Non condensing system boiler minimum flow rate

[muh3]

Hi all,

I have a 10 year old Boulter Camray 5 (non condensing) and had some plumbing done. All on S Plan. I also had a Alpha 2L pump fitted and are currently trying to set the correct speed for me.

Can anybody tell me what the minimum flow rate through the boiler should be. Instruction does not mention anything.

Thanks.

 

[D_Hailsham]

Which kW output version of the Camray 5?

 

[muh3]

smallest, out of the top of my head 11.6kw. Thanks

 

[D_Hailsham]

smallest, out of the top of my head 11.6kw.

Not a bad guess ; according to the manual, the smallest is 11.7kW

It also (page 12 para 3.2) gives the water resistance for an 11C temperature rise. So we can safely assume the boiler is designed for an 11C rise. The flow rate will therefore be:

11.7 / (4.18 x 11) = 0.254 litres/sec = 0.92m³/hr

Do you have the 15/50 or 15/60 version of the pump?

 

[muh3]

Thank you, I have the 15/60

 

[D_Hailsham]

Thank you, I have the 15/60

Last question: do you have a bypass? If so, what type - manual or automatic?

 

[muh3]

Hi, we are getting where

I currently have a automatic bypass but looking at the pump instruction I believe it should be changed to an manual one (not a problem to get it done)

I'm currently using trvs on all radiators. Which could be potentially all closed with the pump still running so I do need a bypass device.

Hope this helps. Thank you again.

 

[D_Hailsham]

I currently have a automatic bypass but looking at the pump instruction I believe it should be changed to an manual one (not a problem to get it done).

A manual one is better than an auto, but it still means that some of the heat is always sent straight back to the boiler. A better solution is to put a manual and auto valve in series. The auto ensures that the valve only opens when necessary; the manual sets the maximum flow. This assumes you set the pump to one of the variable speed settings.

If you use one of the three fixed speeds, an auto-bypass is OK on its own.

I'm currently using trvs on all radiators.

What turns the boiler off when all the rooms are up to temperature??

You should have a room thermostat, with NO TRV on the rad in the same room. It's a Building Regs requirement.

 

[muh3]

I currently have a automatic bypass but looking at the pump instruction I believe it should be changed to an manual one (not a problem to get it done).

A manual one is better than an auto, but it still means that some of the heat is always sent straight back to the boiler. A better solution is to put a manual and auto valve in series. The auto ensures that the valve only opens when necessary; the manual sets the maximum flow. This assumes you set the pump to one of the variable speed settings.

If you use one of the three fixed speeds, an auto-bypass is OK on its own.

I'm currently using trvs on all radiators.

What turns the boiler off when all the rooms are up to temperature??

You should have a room thermostat, with NO TRV on the rad in the same room. It's a Building Regs requirement.

Thanks D_Hailsham, I appreciate your patience.

I do use a multi zone system with danfoss link cc, boiler control and danfoss living trv's. Downstairs with danfoss rs.

lovely stuff... (not available in the uk, shame) However the trv close and open to find the right pressure point, so you end up with a s plan, pump running and nowhere to go.

 

[D_Hailsham]

I do use a multi zone system with danfoss link cc, boiler control and danfoss living trv's. Downstairs with danfoss rs.

lovely stuff... (not available in the uk, shame) However the trv close and open to find the right pressure point, so you end up with a s plan, pump running and nowhere to go.

New to me, so I looked it up; it seems similar to Honeywell's Evohome.

Have a look at the documents in this link: Grundfos Alpha 2. They explain all about balancing, bypasses etc.

You should really balance the system first, as that is the only way of ensuring the pump is set to the correct speed. Instructions on balancing can be found in the Wiki /Plumbing & Heating/FAQ section.

 

[muh3]

Got it, makes all a bit more sense now

Would it work if I get a gate valve (as manual bypass valve) and adjust it to a 11C temp difference on the boiler with all trv's closed. which should give me the correct flow?

The rads are all balanced.

 

[D_Hailsham]

Would it work if I get a gate valve (as manual bypass valve) and adjust it to a 11C temp difference on the boiler with all trv's closed. which should give me the correct flow?

Not really, you will have a permanent heat leak back to the boiler. It would be better to set the pump to a fixed speed and adjust the ABV so it only opens when necessary.

I assume you have a thermometer. If so, open all TRVs to max and adjust the pump speed so you get an 11C drop (or as close as possible) at the boiler.

Which pump speed is that?
Which ABV do you have?

 

[Agile]

I would have to disagree that a manual bypass is better.

Apart from any other considerations it is not what the best practice advice advocates!

Tony

 

[muh3]

Would it work if I get a gate valve (as manual bypass valve) and adjust it to a 11C temp difference on the boiler with all trv's closed. which should give me the correct flow?

Not really, you will have a permanent heat leak back to the boiler. It would be better to set the pump to a fixed speed and adjust the ABV so it only opens when necessary.

I assume you have a thermometer. If so, open all TRVs to max and adjust the pump speed so you get an 11C drop (or as close as possible) at the boiler.

Which pump speed is that?
Which ABV do you have?

I get the temp difference at speed II. My ABV is one of them:
http://www.toolstation.com/shop/p36612

EDIT: I would prefer the variable speed if it makes any sense.

 

[D_Hailsham]

I get the temp difference at speed II. My ABV is {a Salus}.

I don't have instructions for the Salus ABV, and there are none on their website. This diagram shows what's needed:

Click to enlarge

Alpha 2L 15-60 graph

• D_Hailsham
• 25 Sep 2014
• 1

The vertical red line is the flow of 0.92 m/hr; the horizontal red line shows ABV so it only opens if the pressure exceeds that amount. Fortunately the control line at speed 2 is almost horizontal, so it will never open very much.