Split ASHP disadvantages

[rbw]

I am coming to the conclusion that despite my site having mains gas I’m going to go the ASHP route for UFH and DHW. This is primarily driven by the seeming faff of installing a gas boiler in the basement plant room - flue routing is a nightmare in our instance. Likely I’ll want to add solar PV at some point in the future too which I understand can be more advantageous in an ASHP system. 

 

However,  for aesthetic reasons I’d like to hide the ASHP somewhere - the house is built into a bank so I can’t easily stick it around the back out of site. This leads me to the conclusion that I need to go for a split ASHP but I’d love to understand what drawbacks, if any, this type of system brings. 
 

Could anyone provide their experiences or links to some good units? Still not sure what size I need but I’m guessing around the 8 - 12kW range. 

 

many thanks. 

[A_L]

@rbw split units generally have outside units, similar if a little smaller than monobloc types and they almost all do not do hot water. There are single room units which pipe air in and out and only have vents externally

[rbw]

@A_L that’s interesting thanks, especially what you say about not being able to do DHW. I was sure I’ve seen some split Daikin units (Altherma?) that do both heating and DHW. 

[A_L]

@rbw Sorry, yes that's true, but it still has an outside box. I was really referring to 'air-conditioning' type splits. I know of one, quite small air conditioning, single room, no-outside box system that does DHW.

 

https://www.olimpiasplendid.com/without-outdoor-unit/unico-boiler

 

Usual health warnings apply

 

[rbw]

@A_L thanks... by split ASHP I mean one that has the fan unit outside and another unit (compressor?) inside. I understand with these the fan unit can be placed some distance away. 

[Pocster]

1 hour ago, rbw said:

@A_L that’s interesting thanks, especially what you say about not being able to do DHW. I was sure I’ve seen some split Daikin units (Altherma?) that do both heating and DHW. 

Exactly what I have installed . Does ufh and dhw 

[Pocster]

27 minutes ago, rbw said:

@A_L thanks... by split ASHP I mean one that has the fan unit outside and another unit (compressor?) inside. I understand with these the fan unit can be placed some distance away. 

Essentially as I understand it ashp ( fan ) is placed a distance from the property . Inside is effectively a Uvc .

[Nickfromwales]

53 minutes ago, pocster said:

Essentially as I understand it ashp ( fan ) is placed a distance from the property . Inside is effectively a Uvc .

Do you have a monoblock? Do you have an internal compressor unit and THEN an UVC? 
OP is asking about a true split system which has the compressor indoors ( like a GSHP does ). 
 

[Pocster]

Just now, Nickfromwales said:

Do you have a monoblock? Do you have an internal compressor unit and THEN an UVC? 
OP is asking about a true split system which has the compressor indoors ( like a GSHP does ). 
 

Erm , I did try to be ‘knowledgeable’

Now you’ve shown me up ! . In theory the install completes Monday - perhaps I’ll know by then ????.

[Nickfromwales]

2 hours ago, rbw said:

I’d love to understand what drawbacks, if any, this type of system brings. 

Noise is one. The internal units can range from sounding like a very noisy fridge to sounding like a really quiet washing machine. Choose well and with units that have good reviews / live feedback from such adopters. 
The one I was I a absent with would have pissed me right off of it was ANYWHERE in my house ( other than the basement ) as it was annoyingly noisy / vibrations etc. That was a Daikin iirc. 
 

Re temperature, you can select a ‘high temp’ split which will go north of 65-70oC with ease ( reliably ) as the one I worked on had to go above 65 to melt the PCM58 in the trio of SA units. Did that PDQ too.

[Nickfromwales]

7 minutes ago, pocster said:

Erm , I did try to be ‘knowledgeable’

Now you’ve shown me up ! . In theory the install completes Monday - perhaps I’ll know by then ????.

[patp]

We are at the stage of selecting our heating and hot water system. We have heard that carpets are a no-no with UFH. I am a lover of carpets! Is there any way around the problem (I even have kitchen carpet). I am fairly prepared to consider giving up the kitchen carpet (Flotex which is quite thin) and bathroom (yes I have it in there too!) and even the hall but am very reluctant to dispense with it in the lounge and dining room and bedrooms. Any suggestions ?

 

We do not have mains gas, so it will be oil or calor gas if we do not find a solution to the carpet dilemma. It is a bungalow.

Edited September 26, 2020 by patp
.

[joe90]

You can get low tog carpets that are acceptable for UFH.

[rbw]

2 hours ago, Nickfromwales said:

Noise is one. The internal units can range from sounding like a very noisy fridge to sounding like a really quiet washing machine. Choose well and with units that have good reviews / live feedback from such adopters. 
The one I was I a absent with would have pissed me right off of it was ANYWHERE in my house ( other than the basement ) as it was annoyingly noisy / vibrations etc. That was a Daikin iirc. 

