I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.

The electronic ones will have it programmed in, whereas the mechanical ones
tend to have it as a natural result of the quick-snap switching action.

I suspect the digital ones will have it rather tighter than the mechanical
ones, but it will be there and will be some amount that may or may not be
documented.
--
Tim Watts

Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.
Why not make them so they only switch once every five minutes, like the
auto mono/colour switching in a CCTV camera??

Bill

Bill Wright wrote:

Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.
Why not make them so they only switch once every five minutes, like the
auto mono/colour switching in a CCTV camera??

Bill

That's another option of course, that is not readily available with a
mechanical design.
--
Tim Watts

On 04/03/2012 18:28, Tim Watts wrote:
Bill Wright wrote:

Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.
Why not make them so they only switch once every five minutes, like the
auto mono/colour switching in a CCTV camera??

Bill

That's another option of course, that is not readily available with a
mechanical design.

So called "anti cycling" logic is often built into modern boilers...

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
On 04/03/2012 18:28, Tim Watts wrote:
Bill Wright wrote:

Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2
degree 'delay'. Are the digital ones any better in this
respect? If so, what's a good one to buy? I don't want
anything fancy. Also, are the radio ones any good?

Bill

All thermostats will have hysteresis or they will "chatter"
around the setpoint.
Why not make them so they only switch once every five minutes,
like the auto mono/colour switching in a CCTV camera??

Bill

That's another option of course, that is not readily available with
a mechanical design.

So called "anti cycling" logic is often built into modern boilers...

But what happens if you have 2 combis and only one stat?

--
Adam

On 4 Mar,
Bill Wright wrote:

Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.
Why not make them so they only switch once every five minutes, like the
auto mono/colour switching in a CCTV camera??

My quite old one goes into a 'proportional mode' once it is up to near
temperature. It switches in a 10 minute cycle with the mark/space depending
on where it is in a small band close to set point. I think it's +- 1degC for
proportional mode.

More modern ones (Honeywell?) have this programmable.

--
B Thumbs
Change lycos to yahoo to reply

In article , Bill Wright
writes
Tim Watts wrote:
Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

All thermostats will have hysteresis or they will "chatter" around the
setpoint.
Why not make them so they only switch once every five minutes, like the
auto mono/colour switching in a CCTV camera??

If that's what you're looking for then honeywell digital ones are what
you want, they use proportional control (no choice) and can maintain
temperatures very close to the demand (in the room with the stat).

In my view however they are too b'ldy clever by half and cause to much
boiler and control cycling. Usually the stat feeds a motorised valve
that in turn causes the boiler to fire when it is fully engaged. That
means that every time you cycle the stat you cycle the valve motor
causing it to wear out prematurely. Honeywell stats cycle 6 times an
hour by default (programmable 3 - 12) so you could wear out a valve in a
year or two (my multizone system has 8 so you'll see why I'm concerned).

I have one of their CM/CT907 wired stats here that I will be swapping
out for something else soon for the reasons above but I have installed
the wireless CM/CT927 at 2 locations with unzoned systems where the
owner is perfectly happy with them. Note though at both of these
locations I have had wireless link failures which required re-bonding of
stat to receiver following boiler power disconnections. I reported these
failures here but no-one appeared to have had a similar experience.

My suggestion would be a digital stat that has lower hysteresis or a
programmable option to switch between proportional and bang-bang
control. No model numbers to hand I'm afraid, cheaper digitals are
generally bang-bang. There is a mid-ranged one that is propo/switched
selected by jumper, if you're keen I'll see if I can track it down
again.

Others' cautions about having the stat in a room with an auxiliary heat
source are valid, sometimes controlling the hall with TRVs controlling
the room temps is the right way to do it.
--
fred
it's a ba-na-na . . . .

On Mon, 5 Mar 2012 16:46:13 +0000, fred wrote:

Note though at both of these locations I have had wireless link failures
which required re-bonding of stat to receiver following boiler power
disconnections.

No problems with the Danfoss TP75 or TP7000, I have both in use and
both are RF versions. Power glitches haven't caused any required for
either of them to be paired with their respective receivers again.
And the older one should work with the new RX and vice versa though I
haven't actually tested that.

My suggestion would be a digital stat that has lower hysteresis or a
programmable option to switch between proportional and bang-bang
control.

The TP7000 has a DIL switch on the back to select:

5/2 or 7 day mode.
On/off of the Optimum Start Control (start the boiler at the
appropiate time to hit the first set temp on time)
On/off of the proportional control.
6 or 3 periods for the proportional control.

The instructions warn against using proportional control on a system
with motorised valves.

--
Cheers
Dave.

In article o.uk, Dave
Liquorice writes
On Mon, 5 Mar 2012 16:46:13 +0000, fred wrote:

Note though at both of these locations I have had wireless link failures
which required re-bonding of stat to receiver following boiler power
disconnections.

No problems with the Danfoss TP75 or TP7000, I have both in use and
both are RF versions. Power glitches haven't caused any required for
either of them to be paired with their respective receivers again.
And the older one should work with the new RX and vice versa though I
haven't actually tested that.

