@davidnolan22 I genuinely do not know the answer, unless your home is 500m2 I doubt you need that many pumps and there would still be a better way to do it even if it was.

I think the main issue can be zoning, so many installs the engineers zone in smaller houses, what we know is they work better with less restrictions but I your point, if it performs like they advised then what can you do?  

It’s the complete lack of design, planning and execution in so many installs that really gets to me.

Our original system was bodged from day one. Every time we raised concerns, the stock response from the installers was, “We’ll add another pump.” By the end of it, we had four pumps and no real improvement.

Fast forward to our recent so-called “retrofix,” and the pattern repeated itself in reverse. The installer scoffed and mocked at the four pumps, ripped them out and replaced them with one massive pump. Same logic, just a bigger plaster on the same wound. Still no design, no evaluation of pipe sizing, no system thinking. Just “add more force.” 

That approach doesn’t work. It never has in heat pump installations. It’s a cowboy mindset… the idea that you can blast your way to success instead of taking the time to plan, calculate and understand what you’re working with. I know it takes time. I know it takes effort. But that’s the job of a heat engineer. That’s essentially what you’re paying for as a customer.

In spring, we’ll be tackling a proper retrofix (built on design, maths and strategy) to show how thoughtful planning delivers uniform, efficient heat across a property, even a complex-ish one like ours.

Heat pumps demand respect and understanding, not guesswork and brute force. Especially with multiple zones, you can’t wing it. These systems need thought and it’s long overdue that the industry started showing some.

@davidnolan22 

So far as I can tell from the 'other place' (buildhub) there are customers that absolutely insist on microzoning however much their peers on the forum tell them otherwise.  It's perhaps therefore understandable that some installers zone more than is ideal!

Whilst it's true that, if it works to an adequate spec,* there may not be much you can do legally, you can still do a lot practically.  Obviously you can't fix the fact that 6 pumps consume roughly 6 times the energy as 1 pump, but other than at the ends of the season that is hopefully a small proportion of the total.   However you can:

Attempt to minimise the buffer penalty by ensuring that the volume flow rate on the ashp side is larger (ideally only just larger) than the volume flow rate on the emitter side, so that the thermocline is at the bottom not top of the tank, and thus there is negligible dilution of the flow temperature by return water.

Operate as a single zone by setting any zone thermostats a couple of degrees above target so they act as limiters not controllers

Adjust your WC curve down as far as possible so that the house when operated 24*7 single zone, is just at the right temperature and no more

If necessary balance the zones for equal temperature (or desired temperature difference) by adjusting pump speed, flow regulating valves or lsvs

Obviously keep a note of anything you change and do it methodically, slowly (leaving it to stabilise for a day or more between changes) and make notes so you can retreat if you need to.

I suspect you know most of this so forgive me if I'm stating the obvious.  

If you do the above well you should end up with something quite close to single zone open loop operation at the optimum flow temp with hopefully a relatively small buffer penalty.

Feel free to ask for guidance or explanation if you do decide to take this approach.

* building regs require that heating systems are designed to be as efficient as reasonably practical which could form the basis of an argument for scop>2.8, the min requirement for BUS.  If you do invoke this check precise wording!

@jamespa 

Posted by: @davidnolan22

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The thing that bothers me most is just the lack of any care on the design.  

I completely agree, really I do.  

However I also know that the whole construction industry has a fair number of chancers, and like it or not they mostly get away with it.

For that reason I pretty much assume that if I get any construction work done I may have to clear up the mess myself and certainly I need to supervise it very carefully. Obviously I try to avoid this scenario and mostly, but certainly not always, I am successful (only a couple of years ago I was scammed for a £5000 faulty roof).  I guess I'm pretty much resigned to life as it is not as I would like it to be.

Sad I know, but not special to heat pumps or to the UK so far as I can tell.  Don't forget that we have almost all been paying 10% more for our gas heating than we needed to, and enjoying lower levels of comfort, because condensing boilers are almost always set up in the UK so they don't condense.  The industry has had since 2005 to adapt, but it hasn't.  When my gas boiler was last serviced the guy even reset the flow temp, which I had turned down, back up to max before he left!  That says it all.

