radiator balancing with multiple zones

[D4dog]

I have installed a three zone system - simple question, I know how to balance the system, but not sure whether I should do each zone seperately, or the entire system with all zones fully on?

I also need a hint about balancing DHW - I have a fourth valve which supplies DHW, via 22mm - clearly, i need to reduce the flow to the tank, if heating is to operate correctly. Cannot find a 22mm in-line lockshield, so I will use a 22mm gate valve with the handle removed. But how much do I close it by? System has an automatic bypass (currently set to 0.4 bar), so possibly - DHW only on, and close valve until just before the bypass operates? Or is this too far?

Any advice gratefully received.

 

[D_Hailsham]

I have installed a three zone system - simple question, I know how to balance the system, but not sure whether I should do each zone seperately, or the entire system with all zones fully on?

A four zone system, to be more accurate.

I have found Commision Instructions very helpful. Although they are written with Drayton TRVs in mind, the contain useful general advice.

1. The first thing to do is get the pump speed correct: Open all rad valves (both ends); open all CH zone valves; close HW zone valve. Adjust pump to give correct temperature drop at boiler (usually 11C).
2. Adjust auto bypass as per boiler mfr instructions.
3. Close all lockshield valves.
4. Balance each rad, starting with the one nearest the pump. As you have 3 zones, I would do the nearest from zone 1 followed by nearest in zone 2 then nearest in zone 3.
5. Repeat 4 moving to the next radiator in each zone.

I also need a hint about balancing DHW - I have a fourth valve which supplies DHW, via 22mm - clearly, i need to reduce the flow to the tank, if heating is to operate correctly. Cannot find a 22mm in-line lockshield, so I will use a 22mm gate valve with the handle removed. But how much do I close it by? System has an automatic bypass (currently set to 0.4 bar), so possibly - DHW only on, and close valve until just before the bypass operates? Or is this too far?

You have to adjust the gate valve just like a lockshield to give an 11C drop across the cylinder.

Just a thought What pump are you using? An automatic (Grundfos Alpha+ or Alpha2) might be worth considering with so many zones.

 

[Agile]

If the bypass is set to 0.4 Bar then it will never open!!!

I would recommend you balance with all zones and HW on and set HW temperature differentiol to about 18° c if its a condensing boiler or 11 °C if not.

Same with rads.

Set auto bypass last with just HW on to just allow a very small flow as measured by both sides getting hot.

Tony

 

[D4dog]

thank you - the pump is a grundfoss three speed, but not automatic - I will have a look at the auto ones.

On the zones - given that you normally balance closest radiator first, would it be worthwhile applying the same logic to the zones, ie balance the ones with least resistance first? One of the zones is for the conservatory, and only has one large radiator (using a zone valve so I can leave the heating on whilst away, without heating the entire house!!). My logic suggests I should balance this first, then the upstairs (lower resistance than downstairs, and fewer rads).

As for the bypass - the downstairs circuit offers quire a high resistance, so needs a little pressure from the pump. The valve has settings from what appears to be zero, to about 0.6. General advice seems to be to set this to operate when all the TRVs are closed (even though each zone has a none TRV rad closest to room stat). Not sure how that then messes up the DHW!

As for geting 11c across DHW - I assume that is with the water in the tank completely cold? (or is that a really stupid question?)

 

[Agile]

All of these are totally approximate!

The bypass is primarily to allow a flow through the boiler when all the zone valves are off for boiler over run purposes.

You can turn all lockshields off and then back on by 1/2 turn as a starting point. You could probably leave it like that as it will then be approximately balanced.

Same with the HW circuit but there can be quite a bit of hysteresis in a gate valve.

Always set the lockshields as opening! If you wanted to close one a bit then close it completely and then open to the lesser amount.

Its all approximate and very interdependent on the number of zones operating.

Tony

 

[D4dog]

thank you, Agile - I will give the half-turn method a go, and if I ever get hold of a couple of clip on thermometers, I might try a little more accuracy.

As for the gate valve - not sure what other options I have, to be honest. Cannot find an in-line lockshield. I will try a half turn, and see how I get on - no doubt the first time the HW runs out, or takes to long to come on, i will get an earful from the boss!

 

[Agile]

The gate valve is fine.

You can feel the temperature difference with your hands.

But it takes about 5-10 minutes after making an adjustment for the temperature to stabilise.

Do the adjustments as angular changes with just a tiny movement at a time.

Close hot rads and open cooler ones but start with 1/2 turn.

The mistake so many make is to expect to balance with the valves nearly open. All the adjustment is in the first turn!

Tony

 

[D_Hailsham]

On the zones - given that you normally balance closest radiator first, would it be worthwhile applying the same logic to the zones, ie balance the ones with least resistance first? One of the zones is for the conservatory, and only has one large radiator (using a zone valve so I can leave the heating on whilst away, without heating the entire house!!). My logic suggests I should balance this first, then the upstairs (lower resistance than downstairs, and fewer rads).

Try it and see; it will give you plenty of exercise.

As for the bypass - the downstairs circuit offers quire a high resistance, so needs a little pressure from the pump. The valve has settings from what appears to be zero, to about 0.6. General advice seems to be to set this to operate when all the TRVs are closed (even though each zone has a none TRV rad closest to room stat). Not sure how that then messes up the DHW!

What make/model ABV is it? You may be able to find the instructions on the mfr website. The idea is that the ABV is closed when everything else is open; and opens gradually as the TRVs and zone valves close. This maintains a constant flow through the boiler.

