Flow temperatures

[Johnytuono]

The installation instruction state :
Available pump head at 20 °C system temperature rise 2.0
It's a Bosch Type UPS 15-60 HU1 3 speed pump
7 rads + towel rail , mid size 3 bed terraced house
I wouldn't even know where to start re curves, heads etc

 

[Johnytuono]

Just another quick question regarding balancing John. Instead of balancing my rads at 60c to achieve a return of 50c (10c difference and a flow of 0.902), going off your charts, could I do the balancing at 45c to achieve (about 5c difference) or would the flow rate be different? What I'm trying to say is, do I need to balance at the higher temperatures to achieve the desired flow then leave well alone (no matter what the temp difference) when using lower flow temperatures?

 

[Johntheo5]

Cant you see from the numbers in post #26 that you will get that when you balanced at 60C to give a dT of 10C?

 

[Johnytuono]

Cant you see from the numbers in post #26 that you will get that when you balanced at 60C to give a dT of 10C?

Yes, but I think the mistake I made was that I balanced for around 10c difference when running at a 48c (and not 60c) boiler flow temp, so, I think my flow rate would be too slow ? If I've got that statement right then I think I've got it (finally). I really should be aiming for a flow rate of 1.4 LPM (i.e.75/65 gives that) and then not alter the delta when I use lower flow temps as the LPM stays the same but my Delta will automatically reduce.
I know, I sound a bit thick when it comes to this

 

[Johntheo5]

Yes you can rebalace at 75C to give a 10C dT = a flowrate of 1.43LPM but I feel that balancing at 60C dT 10C = flowrate of 0.902LPM, will overall give better boiler efficiencies, and you can still get 100% output by increasing the flowtemp to 77C.
However if you just leave it at 48C/dT10C flowrate 0.52LPM you will still get 83.5% output at 75C/52C dT 23C and 92.8% at 80C/54.4C/26C flowrate in all cases 0.52LPM.
So maybe just leave it for now and see how it goes, you can allways rebalance at 75C or 60C, the choice is yours.

 

[Johnytuono]

Yes you can rebalace at 75C to give a 10C dT = a flowrate of 1.43LPM but I feel that balancing at 60C dT 10C = flowrate of 0.902LPM, will overall give better boiler efficiencies, and you can still get 100% output by increasing the flowtemp to 77C.
However if you just leave it at 48C/dT10C flowrate 0.52LPM you will still get 83.5% output at 75C/52C dT 23C and 92.8% at 80C/54.4C/26C flowrate in all cases 0.52LPM.
So maybe just leave it for now and see how it goes, you can allways rebalance at 75C or 60C, the choice is yours.

That makes sense John thanks
What’s the actual formula please for working this out

 

[Johntheo5]

Formula?, you balanced the rads by throttling the rad lockshield/ valves (I hope, and thought you said you did?) to get a dT of 10C with a flowtemp of 48C.
If so, then, but check the attachment, below
Flow.degC/Return.degC/dT.degC/radoutput.kw
48.0C/38.0C/10.0C/36.4%
56.2C/42.47C/13.73C/50%
70.4C/49.75C/20.45C/75%
80.0C/54.49C/25.51C/92.9%

 

[Johnytuono]

Formula?, you balanced the rads by throttling the rad lockshield/ valves (I hope, and thought you said you did?) to get a dT of 10C with a flowtemp of 48C.
If so, then, but check the attachment, below
Flow.degC/Return.degC/dT.degC/radoutput.kw
48.0C/38.0C/10.0C/36.4%
56.2C/42.47C/13.73C/50%
70.4C/49.75C/20.45C/75%
80.0C/54.49C/25.51C/92.9%

Sorry, yes I did balance like that, realised I can put different flow temps in the spreadsheet to get the info I wanted

 

[Johnytuono]

Attached is my pump curve, looking at it, I'm thinking best to be on speed 3?

 

[Johntheo5]

Yes, probably, speed2 will only have a head of ~ 2.0M at the flowrates you may require.

 

[Johnytuono]

I actually rebalanced last night
EDIT: At the rads it was 60c in 50 out on pump speed 2, so it will be as I initially stated .902 LPM (so maybe just on the limit of the head with all trv's open ?)
Will have to rebalance again though if using speed 3?

 

[Johntheo5]

Looking at that pump curve again then speed3 will result in a head of ~ 4.7M which would more than likely cause noisy TRV operation when they throttle down so if you all your rads are heating up, leave as is.

 

[Johnytuono]

Thanks John, I really appreciate your time.
What I have noticed though is that the last 2 rads on my system (2.2kw and 1.9kw), these happen to be where the room stat is, that even with the L/S fully open the temp difference is about 13c, so even if I wanted a lower temp difference, I couldn't get it. Is that because of the pump speed ? If I set a flow temp of, say, 45c, then I notice it is about 42c at the flow side of the last 1 or 2 rads.
Tbh I never noticed this issue before because I had never balanced until the last few days.
When you say speed3 (using a head of approx 4.7M) is that with the flow rate (ie my balance) of .902 LPM? The reason I ask is so that it enables me to understand (and read) the curve.
Also, before when you said I would (probably) need about 3 to 3.5M pump head, is that a rough working off my total rad(s) output?
Again, sorry if this is basic stuff to you.

 

[Johntheo5]

7 rads + a towel rad, say 8 rads if you have throttled the towel rad as well, 8x0.902 = 7.22LPM = 7.22/16.66 = 0.43m3/hr. say 0.5m3/hr, come vertically up on chart = 3.0m.at speed1 & 5m at speed2, try speed3 and keelp throttling one or two of the TRVS, if no noise then let pump on speed3 for a good while to let the TRVs do their own thing re throttling etc and noise then re balance perhaps?

 

[Johntheo5]

Those pump curves are for a Grundfos Selectric, they gave up making them about 15 years ago I think, is your pump that old? Anyway seems you require speed 3 one way or the other.