Which ASHP...

[BartW]

Hi All,

 

I thought I had it all selected, and decided on, but...

 

Clearly not.

 

So here goes:

 

I was heart set on Vaillant Arotherm plus 7kW (or 9kW) + Unistor / tower and all gubbins (around 210L tank).

 

Having read some posts here, I started reviewing. Vaillant is vague about COP in their literature. Only SCOP values get quoted...

I looked at what other market options are available, and figure that most claim similar COP, i.e. 4.5 @ A7C/W35, 3.5 @ A2C/W35. Lower A temps are less of a concern for us, as we are in Oxfordshire, and whilst we may observe temps dipping below 0C at night, we could have things set to utilise excess energy from 5.5kWp solar PV to charge the tank, and generally use 5p/kWh night tariff if need be.

 

But then come the choices:

- Panasonic HP

- Panasonic TCAP (expensive and really meant for severe Winter weather)

- Daikin?

- Samsung? (being 40% less than, say Panasonic)

- Mitsubishi?

- LG Therma V (similar money to Panasonic)

 

The other dilemma is whether to go:

- all separates

- Monoblock + tank + buffer inside

- Monoblock + All-In+One

 

Any benefits to the above three solutions? And does paying £3.5k for a "good pump" pay off in the long run vs buying one for £2k?

 

On a separate note, I can see that some sources (manufacturers) show Low Loss header in their schematics vs Buffer tank. Would one ever do that? I suppose, it's cheaper but surely the tank is the correct thing to consider?

 

PS. The house is going to be 0.15 uVal all around and with MVHR. 180m2 build, if that helps things and the perspective.

 

 

Apologies for the barrage of questions, but I have now managed to hit the wall without being any smarter, or more decided.

 

Many thanks!

 

Bart

 

 

 

 

 

[Dan F]

1 hour ago, BartW said:

I was heart set on Vaillant Arotherm plus 7kW (or 9kW) + Unistor / tower and all gubbins (around 210L tank).

We have this one, also 7kW.  Next size up is 10kW.  We have it set up with the Vailant Hydraulic Unit (3-port valve, controller, diverter, backup heater) and a 25L non-vaillant buffer tank.

 

Quote

Having read some posts here, I started reviewing. Vaillant is vague about COP in their literature. Only SCOP values get quoted...

They do also quote some COP figures in manual/literature, but I agree it is limited compared to other manufactuers.  I have all the very detailed COP and power ouput data I found if you need it.

 

1 hour ago, BartW said:

COP, i.e. 4.5 @ A7C/W35, 3.5 @ A2C/W3

 

The 7kW aroTherm gives you 

-  A7/W35:  COP 3.9 at 100% compressor providing 12.3kW output, COP 4.8 at 50% compressor providing 6.3kW output.

-  A2/W35:  COP 3.3 at 100% compressor providing 10.4kW output, COP 4.1 at 50% compressor providing 5.4kW output.

(No manufacturs quote COP at max compressor though, as the idea is that ASHP is sized to not need to run at full-filt.)

 

Various other great manufactuers out there, but R290 does have some advantages in terms of range of operating temperatures and max flow temp.

 

Edited January 22, 2022 by Dan F

[BartW]

Thanks Dan,

This is useful, and fills the gap in the spec that I was after.

 

What were the reasons you went for the AroThermPlus? 

To me the initial choices were based on:

- quieter than others (debatably?)

- higher max temp, ref: Legionella heat cycle

- it is prettier (ok, I know, I know...)

- it is Vaillant

 

Also, what is your setup? Did you go for the full unitower?

 

 

 

[Dan F]

21 minutes ago, BartW said:

What were the reasons you went for the AroThermPlus? 

 

I'm not sure if COP and sound were necesarily the best, but certainly amoung the best.  But one of the things that pushed me towards this model was the fact it's R290-based which is:

1) Better for the environment (lower GWP)

2) Has really good operating range (can still do 60C DHW down to -10C for example, not many can)

3) Ability to easily reach 70C DHW temps in UK climate at almost any time of year (-5 -> 25C external)

 

Why was I interested in high DHW temps:

- Firstly, while the plan was to run UVC at low temps, I was concerned about capacity (e.g. when having guests).  One way to solve this capacity issue (temporarily) is to use a hgher temperatures, and you can do this with aroTherm without needing to use immersion.

