Contemplating unvented Indirect hot water upgrade

Hi,
I'm seriously contemplating upgrading my domestic h/w supply to use a modern indirect unvented cylinder.
Goal is to increase pressure, eliminate requirement for a power shower, make space for an attic conversion (through elimination of header tank) and generally apply 21st century technology instead of 19th.
Any opinions on relative merits of the various brands out there? ARISTON, ALBION, TITAN, HEATRAE, SANTON or others?
Any horror stories worth sharing?
David
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On Thu, 27 Nov 2003 13:06:25 -0000, "vortex2"

Two points.
1) Do make sure that your mains water supply is good enough in terms of flow rate before committing to this, because it could otherwise be an expensive mistake. I fitted a mains pressure capable cylinder a year ago with the eventual intention of making it unvented. However, the water supply rate is only 12-15 litres per minute and that is not adequate as far as I am concerned. To upgrade the main would involve replacing a fairly long length of pipe on my property and relaying the drive - total cost over 5k. I will do that eventually, but I would have hated to install an unvented tank only to discover that I had made a system that works well work poorly.
2) To install an unvented cylinder, Building Regulations require that you use an Institute of Plumbing trained and approved plumber. Not a DIY job, I am afraid.
.andy
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Avoid. Superior alternative is a heat bank. Do a Google on this ng on "pandora", See: http://www.heatweb.com for an explaination of heat banks.
Christian on this ng, is fitting a heat bank right now and using a Worcster-Bosch Greenstar high efficiency condensing boiler to heat it. Both very good choices. Another heat bank alternative is the Gledhill Systemate with the Switch electric backup. http://www.gledhill.net/docs/sm2000.htm
The Systemate controls the boiler and even has the CH pump inside the casing, complete with frost control. The insulation of these unit is very heavy (even under the cylinders it is insulated) and suitable for garages. It also has "very" smart self adaptive microprocessor based controls.
Also look at the Boilermate, however with the Systemate is better when mated to a condensing boiler as the CH is heated directly from the boiler, so the Glow Worm will modulate the burner down when the house reaches temperature, promoting efficiency. I have a Systemate with a condensing boiler and it works brilliantly.
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My parents have a Heatrae Megaflo (unvented cylinder). I have a DPS Pandora (heat bank). Both are excellent, well made devices that provide lashings of high pressure, high flow water without the noise and unreliability of a pump. I simply wouldn't have a hot water system that didn't provide stored energy, mains pressure water.
Advantages of unvented vs heat bank: 1. Understood by many installers (certainly not all of them!) 2. Higher potential flow rate (70 lpm vs 40 lpm) 3. Better heat stratification (runs cold suddenly instead of going tepid for a while) 4. Lower return temperature suits condensing boilers 5. Will provide hot water during power failure (won't reheat, though) 6. Many suppliers, off the shelf
Advantages of heat bank vs unvented 1. Easy DIY installation. 2. Actual DHW not stored, so can use as drinking water. 3. No overflow/pressure relief needed (easier to install in awkward places, such as lofts or internal airing cupboards). 4. Less regular maintenance required. 5. Higher heat capacity for same volume.
Both types of systems can have electrical heating backup (immersion heater). Both can use standard central heating controls. However, the heat bank requires a high flow temperature. They have similar purchase costs, although a heat bank would be cheaper to install as it simply requires 4 pipes to be connected up (CH flow & return, cold in, hot out) and electricity connected.
Christian.
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If your mains can provide that level of flow.

Not so. Heat banks can have the same stratification as an other cylinder.

Using a flow/return blending valve low temeratyres can be obtained for much of the re-heat.

So will a heat bank. A simple immersion is al that is needed in the cylinder.

Many suppliers of heat banks off-the-shelf: Range, Albion, Gledhill, and many smaller companies too.

yes.
yes. Also eliminates legionalla.

yes.
yes.
yes.
6. Works on low pressure 7. No pressure controls.

