3 Air to Air heatpumps WITH hot water tank. But are they any good?

[JtG]

Hi, 

 

Has anyone had experience with an A2A with DWH?  Would love to have feedback please.

 

I'm weighing up my options for a modest retrofit on my 2 bed bungalow in Norfolk.  Indeed I have a airtightness test with energy audit on its way that should help me know the order to do things etc including greening space temperature.  This winter I reduced my space heating from 8000kwh to 3000kwh with far Infrared heaters plugged into smart sockets so I can live with that for a while.  But as I use an 15 year old mitsubishi air-conditioner all summer (using cold to manage pain), finding an a2a heat pump with a water tank seems a good way to get the water heating off gas.  And there are 3 that I've found!

 

Argo iseries with their Emix tank - that heats even when AC is on, and uses waste heat from cooling for the water tank

Daikin Multi plus - with a 120l tank that could go above the washing machine

Panasonic Aquarea Ecoflex - may only just be available. - again reuses the waste heat 

 

How effective the filters are is another issue for me to consider - panasonic seem to have gone all out in that respect.

 

So has anyone installed these please?  What is the COP for the heating, cooling and hotwater like in real life?

Do you know of any more models?

 

Regards,

 

Jt

[RichardL]

Watching - and intending to go A2A for DHW once the heating is off the oil boiler.

A2W doesn't seem a great idea on a house (my house) that is insulated but has built in ventilation and needs more of a punch than 50ºC rads to keep warm.

Dependent on the planning process for more outside units for a couple of months.

[JtG]

Aha - a fellow traveller - Welcome- have you found any other brands that do A2A with DHW? 

 

I am attracted by the Argo one but can't find any reviews in the UK - I suspect Argo may be more used on the continent but am puzzled as to how to get real life opinions from there. 

 

 With A2W the installation and refinement afterwards seem key to achieving the COP, do you think its the same for A2A?

 

Jt

[JtG]

ARGO RESEARCH - Started with Italy as it is an italian brand - pompa di calore = heat pump.  Lots there - this chat includes info about Argo for a newbie....

 

https://www.energeticambiente.it/forum/sezione-ecologia-e-ambiente/risparmio-energetico-ed-efficienza-energetica/61263-ristrutturazione-appartamento-e-scelta-impianti-per-riscaldamento-raffrescamento-e-acs

 

[RichardL]

To be honest I was going to keep the DHW completely separate from the space heating.
Especially with the self contained heatpump/tank kit - there didn't seem any reason to change DHW at the same time as heating generally.

I'm Mitsubishi Electric for A2A space heating.
Valliant Arostor was on the shortlist for hot water - but need to do the space heating first.

[JtG]

Yeah I thought about an all-in-one  water heater/heat pump.  I wasn't keen on the heat pump extracting heat from the room that the tank in

 

Someone has suggested two heat pumps outside: one for the air and one to heat water. (And one to rule them all)

 

But surely two can't be more energy efficient than one?

 

😎Jt

 

[Gone West]

5 hours ago, JtG said:

Yeah I thought about an all-in-one  water heater/heat pump.  I wasn't keen on the heat pump extracting heat from the room that the tank in

Use one that ducts air in from outside.

 

https://www.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

 

https://www.orionairsales.co.uk/cool-energy-ecostore-200l-all-in-one-air-source-heat-pump-hot-water-system-ce-es200-solar-thermal-16610-p.asp

 

https://www.clickonbathrooms.co.uk/3069426-ariston-nuos-fs-200-floor-standing-direct-air-source-heat-pump-water-heater-nuos200d-c2x12743911

 

https://www.orionairsales.co.uk/giona-all-in-one-indirect-unvented-air-source-heat-pump-with-250l-cylinder-288kw--10000btu-240v50hz-4682-p.asp

 

https://www.dimplex.co.uk/product/edel-hot-water-heat-pump

[JtG]

Hi - thanks for directing me onto the all in one heat pump water heaters.  Been trying to get all info and also quotations to install.

