Automatic bypass Valve plan, your thoughts

[Me-again]

Since i installed evohome on an old system were only two thermostatic rad valves were fitted the system can get a bit noisy when all HR92,s have closed, so i think an Automatic bypass Valve could be the answer. In the immersion cupboard were most of the pipework pump and motorized valves are it is easy to install the bypass for its incoming/flow side, its a 22mm pipe but there is no 22mm return pipe. The only return pipe is from the vented indirect cylinder and its 15mm this pipe drops down to a space under the immersion cupboard then heads off under a bedroom floor were it must either connect to its own 22mm return pipe or feed into the Radiator 22mm return pipe. Being that this pipework is under a chipboard floor which has been overlayed with laminate flooring getting at this pipework is not an option.

So the flow from the bypass will eventually have to be reduced from 22mm to run into the 15mm return at some point, is that OK. I also have an idea of maybe sending any output from the bypass to the hot water input on the Hot water cylinder this is fed from a 15mm pipe which is controlled by the DHW motorized valve i think would be less wasteful. If the DHW motorized valve is turned off (no demand) then any flow from the bypass cant back feed past the closed motorized valve and will flow through the cylinder coil and out through its 15mm return pipe, were if I don't do it this way the output from the bypass would end up anyway.

How does this idea sound to you.

[rdgarner]

Hello,

Long time lurker but first time poster, I hope this isn't considered rude to reply to this slightly old post.

I had a similar issue after installing Evohome and HR92's, but I went about a fix in a different way. At the time I installed Evohome, I had an old Grundfos UPS15-50 pump, which is fixed flow rate. I found out about their "Alpha2" pumps with their "autoadapt" feature, which backs down the flow rate when it detects that backpressure increases. Better still, I found that the pump bodies between the UPS and the Alpha2 are identical, meaning I could close the union valves and simply change the pump head over without having to change the whole body over. I have had no noisy TRV valves since.

Depending on your boiler, you might also find that backing down the flow rate means cooler return flow, and more time spent in "condensing" mode, which I understand is supposed to be more efficient.

[bruce_miranda]

Adaptive pumps and ABV don't work well together.

[Me-again]

rdgarner, I wouldnt worry, the posts not that old. Thanks for your input sounds like a good plan but auto bypass valve already bought. I will make a note in my usefull info folder though. I will get round to doing my proposed idea but there never seems to be enough hours in the day and covid hasnt helped with sourcing bits and pieces. Even getting hold of copper pipe is difficult at a reasonable cost, i know toolstation wont deliver copper pipe unless you buy in bulk i dont know if screwfix is the same.

[DorrisMancer]

Adaptive pumps and ABV don't work well together.

That's interesting, is there any info available about this?
I have an auto-bypass valve and a Grundfos UPS2 on a large'ish heating system. The pump is currently set to one of the adaptive positions (mid, I think) and the system is much quieter than when it's on the mid non-adaptive setting.

[bruce_miranda]

In order for the ABV to work, it needs a constant pressure of the pump to push it open. If the pump is constantly changing its pressure, where and how would you set the ABV?

[DBMandrake]

That's interesting, is there any info available about this?
I have an auto-bypass valve and a Grundfos UPS2 on a large'ish heating system. The pump is currently set to one of the adaptive positions (mid, I think) and the system is much quieter than when it's on the mid non-adaptive setting.

The problem is a variable speed pump speeds up when it senses an easier flow path. (Less flow resistance) The intention is that when most radiators are closed right down the pump slows down to prevent the pressure climbing too high and when radiators open and flow becomes easier it speeds up and prevents the pressure differential dropping too low.

When the ABV opens the pump will sense an easier flow path and speed up - this will increase pressure differential and open the ABV further - before you know it the pump is working at a high speed and just pumping around the ABV loop - exactly as if it was set in a fixed speed mode.

Due to the weird way variable speed load sensitive pumps work the ABV will cause a kind of positive feedback effect that results in either a very high or very low pump speed.

[mtmcgavock]

Good old fashioned way of a Gate Valve cracked open 3/4 of a turn is the best thing IMO, then remove the top.

[DorrisMancer]

The problem is a variable speed pump speeds up when it senses an easier flow path. (Less flow resistance) The intention is that when most radiators are closed right down the pump slows down to prevent the pressure climbing too high and when radiators open and flow becomes easier it speeds up and prevents the pressure differential dropping too low.
When the ABV opens the pump will sense an easier flow path and speed up - this will increase pressure differential and open the ABV further - before you know it the pump is working at a high speed and just pumping around the ABV loop - exactly as if it was set in a fixed speed mode.
Due to the weird way variable speed load sensitive pumps work the ABV will cause a kind of positive feedback effect that results in either a very high or very low pump speed.

Thanks. I hadn't thought it through before but that makes perfect sense. I'll screw-down the bypass valve a couple of notches.

[bruce_miranda]

And they also mess with boilers that need a minimum flow rate through them too