Indirect Pandora Heatbank and Man Micromat/Boiler compatability

[rjb9999]

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

[Andy Hall]

On Sat, 20 May 2006 10:44:58 +0100, [e-mail] wrote (in article ):

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.

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

[rjb9999]

Andy,

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

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.

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 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?

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

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

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?

Utlising the pre plumbed S plan setup? 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!

[Doctor Drivel]

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

[Andy Hall]

On Sat, 20 May 2006 19:02:49 +0100, Doctor Drivel wrote (in article ):

.

There is a setting on the controller in the boiler to select whether the DHW demand sensing is by a contact closure (i.e. thermostat) or a temperature sensor.

There is a similar one for CH control where the sensing is between thermostat contact, a PWM signal from a Siemens or other controller or 0-10 or 0-3v analogue control.

[Andy Hall]

On Sat, 20 May 2006 16:47:56 +0100, [e-mail] wrote (in article ):

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.

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.

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.

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

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.

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.

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

[rjb9999]

Thanks again Andy, the situation does seem a little clearer to me - it is only that involving an external party (installer) in my installation means additional complications especially as the boiler isn't an "off the shelf" product it seems to be easier for him to say it can't be done etc as opposed to looking into things in a bit more detail. Perhaps I should be finding someone who is a little more flexible...

Apologies for continually rehashing my questioning but you seem to have the practical input that neither DPS nor Eco's could feed back to me, you don't do callouts do you !? :)

If I go for H series boiler and no additonal zone valves on the heatbank I will still need some form of diverter (either from Eco's or an off the shelf diverter?) presumably so the flow can be directed appropriately? The wiring for this seems straighforward and goes directly into the mains rail of the boiler?

I can specify a Heatbank without any additional zone valves ie the only additional items on the cylinder are a circulating pump / flow switch / backup immersion element (DHW controls) and thermostats (only item affecting boiler behaviour). The suggested wiring diagram for this setup appears relatively strightforward however it still outputs a single swiched live to the boiler, however, I don't see that this is any dfferent to standard cylinder installation and akin to the type 2 installation schematic on the MHS technical manual? The Eco manual is a little lacking here and they describe the equivalent as the wiring for the room stat however whether it's room stat or cylinder stat the boiler should know that it is being called upon and fire up and then the diverter should take care of diverting the flow appropriately?

AIUI the heating side would then just be a case of wiring in the low voltage outside weather compensator and RE2132 onto the low voltage rail?

Thanks again in advance Robin

[Doctor Drivel]

When a stat detects DHW is calling the boiler just then runs up to what the maximum temperature the boiler is set at? Demand sensing - this will be a DHW setpoint (cylinder temp) set at the boiler. Below and the boioer runs up the the max boioer temp set?

External control which incorporates the burner modualtion rather than on-off.

[Andy Hall]

On Sun, 21 May 2006 09:54:42 +0100, [e-mail] wrote (in article ):

You could either use a diverter valve arranged so that when energised, flow goes to the cylinder, or you could use a zone valve for the cylinder from the same output and then a second zone valve for the CH run from the second output normally used for an auxilliary CH pump. I went for the latter approach because I needed to run a second heating circuit for some additional radiators and it was much more convenient to take that from nearer the boiler than after the normal split in the flow some metres away. I simply wire both CH zone valves to the second output

You could do that. All that would then be needed is an additional relay run from this output from the cylinder wiring and then used to provide contacts for the boiler.

The boiler will provide a live to open the DHW zone valve.

If you use the RE2132 then that goes directly to the boiler LV rail as you say, along with the outside sensor connection

[Andy Hall]

On Sun, 21 May 2006 10:08:05 +0100, Doctor Drivel wrote (in article ):

Exactly.

Yes again.

Yep. (You're getting good at this :-) )

The Siemens (was Landis & Gyr) RE2132 controller which is specifically intended for this boiler, AFAIK, (possibly special firmware), has a setting to adjust the relative balance between the external weather sensor and internal sensing. Thus one can have different response behaviour according to nature of house. It takes care of optimised start as well.

