Mega Flo vs Thermal store

[JonasX]

I did some looking. Many here have obsessions with unvented cylinders.

- A 200 litre indirect unvented cylinder can be bought for £600 or less.
- An Intergas combi for £850 (can be any combi that can take hot water in the DHW cold inlet [solar preheat which is quite common])
- A bronze pump for £130.

a) Use a combi to heat the cylinder. The Intergas combi, and many others, can receive hot water into the cold inlet. The combi regulates the DHW outlet to temperature to 60C.

b) Use only the hot water section to heat the cylinder. Use a bronze pump on the cold inlet to the combi. The cold inlet is taken off the bottom of the cylinder, either via a Surrey flange or a spare port, which most cylinders have. The hot inlet to the shower connection at the top of the cylinder. Many makes approve of heating a cylinder this way. Do not use the CH section of the combi. Connect CH flow to return and charge up, never to be used. This keeps the heat exchanger squeaky clean if not using say an Intergas combi which effectively has two heat exchangers in one unit. No sludge or sediment gets into the main gas heat exchanger. Combis give higher kw outputs when heating DHW.

The cylinder is now heated top down by 60C water - no blending valve needed. It can give useful water within a minute or so at the taps. It delivers far more DHW than a coil heated cylinder. A cylinder stat can be set to just under 60C.

Fit a time clock for DHW.

c) Use the coil for the CH. There is now a large coil in the cylinder. Use this for the CH take off using a Wilo Smart pump and TRVs on all rads. Have no centralised electric room stat, so all rooms are independently temperature controlled. Fit a sealed system kit on the CH loop. A time clock for the CH. The isolated from the cylinder CH section will not put sludge into the cylinder.

The rads have to be sized to run at a high efficient 60C being very economical heated via an efficient condensing combi.

So what we have is:

1. A pressurized thermal store in which the water is used for DHW purposes, as per usual.

2. It has rapid heat recovery via plate heat exchanger provided by the combi.

3. More DHW is produced than a coil heated unvented cylinder.

4. No boiler cycling.

5. Condensing operation in near 100% of boiler run time

6. Independent temperature control of rooms.

7. It can have full CH & DHW electric backup.

8. The boiler does not cycle reheating the cylinder in one long burn.

9. The main gas heat exchanger stays squeaky clean, as it only heats a plate heat exchanger, raising efficiency.

This a very cheap way to get thermal storage.... and a highly efficient and cheap to run system. Cost effective all around. The comfort conditions are far superior and a higher DHW delivery being heated by a plate heat exchanger.

Why don't we ever see them?

 

[SimonH2]

Why don't we ever see them?

OK, so when the "average" plumber rides in

http://www.party-warehouse.co.uk/2005_shop/product.asp?productID=1318&categoryID=279

He's going to have a loooong hard suck through his teeth, before telling the owner it's a load of rubbish and needs to be ripped out. Not because there's anything wrong, but because he won't stand a chance of figuring how it works. Apologies to the better plumbers in here, but sadly, that is the reality - a great many plumbers who would take offence at such criticism as they've "been doing this for decades" simply will not be capable of figuring this out.

Apart from that, seems a good enough system to me.

A couple of details ...

If you use an open vented cylinder, then it's even cheaper - you lose the pressurised hot water, but gain storage which may be an issue if your supply is poor in flow capacity or unreliable.

I'm not sure why you suggest a time switch for the DHW. I'd just use a cylinder stat at a suitable level - it needs to be low enough that the CH coil can always get enough heat to work.

 

[JonasX]

Apart from that, seems a good enough system to me.

A couple of details ...

If you use an open vented cylinder, then it's even cheaper - you lose the pressurised hot water, but gain storage which may be an issue if your supply is poor in flow capacity or unreliable.

I'm not sure why you suggest a time switch for the DHW. I'd just use a cylinder stat at a suitable level - it needs to be low enough that the CH coil can always get enough heat to work.

