Wilo Pump Setting

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Hi,

We have a Kingspan Tribune Xe unvented hot water cylinder with internal thermal expansion.

The boiler is an Ideal H24. The house was built in 2019 and the heating system has 2 zones, upstairs and downstairs, feeding normal radiators with thermostatic valves.

The Wilo pump in the airing cupboard is set to the factory setting of Constant Speed III. Having read the operating instructions recently, it appears that the pump has 3 different control modes.

1 - Variable Differential Pressure - recommended for two-pipe heating systems with radiators to reduce the flow noise at thermostatic valves

2 - Constant Differential Pressure - recommended for underfloor heating

3 - Constant Speed - recommended for systems with fixed system resistance requiring a constant volume flow

Kingspan advised that the setting makes no difference to their system. I know option 1 has some energy savings, hence my interest in checking the settings.

Any advice gratefully received!
 
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How many radiators do you have?

The best thing you could do right away is get a weather compensation unit installed then cross your fingers that the radiators are oversized. This will allow you to actually get your boiler to condensate.
 
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Upstairs: 10 radiators - including 3 towel rails
Downstairs: 9 radiators

Can you explain what you mean about the weather compensation unit and getting the boiler to condensate?
 
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A modern boiler only achieves the 90%+ efficiency they are rated for when they get a flow back to the boiler that is quite low temperature. About 45 degrees.

So if you run your boiler at a central heating temperature of 75 degrees all year, despite it being 15C outside then the boiler will never condense.

The weather compensation unit is a basic add-on that automatically sets the boiler temperature to what's required without you having to do it manually.

Your boiler can only modulate down to 4.2kW. So if demand is less than that all the extra energy will be wasted and going out the flue or wasted as the boiler cycles rather than modulates.

It's very likely your pump setting is far too high. Reduce it to the lowest and see if your rads heat up and importantly if the rooms heat up to your satisfaction in a time you find acceptable.

It might also be likely that your system was never properly commissioned and balanced.

If your radiators are oversized, you can run them at a lower, more efficient temperature for the same heat output than a smaller radiator at higher temperatures.
 
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Thanks for this information.

After looking into the weather compensation unit, the problem I will have is positioning the sensor on a north facing wall. It will be very complicated and will involve a long run of cabling.

I balanced the radiators when we moved in last year, and I'm generally happy that the house is being heated in a consistent and even manner.

I'm still interested about the pump settings. In particular, whether I could use control mode 1 as described above.

What is a fixed resistance system?

Thanks in advance.
 
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In essence it does not make sense to have a pump running at continuous set speed for systems with varied hydraulics. Set speeds are for something with constant hydraulics like a charging loop for a hot water tank, where your main goal is to avoid cycling the boiler before the tank thermostat is satisfied rather than saving energy with a pump set too high.

In a radiator heating loop the TRVs are the reason for the wide variability of the hydraulic resistance in the system.
  • As demand drops, the control valve starts to close.
  • The closure of the control valve causes system flow to drop.
  • As the control valve closes, a sensor recognizes an increased pressure differential.
  • This increase in pressure differential prompts the pump controller to slow the pump speed down
  • The pump slows down until the control differential pressure is restored.
This control scheme is called proportional pressure control. It starts with the assumption that about half of your pressure loss in the system will be in the distribution pipe while the other half is lost in the radiators. The pump is controlled such that it will respond to a decrease in flow with a reduction of its head and that at zero flow, when all valves are closed, it will provide half the head pressure it has at maximum flow.

The pump needs to be strong enough to provide heat for the whole house, and therefore you should set it to reach maximum head when all valves are open. If you know your maximum design flow, you can pick that point out of the pump diagram. If not, you open all the thermostats in the house fully (assuming hydraulic balancing has been done), and then increase the power setting slowly until you see that the head pressure is not increasing anymore.

If you settings are bad: On the low side, you may experience boiler cycling and insufficient heating. On the high side, you may get “whistling” thermostatic valves.

Constant pressure control is ideal when the distribution pipe is non-existent or very short, like for underfloor heating.
 
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Thanks for the detailed explanation.

So if I'm reading it correctly, control mode 1 might be the way to go?
 

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