Posted by: @jwilliams89

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Questions I want to ask them are:

- can we dispense with anything but the Grant/chorfu controller as that seems to be the best option

- will they make sure they enable WC for me

- Does the setup come with Eddi (if not can I supply)

- will they set pump flow and max flow temp low instead of full/high

WC and flow temps - main thing is that they set WC , but also give you instructions on how to change it. likely scenario is that if they set it at all they will set it too high. so you need to know how to tune it.

circulating pump flow rate is a different thing - generally this wants to be high in a HP system (roughly 4x that of a boiler based system) so you need to know how to change it. If the heat pump chosen has the capability (I don't know if it does) then the heat pump should control the circulating pump's flow rate based on the load.

Eddi I'd deal with separately. a heating engineer is likely to know nothing about that. Find a decent electrician who knows PV systems.

Grant controller I dont know - hopefully a Grant user will be along shortly.

Posted by: @jwilliams89

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- I'm currently trying to work out if I want to ask them not to fit TRVS. I understand the need for using the pump to modulate and for WC as opposed to thermostatic adjustment, however is there a benefit to having the trvs and simply setting them open.

the perceived wisdom is TRV's in bedrooms only (if you want them to run cooler). the temperature rest of the house is controlled by getting the radiator sizes right, the radiators balanced, getting the HP's mean flow temp as low as possible so that it continually replaces heat at the same rate the house loses it. with a main thermostat only as a last-resort "too hot" shutdown.

 A bunch of discussion on the openenergy forum has led to a strong pointer to danfoss RLV or IMI lockshield valves. You will need to be able to balance your radiators (unless you can get the installer to, but thats rare for them to do it properly if at all) and in practice you'll be tweaking the balancing frequently in the first cold period anyway. Good lockshields make balancing easier.

Posted by: @jwilliams89

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- Not too sure if I need to be pushing them towards a buffer and not a LLH. Currently researching this one.

push for no buffer no LLH. Ask for what is called a "single loop" system. In that system there is only one circulation pump . Always more efficient. But to run it they have to get the pipework right - there has to be enough flow rate to run the system, meaning large enough pipes, valves and other fittings (such as filters) that that don't constrict flow. make sure the pipes are at least 28mm from the HP to any central distribution point (likely to be loft in your case) and no less than 22mm to a group of radiators, perhaps if yours is going in loft then it needs to carry on in 28mm most of the way. If you have any possibility to do this, go for manifold with each radiator led back to it individually.

they may push against this along the lines of "LLH makes life easier for them" which it will do: you can't get flow rate errors with an LLH / Buffer, but you also get a inefficient system, it'll always drop at least 1C across the LLH/ buffer therefore lowering the mean WT in the radiators... so the HP has to run hotter.. less efficient.

Also given that you mentioned it going in loft - be really picky about what insulation goes round whatever's in the loft. Its effectively outside so has to be insulated to that standard. Or be prepared to remediate it yourself (build an insulated box around the tank and pipe works).

Posted by: @jwilliams89

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- Do I need to ask them to over spec the size of the pump slightly.

this one is the ****er.   you have two factors which work in opposite directions:

- at low load (say 7-10C) the HP needs to modulate down because your heating load is way lower. If too big, it won't modulate low enough and can be inefficient due to cycling. very few mfrs publish modulation specs. loads of discussion about this on this board and others.

- at cold damp weather (-2C to +2C) your HP is likely run approximately up to 15% worse than its specified rating at those temps due to frequent defrosts due to the UK's damp climate causing very very high humidity at  those temps.

the input to those two factors is the heat loss of your house. This is compounded by the assessment methods for heat loss that MCS use typically way-overestimating.  

short answer: (as per below) work out your own heat loss and post your workings and the hive mind will try to help.

Posted by: @jwilliams89

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- There will be two zones in a 3 bed house, with the downstairs being mostly open plan and a big woodstove in the lounge. Is there a best position for the thermostats in this situation?

why two zones?  with a HP , you want as many emitters as possible running as much as possible.