Simon, the DHW timeswitch is for summer.

A vented stainless steel coiled cylinder? That means a tank and power shower pump. Mmmm, no.

The normal cylinder stat 1/3 of the way up will do. Some stats have a built-in temp differential setting to keep a lag of switch in in and out time. Off at say 59C and on at say 55C.

The cylinder stat could still be used also with a pipe stat on the return pipe from the cylinder to the combi, then you are certain the cylinder is charged with 60C all the way down maximizing heat storage. This could an anti-cycle arrangement using a relay working with the cylinder stat. This may be too complex for jobbing plumbers.

The jobbing plumbers are obsessed with unvented cylinders. They think they the equiv to a thermal store - how wrong they are. Heating a cylinder with plate heat X is far more efficient than using a coil. No contest. Proven. The knowledgeable, like Dan, have proven that.

I was emphasizing that with two items these jobbing plumbers are familiar with, they can fit a highly efficient system for next to nothing.

1. Combi (with solar preheat capability is is now common) Combis are cheap.
2. Unvented cylinder.

Then put in:

a) Smart pump
b) Bronze pump
c) sealed system pack

No need for complex wiring of Y or S plan zone valve setup. Or even a Magnaclean filter.

The system is transformed in efficiency. The boiler is running near 100% of the time in very high low-temp efficiency. The main gas heat exchanger stays highly efficient as no sludge get in baking onto the inner walls. Getting the efficiency high from the heat sources (boiler) to the stored water is the key.

This is far superior to the inefficient direct rad heating boiler with an efficiency dropping by-pass valve, troublesome, complex Y plan valve, central room stat and inefficient unvented cylinder. Then there is sludge in the main gas heat exchanger, exchanger wearing out because of restricted flow due to TRVs, boiler controls wearing out because of cycling, etc.

BTW, the combi can be replaced by a say a Rinnai gas multi-point water heater. Rinnai use these to heat cylidners.
http://www.gasproducts.co.uk/acatalog/Rinnai_Condensing_Gas_Water_Heaters.html
They are quality, but they are a bit expensive and much cheaper combis can be bought, using only the water section, to do the job I outlined.

 

[JonasX]

On the Continent is common to heat a direct cylinder via the water section of a combi using a bronze pump to give the circulation. The combi has a nice built-in plate heat exchanger and temperature control. Hey presto, just what you need all in one neat package thought out for you.

British jobbing plumbers rarely do this, using complex, expensive Y and S valves with large expensive, inefficient, coiled cylinders and all the rest of it, thinking is is simple and more reliable and cheaper. How wrong they are! Why don't they do it the cheap, easy and efficient way? They would get more business.

 

[SimonH2]

Simon, the DHW timeswitch is for summer.

Sorry, still don't see it.
Tank hot, boiler sits there and does nothing. I use hot water, eventually the boiler kicks in to top it up. Where does the time switch come in ?

A vented stainless steel coiled cylinder? That means a tank and power shower pump. Mmmm, no.

Err, no. You can have a decent shower with just 6 foot of head - that's not just theoretical, it's what I do just about every morning.

The jobbing plumbers are obsessed with unvented cylinders. They think they the equiv to a thermal store - how wrong they are. Heating a cylinder with plate heat X is far more efficient than using a coil. No contest. Proven. The knowledgeable, like Dan, have proven that.

I was emphasizing that with two items these jobbing plumbers are familiar with, they can fit a highly efficient system for next to nothing.

I think you misinterpreted my post. I wasn't disagreeing with you, just suggesting that the same setup without the pressurised, unvented aspect would be even cheaper - as in you can pick up a reasonable open vent copper cylinder for considerably less than an unvented cylinder. Set it up as you describe and get the same effect - although without the high pressure hot water.

 

[JonasX]

Simon, the DHW timeswitch is for summer.

