How to steal heat from yourself by putting a water heater with its own heat pump in your warmish garage: calculation

[Garald]

3-speed. Sure, it's just a matter of adjusting speeds. But I'd like to know how much power I'd be producing!

[Iceverge]

1 hour ago, Garald said:

Yes, 11kW is too much, but the next one in Daikin is 8kW (which is really 7kW under some conditions), and, while that should certainly be fine given my calculations (and he seemed inclined to agree in person

 

I don't know much about ASHP sizing, need to do more reading on here. 

 

Could there be a case for the 8Kw unit and a couple of supplementary resistance heaters for those exceptionally cold days. 

 

Maybe there's a benefit of oversizing the unit too, I don't really know? 

 

If you have PV you may not need to run the ASHP in summer. 

[Nickfromwales]

1 hour ago, Garald said:

3-speed. Sure, it's just a matter of adjusting speeds. But I'd like to know how much power I'd be producing!

That’s the problem with a heat pump  Nobody knows until you fit it in it’s new surroundings and switch it on. Ambient air temp, target flow temp, external air temps etc etc all go towards the output power. Output power is only ever stated as a hypothetical, and the design / suitability / expectations get managed by “running the numbers”. Each instance differs so it’ s down to the individual circumstances which will dictate ‘power’. 

[Garald]

Well, just wrote to the installer. If he accepts there's an issue, that's a point in his favour.

 

If not, and he gets upset, I have an alternative - the Atlantic installer (who, however, did not see right away the problems with the arrangement proposed by the competitor). I really hope the Mitsubishi installer will finally visit...

[Garald]

Grrr! The installer we are talking about seems to have relented in his plans to make my bike shed into a fridge, *and* I convinced him to give me a quote for a Mitsubishi - his price does not too insane - but: while the Mitsubishi without DHW would be available immediately, there would be a wait of 3-4 months for the one with DHW! Arghh!!

 

Hope I have better luck with the official Mitsubishi installer. Or is there a third alternative for DHW storage I haven't thought of? Can one have a device that accepts and stores water from a "heating-only" Mitsubishi heat pump?

 

(Zubadan Silence 11 Duo 200L R410A)

[JamesPa]

10 minutes ago, Garald said:

Grrr! The installer we are talking about seems to have relented in his plans to make my bike shed into a fridge, *and* I convinced him to give me a quote for a Mitsubishi - his price does not too insane - but: while the Mitsubishi without DHW would be available immediately, there would be a wait of 3-4 months for the one with DHW! Arghh!!

 

Hope I have better luck with the official Mitsubishi installer. Or is there a third alternative for DHW storage I haven't thought of? Can one have a device that accepts and stores water from a "heating-only" Mitsubishi heat pump?

 

(Zubadan Silence 11 Duo 200L R410A)

So far as I am aware the Mitsubishi packaged systems are just a combo of the heat pump, a cylinder with some  pre plumbing, and the flow temp controller.  They make it easy for the installer and maybe cheaper, but there is nothing special otherwise which prevents you using the standalone pump with another cylinder. 

[Garald]

12 minutes ago, JamesPa said:

So far as I am aware the Mitsubishi packaged systems are just a combo of the heat pump, a cylinder with some  pre plumbing, and the flow temp controller.  They make it easy for the installer and maybe cheaper, but there is nothing special otherwise which prevents you using the standalone pump with another cylinder. 

 

Right, but how do I get another cylinder to accept the hot water coming from the heat pump? Is it tricky? I'm getting the feeling that this installer won't do it.

[Garald]

With this installer, given that I can't wait for several units for the Mitsubishi with DHW to materialise, I think my only option is to have a Mitsubishi PAC and a "thermodynamic" water heater *with its input and output ducted to the outside air*. He's offering an Atlantic Calypso 200L - I think this has already been recommended in this forum. My architect will probably be upset at the last minute change, but also relieved that we are finally getting things done. Hopefully the carpenter hasn't got that far in his work on the garage door yet, as that may need to be modified a little.

