On Sat, 4 Sep 2004 21:53:07 +0100, "IMM" wrote:
..
It does if it is going to be involved
in an efficient control system
where the heat output to the radiators
and the heating space are
measured
They are measured by the weather compensator, with any room temp influence
to drop the slope if need be.
It should be the other way round of course. We are not trying to
control the weather here, but the temperature in the house.
The outside temperature is monitored to provide a correction to the
slope.
and controlled without lag,
then it most certainly does.
No lag. A mass of water the temperature required is available.
OK, so you don't understand the meaning of the term "lag" in a control
system. There is no point in discussing its influence in that case.
I said *may*, and it will only be in so
far as a difference between an
analogue sensor on the cylinder
and a thermostat with substantial
hysteresis on the boiler.
Thermostat on the boiler is on full, and will rarely cut out on this.
OK, so this means that you are relying on the external weather
compensator, which is controlling the boiler by switching.
So are you saying that the external
controller doesn't control the
boiler by turning it on and off.
No.
That's good. I just wanted to be clear on that.
You'll be telling me that it
operates a motor on the gas tap next.
Nope I will not.
That's a relief.
and b) not operating
at the optimum temperature
Failed again.
If it is a condensing boiler, on/off control with full output or
nothing will not operate it efficiently.
You fail to understand condensing boilers, or boilers at all.
It seems that I understand rather more than you do.
A boiler will
only raise water a certain temperature with a given flowrate through the
heat exchanger.
Correct - actually it's more like maximum temperature.
The flow through it can be constant, as no TRVs used. If
say at x flowrate it raises the water 25C, if the return is 30C only 55C
come out of the flow. Way below the boiler stat set to 82C. When the mass
of water is heated the boiler stat would have never have cut in to cycle the
boiler, so one long efficient burn.
Obviously the boiler won't be cycling on its internal thermostat,
assuming it is set high. It will be being switched by the fact
that the rate of heat production will exceed the use by the CH.
This cannot be as efficient as running the boiler continuously at the
level of the radiator heat load. You are also assuming an ideal
(in the engineering sense) heatbank where there is no mixing and
churning of the internal water. This will have the effect of
raising the temperature sensed by your controller higher than it would
otherwise be and reducing the run time. If the return were directly
from the radiators there would be much less mixing and the return
temperature is therefore much more indicative of the actual real load.
- unless you are talking about a
non-condensing boiler as well, of course.
If you use a modulating boiler
and attempt to control it in an on/off
fashion as an external simple weather
compensator will try to do, then
the efficiency will be worsened as
compared with allowing the boiler
to monitor the radiator water temperature
directly.
Failed again. When on it heats a large
mass of water. This confuses you.
That is sad.
The trouble is that it doesn't.
You are rarther silly now.
If that is your best reply, then there is no point in discussing the
point further.
On the one hand you are saying that you are going to have part of a
heatbank operating at a set point and being maintained that way by
controlling the heat going in. By definition, if you do that with a
non-modulating boiler with power output level larger, probably
substantially larger than the rate of use by the radiators, then you
will have to cycle the boiler.
The boiler does not cycle when re-heating the mass. Operation: heats the
mass of water mass cools - mass is reheated all at once with "no" boiler
cycling - heat extracted from the water mass by the rad circuit - mass is
reheated all at once with "no" boiler cycling .
This is physically impossible. If the heat input from the boiler is
greater than the heat use and you are not modulating the boiler
output, by definition your controller has to cycle it off and then
back on again. This is less efficient than matching the boiler
output accurately to the load.
not because of running temperatures). If you do that, you
are going to have to let the heatbank (or part thereof in use)
discharge all of its heat before running the boiler again.
This will result in cooling and heating of the radiators, a
fluctuation in heat output and a variation in room temperature.
Any fluctuation would be minimal.
That will depend on how you set the operating window of the heatbank.
the mass of water takes time to cool.
It will cool at the rate determined by the use through the radiator
circuit.
It
is not like hot water running though a rad circuit return pipe. very little
mass and less mass in the whole rad circuit than in the stored water mass by
at "least" half as much. The water mass stabilises operation.
It simply causes control lag, but I know that you don't understand the
concept. I know that you don't know what "mass" means.
Your supposition assumes that the volume of water in the heatbank is
twice that of the radiators and pipes. Are you seriously suggesting
installing a 200l heat bank just to run the radiators?
You can't have it both ways.
The element that is intended to be
controlled is the room
temperature, not the water temperature
of the heatbank.
Your comprehension is poor. The boiler/heat bank
maintain the lowers section
of the heat bank at the temperature that
the rads require for optimum
performance. That is very simple.
It is very simple, and you have it wrong.
Failed again. It is right it is just above.
As I said, you can't have it both ways.
