"Peter Watson" wrote in message
...
In article ,
says...

4) I'm planning on a system with two zone valves, one for CH and one
for HW ("S-plan" in Honeywell speak). I'd probably be looking at
a programmable room stat (e.g. the Honywell CM-67 or similar) for
controlling the main room temp downstairs and thermostatic valves
everywhere else.

5) If I go with the room stat as described above, this provides both
temp and time control for the heating. What is the customary way
of providing time control for the HW? I can use a normal HW/CH
programmer but this seems overkill for one channel. Do people tend
to rely only on the cylinder stat and leave it on all the time
(does this meet building regs?)?

I have a Honeywell CM67 for heating (mounted in the Hall with TRVs
fitted to all other radiators) and a Horstmann CentaurPlus C11 single
channel timer, in conjunction with a Honeywell cylinder stat, in the
airing cupboard for the HW.

The above is the way, except have a CM67 do upstairs and one do downstairs.
Two totally separate CH zones and independent DHW zone. Do not have a TRV
in the same room as the CM67s



---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

"Dale Shuttleworth" wrote in message
...
Hi,

I'm just getting round to sorting out my new central heating system
and I have a number of things to sort out on the control (and
boiler!) side.

The plan is to use a condensing boiler with normal radiators,
specified for a 60 degree average temperature (i.e. 40 degree
differential). I have a Telford Typhoon H/W cylinder.

Comments are welcomed on the following:

1) I want hot water at 60 degrees, what flow temperature does the
boiler need to be set to to achieve this in a reasonable time?
The Typhoon heat exchanger claims to be rated at 25kW but neglects
little details like the temperature differential necessary to
achieve this.

2) I want to run the radiators at as low a temperature as possible
- for most of the year I suspect they will be sufficiently over-rated
to operate with a 60 degree or even 50 degree flow.

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

The Ravenheat CSi system boiler has a DHW mode. This means wiring the
cylinder stat into the boiler and having a priority system using a 3-way
diverter valve. When the cyl stat switches, the boiler runs up to max
heat, then modulates when back on CH mode.

The MAN, also badged as a ECO-Homtec, has all the control you want. It is
not cheap but if you buy all the controls as separate items you would pay
more. Andy gives a good breakdown on his.

The Celsius will sense the heat load of the cylinder and ramp up the burner
to suit.

4) I'm planning on a system with two zone valves, one for CH and one
for HW ("S-plan" in Honeywell speak). I'd probably be looking at
a programmable room stat (e.g. the Honywell CM-67 or similar) for
controlling the main room temp downstairs and thermostatic valves
everywhere else. Any comments on the best place to site the room
stat (i.e. would the landing be better - the hall is not really a
sensible option since it is very small and hence prone to drafts
when the front door is open)? Any thoughts on the best choice of
stat?

5) If I go with the room stat as described above, this provides both
temp and time control for the heating. What is the customary way
of providing time control for the HW? I can use a normal HW/CH
programmer but this seems overkill for one channel. Do people tend
to rely only on the cylinder stat and leave it on all the time
(does this meet building regs?)?

6) I have noticed things like the Honeywell "Smartfit" system. This
looks like it has everything conveniently integrated with control of
both the CH and HW readily to hand. Does anyone have any views on
things like this? I can see the convenience, I can also see the
nightmare getting spares in ten years time...

7) Bearing in mind that there is really only space for a single flow
and return in the route between the boiler and the rest of the house,
is there a better option than what I'm proposing? I'm quite happy
to look at boilers with more integrated CH/HW control for example
but it needs to be fairly cost effective.

8) Are radiators supposed to radiate - i.e. is there much benefit
to be gained by going for larger single panel radiators rather than
smaller double panel ones? I suspect that most of the heat is lost
in convection in either case but a larger radiant area might have
comfort benefits? (Yes, I have read and understood the underfloor
heating thread - well, the interesting bits anyway, no I'm not
going to install underfloor heating!)

What do you think?

Assess an open vented "integrated" heat bank eliminating the cold water
storage tank. The heat bank can supply the CH and of course instant DHW.
The upstairs and downstairs CH circuits can be taken off the lower part of
the cylinder. Just have a pump and non-return valve on each. You have to
specify the two separate CH take-offs to the maker.