Posted by: @jwilliams89

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 - As I say their design work isn't going to be the best I suspect, however I presume I'm best asking for the biggest rads possible?

in short yes, but do your own heat loss and radiator size calculations as much as you can. tools available on this forum and numerous other places e.g https://openenergymonitor.org/heatlossjs/ and https://heatpunk.co.uk/home

If they you can target a mid 30's flow temp, with rads sized for that, you will get the best efficiency. if over 40, it'll be noticeably worse.

@iancalderbank Thanks for the detailed response. I emailed the company with the questions I had, along with more based on what you had said. They responded to say that due to the system being fitted under the ECO 4 scheme, I have no control over what is fitted or how they design the system. This means: I have to have multiple zones, I have to have TRVS on all rads, there can be no manifold, there has to be a buffer or LLH, I have to have thermostats (EPH), and the system has to be designed to run at 48 degrees. All very frustating. I appreciate that the system is free to the end user, and that they are designing for folk who don't want to do any more than turn it on and off, however the fact that I have no control over how my own system is set up doesn't feel great. I'm now at the stage where I'm hoping I can convince the installers to fit the main controller outside the loft, and will then develop/retrofit the system myself. One plus is they said that WC will be turned on and that I'll be shown how to use it, so at least that is a start.

I'll look into the heat loss calculations myself, and see what adjustments I can make to the system based on that. We are fitting double glazing and extra internal wall insulation which they won't be taking into account in their calculations, so I'm hoping that helps me run the system at lower temps than designed for.

@jwilliams89 so I am not an expert on ECO4 never having had anything to do with it, but from what I have read ( from people who should know  in the industry, not just random facebook commentards) I would advise you to be very very wary. This discussion for example https://www.linkedin.com/feed/update/urn:li:activity:7138110761519734784/ has a number of knowledgeable industry experts on it including @grahamh who contributes here.

What I have read tells me that it seems to be a system for "grant farming" , and only a small amount of the overall pot gets spent on the actual system, the end user ends up with a poorly designed system that is installed as cheaply as possible and costs a fortune to run  and/or runs badly (won't heat the house when its cold out). others may have views I'm just repeating what I've read.

However: what isn't up for debate, is this. All of the things you've just said your installers are insisting on (multizones, TRVs, LLH, designed for 48 degrees flow temp) are very strong pointers to a poor design that will cost a lot to run or will not run properly at all.  if they fit it that way, IMO you will have to plan to pretty much rebuild it to get a well running efficient system.   that would be assuming that the fundamental components (the heat pump itself primarily) and then all the radiators, are the right size and re-usable.  its obviously better to set out with a design that is right in the first place. My advice would be to seek different installers.

@iancalderbank im no eco 4 expert i tend to steer well away from this sort of thing sorry

Posted by: @grahamh

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im no eco 4 expert i tend to steer well away from this sort of thing sorry

@grahamh no indeed , me neither, but would you concur at least, that the OP is being steered towards a system that is unlikely to be fit for purpose / will need a whole load of remediation ?

(and the implication is, its the ECO4 process that's doing that)

@iancalderbank I would agree with everything you say. It seems that in order to tick the boxes the funding requires the company are unable to do anything but fit it this way. It also seems that they must be getting a lot of money per job, and the fact that the companies themselves are so underregulated, as well as the information available being so obscure makes the whole thing a joke really. Unfortunately, as with many things like this, to qualify for the scheme tends to mean you have no other options. We are moving into a badly maintained house with an incredible poor and expensive old electric heating system, and so all of our money is going on renovating and insulating. It's a case of this or no heating at all. Which is a crazy position to put folk in, especially as funding for this comes from our energy bills (3-4% of what everyone pays on their bills goes on funding schemes like this). It's a case of making the most of a bad job, and trying to get the installers to adjust certain things as the office aren't interested. A point to make is that after doing quite a lot of research the company I'm using seem to be one of the best of the ECO 4 fitters.

I guess at this point my thinking has to be along the lines of how easily can I bypass the thermostats and TRVs, or take them out completely. Can I reduce the working temp of the system by adding more rads myself if that seems to be called for once I do my own heat loss calculations, and if I get a proper ASHP heating engineer in after the fact what can they do to rectify certain failings within the system. Thanks again for all advice, V much appreciated.

