Alternative to Caleffi 533118 Monobloc?

[Dan F]

We have had one of these supplied and installed along with our UVC (Mixergy).  Couple of issues I'm seeing though:

- The hot static pressure is restricted to just under 3 bar, but the cold is 2.4 bar (aren't they suppoed to be balanced?)

- The dynamic pressure through the PRV is signficiantly below the static pressure.  The cold, for example, drops from 2.4bar (static) to 1.6bar (dynamic) at just 6.5L/min when flushing a loo.

(Our mains supply is a new 32mm connection specificed for 1L/s with static pressure of 5bar and a dynamic pressure, at 12-15L/min, of 4.5+ bar)

 

Is there an alternative approach or product(s) that would allows us to get closer to 3 bar dynamic pressure at shower flow rates (12L/min)?   I read somewhere that a PRV that limits dynamic pressure to 3 bar is not suitable, as the static presure can creep up and this is an issue, is that correct?

 

The reason this is aa concern is that we are only getting 1bar at first floor shower mixers and therefore flow rates are approx 7L/min rather than closer to 12L/min I'd assumed we'd get based on calculated losses and shower PQ chart.

 

Edited January 12, 2022 by Dan F

[fezster]

What size is the pipework internally? There are calculators online you can use to try and predict what the pressure drop will be, although it is not entirely easy to predict how this will translate to real world.

 

In general, though, you want to try and have 22mm pipework all the way to shower valves, and with a 32mm incoming mdpe, I went for 28mm pipework between the mains and the PRV (which was also upgraded to 28mm) to the unvented cylinder and out, before reducing to 22mm.

[Dan F]

5 hours ago, fezster said:

What size is the pipework internally? There are calculators online you can use to try and predict what the pressure drop will be, although it is not entirely easy to predict how this will translate to real world.

Internally I have a mix of pipe sizes. I used the online calcuatora to trade-off pressure loss with the time it takes for hot-water using shower manufactuers PQ charts.  What I didn't account for in these calculations though was the pressure loss due to the PRV!  While the PRV is set at 3bar (static) it has a pressure loss of 0.5bar+ (depending on flow rate) which I hadn't taken into account.

 

Quote

I went for 28mm pipework between the mains and the PRV (which was also upgraded to 28mm) to the unvented cylinder and out, before reducing to 22mm.

I have a 28mm supply which is reduced to 22mm (primarily because the monobloc is 22mm) which then splits off into 22mm for UVC and 22mm cold from the monobloc.

 

What I think I need to do is:

i) Get rid of the 22mm monobloc and replace it with standalone 28mm PRV (which will have lower pressure loss than the 22mm monobloc) and add in a standalone 6bar pressure relief valve.

ii) Ideally use 28mm all the way unti the point that hot/cold split.

 

Edited January 23, 2022 by Dan F

[fezster]

18 hours ago, Dan F said:

What I think I need to do is:

i) Get rid of the 22mm monobloc and replace it with standalone 28mm PRV (which will have lower pressure loss than the 22mm monobloc) and add in a standalone 6bar pressure relief valve.

ii) Ideally use 28mm all the way unti the point that hot/cold split.

 

 

Yes, this is exactly what I did. Reliance 315i pressure reducing valve. Except I teed my balanced cold in 28mm and upgraded to 28mm in and out of the UVC. I also had a separate 22mm relief valve fitted.

 

The pressure loss across the 28mm PRV is still considerable at higher flow rates, but there's not much you can do about it.

[Dan F]

7 hours ago, fezster said:

Yes, this is exactly what I did. Reliance 315i pressure reducing valve. Except I teed my balanced cold in 28mm and upgraded to 28mm in and out of the UVC. I also had a separate 22mm relief valve fitted.

 

The pressure loss across the 28mm PRV is still considerable at higher flow rates, but there's not much you can do about it.

 

I tried to insist on 28mm to the UVC but heating engineer argued it was pointless because the monobloc outlet was 22mm (which isn't really true, but still).  That said 22mm isn't bad, if it's just hot or just cold.   The 22mm monobloc is terrible for pressure loss though and a 28mm dedicated PRV version is quite a bit better!

 

There is a slightly longer story behind this as I currently have 28mm PRV and a 22mm monobloc PRV in series, producing 0.8bar pressure loss when just flushing a toilet!  We have improved things by having the first one set at 4bar and the monobloc set at 3.5bar, but getting rid of the monobloc is the best solution.

 

(The first PRV was added to allow for a gate valve between supply water (before softener) and balanced cold while still using the monobloc supplied by with UVC.  We  wanted fully softened hot water, but only semi softened cold water as it impacts rinsing ability)

 

Edited January 24, 2022 by Dan F