Sorry, still don't see it.
Tank hot, boiler sits there and does nothing. I use hot water, eventually the boiler kicks in to top it up. Where does the time switch come in ?

A single person may just need one reheat of the cylinder to provide DHW all day. It cools at night and when reheating in the morning, heats it efficiently, as the cylinder is mainly cold. Many store makers say leave it on 24 hrs. Gledhilll had an external time clock option

A vented stainless steel coiled cylinder? That means a tank and power shower pump. Mmmm, no.

Err, no. You can have a decent shower with just 6 foot of head - that's not just theoretical, it's what I do just about every morning.

Most will not have a shower like that - neither would I Hence why power shower pumps are selling like hot cakes.

I think you misinterpreted my post. I wasn't disagreeing with you, just suggesting that the same setup without the pressurised, unvented aspect would be even cheaper - as in you can pick up a reasonable open vent copper cylinder for considerably less than an unvented cylinder. Set it up as you describe and get the same effect - although without the high pressure hot water.

I realized you were with me. Yes, a very cheap way is a normal cheap, vented copper cylinder with loft tank and a combi & bronze pump.

Stainless cylinders are cheap enough these days. The unvented gives high pressure DHW. I am no fan of unvented cylinders due to the explosion risks and the G3 annual service and installation.

You could buy a cheap copper cylinder and one of these B&Q combi specials. They will only be heating the plate heat exchanger in one long burn so it will last longer. You can disable the three way valve and have it running straight through, so no valve to fail either. Some makers will tell you how to do it when using the combi as a multi-point.

That is one cheap and simple way of doing it.

This only all applies to using the stored water as potable water. Using the stored water a heat transfer fluid, a normal boiler is the cheapest way.

 

[SimonH2]

a) Use a combi to heat the cylinder
b) Use only the hot water section to heat the cylinder
c) Use the coil for the CH

I think this is something like you had in mind. I've omitted expansion vessels etc, but included the fill loop (which could be done in several ways). The cylinder stat would need to be below the level of the top of the coil to ensure the cylinder is always recharged to low enough to heat the coil.

Untitled

• SimonH2
• 23 Oct 2011
• 1

Using a combi to directly recharge an unvented cylinder, and using the cylinder coil to run the...

 

[JonasX]

That is it. An off-the-shelf unvented cylinder would do it. The cyl stat is usually below the top of the coil which will be used for CH only. A pipe stat on the return to the combi would help and render the cyl stat position not too critical, as when this is 58C or so, the cylinder is up to temperature all the way down maximizing the energy storage.

Some combi's limit the hot water to 60C, others via the software can be cranked a bit higher.

 

[JonasX]

Come to think of it, just having a pipe stat on the return to the combi right near the cylinder would be OK. A switch could be used to switch between the cylinder stat and pipe stat. A summer/winter switch, or an eco switch. The pipe stat also prevents over heated water entering the combi - the immersion could have been used.

As the cylinder is heated top down, that is a line of 60C heat moves down the cylinder, when the line of 60C water hits the cylinder stat the boiler cuts out will ensuring that the bottom third stays cool, not heating the full cylinder. The Winter mode will ensure the full cylinder is heated.

The pipe stat is best to have a pocket with stem stat that protrudes into the cylinder tapping. That means a tee at the point of the tapping.

That is simple. You could have the two stats operating as anti-cycle stats when in winter mode. Quite simple to do.

 

[JonasX]

a) Use a combi to heat the cylinder
b) Use only the hot water section to heat the cylinder
c) Use the coil for the CH

I think this is something like you had in mind. I've omitted expansion vessels etc, but included the fill loop (which could be done in several ways). The cylinder stat would need to be below the level of the top of the coil to ensure the cylinder is always recharged to low enough to heat the coil.

Untitled

• SimonH2
• 23 Oct 2011
• 1

Using a combi to directly recharge an unvented cylinder, and using the cylinder coil to run the...

