Vaillant Arotherm Plus

[ash_scotland88]

In my constant internal debate of gas vs ASHP for our new (old and no CH) house latest research lead me to the arotherm plus, promising a whole world of wonders.

What confuses me is the 190L UniTower it launches with claims to provide enough hot water for a 5person house, or atleast one product launch I read about it last night did - typically when I try to find the article to link to I can't.
How can 190L provide so much hot water, if true? Is it because 75C water temp will be mixed with cold water at the shower, if so for higher efficiency and COPS isn't it better to have a larger tank stored at a lower temperature?
Interestingly the CH flow rate is only upto 55C which may not be hot enough for some of the retrofit properties it advertises for, or am I wrong in this presumption?

Any-one have any general thoughts about this product?

[ProDave]

190L at 55 degrees won't do a 5 person house.  Who claimed that? Vailant themselves or some third party?

 

You won't get much more than 55 degrees from an ASHP you either need over sized radiators to work with that or under floor heating.

 

If it is an old house, make sure you really know how much heat you need, most disappointment seems to be when you need a lot more than you think and the chosen ASHP can't deliver it.

[ash_scotland88]

21 minutes ago, ProDave said:

190L at 55 degrees won't do a 5 person house.  Who claimed that? Vailant themselves or some third party?

I really wish I bookmarked it last night, it was a third party site announcing the launch, I knew deep down this is was wrong but wondered if having a high water temp could help with this claim or if the unitower could top up with hot water  upto a certain point before tank was drained, eg for every 1L used it could refill with 0.5L till the tank was cold.

 

23 minutes ago, ProDave said:

 

You won't get much more than 55 degrees from an ASHP you either need over sized radiators to work with that or under floor heating.

 

If it is an old house, make sure you really know how much heat you need, most disappointment seems to be when you need a lot more than you think and the chosen ASHP can't deliver it.

 Until we are in the house we can't do calc's to really know what is required, beyond the EPC from the home report but the more I read and the more I think about it about it I do think it will be gas in the end. It's the safer option. I'm coming to think unless three (minimum for quotes) heating installers quote a ASHP could heat the house comfortably and have spare capacity if we ever decide to take up naked sweatbox yoga in the house* then it's too much of a risk.

To give you an idea the lounge is 6.5mx5.5m (at the biggest points) with a box window and two patio doors and fireplace, not exactly air tight.

*exaggeration, it's only fun when in a class....

[Temp]

https://nottenergy.com/resources/energy-cost-comparison/

 

[gavztheouch]

Have you had a quote for the arotherm? I think the ASHP will only heat the water to 55 or so then a heating coil will do the rest.

[ColB]

14 hours ago, ash_scotland88 said:

I really wish I bookmarked it last night, it was a third party site announcing the launch, I knew deep down this is was wrong but wondered if having a high water temp could help with this claim or if the unitower could top up with hot water  upto a certain point before tank was drained, eg for every 1L used it could refill with 0.5L till the tank was cold.

 

 

 

It's mentioned in Vaillants brochure on the Saltire.co.uk website in the following link  

https://saltire.co.uk/wp-content/uploads/2020/09/Vaillant-B2C-aroTHERM-plus-leaflet.pdf

 

On page 4:- "190 litre cylinder capacity delivers up to 380 litres of hot water for up to five people including the use of rainfall showers."

 

 

I'm not sure about the UniTower, however we're getting a 12kW aroTherm Plus and Unistore 300L Unvented Cylinder installed in the next week or two into our new build located in Fife. We'd been struggling to get a Mitsubishi EcoDan for months because of shortages so in the end we plumped for Vaillant who only had one left in stock.

 

I'm no expert but the plus points for us with the Vaillant is that it uses a different refrigerant (R290/propane) over most other ASHPs  so can manage higher temperatures, plus a coding resistor can be installed quite easily so it can also cool without affecting RHI

 

Hope this helps.

C.

 

 

 

Edited January 23, 2021 by ColB

[PeterW]

20 hours ago, ash_scotland88 said:

What confuses me is the 190L UniTower it launches with claims to provide enough hot water for a 5person house, or atleast one product launch I read about it last night did - typically when I try to find the article to link to I can't.
How can 190L provide so much hot water, if true? Is it because 75C water temp will be mixed with cold water at the shower, if so for higher efficiency and COPS isn't it better to have a larger tank stored at a lower temperature?

The unitower specs are thin on the ground - I’ve emailed Vaillant as it’s not on the installer portal currently and I’d like to see flow rate and recovery rate etc. 
 

The unitower itself is pretty simple. It is a 190 litre UVC, 25 litre expansion tank and what looks like a 18 litre low loss header in a nice box with their standard controller integrated into the front. 
 

