On Sat, 20 May 2006 16:47:56 +0100, wrote
(in article .com):

Andy,

Many thanks for your thorough and speedy response. If I may just raise
a few issues/questions underneath snipped parts of your post:


It is desirable to run a heatbank at 80 degrees plus if you can for DHW
purposes, simply because you can store more energy and have a greater run
time before the store runs out. However, if the store is fairly large, as
you are suggesting, this may not be an issue. Keep in mind as well that
the boiler can be arranged to fire quite early on following a tap being
turned on and will start contributing heat back into the heatbank
immediately, thus lengthening run time.

As per normal usage ie cylinder stat or similar kicking in or via the
installation of a flow switch? Under normal usage conditions I agree
that heating to 70 degrees should be sufficient with a 180l store.

In my case, with the analogue sensor, it is installed in a pocket in the
cylinder. Basically this is a tube into the side of the cylinder with
stopped end. The probe is inserted into it and is thus is sensing the
temperature in the centre and not surface of the cylinder. It appears that
the behaviour of the boiler controller is to sense the rate of fall of
temperature of this as well as the absolute temperature. Normally there is a
hysteresis of about 5 degrees so that the boiler doesn't fire until 55
degrees is reached when the temperature is dropping slowly - i.e. small
amounts of water used. However, if a bath or shower is started, the boiler
begins to fire very quickly (less than a minute) and before the temperature
display has hit 55 degrees. I run the cylinder at 60, I should add.

You could use a flow switch, of course, but you would also need a thermostat
to make sure that the cylinder is brought back up to tempertature after the
flow stops.




I use the analogue temperature sensor for the DHW cylinder and it works
well.However, it is also possible to use a conventional thermostat if you
like.

The Pandora can come with 1 or 2 immersed Danfoss stats that sound very
similar to the Man immersed stat - I had considered a straight
replacement for the Man one but given the benefit of reaching a higher
temperature it is probably better to opt for the Pandora's own.

The principle is different. The MAN one is a temperature sensor. The boiler
is able to know the actual temperature and work with that - cylinder temp is
set on the boiler. With a thermostat, the boiler is only given a signal
to fire or not. If you are going to go for a thermostat, try to get one
that is electronic rather than bimetal strip or capillary. these tend to be
rather crude on setting and sensing.




The
issue I have is how to decipher the wiring back into the boiler as
Eco's stressed that the boiler is primarliy designed for low voltage
connections ie the Man RE2132 unit/outside weather compensator and
cylinder probe all attach via the low voltage rail whereas the heatbank
cylinder probe(s) would be wired into the wiring centre on the heatbank
itself?

If the thermostat has no-volt contacts - meaning a switch contact rather than
wanting to feed mains, then you can use low voltage wiring.

However, if you do, then it would be a good idea to keep this wiring
completely separate and not connect it in the wiring centre, but put in a
separate one.





Let me answer a few of your points.

- The boiler temperature for DHW can be set to up to 70 degrees, not 65. I
just checked.

- You can have separate temperatures from the boiler for DHW and CH. I do
exactly this. It is a case of choosing the correct function number on the
boiler. I use number 38, which is not one that Eco Hometec was familiar
with. This uses the weather compensation sensor and the 2132 room
controller for the heating. It also allows the max flow temperature to be
85
degrees. There is a similar setting if it were preferred to use a
conventional room thermostat. As you have probably read, there is an
integral pump and on some models an internal diverter valve. I went for
the
boiler without diverter valve because I wanted to have S-plan with a number
of valves.

So no additional diverter in your system or you use an external
diverter in addition to the zone valves?


No additional diverter. The boiler opens the relevant zone valve according
to whether CH or DHW is being done. DHW has preference.




In this case, the boiler has two mains outputs. Normally, only
one is used
and is for operating an external diverter valve. This behaviour happens
for
the low numbered function settings and the second output isn't used.

