OFCH - heating issues.

glog

Hoping to get a bit of advice on how to proceed with my trouble shooting.
I have a 3 Zone (Water, Upstairs and Downstairs) OFCH system. Each Zone has it's own Stat and zone valve
The circulation pump which was replaced last year is a Grundfos Alpha 1 25-65.
This was set to speed 1 when installed - the same as the old one taken out.
Boiler stat is set to about 2/3's.
I have bled all rads in the system - some had no air, some had quite a lot.

The current cold spell has made my issues more noticeable.

- With only Water zone on, water heats in Tank
- With Only Downstairs zone on, Rads heat up fine and hot
- Water and Downstairs zone on, water heats and rads heat up fine.

- Upstairs zone only on, 2 rads get very hot others are very slow.
I closed off the flow on these two rads and all others heat up reasonably, though not as hot as downstairs.
- When Upstairs and Downstairs zones are both on then Upstairs is slow and only gets warm at best.

So, basically to heat my upstairs effectively, I need to have only that Zone on.

The two 'Hot rads' issue looks like I have that sorted. The flow was wide open on them, so closing them down then opening them half turn should suffice to keep upstairs balanced ( this is still work in progress).

Any advice on how to proceed with getting all zones working effectively together?
Pump Speed setting?
In this set up, would the professionals balance the whole system or balance the zones individually?

Thanks in advance.

listermint

Open the zones and balance all rads from scratch starting with the one that's the hottest and work out. Did mine in an hour or so .

John.G

A Grundfos Alpha 1 on fixed speed (constant curve) 1 will pump practically nothing as the head is less than 1M. Just confirm the setting and the power in watts.

glog

John.G wrote: »

Just confirm the setting and the power in watts.

Thanks John - What do you mean by this?

John.G

The pump should look like this, if so, can you post the LED that's lighting and the the power W.

glog

Here is a link to the pump I have:
https://product-selection.grundfos.com/ie/products/alpha/alpha1-l/alpha1-l-25-65-130-99199582?tab=variant-curves&pumpsystemid=1216957409

This is what it's showing in attachment.
So, its speed 1 set and set to Radiator mode.

John.G

OK, press the setting button until you get it on speed setting 2, (radiator mode) that will give you 3M which should sort you out and allow you to open everything up again, will have a look at the other settings shortly.

John.G

Can't find the model but would suggest going to fixed speed 2 until I find the speed settings.

glog

I appreciate the input John - I'll go at it again tomorrow, don't want to disturb the household in bed etc.
First thing I'll try then, is to up the speed setting to 2.

John.G

I've had a good look at your speed curves and (fixed) speed setting 1 is 4.5M which should be quite adequate, fixed speed 2 is over 6M which should not be required, you have it on radiator mode which is a proportional (PP)speed setting but is a bit weak, UFH setting is also a reasonable setting at a constant head of 3M.

John.G

glog wrote: »

I appreciate the input John - I'll go at it again tomorrow, don't want to disturb the household in bed etc.
First thing I'll try then, is to up the speed setting to 2.

Have you upped your settings?.

glog

I spent a bit of time going through the rads before I did anything else.
To be clear, before today I haven't adjusted any of the rads, so all settings were inherited from the last owner (4 years ago).

Downstairs, the main rads are getting hot within 10 mins. Some were getting too hot and I've adjusted by turning down the flow.
Other rads downstairs were slower to get hot but did so in the end.

Upstairs, most have(or had) TRV's which are mostly set full open. The flow side appears to be fully open on most of the rads also.

Again, the couple of 'hot' ones I turned down the flow.
With just the Upstairs Zone on they all get fairly hot but not particularly quick.
However, it still struggles with Upstairs with both Downstairs and Upstairs going at the same time.

@John. G - I haven't yet upped the speed, after your last post regarding the settings being adequate, I just wanted to check that I can't damage anything by doing so?

John.G

Absolutely not re changing settings, you can always revert back with the press of the setting button.
your present setting is inadequate.

You are presently running in rad mode (there is only one rad mode and only one UFH mode).
If you want to proceed with ultra caution just change to "UFH" mode, ufh mode is just a constant head mode and should give you a modest increase in head and flowrate.

Rad mode, present setting. green and second last yellow.

change (now) to ufh mode. green and last yellow.

you just press the setting button to change

Feel your coldest rad and see if its increasing in temp, if still inadequate go to...
Fixed Speed 1 Green light ONLY on.

glog

Thanks again for your input John.G
So I set my pump setting to Fixed Speed 1 Green light ONLY on.

It certainly improved the situation. There is definitely less variance in downstairs and upstairs with the temperature rise more linear across the board.
I did find that most of the downstairs rads had the flow jammed fully open with a TRV at the other end.
I have turned these down and continue to try and balance the system.
Once they are all balanced I may try and knock the pump back a notch, just to see.