A great advantage is that a cheap condensing boiler may be used. I suggest
the Ravenheat heating condensing boiler. It is only £399 inc VAT from B&Q
and can be open vented. It is a reasonably reliable boiler unlike the old
Ravenheat combi's. Or the Baxi condensing boiler, which can have its load
compensation control switched off by removing a jumper. Again it can be
open vented. The condensing boilers will be efficient enough and depending
on the return temp will condense gining good efficiencies.

A simple, highly effective with many superb advantages and also cheap
solution if your mains supply is adequate.



---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

"IMM" wrote in message
...

"Dale Shuttleworth" wrote in message
...
Hi,

I'm just getting round to sorting out my new central heating system
and I have a number of things to sort out on the control (and
boiler!) side.

The plan is to use a condensing boiler with normal radiators,
specified for a 60 degree average temperature (i.e. 40 degree
differential). I have a Telford Typhoon H/W cylinder.

Comments are welcomed on the following:

1) I want hot water at 60 degrees, what flow temperature does the
boiler need to be set to to achieve this in a reasonable time?
The Typhoon heat exchanger claims to be rated at 25kW but neglects
little details like the temperature differential necessary to
achieve this.

2) I want to run the radiators at as low a temperature as possible
- for most of the year I suspect they will be sufficiently over-rated
to operate with a 60 degree or even 50 degree flow.

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

The Ravenheat CSi system boiler has a DHW mode. This means wiring the
cylinder stat into the boiler and having a priority system using a 3-way
diverter valve. When the cyl stat switches, the boiler runs up to max
heat, then modulates when back on CH mode.

The MAN, also badged as a ECO-Homtec, has all the control you want. It is
not cheap but if you buy all the controls as separate items you would pay
more. Andy gives a good breakdown on his.

The Celsius will sense the heat load of the cylinder and ramp up the
burner
to suit.

4) I'm planning on a system with two zone valves, one for CH and one
for HW ("S-plan" in Honeywell speak). I'd probably be looking at
a programmable room stat (e.g. the Honywell CM-67 or similar) for
controlling the main room temp downstairs and thermostatic valves
everywhere else. Any comments on the best place to site the room
stat (i.e. would the landing be better - the hall is not really a
sensible option since it is very small and hence prone to drafts
when the front door is open)? Any thoughts on the best choice of
stat?

5) If I go with the room stat as described above, this provides both
temp and time control for the heating. What is the customary way
of providing time control for the HW? I can use a normal HW/CH
programmer but this seems overkill for one channel. Do people tend
to rely only on the cylinder stat and leave it on all the time
(does this meet building regs?)?

6) I have noticed things like the Honeywell "Smartfit" system. This
looks like it has everything conveniently integrated with control of
both the CH and HW readily to hand. Does anyone have any views on
things like this? I can see the convenience, I can also see the
nightmare getting spares in ten years time...

7) Bearing in mind that there is really only space for a single flow
and return in the route between the boiler and the rest of the house,
is there a better option than what I'm proposing? I'm quite happy
to look at boilers with more integrated CH/HW control for example
but it needs to be fairly cost effective.

8) Are radiators supposed to radiate - i.e. is there much benefit
to be gained by going for larger single panel radiators rather than
smaller double panel ones? I suspect that most of the heat is lost
in convection in either case but a larger radiant area might have
comfort benefits? (Yes, I have read and understood the underfloor
heating thread - well, the interesting bits anyway, no I'm not
going to install underfloor heating!)

What do you think?

Assess an open vented "integrated" heat bank eliminating the cold water
storage tank. The heat bank can supply the CH and of course instant DHW.
The upstairs and downstairs CH circuits can be taken off the lower part of
the cylinder. Just have a pump and non-return valve on each. You have to
specify the two separate CH take-offs to the maker.