A recently gave a better assessement:
Advantages of Heat-Banks
Instant high pressure hot water - When the thermal-store has reached the set temperature, water is delivered instantly at the taps.
Usable hot water in a matter of minutes - when using a boiler flow/return blending valve.
Very high water flow-rate - The high-end heat-banks have a flow-rate up to 45 litres/min.
Operates on low incoming pressures - Requires a supply pressure of 1 bar to obtain a good flow-rate.
Long efficient boiler burn - Reduces boiler on-off cycling increasing efficiency. Inefficient boiler cycling is no longer a "major" problem with boilers with forced flues, but wears out gas controls prematurely.
Maintains optimum boiler temperature range - If a blending valve on the boilers flow and return is used, it will deliver only the required high temperature to the heat banks, but also maintain the flow/return temperature differential.
Combines the output of the stored water and the boiler - Some versions can do this.
Cylinder may be smaller for a similar performance
Cylinder at low pressure - Unlike an unvented cylinder it does not store water at high pressures. Although some version do.
Fast cylinder recovery rate - When the boiler is connected directly to the heat-bank or an indirect coil, the recovery rate is rapid.
Legionella bacteria eliminated - The Legionella bacteria cannot survive in the high temperature sealed conditions of a heat-bank.
No scale build-up in heat-bank - Containing primary and not secondary fresh water, scale does not build-up inside the heat-bank.
Cold water storage eliminated - No need for cold water storage tanks.
Solar heating storage - Water heated via solar panels may be stored in the heat-bank via a solar coil.
Easy maintenance - If an external plate heat exchanger requires cleaning or replacing it is a matter of draining down the heat-bank, or closing isolating vales, and unscrewing the plate heat-exchanger. In some rare instances plate heat-exchangers are fitted directly inside the heat-bank preventing on-site maintenance.
Easy to improve hot water flowrates - By simply adding additional plate heat-exchangers in parallel, hot water flow rates may be improved. Retrofit additions are possible if extra bathrooms or showers are installed.
Stored water vessel need not be cylindrical - As no internal coil is used for hot water heat transfer the stored water vessel may be any shape, as opposed to a thermal store which has to be cylindrical for maximum efficiency. This has advantages where space is limited, promoting excellent packaging.
Disadvantages of Heat-Banks
The store needs be fully up to temperature to supply baths - Before any hot water is drawn off, the heat-bank must be up to temperature. Many later versions use a blending valve on the return to the boiler to ensure only up to temperature water is pumped into the store by the boiler. This prevents agitation of the stored water, and aiding heat stratification within the store giving useful water at the top of the store within a very shot time.
May not take full advantage of a condensing boiler - Maintaining the stored water at 75o to 80oC results in a generally high boiler return temperature. This will not take full advantage of a condensing boiler, which increases in efficiency with lower return temperatures. With the superior heat stratification of taller cylinders this problem will be reduced. Condensing boilers with a high operational flow and return temperature differential are best suited to thermal stores and heat banks. Fortunately most have a wide temperature differential.
Lower water temperatures with fast flow-rates - As with Combi boilers, fast flow-rates through the plate heat-exchanger results in lower water temperatures. This is not so pronounced with heat-banks as with thermal-stores.
More controls - An extra pump, thermostatic blending valve, flow switch and thermostatic controls are required over a conventional cylinder. An unvented cylinder system requires extra pressure controls.
Heat loss - Storing water at high temperatures is not efficient as heat loss is more pronounced. Heat-banks are more efficient when constantly used being less efficient when used in houses of infrequent occupation. Some Gledhill heat banks have super high levels of insulation, even under the cylinders, negating this point.
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That isn't my experience. As expected, the flow through the heat exchanger causes tepid water to enter the bottom at a rate greater than the energy is withdrawn. This does lead to destratification as the same water cycles round and a much slower rundown from high to low temperature. This can be overcome by slightly oversizing, which isn't much of an issue due to the fact that the energy storage is higher to begin with due to high store temperature. It is also mitigated as a TMV is used on the output, so the output temperature is steady until the heat bank water drops quite a lot of temperature.

Probably didn't explain properly. I meant during an electrical power failure, not the failure of the boiler.
P.S. Some of your list assumes a direct type connection to the boiler, rather than indirect coil. Some of the benefits are lost when an indirect system is used. However, the indirect system has substantial advantages, such as being able to use most modern boilers, which frequently require a sealed pressurised primary system, and being able to place the boiler above the level of the cylinder. You can also keep the circulating water separate, which enables one part of the system to be drained down, with the other part still in use, saving down time and the cost of replacing inhibitor unnecessarily.
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I have a Gledhill which varies the pump speed to suit the hot water draw-off temp of 55C. High flow when more taps are on and faster pump speed to maintain the 55C. Not a problem. No blending valve or flow switch is required.

Have a flow switch on the pipe to the heavy hot water users (bath and shower) when this switches in it brings in the boiler irrespective of what the cylinder thermostats want. Use blending valve on the flow-/return and only 75-80C water enters the cylinder, ensuring the hottest water at the top.

That is the same for just about everything in heating, unless you have an electricless multi-point.

Not to great extent, no. Using a quick recovery coil the length of the stores cylinder will alleviate that.

That is so. But some top of the range boilers can be open vented and connected directly.

