I see, that's what has confused me.
So it seems things are normal then but still leaves the question of which pump mode to use from PP1, PP2, CP1 or CP2, how should I determine which to use?
Grundfos Alpha 2 15-60 130 Setting?
- Thread starter woodpeckerx
- Start date
So it seems things are normal then but still leaves the question of which pump mode to use from PP1, PP2, CP1 or CP2, how should I determine which to use?
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CP1 at 3M would be my choice as it gives excellent contol, I have a 6M Wilo Yonos Pico where I can incrementally change the CP & PP settings in 0.1M steps, I run at a PP setting of 4.6M which gives me a 3M head and 22/24W with all the TRVs full open, it will then fall to ~ 2.4M and 15/16w when TRVs throttle in, I couldn't achieve this with the above pump.
Thanks, I'll try CP1
Another question, what is the formula to calculate the approx LPM per kW for a given dT?
Another question, what is the formula to calculate the approx LPM per kW for a given dT?
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Me too, thanks again for your help!
Slight correction on my own set up, I have 10 rads with a outut of ~ 12kw, I have the pump set to a PP setting of 4.0M which gives me 12.0 LPM at a 3M head.
If I used the Grundfos at a PP setting of 3M then I would get a actual flow of 9.5LPM at a 1.9M head. (see below)
Of couse your system may have bigger diameter flow and return piping than mine so with all rads on, PP2 at 3M may be OK, you can obviously play around with the different modes/settings.
If I used the Grundfos at a PP setting of 3M then I would get a actual flow of 9.5LPM at a 1.9M head. (see below)
Of couse your system may have bigger diameter flow and return piping than mine so with all rads on, PP2 at 3M may be OK, you can obviously play around with the different modes/settings.
Reading about the above, if you have a 1000W rad and you require a 20C dT then you set the index to 4?. which should give a flowrate of 43LPH even if the dP across the valve changes, (auto balancing). Presume you can still set the required room temperature on these type? like normal TRVs that just throttle and reduce the flowrate as the room heats up.
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They use the same TRV4 head on the valve or a Wiser smart head to shut it down for temperature control.
I'm still struggling with the whole system though.
With the all the TRV heads removed and the balance values set for dT20 all the valves added together should allow a flow through the system of 835lph, this is more than the minimum boiler requirement of 774lph but the boiler just short cycles, its near impossible to measure the flow as the pump jumps in 1W increments. The only way to get the boiler to run properly is to reduce the ABV setting to allow some flow through it.
Next I opened up all the valves to the dT15 setting, this should allow 1090lph via the valves but on the CP1 3M head pump setting the boiler was still short cycling, it seemed to be just about hanging on with it set to CP2 4.5M head.
Am I missing something obvious about these valves? By adding them in the system it would appear the valves have reduced the lph flow to around or below the minimum flow requirement stated in the boiler manual, if my understanding is correct?
OK, what was the pump power on CP1 and on CP2
If 774LPM is the minimum flowrate required then if the boiler if firing at 30kw will have a dT of 33.3C anf IF 19kw is its minimum output the dT is 21C. Minimum flowrates are generally given at max output at a dT of 20C, in which case flowrate should theoretically be 1290LPH (21.5LPM). but more to that later.
I see a valve coefficient of 0.35m3/hr for those TRVs which = 1.84LPM at a 1M dP presumably with the balancing index at it lowest setting which is the greates flow?? (check this) so maybe set all the TRVs to max flow and see what happens>
Anyway post your readings for CP1 and CP2 espcially CP2 as it may not jump around as much.
How many rads have got??.
If 774LPM is the minimum flowrate required then if the boiler if firing at 30kw will have a dT of 33.3C anf IF 19kw is its minimum output the dT is 21C. Minimum flowrates are generally given at max output at a dT of 20C, in which case flowrate should theoretically be 1290LPH (21.5LPM). but more to that later.
I see a valve coefficient of 0.35m3/hr for those TRVs which = 1.84LPM at a 1M dP presumably with the balancing index at it lowest setting which is the greates flow?? (check this) so maybe set all the TRVs to max flow and see what happens>
Anyway post your readings for CP1 and CP2 espcially CP2 as it may not jump around as much.
How many rads have got??.
Just reading back your posts, you say you have the TRVs heads removed so that should mean that the valves are fully open with their operating pins fully out so you can't do any better than that from a flow point of view?
Last readings I took were with all TRV heads removed, valve balance index set for dT15 degrees, CP1 fluctuacted between 15/16W, CP2 between 26/27W.
On CP1 the boiler was short cycling, close to kettling I would say, CP2 seemed to just about hang on.
The boiler has a max rating of 31kW but as far as I can tell its set at the factory default setting of 18kW.
The manual says:
The flow rate through the boiler must not be allowed to fall below that given in Table 3.
The valve is stamped on the top that the lph is the index x10 so an index of 6 is 60 lph, 15, 150lph. There is a calibrate mark which is the widest open setting suggested for commissioning only. Also on the boxes it says dp min 10-100lph = 0.1 bar and 100-150lph = 0.15 bar, dp max = 0.6 bar.
13 + 2 towel rails
Yes, nothing on the valve body, pins out, only restriction is the valve itself. All lockshields are wide open as recommended.
Something seriously wrong here.
CP1 at 15W is giving a flowrate of 3.3LPM and CP2 at 26W is giving ~ 4.0LPM, its no wonder you have to open the ABV. A boiler output of 18kw with a flowrate of 4.0LPM will result in a dT of 64.5C, impossible as the burner will shut down in a matter of seconds.
You were getting ~ 8LPM (11W) on PP2 with only a few rads, 3? on originally.
Just to be clear, how mamy rads are on now??, if all 13 on then points to a pump problem IMO, just switch back to PP2 and note the power and then switch to max speed setting 3 and again note the power.
How old is the pump?.
CP1 at 15W is giving a flowrate of 3.3LPM and CP2 at 26W is giving ~ 4.0LPM, its no wonder you have to open the ABV. A boiler output of 18kw with a flowrate of 4.0LPM will result in a dT of 64.5C, impossible as the burner will shut down in a matter of seconds.
You were getting ~ 8LPM (11W) on PP2 with only a few rads, 3? on originally.
Just to be clear, how mamy rads are on now??, if all 13 on then points to a pump problem IMO, just switch back to PP2 and note the power and then switch to max speed setting 3 and again note the power.
How old is the pump?.
That's my feeling but maybe I've missed something stupid?
All rads on, 13 plus 2 towel rails. PP2 showing 9W, speed 3, 38W, did show 42W earlier, ABV is max setting so its closed.
From the date code 1806 I assume June 2018? nearly 5 years old?
My only other thought is whether I have air trapped in the system, I am getting some gurgling and bubbling and water running sounds near the boiler pipework. Bled the rads multiple times, only very small amounts coming out with recents bleeds.
Open vented system? with feed&expansion (small) tank in the attic, check that its "full". possible blockage in the cold feed where it joins the system.
Any zone valve on the system?.
suggest final test (tonight) just open thje ABV fully with pump on full speed 3 and note power then full open on CP1, again note power.
Any zone valve on the system?.
suggest final test (tonight) just open thje ABV fully with pump on full speed 3 and note power then full open on CP1, again note power.
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