A great advantage is that a cheap condensing boiler may be used. I
suggest
the Ravenheat heating condensing boiler. It is only £399 inc VAT from B&Q
and can be open vented. It is a reasonably reliable boiler unlike the old
Ravenheat combi's. Or the Baxi condensing boiler, which can have its load
compensation control switched off by removing a jumper. Again it can be
open vented. The condensing boilers will be efficient enough and
depending
on the return temp will condense gining good efficiencies.

A simple, highly effective with many superb advantages and also cheap
solution if your mains supply is adequate.

I just looked at the B&Q web site. The Ravenheat appears not to be there
anymore. The Celsius is now cheaper than the Baxi. The Glow Worm is well
priced.
http://www.discountedheating.co.uk/s..._Condensing_Co
mbi_Boiler.html




---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

"Ed Sirett" wrote in message
...

I thought that I might have a problem with the single control on my own
Keston C. 25

I have experimented quite a bit to see what is the lowest setting I can
run the boiler on and still get HW.

The cylinder (Standard modern copper with fast coil)

Is this a proper quick recovery or a stardard Part L?




---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

Hi,

Andy Hall ) wrote:
: On Fri, 29 Aug 2003 23:26:54 GMT, (Dale
: Shuttleworth) wrote:

[...]

: 1) I want hot water at 60 degrees, what flow temperature does the
: boiler need to be set to to achieve this in a reasonable time?
: The Typhoon heat exchanger claims to be rated at 25kW but neglects
: little details like the temperature differential necessary to
: achieve this.
:
: You could contact the manufacturer for this but it would be 10 degrees
: approx for a conventional boiler, normally 20 for a condensing model.

Sorry, I was talking about the differential between the HW and the
boiler flow. Obviously, a given flow/return temp differential at a
given flow rate will deliver a given amount of power to the water,
I was hoping that I could deliver a reasonable amount of power with
a small flow / HW differential.

[...]

: 2) I want to run the radiators at as low a temperature as possible
: - for most of the year I suspect they will be sufficiently over-rated
: to operate with a 60 degree or even 50 degree flow.
:
: Almost certainly yes. I assume from what you've said that you have
: done the radiator derating calculations. Don't forget to derate
: further if you plan to do anything that obscures radiators like
: covers.

Yep, I've done the necessary derating calculations, looked at
radiators, got confused when there was a significant difference
in radiator size between Myson and Barlo for the same output,
scratched my head, read the data sheets again, realised that they
each quote based on different temp differentials, did my calcs
again and (I hope!) got it right. (Too late now - I got the
rads today!).

: 3) If I go for a simple boiler like the Keston Celsius then I suspect
: that the two requirements above may be somewhat incompatible.
:
: The Celsius will still do a respectable job, because it will attempt
: to supply heat as required by the load. For the radiators, when the
: weather is warmer, the TRVs will tend to close down and reduce the
: heat demand. The pump speed will drop, as will the boiler firing
: rate. Since the boiler is monitoring all the temperatures, it will
: try to get the flow and return to as low values as possible, while
: still delivering the required load.

This is the bit I don't understand. What is the boiler control
attempting to control? In the case of the Celsius, I assume that
it is attempting to control the flow to a temperature set by that
little knob on the front of the boiler. In addition, I assume that
once the temperature set point is reached, the boiler reduces its
output to maintain the minimum possible return temperature whilst
still maintaining the set flow temp.

The upshot of this is that I would think that the flow temperature
will remain constant but the return temp will fluctuate with demand.

In the absence of other inputs, the boiler cannot possibly know the
real heating load since the load is proportional to the flow temp.
If the boiler backed off the flow temperature when the return
temperature was high for example then it would effectively back off
the load leading to a very economical but ineffective system.

Of course, in the case of a clever boiler like the Micromat then
there are other inputs and the boiler can play games with the flow
temperature to reach maximum efficiency.

: When there is demand to heat the DHW, the boiler will "see" a fairly
: heavy heat load. This is because by the time the cylinder thermostat
: operates, there is already going to be a fair amount of cold water in
: the bottom of the cylinder. Therefore, the return water temperature
: will be fairly cool as well and the boiler will view it as a hefty
: heat load and fire up accordingly.
:
: As the DHW temperature approaches the set point, the boiler may start
: to back off a little as it sees the return temperature rising.

