Indirect water cylinder

[fixitflav]

I actually think that programmer may be fine - once the hot water is satisfied, then the cylinder stat switches over and sends the SL to T6, that then connects to the CH common, the reason for the double connection - from HW S (off) to the CH - will be for when the HW isn't being called for by the programmer, it then sends the HW off SL to the CH.

Can't agree with that. With the type he's got, when CH is called on the programmer (and the elusive roomstat calls), the diverter valve goes to CH, even if HW is called. That's not PDHW. In that situation, the boiler (I think) goes to HW temperature, so no W comp.
That's my take on it anyway.

 

[fixitflav]

Can't agree with that. With the type he's got, when CH is called on the programmer (and the elusive roomstat calls), the diverter valve goes to CH, even if HW is called. That's not PDHW. In that situation, the boiler (I think) goes to HW temperature, so no W comp.
That's my take on it anyway.

I found a Potterton EP2 programmer which is suitable, attached (couldn't rotate the image). The link L to 5 removed from L and connected to 1

 

[fixitflav]

This one from Salus might be worth looking at. The contacts are volt-free

 

[fixitflav]

Haven't heard anything on this for a while. Did you get it sorted?

 

[desktop987456]

Haven't heard anything on this for a while. Did you get it sorted?

No Sir, I have been away so couldn't respond.
To cut the long story. The DHW distribution piping and location of old cylinder were not optimal.
I have sorted it out and now have placed the cylinder to a more optimal location of the house where it can supply DHW to all outlets (I think!).
I am installing a dedicated boiler to feed indirect (debatable but I got a boiler for the same amount as viessmann relay box). Another 19kw Vitodens OV!
The flow and return tappings on boiler is 22mm. The spec sheet of indirect says to get 60DegC water is attached.
Math tells me that boiler 19x3412 = 63000btu, With DT of 30DegC it should give 15lit/min HW output. Correct?
Questions : Should I be fine with 22mm or go for 28mm copper pipe from boiler to indirect? The indirect's tapping for flow and return are 1.25" (35mm).
Since the boiler is dedicated to indirect so will only have one loop to indirect, where should the pump be located on flow to indirect or on return to boiler HEX?
The resistance through indirect's coil is 3.2ft. The boiler and indirect are only 20ft apart.
Thanks

 

[Johntheo5]

19kw with dT of 30C willl give,19*860/60/30,
9.08LPM??.

 

[desktop987456]

19kw with dT of 30C willl give,19*860/60/30,
9.08LPM??.

I stand corrected; 2.4gpm = 9 l/m.
Would I be fine using 22mm for primary piping to indirect even though its inlet coil connections are 35mm?

 

[Johntheo5]

What make etrc is the cylinder?
Looks like a tank in tank.

The numbers you've quoted/highlighted above are the continuous HW output at 60C with a boiler temp of 70C,
The primary flowrate is 3m3/hr, 50LPM, your boiler hasn't a hope of supplying this flowrate, most boilers design flowrates are calculated using a dT of 20C so a 20kw boiler would have a design max flowrate of 20*860/60/20, 14.3LPM, this might result in a dP through the boiler HEX of anything from 2.0M to 3.5M, it might be in the boiler MIs. Anyway, for info, 40ft of 22mm piping flowing 50LPM will have a dP of ~ 5.8M alone but 28mm piping would reduce it to 1.5M.

Why are you quoting the continuous HW output from the HW cylinder?, in your case, 352LPH, 5.87LPM at 60C, or 9.78LPM (9.08LPM with 19kw boiler) when mixed with mains at 10C. You installed the cylinder because you didn't want/require a combi.
a 120L cylinder at 60C will provide nearly 200L at 40C so will "last" for 20mins at 10.0LPM, 13mins at 15LPM etc, you will then have to wait for the cylinder to recover which will be a good bit longer than the quoted numbers since realistically you'r primary flowrate will probably be more like 20LPM, you could all ways, if necessary, increase the boiler flowtemp to 80C which would compensate to a large degree.

 

[fixitflav]

No Sir, I have been away so couldn't respond.

No problem, hope you enjoyed the break!
Separate boilers for CH and HW keeps the controls simple. You will need a HW cylinder-stat.