Out of interest, do you happen to know roughly what is the recommended max temperature of the rads?
Using a heat thermometer I can see my output form the boiler is about 72 degrees at the circulation pump.
Measuring the temp of the rads I find that anything above 60 degs feels like it could be a burn danger to the smallies.

With this in mind, once balanced, I may look at dropping the boiler stat too.

Wearb

glog wrote: »

Thanks again for your input John.G
So I set my pump setting to Fixed Speed 1 Green light ONLY on.

It certainly improved the situation. There is definitely less variance in downstairs and upstairs with the temperature rise more linear across the board.
I did find that most of the downstairs rads had the flow jammed fully open with a TRV at the other end.
I have turned these down and continue to try and balance the system.
Once they are all balanced I may try and knock the pump back a notch, just to see.

Out of interest, do you happen to know roughly what is the recommended max temperature of the rads?
Using a heat thermometer I can see my output form the boiler is about 72 degrees at the circulation pump.
Measuring the temp of the rads I find that anything above 60 degs feels like it could be a burn danger to the smallies.

With this in mind, once balanced, I may look at dropping the boiler stat too.

Be careful turning the boiler stat down too low. It can rot out the boiler if not plumbed to allow this. Most are not.

John.G

I would suggest a boiler setting of ~ 60C to 65C minimum, as these boilers cycle on/off continuously then a setting of 60C will give a average boiler/rad temp of 55C with a return of ~ 45C and a setting of 65C a average boiler/rad temp of 60C & 50c return. I think most condensing rads don't recommend a return of less than 40/45C to prevent corrosion so should be OK with these settings both from child protection and boiler protection!. You can measure the temps with your scanner. Also remember that the lower temps will result in reduced rad outputs to ~ 50/60% of their rated output.
Your pump setting I would think is pretty good.

Wearb

John.G wrote: »

I would suggest a boiler setting of ~ 60C to 65C minimum, as these boilers cycle on/off continuously then a setting of 60C will give a average boiler/rad temp of 55C with a return of ~ 45C and a setting of 65C a average boiler/rad temp of 60C & 50c return. I think most condensing rads don't recommend a return of less than 40/45C to prevent corrosion so should be OK with these settings both from child protection and boiler protection!. You can measure the temps with your scanner. Also remember that the lower temps will result in reduced rad outputs to ~ 50/60% of their rated output.
Your pump setting I would think is pretty good.

Is this a condensing boiler?

glog

John.G wrote: »

I would suggest a boiler setting of ~ 60C to 65C minimum, as these boilers cycle on/off continuously then a setting of 60C will give a average boiler/rad temp of 55C with a return of ~ 45C and a setting of 65C a average boiler/rad temp of 60C & 50c return. I think most condensing rads don't recommend a return of less than 40/45C to prevent corrosion so should be OK with these settings both from child protection and boiler protection!. You can measure the temps with your scanner. Also remember that the lower temps will result in reduced rad outputs to ~ 50/60% of their rated output.
Your pump setting I would think is pretty good.

Very informative - Thank you.

John.G

Wearb wrote: »

Is this a condensing boiler?

If it is, then using the Grant Vortex as a example, the boiler thermostat setting range is 65C to 75C so at its lowest setting of 65C the average flow temp will be 60C assuming a stat hysteresis of 10C. so the return temp can't be lower than 40C even with a rad deltaT of 20C.
UFH is different as a TMV is used and the return could be as low as 30C which could certainly lead to corrosion?.

I have a 15 year old SE Firebird and due to the rad TRVs throttling in I have seen return temps as low as 35C and returns of 40c very regularly but as the flue gas temperature is ~ 230C then I don't think I have/will have any problems with corrosion.

Wearb

John.G wrote: »

If it is, then using the Grant Vortex as a example, the boiler thermostat setting range is 65C to 75C so at its lowest setting of 65C the average flow temp will be 60C assuming a stat hysteresis of 10C. so the return temp can't be lower than 40C even with a rad deltaT of 20C.
UFH is different as a TMV is used and the return could be as low as 30C which could certainly lead to corrosion?.

I have a 15 year old SE Firebird and due to the rad TRVs throttling in I have seen return temps as low as 35C and returns of 40c very regularly but as the flue gas temperature is ~ 230C then I don't think I have/will have any problems with corrosion.

Would a closing trv not increase the return temperature?

From my experience, it seems that temporary low return hasn't had a detrimental effect. But with prolonged low return, I've seen them rot in less than 4 years.