Pricing has been hard to get but about £5k for the 12kW with Unitower has been where I have seen it - would be interesting to know because on one side you get Vaillant saying “go to our installation partners” and then they appear as a special in Wolseleys..!! 
 

OK - found it..!

 

High hot water comfort: aroTHERM plus can provide up to 25% more usable hot water with a 75°C flow temperature,

 

So they are using the higher temperature. At 75°C (assuming no cooling during use ..!) then a 190 litre cylinder will give you 344 litres at 45°C. At 60°C tbat would be 267 litres, 55°C it would be 241 litres so you can see how they  are working this out. 
 

 

[ProDave]

So what refrigerant is this using to get to 75 degrees?  And can it still do that when it's very cold?  e.g -15 here this morning (new record for us) so it would be trying to heat DHW to 90 degrees above air temperature.

[A_L]

1 hour ago, ProDave said:

So what refrigerant is this using to get to 75 degrees?

 

The Arotherm plus uses R290 (Propane)

[ash_scotland88]

2 hours ago, PeterW said:

The unitower specs are thin on the ground - I’ve emailed Vaillant as it’s not on the installer portal currently and I’d like to see flow rate and recovery rate etc. 
 

The unitower itself is pretty simple. It is a 190 litre UVC, 25 litre expansion tank and what looks like a 18 litre low loss header in a nice box with their standard controller integrated into the front. 
 

Pricing has been hard to get but about £5k for the 12kW with Unitower has been where I have seen it - would be interesting to know because on one side you get Vaillant saying “go to our installation partners” and then they appear as a special in Wolseleys..!! 
 

OK - found it..!

 

High hot water comfort: aroTHERM plus can provide up to 25% more usable hot water with a 75°C flow temperature,

 

So they are using the higher temperature. At 75°C (assuming no cooling during use ..!) then a 190 litre cylinder will give you 344 litres at 45°C. At 60°C tbat would be 267 litres, 55°C it would be 241 litres so you can see how they  are working this out. 
 

 

Hoped someone would come along and explain it.

I suppose the unitower saves buying the expansion vessel, heat exchanger (that's the hydraulic unit they talk about?) and tank all separately. I like a nice long shower so worried the tank may not be enough, but I suppose a gas boiler 300l tank may be specced.

Where did you see £5k for 12kw? I think I've seen £7k.

On installation costs only with the RHI payment we would be "in profit" at the end of 7years, even at £7k. This is where the temptation to go ASHP comes from.

 

[gavztheouch]

Propane works well at higher temps but the arotherm plus still performs best at the lowest temp possible. If you go above 45 for space heating you still take a massive hit to cop values

[Dan F]

Why would you use a UniTower and not spec your own UVC, though?

 

The temperature isn't limited, rather they don't actively promote it for >55C as COP above this isn't great and I think there is also something about RHI needing a COP >2.5.   While you could theoretically use this for retrofit with standard radiators, I'm not sure thats a good idea personally.

 

14 hours ago, ash_scotland88 said:

if so for higher efficiency and COPS isn't it better to have a larger tank stored at a lower temperature?

Yes, if you have the space. 

 

We have one on order.  We'll unlikely ever use 75C flow, but who knows.. if we are expecting guests we could potentially temporarily increase the  temperature from 55 -> 70C to increase the effective capacity of the 305L UVC from 460L to 610L. The main reason to choose this model was efficiency, minimal noise and low global warming impact. 

 

There are a number of manfuacters that do the newer R32 models that are all pretty good, some of which go up to 65C.  Be careful though, because these maximum temperatures are only supported when the external air temperature is within a certain range as @ProDave also pointed out..

 

2 hours ago, ProDave said:

 And can it still do that when it's very cold?  e.g -15 here this morning (new record for us) so it would be trying to heat DHW to 90 degrees above air temperature.

At -15C, it can still do 60C DHW, which is pretty good.  By comparison the new R32 ecodan can't do more than 50C DHW at that temperature and the LG Therm V R32 maximum is 55C

 

.

 

[Dan F]

3 hours ago, gavztheouch said:

 If you go above 45 for space heating you still take a massive hit to cop values

 

It drops off yes, but it's not massive.   SCOP at 55C (3.4). is only 22% less that SCOP at 35C (4.4).   

 

I agree heating with standard radiators at 75C isn't a geeat idea. The SCOP for 65/75C isn't published.  The COP for A7/W65 is 2.8, but if I understand correctly, that'll be fair bit worse when it's colder outside which is when you need the heating!

 

[ColB]

3 hours ago, ash_scotland88 said:

Where did you see £5k for 12kw? I think I've seen £7k.