 

I have settled on the Dimplex Edel 170l as it has quietest operation, and it will be in the attic above my carer's bedroom.   There's only the 2 of us, and only one of us uses hot water so 170l should be more than adequate.   I  have had trouble getting prospective installers to understand what they are and to quote. 

 

 I've had a quote of £1000 that was withdrawn, and 2 quotes of £2500 - that's installation and materials and vat on those. but not the cylinder or ducting.

 

Could anyone advise me if that is reasonable please?  How many half days of work should that cover, please?   

 

Its to put marine ply, in the attic area, where we are placing the cylinder, bringing up a electric cable up from the boiler cupboard below, and removing the boiler from the kitcehn, and capping the gas, and installing the new system.  It going directly above the boiler cupboard so I hope that reduces the amount of change to my piping.

 

Also could anyone comment on the VAT, please?   I have reviewed the energy saving materials and 2.20 includes heat pumps and does say spare OR WATER HEATING.   So I think 0% is right...

 

 

"2.20 Air source heat pumps

Air source heat pumps use the air as a source of heat. They absorb heat from the outside or surrounding air and transfer that into useable heat in the home for space or water heating, or both."

 

https://www.gov.uk/guidance/vat-on-energy-saving-materials-and-heating-equipment-notice-7086

 

 

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For others who are interested in researching them. I found that these are being installed in Australia (heat pump HWS), America and in various countries on the continent - with government subsidies and rebates too.   There's a facebook group MEEH where the australians discuss them, and a dutch group called Tweakers.  Durability is a key issue, but the prevailing view is that buying good quality removes that worry (one australian has had one installed for 20 years!)   Noise is also a factor if the cylinder is being installed in a sensitive location.  In Europe there are many brands LG is interesting ,with its 10 year guarantee, Daikin, Panasonic and a brand called Atlantic...  LG told me that UK regulation is an obstacle *sigh*   

 

A british heating engineer reviews his experience (all good) on Youtube here

 

 

 

 

 

[DanDee]

1 hour ago, JtG said:

For others who are interested in researching them. I found that these are being installed in Australia (heat pump HWS), America and in various countries on the continent - with government subsidies and rebates too.   There's a facebook group MEEH where the australians discuss them, and a dutch group called Tweakers.  Durability is a key issue, but the prevailing view is that buying good quality removes that worry (one australian has had one installed for 20 years!)   Noise is also a factor if the cylinder is being installed in a sensitive location.  In Europe there are many brands LG is interesting ,with its 10 year guarantee, Daikin, Panasonic and a brand called Atlantic...  LG told me that UK regulation is an obstacle *sigh*   

 

Have a look at this, send an enquiring email to them. Instead of trying to heat the whole tank, it's starting from the top down as it's built different than the rest.

 

https://mixergy.co.uk/news-and-insights/introducing-mixergys-new-award-winning-heat-pump-cylinder-the-ihp/

 

 

from the comments on youtube

 

When will a spec sheet be out. Particularly interested in running noise levels, capacities and recharge times versus your “traditional” cylinders

 

Mixergy Ltd

Please send us an email, and we can provide this information enquiries@mixergy.co.uk

To speak to the Mixergy team, please call 01865 884 343.

We are available Monday to Friday from 9am to 5.30pm.

 

 

Edited May 5, 2023 by DanDee
extra details

[JamesPa]

5 hours ago, DanDee said:

 

Have a look at this, send an enquiring email to them. Instead of trying to heat the whole tank, it's starting from the top down as it's built different than the rest.

 

https://mixergy.co.uk/news-and-insights/introducing-mixergys-new-award-winning-heat-pump-cylinder-the-ihp/

 

 

from the comments on youtube

 

When will a spec sheet be out. Particularly interested in running noise levels, capacities and recharge times versus your “traditional” cylinders

 

Mixergy Ltd

Please send us an email, and we can provide this information enquiries@mixergy.co.uk

To speak to the Mixergy team, please call 01865 884 343.

We are available Monday to Friday from 9am to 5.30pm.

 

 

Note however that, so far as I can tell from the literature, the advantage @DanDeerefers to (heating only the top) is lost should you subsequently fit an ashp.  They sell an ashp conversion kit comprising PHE and pump which must surely destratify the tank.

