Vaillant anti-cycle time question

[fezster]

Ask him to note the use of the two port valves. They act as a high temperature non return valves. The call from the zone powers the secondary pump and activates the valve. The orange is switch live as normal and the boiler controls the primary pump. Piece of cake, but there's a lot of materials and work there, so sit down when he gives you the price.

I was hoping to use a single pump to drive all 3 zones on the secondary side (I actually have 3 spare pumps from previous efforts to resolve my issue, so cost of buying is not the issue, but my thinking is a single pump would keep running costs lower). The downstream circuits all have a relatively low head loss (< 2.5m) compared to the boiler which has a high head loss across the HE on the primary side (for which I have my Grundfos 25-80 if needed). The only issue I see here is that all 3 zones would be teed off of a single output from the LLH, rather than having individual outputs from the LLH (as per your picture). Any issue with that?

One other question please - how does a LLH behave when one zone requires a much higher temperature than the others? If the rads are heating slowly from cold and someone jumps in the shower whilst the HW is on, the cylinder will need reheating, but at a relatively higher temperature compared to the rads. Can the LLH help with this scenario by allowing the higher flow temp to the cylinder whilst a lower flow temp feeds the heating zones? And if so - would this necessitate a separate feed for HW from the LLH (or does it not matter)?

 

[GuessMan]

A separate pump per zone is my choice as it allows pump speeds to be set as required to each one, fixed to the cylinder and variable to the heating zones.
Your system flow temp is not altered by the load the return is, unless you have a variable temperature zone downstream of the LLH.
The LLH is there to separate hydraulically the boiler from the various heating loads of the system. You can google how they work, but it's more info than you really need and very involved.
I could guess all day about your set up and would inevitably go down the wrong road, you need a man in front of the pipes to help you further.
FYI I was told the reason the 46 kW EcoTec is called a commercial is so a LLH would be fitted, high output low water content boilers need good systems. That's only 8 kW bigger than yours.

 

[fezster]

Appreciate your advice. I'll speak to the heating engineer next week and refer to what you've said if needed. Thanks again for taking the time to respond.

 

[GuessMan]

You're welcome.

 

[scoobydo123]

Guessman has took the guess work out of it. Dont worry abut running costs of the pumps that is negligible in the scheme of things.Do come back with the price. If too much then you ma need to fudge it, with the various options ,non guaranteed as we dont fully know how the logic works on the boiler.