@bart Best of luck moving forward, I look forward to hearing when all is settled and corrected for you. Please let us know once you have everything sorted.

By way of an update: NAPIT's initial overview is more than a little disconcerting advising that PAS2035/PAS2030 only applies to RIWI/ventilation and concluding that ASHP oversizing and inappropriate use of volumiser is not evidenced by design calculations.

Specifically regarding ASHP sizing given a 3.6kw property heat loss and the provision of a 6kw system this seems unconscionable however I can't find any MCS requirement better than the below (ie. 'design calculations' require its bigger than 3.6!) - does anyone know of a more robust requirement regarding appropriate sizing please as NAPIT's 'impartial' investigation would seem disinclined to help? 

My current combined SCOP is 2.3, which broadly matches manufacturer's data. Whilst I would hope that "reasonable skill and care" would require a more appropriate selection (ie. a 5KW system) given that manufacturer data (1) at my capacity confirms the system cannot meet MCS ASHP SCOP predictions (2) when a 5kw system would and a volumiser wouldn't appear to be required (3).

Regarding accuracy of predictions the best I've found from MCS documentation is that +/-30% would not be unreasonable (ie.-30% ASHP SCOP at design stage would seem unreasonable) but a more robust requirement for either efficiency or sizing would be greatly appreciated.  

@bart, I think you're right to focus on that section of MCS MIS 3005-D Issue 2.0, which says:

“A heat pump shall be selected that will provide at least 100% of the calculated heat load taking into consideration the flow temperature at the heat pump and without input from any supplementary electric heater.”

At your local design outdoor temperature, the heat pump must, by itself, cover 100% of the heat loss at the design indoor temperatures with no help from the backup heater. The heat pump’s output should be calculated at a flow temperature of 55°C (unless the design is specifically lower temp with low temp emitters and properly justified).

So if your house has a 3.6kW heat loss at your location’s design temp (let’s say -3C for example), then the installed heat pump must deliver at least 3.6kW of output at that temperature and at the required flow temp. 

Your combined SCOP of 2.3, which aligns with the manufacturer’s performance curve, shows it’s running inefficiently and that makes sense if it’s frequently cycling or needing a volumiser just to run stably. A correctly sized system should modulate down without short cycling, and should not need a volumiser just to mask design oversights.

Document exactly what the 6kW unit actually delivers at design conditions vs. your heat loss: this is your smoking gun.

I'm going to give this more thought as to how we can drive this to a resolution.

@heacol, if you're around, can you please provide some insight into this?

Posted by: @bart

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By way of an update: NAPIT's initial overview is more than a little disconcerting advising that PAS2035/PAS2030 only applies to RIWI/ventilation and concluding that ASHP oversizing and inappropriate use of volumiser is not evidenced by design calculations.

@editor @bart Hi, I can see a few problems with your installation, and possibly why you are getting very low performance levels. It however, very difficult to diagnose and correct errors if on-site diagnosis is not possible, however, I will give it a go but stand to be corrected. 

• It does appear, you heat pump is oversized and the minimum run down is basically the heat load. This is not the end of the world, but it will be difficult to get exceptional performance, bit good performance should not be a problem. 
• The temperature sensors should be in a pocket or wrapped in aluminium or copper foil and insulated. Contrary to common belief, there is little difference between the 2 methods on a heat pump. 
• The glycol will be exaggerating the cycling and the lack of flow as it has a lower heat capacity and the viscosity is much higher, I would remove it and just use a good inhibitor. The first unit from your manufacturer (Yes I recognise the unit) was nearly 20 years ago, I have never used glycol and not a single one has been damaged by frost. This will increase your flow rate considerably allowing more heat to be taken from the unit, in to the house. 
• The valves you have installed will be reducing the flow but possibly not a very big problem.
• The position of the volumiser, is, well what can I say. It needs to be moved the flow, not the return, this will significantly reduce the cycling. It will be charged with the higher flow temperature which will significantly increase the time between on and off cycles.
• If you have a thermostat, remove it and run only on load compensation from the controller or pure weather compensation. 
• Remove all TRV valves except in the bedroom, and I would install the new FRV valves (you can get a discount code here) on the radiators to confirm you are getting the correct flow through all radiators, if you do not have the correct flow, the design of the system will be incorrect and the chance of poor performance is significantly increased. 
• Once these changes have been made, confirm the correct flow rate through the system and the radiators, if still low, then you will need a bigger pump, the pump is the smallest you can get in this range.
• You do not have to insulate the pipe within the heat loss perimeter, except the primaries to the cylinder, ther will be no benefit. The pipework in the loft MUST be insulated, you will be loosing significant heat.  

