Water Softener for combi in very hard water area

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John,
Your title says combi, so.. With combi's the most important figure is the flowrate. 11 litres/min is fine for showes and the odd slow filling bath. Here is a recent post of mine...
For an even better flow rate and cheap too for what you get, assess using two Worcester-Bosch Junior combi's.
For high flowrates it is cost effective to use two Juniors and combine the DHW outlets. Worcester-Bosch will supply a drawing on how to do it, or ask me here. Two Juniors are available for around 1000 to 1100 depending on what sized units you buy. They have 24 and 28 kW models, you could use two 24kW or two 28 kW combi's or one of each. That is cheaper than the Worcester HighFlow 18 litres/min floor mounted combi and can deliver about 21.5 litres/min and never run out of hot water. The highest flowrates of any infinitely continuous combi is 22 litres/min, which is the ECO-Hometec which costs near 2K.
Have one combi do the downstairs heating on its own programmer/timer (Honeywell CM67 or equiv) and one do upstairs. Natural zoning, so you don't have to heat upstairs when you are not up there saving fuel. The running cost will be approx the same as a condensing boiler heating the whole house. No external zone valves either, and simple wiring up too. The Juniors are simple and don't even have internal 3-way valves.
Also if one goes down you will have another combi to give some heat in the house and DHW too. Combine the outlets for the DHW bath pipes and all the baths you want very quickly and no waiting. Best have the showers on separate combi's. It will do two showers no problem at all.
The Juniors are not condensing combi's, yet overall heating costs will be equivalent to a one condensing boiler as the upstairs will not be heated most of the time.
A win, win, situation.
Its advantages are:
- space saving (releases an airing cupboard). Both can go in the loft, or at the back of the existing airing cupboard. - never without heat in the house, - high flowrates (will do two showers and fill a bath in few minutes, - No waiting for a cylinder to re-heat - Natural zoning, one does upstairs and one does down - hardly any electrical control work (running a wire to a programmers/stat and power to each, - simple no brainer installation, - minimal components used. - less piping used - cheap to run overall as upstairs would be off most of the time - etc.
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Your main issue here is choosing a boiler that can maintain a low flow temperature for the underfloor for efficiency reasons, whilst giving a high temperature to the hot water system and radiators. I believe the MAN Micromat can be set up to do this, and Andy Hall may be able to advise on such a system.
Otherwise, you'll just need to set a high temperature and rely on the underfloor thermostatic mixing valve to produce a low return temperature, which may be enough for reasonable efficiency anyway. Should the Micromat's price put you off, I'm very happy with my Worcester-Bosch Greenstar 28HE, which is a mid-high end boiler at a much lower price.
For frequent baths and superlative multiple showers, install either an unvented hot water cylinder (i.e. Heatrae-Sadia Megaflo) or a heat bank system (i.e. DPS Pandora). If having it installed professionally, you'll find more installers familiar with the unvented cylinders. However, for DIY installation, the heat bank will be an easier job, although will require a higher flow temperature than is optimal.
Your ion exchange water softener should be a high flow type, such as a Kinetico 2020c HF. Whatever you buy should be metered, not timed.
Christian.
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(http://www.man-heiztechnik.de/_html/produkte/micromat.php ) but all the information is in German.
From what I read on this newsgroup, the condensing boiler will not operate at its best efficiency if it has to heat water up to the temperature required for conventional radiators. Any way around this for a mixed underfloor/radiator solution? (Other than doubling the size of the rads!)
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On Fri, 16 Apr 2004 00:19:06 +0100, "John Aston"

There's an English section if you go to
http://www.man-heiztechnik.de/index_e.php
Look for the Micromat, and yes it is condensing.

Yes and no.
You size radiators to meet the worst case heat loss - ie. a cold winter's night. With a non-condensing boiler, this is done at 82 flow, 70 return.
A condensing boiler's efficiency increases with reducing return temperature. When the dew point around 54 degrees is reached, the graph of efficiency vs. temperature shows a knee in the curve and the efficiency increases at a greater rate below this as condensing happens. It is not correct to say that there is a sudden step change in condensing mode - purely a rate of change - so 53.5 is not hugely better than 54.5
When the weather is warmer, the weather compensator sensor causes the flow temperature and return temperature to be reduced by reducing the boiler burn rate and pump speed. Thus it will be working at higher efficiency anyway.
If you size the radiators larger, you can run the flow at a top temperature of 70 (return 50) and the boiler will modulate down further. Therefore it is true to say that it will generally be more efficient.

I replied to your email and basically I think you could do three scenarios.
- 85 degree radiator design and UFH connected using a blending valve
- 70 degree radiator design and UFH via blending valve
- 50 degree for both. However, the radiators would then be quite large.
.andy
To email, substitute .nospam with .gl
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