 

Unless I (and    @sharpener) misunderstood what they are saying

[DanDee]

12 minutes ago, JamesPa said:

Note however that, so far as I can tell from the literature, the advantage @DanDeerefers to (heating only the top) is lost should you subsequently fit an ashp.  They sell an ashp conversion kit comprising PHE and pump which must surely destratify the tank.

 

Unless I (and    @sharpener) misunderstood what they are saying

 

This product it's a heat pump cylinder in itself, but instead of having the condenser coil inbuilt around the exterior of the tank, they try something different by having the HP module separated on top, by piping the water through a condenser heat exchanger pulling from the bottom so that the heated water it's fed through the top. The tank it's specifically designed to a degree to avoid mix. What literature have you seen? 

 

 

 

 

 

 

 

[sharpener]

It's clear from the pictures in their own literature that there is very little stratification in the heat pump version of the standard Mixergy tank:

 

Edited May 5, 2023 by sharpener

[DanDee]

8 minutes ago, sharpener said:

It's clear from the pictures in their own literature that there is very little stratification in the heat pump version of the standard Mixergy tank:

 

Well that has nothing to do with the new product, so will it mix or not or how much remains to be seen when they hit the market and people talk about it.

It has a diffuser, the HP output it's only 1.5kW so low flow rate in general.

[sharpener]

Yes confusing isn't it. The bottom picture in yr earlier post is from this Mixergy news article and shows the "conventional approach" with the refrigerant coil wrapped around the cylinder which Mixergy are at pains to say they do not use.

 

The key to achieving stratification is to have the flow circulating at only the rate at which the water can be heated. Notice how small the circulating pump is in the picture. If they can be obtained readily it would be the ideal pump for adding to a conventional cylinder - with or without a heat exchanger - as discussed by @JamesPa and me in the other thread.

 

<The Stratos instantaneously heats hot water which is drawn from the bottom of the cylinder and returns it back to the top to achieve very quick reheat times. Alternatively, a flow path back to the bottom of the cylinder allows the system to achieve the highest possible COP on a full reheat cycle.>

 

from this Mixergy seem to think that for the best CoP the optimal strategy is to return the hot water to the bottom of the tank. I had been debating which was the best approach but don't understand why this is better than having the coldest water descending slowly to the take-off point as in their Boost mode (which achieves a CoP of between 2 and 3), maybe someone can elucidate?

 

Edited May 5, 2023 by sharpener

[DanDee]

9 minutes ago, sharpener said:

from this Mixergy seem to think that for the best CoP the optimal strategy is to return the hot water to the bottom of the tank. I had been debating which was the best approach but don't understand why this is better than having the coldest water descending slowly to the take-off point as in their Boost mode (which achieves a CoP of between 2 and 3), maybe someone can elucidate?

 

You mix the water so you can have the lowest dt and higher COP when slow heating, isn't this known as a general thing with HP's? Only CO2 HP's do well with high dt.

[RichardL]

There's another thread (might be this one further up) on the economics of simple tank+immersion vs. heat pump tech above.
i.e. heat pump high initial cost + low running, vs tank+immersion/resistive low initial cost higher running.

The mixergy iHP option looks really interesting TBH, any experience of their other products - reliability/support etc?

Context - moving from oil DHW

Thought -  if mixergy iHP needs a top and a bottom side inlet to a tank - thats just a standard pressurised hot water tank?
(or could be)

I'd 100% be interested in there mixergy compressor/tech part if it would work with an off the shelf pressurised tank (which is already sitting in my house) The heating coil in the tank becomes redundant - but the cold in and hot out should be just right?

Edited May 5, 2023 by RichardL

[Iceverge]

@JtG

 

Have you measured your DHW use? Heating a large UVC with a cheap time of use tariff has the cheapest lifetime cost for low volume users with my sums. 

 

 Heat pump DHW is only really cheaper over a lifetime for higher volume users. 

