Posted by: @bontwoody

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Posted by: @bontwoody

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So after waiting over 3 weeks for a replacement cylinder, it arrived yesterday and the installer arrived this morning. Unfortunately he didnt know what the job was prior to getting here and didnt have the required fittings so will have to come back (3 hour drive from Brecon).

 

The amount of times this happens is staggering. Driving across the country to do a job and not fully briefed or prepared. Was this an installer from Mixergy or someone that was assigned to you? Truly staggering.

 

Sorry to say this but the is NOT in any way special to the plumbing industry. 

I saw this all the time when I was working full time, and still do.  For example we had five visits from different Openreach engineers to make a single copper telephone connection to a refurbished building.  On no occasion did the engineer who turned up know what he was supposed to do or any of the history of what previous engineers had discovered.  So each engineer was surprised to discover what was there or even what the job was and went away without completing the job.  In the end we made a decision what route the cable was going to take, fully prepared it for them, and then made sure we were ready to show them where the connection points were both at our end and to the live network at 'their' end.  All they had to do was pull a cable through a duct, fit an NTU and punch the other end down onto a couple of IDC terminals.  Yet amazingly one engineer turned up with insufficient length of cable because, (or so he claimed), theft of copper is so rife that the Openreach engineers carry only the exact amount of copper cable allocated to the job!  About 9 months later we finally got our telephone connection!

One exception was UKPN who seem, at least in my experience, to have a joined up team, which is perhaps why several of the people I encountered told me how much they enjoyed working for the company.  But that appeared to be an exception to prove a rule.

Long ago I adopted the defensive tactic of assuming that whoever turns up for whatever the job is wont have a scooby what they are supposed to do and quite possibly wont have the tools.  This means that I make it my business to know what is going on, what needs to be done, why, and to the extent I can, how to do it.  You may say that this should be unnecessary, and it should, but the fact it that it isn't!  Resistance in this case is useless!

Makes you wonder how these companies can make a profit with all that waste!

Looking for a silver lining in the Indirect v Direct cylinder debacle, I currently heat my hot water with the immersion during off peak. The payback time for buying a heat exchanger to use the heat pump was considerable.

While I know it wont be ideal, I wonder how good the indirect coil would be when used with the heat pump? Anything above a COP of 1 would be better than I have. I cant find any detail on the Mixergy coil size though. Anyone have any idea?

Posted by: @bontwoody

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While I know it wont be ideal, I wonder how good the indirect coil would be when used with the heat pump? Anything above a COP of 1 would be better than I have. I cant find any detail on the Mixergy coil size though. Anyone have any idea?

Mixergy used to (and so far as I am aware still do) sell a heat pump add on kit comprising a circulator pump and plate heat exchanger which replaces the internal coil.  

If you have an R290 pump or even R32 and a modestly sized cylinder you may well get a tolerable result with the standard internal coil so long as you dont want to end up with water that is particularly hot.  The Vaillant 200l heat pump cylinder has only a 1.4 sq m coil area.  Nevertheless my Vaillant 7kW heat pump will happily heat it to >65C on the legionella cycle, and the DHW COP is over 3.  The Mixergy coil is very probably only 0.6sq m, so half the heart transfer at any given temp diff, but that may still be OK at say 48C target.  If your target is COP>1 I would say you have a good chance of achieving it!

@jamespa Yes, the heat exchanger kit for mixergy was what I was referring to. I reckon is about a 5 year minimum payback time for me using Octopus Go 🙁

I will take a "tolerable good result" all the way to the bank 🙂 Even if I have to top up with the immersion. Hopefully I can convince the fitter to pipe it up for me too!

Posted by: @bontwoody

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Even if I have to top up with the immersion. Hopefully I can convince the fitter to pipe it up for me too!

Im not sure you have anything to lose by getting it piped up, if it doesn't work just don't use it.  I presume the diverter valve is already in place if not dont forget you need that also.

I'm not sure which cylinder they have sent you, but I found data sheets for some Mixergy cylinders here which show coil rating of around 17.8-20kW for their smaller indirect cylinders:

https://support.mixergy.co.uk/hubfs/2024-Mixergy%20X-datasheet-485-582.pdf?hsLang=en

In your favour, you only have a 5kW heat pump and can run it in Quiet Mode to further limit it's output, meaning you are not pumping out huge amounts of heat for the coil to transfer, so a smaller coil will be less of an issue than to someone like myself with a 12kW heat pump. Heating low(er) and slow(er) will allow the coil more chance to transfer it's heat, and as you'll be reheating overnight on cheap rate, it makes no difference how long it takes.

For comparison, my Joule Kodiak 160L indirect cylinder has a coil of 1.9m2 surface area and is rated at 39kW. I note some smaller Joule cylinders only suitable for heat pumps upto 8kW have smaller coils rated at 25-26kW output. Given your heat output maybe half that of an 8kW heat pump when running in quiet mode, a coil output of 18-20kW would not appear to be limiting, so I agree with @jamespa that it should work fine.

@jamespa Yes. I plumbed it all in ready for a heat exchanger at a later date 😁

@old_scientist Super. Thanks for all that info. My day just keeps getting better 😆

@bontwoody when’s the installer coming back with the required nuts and bolts?

We’ve had guys visit in the past, knowing the job they were coming for, only to arrive and ask if there was a merchant nearby to buy bits and pieces. I don’t understand this from a sheer business operation perspective.

@editor He couldn't give me a definitive date but hoped next week. He asked me about merchants nearby but they didn't have accounts with those in my area.

@bontwoody, ridiculous, and I assume you're still running off the immersion.

@editor lol. I wish. They told me to switch everything off. I jury rigged a shower from an instantaneous water heater i had lying about.