- Secondly, I was really keen to be able to load-shift (i.e. heat tank at night, use water during the day).   The two approach to load shifting I looked at (Sunamp, Mixergy) both required higher flow temperatures.

 

Yes, higher flow temperatures have lower COP but; in my first scenario this is better than i) immersion of ii) running out of hot water, and in my second scenario heating 30% of the UVC/Sunamp with 60/65C water, is still better than heating a full tank to 50/55C if you might not use the full 300L for a few days.

 

That was my thought process anyway.  Ended up going with a Mixergy tank (so no Unitower) and we are heating it via top/indirect coil rather than low-temp heat-pump assembly to achieve what they call "partial charging" .  It does actually work really well, just it doesn't keep partial charge state over multiple days as well like a Sunamp would. It's a bit more short-term (given losses and I assume heat transfer through thermocline etc.)

 

Edited January 22, 2022 by Dan F

[SteamyTea]

2 hours ago, BartW said:

Vaillant Arotherm plus 7kW (or 9kW)

 

2 hours ago, BartW said:

4.5 @ A7C/W35, 3.5 @ A2C/W35.

 

What are your calculated heat loads at those temperatures?

[Kevm]

This is some detail from Mitsubishi for comparison.  The grey rows include a defrost allowance. 

IMO it's more important to get the design and operation right than which reputable manufacturer you choose.

 

I have the 14kW Ecodan installed with no LLH/buffers and it seems to work fine. 

2 hours ago, BartW said:

 

 

 

 

 

 

 

[BartW]

1 hour ago, Dan F said:

That was my thought process anyway.  Ended up going with a Mixergy tank (so no Unitower) and we are heating it via top/indirect coil rather than low-temp heat-pump assembly to achieve what they call "partial charging" .  It does actually work really well, just it doesn't keep partial charge state over multiple days as well like a Sunamp would. It's a bit more short-term (given losses and I assume heat transfer through thermocline etc.)

 

 

This got me really interested, and I started reading about Mixergy tank. Really impressive! With the anticipated 200L tank as specified by BPC, would one choose same tank size in Mixergy? The price difference between 150L and 300L is within £200. So not a huge deal of a difference. Is there a point in "future proofing" for multiple guest visits? We would (eventually) be a family of 2 + 2, with potential parents, in-laws, and friends visiting (admittedly, not all at the same time).

 

 

 

1 hour ago, SteamyTea said:

What are your calculated heat loads at those temperatures?

 

Sorry, I don't think I understood you. I am just quoting "the brochures".

 

1 hour ago, Kevm said:

have the 14kW Ecodan installed with no LLH/buffers and it seems to work fine. 

 

Does it not short cycle?

 

 

 

 

 

 

 

 

Further to the above, I am starting to think that a cheaper pump would equally do the full job.

 

I particularly am liking the Mixergy tech.

 

The thought process here is that I could:

- charge at night @ 5p/kW for four hours through the ASHP

- utilise excess energy from 5.5kWp solar PV during the day, and either run ASHP at that time, or 3kW immersion heater element

 

 

Now, is there a way to store energy for space heating during the day when excess energy is available, or at night when the tariff is cheap, with view to, say, discharging the heat into the UFH in time before everyone gets up in the morning?

 

Thanks!

 

Bart

 

 

 

 

 

 

 

 

 

 

[SteamyTea]

1 minute ago, BartW said:

1 hour ago, SteamyTea said:

What are your calculated heat loads at those temperatures?

 

Sorry, I don't think I understood you. I am just quoting "the brochures".

Your house will have a heat load, basically the power the heating system needs to supply at different outside temperatures to keep the inside at the temperature you want. Often expressed as kW/⁰C.

This is what you need to know when choosing any heat source. It is more important with an ASHP as the performance varies with outside air temperature and humidity. ASHP and gas/oil boilers are calculated differently, even though they are doing the same job usually.

[BartW]

5 minutes ago, SteamyTea said:

Your house will have a heat load, basically the power the heating system needs to supply at different outside temperatures to keep the inside at the temperature you want. Often expressed as kW/⁰C.