Yes, but I assume it won't back off the flow temperature, only the
power input, maintaining the flow but dropping the return temp.

The real question I have is that assuming I want hot water at 60
degrees then how low can I set the flow temperature on the boiler?
I'm hoping for something like 65 degrees.

[...]

: 4) I'm planning on a system with two zone valves, one for CH and one
: for HW ("S-plan" in Honeywell speak). I'd probably be looking at
: a programmable room stat (e.g. the Honywell CM-67 or similar) for
: controlling the main room temp downstairs and thermostatic valves
: everywhere else. Any comments on the best place to site the room
: stat (i.e. would the landing be better - the hall is not really a
: sensible option since it is very small and hence prone to drafts
: when the front door is open)? Any thoughts on the best choice of
: stat?
:
: Remember that if you use the living room as your controlled room, you
: can't really have any other form of heating in there like a gas fire
: because it will have the effect of backing the heating off to the rest
: of the house.

My concern at the moment is that I know the radiators upstairs will
be grossly overrated so I'm reluctant to put the thermostat on the
landing, even though all the rads will have thermostatic valves. The
radiator for the hall (and hence landing) is slightly underrated due
to space constraints. Last year with no radiator in the hall, there
was a very discernable temperature gradient as you went down the
stairs - there is a risk that I will have the same thing again but
to a lesser extent this year.

The downstairs radiators are fairly close to the mark for the rooms
they are in but at the moment downstairs as a whole is 1500W short
since I haven't planned anything for the kitchen - nowhere to put
anything (see question below). I have no other heating downstairs
at present (but I do have a hearth for a gas fire - if I do install
something it will be decorative rather than for heating though).

The hall or main room downstairs seem like the best bets under these
circumstances. (Someone suggested the kitchen but I think thats
cheating!).

[...]

: 6) I have noticed things like the Honeywell "Smartfit" system. This
: looks like it has everything conveniently integrated with control of
: both the CH and HW readily to hand. Does anyone have any views on
: things like this? I can see the convenience, I can also see the
: nightmare getting spares in ten years time...
:
: It is potentially quite a nice solution and can also be integrated
: with some home automation systems like www.comfort.org.uk
:
: Since it is Honeywell,who enjoy a good reputation, I would not be
: overly bothered, but the valves are proprietary.

I've decided to give it a try.

[...]

The only remaining issue now is the kitchen. At the moment I'm
probably going to survive this winter with it being heated
incidentally from elsewhere downstairs. There isn't space for a
radiator and I'm wary of the reliability of these fanned under
unit things - anyone have any experience of them?

Dale.

Hi,

Ed Sirett ) wrote:

[...]

: I thought that I might have a problem with the single control on my own
: Keston C. 25
:
: I have experimented quite a bit to see what is the lowest setting I can
: run the boiler on and still get HW.
:
: The cylinder (Standard modern copper with fast coil) is set to 60C. If I
: run the boiler at 50% setting the
: behaviour is stunningly good. 30 seconds full power, then a glide down
: to minumum over 10-15minute, then off because the cylinder has been
: reheated.
:
: If I had longer flow return circuit to the cylinder the inital flat out
: might be longer.
:
: When I run the boiler at about 45% then the glide down is faster and the
: boiler will spend a bit longer on its lowest setting.
:
: When I run the boiler at 40% then the minimum setting goes on for about
: twenty minutes. The boiler then indicates 'can't go low enough' (fast
: red flashing) but still heats the tank.
:
: I moved it to 50% and am totally happy with the operation. I guess if I
: wanted the 'standard' 65C HW then I'd have to move the control up a bit.
: Because the reheat time is so short it permits having the HW cylinder a
: bit less hot.

Thats extremely useful info - thanks Ed.

Am I right that the little knob effectively controls the flow temp by the
way? - None of the Keston literature actually says anything useful about
what it does.

Dale.

"Andy Hall" wrote in message

As to whether or not to leave the HW on, I think it depends on pattern
of use and on the cylinder.
I have a situation with humans and teenagers, where there may be a
requirement for a bath or shower at any time apart from about 4 hrs in
24.