Thanks @Nickfromwales - this could be an issue. The unit will definitely be in the basement with the ground floor being 200mm concrete slab then 100mm celotex, the ufh then flooring so likely to be okay from floor above. Issue is that the adjoining basement room may be used from time to time, not sure what as yet though. 
 

Am I right in thinking that a monoblock unit needs to be within 6m of the house, preferably as a close as possible?

[Thorfun]

2 hours ago, joe90 said:

You can get low tog carpets that are acceptable for UFH.

did I also read somewhere that for low tog carpets it's best to run the UFH pipes closer together to get more heat per m2?

[SteamyTea]

Is there really a problem putting monoblock ASHP a few extra meters from the house, surely it is just a case of properly insulating the pipework, which you will have to do with a split system anyway.

The more important part is the routing from where the pipework enters the house and to where it is distributed to the UFH/Buffer, Thermal Store, UVC or whatever.

[rbw]

12 minutes ago, SteamyTea said:

Is there really a problem putting monoblock ASHP a few extra meters from the house, surely it is just a case of properly insulating the pipework, which you will have to do with a split system anyway.

I would love to know! But it may be more than a few metres, in my ideal world it would be more like 20m. I know some of the LG split units say that they can be sited up to 50m from the property,  but they don’t seem to tell you if there are any implications to that ?

 

12 minutes ago, SteamyTea said:

The more important part is the routing from where the pipework enters the house and to where it is distributed to the UFH/Buffer, Thermal Store, UVC or whatever.

What exactly is important here in your opinion? I think in our instance we can just lay a duct if required and have it entering basement wall at a suitable location with the Internal ASHP unit and UVC etc nearby. 
 

thanks for your input!

[SteamyTea]

6 minutes ago, rbw said:

may be more than a few metres, in my ideal world it would be more like 20m

The thermal losses will probably be the same, so the loss of CoP is probably similar.

Any pipework needs to be very well insulated if it is to be buried in the ground.

 

8 minutes ago, rbw said:

What exactly is important here in your opinion?

Keeping pipe runs as short and straight as possible.

 

KISS

[DamonHD]

Two near identical houses walking distance from here, have had identical ASHPs put in.

 

One had the external unit mounted directly on the exterior wall.  The other insisted on it being some way down the garden.

 

Latter house gets about half the CoP of the former...

 

Rgds

 

Damon

[rbw]

51 minutes ago, DamonHD said:

Two near identical houses walking distance from here, have had identical ASHPs put in.

Thanks @DamonHD - were both of them split ASHPs or were they monoblock units?

 

[rbw]

10 hours ago, SteamyTea said:

The thermal losses will probably be the same, so the loss of CoP is probably similar.

Any pipework needs to be very well insulated if it is to be buried in the ground.

 

Keeping pipe runs as short and straight as possible.

 

KISS

If this is the case can anyone explain why manufacturers state that their monoblock units must be placed close to the property but that their split alternatives can have the fan unit placed up to 50m (for example LG) away from the building? 

[SteamyTea]

4 minutes ago, rbw said:

If this is the case can anyone explain why manufacturers state that their monoblock units must be placed close to the property but that their split alternatives can have the fan unit placed up to 50m (for example LG) away from the building? 

Probably to keep it simple, there may also be a difference in the fluid circulation between the outside heat exchanger and the inside pump units that for splits and monoblocks.

 

I suspect that split units were originally designed as air conditioning units for high rise flats, where the external heat exchanger is on the roof.  On that basis, I suspect that monoblocks were designed to be a replacement for traditional boilers, or furnaces, and have been designed not to scare plumbers too much.

 

I personally cannot see a problem with it being a fair distance from the house, some houses are quite large and there is no difference.  Juts make sure everything is insulated properly.

[zoothorn]

20 hours ago, rbw said:

I am coming to the conclusion that despite my site having mains gas I’m going to go the ASHP route for UFH and DHW. This is primarily driven by the seeming faff of installing a gas boiler in the basement plant room - flue routing is a nightmare in our instance. Likely I’ll want to add solar PV at some point in the future too which I understand can be more advantageous in an ASHP system. 

 

However,  for aesthetic reasons I’d like to hide the ASHP somewhere - the house is built into a bank so I can’t easily stick it around the back out of site. This leads me to the conclusion that I need to go for a split ASHP but I’d love to understand what drawbacks, if any, this type of system brings. 
 

Could anyone provide their experiences or links to some good units? Still not sure what size I need but I’m guessing around the 8 - 12kW range. 

 

many thanks. 

 

Warning.

