RE: Solenoid Radiator valves

["Neil Ball" <neilball@xxxxxxx>]

You've found the problem with a single zone boiler control solution when
multi-room zoning is required I'm afraid. You either have to take the
approach where the controlling sensor is fitted in the coldest room to
ensure heating is available everywhere else and that when that control
sensor is satisfied then by definition so to is the rest of the house. The
only other solution is to add additional sensors as you need to measure
before you can control.

The next problem is that if you control the boiler directly from it's 0-10v
input then you have got to write all of the necessary control strategy to
achieve the end result. The difficulty here is simply that it is not easy
t=
o
design from scratch when you do not have a clear idea of all of the
individual features that will be required, from management/protection of
th=
e
boiler plant to heating control loops, optimum start calculations etc. The
reason why much of the equipment around today is so expensive is that it is
tried and tested solutions based on commercial controls where these highly
effective and efficient control techniques are now mandatory in most
non-residential buildings. Factor in the very low demand in residential
markets and you get left with high cost. One other word of caution, be wary
of the programmable BMS type systems as they really are not at all
appropriate for residential use. Most have very obscure bespoke programming
languages, and the tools to program them are only available to the
manufacturers system installers. This makes the installation expensive, but
more importantly they are often designed to limit local access to avoid
tampering, and maintenance can be very expensive as well.

With regards to outside weather compensation, this is one method to
conside=
r
where the boiler flow temperature is dependent on outside air temperature
o=
n
the basis that heat loss from the building is directly related to external
conditions. Again it has it's advantages, and can also be used for the
optimum start calculation where the pre-heat time becomes a factor of room
temperature, room setpoint and outside air temperature. You may well find
though that if you have a well insulated/air tight house that the only
dominant factor is room temperature versus setpoint therefore you could
simplify your intended control by omitting outside air influence all
together. I would still recommend retaining the outside sensor though as
yo=
u
can use it for frost protection strategies when the building is unoccupied.

Finally, the company I work for has a technical area on it's web site, and
if you look at the datasheets for the boiler module and zone controller you
should get a good idea of the kinds of strategies we employ. As mentioned
previously though, the prices are still very high for most people and
typically most of our installations cost from =A35,000 upwards.=20





-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]=20
Sent: Monday, April 07, 2003 17:48
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


I have been meaning to have a go at this (modulating the boiler directly)
currently I have a modulating condensing boiler feeding about 8 zones  some
of which are single rooms  I did this where there were more than one
radiator in a room  and particularly where they were the old cast iron ones
having previously cracked a radiator fitting new valves.

I went originally with the recommended controller which is both
fancy and dumb !  It runs on a single pair of wires to the boiler and
provides full monitoring and display of all the various temps, boiler,
flow=
,
return, room, hot water, outside etc  however it cant program HW separate
>from
big problem though is it modulates to create a flow temperature to maintain
the temp in the room it sits in  so I have had to mount it in the hall  the
coldest room. It is supposed to compensate such that the room always
reache=
s
the setpoint at exactly the same time each day  effectively coming on
earlier if it is cold outside or the room needs extra heating. Now , caused
by my meddling it fails to do this.

My problem was  that once that room is satisfied the water circulation
drop=
s
in temp and so if other rooms need extra heat they cant get it. I sort of
worked around this by setting the desired temp very high in the hall  and
then also reducing the flow through the radiators there to cause it great
difficulties in becoming satisfied but the nett effect was that the boiler
is confused I think with the heating characteristics of that room and knows
that it cant heat it predictably so it ambles along at a mid temperature
this has allowed other rooms to become satisfy when needed but has negated
the whole advantages of fhe modulating approach  I need to rethink it all
either by a manual approach or by using a multi sensor arrangement across
the house  unfortunately I know little about this and although I have asked
Potterton (commercial) for help the two different companies they
recommende=
d
were not very conversant with the solutions  one volunteering a 5K
building=
s
management package and one saying they didnt know.

The fortunate thing is that I can modulate my boiler with 0-10V and so =
I
think I may have a go myself. I am told it is a science getting the
respons=
e
curves right and I have never really understood why the external
temperatur=
e
is so vital  I would have thought that you would just calculate that to
raise a room from say 13 to 22 degrees takes 20 minutes  I can see that the
outside temp has some effect on this  if it is cold outside it will take
longer than if it is warm but is that the only effect > ? effectively
the
heat loss caused by the differential ? I am also a little loathe to
overrid=
e
the boilers control of all these sensors, flow return , outside, room etc
a=
s
it is supposedly a clever piece of kit  it has European House style models
built in  but I cant find a reasonable cost way of expanding its operation
>from

=20

BTW  If anyone with  a commercial interest / expertise in  this would like
to talk to me I would welcome it  I am very willing to buy in a reasonable
cost solution. It is a Potterton EuroCondense 65 boiler.

=20

Kevin

=20

-----Original Message-----
From: Neil Ball [mailto:neilball@xxxxxxx]=20
Sent: 07 April 2003 15:49
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves

=20

I can see the problem now Kevin - as you say, most valves do not give
balanced flow across their opening range, most have almost 100% flow as
soo=
n
as they are partially opened which gives very little controllability.

