Mega Flo vs Thermal store

[JonasX]

Yes it's plate heat,but like I said chosen because of the 40Kw solid fuel burner.

But what size cylinder?

 

[Biggles..]

Would have to check my paperwork but 250 springs to mind

 

[JonasX]

We have fitted several of those DPS (now Specflue) units and their performance is excellent. The idea is to have a large output system boiler to drive the plate as hard as possible.

Mikrofill only do huge units mind you.

Here are the last two DPS ones we fitted. Rather embarrassingly, the first one was one of the last ones DPS made before going under, and there were several components incorrectly fitted. Made for a rather noisy reheat

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• Dan Robinson
• 17 Oct 2011
• 2

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• Dan Robinson
• 17 Oct 2011
• 1

What is the make and type of pump on the 2nd photo?

 

[JonasX]

Would have to check my paperwork but 250 springs to mind

Which conforms to DPSs 250 litre cylinder sizing using a plate heat exchanger and cylinder supplying a similar sized house.

A small 100 litre cylinder using a plate to heat it, can be the equivalent of a cylinder heated by a coil three times the size if heated by say a 20-24 kilowatt boiler.

 

[Biggles..]

It would conform to DPS sizing as it one of there thermal stores,trouble us though it requires a minimum of 40kw heat input to keep the hot water and the ufh going in a single storey dwelling.

Please expand on your 100 lite quote as I'm trying to get my head round what your using the plate heat for ie heating the cylinder or the DHW output.

 

[gaswizzard]

Difficult to keep up here as JonasX keeps editing his posts.

 

[Dan Robinson]

Jonas - 24kW wouldn't provide the amount of water you think it would. You would require 40kW to get the equivalent performance of a 300 litre cylinder.

The pump on the second picture is a Wilo Bronze as supplied by DPS. the two boilers are operating on a 25-55 Grundfos (just out of shot).

That is a 250 litre cylinder heated through the plate.

We have installed twin 90 litre cylinders operating in tandem that are heated off around 36kW. They work very well, but the demand is only one (big) bath and drench shower.

 

[indus]

Anyone specified a heat web/DPS unit lately,I did the other week it was nearly £6k,would have cost no more than £2.5k previously,spec flue have put prices up beyond belief.
The units aren't that good to justify those prices,which is a shame as I've fitted loads.

View media item 19282
That does 6 bathrooms with 2 baths and 5 mira discovery showers quite easily.
Only reason I went for it was for solid fuel input otherwise 2X HD70i would have given the same if not better flow/temperature range,and based on today's DPS prices would have been 2-3K cheaper.

Thanks lcg. Can you tell me exactly what that set up is and does it use just a solid fuel input?

Could you also tell me how HD70i would work? I've gone onto their website but still can't understand it.

Thanks

 

[indus]

We have fitted several of those DPS (now Specflue) units and their performance is excellent. The idea is to have a large output system boiler to drive the plate as hard as possible.

Mikrofill only do huge units mind you.

Here are the last two DPS ones we fitted. Rather embarrassingly, the first one was one of the last ones DPS made before going under, and there were several components incorrectly fitted. Made for a rather noisy reheat

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• Dan Robinson
• 17 Oct 2011
• 2

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• Dan Robinson
• 17 Oct 2011
• 1

Hi Dan, could you also be kind enough to explain what the set up on the right consists of? (inc which boilers you've used)

Many thanks

 

[JonasX]

Jonas - 24kW wouldn't provide the amount of water you think it would. You would require 40kW to get the equivalent performance of a 300 litre cylinder.

The pump on the second picture is a Wilo Bronze as supplied by DPS. the two boilers are operating on a 25-55 Grundfos (just out of shot).

That is a 250 litre cylinder heated through the plate.

We have installed twin 90 litre cylinders operating in tandem that are heated off around 36kW. They work very well, but the demand is only one (big) bath and drench shower.

Drenchers exhaust a cylinder very quickly, as many have found out to their dismay when they get the local jobbing plumber to fit the shower. Then a big bill to upgrade the cylinder.

OK you have 180 litres heated via plate heat exchangers and a 36 kW boiler. That is the equivalent of around 400 litres cylinder size using coils in the cylinders? I will have to get my calculations book out. You are right a 100 litre cylinder heated via 40 kw boiler will be the equiv of a around 250 litres cylinder heated via a coil. A 80 litre cylinder can go under your kitchen worktop. Heat that with 35 to 40 kw and it will pour out the hot water.

