Flow rate in central heating system

What would be the recommended course of action... new pump? If so, how big? Rebalance system? Powerflush?
 
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In my first post I suggested that a cheaper solution would be to fit install a low loss header, with the UPS25-55 in the primary loop and an Alpha 2 in the secondary.

The alternative, fitting a larger pump has problems of its own. If you fit a UPS 32-60 your consumption will be about 830kWH pa (Grundfos estimate) and there is still a danger that the boiler will not be running at the correct temperature/flow rate as you are limited to running "on the curve".

If you fit a Magna 25-60 your consumption will be 249kWH pa (Grundfos est) but you will run at the correct temperature/flow rate. The cost is however much higher.

An Alpha 2L pump will cost about £100 and a low loss header about the same. This is less than the cost of a UPS32-60 (£300+) or a Magna 25-60 (£470+).
 
Can I ask how you have calculated the Magna 25-60 would be sized correctly?

My preference would be to have a simpler system with a single pump (and less electrical consumption) even if the intial cost is higher.
 
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Do not fit a variable as a primary pump to these boilers it will still give s codes.

No point fitting an 11/4port to inch pipe the 25port pump is right for your setup.

Low loss is always going to work by removing the boiler head from the system but means mote electrics controls.Vaillant llh 45kw is the nest one for you but dh price is way out.

Practicle experience also needed one these as well as theory.

You want to save money by fitting a a rate variable you'll have to have a low loss
 
Do not fit a variable as a primary pump to these boilers it will still give s codes.

No point fitting an 11/4port to inch pipe the 25port pump is right for your setup.

Low loss is always going to work by removing the boiler head from the system but means mote electrics controls.Vaillant llh 45kw is the nest one for you but dh price is way out.

Practicle experience also needed one these as well as theory.

You want to save money by fitting a a rate variable you'll have to have a low loss

The Magna 25-60 and 25-100 seem to be fundamentally more efficient than the UPS series, even when running at a constant output. So they are probably more economical pumps to go for over a longer term, which is what I'm thinking about. (This is why I'm thinking about a Magna, not because I want a varaible rate pump.)
 
The magna is only a rated when modualting.fixed speed worse Efficency
 
Magna cost is double a ups so is it worth it on apump that will last maybe 10years
 
Do not fit a variable as a primary pump to these boilers it will still give s codes.
Why?

I assume that this would be caused as the house gets up to temperature, valves close, head reduces, the pump speed drops and temperature delta across the heat exchanger increases above the defined limits. (Or maybe I mean valves are open in a cold house, and head is small.)
 
As above and boiler modulatIon and pump modulation class causing same problem.I found out the hard way regardless of the theory
 
Plus the instructions state any pump
must be set to it's highest speed thus infering fixed speed pumps not modulating.
 
Can I ask how you have calculated the Magna 25-60 would be sized correctly?
This assumes that your original boiler Mexico boiler was working correctly.

From the Mexico manual the output is 36.6kW so at an 11C drop the flow rate is 36.6/(4.2 x 11) = 0.79 l/sec (47.5 l/min, 2.85m³/hr). From the flow rate/pressure loss graph on page 7 of the manual we find that at that rate the boiler loss is about 110 mbar.

This graph shows the Mexico data plotted as the purple line


At the required flow rate the head will be 4m or approx 400mbar. We know that the boiler loss is 110 mbar, so the loss though the rest of the system must be 400-110= 290mbar.

Now pressure loss is approximately proportional to the flow rate squared. We know that the flow rate of the Ultrcom at max output is 1.633 m³/hr, so the circuit pressure will reduce to approx 290 x (1.633/2.85)² = 95 mbar.

The loss through the Ultracom is 4.05m or approx 400 mbar so the total loss is 400+95 =495mbar, say 500 mbar or 5 m. The green line shows that at the required flow rate the pump can only deliver 4.75 metres, so the flow rate decreases until it can it deliver 5m.

If we now put the new boiler data (flow=1.633, head = 5m) into Grundfos's sizing tool is comes up with either the UPS 32-60 or the Magna 25-60. The left graph shows the data plotted for the UPS, the right for the Magna. You will see that the Magna has plenty of spare capacity to cope with higher pressure, if necessary. The UPS suffers from the complaint of all fixed speed pumps - you have to run on the curve all the time. The numbers 1,2 3 and 4 show how the pump operates under reduced load at various times of the year.

You mentioned constant pressure control. Grundfos only recommend this for systems with a relatively low small head losses. The recommended setting for high losses is either Autoadapt or proportional pressure.

Unlike the UPS type pumps, the Magna does not have fixed speeds, the speed electronically controlled by sensors which measure the flow temperature and differential pressure.


Hope that's enough info.

On the question of balancing, the system will have been balanced for an 11C differential. Because the pressure has changed all round the system, due to the reduced flow rate and higher head of the pump, the current balancing will no longer be correct.
 

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