Posted by: @jamespa

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Posted by: @simonwig

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I have a related query, feel free to move it to a new thread if preferred.

I have an Ideal Logic Air 10kW.

The flow rate showing on the Halo was 25 – 30 l/min, but often quite a low dT, maybe 2 - 3C.

I’ve noticed that it is possible to set the pump to modulate to maintain a dT of a variable number so as an experiment I’ve set it at 5C, (default is off for this setting, 5 if it's on).

It’s also possible to set the minimum pump speed %, I’ve set it to 50% (default is 70%), it’s unclear when this actually operates if the Modulation is off.

The pump is now generally running slower, currently 16l/m. House still maintaining temperature.

I’m really asking if there is any value in doing this

Not particularly unless you have a problem with noise in the pipework

Posted by: @simonwig

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it seems logical to run the pump slower and maintain the dT.

No, but there is a bit of a trade off and its not straightforward. 

The heat pump will be more efficient at lower deltaT.  However the water pump will consume less energy if its operating at a slower speed, which will mean less flow so higher deltaT.  Since the heat pump is likely to bne consuming 100s of W and the water pump 50W max, the heat pump will usually dominate. 

The sweet spot is dependent principally on your house loss.  The folks on openenergymonitor did a calculation and, for their particular set of circumstances, the optimum deltaT at the design OAT was ~2C (which implies that deltaT will be less at higher OATs).  Im pretty certain this was a ~5kW house.  The upshot of this, given that normally heat pump systems are designed for DT5 or thereabouts, is that for most cases the optimum is going to be to run the water pump at the highest comfortable speed, which likely will give a DT between 2-5 if its been designed correctly.

In short if its operating at 2-3C most of the time dont worry about it.

 

Hi, I have a similar situation as Octopus changed the downstairs radiator based on the heat loss but left the oversized radiators upstairs. I tried to restrict the flow Upstairs to almost close, as I think the flow valve are not that gradual in shutting down, and had to limit the temperature with the trv to not over heat. They are tado, that we still have from the gas boiler and seems to restrict the flow not shutting the radiator completely. I left downstairs fully open. You mentioned to not leave a towel rail radiator with flow completely open, can I ask why? Sorry trying to learn as much as I can.

For us the towel rail is the first in the heating circuit and Octopus changed it to a bigger one to meet the heat loss of the bathroom. Especially when the flow rumps up you can hear flushing noise from it like water running, mainly when the heat pump is switched off. Is there anything that we can do to to limit the noise. So far has been left fully open, based on the point above should we restrict the flow and will it potentially reduce the noise?

Thanks for the help

@rikiarn Might there be some air in the towel rail fitting? It rather sounds as though as it is the first in line from the heat pump, it has accumulated the residual air from the system. It may well be worth bleeding that rail - our system has the towel rail and bathroom radiator as the first port of call for the water from the pump (well, via the LLH) and it will collect any air for me; this is convenient as all other radiators remain clear of any air bubbles. Regards, Toodles.

@toodles I bled the radiator and it's fine, the noise is mainly coming from the flow pipe and return pipe that goes into the radiator not much from the radiator itself and it's more noisy when the flow rate on the heat pump is higher at 15-20l/m. Completely fine when it's at 6l/m 

Posted by: @rikiarn

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Hi, I have a similar situation as Octopus changed the downstairs radiator based on the heat loss but left the oversized radiators upstairs. I tried to restrict the flow Upstairs to almost close, as I think the flow valve are not that gradual in shutting down, and had to limit the temperature with the trv to not over heat.

@rikiarn I have the same issue really, although 13 out 15 radiators were changed.  Both upstairs and downstairs overheat when the weather is colder (< 4c) but I've buttoned them down to quite cosy when warmer than that.  The annoying thing, apart from sweltering indoors, is that I have to pay to warm that water up when it isn't actually needed or warranted.  I think Octopus's implementation of their Cosy heat pumps is poor and seems to be on the basis of a firmware approach that "one size fits all".  I'm still waiting for help from them.

I am formulating a plan of action as I have a small window where I have some time to dedicate to this where I can tinker without Commander in Chief Domestic being affected too badly! I am going to assemble some of the parts needed (de-aerator and a new three way valve) I have missed my window this year to install the de-aerator but I can gather the bits and bobs and book a plumber in for the spring. 

I have a bunch of decorator caps. I am going to bleed the system again then with all the lock shields open I am going to try to balance the system using the TrV side but using the decorator caps to close down the flow (heat input) into certain rads that don’t need too much heat and hopefully pushing the heat to the areas we want more heat. I need to rewatch the HG video on heat authority and re-read the article about using the trv valve etc but hopefully I can get further than my last effort! 

@rikiarn ☹️ It may be that the pipe joints themselves may be the culprits then. Are those joints sharp 90 degree joints or are they swept joints. Sharp bends can cause turbulence in such circumstances. All our pipework other than the runs under the floor and the risers to the radiators were renewed during our retrofit and swept joints were used throughout; the system is almost silent as the only sound in the house is a very faint whirr from the Wilo Pico secondary pump that is running at ~7 lpm. Toodles.

@grantmethestrength Hope that goes well for you, I’ll be interested to hear how control with the LSV’s wide open using the TRV side goes please. Toodles.

That's interesting about the joint I will have a closer look. Is there any reason why towel radiator should be partially closed on the flow valve, or any reason to keep it fully open?

Posted by: @rikiarn

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That's interesting about the joint I will have a closer look. Is there any reason why towel radiator should be partially closed on the flow valve, or any reason to keep it fully open?

I have seen it said that towel radiators should always be fully closed because they have very little flow resistance so are pretty much a 'short circuit'.  Obviously that might depend on the radiator, but it is certainly true of mine (so the valve is almost closed)

@rikiarn At the risk of contradicting @jamespa!😳… At this stage please accept a Mega Huge Caveat as I have a Dual Fuel towel rail so my experience is based on this type.

The valves on our towel rail are both fully open and the pipework runs in parallel with the bathroom radiator below it. The emitters are the first in the line in the system and there are no problems at all.

I find that the lower temperature of the heat pump water compared with the electrical element that is used during non-heating months means the towel rail is somewhat cooler than with the element doing the work. It may be that the element causes a restriction in the pipework and thus reducing the water flow - I don’t know, but I see no reason to reduce the heat pump water flow. It may well be that the restriction your valve is causing is also causing the noise you are experiencing. (Sorry James!) Toodles.

@toodles I will do, it can’t go any worse than my last attempt even with an excellent guide!!!