Circulation pump with electrical speed switching for wood boiler stove

[David00]

Can anyone help, please? I'm looking for a heating system circulation pump for a domestic install, with 3 speeds, where the speed can be toggled electrically as well as via a push switch on the pump body.

I'm using this pump with a wood boiler stove, where I want to run the pump at its slowest speed when the boiler is heating up, so that returned water from the cylinder & rads to the boiler doesn't cool it down too much. Only when the entire system is hot do I want to pump to run at its fastest speed, which is contrary to what many modern pumps want to do. This is not subject to UK building regs - so no need to comment on these.

Grundfos 100 series (UP, UPS, etc) had a terminal block with 8 screw connections inside the pump - that apparently allowed this. Although I can't find a description of the wiring. But their 200 series doesn't seem to support this.

I just want to select one of the 3 speeds using an electrical connection (i.e. pipe thermostats closing). I'm not looking for mobile remote control or digital inputs, and these or more modern pumps features like constant pressure/PROADAPT aren't of any use for my application.

 

[John.g]

If you look at the basics first, you would normally select a pump head that would give (near) continuous pump running at your maximum stove output and required dT, if you require a dT of say 12C and the stove has a max output of 5kw then you require a flowrate of ~ 6LPM, 0.36m3/hr, a pump head as low as 1.5/2.0M head should be adequate, if the stoves max output is say 10kw then the required flowrate is 12LPM, 0.72m3/hr and you may require a pump head of ~ 3.5M. You will have a pipestat on the stove flow set maybe to 45C so when the stove is cold then it will still start the pump at 45C but will stop it at ~ 37C (stat hysteresis) so you have a form of control with this?, as the stove heats up then the pump will run for longer and longer. One problem with this is that the head required to give continuous running at the stove's full output may not be matched by the any of the pumps 3 fixed speeds or any of the 2 or 3 constant pressure settings. A pump like mine (Wilo) can be set to any pump head you require to match the stoves max output and the pipestat takes care of the cold boiler or very low stove output when the fire is dying down at night.
Your requirement of automatically? switching fixed pump speeds will work to a degree because the lowest pump head on most 5 or 6M pumps is still ~ 2M, some like the Grundfos 1L goes as low as 1M but that, like mine is a A rated pump. Some pumps like the Alpha 1L have PWM (pulse width module) speed control but you require some form of external controller for this.

 

[David00]

If you look at the basics first, you would normally select a pump head that would give (near) continuous pump running at your maximum stove output and required dT, if you require a dT of say 12C and the stove has a max output of 5kw then you require a flowrate of ~ 6LPM, 0.36m3/hr, a pump head as low as 1.5/2.0M head should be adequate, if the stoves max output is say 10kw then the required flowrate is 12LPM, 0.72m3/hr and you may require a pump head of ~ 3.5M. You will have a pipestat on the stove flow set maybe to 45C so when the stove is cold then it will still start the pump at 45C but will stop it at ~ 37C (stat hysteresis) so you have a form of control with this?, as the stove heats up then the pump will run for longer and longer. One problem with this is that the head required to give continuous running at the stove's full output may not be matched by the any of the pumps 3 fixed speeds or any of the 2 or 3 constant pressure settings. A pump like mine (Wilo) can be set to any pump head you require to match the stoves max output and the pipestat takes care of the cold boiler or very low stove output when the fire is dying down at night.
Your requirement of automatically? switching fixed pump speeds will work to a degree because the lowest pump head on most 5 or 6M pumps is still ~ 2M, some like the Grundfos 1L goes as low as 1M but that, like mine is a A rated pump. Some pumps like the Alpha 1L have PWM (pulse width module) speed control but you require some form of external controller for this.

@John.g, thank you for the helpful answer.

How do you calculate the pump head required to achieve a certain flow rate? I’ll probably need up to 16 LPM, assuming 13 kW max water heating output and a dT of 12 deg.

Which Wilo pump are you using please?

As you’ve noted, I’ll use a pipestat to start the pump at around 45 deg - but then all of the water in the boiler gets replaced by cold water from the rads and cylinder. That's why I was looking for a electrically controlled pump, ideally keeping the water in the boiler at 45 deg, until all the water in the system has reached that temperature. Perhaps the solution is to use a boiler load valve…

 

[Basher]

Looks like there are such things as temperature controlled pumps, but couldn't find details ☹️!

Temperature control mode

Temperature controlled water pumps from Grundfos include a broad range of circulator pumps and in-line single stage pumps for heating applications.

www.grundfos.com

 

[John.g]

@John.g, thank you for the helpful answer.

How do you calculate the pump head required to achieve a certain flow rate? I’ll probably need up to 16 LPM, assuming 13 kW max water heating output and a dT of 12 deg.

Which Wilo pump are you using please?

As you’ve noted, I’ll use a pipestat to start the pump at around 45 deg - but then all of the water in the boiler gets replaced by cold water from the rads and cylinder. That's why I was looking for a electrically controlled pump, ideally keeping the water in the boiler at 45 deg, until all the water in the system has reached that temperature. Perhaps the solution is to use a boiler load valve…

You don't need to calculate the head required, a Wilo Yonos Pico displayes the flowrate in m3/hr when running in any mode and the pump head can be incrementally changed in 0.1M steps in CP (constant pressure) or PP (proportional pressure)modes to give any required flowrate.

Have you a schematic of your (proposed?) system.

 

[David00]

@John.g

It’s a fairly standard system, wood boiler with gravity flow circuit to hear dump rad (and F&E tank), separate pumped feed to 8x rads plus a heating coil within a solar hot water cylinder (for the winter), magnaclean then pump on the return just before the boiler. I’m in Greece, where most boilers are 2 port, so will use an injector T.

In addition to the heat dump rad, I’m going to fit a boiler load valve so that once the pump starts running (triggered by a flue stat), it initially recirculates through the boiler until the water temp gets up to 60 deg, and then the load valve starts passing some water it to the rads & cylinder.

Thanks for the Wilo suggestion, their pumps look good.

 

[John.g]

Are you controlling the stove flow temperature with this loading valve?.