Auto bypass setting

[fezster]

Turn partial load off of auto and rate it for the smallest zone?

I did do this at one stage, but found the system was very slow to heat up with both upstairs and downstairs calling for heat.

 

[albatross]

but am still curious as to how one would setup a system from scratch to cater for multiple zones (without a low loss header).

Short answer is you can't do it. You balance a system perfectly on full load but it will go to pot as soon as trv's and zone valves close. One reason variable speed pumps, modulating boilers and auto bypasses were invented to cope with modern systems that have a constantly changing flow rate.

 

[TBServices]

If your rads are oversized, by a similar percentage for each, you should be able to run your system at a lower temp to get the design temp for the rooms.

You can range rate the boiler down to stop it firing too high.

 

[happyflyer]

Modern boilers have a very sophisticated way of measuring the rate of temperature rise different between the Flow and Return,, they will let you know when you have not got the correct flow with an error code. They no longer dance off the wall.

 

[Ermintrude]

Set partial load to 12kw, comfort off. Set flow at 63.

Your system is overshooting , it's like giving a 3 year old 4 cans of coke and a kg of smarties. No way he's sitting down quietly and his teeth won't last.

Far better to allow a small and controlled amount in

Boiler temp is measured by a pid control mechanism. Integration and diff calc used to forecast set point on gas valve that's why it modulates up and down seemingly by magic

 

[chris watkins]

You should have fitted a MAGNA1 25-60 or 80 not the UPS, as it does not conform to the EU pump energy saving directive which came in this time last year but then had you employed a proper heating engineer who understood large systems they would have known that.
Installing an energy saving speed controlled circulator would have gone some way to saving the energy now being wasted through not installed low loss header along with an incorrectly set ABV which means the boiler is rarely in condensing mode.

Throw in & stir the mix:boxing_smiley:

 

[doitmyself]

the data you gave appear to indicate that you cannot drop the boiler flow less than 0.45 ls so this is the max and min flow rolled into in, in other words the boiler manufacturer doesn't want any reduction in boiler flow at any time.

I'm having difficulty with accepting this.

A minimum flow at max output is understandable as it determines the temperature differential across the heat exchanger. A lower flow rate would mean the differential will exceed the spec of the hex manufacturer. But if the flow rate is maintained when the boiler modulates down, the differential will also reduce. If the differential is 20C at max output and the boiler has a 4:1 modulation ratio, the differential will be 5C at minimum output.

Whether this is a good thing or not, I don't know. Does any one have an answer?

A variable speed pump muddies the water even further as the boiler has no direct control over the speed, which would seem to be a logical requirement.

 

[Ollieg]

The problem with Vaillant 438 is even if you range rate the boiler down to 12 kw it will still fire at 60percent of its max ( 60% of 38kw) and then ramp up!!! Yes UP before it come down to 12kw. S53 is a soab. Your primary's sound ok. I would just set the bypass to keep your boiler working. Forget a small amount of let by when one zone is closed.

 

[doitmyself]

The problem with Vaillant 438 is even if you range rate the boiler down to 12 kw it will still fire at 60percent of its max ( 60% of 38kw) and then ramp up!!! Yes UP before it come down to 12kw.

The latest version of the PCB is supposed to cure this problem; but the OP already knows this and has the new board installed. We don't know if it has had any effect.

 

[fezster]

The latest version of the PCB is supposed to cure this problem; but the OP already knows this and has the new board installed. We don't know if it has had any effect.

I wouldn't say cured, but does seem to have helped, as the "ramping up" seems to be more controlled. What I can say is that a lower d0, the boiler behaves differently on initial start up, so Im not sure 60% of 38KW is correct. Perhaps x% of d0.

You should have fitted a MAGNA1 25-60 or 80 not the UPS

MAGNA1 was over £400. I decided to buy the UPS 25-80 as it was considerably cheaper, and in a brand new condition. Fitted myself.

Set partial load to 12kw

Interestingly, I didnt notice the word "partial" before. This would indicate you set it to the load of a single (or smallest) zone. However, as said, setting this too low results in ridiculously long heat up times. Not sure if the boiler modulates up or not.