Well, last night I decided to try and set the temperature back overnight. I haven't got around to working out the programming on the room stats yet so just switched it to low which is 16.5. Stats were on 18.5 when I did this at 22:30. I woke up at 02:40 and thought I'd check the stats as I passed them. They were on 16.5 so I put them back to the 21 degree setting as my back stop. I'm having trouble sleeping so checked again at 04:00 and nothing had happened. The heating hadn't kicked in. 🤷

Our hot water heating cycle runs from 00:00 to 01:00 and the flow temp was showing at 31 degrees. 

Did it not start straight away as the flow temp was deemed warm enough? It was pushing it around the rads and all rads were cold. 

It eventually started at 04:45 once I put +5 on the wired remote then the flow temp rapidly dropped, I stuck it back to 0 and it's run fine since. 

This isn't something I've played with yet? Is this normal? 

Thanks 

Posted by: @craig1980

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I woke up at 02:40 and thought I'd check the stats as I passed them.

I love that sentence as it summarizes the heat pump owner to a tee. I bet most heat pump owners have woken up at some ungodly hour to feel the rads or check the stats. 

Posted by: @editor

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Posted by: @craig1980

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I woke up at 02:40 and thought I'd check the stats as I passed them.

I love that sentence as it summarizes the heat pump owner to a tee. I bet most heat pump owners have woken up at some ungodly hour to feel the rads or check the stats. 

 

I'd take that bet: I reckon more stay asleep but have woken to a cold house at some point!

Although, that also happened in an old home when an unfavourable wind blew the pilot flame out.

@editor honestly, I'm considering redesigning the house so I can fit a chair by the UVC to watch the figures and fiddle with the settings. 🤣🤣

@mjr, you're right. In the early days, when the house was cooler than normal at 3am, I'd get up and touch the rad. If it was cold, it was a matter of going downstairs and seeing what the error was. There typically was one. There was a time (which is thankfully behind us now) where that involved us having to go outside and clean out the filter, which was very, very unpleasant.

Nevertheless, our early morning antiques go some way to showing how 'paranoid' homeowners are about heat pumps, and we love to mollycoddle these machines.

@craig1980, "I woke up at 02:40 this morning to check my heat pump" should be a on a T-shirt or it be should be a manufacturer's slogan.

@editor - Mars, a dozen tee shirts with "I woke up at 02:40 this morning to check my heat pump" emblazoned on them should definitely be included in the handover pack given to all new ASHP owners. I gather psychiatrists have already decided on a name for the condition, its called HPDHD, Heat Pump Deficit Hyperactivity Disorder.

Our first winter with ASHP and - after a week of consuming around 130kWh a day (!) with pumps really struggling to keep the house warm - my thoughts are rapidly turning to how I can optimise the system.

We have 2 x 12kW Samsung heat pumps c/w 180 litre buffer tank; the main heat pump provides heating and DHW, with the second just heating. I've not yet made any adjustment to the installer's weather compensation settings (50°C at 2°C outside, 42°C at 15°C) although these seem far from optimal, particularly when not so cold outside.

I'm particularly interested to hear from anyone operating a twin pump system like this. 

• I've noticed the outlet water temperature on the second pump is consistently some 6°C lower than the first pump. I don't expect them to be exactly the same but is this normal or is it merely introducing cooler water into the buffer tank and reducing the temperature and efficiency? What run signal does the second unit typically use to tell it to come in? 
• My monitor is consistently recording a zero (or virtually zero) heat generation from the second heat pump. For example, so far today, 4.4kWh consumed but 0kWh recorded generation. Whereas heat pump one is showing a COP of 2.5 or thereabouts at 4° outside. Any explanation for this? I am assuming it's a measurement issue and nothing more fundamental. 
• Finally, during last week's cold spell I noticed the outlet water temperature of heat pump 1 never quite achieved its 50°C WC set point, with 45°C being more typical. Is it to be expected that the units struggle to reach water set points in very low external temperatures?

I've posed these questions to my installer and am waiting on a response.  In the meantime, all enlightement gratefully received! 

Simon

@dunlorn I have a similar issue but instead have two Daikin 14kW units. How big is your house and how are yours 'joined' together? Are there electronics to decide which one to use or is it just down to plumbing like mine, through a low loss header (LLH). My house is about 250 sq. m..

Last week I turned one off (as much as I could as I still needed it to do hot water) and there was no difference in terms of how the heating worked. However, when it's cold, the antifreeze protection runs the circulation pump at 40 l/min into the LLH which again basically robs some for the flow and warms the return - see below.

I'm beginning to think some of this is due to flow - I don't think I can get 28kW down my (radiator) pipework. In other words I have far too much 'power' and I don't need it.

Mine are set a few degrees apart which is supposed to be something called lead and lag operation and is used with gas boilers. 

My COP is also low - sub 2 on some days. It should be better. If I run both one produces less heat but also at much worse COP around 1.5. I think it's compounded by distorted flow in the LLH which is warming the return and causing the Heat Pump to work inefficiently. My flow across the LLH is certainly not balanced. Compounded by the circulation pumps that change flow with load. My WD curve is working about right and I set a demand so that TRVs in the main rooms don't shut, but others do as we don't need to heat the whole house all the time with two of us!

On warmer days as we've had today and yesterday again running on one, COP is better (got over 3 yesterday!!) but now I need so little power it's cycling causing inefficiency too.

Don't know what the answer is yet. I'm beginning to wonder whether some of these high cost issues are nothing to do with the basic heat pump rather legacy issues from existing infrastructure i.e. the radiators and piping, and were unnoticed with high power systems i.e oil or gas. Installers as far as I know don't do a health check on the basic system.

Another issue I think is that they sized the system on worst case scenario i.e.-2 outside and 21 degrees inside etc. They didn't ask how we use the house most of the time - three bedrooms not used very often etc.. But I suppose we do want the ability to heat everywhere...

It's nice to have the ability to heat hot water without dropping heating. I think we should have had two smaller units, say 8kW linked with electronics to decide how much to use.

Thanks for your note @chrislay. To answer your point, my property is around 174m2 and of solid stone wall/suspended floor construction. So, insulation not great but we're making improvements.  As to how the second unit is controlled, I don't know for sure and it's one of the questions I've asked my installer. My handover effectively comprised "you don't need to touch this" and the manual is the most impenetrable work you could imagine. I can't find any mention of using two pumps so no idea if run signal is linked to a certain ambient temperature, return temperature or simply plumbed together like yours. I've been switching the second unit off a lot as not convinced of it's worth but lately when I do use it its run time is virtually the same as the 'lead' pump anyway, albeit at lower power demand. What I can't understand is why it should operate at a lower water temperature. I'll keep prodding my installer until I can get something meaningful.....