. Whether it is worth it in cash terms, I doubt it.

Errr ... my hot water is potable, is on a circulation loop, and is based
on a 300 litre unvented cylinder. Search for potable dhw circulation
pump for more info.
I agree that it's probably not financially worthwhile to have a
circulation loop, but in a large house (or hotel) it's a convenience
that's worth paying for. My boiler and DHW cylinder are in a plant room
(the old coal store) with quite long runs to the furthest bedroom and
bathroom; when the circulation pump is off it can take a very long time
to get hot water out of the tap or shower.
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