That is a very minor point and can be rectified by using simple isolation valves.
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I can see how that would provide superior stratification performance. By slowing the pump speed down, you can ensure that the water enters the bottom almost as cold as the incoming mains, which maintains good temperature differential. The only problem could be that without a TMV, the output temperature may prove more variable (i.e. less responsive to flow rate / incoming temperature changes). I might try turning the pump on mine down a peg. If it can still maintain temperature at the full flow rate at the TMV output, then I should get superior stratification performance.
As you have one, how much does the Systemate 2000 cost? It doesn't look cheap.

No, a standard gravity or unvented hot water cylinder can provide hot water in the event of electrical failure. I don't consider it an important issue, but maybe out in the sticks you might get power failures frequently. I'd certainly be tempted to take a bath if I couldn't get on with what I was doing due to mains failure.

Still a pain, though. Some, like the specific DPS model I have, won't accept a boiler higher than themselves, as they have an integral vented expansion vessel. Also, depending on how the water expansion/venting is handled, you may not get the substantial benefits of sealed pressurised primary systems.
Christian.
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It is very accurate, controlled electronically.

It is not. Everything is inside, even an the auto by-pass and all pumps. No zone valves are used and the room stat is run back to the unit. It is two parallel cylinders with a take off coil from the boiler. All you need do is install a cheap condensing heating boiler. I also installed an outside weather compensator. When heating the store the CH pump is switched off until it reaches 64C. It is self adaptive, in that is learns how quickly the boiler heats up the cylinders and then decides what temperature to switch in the boiler in. It uses a microprocessor which is programmed. It stores water at 80C and decides when to bring in the boiler on cooling. It has error codes and various temps can be see by pressing various buttons on the PCB board and also frost control and periodically turns the CH pump in summer too. It comes with an external pressure vessel for the CH circuit. The store water has a small header tank which can have an overflow or not. The unit is highly insulated.
Cost? I believe somewhere between 750 and 1,000. I paid 100 for two, (well I bought 4 and fitted two in friends and reelatives houses) having one for a spare in the loft next to the working one. These were fitted in houses by a contractor company, who installed the wrong units. They were installed for a month or so, until the client spotted they were the wrong units, so they were taken out before the houses were sold/let. They have had no real use.
Gledhill, like Elson and Powermax when IMI, prefer to deal with large contractors doing development work, that is why they are not a household name and not know to small plumbing/heating companies, yet housing estates are full of them. At one time they would not sell to individuals, although would sell to selfbuilders. T&P can source them, but I'm not sure it would be the best deal.

Hybrid heat banks/thermal stores are available that use an immersed pre-heat coil as a pre-heat and a pump driven plate heat exchanger. cold water enters the coil, out and into the plate heat exchanger. This will produce hot water in a power cut. It also prevents the plate heat exchanger pump cutting in when a tap is switched on for a second or two; as with the down market combi's. The immersed coil will provided low flow rate hot water and the plate heat exchanger pump cuts in with high flows. The total flow rate is naturally very high.
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On Thu, 27 Nov 2003 13:06:25 -0000, "vortex2"

David,
I had an Albion Stainless 150ltr unvented cylinder fitted on Friday.
I'd recommend it - lots of piping hot water at high pressure.
The Albion Stainless isn't pre-plumbed with all the valves and fittings so it took my plumber a while to pipe it up. He made a very neat job of it though.
I understand that the Titan Flomaster and Heatrae Sadia Megaflo are pre-plumbed which may make for an easier installation.
Trevor.
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wrote:

Except a DIYer can't fit one.
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IMM wrote:

A DIYer can, but you are supposed to get the installation signed off by a registered jobsworth.

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wrote:

I believe you can be prosecuted if you fit one and are not approved. You can also rob a bank, but they prosecute you for that too.
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Trevor Budd wrote:

The end result is very good, and these things are all made to rogourous uqailty, generally from stainless steel. They shgold be checked over by a plumber who knows what they are doing, and the safety piping needs specail treament, but if yu can vebear the cost of connecting it, its IMHO the best technical solution. Not cheap tho. Lots of pipework and installation issues.

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wrote:

They have to be BBA approved!!!!!

The overflow is 28mm, and most of them have to be "serviced" every year.

The best technical solution, and by far the safest, is the heat bank. But you had never heard of them when you fitted your unvented cylinder. That is sad.
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"The Natural Philosopher" wrote in message

C|N>K :-) Tehri quailty mystse si yullf cetrifeid ot IOS 1090, premusably.
It really is about time you fixed that intermittent fault on your keyboard, you know.
--
Andy



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Keyboard? Nothing wrong with that. It's in his head.
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writes

Black the pot the kettle calling please rearrange to form a well known proverb
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Maxie, you really have thing about my tango dancing don't you?
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On Sun, 30 Nov 2003 12:15:43 +0000, Trevor Budd wrote:

months.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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