 

Hi I have a 7kw unit.. I know its a bit short for your plan, but thought Id say a few things about my split 'Arotherm' Vaillant system 6 weeks installed.

 

Its impossible to live with causing me huge stress: reason- noise. All dB info (on the pdf techhy pages) refers only to the fan/ compressor unit outside > & relative to a point measured outside. This unit is not a problem, standing even close to it its an unobtrusive purr.

 

The problem is in the inside unit(s), the boiler primarily. Compressor noise (eminating from outside unit > entering house via 2 pipes) I had to try to eleiviate by expensive calls to Vaillant, &, not being able to rid it.. had to set the HW to go on at 7.30am, so this wretched noise doesn't drive me mad & actually wake me up in the adjacent bedroom before 7.30. This means I now can never have HW in the morning until 8.30 being an hour for it to do its compressor on/ off/ on thing for an hour in order to get HW up to temp.

 

Once I'd done this, I could at least sleep strees free until 7.30, when it woke me up. Dreadful IMHO.

 

I ran the CH for 1st time fri, & rads didn't get even my most modern insulated bedroom warm (more a distinctly average 'not cold'), my stone cottage rooms.. weren't adequately heated at all. My kitchen I have to revert back to a trusty £5 fan heater & just forget putting on the rad. Very poor, but it gets alot worse.

 

The next morning, yesterday, & again today, I've been woken at 6.45 by the boiler (not the outside compressor to it noise entering house) making a very prominent electric motor noise on/ off/ on/ incessantly for 1 hr yesterday.. & 2 hours today. Absolutely infuriating. This is the 1st time in 6 weeks Ive had in installed, that Ive heard this motor start up/ off/ on/ off whining drone. Its so loud I can hear it downstairs & 1 room away, even in a new extention the noise is transsmitted along the rad pipes.

 

I had planned to start a b&b with the two bedrooms: but now totally impossible due to this wretched boiler noise (motor noise is very prominent from it > to the cylinder  in same room too).. so my future is affected, income etc, as one night spent in the room (the boiler's in the spare bed cupboard, as is the cylinder- where old one was removed, & where alot of people have them) will undoubtadly mean negative comments, & Id be unhappy to let it outs it is anyway. The next bedroom.. if I get woken up in here, then I cannot too let this room out really.

 

I called Vaillant & my fitters about the compressor noise, who said it is normal, so there is no 'problem', & so I am stuck with having no HW ever before 8.30am (& the noise from this is still prominent IN the house after 7.30). But this new motor noise is so bad I cannot possibly live like this/ so I now have to spend £thousands getting it ripped out & something in its place instead. I am furious about it. I have a whole morning of expensive calls to make -again- to Vaillant to see if there's -any- possibility of roidding this new motor noise, or rather shifting it at the least to 7.30 am.. but I doubt it. Its not a fault too- its just how the damn thing is.

[zoothorn]

If you are determined to have one, Id strongly suggest fitting the boiler & cylinder as far away as possible/ farthest corner of house (& in a soundproofed enclosure too, seriously).

 

The reason I think these are dished out foc (as mine has been so at least I'm not £10k out of pocket) is bc they aren't designed adequately enough to tamp the noise. No pdf info on any dB considerations for the inside units.. is fishy to me. When I saw the boiler sides clad in cheap black styrofoam.. & was told 'its sound insulation' once it was being fixed to my spare bedroom cupboard wall.. my alarm bells rang, but too late & I just had fingers x'd etc. But my worst fears have been passed in last 2 days. I cannot have this tmrw 6.45, so this ev I'll have to turn the whole system off.

[simon45089]

I am planning to site a Mitsubishi ecodan (monobloc) ashp unit 25 metres from the compatible Mitsubishi cylinder which will be in the house,  to minimise any intrusive noise and due to the layout of my barn conversion. This week I confirmed with the mitsubishi technical chap that this would be fine and would not affect performance as long as insulated dual pipe was used to connect the ASHP to the cylinder. I have sourced the pipe through a company called Mibec.Its overall diameter is 125mm, with two 32mm pipes within. A 25 metre run with fittings is around £675.00 I think. The guy at Mibec said this is now a common approach and the pipe is very popular. Other manufacturers make it of course. He said heat loss over the 25 meters would be negligible.

After  reading comments above I hope what I have been told is true!  I queried the distance I am going for with the mitsubishi chap and said I thought I read somewhere in my research that the distance should be limited to about 12 metres. i think he said that was the case when the refrigerant was circulated, but now it remains in the ashp so distance is no longer an issue. The only proviso was that you may need an extra pump added to the system if the integral one cant manage on its own but by using 32mm pipes it may be fine. ( The minimum recommended pipe diameter for the ecodan is 28mm).

 

Edited September 27, 2020 by simon45089