My suggestion would be a digital stat that has lower hysteresis or a
programmable option to switch between proportional and bang-bang
control.

The TP7000 has a DIL switch on the back to select:

5/2 or 7 day mode.
On/off of the Optimum Start Control (start the boiler at the
appropiate time to hit the first set temp on time)
On/off of the proportional control.
6 or 3 periods for the proportional control.

The instructions warn against using proportional control on a system
with motorised valves.

Thanks for the reminder, yes, that was the one I had in mind but pretty
they aint. Good to see the propo warning in the instructions (I had
missed that).

Honeywell are the prettiest but it's a shame that none have the option
to turn off propo. Maybe it's to support their replacement valve market.

I decided to look again and the Siemens Rev13, 17 and 24 have it
switchable too and have tight temp accuracy but prices are variable.
Touchscreen model Rev100, 200 too but overpriced IMV.
--
fred
it's a ba-na-na . . . .

On Sun, 04 Mar 2012 17:42:08 +0000, Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'.

Enough to be annoying and get SWMBO'd up to the stat to turn it up at
the cool end of it's switching range.

Are the digital ones any better in this respect?

Much better. Ours maintain the room temp within about 0.5C. If it's
set to 18.5C it calls for heat at 18.4 and switches off at 18.5, the
thermal inertia of the rads/room give the overshoot.

If so, what's a good one to buy? I don't want anything fancy.

I quite like the Danfoss TP75 (TP7000 now I think) but others will
swear by the Honeywell CM67. These may fall into "too fancy" category
but having a stat that can vary the set temperature across the day is
good. Saves fuel and gives much better comfort.

Also, are the radio ones any good?

Both ours a radio based. They work, what more to say? Also means you
can move the stat about if you want to.

--
Cheers
Dave.

On Sun, 04 Mar 2012 19:02:31 -0000, Dave Liquorice
wrote:

On Sun, 04 Mar 2012 17:42:08 +0000, Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'.

Enough to be annoying and get SWMBO'd up to the stat to turn it up at
the cool end of it's switching range.

Are the digital ones any better in this respect?

Much better. Ours maintain the room temp within about 0.5C. If it's
set to 18.5C it calls for heat at 18.4 and switches off at 18.5, the
thermal inertia of the rads/room give the overshoot.

If so, what's a good one to buy? I don't want anything fancy.

I quite like the Danfoss TP75 (TP7000 now I think) but others will
swear by the Honeywell CM67. These may fall into "too fancy" category
but having a stat that can vary the set temperature across the day is
good. Saves fuel and gives much better comfort.

Also, are the radio ones any good?

Both ours a radio based. They work, what more to say? Also means you
can move the stat about if you want to.

Now I am feeling really thick. Never occurs to move ours into the dining
room when we have the gas fire alight in the lounge where it normally
lives.

Reliable though and keeps the temperature within 1 degree.

On Sun, 04 Mar 2012 19:20:14 -0000, "Hugh - Was Invisible"
wrote:

On Sun, 04 Mar 2012 19:02:31 -0000, Dave Liquorice
wrote:

On Sun, 04 Mar 2012 17:42:08 +0000, Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'.

Enough to be annoying and get SWMBO'd up to the stat to turn it up at
the cool end of it's switching range.

Are the digital ones any better in this respect?

Much better. Ours maintain the room temp within about 0.5C. If it's
set to 18.5C it calls for heat at 18.4 and switches off at 18.5, the
thermal inertia of the rads/room give the overshoot.

If so, what's a good one to buy? I don't want anything fancy.

I quite like the Danfoss TP75 (TP7000 now I think) but others will
swear by the Honeywell CM67. These may fall into "too fancy" category
but having a stat that can vary the set temperature across the day is
good. Saves fuel and gives much better comfort.

Also, are the radio ones any good?

Both ours a radio based. They work, what more to say? Also means you
can move the stat about if you want to.

Now I am feeling really thick. Never occurs to move ours into the dining
room when we have the gas fire alight in the lounge where it normally
lives.

Reliable though and keeps the temperature within 1 degree.

I was pondering on that as I screwed mine to the hall wall, but it had
to go there because it covers the gap in the wallpaper where the old
thermostat lived.

--
Graham.
%Profound_observation%

On 4 Mar, 19:20, "Hugh - Was Invisible"
wrote:
On Sun, 04 Mar 2012 19:02:31 -0000, Dave Liquorice


Now I am feeling really thick. Never occurs to move ours into the dining
room when we have the gas fire alight in the lounge where it normally
lives.

Reliable though and keeps the temperature within 1 degree.

Is there any point if you are in the living room with the fire?

Jonathan

On Sun, 4 Mar 2012 22:57:03 -0800 (PST), Jonathan wrote:

Now I am feeling really thick. Never occurs to move ours into the
dining room when we have the gas fire alight in the lounge where
it
normally lives.

Is there any point if you are in the living room with the fire?

The point is that, presumably, the gas fire isn't normally lit but
the lounge and that is the room that is normally occupied. So you
need the stat in there to make that room the most comfortable. Light
the gas fire though and the lounge warms up, stat becomes satisfied
and the rest of the house cools. Moving stat to dining room means it
still keeps the rest of the house warm.

