direct fired gas water heater

[johno12345]

does anyone have any experience with them?

im looking to have a replacement installed.

its replacing two 300l direct electric calorifiers that lack in capacity, id like to have a single calorifier, gas fired, about 800l stored, room sealed, pumped return with a half decent recovery time.

interested if anyone could recommend brands or anything

thanks

 

[hard-work]

What you mean is, the burner is under the cylinder? Not many make these and those made are all decent quality. It is a matter of getting a decent deal. Do not use anything less than stainless steel cylinders. They are unitised so save space.

 

[johno12345]

yeah, burner in/under the cylinder, to save on having a standalone boiler, pump etc. I was planning to justify it based on cost savings against using electric heat, but they are serious money! Im looking at Hamworthy

 

[hard-work]

Try ACV. http://www.acv.co.uk
For e.g., their 315 litre cylinder has a continuous flow at 45°C of 2,172 Litre/hr. As they have a tank-in-tank high recovery rate the volume of stored water can be greatly reduced. Find out what your usage is in litre per min or hour and work from that. Your 600 litres of storage may be fine with a high recovery rate. You may be surprised and need less.

Look at the Japanese Rinnai instant water heaters - quality jobs. They do some beefy commercial jobs. They can use two of them, staged, so the second only comes when there is a high demand. The likes of MacDonalds use banks of them a lot where they can. Having more than one means no down time, which is important in a commercial operation. Having white boxes on the wall may save a lot of space as well.

https://www.rinnaiuk.com

 

[johno12345]

i did wonder about the recovery rate, obviously with 15kW that we have on 600l the recovery is quite slow. I reckon it needs designing properly. Ill get a water meter fitted to the inlet to the calorifiers , and the consumption monitored too.

 

[hard-work]

Good idea. 15kW Wow, so small, some electric showers are about that. You may need far less than 600 litres. If 60kW is being pumped into the cylinders that is 4 times the recovery rate you now have. Not only that the likes of ACV tend to put the heated water at the top of the cylinder where it can be drawn off immediately.

Look at Rinnai instant water heaters. They never run out of hot water.

 

[hard-work]

This reduces the size of a cylinder greatly by having a high recovery rate using a plate heat exchanger. It puts heated water at the top of the cylinder where it is needed. Heating from the bottom means more water storage. But you will need a separate boiler with this. But if you get rid of one cylinder the boiler may take its space.

https://www.mcdonald-engineers.com/products/plateflow-plate-heat-exchanger

 

[hard-work]

Using the plateflow you may be able to retain the two existing cylinders. But a new boiler would be needed. Worth looking into the options.
https://www.mcdonald-engineers.com/products/plateflow-plate-heat-exchanger

 

[johno12345]

the ACV generators look interesting, how do they (and the others i guess) work with the secondary return on the hot water?

we dont have any boilers anymore, the existing cylinders dont have coils in them so they would have to go no matter what happens.

 

[hard-work]

The existing cylinders can remain by having the flow & return pipes from an external plate heat exchanger, heated via a boiler, on the hot water draw off and the cold feed. The plate replaces an internl coil. It heats the cylinder from top down. I assume you have an adequate gas supply?

ACV's have a cylinder inside a cylinder. The outer cylinder is heated (the space between the two). This heats the inner cylinder very quickly. Some ACVs also have a flue running up the centre of the two cylinders heating the cylinder from inside and out.

 

[johno12345]

ok, i get it now. I spoke to one of the manufacturers who has specced a system at 30kW. the gas supply is 70mbar 8" so should just about manage it

its certainly given me some good stuff to consider

Thanks