So...

No. of kW =

Quantity of water in litres X Temp rise degrees C X Specific heat of water
(4.2)
__________________________________________________ ______
Number of seconds in an hour


So for 100 litres with a 45C temp rise to get to 60C

100 X 45 X 4.2
_____________
3600

= 5.25 kW/hr

So, it takes 5.25 kW one hour to raise 100 litres from 15C to 60C.
Double that result to get 1/2 hour, which is, 10.5 kw to raise 100 litres from 15C to 60C.

Quarter it and 21 kW. So. 21 kw reheats 100 litres in 15 minutes.
Half it again and 42 kw to reheat 100 litres in 7.5 minutes.

It follows that 400 litres can be heated by a 42 kw boiler in 1/2 hour.

Using a plate heat exchanger will pay dividends in using a much smaller cylinder. Compare the reheat times of a coiled cylinder given by the makers, which is always exaggerated. A 300 litre coiled cylinder will not take 40 kw, more like 20-24 kw maximum. Using a plate will take nearly all the 40kw of the boiler's output. And the boiler runs at high efficiency all the way doping reheat.

Dan, you are right about 40kw boiler to make a 100 litre cylinder perform like a 250-300 litre.

Reheating cylinders via coils looks like a rather dumb idea. All it does it give large, expensive, space consuming cylinders. This is where combis come into play that allow hot water on the DHW cold inlet; there are a number about, like Alpha and Remeha and others. Use the water section with a bronze pump to reheat the cylinder. The combis dump a controlled 60C out of the hot outlet pipe. All you need is the combi and a cheap, smaller, direct, cylinder and bronze pump. The combi does the work for you. This is very cheap to install and very efficient all around.

 

[Dan Robinson]

Indus - both system are using a pair of Atmos Inter-system HE26 boiler plumbed as a Siamese pair.

The system on the right is a 250 PHE (actually it might be a 300 - will have to check) recovered unvented cylinder.

The house has 3 bathrooms and 3 showers (plus the usual sanitary and kitchen stuff) with up to 12 people staying for several weeks of the year.

The heating is split into 3 rad zones, an underfloor zone (with 3 sub zones); a towel rail circuit and the cylinder.

All this is plant located in a cupboard 1600 wide and 500 deep. Thankfully it was there when we fitted it . It is in the cellar next to the gas meter, although the G3 termination is stretching the rules a little.

Everything is controlled with Honeywell CM907 stats (including the Nu-Heat underfloor) and there hot water has a secondary return that is both timed and temperature regulated.

Just checked our price breakdown and it was supposed to be a 250 litre cylinder - it just came with a mahoosive EXV.


These PHE recovery cylinders are top loaded remember, so there is a risk that the top of the cylinder can reach upwards of 80 degrees. As it comes off the plate. This is why they use a Danfoss RAV-K valve to limit the top temperature to IIRC) 60 by throttling the return.

The boilers are set at slightly different running temperatures to act as a cheeky way of giving one boiler an easier time. Each year they are swapped round. We could have put a proper cascade management system in, but the budget was getting really pushed; along with my patience of working in a basement with no mobile reception and banging my head the whole time

 

[Biggles..]

Indus, the one in my photo has solid fuel and open vented gas boiler inputs both around the 40kw mark.
Heating is a sealed system consisting of 2 zones, upstairs loft radiators and a 12zone underfloor heating layout down stairs.
Hot water is done through a plate heat exchanger.

Thermal store has GX built in.

 

[Dan Robinson]

Phew - I thought you implied it was an Unvented PHE heated cylinder... But I was sure I was looking at a TS

Glad you clarified that one

 

[JonasX]

I know one guy who on fitting large cylinders always fits direct cylinders with his own plate heat exchangers and a bronze pumps. He finds it is cheaper for the same water delivery using smaller cylinders.

When being called out to cylinders with holed coils, he caps up the coil and fits an external plate heat exchanger and bronze pump; cost is about £260 plus a few fittings. This works out cheaper, and quicker, than replacing say a 250 litre coiled cylinder. His feedback is that the owners are amazed they never run out of hot water like they previously did when heated via the coil.

 

[indus]

Dan, I might give you a call if thats alright? I don't think you are too far away from me.