Constant flow automatic bypass valves

[Brambles]

A spot on reply Chris

 

[decomplexity]

Excellent.

 

[decomplexity]

After some thought as to whether the towel-rail substitute for an ABV was the right long-term solution, I decided to replace the Honeywell DU144 pressure-driven ABV by a Caleffi Autoflow 127 from Altecnic that limits bypass flow to 0.2m3/hr (the boiler’s recommended minimum).
The Grundfos UPS2 25-80 pump was then switched into the lowest of the three proportional-pressure modes. With all the TRVs (now including the towel rail) almost shut on hot days the pump should be running at a head of just over 2m and the system is very quiet, but it heats up as quick as ever on cold days.

The Caleffi valves are about £10 more (plus a couple of BSP-to-compression adaptors) than Honeywell ABVs but should be the right solution, whereas in my view the Honeywell (and any other pressure-driven) ones aren’t.

 

[doitmyself]

I decided to replace the Honeywell DU144 pressure-driven ABV by a Caleffi Autoflow 127 from Altecnic that limits bypass flow to 0.2m3/hr (the boiler’s recommended minimum).

So now you have a continuous flow through the bypass, even if it is limited to 0.2m3/hr.

Grundfos recommend a Taconova Setter valve (does the same job as a Caleffi) in series with the ABV. The bypass then only opens when the pressure exceeds the ABV setting and the flow is restricted by the Setter if the pressure rises.

 

[John.g]

IMO, to satisfy a PP1 setting of 2.0 M above then the ABV setting would have to be set as low or lower than this to give any flow if all zone v/vs, TRV's etc are closed, then as the heating demand increases the Tacosetter will restrict the flow rate which would otherwise be enormous using the ABV on its own, also I thought the tacosetter is more or less a adjustable fixed setting with a flowmeter and is not automatic so, for example if its set to flow 0.2M3/hr @ 2M head then if the heating demand increased to require a PP head of say 4M then the flowrate would increase to almost 0.3 M3/hr whereas, theoretically anyway, the Caleffi will maintain 0.2M3/hr even if the head increased to over 20M(200 kpa).

 

[decomplexity]

Re John.g's reply: spot on!
I was writing identical comments but was beaten to the draw.
The underlying problem is that a pump such as any in the Grundfos domestic range running in proportional-pressure mode has its lowest pressure at lowest flow (or no flow) - typically when all the TRVs shut on a hot day or when there the CH + DHW demand ceases and the boiler tells the pump to overrun for a few minutes. A pressure-driven ABV set to this pressure will simply open all the time.
And when I looked at the Tacosetter's tech spec, it appeared to operate as a fixed valve with a flow meter. Perhaps the flow set-point is resilient to pressure changes but this wasn't obvious from the spec: perhaps someone more familiar with them can correct me.

 

[John.g]

Re John.g's reply: spot on!
I was writing identical comments but was beaten to the draw.
The underlying problem is that a pump such as any in the Grundfos domestic range running in proportional-pressure mode has its lowest pressure at lowest flow (or no flow) - typically when all the TRVs shut on a hot day or when there the CH + DHW demand ceases and the boiler tells the pump to overrun for a few minutes. A pressure-driven ABV set to this pressure will simply open all the time.
And when I looked at the Tacosetter's tech spec, it appeared to operate as a fixed valve with a flow meter. Perhaps the flow set-point is resilient to pressure changes but this wasn't obvious from the spec: perhaps someone more familiar with them can correct me.

Could this be Honeywell's answer to the Caleffi?.

 

[ShaunCorbs]

Could this be Honeywell's answer to the Caleffi?.

No as it’s a trv

 

[chris watkins]

Pressure Independent Control Valve (PICV)
All leading manufacturers now do their own version, but not so sure how you would use it in a by-pass.
Very cleaver but I am with Shaun too much for a domestic system.

 

[ShaunCorbs]

Sorry I’m lost why is this a problem if you don’t want a bypass valve install a bypass rad eg airing cupboard

Depending on the sys it’s more to go wrong and service it’s only a domestic system