Are teenagers not human?

Suzanne
"You can't scare me, I've got children."

In article , Dale Shuttleworth
writes
Hi,

I'm just getting round to sorting out my new central heating system
and I have a number of things to sort out on the control (and
boiler!) side.

The plan is to use a condensing boiler with normal radiators,
specified for a 60 degree average temperature (i.e. 40 degree
differential). I have a Telford Typhoon H/W cylinder.

Hi Dale, sounds like you are in the same position as I was about 8 months
ago. In the end I chose a Keston Celsius 25 boiler and a huge Range
Superduty cylinder .

Comments are welcomed on the following:

1) I want hot water at 60 degrees, what flow temperature does the
boiler need to be set to to achieve this in a reasonable time?
The Typhoon heat exchanger claims to be rated at 25kW but neglects
little details like the temperature differential necessary to
achieve this.
Mine is very happy set to 65deg. This has the boiler firing flat out (4lights
25kW) for most of the reheat time then dropping to about half power for the
last few minutes as the differential drops. I played with it a little lower but
(as expected) it took ages on the lowest modulation to reach final heat
(stat at 60deg)

2) I want to run the radiators at as low a temperature as possible
- for most of the year I suspect they will be sufficiently over-rated
to operate with a 60 degree or even 50 degree flow.
Yup, I like to turn the boiler stat down & just have a background heat, very
comfortable and sort of self regulating as the temp diff between rads and
room reduces.

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).
It was these two boilers I shortlisted for my installation. IMO the MAN ,
with it's proportional control, DHW setting and very low minimum
modulation, walks all over the Keston for this kind of job, but in the end I
just couldn't justify the extra cost. The lack of a separate DHW demand on
the Keston is a major flaw, but I plumped for it knowing that I would be
attempting a bodge to correct the problem. The solution relies on pulling
the output of the boiler stat control when DHW demand is on. This is a
straightforward job as the control panel board is separate from the main
electronics and can be achieved with a mod to the loom comprising a relay
and a few resistors. If discovered, it would of course in validate your
warranty so is not for everyone. I will publish the mod here when it is fully
tested.

4) I'm planning on a system with two zone valves, one for CH and one
for HW ("S-plan" in Honeywell speak). I'd probably be looking at
a programmable room stat (e.g. the Honywell CM-67 or similar) for
controlling the main room temp downstairs and thermostatic valves
everywhere else. Any comments on the best place to site the room
stat (i.e. would the landing be better - the hall is not really a
sensible option since it is very small and hence prone to drafts
when the front door is open)? Any thoughts on the best choice of
stat?
I went a little daft here and have one zone per room . . . . Individual stats
(small remote electronic affairs) are being added to the rooms as I
refurbish. In the mean time I just rely on the TRVs and have constructed a
long duration lockout to stop the boiler short cycling. I'm not a fan of the
single stat master control type system but I realise that is what most
people have to work with. From what I gather, don't put it in a room with
auxiliary heat sources, kitchen or lounge. Hall sounds bad (cold), landing
sounds bad (rising heat), how about half way up the stairs . . . . no really.

5) If I go with the room stat as described above, this provides both
temp and time control for the heating. What is the customary way
of providing time control for the HW? I can use a normal HW/CH
programmer but this seems overkill for one channel. Do people tend
to rely only on the cylinder stat and leave it on all the time
(does this meet building regs?)?
Mine is on all the time, but can be switched off manually. With an 8 deg
differential on my cyl stat, I haven't found the boiler cycling to maintain 60.

