Grundfos UPS3 - Proportional Pressure or Constant Pressure?

[stem]

The Grundfos UPS3 instructions recommend that the Constant Pressure Mode is used with a one pipe system, and Proportional Presure Mode used with a two pipe system. What do you reckon would be the best setting to use, and why, for a hybrid Y-Plan system with 7 radiators plumbed as one pipe, and 4 as a two pipe? There isn't an automatic by-pass.

 

[Johntheo5]

What do you mean by one pipe?, do you mean that the the rad(s) flow&return go into the same pipe and that pipe goes back to the boiler. do you mean by a two pipe that the rads flow and return are like the rungs of a ladder where the flow just supplies one end of the rads and the other ends all go into the return, this the normal system.

 

[stem]

There is a loop of pipe between the boiler flow and return with 7 radiators sat atop the loop. Water is pumped around the loop. This is the 'one pipe' part.

Then there are 4 other radiators also connected across the same flow / return / pump each with a separate flow and return connection. This is the two pipe part.

Grundfos recomend Constant Pressure Mode is used with a 'one pipe' system, and Proportional Presure Mode with a 'two pipe' system. But this one is a hybrid.

 

[pcaouolte]

Just set it to constant speed I II or III

 

[Johntheo5]

Unfortunately, while the the UPS3 gives very good flowrates in CC & CP mode, the PP settings are far too low, PP2 should be 4.6/4.8M.
Your hybrid system will require much higher flowrates for the 7 one pipe rads but for the moment assume the whole 11 are 2 pipe and say the 11rads output is 16.5kw total (1.5kw/rad), a flow rate of 1LPM/kw will give a dT of 15C, so total flowrate required 16.5LPM or almost 1.0m3/hr. PP2 will circulate that at a pump head of 2.4M which I doubt very much will be sufficient except you have very large flow/return piping,
I would suggest CP1 at the very least (3M pump head) but would think that CP2 at 4.5M head would be a good choice and will work perfectly well with 2 pipe radiator systems.

 

[Johntheo5]

Just came across some calcs I did years ago but not as far back as the last one pipe system I encountered which was in "college" over 60 years ago, I can't remember how hot the cast iron rads were but the one pipe(s) were certainly roasting.
Your system might look something like below, let us know how you get on after balancing them.

 

[stem]

Interesting chart, and I suspect that's representative in my case. I can tell that last two radiators on the one pipe loop (Hall & Dining Room) aren't quite as hot as the earlier ones, and they are also the biggest but they still heat up their respective areas well enough. It's a 1960's house with a ground and first floor, and the ceilings are quite low, so not a big head.

All in all, the system actually works fine. I had intended to replumb it as a two pipe when I moved in 25 years ago but after using it for the first winter I found it worked well, so apart from replacing the boiler ( Baxi Solo III, non condensing) and converting it to a fully pumped system with a motorised valve and adding TRV's it has stayed as it was.

With regard to balancing, all of the lockshields on the one pipe rads are actually fully open, which I did because the pumped flow through the one pipe loop is constant all of the way around the loop. The two pipe radiators were added with an extension in 2006 and their lockshields are just open slightly, not sure how much, as it's 16 years since it was set up and I've never had a reason to readjust them, but I seem to remember they are all about the same with the excpetion of the downstairs loo which is just cracked open as little as possible as it's just a small towel rail and only needs a tiny flow to heat it up.

Historically I ran the old pump on the slowest fixed speed and it's always been fine, but with the new pump there are the additional control settings, so I was wondering if they would offer me any advantages, and if so, what they would be. The new pump was originally set on constant speed I, but I've moved it now to constant pressure as suggested by @Johntheo5.

 

[Johntheo5]

A setting of CP1 will give a higher head/flow than the old pump's lowest setting so suggest giving this a go, if not already on it.
What is the boiler flow temperature set to?.

 

[stem]

What is the boiler flow temperature set to?.

Good question!

 

[Johntheo5]

Possibly ~ 65C depending on the scale and oil or gas boiler.

 

[stem]

OK, so I tried both suggestions. 'Constant Pressure 1' for a week and 'Constant Speed 1' for a week. Both worked well and I couldn't detect any noticeable difference in the operation of the heating.

So, which one to settle on? Is there an advantage in choosing one over the other? For example, does the pump suffer less wear in one mode than the other? Consume less power? Have some effect on the rest of the system? etc etc.

@Johntheo5 as an experiment and out of interest I tried the PP1 setting, and you are right; too slow in my case. In fact, the pump was that slow I wondered if it might have even stopped

 

[Johntheo5]

You can see below that since you didn't notice any big difference between CP1 and CC1 that the circulating demand is around 1.35m3/hr as CC1 ("fixed speed) is producing a 3M head as well. If the circ demand goes lower than this due to TRVs etc throttling in then the CC pump head will rise and consume a little more power, if the circ demand increases beyond 1.35m3/hr then the rads may run cooler as the CC pump head will start to fall.

Interestingly PP 2 (not PP1) gives the almost the exact same head (it gives 2.9M) at this circ rate and can give very big savings under the right conditions as you can see the head falling with reducing circ demand, probably not the best for a one pipe system but maybe worth a try, if only for interest?.

 

[stem]

So, if I understand correctly:

Q= Flow rate in m3/hour
H = Head in metres

The two horizontal lines with red arrows below are the CP settings
The two bottom lines are the PP settings, the top one PP 2 giving the 2.9m head close to it meeting CP 1.

I'm not sure that the circulation demand will fall much because most of the radiators are on the one pipe loop which I imagine has a fairly constant flow around it regardless of the TRV positions. Also, three of the two pipe radiators are small (2 are towel warmers) and their lockshields are just cracked open anyway . I'm ignoring the DHW as it's only on for a couple of short bursts each day.

So based on that, my understanding is that if the circulation demand did fall, the head would fall, and the pump energy consumption would drop. Is that correct?

 

[Johntheo5]

Correct, I have a Wilo Yonos Pico circ pump and I can set the CP & PP modes incrementally in 0.1 m steps, I have a 2 pipe system with 10 rads and I have the pump set to PP 4.6M which gives me - the 3.6M head required. As the TRVs throttle down the pumphead falls to - 2.5M and the power fom 22W to around 14/16W.

 

[Richard28]

I have a similar issue and would appreciate advice. I have a UPS3 Grindr’s pump and it says I shpuld
Use PP settings for a 2 pipe system. I have selected the higher PP II setting. I have 16 radiators of which 5 are doubles. The radiators take a long time to get fully hot.

Is the PP II setting on or do I need a faster setting?

Thank you.