I am sorry you have been left in this position, if you make the changes above, which will not cost much, you performance will significantly increase. 

Wishing you the best of luck.

Brendon

@editor Thanks for the headsup.

Having a look at the 2nd version of the heat loss survey (after nearly every variable was out on nearly every room for their 1st effort) I've now noticed the location design temp has been inputted wrongly (-3 instead it should be -5) my ballpark is about +10% on total 3.6kw figure?

Also air changes looks to have been overlooked completely (100mm combustion vent+ extractor fans must far exceed 1.5/2).

Combined this might explain why we can't reach 21 degrees downstairs where additionally @delta30 all rads are rated as @1.2 of heat loss but our kitchen is @0.6 further compounding the issue.

Review of further documents has raised more issues with PV shading having been totally underestimated (my calculations based on MCS guidelines suggest x0.4 not x0.8 for impact on total output. Given they already underdelivered by 30% from their proposal its little wonder our costs have dramatically increased.

Given the efficient working parameters of ASHPs I'm still struggling to believe that there isn't any requirement for appropriate sizing of the ashp:heat loss. Thanks to a headsup via mail I note building regulations require 'an efficient system' and given mine cannot achieve MCS predictions you can only hope...

@heacol thanks so much for the input, your time, as with others on here, is very much appreciated. Whilst I'm glad things can be improved, it is telling that professionals such as yourself can remotely diagnose and offer advice on how to improve things while our installer has done nothing.

Unfortunately, as above, I'm on a complaint conveyer belt that requires I don't make any changes. Given the serious nature of some of the issues raised (indicative of the systemic failure) I'm unable to share more detail here, but as soon as I can I will definitely implement and feedback if that's ok? 

@bart It's a pleasure. If you need anything else, feel free to ask. You are right about a systemic failure. MCS has failed to deliver on the promise they made to you. That is why many in the installer base are trying to stop DESMZ from making them the sole certification provider. The new option coming soon, if allowed, would have sorted your problem very quickly. I have been privileged to see what they intend to do. It will make a huge difference. If you, or anyone else, wants to help, please write to your MP. I am sure @editor will be able to supply more details.

Posted by: @heacol

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That is why many in the installer base are trying to stop DESMZ from making them the sole certification provider. 

@heacol Is there anything we, as consumers, can do to assist this.  I did respond to the consultation recently with a very clear message that making MCS the sole provider is likely to be a disaster, but as a consumer I feel confident I will be ignored.

@jamespa The only thing I can think of is to write to your MP, get them fired up to ask questions, if more questions are asked by those in power to DESNEZ they may think twice. I have already sent a letter to the climate change committee highlighting the inadequacies of MCS compared to Gas Safe and OFTEC, and how MCS is holding back the rollout of low-carbon heating and the electrification of the grid. The letter was delivered by the director of the biggest private housing rental provider in the country, on their letterhead. Fairly powerful, I think. 

Everyone must try to do their part to stop this travesty.

Posted by: @heacol

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@jamespa The only thing I can think of is to write to your MP, get them fired up to ask questions, if more questions are asked by those in power to DESNEZ they may think twice. I have already sent a letter to the climate change committee highlighting the inadequacies of MCS compared to Gas Safe and OFTEC, and how MCS is holding back the rollout of low-carbon heating and the electrification of the grid. The letter was delivered by the director of the biggest private housing rental provider in the country, on their letterhead. Fairly powerful, I think. 

 

Everyone must try to do their part to stop this travesty.

Are there any statistics/facts you can share to make the argument more solid.  If not don't worry, but a letter to an MP from someone whose installation works very well is a bit weak.  Obviously I can lean on what's here but any further data would be good.

@jamespa @editor can you help with some statistics and examples from this platform? It does appear to be illegal and against competition rules. It also appears that DESNEZ consulted with MCS prior to the consultation, as they are mentioned as the preferred option. Again, it is highly illegal for a government department to collude with a private entity for the financial gain of that entity whilst excluding competing organisations with the same certifications and qualifications. Especially as all government legislation for the renewable industry has stated "MCS or another certifying body"