@jwilliams89 As someone who's had a Grant installed under ECO4, part of the problem (I suspect) is in the company trying to tick all of the required building reg boxes (to be eligible to fit under ECO4 the company must be TrustMark accredited, so they have to capture evidence of conformance with regulations), but those boxes being inappropriate for ASHPs. Part L building regs says that each radiator (apart from those with the room stat in) needs a TRV, and it also states that you must zone when parts of a house vary by "type of use" or "pattern of use" and upstairs/downstairs usually fits that bill. They don't appear to reflect the different running characteristics of HPs. Very little reference is made to HPs at all in the regulations (they get 3 paragraphs, one of which reinforces zoning of the home).

The LLH seems to be how the manufacturer, Grant, now recommend to install their HP - all of their installation kits come with one, and it's mentioned in their literature since at least 2022.

Hopefully, the least you'll get out of this is decent insulation; correctly sized pipework; correctly sized radiators; and a heat pump. If you get that much, then you have a starting point to improve efficiency, and it ought not to be that costly if you need to do remedial work (e.g. bypass LLH; amend room controls; remove zoning). As you say, finding a decent 'post-installation' expert who knows about HPs would be useful. The installer probably won't be hanging around to fix issues.

@jwilliams89 hopefully you can at least make them get the rad sizes right. thats a pain to change afterwards.

can you persuade them to do something like this diagram ? then you can bypass the LLH by moving the isolators, without a re-plumb.

with the 1-2-3-4 open, 5-6 closed its in LLH mode and they are "complying" with whatever they have to. reverse that, disconnect 2nd pump, you get a single loop system. 

 No "re-plumbing" needed. one of the circulating pumps need to be sized for the whole system not just half the system.

the "X"s in the diagram are isolation valves. ok so its more expensive by 6 valves and some pipework, but thats a lot less than a full rebuild.

the same could be done for zoning (not drawn but same idea) if it has to be in for compliance then you can isolate it out without a rebuild.

Highly likely a Grant scheme installed under ECO4 will have a LLH and secondary circulating pump. They are not the most efficient system installation, but if the LLH is balanced with equal primary and secondary flow rates, thermal losses in the header are minimal and it's not adding massively to the running costs. A Grundfos UPS3 secondary circulating pump is about 50W or 1.2kWh per day on 24/7. Better not to have it of course, but don't forget system flow and pump head pressure is the more or less the same with or without LLH + secondary circulator, so the primary pump will consume more power and be on a higher speed setting in a single pump circuit. With a LLH the circulating pump in the ASHP can usually be on speed setting 1 and provide adequate flow.

Grant is working on new smart ASHP controllers, WIFI base station and remote smart thermostat/control interface +phone app, which would negate the need for HIVE or other 3rd party products wired into the Chofu controller. Smart control option includes flow and return pipe, outdoor temperature and flow rate sensing to enable active responsive control. Product launch is soon. The Chofu controller is ditched and a new smart control hub replaces it. This can only be good news, it should be retrofittable to Aerona3 systems.

At the moment Grant systems have a flow setter valve, but no flow sensing. The systems with smart controllers can be installed 'open loop' without LLH or buffer (provided system volume is adequate) as active sensing of flow is an analogue input that the controller can monitor and make control adjustments on. The Aerona ASHP pump is fixed speed however, manually selected to one of 3 flow/head curves. This will be a positive move for Grant as all their recommended system diagrams currently include LLH and 1 or 2 secondary circulating pumps. Installers tend to follow these and be very reluctant to deviate.

@allyfish This sounds very positive, although I'm a little sceptical at the moment. I hope they can retrofit these better controls, as the current ones as sub-optimal (and unfriendly). There's easy wins with DHW which I hope they address: don't run a DHW cycle if current water temp is higher than the target; don't add water to the cylinder which is colder than what's already in there; once the target temp is hit, go back to CH mode. The savings are small in terms of cost for DHW heating, but not losing time off CH would be a bigger win during colder periods.

@mikefl Yeah this is my hope, as you've stated in previous discussion Eco Providers Ltd don't seem to be the worst possible installers, and if I can get the team on side I should be able to get something I can develop. I'm wondering whether to get them to put in some extra pipe loops through other sections of the downstairs walls (since I've stripped all the walls back from the pipework and insulation) which could then have extra rads added to in the future if this was deemed to be a way to improve the efficiency of the system.