In article ,
David Hansen wrote:
After only a few years I have seen tanks with proper lids and by-law
kits fitted with crud and insects in the water.

And I have not.

But dribble would obviously 'see' lots of such things so he can recommend
his magnetic water conditioners.

--
*Why is it that most nudists are people you don't want to see naked?*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" through a haze of senile
flatulence wrote in message ...
In article ,
David Hansen wrote:

After only a few years I have seen tanks with proper lids and by-law
kits fitted with crud and insects in the water.

And I have not.

But

.....On the good ship Plowman they all did sail
.....he was the skipper to no avail

.....he sent the crew atop the mast
.....until he spouted to them at last

.....I'll keele haul ye, I will be jabers
.....so cut the masts and make em into cabers

.....because of cabers the ship did wreck
.....I have my cabers said cap'n, so what the heck

.... the breaking of law the police did pursue
.....Cap'n Plowman was dragged into public view

.....the judge did say in all his day
.....a case so bad he did not sit
....."the mans a fool I will commit"

.....the judge, he screamed, "an idiotic fool"
.....the capn' now resides as uk.d-i-y newsgroup tool

The message
from "Set Square" contains these words:

Andy, do you happen to know what the earliest start time is for a CM67? I
had a feeling that it would start up to 2 hours before the target time - but
when answering a call of nature early this morning, I found that the
radiators were hot two and a half hours before the target time - so it must
have started even earlier. Is this normal?

Presumably you have it set to a particular temperature over night. Could
it be that which triggered a heating cycle?

--
Roger Chapman

In an earlier contribution to this discussion,
Roger wrote:

The message
from "Set Square" contains these words:

Andy, do you happen to know what the earliest start time is for a
CM67? I had a feeling that it would start up to 2 hours before the
target time - but when answering a call of nature early this
morning, I found that the radiators were hot two and a half hours
before the target time - so it must have started even earlier. Is
this normal?

Presumably you have it set to a particular temperature over night.
Could it be that which triggered a heating cycle?

I did wonder about that. It's controlled at 22 degrees until nearly
midnight, and then set back to 12 degrees until 07:30. I would be surprised
if my well insulated house *actually* got down to 12 degrees - but I can't
be certain that it didn't.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:


That's easily addressed by having a thermostat with learning
capability which will start the heating a little earlier if it's very
cold.

Andy, do you happen to know what the earliest start time is for a CM67? I
had a feeling that it would start up to 2 hours before the target time - but
when answering a call of nature early this morning, I found that the
radiators were hot two and a half hours before the target time - so it must
have started even earlier. Is this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf

The Danfoss Randall TP7000 has settable curves - i.e. you can control
the start time limit.

http://www.danfoss-randall.co.uk/Sit..._-_UK_only.pdf


Having said that, this does seem a bit dubious, because the thermostat
should have a learned history of how long it takes for the house to
warm up.

However, it is limited because the thermostat can only take into
account the air temperature and elapsed time.

It doesn't know directly about the behaviour of the boiler and
radiators - i.e. potential cycling, nor does it know about the outside
temperature.

If the rate of change of outside temperature on a day to day basis is
relatively small, then this type of thermostat can optimise reasonably
well. It can also calculate how long it takes to raise the
temperature from a starting temperature to the desired one. This
gives an approximation that will be related to the outside temperature
since the starting temperature will be lower if the outside
temperature is lower.


I have a system where there is an outside temperature sensor and where
the room thermostat feeds the temperature via a digital proportional
connection to the controller in the boiler - i.e. the boiler knows
both interior and exterior temperatures. The boiler then also
monitors flow and return temperatures and controls burn rate (via fan
speed) and pump speed. I can get an output of all of this lot as
data or a graph on a PC.

The thermostat has a night setback which is normally set to 14
degrees.

The radiators have been sized to achieve the design room temperatures
for -3 degrees outside with 70 degree flow, 50 degree return which is
the recommendation to improve condensing boiler efficiency.

However, on the boiler, I can set a maximum temperature as well as the
slope related to compensation for outside temperature.

If I set the max boiler temperature to 85 degrees, if it is really
cold, the boiler will wind itself up to that temperature quite quickly
and the house will warm up quickly as well. The boiler does back off
as the room temperature set point is neared to avoid overshoot.
However, the boiler will be running less efficiently during the later
part of the warm up as the flow gets to 85 degrees.


If I set the max boiler temperature to 70 degrees, for an equivalent
outside temperature, it will come on earlier to achieve the required
temperature at the time required. It will run more efficiently too
since the flow never exceeds 70 degrees.

I logged the data for a few days each way for the same outside
temperatures. I measured gas use by looking at the figures for the
fan speed (relates to burn rate) each minute from the PC log.