Just another thought, are you measuring room temperature with sensors? If
so, have you considered controlling the boiler output based on heating
demand (direct boiler compensation)? Most commercial systems use either
outside weather compensation control, heating demand compensation based on
room sensors, or a combination. Here you reduce the effects of the poor
valve authority as instead of only allowing a very small amount of high
temperature water into the radiator you allow much more at a reduced
temperature thereby increasing the overall level of control. Works very
wel=
l
with condensing boilers as it maximises the time the boiler is in full
condensing mode for much of the heating season. You'll need to add at least
on pipe sensor and use the heating demand to calculate the required boiler
flow temperature, and control the boiler temperature through simple on/off
switching. You might also have to add a hot water sensor to make this a
zon=
e
so that can influence this calculation as well and boost the boiler
temperature when the cylinder needs heating.

With regard to positioning raise/lower valves then it is not too hard - you
simply roughly position the valve based on room heating demand, and then
pulse the valve in small increments thereafter based on room response. As
long as you measure the full stroke time of the valve it becomes a
time-based operation, and you can always use the full stroke time plus a
margin whenever the valve is moved fully open or closed to ensure it gets
registered to the extreme of it's travel. In reality you get pretty good
positioning without the expense of 0-10v control (bear in mind that most
0-10v actuators simply turn this signal back into a raise/lower signal
internally to drive the motor anyway).

Let me know how you get on.

Neil.




-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]=20
Sent: Monday, April 07, 2003 13:58
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


I have played quite a bit with the algorithms for the ON OFF control  which
I have in about 4 rooms here. My problem comes because of the heat
retentio=
n
in the radiators. They are the very old fashioned cast iron ones. Now as
soon as the valve is opened they heat up very quickly (as the water flowing
past is already very hot) but they hold heat for a long time, causing the
overshoot  so I am faced with almost pulsing the valves open for a very
short time to only heat the radiator up a little. I even played with a temp
sensor attached to the radiator. Unfortunately this then also gets
complicated by the flow temp at the valve and the flow rate or pressure
both these being effected by other demands from TVRs and zones. In one of
the rooms the radiators are more modern meaning they are far more efficient
at radiating heat and hence cool much faster  this room I have managed to
cater for the hysteresis far better with an algorithm.=20

TBH I had intended all my valves to be proportional type 1 or raise/lower
type 2 below, but I had installed the traditional zone valves assuming I
could just exchange the actuators at a later time for proportional ones 
bu=
t
you cant get proportional or raise/lower exchange actuators for standard
zone valves  so I had to work around or fit new valves as well.

Neil  when I said proportional I meant to include raise/lower in
that category  I think we are talking about three types here arent we ??

1)       The type that is either fully open or fully closed (but takes a
fe=
w
secs to move from one to the other)

2)       The type that you apply say 0-10V to and they are proportional ie
3V is 30% open

3)       The raise lower type  you drive them with a succession of pulses
t=
o
move them from one position to the next ( or maybe even a timed voltage
application)  then they stay wherever they are left  if you drive them 2/3
open then that is where they stay. These take a little tracking and have to
be calibrated against end positions periodically  I think these are the
lowest cost of the 2 and 3 and what I will probably end up using.

There is a fourth type which is what most of my radiators use at the moment
it is a sort of bodged TVR. Basically I have TVRs with a capillary and
remote sensor mounted in a small plastic box. You set the required
temperature on the standard mechanical rotary TRV. However also mounted in
the little sensor box is a small electric element that applies heat to the
sensor in proportion to the voltage applied to it. Hence you can set back
that room by 2 degrees by applying 2V or by 5 degrees by 5V etc. This works
very well to regulate the room as the control is effectively truly
proportional  you can also effectively turn a  room ON or OFF this way. I
a=
m
not sure these are manufactured anymore  they were made by Danfoss.



I am really interested in this subject as I have yet to implement most of
m=
y
control here  so please do keep us updated on anything you find



Kevin





-----Original Message-----
From: Dave McLaughlin [mailto:dave@xxxxxxx]=20
Sent: 07 April 2003 12:36
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves



Hi Kevin,

I am also looking to replace mine with solenoid or proportional valves. Did
you have any kind of hysterisis in your control loop? Wouldn't adjusting
this have taken out the oscillations?

Regards
Dave...
-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]
Sent: 07 April 2003 01:17
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


You should also consider using a proportional valve rather than just
ON/OFF.
I have some ON/OFF ones and I still get oscillation around the setpoint
due
to retained heat (forgotten the tech word) within the radiators. (I was
basically using zone valves)

I have researched a few inline / TVR replacement options  You can get
plain ON/OFF down to about 25 but proportional all seem to be circa 60
plus. There is a very low cost device (TVR replacement) that works on
thermal expansion  basically you apply voltage and it heats and expands
but
the response time is quite slow.

Kevin


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