IS THIS GOOD PRESSURE?
- Thread starter bobby62
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B
BigBurner
This is a school, which is quite larger. If the accumulator can take 7 bar then all is fine. Dropping the pressure after the accumulator ensures more pressure stored in the accumulator. 7 bar stored in the accumulator rather than 1.5 to 2 bar, will ensure it will last longer before being exhausted.
Cost may be a problem and a cheaper lower pressure accumulator dropped to 2 bar at the mains stoptap may be the cheap way. If the accumulator cannot take 7 bar then drop to 2 bar and have a pressure relief valve set to 3 bar to protect the accumulator in case the pressure reducing valve fails.
An AVC tank-in-tank, which is a hybrid thermals store, or plate flow heat exchanger is the only way to ensure no DHW exhaustion.
Two points that must be focused upon, which will give a cost effective system:
- Balancing all the water outlets with flow regulators. Balancing the water system is crucial to ensuring no exhaustion of DHW and adequate flow and pressure to the showers (they are important and must take priority over other outlets)
- Ensuring a rapid reheat of the cylinder. This ensures no exhaustion of DHW and using plate heat exchanger will mean when the cylinder is exhausted the boilers energy will provide DHW in an instant manner.
Many plumbers do not do the above and just oversize cylinders and such hoping it will just work.
I recall a hotel that had the water system balanced. It took a few men a number of days inserting flow regulators in tap tails, shower hoses etc. The hotel made the cost back a matter of weeks as when a guest complained they ran of of hot water when having a shower, they dropped the bill. Not once did they compensate anyone for not having a hot shower. No one complained that the showers were poor either.
In this situation it may be more cost effective to install a bank of Rinnai multi-points - perfect for this application. I would consider this route:
http://www.rinnaiuk.com/product_water_manifold2.htm
Rinnai have multi-points that can be fitted "outdoors" too. 600 litre unvented cylinders are not cheap. You will still need the accumulator though.
http://www.discountedheating.co.uk/shop/acatalog/Andrews_LWX42_LPG_External_Water_Heater.html
At £720 a unit and you will need about three of four of them banked, that automatically come in when demand increases, that is say £2800. That is the approx price of a poor performing coiled indirect unvented cylinder. The multi-points will never run out of hot water and no large cylinder taking up space, which can explode (another safety consideration for a school and kids). If one banked multi-point drops out the other three still work, so backup.
I would be inclined to go the multi-point route as it has many advantages and price being one.
Thanks for your replies. The accumulator store seems like the best and most feasible option, you have said an accumulator with 600 litre capacity and mentioned 6 showers at 10 litres/min = 60 litres/min. Presumably the accumulator will be adequate for the 6 showers running for 10 mins (worst case).
Also, I know there has been many discussions on this but, am I correct in saying that by fitting an accumulator this will improve flow the rate provided you have good pressure (we have 7 Bar static) but only 30 ltrs per. minute flow rate?
Also, I know there has been many discussions on this but, am I correct in saying that by fitting an accumulator this will improve flow the rate provided you have good pressure (we have 7 Bar static) but only 30 ltrs per. minute flow rate?
B
BigBurner
That should be fine with a rapid re-heat cylinder. Plate Heat exchanger or ACV tank-in-tank.
The accumulator is designed to improve the flow rate. It stores cold water under pressure. When you stop drawing off water it immediately recharges. That is why I say have one that can take 7 bar and reduce pressure after. It will recharge faster. It also recharges as water is being drawn off too, if the draw-off pressure is less than the mains can give. It also stores cold water in case of an outage. So the toilets can still work. They are simple devices.
Look into the Rinnai multi-point route. that looks ideal in many ways for what you need.
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On this occasion BB is right, IMHO.
However, an accumulator running at 7 bar is risky because of the load on the diaphragm. I would put a PRV in front of it.
The Rinnai stuff is good but a bank of them would need a large gas supply; this might cost more to lay on than the rest of the job together. I would consider using a Rinnai with a heatbank cylinder buffer.
Or 4 Broag Avantas connected together
However, an accumulator running at 7 bar is risky because of the load on the diaphragm. I would put a PRV in front of it.
The Rinnai stuff is good but a bank of them would need a large gas supply; this might cost more to lay on than the rest of the job together. I would consider using a Rinnai with a heatbank cylinder buffer.
Or 4 Broag Avantas connected together
On this occasion BB is right, IMHO.
However, an accumulator running at 7 bar is risky because of the load on the diaphragm. I would put a PRV in front of it.
The Rinnai stuff is good but a bank of them would need a large gas supply; this might cost more to lay on than the rest of the job together. I would consider using a Rinnai with a heatbank cylinder buffer.
Or 4 Broag Avantas connected together
Thanks for your replies, I take on board all your comments. I agree to fit a bank of gas Rinnai's would need a large gas supply, to which I don't think would be available, also the space required / flueing and whole installation (not to mention servicing) would seem more expensive than a 600 litre ACV for instance. This isn't a hotel at the end of the day.
B
BigBurner
It depends on the makers specs.
A U16 may do it with lots to spare. It also depends on what the other gas appliances consume too: boiler for heating, cookers, etc. The gas supply is worth looking into, as it may be suitable.
That is a good alternative.
How odd.
So BB what would a U16 give you in KW eh?
B
BigBurner
I doubt there would be much in it, in cost, between a large cylinder and three or four Rinnais. The demand is intermittent high demand. All the showers will be on at once - not too dissimilar to a hotel. The Rinnais will never run out of hot water. Fluing? Through an outside wall as per any small boiler. Or the outdoor mounted units have no fluing whatsoever. Just a slit at the top. This is not a Rinnai but similar.
The gas supply may already be OK. If so, seriously consider the Rinnai route. Also, they are easily expandable. If there are more showers built or whatever, you just add another Rinnai to the bank. Try doing that to a cylinder. The Rinnais will guarantee the DHW flow and never run out. and easily expandable. Rinnais are exceptionally reliable and a typical quality Japanese product. The standard configuration in every MacDonalds in the world, where they can do it, is banked Rinnais. They don't like running out of hot water. If one drops out the others still work.
The existing UK skills base has this fixation with cylinders - many are stuck in the 1960s. The rest of the world is amazed that we still have tanks in lofts in homes - the UK and Ireland are the only countries to do this on a large scale. While in Japan they think very differently. The largest DHW multi-points are made in Japan - sadly the larger units are not imported.
http://www.bsria.co.uk/news/1885/
B
BigBurner
Soooo what is it?
B
BigBurner
You don't know that? You are in the wrong job.
Point of order BB .... I know the answer...... YOU don't seem to!!
B
BigBurner
Is this a quiz? Are you the quizzing quizzer?
Limit your showers' flow. Remember a 10kW electric shower only give about 4 litres/minute and the kids wouldn't complain. As you say, it isn't a hotel. It'll cut your bills too.
Be wary of putting all your eggs in the "high mains pressure" basket. We put 2 combis in a stable block, which has long supply pipes from the road. It was fine when the water provider were saying their 5 bar was reliable, but when they cut it to under 2 bar there was a problem. They only guarantee 1 bar at a piddly flow rate.
Cistern and pump was solution for them.
Be wary of putting all your eggs in the "high mains pressure" basket. We put 2 combis in a stable block, which has long supply pipes from the road. It was fine when the water provider were saying their 5 bar was reliable, but when they cut it to under 2 bar there was a problem. They only guarantee 1 bar at a piddly flow rate.
Cistern and pump was solution for them.
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