 

The manufacturer's claim is that the unit produces 50dB when it's 7C outside - I guess that's a level we can deal with by insulating/sound-proofing the garage ceiling (it is right under part of my library)? Washing machines are louder.

 

Alternatively, perhaps the third installer will have a Mitsubishi with DHW in stock. Let us see...

Edited February 5, 2023 by Garald

[JamesPa]

On 03/02/2023 at 17:28, Garald said:

 

Right, but how do I get another cylinder to accept the hot water coming from the heat pump? Is it tricky? I'm getting the feeling that this installer won't do it.

From the PoV of the cylinder the HP is just a source of hot water, as long as hot water passes through the coil the contents of the cylinder will heat up. 

 

As far as the HP is concerned I think its as simple as fitting a diverter valve in the flow, running a temp sensor from the DHW tank to the FTC (Mitsubishi control unit), telling the FTC that there is an immersion heater and telling it when you want to set it to heat.  Not very different to any gas fired CH system at least in the UK (I don't know how they plumb them in France).  The prime difference is that the valve is either/or not one or both, ie either Ch or DHW receives a feed but not both simultaneously.  Many people on this forum are using third party cylinders and I plan also to do so. 

 

You do ideally need a cylinder with a large coil area (3sq m is often recommended) (because the flow temp is lower) otherwise reheat times might be quite long.  Usually you would specify a cylinder with a 3sqm coil and an immersion heater, Joule and Telford make them and doubtless others.

 

This diagram from the Mitsubishi A2W databook https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_ATW_Databook_R32_Vol5_5 illustrates the set up.  The Mitsubishi pre-plumbed cylinder includes the diverter valve and tank water temp sensor pre-wired, but otherwise its the same.

 

I would be concerned that your installer doesn't seem to want to do this.   It suggests he is not familiar with the technology/not able to read manuals.  But i know coming by an installer is difficult so you may have no choice.

 

[Garald]

Right, I would hope he would propose something like this. What he is proposing now is to get a Mitsubishi without hot-water storage and add a water-heater (Atlantic Calypso) with its own heat-pump and ducting to outside air that would take care of hot-water production throughout the year. The specifications of the Atlantic Calypso are not bad, but those of the Mitsubishi are better. It may make more sense to use the Mitsubishi during the winter, but he seems to think that it's necessary to get a Mitsubishi with its own hot-water storage (thereby duplicating costs) in that case.

[JamesPa]

42 minutes ago, Garald said:

Right, I would hope he would propose something like this. What he is proposing now is to get a Mitsubishi without hot-water storage and add a water-heater (Atlantic Calypso) with its own heat-pump and ducting to outside air that would take care of hot-water production throughout the year. The specifications of the Atlantic Calypso are not bad, but those of the Mitsubishi are better. It may make more sense to use the Mitsubishi during the winter, but he seems to think that it's necessary to get a Mitsubishi with its own hot-water storage (thereby duplicating costs) in that case.

Well he is wrong, but if he wont do what you want then you will either need to accept his view or go elsewhere.  perhaps the parts aren't available in France because the usual CH/DHW layout is different to UK.

[Garald]

Right. I'm trying to arrange for a visit from a Mitsubishi installer next week - hopefully he'll have a machine with DHW included available. Otherwise I'll have to choose between this installer (he doesn't have Mitsubishis with their own hot-water heater incorporated available - it would be the combination of Mitsubishi without DHW and an Atlantic Calypso) and the installer that has an exclusive deal with Atlantic for heat pumps.

 

Word on the (French) street is that Atlantic heat pumps are good (clearly better - whatever that means - than Saunier-Duval aka Vaillant) and good value, but that the noise of their outside unit, while OK on paper (62dB) is very noticeable, presumably because Atlantic uses a Fujitsu double-rotor compressor rather than a spiral compressor. That's for the main heat-pump - the little heat-pump in the DHW heater is 50dB, and I can and will insulate the garage ceiling, so it doesn't matter.