John.G

The TRV slows down the flow through the rad, the flow temperature remains the same but the return temperature reduces,
for example, if a rad had flow/return temps of 70C/60C, mean temperature of 65C, then with a room temperature of 20C this rad is now a "45deg" rad and will emit (45/50)^1.3 or 87% of its 50 deg rating, if the TRV throttles in further to maintain a room temp of 20C the rad may have a flow/return temp of 70C/40C, mean temp of 55C and is now a (55-20) "35deg" rad and will emit (35/50)^1.3 or "only" 63% of its 50 deg rating and so on.

When you say less than 4 years are you talking about a condensing boiler?.

Wearb

John.G wrote: »

The TRV slows down the flow through the rad, the flow temperature remains the same but the return temperature reduces,
for example, if a rad had flow/return temps of 70C/60C, mean temperature of 65C, then with a room temperature of 20C this rad is now a "45deg" rad and will emit (45/50)^1.3 or 87% of its 50 deg rating, if the TRV throttles in further to maintain a room temp of 20C the rad may have a flow/return temp of 70C/40C, mean temp of 55C and is now a (55-20) "35deg" rad and will emit (35/50)^1.3 or "only" 63% of its 50 deg rating and so on.

Finding it hard to get my head around this. If the flow rate remains constant. The boiler stat remains constant, but the demand decreases, so you have perhaps a 20kw boiler now feeding a 10 or 15kw demand, does the return temp drop?

When you say less than 4 years are you talking about a condensing boiler?.

No, SE. Condensers are more forgiving for obvious reasons, but not exempt from this either.

.

John.G

The flow rate does not remain the same, the TRV throttles it so the outlet temp falls as the rad is still emitting quite a lot of heat. If you just go to to a rad without a TRV and just barely crack open one isol valve you will see that the water exiting it is much cooler than the inlet which remains constant.

I have read that some condensing boilers can suffer leakage in the (is it called primary or secondary) HOT heat exchanger as the cold exchanger is SS but the other isn't and if the water is too cold then corrosion can set in, I would like to know if the flue gas temperature between the two exchangers is similar to my SE exit temp of ~ 230C. I wasn't aware of the same problem with SE boilers.

Wearb

John.G wrote: »

The flow rate does not remain the same, the TRV throttles it so the outlet temp falls as the rad is still emitting quite a lot of heat. If you just go to to a rad without a TRV and just barely crack open one isol valve you will see that the water exiting it is much cooler than the inlet which remains constant.

Much cooler, but a lot less of it? I am talking of a system with an old type pump.

I have read that some condensing boilers can suffer leakage in the (is it called primary or secondary) HOT heat exchanger as the cold exchanger is SS but the other isn't and if the water is too cold then corrosion can set in,

Yes it can happen. I've heard of it and saw it once, where a customer thought he was doing great by dropping down the nozzle way too much. He got it into his mind that it would save fuel.

I would like to know if the flue gas temperature between the two exchangers is similar to my SE exit temp of ~ 230C.

I don't know the answer to that, but probably lower due to advances in heat exchanger design.

I wasn't aware of the same problem with SE boilers.

I don't understand. "Same problem"?

.

John.G

What I meant by the same problem, I mean I wasn't aware that SE boilers suffered leakage problems due to low return temperatures.

Flow rates:
Assume a total rad heating demand of 15kw, if all the rads are running with flow/return/room temps of 75C/65C/20c then the rads will produce 15kw and the total flowrate will be (15*860/10/60), 21.5 LPM.
If the outside temperature rises sufficiently to only require a rad output of 9.4kw then the flow/return/room temps will be 75C/35C/20C (TRVs throttling in) and the total flowrate is now (9.4*860/40/60), 3.37 LPM. The old type pump head will just increase, this is one reason "smart" circulating pumps were introduced, to save (pumping) energy by reducing the head to keep the TRVs much further open but still allowing the required circulation flow rate, my Wilo A rated pump runs at 22/24Watts with all rad TRVs full open but when house fully warm only ~ 14/18Watts.

jimf

John.G wrote: »

The flow rate does not remain the same, the TRV throttles it so the outlet temp falls as the rad is still emitting quite a lot of heat. If you just go to to a rad without a TRV and just barely crack open one isol valve you will see that the water exiting it is much cooler than the inlet which remains constant.

I have read that some condensing boilers can suffer leakage in the (is it called primary or secondary) HOT heat exchanger as the cold exchanger is SS but the other isn't and if the water is too cold then corrosion can set in, I would like to know if the flue gas temperature between the two exchangers is similar to my SE exit temp of ~ 230C. I wasn't aware of the same problem with SE boilers.

if you take the flugas sample from the combustion door of a grant euroflame he boiler the sample temp will be there or therabout the same as a se boiler as the heat has at this stage not passed through the secondary heat exchanger

that is why you can use this point to check co and smoke no but not for overall boiler eff