It worked out to about 5-8% less gas use for the 70 degree setting
during the warm up phase for a given outside temperature around 0
degrees compared with 85 degree use. At higher outside temperatures,
the difference is less since less time is spent in the warm up phase.
So from a saving perspective, it is not a lot - however, there is
optimisation to avoid overshoot, and I think that that is one of the
main areas where there is an effective waste in many systems.

I've found from a comfort perspective, I would prefer that the boiler
starts raising the temperature from the setback to the set point over
a longer period - which is one of the effects of a lower flow
temperature. This is because I tend to sometimes get up earlier than
others and I would prefer for the house to have warmed to 16-18
degrees a bit earlier than to have a steeper rate of change nearer to
the set point time.

I think it's a matter for the individual. Some people are perhaps
more tolerant of the set point not having been achieved when they get
up but that the temperature continuing to rise. Others may prefer
having a something earlier.




--

..andy

"Andy Hall" wrote in message
...
On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:


That's easily addressed by having a thermostat with learning
capability which will start the heating a little earlier if it's very
cold.

Andy, do you happen to know what the earliest start time is for a CM67? I
had a feeling that it would start up to 2 hours before the target time -
but
when answering a call of nature early this morning, I found that the
radiators were hot two and a half hours before the target time - so it
must
have started even earlier. Is this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf

The Danfoss Randall TP7000 has settable curves - i.e. you can control
the start time limit.

http://www.danfoss-randall.co.uk/Sit..._-_UK_only.pdf

Having said that, this does seem a bit dubious, because the thermostat
should have a learned history of how long it takes for the house to
warm up.

However, it is limited because the thermostat can only take into
account the air temperature and elapsed time.

It may be in a very cold hall or room that drop sharply in temperature to
the rest of the house, sensing temperatures that are representative.

"Andy Hall" wrote in message
...
On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:


That's easily addressed by having a thermostat with learning
capability which will start the heating a little earlier if it's very
cold.

Andy, do you happen to know what the earliest start time is for a CM67? I
had a feeling that it would start up to 2 hours before the target time -
but
when answering a call of nature early this morning, I found that the
radiators were hot two and a half hours before the target time - so it
must
have started even earlier. Is this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf

The Danfoss Randall TP7000 has settable curves - i.e. you can control
the start time limit.

http://www.danfoss-randall.co.uk/Sit..._-_UK_only.pdf

Having said that, this does seem a bit dubious, because the thermostat
should have a learned history of how long it takes for the house to
warm up.

However, it is limited because the thermostat can only take into
account the air temperature and elapsed time.

It may be in a very cold hall or room that drop sharply in temperature to
the rest of the house, sensing temperatures that are unrepresentative.

In an earlier contribution to this discussion,
Andy Hall wrote:

On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

Andy, do you happen to know what the earliest start time is for a
CM67? I had a feeling that it would start up to 2 hours before the
target time - but when answering a call of nature early this
morning, I found that the radiators were hot two and a half hours
before the target time - so it must have started even earlier. Is
this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf


Thanks for that Andy. It turns out that I must be blind - because I have
that leaflet but hadn't previously been able to find the reference to 3
hours!

Do you have any views about the likely effects of adjusting any of the
variable parameters on a CM67 - particularly Minimum ON Time, Cycle Rate,
and Preportional Bandwidth?

Minimum ON Time defaults to 1 minute - but can be changed to up to 5
minutes. One minute seems a very short time to me and, even with a
reasonably well balanced system, some radiators hardly get hot in that time.
However, a longer time may result in more risk of overshoot? I think mine is
currently set to 2 minutes and, in mildish weather, the heating will run for
a bit - with some overshoot - and will then be off for a long time, with
some rooms feeling quite chilly before it comes on again. [I haven't
currently got any TRVs].

Cycle Rate defaults to 6 per hour - but can be set to 3, 6, 9 or 12,

Proportional Bandwidth defaults to 1.5 deg but can be increased up to 3. The
leaflet seems to suggest that increasing this may reduce the overshoot in
some circumstances.

Any thoughts about a methodology for arrivinmg at the best combination of
these parameters?
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

On Fri, 25 Nov 2005 12:37:54 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:

On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

Andy, do you happen to know what the earliest start time is for a
CM67? I had a feeling that it would start up to 2 hours before the
target time - but when answering a call of nature early this
morning, I found that the radiators were hot two and a half hours
before the target time - so it must have started even earlier. Is
this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf


Thanks for that Andy. It turns out that I must be blind - because I have
that leaflet but hadn't previously been able to find the reference to 3
hours!

Do you have any views about the likely effects of adjusting any of the
variable parameters on a CM67 - particularly Minimum ON Time, Cycle Rate,
and Preportional Bandwidth?