Failed again.
It seems that you have,
You have added a bunch of complexity and achieved poorer efficiency.
Less complexity, as simple cheaper boiler is used.
Plus an extra controller, an extra pump, valves and sensors.
You haven't saved any money either
No expensive 1.5K bpoioer to be bought.
The only person who raised the subject of £1500 or £1000 boilers was
you in an attempt to divert attention away from your farcical idea.
Sorry, but it won't wash.
You also introduced the idea of an external boiler controller using an
outside sensor and applied in a way for which it wasn't designed and
controlling a boiler in an inappropriate way. You can't even find
one that is suitable for what you think you are trying to do.
Please provide a make and model
number of one of these "simpler boilers"
at around £400 Discounted
Heating prices, that is anywhere near the
quality of a WB Greenstar.
You have a thing about £400.
I do, because that is the comparison point; not your £1500 figure.
Further to that there is nothing to be
gained by having a heatbank in the
radiator part of the load at all in
this instance.
A heat bank a neutral point. A great advantage.
Only in circumstances where
a) multiple heat sources are being combined or
b) when there is a need to store heat because of the requirement of
large amounts to heat water, or
c) when the boiler, because of its sizing and limited or no control
range would naturally cycle.
This is not any of those cases.
It is. Even a modulating boiler cycles when demand is below the minimum kW.
Yes of course it does, but at that point - usually around 4-7kW, it
doesn't matter anyway. In practice, this only happens for a very
short period anyway.
With a heat bank, no cycling.
It is cycling because the controller is switching it off and on, and
as part of the normal operation. It *always* does this.
The boiler and rads operate
independently of each other. Constant flow can be through the boiler at
all
times.
That's clearly nonsense.
Failed again. The boiler and rads operate independently of each other.
Once again your normal MO when you don't understand something -
selectively clip.
It is anyway irrelevant if the flow is continuous through the boiler -
there aren't any sensors as there are with a modulating boiler.
The only way that they can operate truly
independently is by having two heat banks.
Are you advocating that now?
failed again.
So is it two heatbanks or one?
The heat requirement into the cylinder will be quite different for DHW
vs. CH. In the former case, it will be maximum transfer after water
has been run. In the latter, either the heat will have to be fed in
at the rate of use (less than the boiler maximum output) or at full
power for short periods.
failed again. Full power for the re-heat time in one burn.
Sigh.... Until the heatbank depletes, the thermostat on the cylinder
comes on and the boiler runs again, then goes off because the
thermostat is satisfied, ad infinitum. This is cycling.
Where you have got the idea of constant flow from, goodness only
knows. If you mean constant water flow, regardless of demand, it is
going to be wasteful when neither CH nor DHW are demanding heat.
More failure. Boilers have an optimum flow through the heat exchanger.
Which is obviously dependent on the rate of heat production for
optimised results and why some modulating boilers also modulate the
pump.
You have not only a switched boiler, but one which always runs at full
power and with the same flow rate. Three efficiency reducing factors.
No silly pressure diif valves needed. Rads with TRVs can be
virtually off and the boiler doesn't know or care.
There aren't anyway. If the pump is integral to the boiler,
Heating boilers don't have them integrated, well most don't.
The term is semantic, which is why I was careful to say "integral
pump".
I'm not repeating the obvious, and I'm certainly not about to educate
you about control systems.
Be sure, you will not educate me on control systems.
Believe me, I reached that conclusion a very long time ago!!.
Not if the controller is operating
the boiler by turning it on and
off, which it will have to do in the
case of a non modulating one.
Switches on - one long bur to setpoint - switches off. Simple.
Yep. Simple cycling.
This is how the BEM5000 works.
All that the heatbank is doing is to
add a lag in the control path.
failed again. not so.
There's little else
c) A commercial system, where there is an external energy management
system having multiple analogue sensors inside and out, and able to
monitor the water temperatures. This type of controller is able to
control a boiler or boilers which are able to modulate, but by the use
of some kind of digital signal (PWM or coded), or via an analogue
control voltage or current (e.g. 4-20mA, 0-10v etc.)
Your proposal is for something that is basically a type a)
arrangement, but you are claiming that it is equivalent to or better
than type b) or c). This is patent nonsense.
None of your points has a heat bank incorporated, so squewed.
Again. All that the heatbank does is to
introduce a lag in the control system.
You can either choose to keep it topped up with heat
on a tight setpoint window, in which case the boiler will have to be
cycled a lot, or you can let the heatbank temperature drop by the use
of a wide window in which case it will cycle less and the radiator
temperatures will drop.
drop by not much at all.
It will drop by what you want it to drop by. Either you can maintain
the temperature near the set point and the boiler will cycle more
frequently, or you can allow a larger drop and the radiator
temperatures will drop.