6) I have noticed things like the Honeywell "Smartfit" system. This
looks like it has everything conveniently integrated with control of
both the CH and HW readily to hand. Does anyone have any views on
things like this? I can see the convenience, I can also see the
nightmare getting spares in ten years time...
Dunno

7) Bearing in mind that there is really only space for a single flow
and return in the route between the boiler and the rest of the house,
is there a better option than what I'm proposing? I'm quite happy
to look at boilers with more integrated CH/HW control for example
but it needs to be fairly cost effective.
Dunno

8) Are radiators supposed to radiate - i.e. is there much benefit
to be gained by going for larger single panel radiators rather than
smaller double panel ones? I suspect that most of the heat is lost
in convection in either case but a larger radiant area might have
comfort benefits? (Yes, I have read and understood the underfloor
heating thread - well, the interesting bits anyway, no I'm not
going to install underfloor heating!)
Mainly convection. I view double panels as ugly and horribly point sourced
heat wise, single convectors to be huge but best for comfort as the heat
comes from a large area. I compromised with plenty of Stelrad P+ rads
which are double panels with a single convector, just a bit slimmer and
less obtrusive than double panels. I used mainly 600mm high units as
these seem to blend in quite well, plus taller ones where more heat density
was required and smaller single panels near large windows.

What do you think?
sounds good :-)

Good luck
--
fred

"fred" wrote in message ...
In article , Dale Shuttleworth

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

It was these two boilers I shortlisted for my installation. IMO the MAN ,
with it's proportional control, DHW setting and very low minimum
modulation, walks all over the Keston for this kind of job, but in the end
I
just couldn't justify the extra cost. The lack of a separate DHW demand on
the Keston is a major flaw, but I plumped for it knowing that I would be
attempting a bodge to correct the problem. The solution relies on pulling
the output of the boiler stat control when DHW demand is on.

"pulling the output"? What do you mean?

This is a
straightforward job as the control panel board is separate from the main
electronics and can be achieved with a mod to the loom comprising a relay
and a few resistors. If discovered, it would of course in validate your
warranty so is not for everyone. I will publish the mod here when it is
fully
tested.

Are you forcing the boiler to full unmodulated power when DHW calls? BTW,
the Ravenheat CSI system boiler has this function. Why any load
compensation modulating boiler does not have this simple function is beyond
me. It can be selectable, by moving jumpers, if need be.




---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

In article , IMM abuse-
writes

"fred" wrote in message ...
In article , Dale Shuttleworth

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

It was these two boilers I shortlisted for my installation. IMO the MAN ,
with it's proportional control, DHW setting and very low minimum
modulation, walks all over the Keston for this kind of job, but in the end
I
just couldn't justify the extra cost. The lack of a separate DHW demand on
the Keston is a major flaw, but I plumped for it knowing that I would be
attempting a bodge to correct the problem. The solution relies on pulling
the output of the boiler stat control when DHW demand is on.

"pulling the output"? What do you mean?
Wait for the published white paper :-) . . . .

The control is set by a potentiometer, by judicious use of a few resistors
and a relay, the control board can be fooled into thinking the demand on
the pot is set to a higher level when DHW demand is on.


This is a
straightforward job as the control panel board is separate from the main
electronics and can be achieved with a mod to the loom comprising a relay
and a few resistors. If discovered, it would of course in validate your
warranty so is not for everyone. I will publish the mod here when it is
fully
tested.

Are you forcing the boiler to full unmodulated power when DHW calls? BTW,
the Ravenheat CSI system boiler has this function. Why any load
compensation modulating boiler does not have this simple function is beyond
me. It can be selectable, by moving jumpers, if need be.
Output level for DHW set by a separate trimmer pot, not necessarily full
power. Quite a failing I think, from speaking to them they didn't seem to
think so tho', "the 40 has got it", er yes. Perhaps that makes the
Ravenheat a better choice for this app then, I have no experience of them.

--
fred

"fred" wrote in message ...
In article , IMM abuse-
writes

"fred" wrote in message ...
In article , Dale Shuttleworth

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

It was these two boilers I shortlisted for my installation. IMO the MAN
,
with it's proportional control, DHW setting and very low minimum
modulation, walks all over the Keston for this kind of job, but in the
end
I
just couldn't justify the extra cost. The lack of a separate DHW demand
on
the Keston is a major flaw, but I plumped for it knowing that I would
be
attempting a bodge to correct the problem. The solution relies on
pulling
the output of the boiler stat control when DHW demand is on.

"pulling the output"? What do you mean?
Wait for the published white paper :-) . . . .

The control is set by a potentiometer, by judicious use of a few resistors
and a relay, the control board can be fooled into thinking the demand on
the pot is set to a higher level when DHW demand is on.