--
Cheers
Dave.

On 5 Mar, 08:14, "Dave Liquorice"
wrote:
On Sun, 4 Mar 2012 22:57:03 -0800 (PST), Jonathan wrote:
Now I am feeling really thick. Never occurs to move ours into the
dining room when we have the gas fire alight in the lounge where
it
normally lives.

Is there any point if you are in the living room with the fire?

The point is that, presumably, the gas fire isn't normally lit but
the lounge and that is the room that is normally occupied. So you
need the stat in there to make that room the most comfortable. Light
the gas fire though and the lounge warms up, stat becomes satisfied
and the rest of the house cools. Moving stat to dining room means it
still keeps the rest of the house warm.

--
Cheers
Dave.

I think I would rather save the money on not heating the rooms that I
am not in.

Jonathan

On Mon, 05 Mar 2012 10:57:20 +0100, Martin wrote:

The modern ones are also adaptive, they will work out how long it
takes to reach the required temperature and start up early enough for
you to have a warm room when you get up/come home from work etc.

I don't think any of them have the adaptive feature on all, or an
given, set point other than the first of the day.

--
Cheers
Dave.

On 05/03/2012 09:57, Martin wrote:

The modern ones are also adaptive, they will work out how long it
takes to reach the required temperature and start up early enough for
you to have a warm room when you get up/come home from work etc.


Many - but not all - have that feature. But it can usually be turned off
if you don't want it. This feature is turned off on all of my stats for
reasons recently discussed in another thread.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Sun, 04 Mar 2012 17:42:08 +0000, Bill Wright
wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

Apart from the small amount of thermal inertia in the bead thermistor,
there is no reason why an electronic thermostat need have any
hysteresis. This won't always be a good idea though, as short term
cycling of boilers is an inefficient way to run them so I suspect the
designers put a controlled amount of hysteresis back in.

--
Graham.
%Profound_observation%

In message , Graham.
wrote


I suspect the
designers put a controlled amount of hysteresis back in.


My Towerstat RF has a switch setting to give a hysteresis of 1, 2 , 3
or 4 degrees C.
--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

On 04/03/2012 17:42, Bill Wright wrote:

I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy.

For a basic programmable stat (i.e. the ability to specify different
temps at different times of the day) I find the seven day Centaurstat
quite good and reliable (under £30 at SF etc)

It does not try to do any of the optimum start type tweaks to the timing
itself though.

Also, are the radio ones
any good?

Generally yes if you go for a decent one. Can save a bit of wiring, and
/or let you move the sensor bit around with you.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/03/2012 17:42, Bill Wright wrote:
I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

How have you measured the 'delay'? Have you simply twiddled the knob
backwards and forwards, and noted a 2 degree difference between where it
clicks on and clicks off? Or have you monitored the room temperature
controlled by it, and noted a 2 degree range? If the former, there may
not *actually* be a 2 degree hysteresis. Most manual stats have a
built-in 'anti-hysteresis' heater resistor. This generates a bit of heat
whenever the stat is 'on', fooling it into switching off a bit earlier
than it otherwise would, and reducing overshoot.

Digital stats work on an entirely different principle. When near the
desired setpoint, they operate like a proportional controller - and they
proportion the on/off times in a way which usually results in
maintaining the required temperature within no more than half a degree.
They save energy because you don't have to set them over-hot in order to
make sure that the room is still hot enough at the bottom end of the
hysteresis.

As regards makes/models, my experience is limited to Honeywell CM67's
(of which I have 3!). These work pretty well but, as someone else has
said, may come into your 'fancy' class. The wireless ones are excellent
- and very reliable (unless you live in a Faraday Cage!). They have the
advantage that you can move them around, to find the best position - and
you can also programme them on your lap.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Sun, 04 Mar 2012 22:04:56 +0000, Roger Mills
wrote:

As regards makes/models, my experience is limited to Honeywell CM67's
(of which I have 3!). These work pretty well but, as someone else has
said, may come into your 'fancy' class. The wireless ones are excellent
- and very reliable (unless you live in a Faraday Cage!). They have the
advantage that you can move them around, to find the best position - and
you can also programme them on your lap.

I wouldn't call the CM6x Honeywell wireless stats reliable. The UK
ones operate on 433MHz or thereabouts are very prone to outside
interference and clashes of frequency allocations. It's just as well
they default to a set period on off pattern when signal is lost as a
house would freeze if left unattended.

The more recent Honeywell CM9xx series operate on 868MHz and are much
better.


--

On 04/03/2012 17:42, Bill Wright wrote:
I am troubled by hysteresis. The thermostat seems to have a 2 degree
'delay'. Are the digital ones any better in this respect? If so, what's
a good one to buy? I don't want anything fancy. Also, are the radio ones
any good?

Bill

I have had a Danfoss TP9 for some years. It is a two channel programmer
and lives near my boiler. It uses a remote wired sensor in the sitting
room. The temperature control is much better than the previous
Honeywell mechanical thermostat which used the same wiring.

The other big advantage of programmable thermostats is that you can vary
the temperature throughout the day.

--
Michael Chare