 

 

Hi Ash,

The prices are on City plumbing’s online store.

https://www.cityplumbing.co.uk/Vaillant-Arotherm-Plus-12kW-0010037215/p/477552?uiel=Desktop
 

[Dan F]

15 minutes ago, ColB said:

Hi Ash,

The prices are on City plumbing’s online store.

https://www.cityplumbing.co.uk/Vaillant-Arotherm-Plus-12kW-0010037215/p/477552?uiel=Desktop
 

£7k is with unitower.  2k for a UVC is a lot though,  especially if its only 180L.

[BartW]

On 23/01/2021 at 14:56, Dan F said:

£7k is with unitower.  2k for a UVC is a lot though,  especially if its only 180L.

ok, so as someone has asked earlier:

 

what is the benefit of a £2k unistor vs £600 standard uvc tank, other than:

- looks

- it being vaillant

- looks

 

[Dan F]

Just now, BartW said:

what is the benefit of a £2k unistor vs £600 standard uvc tank, other than:

- looks

- it being vaillant

- looks

 

 

Looks like it's £950 for the 300L.  The 7k must have been list price, still not cheap though

 

https://www.cityplumbing.co.uk/Vaillant-Unistor-20235274-Heat-Pump-Cylinder-300-Litre/p/379174?uiel=Desktop

 

[BartW]

5 hours ago, Dan F said:

 

Looks like it's £950 for the 300L.  The 7k must have been list price, still not cheap though

 

https://www.cityplumbing.co.uk/Vaillant-Unistor-20235274-Heat-Pump-Cylinder-300-Litre/p/379174?uiel=Desktop

 

 

I think I confused unistor for unitower. Whilst the former is as you mentioned, the unistor on its own I can't seem to find a price for.

 

Also, I gather that Unistor comes with a built-in expansion vessel, and perhaps all ancillary plumbing, too?

 

 

[PeterW]

1 hour ago, BartW said:

Also, I gather that Unistor comes with a built-in expansion vessel, and perhaps all ancillary plumbing, too?

 

not that I have seen - it’s a dumb cylinder with a box of bits the same as any other. They do a pre plumbed one but so does everyone else. 
 

Looks about 15% more to have a nice manufacturers badge on it . 

[J1mbo]

IIRC MCS only allows certification to 55°C for heating. However the Arotherm Plus can and does provide 75°C flow if so configured. It is used for the weekly legionaires program for DHW, if enabled (which it should be).

 

The SCOP numbers assume weather compensation. it does not deliver 55°C at a COP of 3.4. It does provide 44°C at 0°C at about 3.2. The max output tables give the actual COP at 55°C, which IIRC is about 2.4. The SCOP is higher as most the year it will be running lower, although I don't know the parameters against which it is calculated.

 

The system has various options of DHW. I've ended up with a 250 litre tank running in 'normal' mode with 5 persons that like showers and a tank set point of 48°C. This allows the HP to put more kW into the cylinder as it's being used as the temperature is lower, leading to shorter recharge times. At 65°C it's probably 1:1 so max of about 10 or 11kW. At lower temps it can produce 15kW and more.

 

HTH

Edited March 7, 2021 by J1mbo

[PeterW]

Just now, J1mbo said:

It is used for the weekly legionaires program for DWH, if enabled (which it should be).

Why...?? 

[J1mbo]

HP are typically configured for DHW storage below 60°C (significantly below in my case), so a weekly sterilisation process is needed. Traditionally this was done with an immersion but with R290 the HP can do it itself and with COP > 1, so more efficiently.

[PeterW]

1 minute ago, J1mbo said:

This allows the HP to put more kW into the cylinder as it's being used as the temperature is lower, leading to shorter recharge temps. At 65°C it's probably 1:1 to max of about 10 or 11kW. At lower temps it can produce 15kW and more.

That isn’t correct. You can’t create energy, and a heat pump works by incremental heat increase to the flow and it is when the output temperature is above 45°C then the units are only able to add 1-2°C to the water circulating. The pump is a constant flow so the heat introduced to the tank - or the J/hr - is not linear as the deltaT reduces at higher temperatures. 
 

This is why heat pumps have temperature curves, not linear constants due to thermodynamics. 

[PeterW]

4 minutes ago, J1mbo said:

HP are typically configured for DHW storage below 60°C (significantly below in my case), so a weekly sterilisation process is needed.

No, it’s not...!! There is no legal - in building regulations or water regulations (WRAS) - to provide a legionnaire cycle to a domestic installation. There are no recorded instances of Legionella in a domestic environment - none.  
 

It is a closed system with no way for air or bacteria to enter the system. 

[J1mbo]

1 minute ago, PeterW said:

No, it’s not...!! There is no legal - in building regulations or water regulations (WRAS) - to provide a legionnaire cycle to a domestic installation. There are no recorded instances of Legionella in a domestic environment - none.  

 

interesting, so the manual is erring on the side of caution then. I will adjust accordingly.