 

On another point, an ESHP (all in one) DHW heater can be set to extract heat from the house or the outside. I've not been able to find any accurate data on the COP of said tanks Vs inlet air temperature so I'm undecided which I better. However at full chat they will tend to over ventilate a house.  A simple operable butterfly valve or two in a duct could make this switchable season to season and fine tune it for best ventilation/COP. 

[DanDee]

6 minutes ago, Iceverge said:

A simple operable butterfly valve or two in a duct could make this switchable season to season and fine tune it for best ventilation/COP. 

That's what daikin thinks more or less.

[sharpener]

45 minutes ago, DanDee said:

 

You mix the water so you can have the lowest dt and higher COP when slow heating, isn't this known as a general thing with HP's? Only CO2 HP's do well with high dt.

 

 

Assuming the HP can deliver water at 50C irrespective of the inlet temp (which it seems to be capable of in Boost mode, where the water makes a single pass through the HP) then according to Wikipedia it is inversely proportional to delta T between the cold source (the air) which is constant, and the HP outlet water which as above is also constant.

 

 

What we are missing is an expression which takes into account the water temp at the inlet to the HP which will either (in Boost mode) be constantly cold or (in max efficiency mode) rise slowly as the water is recirculated and the tank as a whole heats up.

 

Clearly the heat input to the water is deltaT x flow. Does this HP (and indeed ASHPs for space heating)

A. control the flow so as the body of the tank heats up and deltaT becomes less the flow rate increases to maintain constant power, or

B. maintain a constant flow in which case the deltaT will remain constant so the outlet temp will not be 50C but will be less to begin with and rise as the tank heats up.

 

Can someone point me to the appropriate theory for this? My undergraduate thermodynamics is very rusty now.

 

 

[DanDee]

14 minutes ago, sharpener said:

A. control the flow so as the body of the tank heats up and deltaT becomes less the flow rate increases to maintain constant power, or

Variable water pump

 

https://patents.google.com/patent/WO2023047111A1/en?assignee=Mixergy+Ltd&sort=new

[JamesPa]

2 hours ago, DanDee said:

3 hours ago, JamesPa said:

Note however that, so far as I can tell from the literature, the advantage @DanDeerefers to (heating only the top) is lost should you subsequently fit an ashp.  They sell an ashp conversion kit comprising PHE and pump which must surely destratify the tank.

 

Unless I (and    @sharpener) misunderstood what they are saying

 

This product it's a heat pump cylinder in itself, but instead of having the condenser coil inbuilt around the exterior of the tank, they try something different by having the HP module separated on top, by piping the water through a condenser heat exchanger pulling from the bottom so that the heated water it's fed through the top. The tank it's specifically designed to a degree to avoid mix. What literature have you seen? 

Apologies, my comment was based on the standard Mixergy cylinder with the heat pump conversion kit.  I hadn't twigged that they had brought out a cylinder with an integrated HP.

[sharpener]

2 hours ago, DanDee said:

Variable water pump

 

https://patents.google.com/patent/WO2023047111A1/en?assignee=Mixergy+Ltd&sort=new

 

Thanks for the link, very useful explanation. They obviously envisage using this two-regime technique in an improved add-on kit for existing tanks too, which may interest @JamesPa. As the full text although worth reading is very repetitious I am including the key bit below (my emphasis, it explains why circulating the water in an existing tank with an externally-fitted pump is a good idea). Pictures taken from espacenet:

 

 

Figure 2 shows a graph illustrating a first example for optimising the COP of the heating. In this example the flow rate of (cold) water into the heat exchanger is selected to enable the most efficient heat transfer. Generally, the higher the flow rate the better the COP is; this can be explained by the higher flow rate producing a turbulent boundary layer further into the heat exchanger, with the turbulent boundary layer providing more efficient heat transfer than the laminar boundary layer. Other factors affect flow speed too; for example for a large plate exchanger a lower flow speed can produce the same heat transfer as a smaller plate exchanger with a higher flow speed. The flow speed may be reduced or increased in dependence on performance of the heat source (be it e.g. seasonal variability or heat pump capability), but for maximum COP the flow speed is generally maintained as high as safely and conveniently available. The COP associated with heating water at 20 °C is around 3.5 whilst the COP associated with heating water at 60 °C is lower, for example 2.9. In this example water in the tank is permitted to heated up gradually, and the COP gradually drops as the tank is heated. In this example, the average COP is 3.2 for complete heating of the tank.