This is what you need to know when choosing any heat source. It is more important with an ASHP as the performance varies with outside air temperature and humidity. ASHP and gas/oil boilers are calculated differently, even though they are doing the same job usually.

 

Ok, so my basic calculation would be:

 

1937sq ft x 8 ft (h) x 15C (5C outside --> 20C target inside?) x 0.15 (uvalue?) = 34,866BTU / 3412BTU*kW = 10.18kW

 

Does this sound about right?

 

 

[Kevm]

26 minutes ago, BartW said:

Does it not short cycle?

 

It cycles about twice per hour when it gets warmer than about 6 degrees outside, maybe three times per hour but no more.  I run it pretty much 24/7 through the whole house though.

 

 

[BartW]

8 minutes ago, Kevm said:

 

I suppose that is not bad.

 

Have you done a cost-to-run chart to see what it is really costing you? Also, how big is the house?

 

 

[Dan F]

2 hours ago, Kevm said:

This is some detail from Mitsubishi for comparison.

Seems Vaillant may be bit better than.  It's also worth comparing operating ranges too.

 

57 minutes ago, BartW said:

Sorry, I don't think I understood you. I am just quoting "the brochures".

@SteamyTea Is making the point that before you specify an ASHP you need a clear understand of you heat demand, to ensure you spec the right size, to get best COP, avoid short-cycling and ensure your house is warm.

 

Our heating load is 3kW, so easily covered by 7kW ASHP while running in eco mode with low compressor speed and high COP.  7kW doesn't give you a very fast UVC reheat time though, so that's another reason we used mixergy with a top indirect coil as it means you can fairly quickily heat the top 30% of the tank and take a nice shower without waiting as long as you'd typically need to wait if you had a heat-pump tank with a large coil lower down.

 

57 minutes ago, BartW said:

Is there a point in "future proofing" for multiple guest visits?

The view I took on this was to calculate tank size for the family based on 50C, knowing that if extra capacity was required I could increase temperature to, say 65C, confidently with the aroTherm. Assuming you aren't using something like Mixergy, this has the advantage of avoiding heating (and associated losses) a larger tank all year round.  The other way we have increased effective capacity (showers you get from a tank of hot water) is via the use of WWHRS units which gives you an extra 30%+ shower time for same hot water usage.

 

57 minutes ago, BartW said:

Now, is there a way to store energy for space heating during the day when excess energy is available, or at night when the tariff is cheap, with view to, say, discharging the heat into the UFH in time before everyone gets up in the morning?

You could use a PCM43 Sunamp for this.  But the simplest and very effective approach that many people on the forum use is to have UFH pipes in your slab and use it as a massive storage heater.  This way you can dump heat into it at night quite easily and not get any real peaks in temperature.  @TerryE has some great posts on this.

 

 

Edited January 22, 2022 by Dan F

[SteamyTea]

32 minutes ago, BartW said:

Does this sound about right?

It is a starts. Rather mixed units.

[Dan F]

33 minutes ago, BartW said:

1937sq ft x 8 ft (h) x 15C (5C outside --> 20C target inside?) x 0.15 (uvalue?) = 34,866BTU / 3412BTU*kW = 10.18kW

 

It's not quite a simple as that because you ideally need to consider:

i) loss through foundation is less.
ii) internal heat gains
iii) windows have lower u-values

iv) losses through ventiliation and/or leakiness.

 

There is a speadsheet available in the forum that @Jeremy Harris put together that gets you really quite close, without having to pay a consultant to model it.   If you are hiring someone to install an ASHP though, it's part of their job to run heat-loss calculations, before specifiying or installing anything.

[BartW]

22 minutes ago, Dan F said:

so that's another reason we used mixergy with a top indirect coil as it means you can fairly quickily heat the top 30% of the tank and take a nice shower without waiting as long as you'd typically need to wait if you had a heat-pump tank with a large coil lower down.

 

Do you refer to the built-in Mixergy coil? I would imagine any night time tariff, and daytime solar PV discharge would nicely play together with it.

 

23 minutes ago, Dan F said:

could increase temperature to, say 65C,

 

It seems that other pumps do that too (perhaps not 65C, but 60C?)

 

24 minutes ago, Dan F said:

WWHRS units which gives you an extra 30%+ shower time for same hot water usage.