An old trick, switch out the pot, with the relay, and bring in a resistance
that equals the desired setpoint on the pot.

With older fixed rate boilers I found it best to keep the boiler stat set to
max for DHW, and switch in a pipe stat on the flow for CH. With load
compensation control on modern condensers, that is impossible.

This is a
straightforward job as the control panel board is separate from the
main
electronics and can be achieved with a mod to the loom comprising a
relay
and a few resistors. If discovered, it would of course in validate your
warranty so is not for everyone. I will publish the mod here when it is
fully
tested.

Are you forcing the boiler to full unmodulated power when DHW calls?
BTW,
the Ravenheat CSI system boiler has this function. Why any load
compensation modulating boiler does not have this simple function is
beyond
me. It can be selectable, by moving jumpers, if need be.

Output level for DHW set by a separate trimmer pot, not necessarily full
power. Quite a failing I think, from speaking to them they didn't seem to
think so tho', "the 40 has got it", er yes. Perhaps that makes the
Ravenheat a better choice for this app then, I have no experience of them.




---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003

Dale Shuttleworth wrote:

Hi,

Andy Hall ) wrote:
: On Fri, 29 Aug 2003 23:26:54 GMT, (Dale
: Shuttleworth) wrote:

[...]

: 1) I want hot water at 60 degrees, what flow temperature does the
: boiler need to be set to to achieve this in a reasonable time?
: The Typhoon heat exchanger claims to be rated at 25kW but neglects
: little details like the temperature differential necessary to
: achieve this.
:
: You could contact the manufacturer for this but it would be 10 degrees
: approx for a conventional boiler, normally 20 for a condensing model.

Sorry, I was talking about the differential between the HW and the
boiler flow. Obviously, a given flow/return temp differential at a
given flow rate will deliver a given amount of power to the water,
I was hoping that I could deliver a reasonable amount of power with
a small flow / HW differential.

[...]

: 2) I want to run the radiators at as low a temperature as possible
: - for most of the year I suspect they will be sufficiently over-rated
: to operate with a 60 degree or even 50 degree flow.
:
: Almost certainly yes. I assume from what you've said that you have
: done the radiator derating calculations. Don't forget to derate
: further if you plan to do anything that obscures radiators like
: covers.

Yep, I've done the necessary derating calculations, looked at
radiators, got confused when there was a significant difference
in radiator size between Myson and Barlo for the same output,
scratched my head, read the data sheets again, realised that they
each quote based on different temp differentials, did my calcs
again and (I hope!) got it right. (Too late now - I got the
rads today!).

: 3) If I go for a simple boiler like the Keston Celsius then I suspect
: that the two requirements above may be somewhat incompatible.
:
: The Celsius will still do a respectable job, because it will attempt
: to supply heat as required by the load. For the radiators, when the
: weather is warmer, the TRVs will tend to close down and reduce the
: heat demand. The pump speed will drop, as will the boiler firing
: rate. Since the boiler is monitoring all the temperatures, it will
: try to get the flow and return to as low values as possible, while
: still delivering the required load.

This is the bit I don't understand. What is the boiler control
attempting to control? In the case of the Celsius, I assume that
it is attempting to control the flow to a temperature set by that
little knob on the front of the boiler. In addition, I assume that
once the temperature set point is reached, the boiler reduces its
output to maintain the minimum possible return temperature whilst
still maintaining the set flow temp.

The upshot of this is that I would think that the flow temperature
will remain constant but the return temp will fluctuate with demand.

In the absence of other inputs, the boiler cannot possibly know the
real heating load since the load is proportional to the flow temp.
If the boiler backed off the flow temperature when the return
temperature was high for example then it would effectively back off
the load leading to a very economical but ineffective system.

Of course, in the case of a clever boiler like the Micromat then
there are other inputs and the boiler can play games with the flow
temperature to reach maximum efficiency.

