How to set a honeywell auto bypass valve?

[iep]

I just fitted Honeywell DU144 auto bypass valve to my central heating system (open vent s plan system). I have found the manual for my Grundfos pump (selectric):

http://www.screwfix.com/sfd/i/cat/pdfs/01/p3983301.pdf

and the manual for my bypass valve:

http://www.screwfix.com/sfd/i/cat/pdfs/50/p4734550.pdf

My GlowWorm Energysaver60 boiler specifies a minimum flow of 17l per minute. This translates to 0.28l per second or 1020l per hour.

My problem is this, I want to run my pump on speed setting 2 (as it creates plenty of heat in all radiators and is nice and quiet at this speed).

The table provided in the pump manual suggests that 0.28l/s translates to about 2m of head at speed setting 2.

The bypass valve manual then suggests that for 1020l/h and 2m of head (200mB), there is no appropriate setting on the bypass valve.

Am I reading this correctly? Have I bought the wrong type of valve?

Cheers,

iep

 

[D_Hailsham]

My GlowWorm Energysaver60 boiler specifies a minimum flow of 17l per minute. This translates to 0.28l per second or 1020l per hour.

My problem is this, I want to run my pump on speed setting 2 (as it creates plenty of heat in all radiators and is nice and quiet at this speed).

I am surprised that you can get the system working with the pump 2. At normal flow rate (23l/min) The boiler resistance is about 0.8m and the pump head is about 1.5m. Which means that the total circuit resistance is only 0.7m. This is much lower than normal.

What temperature differential are you getting across the boiler with the valve closed and all rads working?

Have you balanced the system?

On setting 3 a properly balanced system with the bypass valve set should not be audible.

 

[iep]

Hi D_Hailsham, As ever thanks for the useful info.

You raise a valid point. If I understand correctly, what you are saying is that by the time the pump has driven the resistyance of the boiler, it should have very little oomph left to drive the rest of the system?

The system was balanced two weeks back but that was on pump speed three and, critically, I had a blown zone valve which meant the HW circuit was always open. In short, I need to do it again now.

I haven't measured the send/return temperatures yet either as my IR thermomoeter does not get a good reading on the pipework (my plan is to attach two 2" square pieces of black aluminium to the pipes to give a measurement target for the thermometer).

However, all the radiators do heat up at approx the same rate and achieve a final temperature of about 70 degrees which seems about right. Having said that, the whole system does take a while to warm up so maybe the overall flow rate is a bit low.

If I were to set the pump at speed three, would you agree that (from the tables in the links I had in my first post) the correct bypass settign would be about 0.2bar?

Thanks again,

iep

 

[D_Hailsham]

If I understand correctly, what you are saying is that by the time the pump has driven the resistance of the boiler, it should have very little oomph left to drive the rest of the system?

Yes

The system was balanced two weeks back but that was on pump speed three and, critically, I had a blown zone valve which meant the HW circuit was always open. In short, I need to do it again now.

See How to balance a CH system

I haven't measured the send/return temperatures yet either as my IR thermometer does not get a good reading on the pipework (my plan is to attach two 2" square pieces of black aluminium to the pipes to give a measurement target for the thermometer).

A simpler way of making a target is to wrap some black insulating tape round the pipe for a few turns.

If I were to set the pump at speed three, would you agree that (from the tables in the links I had in my first post) the correct bypass setting would be about 0.2bar?

I will come back to you on that - I have to go out.

 

[D_Hailsham]

If I were to set the pump at speed three, would you agree that (from the tables in the links I had in my first post) the correct bypass setting would be about 0.2bar?

Yes, or slightly lower. The test is that the valve is not open when all rads are working with any TRVs fully open. The crude way of setting an ABV is as follows:

1. With boiler/system cool, set valve to max.
2. Switch heating system/boiler/pump on.
3. Reduce setting until valve is just open (by-pass/valve starts to get hot).
4. Turn adjuster back (anti-clockwise) one revolution (ie. valve closes).
5. Valve will automatically open when system flow reduces.

 

[iep]

Excellent. Sounds like a very intuitive procedure.

Great advice thanks again.

ip

 

[Exacatmi]

Excellent. Sounds like a very intuitive procedure.

Great advice thanks again.

ip

I do agree with you. I am looking for the information about this.

 

[bengasman]

A bypass is a safetysystem, and should not let by under normal working conditions.
Personally, the same as DHailsam, I never look at those tables when fit an automatic bypass on an existing system.
The difference between us, is that I do this for a living, and DH is an armchair google hero, so be careful with following his advice.
Those tables are great theory, but as the reality is that you never know the resistance of an existing system, the tables are pointless.

The function of a bypass is to provide a flow to take heat out of the boiler when the normal flow is not there for whatever reason. It is NOT there to balance the system.

I set the bypass by closing the normal flow, set the pump at whatever the normal working pressure is, and slowly open the abv untill I notice a flow. Another turn for good measure, Bob's your uncle.

Bear in mind that when you set the abv too light, you can waste a lot of money and when it is too high, you could cause damage. If you are not entirely sure that you can do this correctly, get it done by a pro. If you add it to a service, it will cost you little.