Look at the diagram. If DHw is being draw off, say for a a few showers, when the cylinder stat call the boiler the boiler will be pumping 60C heat into the top of the cylinder which most will be extracted by the showers. The boiler and stored energy combine to, in effect, extend the size of the cylinder.

There is an ATAG combi that has an integral GasSaver on the flue. I think it is called the A325EC - it will pour 34 kw into the cylinder, reheating in no time at all. It can have solar preheat which means it will take hot water on the cold inlet. The integral GasSaver only works in DHW as the cold inlet runs through the GasSaver. It is highly efficient producing DHW.

Heat a thermal store cylinder with one of these via the DHW section and the efficiency will be very high. A boiler heating rads directly and coil cylinder with a S or Y plan, will consume far more gas. Heating via thermal stores is cheaper anyhow, it will be cheaper even more.

The ATAG is a RR boiler and Mytub are selling it for £1173 delivered.
The Intergas 24 kw combi is £750. This has no limit on the cold inlet temperature. In DHW the integral pump does not run - no 3-way valve. Very simple. It is possible to use the boiler's DHW circuit without needing to connect and fill the central heating system. But no integral GasSaver.

 

[indus]

I'm back I'm afraid.

I called around a local long established company that came recommended. He has had a look around and said he needs to do some calcs to see what he would recommend. He was also talking about perhaps two Mega Flows, a large one and a small one

He also mentioned that he felt something was not working properly in the current set up and thought it might be the blending valve that was faulty. So he suggested I try replacing that in case that resolves my biggest issue (ie can't get hot water out of two outlets at the same time.


He also mentioned, as one of the suggested items should i decide to rip it all out and start again, to install some kind of Grundfos pump that boosts mains pressure. Is this a good idea?


Thanks for reading

 

[SimonH2]

I called around a local long established company that came recommended. He has had a look around and said he needs to do some calcs to see what he would recommend. He was also talking about perhaps two Mega Flows, a large one and a small one

Interesting, dunno why !
Perhaps he's still thinking slow reheat via coil - and that means you need a small one for fast reheat plus a bigger one for capacity.

He also mentioned that he felt something was not working properly in the current set up and thought it might be the blending valve that was faulty. So he suggested I try replacing that in case that resolves my biggest issue (ie can't get hot water out of two outlets at the same time.

Did you ever try the suggested test - see if the pipe coming out of the store (ie between the store and blending valve) stays hot when using two outlets ?

He also mentioned, as one of the suggested items should i decide to rip it all out and start again, to install some kind of Grundfos pump that boosts mains pressure. Is this a good idea?

No idea, as per earlier postings, you need to determine what your pressure/flow capacity is from the supply.

It should be fairly obvious that the available pressure will drop as you draw off flow - due to the flow resistance in the pipes and fittings. If (and only if) you can get plenty of flow, but not at good pressure, then a booster pump would help. If you can't get enough flow (even out of an open ended pipe with effectively zero pressure) then a booster pump won't help all that much.

You need to measure your supply capability. Only then can you make informed decisions.

 

[Biggles..]

Jonas..... For your info the atag a325 won't tolerate preheated water inthe cold water inlet well at all.

Mines failed twice with an inlet temp of less than 43degc with major consequences.

Be carefully what you suggest from google.

 

[JonasX]

Jonas..... For your info the atag a325 won't tolerate preheated water inthe cold water inlet well at all.

Mines failed twice with an inlet temp of less than 43degc with major consequences.

Be carefully what you suggest from google.

Atag inst instructions are not google. A neighbour has one with a preheat solar panel and no probs.

Atag and others say ok, you, is intimidated by knowlege and superior reasoning, says otherwise.

The intergas is any temp on the inlet, so prob a better choice.

 

[Biggles..]

View media item 27495

My 2nd ATAG after the first filled itself with water after 12hours.
My ATAG has just had to have the internal washers replaced from going soft with pre heated water.

Really intimidated.....