Combi and domestic HW buffer vessel (domestic)

[Paul Barker]

What kind of flow rates do you achieve tho?

dependant on solar element, not as much as you seem to need, I still treat the whole system as a one tap design, but there is no sense of inadequacy with one tap (28kw combi usually fed water above 15 degrees C so delta T result more effective), and when their is a lot of solar heat or only solar heat it has the flow rate of any unvented hot water supply. what is important is that very few days in the year have absolutely zero solar input, so whatever the output would have been for the combi is always increased by the fact the supply water to the combi is pre-heated.

The idea behind the HW buffer is so i have a high flow rate/fast recovery. I suppose it would also be very simple to build a simple controller that recognises what the stored temp is at a set time, then if the Solar hasnt provided enough HW hen it would simply turn the HW circulator on and top the buffer up.

you loose efficiency for the benefit of comfort doing that. To benefit from solar you have to have a cold store of water waiting to benefit whenever it is available. Your method would heat that store so later when the sun comes out you can't benefit from it.

Would you think i would be better off using the existing primaries for solar or the fabricated ones?

works for me.

If you want economy and comfort then you have to have a two coil cylinder and always leave the bottom strata for solar, heat the top strata only for comfort, or have two cylinders one for solar one for comfort feed the output of the solar into the comfort so that at least you always utilise what is heated by solar. the downside is you require double the storage space.

What i find from solar is that you have a low level warm up available to your all year and far too much solar power for a very short part of the year. Really you could export the over capacity to your neighbours as it is simply wasted. if you went for the two cylinder method during hot days you could switch over the comfort cylinder to a second solar store. A sort of weather compensation system in reverse.

 

[looneyfitter]

Thanks for the replies lads. I am thinking over the top of with regards to Control etc, i know this. The reason i was saying about CT circuits is that in general (commercial) UFH/fan convectors etc are fed from these. Where as rads are on VT circuits. So the domestic factor of having the rads and the UFH on VT has just confused me. Viessmann is also new to me and i am still learning as to how they control there product.

So. Lets narrow it down and simplify how it will work/function then we can discuss from there.

For people who arnt sure and are following:

WC= Weather Compensation
V T = Variable Temp (this is a weather compensated circuit)
CT = Constant Temp (This is a constant temp circuit set by the boiler stat)

The boiler flow/return will be (as standard) connected to the UFH primaries and the rad circuits. The boiler will be timed and controlled from the WC.

The WC will have my set curve configured and will come on as per the WC controller/timer. The WC will read the OUTSIDE temperature and the Boiler FLOW temp and from that either increase or decrease the flow temperature to give the desired heat output to give 21deg.


Now with the SUB kit as Mystery has said, I will also have a secondary mixer and flow sensor giving me a second VT circuit. This is fed from the boiler primaries which is also essentially a VT circuit and will feed the Rads.

I cant understand why you would have a dedicated WC VT circuit feeding a seperate WC VT circuit?

Now what i have at my home is 3no. circuits.

1. Upstairs Underfloor heating fed from a blended manifold with each room electronically individually controlled for time and temp as we don't use all the rooms/ heating all the time, i like to be cold going to bed and warm getting up etc . Also there is no point heating upstairs whilst we are downstairs.

2. Downstairs, we have Radiators with each room again individually electronically controlled for time and temp.

3. The conservatory also has its own primaries from the boiler and Local UFH blended manifold and 2 no. radiators (rads are on the primaries obviously)

I have only just installed the rads as last year the conny (5m by 5m glass roof) seamed very slow to warm up. The rads have aided with heat output alot so i may ditch the UFH for this area. (winter will tell)

What i want to be able to do is control at least the 1st 2 circuits independantly ( i will use my stats as timed trv's so not to interfere with the WC)

I also want them both on INDIVIDUAL VT circuits as i cant see the point in sending 80deg to the UFH primaries if i only need 60deg.

The same for the Rads

Is it possible to incorporate a 'mean' room temp for each of the 2or 3 areas into the controls to aid the warm up time of each?

I also want both circuits to be weather compensated. The conny can be fed from the rad primaries if need be.

Or once again am i going way over the top? Its my design and installation head turning on again.

Thoughts and suggestions with how you would set it up would be greatfully appreciated. I am basically trying to see how other engineers would go about this domestic setup as the commercial route seems to be different.

This is the system i have a the moment. It also had the net monitor etc installed.
http://www.heatmiser.co.uk/

Gareth

 

[looneyfitter]

Paul thats a fantastic read mate... I am really new to solar and very interested in it. Storage is not really an issue to be honest. I could always put a second storage cylinder on its side in the loft.. I kinda get what you mean with regards to wasted solar energy (only read it once, still sinking in) DO you have any schematics to clarify the setup further at all?

