Posted by: @dr-h

↑

At the moment I'm thinking of going with a Mitsubishi Ecodan heat pump but if going with another brand would help to make this work then I'd be willing to consider that.

The brand will usually be recommended by the installer as they'll be working (specialising) in certain brands. If you want to email me your location, I can connect you with reputable installers in your area: editor@renewableheatinghub.co.uk

Posted by: @dr-h

↑

Hi All,

I will be having an ASHP fitted this year. We are a family of four who occasionally host one or two guests. There's not a lot of space available for a cylinder (we can squeeze in a 200 litre one), and I was wondering if it might be possible to combine a conventional cylinder that supplies all the bathrooms, with a Heat Geek Mini-Store in the kitchen to supply kitchen sink, hot-feed dishwasher and washing machine, and downstairs w.c.. The mini-store and hot water cylinder would be installed on the same ground-floor level as the heat-pump, which would hopefully make pipework straightforward and I'm hoping it would just be a matter of a suitably-configured controller and valves to make this setup work.

At the moment I'm thinking of going with a Mitsubishi Ecodan heat pump but if going with another brand would help to make this work then I'd be willing to consider that.

Thanks for reading and any thoughts gratefully received!

I cant see any fundamental reason not to have two cylinders and Im not sure that one needs to be a mini store (but it could be). 

The challenge, as you identify, will be with the plumbing and control particularly the latter.  Heat pumps like to 'control' dhw cylinders, and by default allow for one.  Some heat pumps, I believe, think of a cylinder as just another 'zone' and so they might easily cope with more than 1.  Legionella cycles might also confuse.  I would suggest that this detail should be worked out in advance to avoid nasty surprises and equally nasty kludges at install time.  Its clearly not impossible, but might require a bit more ingenuity than some installers can cope with.

That said are you sure 200l isnt enough.  If you heat 200l to 55C you get ~300l of water at 40C.  55 is a bit higher than the fairly normal 48, but not so far out as to be silly.  Sometimes simplicity is better.  Obviously it depends on your needs, if all 4 take 10 minute showers at 20l/s in quick succession, neither will suffice.

@jamespa Thanks for the response. The ministore idea was motivated by the particularly restricted space available for the second cylinder, although I am sure control setup would be much simpler with two conventional cylinders. One thing I'm particularly unclear on is why the pipework for traditional cylinders seems so very complicated relative to a ministore, and whether volumisers are required.

In terms of whether 200 litres is enough - I'm just used to having a combi boiler and never running out of hot water! Although, I guess in terms of the kitchen hot water usage, it would be fairly easy to time-shift the vast majority of the hot water usage so it has negligible impact on availability of hot water for showers/baths.

Posted by: @dr-h

↑

One thing I'm particularly unclear on is why the pipework for traditional cylinders seems so very complicated relative to a ministore,

The only real difference (in terms of complexity of pipework) is the pressure release drain required on a traditional cylinder because of the possibility of explosion.  This can be a pain or can be easy.

Posted by: @dr-h

↑

whether volumisers are required.

That's a separate question, depends on the volume of water in your central heating system in relation to the requirements of the heat pump.

Posted by: @dr-h

↑

In terms of whether 200 litres is enough - I'm just used to having a combi boiler and never running out of hot water! Although, I guess in terms of the kitchen hot water usage, it would be fairly easy to time-shift the vast majority of the hot water usage so it has negligible impact on availability of hot water for showers/baths.

showers/baths are the main determinant of the requirement for many households.  Kitchen appliances are usually cold fill, so its only washing up that uses DHW in the kitchen.

Posted by: @jamespa

↑

Posted by: @dr-h

↑

One thing I'm particularly unclear on is why the pipework for traditional cylinders seems so very complicated relative to a ministore,

The only real difference (in terms of complexity of pipework) is the pressure release drain required on a traditional cylinder because of the possibility of explosion.  This can be a pain or can be easy.

👍

Posted by: @jamespa

↑

Posted by: @dr-h

↑

whether volumisers are required.

That's a separate question, depends on the volume of water in your central heating system in relation to the requirements of the heat pump.

Ah, OK, so it's nothing to do with the cylinder? It's just that I feel like I've always seen a little white or red cylinder installed next to the big DHW cylinder so assumed they kind of went together, but I guess it's just that the install location of the DHW is usually also the best place for a volumiser to go, if required.

Posted by: @jamespa

↑

Posted by: @dr-h

↑

In terms of whether 200 litres is enough - I'm just used to having a combi boiler and never running out of hot water! Although, I guess in terms of the kitchen hot water usage, it would be fairly easy to time-shift the vast majority of the hot water usage so it has negligible impact on availability of hot water for showers/baths.

showers/baths are the main determinant of the requirement for many households.  Kitchen appliances are usually cold fill, so its only washing up that uses DHW in the kitchen.

I'll be using hot-fill washing machine and dishwasher. Better to get the water for those heated by the heat pump than with electric coils in the machines.

Posted by: @dr-h

↑

@jamespa I'll be using hot-fill washing machine and dishwasher. Better to get the water for those heated by the heat pump than with electric coils in the machines.

Fair enough, I didn't know that they existed any more.  Can I ask who produces such things?

@jamespa I've actually made an assumption on the washing-machine front, but I know that many Bosch dishwashers can be programmed for hot-fill (they only have one fill supply pipe, which is by default expecting cold water)

Please note I edited my previous post above after you replied to it.

Thanks for your help.

Posted by: @dr-h

↑

@jamespa I've actually made an assumption on the washing-machine front, but I know that many Bosch dishwashers can be programmed for hot-fill (they only have one fill supply pipe, which is by default expecting cold water)

Please note I edited my previous post above after you replied to it.

Thanks for your help.

I didnt know that about dishwashers - Im off to check the instructions to mine, thanks for the tip-off.

@jamespa I was told some years back that ‘cold fill only’ was now the preferred option (obviously a cost saver for the manufacturers says the cynic in me) as splashing hot water onto greasy plates would ‘bake on’ the residue rather than rinse it away. In addition, they reckon it is better to start from cool and heat the water gradually to avoid thermal shock. That’s the manufacturer’s story anyway. Regards, Toodles.

Posted by: @dr-h

↑

Ah, OK, so it's nothing to do with the cylinder? It's just that I feel like I've always seen a little white or red cylinder installed next to the big DHW cylinder so assumed they kind of went together, but I guess it's just that the install location of the DHW is usually also the best place for a volumiser to go, if required.

That is not a volumiser that's an expansion vessel.  You need one in each pressurised heated system, so one for the central heating (red) and one for the dhw (white)

@toodles hmmm. I think the "thermal shock" thing has got to be cobblers surely? For the Bosch, it says the hot feed should be between 40 and 60 °C. I'm not convinced that spraying an item that's at room temperature with water that's 60 °C is going to cause a thermal shock problem.

I have assumed that even with a hot feed, that the dishwasher does (or can) heat the water further.

@jamespa, examples of Bosch machines that will accept a hot feed are the SMS6ZCW10G and SMS4EMW06G. See the bottom of Page 36 on the respective user manuals. And here is a washing machine with hot fill: https://ebac.com/washing-machines/e-care-8kg-hot-fill