I tried to get info from W-B on this and I'm sure they said you can't have two temps.
Buy a Danfoss BEM 5000, that will do they job for you. I saw one on ebay that went for £22 brand new plus £5 postage. ~£200 worth of compensator for buttons. Most don't understand them and can't see what they can get from them, thinking a modulating boiler is the answer. Modulating on a setpoint boiler temp is not the same load compensation compensation.
The Savastat does load compensation control of a boiler by switching in and and out the burner. It is not that cheap and I would go for the Danfoss BEM
5000 as a weather compensator has feed forward control. Both have anti-cycle control.
Just say it's far more reliable and very cheap to run. That's all they need to know.
As regards the plumber, just lay down the specs and say deliver, what he thinks is irrelevant. When it comes to finer points of heating most haven't much of a clue, just slamming in cheapish boilers in unbalanced systems.
Ah. So the new range doesn't have this option? That's a real shame. I would have thought that more boiler manufacturers would be making such products due to the recent shift in requirements. Central heating systems (both rads and underfloor) are now designed for much lower temperatures than previously both for operational and efficiency reasons. Hot water systems, now often heatbanks or fitted with TMVs, are often designed for higher temperatures to improve capacity, performance and biological safety. Just the provision of a terminal allowing for 2 set temps would be enough.
The W-B techies on he phone wasn't that clued up I may add, and appeared to be speaking from crib sheet. So you might be right.
I fully agree. It is a simple thing to incorporate into a modern boiler. Even Ravenheat have this facility.
But a Danfoss BEM 5000 waether compensator does offer this facility with a stand alone third party product and will enhance efficient condensing operation by lowering the flow temp to the conditions. And you only need a cheapish boiler too. I always did it with a basic weather compensator using a relay switching out the compensators burner signal
Most condensing boiler will be less efficient heating DHW rather than CH, although ACV HeatMaster condenses when heating DHW, because of the way the tank in tank thermal store is configured.
Matt, it knows what the temperature is as it senses the return temperature of the heating.
Matt, you must have brain damage.
The boiler will still modulate. If the flow and return temperature close up the burner modulates. As the compensator knows roughly what the return temp should be in relation to the outside temp and the return temp is stable anyhow, cycling will be minimal. The boiler has anticycle control too.
But these cost a hell of a lot, and having one with DHW priority too (running up the boioer temp to max) is not that common.
A good cheap boiler like the Glow Worm and Danfoss BEM 5000 is highly cost effective way to go.
On Mon, 22 May 2006 09:11:47 +0100, snipped-for-privacy@hotmail.com wrote (in article ):
No I don't think so. The thermostat connection on the mains rail is for the room thermostat.
The DHW thermostat connects to the low voltage rail instead of the cylinder temperature sensor. Try asking DPS if they can supply a thermostat with volt-free contacts. If they can, then you don't have a problem.
On Mon, 22 May 2006 13:50:31 +0100, Doctor Drivel wrote (in article ):
This type of thing is a very poor option in comparison with a proper weather compensation on the boiler controller whereby it knows what the temperature is. It might be worth £22, but certainly not £200.
Control of the boiler is on/off which is the weak part of the whole thing. While it is able to take outside temperature into account and be reasonable if one already has a simple switched boiler, it has to resort to timed anticycle to prevent reduction in efficiency as a result of on/off firing.
The better option is undoubtedly an integrated weather compensator coupled with room temperature sensing and boiler and pump output control.
On Tue, 23 May 2006 00:27:58 +0100, Doctor Drivel wrote (in article ):
In the context of this I am obviously referring to the outside temperature and not the boiler return temperature.
I thought that that was more in your area of life.
Ever thought about why it was only being sold for £22? Doesn't work well for example? Can't sell them?
It will do to an extent, but this can be based only on water temperatures on the boiler because that is the only sensing of temperature available to it.
Other than that, all that it is getting is an on off signal. This will mean that on each operating cycle it will begin by running hotter than needed and will then modulate down.
If the boiler controller has outside and room temperature information by direct measurement, then it only ever needs to cycle off when the room temperature exceeds the set point. Other than that, it can run continuously at (if need be) very low output.
This can never be as good as a single controller having all of the sensing inputs giving measured values as opposed to on/off control and doing complete analogue control of burner and pump as well.
Viessmann do it this way as well.
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The question was about a specific make and model, and that one does have this capability.
There are others such as the Viessmann with the same functionality.
Thanks Andy, I slightly misunderstood the wiring side of things. DPS confirmed that the cylinder stat used is a Danfoss ITC 100 and that it does operate on a low voltage which can be fed into the low voltage rail of the boiler (I also checked the specs on Danfoss' website). Interestingly I considered opting for 2 stats to avoid unecessary cycling but the techie chap at DPS suggested that on a priority system you would be better off having the boiler fire up asap to bring the store back up to temperature and therefore 1 stat would be better suited?
As regards the RE2132 controller I wonder if you could give me your view on it's necessity as re-reading your previous posts suggested that the outside weather compensator and TRV's on the rads would do a satisfactory controlling job of the heating side of things? SWMBO likes the ability to override/amend temperatures so the boiler in the loft doesn't lend itself well to frequent adjustments so some form of remote controlling is desired, however, potentially the RE2132 is a little over the top for my application and a more mainstream solution (Honeywell CM67 is favoured by Eco Hometec) would be better suited? Cost is a consideration but not a major factor in the overall cost of the the whole system if the functionality of boiler is better suited to the RE2132?
This was my thinking also, however, if you do go down the 2 stat route they have suggested that the wiring would need rejigging to make sure that the output will produce volt free contacts. This is something they can do so shouldn't be a problem it was more his assertion that a
The best for Robin is a "direct" DPS CX heat bank that integrates the DHW and CH. The CH water section can be controlled by a Danfoss weather compensator. Store the CH water at the right temp rather than store the water hot and drop the temperature. Then the BEM 5000 controls the boiler directly on CH. This "eliminates" boiler cycling as the mass of water stored acts as an anti-cyle buffer. It also ensures maximum efficiency of condesning boiler operation. A simple cheap Glow Worm HXi condensing boiler can be used. A direct probe sensor for the BEM 500 may have to be bought as an extra to sense the store CH water. Worth for the gains it gives.
The CH circuit is taken off the store and using a Grunfoss Alpha pump and TRVs on all rads no problem at all. That is what I would do. It gives a superior solution all around and more cost effective in installation.
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