@jamespa 

And then there was the window company I had to deal with...... Horrific...... 

I'm not sure how I would go about finding a trades person again.

The more we learn about about an ASHP potentially replacing a standard or condensing boiler heating system, fuelled by oil or gas, and while being enlightened by this insightful RHH resource, the more we might be resigned to upgrade our existing 20+yr conventional oil boiler like-for-like. Even an 'upgrade' to a condensing boiler has drawbacks.

It's early days, currently determining our Heat Loss and also raising our game regards insulation (basically loft), as DG was upgrade 7yrs ago. But, the deal-breaker might likely be the microbore pipework feeding every rad throughout the property (186m²) and the cost to put this right by someone who knows what they are doing; rather leaving it to 'sticking plaster' applied by installers with a borderline skill-set. (... blimey, 6 pumps = 6 problems baked in for the future !). We will not be compromising with pumps, buffers, a partial re-plumb, larger rads, etc.

We still plan on installing PV & Battery as part of an 'energy mix', including a diverter (I know, a moot point) for DHW for the c. 6-7 mths per year the CH will not be needed (deduced from decades of usage).

We are also at a point in our vehicles' life-span where we might well move to one EV; given they now offer a reasonable endurance between charges. At this point in the .gov and energy retailer "bribe-cycle" I see little merit in seriously considering feed-in tarrifs. There will be changes over a timeframe yet to be determined; with AUS and CAN being cases in point. However, the EV industry is maturing: now more 'leading edge' than 'bleeding edge'; that's only my opinion and likely only of value to me.

Regarding having an ASHP, I sincerely hope we can make it work for our house for several reasons: some selfish, some altruistic. However, having been involved in many aspects of engineering: industrial, civil, and military grade; from Apprentice to C.Eng, and admitting that the most enjoyable times were spent holding tools rather than holding meetings, I have developed a 'sensitive nose` when it comes to passing the (my) "sniff test".

That said, I might still be dupable with some of the current cohort sadly being "snake oil" peddlers who can be odourless; akin to carbon monoxide and equally toxic. One example being the way that some ASHP manufacturers 'spec' their wares.

As ever, caveat empor whilst trying to be ebullient.

Hi @colinc. Your concerns are well-founded. At least you can make a well-informed decision either way. The laws of physics and thermodynamics can't be bypassed. High mass flow low delta T design is best for ASHP, using a low design temperature. It can work with microbore, at higher design and higher deltaT emitter temperature, but that largely depends on where the microbore manifolds are, what size pipework feeds them, and how much mircobore there is. You may not want the upheaval and expense of changing it out along with a fair few radiators if you want to design for a lower system temperature.

Also to consider is your lifestyle and how you want to heat the property. If you prefer the heating for a few hours in the morning and evening, and unheated during the day, that doesn't optimise the 'low and slow' heating efficiency of a heat pump. Frankly, you're better off with an over-sized fired boiler to chuck a load of heat into the building quickly. ASHPs can't do that, and are not sized to do that. They have a small % margin of duty-in-hand over the property design heat loss, vs the typical 200-300% oversizing of most domestic boilers. No surprise when people try to run ASHPs like a boiler the house never properly warms up. Most of the low grade heat provided is lost into the cool internal fabric of the building, which has to warm through along with the internal air volume. The interior fabric of the house becomes a big thermal heat sink. This pre-heat load isn't calculated in any ASHP sizing computer programme - they assume a steady-state heat mass flow balance. Again, the laws of physics - we ignore them out our peril.

Our conversion from dirty old oil boiler to ASHP coincided with a shift in work-pattern to WFH, so we've really appreciated the low and slow all-day winter heating. It's affordable for us, and it's great having the whole interior fabric of the building warm. Risk of condensation and mould in wet rooms is eliminated. The old non-condensing oil boiler would have been prohibitively expensive to run all day, and at 26kW with limited modulation, incredibly inefficient for a property with a 9.5kW heat loss. We have leveraged the advantage of also installing solar PV & BESS + a dynamic electricity tariff, which has shifted 90% of our import to low rate and given us a significant energy cost saving compared to oil fired CH and DHW.