 

[D_Hailsham]

A bypass is a safety system, and should not let by under normal working conditions.

A bypass is definitely not a "safety system". It serves two purposes:

1. To supply a path when motorized valves are closed and the boiler has pump overrun.

2. To ensure the flow rate through the boiler does not drop below the manufacturer's specified limit when TRVs close down and the differential pressure across the system increases, thus reducing the flow rate. The modern way of achieving this is to use a variable speed pump, such as the Grundfos Alpha.

Those tables are great theory, but as the reality is that you never know the resistance of an existing system, the tables are pointless.

You don't need to know the resistance of the system, just the minimum flow rate through the boiler and the pump curve, which is in their published literature.

The function of a bypass is ....NOT ... to balance the system.

I agree with that.

 

[gasafengineer]

The crude way of setting an ABV is as follows:

1. With boiler/system cool, set valve to max.
2. Switch heating system/boiler/pump on.
3. Reduce setting until valve is just open (by-pass/valve starts to get hot).
4. Turn adjuster back (anti-clockwise) one revolution (ie. valve closes).
5. Valve will automatically open when system flow reduces.

This is not the correct procedure when setting up an auto bypass valve.

With all TRVs/primary HW shut down open ABV until required flow rate through boiler is achieved , setting ABV when system resistance is low (all TRVs open) will have circulator bypass index circuit with any increased resistance (TRVs shutting down).

 

[bengasman]

A bypass is definitely not a "safety system". It serves two purposes:
1. To supply a path when motorized valves are closed and the boiler has pump overrun.

That prevents the boiler overheating, it's called: a safety.

2. To ensure the flow rate through the boiler does not drop below the manufacturer's specified limit when TRVs close down and the differential pressure across the system increases, thus reducing the flow rate.

That prevents the boiler overheating, it's called: a safety.

You don't need to know the resistance of the system, just the minimum flow rate through the boiler and the pump curve, which is in their published literature.

Flowrate= pressure divided by resistance
Resistance unknown= flowrate unknown.
This is exactly what I mean by the difference between people that actually do the job and armchair google specialists.

 

[helpdad]

The crude way of setting an ABV is as follows:

1. With boiler/system cool, set valve to max.
2. Switch heating system/boiler/pump on.
3. Reduce setting until valve is just open (by-pass/valve starts to get hot).
4. Turn adjuster back (anti-clockwise) one revolution (ie. valve closes).
5. Valve will automatically open when system flow reduces.

This is not the correct procedure when setting up an auto bypass valve.

With all TRVs/primary HW shut down open ABV until required flow rate through boiler is achieved , setting ABV when system resistance is low (all TRVs open) will have circulator bypass index circuit with any increased resistance (TRVs shutting down).

I am not a plumber, but have tried to follow this, as my son had heating fitted a few months go, and it is really noisy (in my opinion). The plumber is supposeed to be coming back, but has twice not turned up. As my son works and I don't, it's me that is sitting around all day!

D Hailshams method seems strightforward, but Gassafes method requires you to know the flow rate through the boiler. How do you know this?

 

[D_Hailsham]

The crude way of setting an ABV is as follows:

1. With boiler/system cool, set valve to max.
2. Switch heating system/boiler/pump on.
3. Reduce setting until valve is just open (by-pass/valve starts to get hot).
4. Turn adjuster back (anti-clockwise) one revolution (ie. valve closes).
5. Valve will automatically open when system flow reduces.

This is not the correct procedure when setting up an auto bypass valve.

That's strange! It was taken straight from Danfoss's Instructions for the AVDO bypass valve!

They also say:

The following is intended to be a simple guide to the setting of the AVDO. As detailed design information is rarely available for domestic systems this approach is usually more appropriate than the more scientific method often applied to the AVDA, AVDSA and IVDA commercial
by-pass valves.

 

[bengasman]

I am not a plumber...
...D Hailshams method seems strightforward...

Neither is DHailsham. His "knowledge" is purely theoretical from google and reading forums.

 

[D_Hailsham]

A bypass is definitely not a "safety system". It serves two purposes:
1. To supply a path when motorized valves are closed and the boiler has pump overrun.

That prevents the boiler overheating, it's called: a safety.

2. To ensure the flow rate through the boiler does not drop below the manufacturer's specified limit when TRVs close down and the differential pressure across the system increases, thus reducing the flow rate.

That prevents the boiler overheating, it's called: a safety.

A safety device is something which comes into play in exceptional circumstances, e.g an overheat device. Something which just opens and closes in the normal course of events can hardly be considered a "safety" device.

You don't need to know the resistance of the system, just the minimum flow rate through the boiler and the pump curve, which is in their published literature.

Flowrate= pressure divided by resistance
Resistance unknown= flowrate unknown.

But you don't need to know the actual flow rate, just the minimum flow rate, which will be given in the boiler manufacturer's Installation Instructions or can be worked out from a simple Formula, which every competent installer will know.

Read Honeywell DU144 Instructions