 

I considered that, and whilst it (apparently) boosts your SAP a lot, I am yet to establish if I will ever see a return on the £500 to £700 unit (multiplied by two out of three bathrooms).

 

26 minutes ago, Dan F said:

many people on the forum use is to have UFH pipes in your slab and use it as a massive storage heater.  This way you can dump heat into it at night quite easily and not get any real peaks in temperature.  @TerryE has some great posts on this.

 

Yes, this is what's rather logical and "free". But will I in effect overheat during the day? Or would I hope that MVHR would, somewhat, redistribute the mass of air across the rest of the rooms?

 

23 minutes ago, Dan F said:

There is a speadsheet available in the forum that @Jeremy Harris put together that gets you really quite close, without having to pay a consultant to model it.   If you are hiring someone to install an ASHP though, it's part of their job to run heat-loss calculations, before specifiying or installing anything.

 

Not using a consultant, hence me trying to understand Hebrew by myself. Also, specifiers / suppliers like BPC , Nu-Heat and so on will specify whatever they want to sell, as long as their choices fall within the bands of criteria. So not unbiased...

 

Above all, whilst I am trying to find a holy grail, I want to make sure that I am not overpaying for solutions that will never see me any return. I am not a purist, and not a tree hugger, either. But if I could make a wise choice, and not kill the planet, then surely I would feel better too.

 

Also, it is likely it will not be a forever home. If it lasts us 10 years, then I think we have done alright. Chances are, we will build another one in 5 years time.

 

Thanks!

Bart

 

 

 

[SteamyTea]

42 minutes ago, BartW said:

1 hour ago, Dan F said:

so that's another reason we used mixergy with a top indirect coil as it means you can fairly quickily heat the top 30% of the tank and take a nice shower without waiting as long as you'd typically need to wait if you had a heat-pump tank with a large coil lower down.

 

Do you refer to the built-in Mixergy coil? I would imagine any night time tariff, and daytime solar PV discharge would nicely play together with it.

 

1 hour ago, Dan F said:

could increase temperature to, say 65C,

 

It seems that other pumps do that too (perhaps not 65C, but 60C?)

 

1 hour ago, Dan F said:

WWHRS units which gives you an extra 30%+ shower time for same hot water usage.

 

I considered that, and whilst it (apparently) boosts your SAP a lot, I am yet to establish if I will ever see a return on the £500 to £700 unit (multiplied by two out of three bathrooms).

 

1 hour ago, Dan F said:

many people on the forum use is to have UFH pipes in your slab and use it as a massive storage heater.  This way you can dump heat into it at night quite easily and not get any real peaks in temperature.  @TerryE has some great posts on this.

 

Yes, this is what's rather logical and "free". But will I in effect overheat during the day? Or would I hope that MVHR would, somewhat, redistribute the mass of air across the rest of the rooms?

 

1 hour ago, Dan F said:

There is a speadsheet available in the forum that @Jeremy Harris put together that gets you really quite close, without having to pay a consultant to model it.   If you are hiring someone to install an ASHP though, it's part of their job to run heat-loss calculations, before specifiying or installing anything.

 

Not using a consultant, hence me trying to understand Hebrew by myself. Also, specifiers / suppliers like BPC , Nu-Heat and so on will specify whatever they want to sell, as long as their choices fall within the bands of criteria. So not unbiased...

 

Above all, whilst I am trying to find a holy grail, I want to make sure that I am not overpaying for solutions that will never see me any return. I am not a purist, and not a tree hugger, either. But if I could make a wise choice, and not kill the planet, then surely I would feel better too.

 

Also, it is likely it will not be a forever home. If it lasts us 10 years, then I think we have done alright. Chances are, we will build another one in 5 years time.

There is so much there that it cannot be easily answered.

 

What size house, number of occupants, embedded renewables, U-Values, and in and on.

 

Is the place still at the design stage, or has construction started?

[BartW]

3 minutes ago, SteamyTea said:

There is so much there that it cannot be easily answered.

 

What size house, number of occupants, embedded renewables, U-Values, and in and on.

 

Is the place still at the design stage, or has construction started?