As for getting 11c across DHW - I assume that is with the water in the tank completely cold? (or is that a really stupid question?)

Interesting not stupid
I would suggest setting it when then water is relatively cold; i.e. when the cylinder stat is about to turn the boiler on.

The 11C is not a hard and fast rule, it's just what rad and boiler mfrs use. Unless your system has been designed from the ground up with everything taken into account and all rads/pipes etc correctly sized, you will be lucky to get exactly 11C drop. The important thing is that the drop is the same across each radiator, the HW cylinder and the boiler. The greater the drop, the lower will be the output from the rad and more fuel you will use.

A rad run with 75C flow and 55C return will give about 16% less output than a rad run with 75C flow and 65C return. This is why some advocate installing oversize rads with condensing boilers.

 

[Agile]

What make/model ABV is it? You may be able to find the instructions on the mfr website. The idea is that the ABV is closed when everything else is open; and opens gradually as the TRVs and zone valves close. This maintains a constant flow through the boiler.

I would not really agree with that. The auto bypass is usually considered as fitted to only ensure that the MINIMUM flow rate is achieved through the boiler to enable it to properly control its temperature and to allow heat to be dissipated on over run.

Returning flow temperature to the return would prevent all condensing action and greatly reduce the efficiency on a condensing boiler. ( I appreciate that the OP is talking as if he has a standard efficiency boiler in this case. )

 

[D4dog]

That is interesting - so provided the boiler and pump are up to the job, I should actually be trying to achieve the lowest drop across the radiators - providing the drop is the same in all cases?

The boiler is a vaillant eco-tec 428 - and I have to say it heats the system up amazingly quickly. Even with the rads set to max! I havent got around to balancing yet, and it is apparent that the older (original house, not extension) rads at the far end of the downstairs circuit take some considerable time to heat up. Having flushed the system, I can only assume it is balancing that is causing them to be so slow.

HOWEVER (there is always one) the boiler reported status mode s.53 when I switched DHW off, and left just downstairs zone on - suggesting insufficient flow through the boiler. What is difficult to understand is that the flow is clearly detectable through the pipes, and from listening to the pump and the outlet temperature drops very rapidly - is this a boiler problem? (sorry - probably needs another thread!)

 

[Agile]

The boiler is a vaillant eco-tec 428 - and I have to say it heats the system up amazingly quickly. the outlet temperature drops very rapidly - is this a boiler problem? (sorry - probably needs another thread!)

You previously accepted a recommendation for a flow return differential of 11 ° C even though you really have a condensing boiler.

You should be aiming for a differential of 15-20 ° C.

You should set the outlet temperature to about 65° C on the boiler! Have you set it to maximum???

Are you reading what I am writing?

Tony

 

[D4dog]

Yes Tony - but not always at my desk! somewhat confused! I wasn't aware that balancing was different for a condensing boiler, so was using the figures I used some time ago for a standard boiler. I will aim for whatever differential is recommended - but out of curiosity, what is the theory behind the different figures for a condensing boiler?

 

[Agile]

Yes Tony - I will aim for whatever differential is recommended - but out of curiosity, what is the theory behind the different figures for a condensing boiler?

The condensing boiler needs a return below or close to 55° C to enable it to condense.

To enable them to operate efficiently they are designed to have a flow differentiol of 20° C and a 75/55 flow/return.

This means a much lower flow rate is required through the rads which enables pumps to be smaller or set lower.

Its a very common fault for DIYers and many so called professionals to have too high a flow and too small a differential. So the boiler does not operate efficiently.

Tony

 

[D_Hailsham]

What make/model ABV is it? You may be able to find the instructions on the mfr website. The idea is that the ABV is closed when everything else is open; and opens gradually as the TRVs and zone valves close. This maintains a constant flow through the boiler.

I would not really agree with that. The auto bypass is usually considered as fitted to only ensure that the MINIMUM flow rate is achieved through the boiler to enable it to properly control its temperature and to allow heat to be dissipated on over run.

Returning flow temperature to the return would prevent all condensing action and greatly reduce the efficiency on a condensing boiler.

The minimum flow rate quoted by manufacturers is normally calculated for the peak output with the stated temperature differential. So Vaillant quote 20.3 litres per minute for the 428 with a 20C differential. (My calcs give 20 litres per minute.)

If the system has properly spec'd and commissioned, the pump will be delivering the required flow when all radiators are in full use. The bypass will not be required, so it will be closed. As soon as a TRV closes, there will be an increase in the head. This will result in a reduction in the flow rate, so the ABV needs to open a little bit to compensate. The ABV will only need to be fully open if all TRVs are closed. This situation is unlikely to occur as the wall thermostat will probably have shut the boiler down.

Danfoss have Simple Instructions and Detailed Instructions on how to set their AVDO valves which are interesting reading.

 

[Agile]

[The minimum flow rate quoted by manufacturers is normally calculated for the peak output with the stated temperature differential. So Vaillant quote 20.3 litres per minute for the 428 with a 20C differential. (My calcs give 20 litres per minute.)

Thats a minimum flow rate at full power for getting the heat out of the boiler!

Its not the same as the minimum flow rate to enable the boiler to control its heat output. The ABV is primarily reauired for the latter.

If it opens significantly above that later minimum flow rate then it reduces the efficiency of the boiler.

Tony