Questions : Should I be fine with 22mm or go for 28mm copper pipe from boiler to indirect? The indirect's tapping for flow and return are 1.25" (35mm).

22mm will be OK. 35mm connections on the cylinder suggest it might be for a gravity circulation system, but no problem pumping it. Unlikely non-pumped would be acceptable for the boiler.

Since the boiler is dedicated to indirect so will only have one loop to indirect, where should the pump be located on flow to indirect or on return to boiler HEX?

I assume Vitodens OV means open vented, and you will have a F/E tank. Could use the same F/E tank as your CH boiler AFAIK. Usual way is boiler - open vent - cold feed - cylinder, but there are other options eg pump on the boiler return.

 

[desktop987456]

You will need a HW cylinder-stat.

Yes, the vitodens has No.5 sensor cables coming out of boiler so its just a matter of putting a thermostat in indirect and connecting the leads to boiler.

OV means open vented

Correct but it can be used for sealed system as well.

Usual way is boiler - open vent - cold feed

Yes, how can I forget it now, we went through 10+pages on this topic when I was installing the CH boiler!

Vitodens HEX has a surface area of 0.9 sq.m (radial type), so it wouldn't hurt to put it on return pipe to boiler?

 

[desktop987456]

What make etrc is the cylinder

Its 160 litre, single coil type a

dP through the boiler HEX of anything from 2.0M to 3.5M, it might be in the boiler MIs

nd MI with HEX friction loss is also given.

You installed the cylinder because you didn't want/require a combi.

I have to connect 3-4 washrooms (3 showers and a kitchen, not baths). so Combi was not an option. 5 adults in house using 3 washrooms.

I hav dedicated this boiler to dhw so I don't mind it recovering as we rarely use showers simultaneously.

40ft of 22mm piping flowing 50LPM will have a dP of ~ 5.8M

I have bought wilo pump with max 6m head so you reckon at full speed it should be able to cope even with 22mm.

I couldn't find friction loss of vitdoens but in manual the surface area for HEX was 0.9 sq.m.

Where should the pump go given it will have a dedicated primary loop to indirect with a short run 20ft one way? on the flow from boiler or return to boiler?

 

[fixitflav]

Yes, the vitodens has No.5 sensor cables coming out of boiler so its just a matter of putting a thermostat in indirect and connecting the leads to boiler.

Strap-on cylinder-stat is the usual way.

Vitodens HEX has a surface area of 0.9 sq.m (radial type), so it wouldn't hurt to put it on return pipe to boiler?

Do you mean putting the pump on the return? I don't see what the HEX area has to do with it

 

[desktop987456]

Strap-on cylinder-stat is the usual way.

Do you mean putting the pump on the return? I don't see what the HEX area has to do with it

Yes, putting the pump on return pipe to boiler. In a system boiler that's where the pump usually is. So it is pumping into the HEX.

I could only find the area in sq.m of HEX. Is there a way you could calculate friction loss in HEX if you have surface area

 

[fixitflav]

In a system boiler that's where the pump usually is. So it is pumping into the HEX.

OK no problem

I could only find the area in sq.m of HEX. Is there a way you could calculate friction loss in HEX if you have surface area

No, the friction loss depends on the water flow passages, not just the area. Most boiler manuals have headloss data vs flow, but I couldn't find it in some Viessmann ones. But what makes you think that will be a problem? The in-built pump should easily handle that and the HW cylinder headloss.

 

[Johntheo5]

Getting a bit confused,
IF your cylinder is the ASB1 single coil, 160, then the coil flowrate is only 10LPM (not 50LPM) so 22mm piping will have no problem with this at a dP of ~ 0.3M, and still only a dP of 1.1M if the flowrate was 20LPM. It states a coil resistance of 0.01mSS at 10LPM, what does mSS mean??.
If the boiler is a system boiler with its own in built pump then most of these are now a 7M head pump so no problem in circulating through the boiler HEX and the cylinder coil.
If a heat only boiler then that 6M Wilo will also be fine, presume this (if) heat only boiler can be sealed so pump on the inlet to the boiler with its external EV teed in just before the pump. If a OV boiler then the pump should be installed on the boiler outlet (flow) with, from the boiler, Vent, Cold feed (no more than 150mm apart) then the pump.