Posted by: @pash44pump

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@jamespa thank you. The "incentive" for using the original installer is that because they accept that they put in an undersized HP at the outset, they have agreed to replace it with a new HP at their cost (kit and installation). The downside is that they are being prescriptive on what they want to fit so I'm trying to find a reasonable compromise. 

Regards

 

 

Ok given that history they aren't going to risk under sizing.  I made a couple of suggestions above.

Is it really impossible to fit R290, the rules aren't quite as restrictive as some claim

Suggestions noted thank you

Just one more thought.  If you have convenient space for the 20kW cascade and your installer is paying then it possibly isnt a bad option.  Most of time only one will be running, possibly at a slightly better efficiency than would be the case with a single larger unit.  You almost have a spare.  Depends on the plumbing of course but if you have plenty of otherwise unused low grade space and the additional cost is paid for by the installer perhaps this shouldn't be ruled out.  Annual service might be double though so mind that.  

@jamespa it's a difficult decision. I am being offered either 2 x 10kW Clivet in cascade or a 17kW Grant R32 Aerona. I tried to get them to provide a Grant 290 15.5kW which meets the 14kW Heat Loss Estimate. As I said before, they won't put anything in that can't do 14kW at 50C flow and -5C OAT because those were the parameters used in the Heat Loss Estimate and given they undersized first time, they are now covering their behinds to ensure that I hit desired internal temps.

The 290 protective zone restrictions I think mean I don't have enough space for one on current siting.

I have concerns about cascade because I'm not impressed with the competence of the installer and 2 x heat pumps operating together suggests a lot more things to get wrong on the installation. However, I am aware that the operation of the Grant at milder temperatures is going to be less efficient than a lower-rated pump that can probably heat our house to desired temperature (given my estimate is 11-12kW of actual heat loss max at very low OAT) and indeed lower than the cascaded heat pumps. 

I can try and get them to do 2 x smaller Grants maybe, no harm in trying. The Clivet (rebadged Midea) doesn't seem to have the best reputation and the monitoring capabilities of the Midea controller I have are absolutely awful so I don't really want that brand as a replacement. @benson did you get Homely on your recent install because the Clivet controller is still poor?

For anyone who has a cascade, what do I need to ensure if I go down that route in terms of installation and setup, which is different to a single ASHP system?

Regards

Posted by: @pash44pump

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The Clivet (rebadged Midea) doesn't seem to have the best reputation and the monitoring capabilities of the Midea controller I have are absolutely awful so I don't really want that brand as a replacement. @benson did you get Homely on your recent install because the Clivet controller is still poor?

@pash44pump I have yet to come across any Clivet or Midea complaints aside from the control panel side of things. There was one post on here a few weeks back regarding a recent Clivet install and I believe they had installed their new Clivet controls which weren't working properly (that is the thread you are probably remembering as their solution was to install homely). The units themselves are fine.

If I could do it all again for our house though I'd ask why not just Midea as they are essentially the same units and the Mideas seem to be a fair bit cheaper.

If you dislike the midea controls then that is obviously a key element to consider as unless you like the look of homely your options are limited- the in house solutions, whether this be the midea app, or clivet options perhaps aren't great (or at least the latter may have some teething problems it would appear). I have grown to like ours as it has been very easy to connect to home assistant via modbus and create lots of graphs and customise controls, but appreciate most people probably just want a simple app where they set their preferred IAT.

As for homely we've found it better to just run pure weather comp- seems a bit more efficient and heating output is steadier. If you are looking to exploit time of use tariffs then it is worth a look.

@curlykatie did you get sorted with this?

Greetings from Greece!

Your posts have been very helpful. We are currently installing a R290 16kw monoblock midea ASHP. The heat loss study (done post insulation) produced a loss of 13.3kw for a ΔT of 27 degrees, so roughly 0.5kw per degree. Design temperature was -7 degrees (rather extreme for our area, but not unachievable). Midea can be downgraded to 14 or 12kw if it turns out to be oversized. We are keeping the oil burner as alternative heating source with manual switch between the two (for the 0.5m snow days we occasionally get)

Detached house of 240 square meters, built in 1983, external 10cm rock-wool insulation added 3 years ago to ground floor and 1st floor, basement is partially buried underground. Double glazed windows.
20 radiators of variable size in seven 16mm single pipe parallel loops (average 3 units per loop). Backbone φ42 to φ28 going up the 1st floor. Radiators are of 22 or 33 type. Overall radiator rated heating capacity circa 42kw at 75/65/20. Water volume is 228lt in the radiators alone (water in the pipes is on top). Single zone, no TRVs.