Minimum ON Time defaults to 1 minute - but can be changed to up to 5
minutes. One minute seems a very short time to me and, even with a
reasonably well balanced system, some radiators hardly get hot in that time.
However, a longer time may result in more risk of overshoot? I think mine is
currently set to 2 minutes and, in mildish weather, the heating will run for
a bit - with some overshoot - and will then be off for a long time, with
some rooms feeling quite chilly before it comes on again. [I haven't
currently got any TRVs].

Cycle Rate defaults to 6 per hour - but can be set to 3, 6, 9 or 12,

Proportional Bandwidth defaults to 1.5 deg but can be increased up to 3. The
leaflet seems to suggest that increasing this may reduce the overshoot in
some circumstances.

Any thoughts about a methodology for arrivinmg at the best combination of
these parameters?


I think that there are several things here.

You could probably make the biggest difference to overall comfort
levels by fitting TRVs. Even if the system is well balanced, it
looks as though heat loss from some for whatever reason is at a
greater rate than others - possibly those with more window and outside
wall area? After adding TRVs, you can arrange that the radiator
where the room thermostat is located is turned down somewhat and that
therefore the other rooms will come up to temperature first and TRVs
will start to back off.

With a simple room thermostat (bimetal or electronic) on the way up,
the temperature is allowed to increase above the set point and on the
way down below the set point by a certain amount. This hysteresis is
to reduce the amount of cycling, but does lead to the room temperature
moving up and down between these settings. Some thermostats do have a
setting for the width of this.

With a proportional thermostat, the hysteresis range is , in effect,
replaced by a proportional control band. Below the lower limit, the
thermostat turns the boiler switch control off, and above turns it on
all the time until the temperature changes to within the band.
Within the proportional band, the thermostat cycles the switched power
to the boiler with the on/off ratio adjusted. So for example, near
the bottom of the band, it might be on for 90%, off for 10% and near
the top on for 10%, off for 90%. The idea is that in steady state,
the amount of heat being output on average matches the heatloss and
the room temperature remains constant - i.e. an on time of 90% on a
20kW boiler equates to an average output of 18kW.

However, there are some practical issues.

The first is the time from switch on of the burner to when the
radiators are contributing heat to the room. That depends on a
variety of factors including boiler design (cast iron heat exchangers
take longer for example), water volume in system, pump speed etc.

The second is whether the boiler would cycle using its internal
thermostat sensing the water temperature. That happens if the rate
at which the heat is dispersed is less than the burn rate. In extreme
cases, it's not very helpful, because it means a loss of efficiency of
the boiler. Also, it is effectively adding another control loop
which can spoil the behaviour of the proportional controller.

Of course, having the proportional controller also deliberately cycles
the boiler. Hence the notion of having adjustable cycle and minimum
on times.

I would begin by checking the extent to which the boiler cycles on its
internal thermostat with the thermostat full up. If that is at a
rate close to or comparable with the minimum and cycle times of the
controller, then it should be addressed. The normal ways are to turn
up the boiler thermostat and perhaps increase pump speed. The idea is
that the controller should be cycling the boiler on and off.

I'd certainly increase the proportional band width up to 3 degrees.
This will make other adjustments easier.

Then it's a case of playing with the minimum on and cycle times so
that the room temperature climbs to the setpoint within the
proportional band reasonably quickly but does not overshoot
significantly nor oscillate too much about the set point.
Unfortunately, this will be a bit of a compromise because the rate of
heat loss will vary with outside temperature. I would start with the
lowest cycle rate and try different minimum on times. It's more
efficient for the boiler to have fewer cycles, but it's at the expense
of poorer maintenance of room temperature. It's also better to let
the boiler get hot on each cycle to avoid unwanted condensing if it's
a conventional boiler.

The adjustment's going to be iterative, I'm afraid.

I would not be at all concerned that the radiators only get slightly
warm sometimes while this is working. Remember that the point of
proportional control with an on/off boiler is to control the average
heat output. It's therefore completely reasonable for the radiators
not to get that hot when the room temperature is in the proportional
band and the outside temperature is mild. Remember that below the
proportional band, the boiler should be firing anyway.


On my own system, which is effectively fully proportional because the
boiler modulates, the boiler can be running continuously on a flow
temperature of 40 degrees sometimes. I just checked it, and it's at
50 degrees with +2 outside.




--

..andy

In an earlier contribution to this discussion,
Andy Hall wrote:

On Fri, 25 Nov 2005 12:37:54 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:

On Thu, 24 Nov 2005 10:52:05 -0000, "Set Square"
wrote:

Andy, do you happen to know what the earliest start time is for a
CM67? I had a feeling that it would start up to 2 hours before the
target time - but when answering a call of nature early this
morning, I found that the radiators were hot two and a half hours
before the target time - so it must have started even earlier. Is
this normal?


That could be.