 

Figure 3 shows a second example where the water is not permitted to heat up gradually, but instead the flow rate of cold water into the heat exchanger is selected to bring the water to the desired use temperature of 62 °C in a single pass through the heat exchanger. Here the COP associated with heating water is 2.9 throughout, and if this is used for complete heating of a tank’s worth of water, then the COP remains 2.9 throughout.

 

 

 

Edited May 5, 2023 by sharpener
Add graphs

[JamesPa]

1 hour ago, sharpener said:

 

Thanks for the link, very useful explanation. They obviously envisage using this two-regime technique in an improved add-on kit for existing tanks too, which may interest @JamesPa. As the full text although worth reading is very repetitious I am including the key bit below (my emphasis, it explains why circulating the water in an existing tank with an externally-fitted pump is a good idea). Pictures taken from espacenet:

 

 

Figure 2 shows a graph illustrating a first example for optimising the COP of the heating. In this example the flow rate of (cold) water into the heat exchanger is selected to enable the most efficient heat transfer. Generally, the higher the flow rate the better the COP is; this can be explained by the higher flow rate producing a turbulent boundary layer further into the heat exchanger, with the turbulent boundary layer providing more efficient heat transfer than the laminar boundary layer. Other factors affect flow speed too; for example for a large plate exchanger a lower flow speed can produce the same heat transfer as a smaller plate exchanger with a higher flow speed. The flow speed may be reduced or increased in dependence on performance of the heat source (be it e.g. seasonal variability or heat pump capability), but for maximum COP the flow speed is generally maintained as high as safely and conveniently available. The COP associated with heating water at 20 °C is around 3.5 whilst the COP associated with heating water at 60 °C is lower, for example 2.9. In this example water in the tank is permitted to heated up gradually, and the COP gradually drops as the tank is heated. In this example, the average COP is 3.2 for complete heating of the tank.

 

Figure 3 shows a second example where the water is not permitted to heat up gradually, but instead the flow rate of cold water into the heat exchanger is selected to bring the water to the desired use temperature of 62 °C in a single pass through the heat exchanger. Here the COP associated with heating water is 2.9 throughout, and if this is used for complete heating of a tank’s worth of water, then the COP remains 2.9 throughout.

 

 

 

So is the inference that you get better cop if you circulate the water than if you don't, in which case adding the Mixergy 'heat pump conversion kit' or equivalent to an existing cylinder, rather than upgrading it to a hp specific one with a large coil, is actually, potentially, rather a good idea!

 

1 hour ago, sharpener said:

 

 

[sharpener]

I think this must be a yes for 3 separate reasons, because (i) with the PHE you will achieve just as good heat transfer as a "heat pump" cylinder would give, but the stirring will (ii) improve it further with turbulence round the coil (if left in circuit) and (iii) improve the CoP by keeping the temperatures low for as long as possible assuming their thermodynamics are correct.

 

The downside is de-stratifying the tank so not being able to draw off water that is properly hot during the heating up phase. In my case this is of no consequence as the times when it is best to heat the water are quite distinct from the times when I want to use it. I can imagine this would apply to many people.

 

Still haven't been able to find the small pump that Mixergy use. But theirs is on the primary circuit, whereas if I fit one to stir my existing tank I will have to have a bronze one.

 

Edited May 5, 2023 by sharpener

[JamesPa]

25 minutes ago, sharpener said:

Still haven't been able to find the small pump that Mixergy use. But theirs is on the primary circuit, whereas if I fit one to stir my existing tank I will have to have a bronze one.

 

Confused by this statement.  The digram in fig 4 above shows the pump (I assume the open circle is a pump) in the heated DHW circuit essentially taking it out from and returning it to the bottom of the tank and thus needing to be WRAS compliant/bronze.  What am I missing?