"Andy Hall" aka Matt wrote in message
...
On Sat, 20 May 2006 10:44:58 +0100, wrote
(in article . com):

We are currently looking at updating our central heating and DHW. The
existing system is old and looks like it has been cobbled together at
various points in the past - for this reason and to facilitate other
house work, we are planning on putting the new boiler and DHW tank in
the loft.

Following research on google we have decided that an indirect Pandora
heatbank best fits our DHW needs (mains pressure is sufficient and the
ongoing safer operation vs a traditional unvented cylinder appeals to
SWMBO).

Apologies if the following appears to ramble - I am not an expert and
profess only to have gained my knowledge from this exceelent group and
many of the learned regular posters...

Not fully DIY but for reasons of speed and time we will be employing a
plumber to do the installing (I am however doing the
design/specifying). As seems to be the norm he was very reluctant when
I first mentioned the Heatbank to him and he was steering me towards an
unvented cylinder ...after running through the spec with him
(downloaded from DPS) in words of 1 syllable he has now come round to
the idea - probably as he can see the pre-plumbing of various parts
makes his life easier...!

The Pandora I have initially specified is 180l / 100kw / inlcuding two
2 port valves (S plan) that would serve heating/DHW.

Now the main issue - choosing an appropriate boiler to cater for the
heatbank and also serve the heating (radiator) system. Following
various discussions with my plumber we have calculated our heating
requirements at around 26kw and to err on the side of caution we are
looking at boilers between 28-31kw.

Following a number of positive posts and reserach into the features
offered by the Man Micromat (outside weather compensation/analogue
temperature DHW sensing/fully modulating pump etc etc) I have looked
into the Man Micromat H or HS series. I like the idea of these
features and also the ability (AIUI) to have a different set
temperature for DHW and a separate temperature for the heating.

Following considerable discussion with Eco Hometec they have raised a
number of issues that are bascially steeering me away from choosing the
Man:

1) The Man DHW probe can only sense temperatures upto 65deg - the
heatbank is suited to be heated to 75/80deg therefore not really
suitable. The Pandora has its own sensor(s) however these do not
directly feed into the boiler. Maybe this isn't a problem?

2) Due to the wiring of the Pandora (?) only one fixed temperature
output from the boiler will be provided therefore the separate setting
of temperatures for DHW/heating is not possible?

3) Due to number 2) the fully modulating room sensor and outside
weather compensator would not be required?

I am slightly confused as all of the literature I have read suggested
the ability to run separate temperatures for heating/DHW and now it
seems as though this isn't possible and therefore all of the additional
features the boiler is capable of are also not relevant? Unfortunately
am not expert enough in all this to argue the toss greatly so was
hoping for some additional input from the group?

a) Does the Pandora negate the need to have a "complex" boiler like the
Man?

b) Would a Pandora without zone valves etc team up with Man and its own
diverter etc?

Perhaps I should just be looking at a simpler 28-31kw boiler to avoid
any unecessary complications?

Many thanks to all replies in advance
Robin


I have a Micromat and have been very pleased with it. I don't use it
with a
heatbank because my mains flow rate is not adequate for my purposes. I
therefore went with a large (200l) fast recovery cylinder and kept the
loft
tank. Considering possible water availability issues, I don't think that
this was a bad idea. However, had I had a decent flow rate, I might have
gone with a heatbank.

Let me make a few comments on the two parts of this:

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.

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.

Eco Hometec give quite good service, but in some areas, their knowledge of
the products is lacking. Their translation of the German manual is poor
in
places and scant in others.



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.
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.

Matt, how does your boiler model know that DHW is calling if fitted with
either a stat or temp sensor?



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.


/andy