The installer guide says 3hrs max for the optimised start

http://content.honeywell.com/uk/home...l/CM/cm67i.pdf


Thanks for that Andy. It turns out that I must be blind - because I
have that leaflet but hadn't previously been able to find the
reference to 3 hours!

Do you have any views about the likely effects of adjusting any of
the variable parameters on a CM67 - particularly Minimum ON Time,
Cycle Rate, and Preportional Bandwidth?

Minimum ON Time defaults to 1 minute - but can be changed to up to 5
minutes. One minute seems a very short time to me and, even with a
reasonably well balanced system, some radiators hardly get hot in
that time. However, a longer time may result in more risk of
overshoot? I think mine is currently set to 2 minutes and, in
mildish weather, the heating will run for a bit - with some
overshoot - and will then be off for a long time, with some rooms
feeling quite chilly before it comes on again. [I haven't currently
got any TRVs].

Cycle Rate defaults to 6 per hour - but can be set to 3, 6, 9 or 12,

Proportional Bandwidth defaults to 1.5 deg but can be increased up
to 3. The leaflet seems to suggest that increasing this may reduce
the overshoot in some circumstances.

Any thoughts about a methodology for arrivinmg at the best
combination of these parameters?


I think that there are several things here.

You could probably make the biggest difference to overall comfort
levels by fitting TRVs. Even if the system is well balanced, it
looks as though heat loss from some for whatever reason is at a
greater rate than others - possibly those with more window and outside
wall area? After adding TRVs, you can arrange that the radiator
where the room thermostat is located is turned down somewhat and that
therefore the other rooms will come up to temperature first and TRVs
will start to back off.

With a simple room thermostat (bimetal or electronic) on the way up,
the temperature is allowed to increase above the set point and on the
way down below the set point by a certain amount. This hysteresis is
to reduce the amount of cycling, but does lead to the room temperature
moving up and down between these settings. Some thermostats do have a
setting for the width of this.

With a proportional thermostat, the hysteresis range is , in effect,
replaced by a proportional control band. Below the lower limit, the
thermostat turns the boiler switch control off, and above turns it on
all the time until the temperature changes to within the band.
Within the proportional band, the thermostat cycles the switched power
to the boiler with the on/off ratio adjusted. So for example, near
the bottom of the band, it might be on for 90%, off for 10% and near
the top on for 10%, off for 90%. The idea is that in steady state,
the amount of heat being output on average matches the heatloss and
the room temperature remains constant - i.e. an on time of 90% on a
20kW boiler equates to an average output of 18kW.

However, there are some practical issues.

The first is the time from switch on of the burner to when the
radiators are contributing heat to the room. That depends on a
variety of factors including boiler design (cast iron heat exchangers
take longer for example), water volume in system, pump speed etc.

The second is whether the boiler would cycle using its internal
thermostat sensing the water temperature. That happens if the rate
at which the heat is dispersed is less than the burn rate. In extreme
cases, it's not very helpful, because it means a loss of efficiency of
the boiler. Also, it is effectively adding another control loop
which can spoil the behaviour of the proportional controller.

Of course, having the proportional controller also deliberately cycles
the boiler. Hence the notion of having adjustable cycle and minimum
on times.

I would begin by checking the extent to which the boiler cycles on its
internal thermostat with the thermostat full up. If that is at a
rate close to or comparable with the minimum and cycle times of the
controller, then it should be addressed. The normal ways are to turn
up the boiler thermostat and perhaps increase pump speed. The idea is
that the controller should be cycling the boiler on and off.

I'd certainly increase the proportional band width up to 3 degrees.
This will make other adjustments easier.

Then it's a case of playing with the minimum on and cycle times so
that the room temperature climbs to the setpoint within the
proportional band reasonably quickly but does not overshoot
significantly nor oscillate too much about the set point.
Unfortunately, this will be a bit of a compromise because the rate of
heat loss will vary with outside temperature. I would start with the
lowest cycle rate and try different minimum on times. It's more
efficient for the boiler to have fewer cycles, but it's at the expense
of poorer maintenance of room temperature. It's also better to let
the boiler get hot on each cycle to avoid unwanted condensing if it's
a conventional boiler.

The adjustment's going to be iterative, I'm afraid.

I would not be at all concerned that the radiators only get slightly
warm sometimes while this is working. Remember that the point of
proportional control with an on/off boiler is to control the average
heat output. It's therefore completely reasonable for the radiators
not to get that hot when the room temperature is in the proportional
band and the outside temperature is mild. Remember that below the
proportional band, the boiler should be firing anyway.


On my own system, which is effectively fully proportional because the
boiler modulates, the boiler can be running continuously on a flow
temperature of 40 degrees sometimes. I just checked it, and it's at
50 degrees with +2 outside.

Many thanks for your comprehensive reply. I'll have a go!
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.