WEhat size of unvented cylinder do I need?

[DerAlteFritz]

Hello
I run a guest house with 7 room, (up to 16 people) which has 2 baths and 5 showers and 7 basins. We also run the kitchen sink from the DHW supply, one commercial dishwasher and two commercial washing machies from the DHW supply. Currently we have a 36KW boiler and a traditional gravity fed system with a 166 litre tank.

We added a 40mm water main last year so have around 6 bar pressure and would like to go for an unvented cylinder but how big would this need to be to supply this demand?

 

[muggles]

In guest houses and the like, it's very important to ensure you can never run out of hot water or your guests will be very unhappy and you'll end up with a bad reputation. I'd be inclined to put in two 300L cylinders connected in parallel, and upgrade your boiler as well, as the cylinder coils could take up to 52kw for the best reheat times.

 

[DerAlteFritz]

If we are talking about upgrading the boiler then we must add a further three rooms and 7 people which are currently serviced on a separate zone with its own Ariston 210 litre unvented cylinder.

So the boiler would have to service all three Megaflows for DHW and the CH demand as well.

 

[dcawkwell]

I suggest you look at semi-instantaneous and cold water accumulators.
The cold mains can only supply so much . There would have been no
need to increase the water main size. Bet that was expensive.

http://www.hrshevac.co.uk/products/semi_instantaneous/as.aspx

Perhaps two of these with multiple boilers so you have backup
and are never without hot water and heating. This is for the 7 room side.

 

[ChrisR]

40mm and 6bar - I doubt you'd need accumulators.
Careful installation to stop one part of the systemn hogging all the water, yes.

My primary requirement would be for more than one boiler for WHEN one fails.

SIze - you have to work out the maximum possible requirement that you're prepared to allow for, simple litres per minute stuff.
Say 80 litres per bath at 60C, plus the showers at whatever design rate you've provided, all at once! You have also to guard against legionella, and not scald your customers, and of course a secondary return circuit to time/insulate etc.. Too much to get from a free web site really!

The commercial kit will tell you what water it uses.

Sie sprechen vermutlich, Hochdeutsch?

 

[DerAlteFritz]

I suggest you look at semi-instantaneous and cold water accumulators.
The cold mains can only supply so much . There would have been no
need to increase the water main size. Bet that was expensive.

The original main was 15mm and has to supply the guesthouse and another building. One consideration in favour of a new larger main is that we are very short of usable space and since this is a historic building, difficult to add more. So a pipe in the ground (allowed by the planners God Bless 'Um) was preferable to another tank in the building.

This is the main reason I am interested in discussing innovative ideas that might save us space and yet deliver the DHW demand we need. This seems a good idea, saving space/storage.

Would a thermal store vented tank such as the Gledall Torrent do a similar job? Which would be the best bet in terms of space saving?

 

[DerAlteFritz]

SIze - you have to work out the maximum possible requirement that you're prepared to allow for, simple litres per minute stuff.
Say 80 litres per bath at 60C, plus the showers at whatever design rate you've provided, all at once! You have also to guard against legionella, and not scald your customers, and of course a secondary return circuit to time/insulate etc.. Too much to get from a free web site really!

Of course the actual design, installation, commissioning will be given to a firm of professionals but I find it helps choose which professionals to use if you have some idea of the solution you want.

I am trying to weigh up the advantages and disadvantages of:
a) unvented cylinders (already use three so have plenty of experience here) - size and performance
b) thermal heat store such as Gledall Torrent or DPS
c) other ideas

So we are aiming for around 100 litres / min max demand with peak demand spread over about an hour and a half in the morning. Max stored water would need to be around 450 litres but could I cut this quite large storage requirement down with a mains fed DHW supply such as with a thermal store?

 

[Agile]

I dont understand why you think that the storage requirement would be lessened by using a thermal store!

Generally about 2 x 300 litre unventeds and I would use two boilers each about 36 kW in order to be able to obtain a quick reheat time.

Its not that difficult to manage a situation like that. Look at what you have now and see how it can be improved.

Tony

 

[dcawkwell]

You haven't mentioned it but including solar hot water
to heat a buffer tank(s) and therefore reduce running costs
would be a good idea.

Given the high volume of water usage.

 

[DerAlteFritz]

I know very little about thermal stores except the principle so I thought it was worth asking if I could save some space.

Also I have quite a challenging site to work on, the building is medieval, listed in a conservation area and getting permission to do anything is frankly a nightmare.

So two 300 litre unvented cylinders, would be great except that they are too high (Ariston Classico height is 1780 plus expansion tank) where the ceiling height is 1700. We do not have the floor footprint for three cylinders. I would have space to add an additional boiler so the idea of shortening the heating time is attractive if it custs down the storage.

I reckon the mximum I could get into the space would be 2 x 210 litre unventeds and a new floor mounted boiler. But is there a better set up that is more space saving and uses my mains water pressure? Could for instance I have a thermal store outside the building in a shed, or unvented cylinders outside?

Solar panels would be a great idea but since a conservation area protects the 'look' of properties, I doubt if I would get permission unless they were ground mounted. But we could add a back boiler to the wood burner in the fire place to give additional heating in the winter.

 

[Agile]

You seem to have very little understanding about the options available. For example you mention floor mounted boilers. There are very few models available any no obvious reason why anyone would want one instead of the normal wall boilers.

You make a lot of the planning aspects and then go on to suggest "sheds" to contain the unventeds! That seems very unlikely to be approved

Have you considered lowering the floor to accommodate the correct size of cylinder?

Tony

 

[DerAlteFritz]

You seem to have very little understanding about the options available. For example you mention floor mounted boilers. There are very few models available any no obvious reason why anyone would want one instead of the normal wall boilers.

You are quite right, I have very little knowledge about the options which is why I am exploring all possibilities. We currently have a floor mounted boiler, because it is not easy mounting a wall mounted boiler on a medieval wall.

You make a lot of the planning aspects and then go on to suggest "sheds" to contain the unventeds! That seems very unlikely to be approved

Anything that does not affect the building and allows it to go back to a more 'natural' state would be approved so long as I can hide the offending shed! So an outside hot water store is definitely on.

Have you considered lowering the floor to accommodate the correct size of cylinder?

Tony

Again they are not going to allow structural changes to the building, so lowering the floor by half a meter is not going to work I am afraid.

So a good option seems to be the largest store I can fit into the existing space and then a very rapid re-heating by adding boiler capacity and a good heat exchanger.

 

[Agile]

Thats an amazing product knowledge for someone who pretends not to work for Viessmann!

It also seems ideally suited to the requirements of the OP.

So Herr OP, what do you see as wrong with that arrangement?

Being German made it will be somewhat more expensive than an Ariston but most heating engineers will consider them to be better quality.

Tony Glazier

 

[mysteryman]

I don't pretend - or comment.

 

[mickyg]

I see Viessmanns advertsing campaign is still in full swing on this forum ! most people use conventional media for advertising, but viessmann it seems sends its employees on to web forums !

Anyway, op, i dont know what room you have, but I always think the better option for hotels etc is a bank of Rinnai water heaters, but you talk about space restrictions quite a bit and I suspect whatever solution you come to will be a compromise of site requirements and best suitability. As Chris has said, you first need to know how much water will be drawn in what space of time in a worst case scenario.
One very large cylinder will mean you are constantly heating a large volume of water all the time, of which you may only use a little. Using water heaters means paying to heat only the water you use, and if one breaks you will still have uninterupted service.
Unfortunately the Rinnai website appears to have a virus of some sort! Which isn't very professional nor helpful, but the product is very good.