It was a leap of faith at the time, and we were ignorant of how to optimise ASHP efficiency. In the early days when all the ASHP commissioning parameters were wrong we questioned our decision. We kept faith, got advice, not least from here, (and now we reciprocate that), and it has been a good investment for us.

I wholeheartedly agree with everything @allyfish has written, and our journey was similar.

Posted by: @allyfish

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Hi @colinc. Your concerns are well-founded. At least you can make a well-informed decision either way. The laws of physics and thermodynamics can't be bypassed. High mass flow low delta T design is best for ASHP, using a low design temperature. It can work with microbore, at higher design and higher deltaT emitter temperature, but that largely depends on where the microbore manifolds are, what size pipework feeds them, and how much mircobore there is. You may not want the upheaval and expense of changing it out along with a fair few radiators if you want to design for a lower system temperature.

We had microbore piping in our old system. Until we started ripping it all out as part of a full re-plumb, I didn't know exactly how much. Turned out we had 22mm copper for most of the heating system, branching down to 10mm microbore to feed individual radiators, so in theory this may not have been too bad if the microbore pipes could carry sufficient heat for each individual radiator. I measured the internal diameter of some of the 10mm microbore piping ripped out, and it's internal diameter was only ~6mm.

The other concern for me was the state of the existing piping and radiators. It had been in place for at least 20 years, maybe longer, on an old oil fired boiler system and had never been flushed or topped up with inhibitor. Flow rates of 5-6L/min for the old system was obviously OK, but using that same heating pipework for a low flow temp system requiring 25L/min flow rates was a complete unknown. I would not want to assume that those high flow rates would be achievable bolting an ASHP onto an existing old dirty system. So we replaced all radiators (no doubt full of sludge) and pipework. I think this is where retrofits are a real risk as large parts of the system design are simply unknown, and I've never heard of retrofit installers undertaking extensive system flushes before bolting a new ASHP onto an old emitter system.

Much of our new copper pipework is now on show, fixed to walls just above the skirting board. It looks a little industrial, and I don't dislike it but I appreciate that may not suit every property or tastes... but I'd much rather see my piping and know it's good than have issues hidden out of sight. The upshot is we have a modern ASHP based system, with 24L/min flow rates and we run flow temps of 30-35C all year. As @allyfish says this makes the house far more comfortable and issues of condensation and mould which had affected us for years are hopefully a thing of the past.

@old_scientist Just to say that during our retrofit, we had 7 out of 10 radiators replaced and the system was (if I remember correctly), given a full flush before the old radiators were removed and a power flush was performed before the system was commissioned with the 7 new radiators and a dual fuel towel rail added to the ‘armoury’. When the system was ‘serviced’ by Daikin (long story related elsewhere), on all 3 occasions, the engineer remarked on the low resistance of the whole system. Regards, Toodles.

@jamespa  When the installers left my property it had a paltry flow rare of 17l/min and constant fault codes. 

The label on the 12kw Panasonic ASHP unit stated "Design Flow Rate 42l/min".

I used Syzer.exe to properly calculate the pipe diameters, which I installed myself, and actually achieved 50-l/min and happiness - and its free to use!

https://www.xylem.com/en-ca/brands/bell-gossett/selection-sizing-cad-esp-online/system-syzer/download-system-syzer-for-windows/  

Posted by: @af1

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 When the installers left my property it had a paltry flow rare of 17l/min and constant fault codes. 

The label on the 12kw Panasonic ASHP unit stated "Design Flow Rate 42l/min".

I used Syzer.exe to properly calculate the pipe diameters, which I installed myself, and actually achieved 50-l/min and happiness - and its free to use!

https://www.xylem.com/en-ca/brands/bell-gossett/selection-sizing-cad-esp-online/system-syzer/download-system-syzer-for-windows/  

17l/min is enough for only 6kW at 5C DT, not surprising a 12kW Panasonic complained!  How did the installer ever think it was going to work?