The other input methods are used in commercial applications when multiple boilers are cascaded and a cascading controller is used to handle up to 9 of the boilers.

[Doctor Drivel]

You should learn how to describe what it does. :-(

[Andy Hall]

On Sun, 21 May 2006 12:41:31 +0100, Doctor Drivel wrote (in article ):

I was trying to keep it simple so that you would understand.

[Doctor Drivel]

Matt, I know what it does. Others reading didn't have a clue, reading what you wrote.

[Andy Hall]

On Sun, 21 May 2006 16:20:54 +0100, Doctor Drivel wrote (in article ):

Then why ask?

Sigh....

[John Stumbles]

...

That's going to be fun to get into your loft! (and to site safely)

That's an awful lot of heat. How many rooms does your mansion have, to the nearest dozen? :-)

Have you checked with the whole-house calculations on

that the latter is wrong for mid-floor flats, at least.)

I'd expect to size a boiler at around 10-15kW for normal sized houses. OTOH if you can afford a Pandora and a MAN then maybe you also have a house with that sort of heating requirement :-)

[Doctor Drivel]

The MAN can go down to 3kW so not a problem for the CH, but will heat the Pandora zippo with DHW priority.

Or he could use a Glow Worm condensing boiler, (modulates down to 5kW) and a stand alone Danfoss BEM 5000 weather compensator (about £190), with has the cyl' stat wired directly into it and gives full heat of DHW and weather compensted on CH. The compensator may be giving a CH flow temp of 45C, but when DHW is called the full 80C is given to the cylinder, modulating down when near heated.

[rjb9999]

Admittedly I have left most of the calculations to the plumber but the house is probably slightly larger than average, detached and rather draughty underfloor (1928 built). As DD has pointed out in choosing a fully modulating boiler it should adjust where necessary...

I could opt for a more economic solution however having reserached the market there seems to be much of a muchness amongst the cheaper to mid range boilers and choosing between them seems to be very difficult however, the Man and a couple of others come highly recommended and do seem to stand a little above the rest in terms of functionality and build quality. Horses for courses I guess as they do cost considerably more as well.

As stated above I am employing an installer to do the actual fitting and this in itself has it's own complications especially as he would rather I go for a cheaper more mainstream boiler but I haven't yet given up hope of converting him.

SWMBO, of course, doesn't understand why I am going to all the trouble of speccing such a complex and expensive boiler :( I am still working on her although as soon as I mention outside weather compensation she sends out a huge sigh!

[rjb9999]

Thanks Andy. I want to keep things as simple as possible especially for the wiring side (for me and the plumber) so if possible I want to avoid the use of additional relays etc so my latest considerations are:

AIUI

HS boiler - 1 flow/return for DHW and 1 flow/return for heating.

Internal diverter to direct flow - this should be pre wired.

Heatbank fitted with 2 cylinder stats. I need to check with DPS on wiring compatability but from the looks of it this can be wired back onto the mains rail of the boiler itself?

Heating controlled by outside weather compensation and RE2132 room unit?

Are the 2 stats on the cylinder and and heating controls sufficient to be classed as the boiler interlocks?

not sure if am missing something?

Any input greatly appreciated. Robin

[rjb9999]

I have looked at the glow worm and it is considerably cheaper and out of what is available seems to be a reasonable product. If I can't get suitable answers from DPS and Eco Hometec regarding the Man and the Pandora then I may yet go down this route.

[Christian McArdle]

Also, consider the Worcester Bosch Greenstar with additional diverter valve (assuming they still make it in the new range). This allows separate temperature settings for DHW and CH. Technically, the DHW is (or was in the previous version) limited to 75C and the CH is limited to 85C, but we couldn't see a reason why you couldn't swap the circuits, although a relay might be required to get DHW priority instead of CH priority.

This way, the boiler can produce 82-85C for the Pandora and drop to 60C for the CH, which is safer and more efficient.

I have the WB and the Pandora, but didn't specify the diverter, which I probably regret now, as I have to run the rads too hot.

Christian.