If you switch to maintaining the temperature
of part of the heatbank to maintain a set point
according to the outside temperature, you
introduce a double control loop.
Nope.
Of course you do. One loop is from boiler to heatbank, the other
from heatbank via radiators to room.
Only one loop. Boiler to heat bank, dictated to by outsoide waether
conditions.
There is also the room thermostat or TRVs as an outer loop.
room stat? no there is not. TRVs are not in the boioere control loop.
The TRVs are in the second control loop. If you remember, you
earlier said that there was only one loop. In fact in your scheme,
there are at least three.
The heatbank is not representative of the characteristics of the
radiator heat load.
It provides a mass of water at the temperaure the rads want. The heat bank
doesn't care about the rad heat load, it just provides the mass of water for
the rads to use.
You're running round in ever decreasing circles now. Earlier you
made a big point about the external weather compensator maintaining an
appropriate temperature for the radiators. Now you are saying that
it doesn't matter. You can't make up your mind whether you want the
heatbank temperature to be maintained or rise and fall dramatically.
In short you are guessing.
es.
It is not the only model. It saves the cost of a 1.5K boiler.
Please provide an example
of a suitable weather compensating
controller at the same or lower price
than the BEM5000.
All the big makers make compensators at low prices.
I see. Please name some and provide the prices.
Please also explain how you believe that on/off controlling a simple
boiler is more efficient than a modulating, condensing one.
Please read all of this thread again.
You have got to be joking.
Please explain where the figure of £1.5k comes into this.
The discussion is around something like a WB Greenstar with price
point of £725. It's not good trying to justify your argument by
adding in £800 of cost which is irrelevant.
biolers with built-in load compensation modulation and waether compensation
are well north of 1K
This is not the comparison that we are making. The simple solution
was of a modulating boiler running the radiators directly. You have
added in all the complexity of weather compensators hooked up to
external controllers whose purpose is to switch cycle old
non-modulating boilers in an attempt to make them a bit more efficient
in the system.
Clearly a modulating boiler with an external temperature sensor
directly hooked in is going to outperform one without and certainly
your scheme. Therefore there is little point in doing a comparison
on this basis.
THe arithmetic is between a good quality modulating boiler at £725 vs.
the cost of some alleged "simple" boiler at £400 plus your controls at
£300.
You are making things up.
You're looking in the wrong place. You're trying to alter the basis
of the discussion to a different price point and different
functionality and efficiency.
Stick to the question. Where are these simple £400 good quality
boilers?
The issue is still one of energy in vs. energy
out.
In and out of what? less energy into the boiler for energy out.
The heatbank, obviously.
Microbore can be used when both go back to one
neutral point.
This is irrelevant as well. Microbore is simply a size of tube.
There is nothing magic about it.
Look up how microbore operates.
I know full well how microbore operates. It's copper tube. End of
story.
The inside analogue sensor would
normally be used on the boiler return,
Or boiler flow, which most operate on.
Used on the heat bank here.
Er no.
Er yes, depending on application.
Sigh.....
The important temperature for condensing efficiency is the
boiler return temperature
Lower the flow and the return follows suit.
Well obviously. Most modulating boilers that I have seen have both
flow and return sensors.
For other control applications this
is also commonplace because it
gives an indication of what the thermal
load is doing.
Using a heat bank the thermal load is irrelevant. The boiler doesn't
care
about it.
Oh dear. Of course it's relevant.
Not as far as the boioer is concerned.
Not directly because your boiler has no sensors. Taking the system as
a whole, it is highly relevant.
You introduced the idea of weather compensation as a means to control
the heatbank temperature, just so that you could hook up the radiators
to it - a completely pointless exercise.
Using a heat bank load compensating modulation is not required.
You can equally argue that with a modulating boiler with a room
temperature analogue sensor that outside weather compensation isn't
required.
You should find out the advantage of weather compensation.
I know the advantages of weather compensation, properly implemented,
quite well, thanks. I have such an arrangement, remember.
I also have the ability to log precisely what the boiler is doing in
terms of burn rate, fan operation, pump operation and 6 different
system temperatures.
So you mean a non modulating boiler?
Yes.
These are not as efficient as
modulating types by definition,
failed again. They are. It depends on how it is controlled and what
conditions it is run in.
Certainly with your suggested method of on off control it is not going
to run at anything like the efficiency of a modulating model using its
own temperature sensing.
failed again. more efficient.
Then please explain why the boiler manufacturers engineer their
products to modulate the burner down and reduce temperature and pump
speed when less energy is required. Clearly you know something that
they don't.
Go away and do some reading up on condensing boiler technology and
control systems. Come back when you've understood it and we can run a
short test. Shall we set the date in 2014 now?
..andy
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