However, in the higher number modes, the second output is intended to drive
an external pump when in heating mode. The complete S-plan solution then
becomes easy. The first output is used to control a zone valve for the HW
cylinder or heatbank. The second for a zone valve for the heating.
Behaviour is then as follows:

- With heating turned on, the boiler runs based on the weather compensator
and room sensor/thermostat. It *can* run at up to 85 degrees flow, but
doesn't. I moved radiators around and replaced some such that I can get
enough heat to deal with the standard -3 degree outside temperature with the
boiler running at 70 degree flow and 50 degree return. In practice, it is
unusual for the flow to exceed 60 degrees except following startup on the
coldest days. Quite often, the flow is as low as 40 degrees and the
boiler
sits running all day like that.

- As soon as there is DHW demand, the boiler cuts power to the second
output, closing the CH zone valve(s) and powers the first output, opening
the
cylinder zone valve. It then fires up to full output and flow temperature
rising to 85 degrees output.

Do you utlise a wiring centre in your setup or do you wire each of the
valves back to the boiler?

I used two wiring centres (one mains and one low voltage) near the cylinder
because that is where the zone valves are located. Wiring from these runs
back to the boiler. Actually wiring is simple, because there only needs to
be mains on/off to open the valves. The sensors are individually run.





This is what I thought I was specifying on the Heatbank ie separate
zone valves for DHW and CH however the issue seemed to be that these
are pre wired into the wiring centre on the Heatbank and for
convenience you have one mains wire intended to go into the boiler (3
perm L N and E and a switched live) - AIUI the boiler is primarily
intended to function via low voltage connections therefore I would need
to install a relay of some kind but even then I couldn't really figure
if this is how the boiler is intended to pick up these signals or not?

I did speak to them about this and considered the HS model as it has 2
flows and 2 returns and I could separate one each for the heatbank and
heating and utilise the internal diverter to do the work however Eco's
suggested that this with contra building regs that required the usage
of additional zone valves - I didn't argue further as I haven't read
the necessary regs in that much detail but it sounded at odds with
logic if the boiler has separate flows and returns for each section and
it has it's own diverter then surely if it's wired up correctly then
there should only be calls on the boiler when required, why would I
need further valves?

That's making it all unnecessarily complicated. You don't need zone valves
on the heatbank, nor do you need them in the boiler.

If the only way that you can buy the heatbank is with a switched live output,
then you would need an additional relay to provide volt free switching to the
boiler. I would ask DPS for a wiring diagram of what they supply. It
sounds as though it's a package intended to work with a simple boiler and to
have all the controls to make a drop in installation with such a boiler. I
think that you would be better off specifiying it without all the extra
gubbins that you don't really need.




So to summarise:

- It's a good boiler and you could team it up quite easily with a heatbank
or
fast recovery cylinder

- You could heat the heatbank to 70 degrees using the analogue sensor or
more
if you went for a conventional cyllinder thermostat or better an electronic
on/off one with cylinder sensor. Danfoss Randall and others make these.
The advantage compared with a crude bimetallic strip type is that they have
better accuracy and tighter hysteresis. The analogue sensor does give the
boiler information about the actual temperature as opposed to a
demand/satisfied signal, but other than detecting the temperature fall when
a tap is turned on slightly earlier, I don't think that a lot is lost.

- There is a considerable advantage in having the outside temperature
detection and the fully modulated pump for CH purposes. You get much
better
control and behaviour of the system in terms of temperature stability plus
the lower average running temperatures for the circuit and greater running
efficiency.

- I would go for the Micromat without diverter and drive the heatbank
directly with it. The boiler will drive the CH very well and control it
on its own. I would buy one again.

Utlising the pre plumbed S plan setup?

I didn't do anything pre-plumbed. The wiring and plumbing were simpler
without.


if so then this seemed to me to
be the best approach however what with the possible issues over wiring
and some of the information I have had back I have rethought my
original plan and ended up confusing myself even more I think!


/andy