: When there is demand to heat the DHW, the boiler will "see" a fairly
: heavy heat load. This is because by the time the cylinder thermostat
: operates, there is already going to be a fair amount of cold water in
: the bottom of the cylinder. Therefore, the return water temperature
: will be fairly cool as well and the boiler will view it as a hefty
: heat load and fire up accordingly.
:
: As the DHW temperature approaches the set point, the boiler may start
: to back off a little as it sees the return temperature rising.

Yes, but I assume it won't back off the flow temperature, only the
power input, maintaining the flow but dropping the return temp.

The real question I have is that assuming I want hot water at 60
degrees then how low can I set the flow temperature on the boiler?
I'm hoping for something like 65 degrees.

[...]

: 4) I'm planning on a system with two zone valves, one for CH and one
: for HW ("S-plan" in Honeywell speak). I'd probably be looking at
: a programmable room stat (e.g. the Honywell CM-67 or similar) for
: controlling the main room temp downstairs and thermostatic valves
: everywhere else. Any comments on the best place to site the room
: stat (i.e. would the landing be better - the hall is not really a
: sensible option since it is very small and hence prone to drafts
: when the front door is open)? Any thoughts on the best choice of
: stat?
:
: Remember that if you use the living room as your controlled room, you
: can't really have any other form of heating in there like a gas fire
: because it will have the effect of backing the heating off to the rest
: of the house.

My concern at the moment is that I know the radiators upstairs will
be grossly overrated so I'm reluctant to put the thermostat on the
landing, even though all the rads will have thermostatic valves. The
radiator for the hall (and hence landing) is slightly underrated due
to space constraints. Last year with no radiator in the hall, there
was a very discernable temperature gradient as you went down the
stairs - there is a risk that I will have the same thing again but
to a lesser extent this year.

The downstairs radiators are fairly close to the mark for the rooms
they are in but at the moment downstairs as a whole is 1500W short
since I haven't planned anything for the kitchen - nowhere to put
anything (see question below). I have no other heating downstairs
at present (but I do have a hearth for a gas fire - if I do install
something it will be decorative rather than for heating though).

The hall or main room downstairs seem like the best bets under these
circumstances. (Someone suggested the kitchen but I think thats
cheating!).

[...]

: 6) I have noticed things like the Honeywell "Smartfit" system. This
: looks like it has everything conveniently integrated with control of
: both the CH and HW readily to hand. Does anyone have any views on
: things like this? I can see the convenience, I can also see the
: nightmare getting spares in ten years time...
:
: It is potentially quite a nice solution and can also be integrated
: with some home automation systems like www.comfort.org.uk
:
: Since it is Honeywell,who enjoy a good reputation, I would not be
: overly bothered, but the valves are proprietary.

I've decided to give it a try.

[...]

The only remaining issue now is the kitchen. At the moment I'm
probably going to survive this winter with it being heated
incidentally from elsewhere downstairs. There isn't space for a
radiator and I'm wary of the reliability of these fanned under
unit things - anyone have any experience of them?

Dale.

I should really have snipped the above...
I think the MO of the Keston is to control the return temperature and
then set the boiler power and pump speed so that the flow temperture is
about 20C hotter. This method of control seems to acheive to lowish
return temperatures.

I am reassured that whilst doing HW only the boiler can still make
condensate.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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

"Keith Refson - real email address in signature" wrote
in message ...
(Dale Shuttleworth) writes:

6) I have noticed things like the Honeywell "Smartfit" system. This
looks like it has everything conveniently integrated with control of
both the CH and HW readily to hand. Does anyone have any views on
things like this? I can see the convenience, I can also see the
nightmare getting spares in ten years time...

Not a long-term view, but I just installed one of these last week. Of
course your guess about the long-term prospects is about as good as
mine. I did get a couple of comments from the Plumb Centre that they
hadn't sold very many, and that it didn't seem to be catching on. I
guess your typical british "heating engineer" is still more
comfortable with mechanical or steam-powered control systems....

From the point of view of installation it was very easy, (apart from
the metal-bashing required to fit the base unit as a replacement for
the programmer in my old boiler). Certainly routing 3 tiny control
cables is a lot easier and neater than 3 twin+earth mains cables for
an S-plan system with HW thermostat

Multi-core cable is easily available and much neater than 2 T&E


---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003