Solar panels of 8kwp, producing 9Mwh annually, o/w 6.5Mwh are available for the ASHP. 

Despite the installer’s advice to install a buffer with primary/secondary circuits (in which case we’d use the existing fixed speed wilo pump in the primary and the existing on/off room thermostat for everything), we have opted for no buffer at all and are connecting the ASHP directly to the radiators circuit, aiming to use weather compensation and hoping that theory won’t betray us…. We are wiring the controller all the way to the living room, for easier access and monitoring and for the case we need to fall back to a room temperature based operation (prior to conceding complete defeat and calling the installer for a buffer).

Based on the midea capacity tables, the ASHP can easily deliver the energy the house needs at the usual OAT range of our area even at LWT as low as 30 degrees, the ability of the radiator network however to transfer and dissipate it, is questionable at best.

So we are embarking on a quest with wc curves at first, armed with optimism and faith in technology! The posts in the forum have been very informative and we’d like to thank you for enabling the exchange of information. 

@mk4 — welcome. You have done your research well. Back here in Blighty I heat my home with a Midea 14kW mono and weather compensation works very well almost all of the time, once it is at the right settings. These need to be determined by trial and error, and it does take time, not least because you need to go through a full range of outside air temperatures to find the best settings for each end of the curve.

A couple of Midea quirks:

(1) going into and then out of the FOR SERVICEMAN (password 234) menu will usually turn the space heating and/or DHW heating off, just turn them on again on the wired controller front page.

(2) don't forget to turn weather compensation on! 

I wish you the best of luck, don't hesitate to post again if you have any further questions.  

@mk4 good luck with the installation your research should be worthwhile. There’s no point turning down the 16kW to lower levels (and it’s unlikely to be an installer setting) because the critical bit is the lowest power the unit can do is unchanged. You haven’t mentioned radiator balancing which you might have to do unless they have currently been perfectly adjusted, which is very rare. There is a good article on the forum on how to do it.

Posted by: @judith

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There’s no point turning down the 16kW to lower levels (and it’s unlikely to be an installer setting) because the critical bit is the lowest power the unit can do is unchanged.

Good point about the lower end output (probably) remains unchanged but it also depends on what the OP's actual heat loss is at lower outside air temps (OATs). The Midea units are notorious for dropping their output at lower OATS eg my badged 14kW unit drops to just over 11kW at around zero OAT. 

It is also worth mentioning that perhaps not all Midea 12/14/16kW units can have their output changed by the owner/installer/any passing joker. Though I have never changed them, mine definitely has a series of three dip switches, with a diagram of the positions (settings) for each output stuck on the inside of the front cover plate. Apparently folks got wise to this, and bought the marginally cheaper 12kW unit and then flipped it to 16kW when it arrived, Freedom and/or Midea then apparently decided this simply wasn't on, and have apparently removed the 'facility', now if you want a 16kW unit you have to buy a 16kW unit. Isn't the market such a wonderful thing.      

@cathoderay @judith 

Thank you for your wishes. The installation will hopefully be completed today and off we go!

Regarding the downgrade, it was the mechanical engineer of the installer who mentioned it to me as a possibility when choosing the model and he confirmed it while discussed during the site survey. I subsequently came across references to the dip switches, which seemed to confirm the claim. 

Furthermore, according to the pdf manual, there seems to be an option in the controller (Serviceman menus) for limiting the current (Amperes), which limits consumption and capacity, although I suspect it's an option offered for regulations/safety reasons. BTW we are installing a 3P model.

Posted by: @judith

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You haven’t mentioned radiator balancing which you might have to do unless they have currently been perfectly adjusted, which is very rare. There is a good article on the forum on how to do it.

Alas, this is an 1983 network alien to the concept of balancing. I would not dare touch the nobs, lest they come of at my hand.... We have never had the same temperature in all rooms and we are OK with it. We aim mainly at being comfortable in the living room and we get along with lower temperatures at the upper floor bedrooms.