 

We have full planning, and probably about 8 weeks away from breaking ground, i.e. foundations, then TF in May. Hoping to have roofs and facades in place by end of Summer / beginning of Autumn, then move indoors and start doing the services. But I am trying to have the full budget fully in, and have a clear plan of what is going in.

 

As for the "variables":

- 180m2 house

- 510m3 of air

- designed SAP @ 93A

- 4/5 bed

- 0.15 uValue all around, i.e. roof, slab, walls

- 65m2 of double glazing @ 1.2uVal average

- 2 occupants, a dog, soon a child, maybe another in the future, in-laws / friends visiting 

- renewables: 5.5kWp PV with anticipated 5500kWh yearly generation going after PVGIS

- MVHR

 

I am sure I will never have it spot on, but neither will the specifiers that have been sending quotes, so I hope to do a better job by researching whilst there is still time

 

Thanks

Bart

 

[Dan F]

37 minutes ago, BartW said:

Do you refer to the built-in Mixergy coil? I would imagine any night time tariff, and daytime solar PV discharge would nicely play together with it.

Mixergy doesn't have a built-in bottom coil as they recommended a different approach for using ASHP with an external PHE See: https://www.mixergy.co.uk/mixergy-heat-pumps-faqs/

This however, is not the approach I'm using, as aroTherm means the limitations mentioned here do not apply.  This two-pager does a good job at summarizing the different approachs: https://www.dropbox.com/s/9091d4a0ut7i5am/Heat pump leaflet V1_compressed.pdf?dl=0

 

37 minutes ago, BartW said:

It seems that other pumps do that too (perhaps not 65C, but 60C?)

Yes, but you need to look at the operating range too. The ones I looked at could only supply 60C between 0-25C which I felt was a bit too tight given the approach I was planning to take.

 

37 minutes ago, BartW said:

I considered that, and whilst it (apparently) boosts your SAP a lot, I am yet to establish if I will ever see a return on the £500 to £700 unit (multiplied by two out of three bathrooms).

ROI from a pure energy usage perspective doesn't add up, unless you have very loong showers.  But if you consider it's "greener" to recover rather than waste heat and it means you can get by with a smaller UVC, it did start to make sense from our perspective. (we didn't care about SAP, as house should score very high anyway).

[SteamyTea]

32 minutes ago, BartW said:

0.15 uValue all around, i.e. roof, slab, walls

If you are having UFH in the slab you really want to improve on that.

Top of my head I think roofs have to be a better U-Value.

[BartW]

2 minutes ago, SteamyTea said:

If you are having UFH in the slab you really want to improve on that.

Top of my head I think roofs have to be a better U-Value.

Roofs uVal for new build I think need to be 0.18 (or 0.16). Graven Hill require 0.15.

 

When I said slab, I meant beam and block with Jetfloor system specified to 0.15. Pipes would be in-screed.

 

 

[SteamyTea]

Just now, BartW said:

Roofs uVal for new build I think need to be 0.18 (or 0.16). Graven Hill require 0.15.

 

When I said slab, I meant beam and block with Jetfloor system specified to 0.15. Pipes would be in-screed.

 

 

You may be right, I can't remember.

Says here 1.1

https://www.burtonroofing.co.uk/blog/u-values-and-building-regulations-for-insulating-your-home/

 

If I was not on the phone I would download the regs and check.

[BartW]

3 minutes ago, SteamyTea said:

You may be right, I can't remember.

Says here 1.1

https://www.burtonroofing.co.uk/blog/u-values-and-building-regulations-for-insulating-your-home/

 

If I was not on the phone I would download the regs and check.

 

I think the detail is in the "suggested". A bit clearer here: https://www.building-innovation.co.uk/the-hub/part-l-changes-2020-what-you-need-to-know

 

 

[SteamyTea]

1 minute ago, BartW said:

 

I think the detail is in the "suggested". A bit clearer here: https://www.building-innovation.co.uk/the-hub/part-l-changes-2020-what-you-need-to-know

 

 

If I get around to it I will reread the regs.

 

[BartW]

Just now, SteamyTea said:

If I get around to it I will reread the regs.

 

Here

 

 

[SteamyTea]

Just now, BartW said:

Here

 

 

Yes.

I am not that far from Bicester ATM.

Shame I cannot read them when I am driving home. Could get the whole set done during the 12 hours I am wasting every weekend.