TBH solar wont be installed until net year now but i want to set the system up for comfort now but obviously incorporate pipework/layout for economy when i add on.

I you was me and going off my last post what would you do? This question also goes for other engineers reading. As said i am looking for more ideas/design stratagy's.

There is always someone with another idea .

Kind Regards

Gareth

 

[looneyfitter]

gareth

for the hot water pauls set up is almost the same as page 8 of the rinnai except instead of having two coils and passing the DHW through one he uses one coil connected to the solar to warm the cylinder and the output of that goes into the combi.

for flow rates the combi will be the restriction because if the pipes are sized right the cylinder will pass in excess of 40lpm.

as for the heating,in all fairness i think your going way over the top with LLH, mixing velves, VT and CT. simple zoning and WC will work better unless your going to start using proper controls measuring return temps,outside temps,circuit temps,floor temps and individual room temps etc.

Cheers mate. This site is fantastic. Its really interesting to discuss/float ideas and methods with other engineers.

for flow rates the combi will be the restriction because if the pipes are sized right the cylinder will pass in excess of 40lpm.

Not quite sure where you coming from tbh mate? I was thinking that with the below setup, minus the coil as you say then i would have the 14.5lpm, from the combi, All the pipwork too and from the combi will be in 22mm (purely for future proofing) DRV on the HWS from the combi. How would i get 40+? Because it's pre-heated?

Am i way out?

 

[Biggles..]

I thought you were concerned about flow rate,a modern unvented such as megaflo happily could give 40lpm,input that into the combi and the combi will restrict it down to the 14 or what ever the book says.

You might actually get better performance than the book due to the fact the waters preheated into the combi,

Combine cylinder output with combi output and you'd have awesome flow,just need to make sue cylinder output does mix if not at the right temp.

 

[looneyfitter]

I thought you were concerned about flow rate,a modern unvented such as megaflo happily could give 40lpm,input that into the combi and the combi will restrict it down to the 14 or what ever the book says.

You might actually get better performance than the book due to the fact the waters preheated into the combi,

Combine cylinder output with combi output and you'd have awesome flow,just need to make sue cylinder output does mix if not at the right temp.

I thought you was on about summit else mate. No your right i agree with you totally. as per the drawing i would only be sending warmed water to the combi which as ive said earlier will increase the flow rate but no where near 40lpm. Were on the same page 100%

So i have to make a choice between comfort and efficiency. What i want is a very clos happy medium. Maybe WE should make a decision with regards to the heating side of things and then concentrate on the HWS setup or vice versa

I will scan a copy of my HWS design in the morning

 

[Biggles..]

Just a thought that's popped into my head is L8.

Most manufacturers show there design of this sort of thing having two coils with solar on one and preheated cold through the other,basically to avoid legionella.single coil connected to solar could see you store volume sitting right where you don't want it in relation to temp.

Paul what do you do to comply with L8 other than hoping you draw enough water off rather than actually killing it through the heating process when your solar input isn't very good.

 

[looneyfitter]

any schematic/link of that design?

How would the pre-heated cold work|?

 

[mysteryman]

I had not realised you were thinking of solar later on. If you are, you will need solar hot water storage, as it is a slow process. Your existing cyl would be good for that - but you mustn't heat all of it up from the boiler. Just keep it as a solar preheat, and supply the hot taps directly from it when it is 50C or above, and via the combi when it is below 50C.

Various guys have talked about high flow rates of 40 litres/min or more. Can your cold main support this?

 

[looneyfitter]

how do you control how and what feeds the taps mate? as said im not up on solar at all.

I have a 32mm main so flow aint a prob

 

[mysteryman]

The boiler burner modulates to give VT for the rads, and the mixer mixes down to the VT for the UFH. Two different VT circuits with just one mixer - simple!

Somebody somewhere makes a suitable valve for switching over between a solar cyl and a combi. Paul mentioned one method. I will investigate tomorrow.

I still think you should check your cold main flowrate at a back pressure of 1 bar. I understand about the 35mm pipe, but you haven't told us the flowrate.

 

[looneyfitter]

agghh right cheers mate.. ill check flow rate 2mro.

Gonna have a word with Viessmann tech aswell

 

[Norcon]

Somebody somewhere makes a suitable valve for switching over between a solar cyl and a combi

This is one.....
http://www.intaeco.co.uk/resources/solar/intasol_installer.pdf

In fact 4 valves in one.

 

[looneyfitter]

Somebody somewhere makes a suitable valve for switching over between a solar cyl and a combi

This is one.....
http://www.intaeco.co.uk/resources/solar/intasol_installer.pdf

In fact 4 valves in one.

cheers mate. Whats the cost on them do you know\?

 

[Norcon]

I was pretty sure Navitron sold them and just popped over to have a look but cannot find them at the moment but from memory I think they cost around £280.