Glad I was sat down!!

[JohnMo]

14 minutes ago, mk1_man said:

7kW or 5kW Arotherm

You may find there is very little in it, a lot of heat pumps are badge engineering and some software tweaks. So the 7 and 5kW could be fundamentally nearly the same unit. One overlooked feature most heat pumps have, is a setting to limit hertz the unit runs at or how much noise it makes (depending on the setting is labeled), so you increase or decrease the rated capacity.

 

6 minutes ago, JamesPa said:

However there are several very sound reasons to believe excessive cycling should be avoided if possible

Below is a snap shot of a cycle from my heat pump, its done in 5min data change cycle, so pretty well averaged.  What you see is a higher electricity demand at startup, it reduces quite quickly for a about the first 5 mins. Basically it is playing catch-up to get water temperature back where it should be. The next 15 mins it's slowly modulates down down until it has no where left to go. In this case it hit a thermostat in the garden room. Of note are the heat pump is set to min hertz setting, at peak load the heat pump is drawing around 1kW.

 

A much longer run and slightly different settings - this time the heat pump had been off for 12 hours or more, doing batch charging the floor, the heat pump ran at full load for 7 hours, the dip at the end you see is a defrost. The first 30 mins increase is the water temp slowly getting hotter. Min hertz in not set, target temp is 35, the heat pump only achieves around 33 Deg. Generally the heat pump is drawing around 1.5kW (50% more than above). Similar flow temperature, colder oat, not being allowed to modulate.

 

 

[JohnMo]

10 minutes ago, MikeSharp01 said:

Or you need to reset / adjust the delta T or turn it off for a period so the next run will be longer.

Does that work? I suspect it's not a very good thing to do for the refrigerant side of the heat pump. Are you possibly better to set a higher target flow temp and increase the compressor restart delta. So it's off slightly longer and runs longer but means temp stays the same.

[sharpener]

38 minutes ago, JohnMo said:

So the 7 and 5kW could be fundamentally nearly the same unit.

 

No, it is the 3kW and 5kW that are basically the same unit, the 7kW is different and taller.

 

The 3kW is restricted to 85 rps by the compressor software, this also means that both models turn down to the same minimum output figures so the dynamic range of the 3kW is less than 3:1 whereas the 5kW is more than 4.

 

43 minutes ago, JohnMo said:

Does that work? I suspect it's not a very good thing to do for the refrigerant side of the heat pump. Are you possibly better to set a higher target flow temp and increase the compressor restart delta. So it's off slightly longer and runs longer but means temp stays the same.

 

The Vaillant control system integrates the error term i.e. the difference between the setpoint and the actual temp. I don't claim to understand the detail but I think the settings can be tweaked to achieve what you describe.

[mickeych]

This is now really making me nervous that we have overspecced our system and maybe got the design wrong. 

We have been given a calculated heating loss of 12.2kW and a heat gain of 26.5 kW (for cooling). We have opted for FCU's rather than radiators to go alongside our UFH to provide active cooling. Due to the distance between the main plant room and the far end of the building (around 75M) we were advised that we should have a second ASHP unit in the middle of the house. So we now have a main plant room at one end of the house and a minor plant area in the middle of the house each with a separate ASHP and UFH system also driving a number of FCU's. We have been recommended a 16kW for the main unit and an 8kW for the smaller unit. 

Question is if the single unit could drive all of the heating needs for the house from a single unit, we would lose some of the cooling capacity but cut a lot of cost.

BTW we are being quoted more than £30K for this setup so this sort of confirms that this is a nonsense amount of money!

[sharpener]

41 minutes ago, mickeych said:

Question is if the single unit could drive all of the heating needs for the house from a single unit

 

Very possibly if you are willing to forgo some of the cooling. Have seen yr pic of the shell, looks a fantastic project.

 

Various questions occur to me e.g.

• 12kW is not a particularly big heat loss, what is the total floor area?
• What is the general layout that explains the 75m distance?
• Why is the heat gain so large? Can it be mitigated with shading somehow? Is it in the UK or overseas? Do you have an idea for the minimum cooling you would accept?
• Is the proposed setup divided hydraulically into area A and area B or are the two HPs supposed to work in tandem on a common layout? That would be more efficient as you would have a greater available turn-down ratio and also some redundancy in case one unit breaks.
• How was the 16/8 split arrived at?

 

 

[MikeSharp01]

12 hours ago, JohnMo said:

Does that work? I suspect it's not a very good thing to do for the refrigerant side of the heat pump. Are you possibly better to set a higher target flow temp and increase the compressor restart delta. So it's off slightly longer and runs longer but means temp stays the same.

I Guess we are saying the same thing to increase the delta you either have to lower the return temp or raise the flow temp. I am not a dedicated follower of the KISS approach to controlling these things, although the simpler the better idiom I do agree with - where we make it as complex as it needs to be to make it better while controlling the complexity. We have access to a vast array of controlling technologies which should enable us to do amazing things with ASHPs including data science, machine learning & internet of things (IoT) and we are really only up against the physics in the corners of this. I tend to think of it as being akin to internal combustion engine management systems development, so, in my mind, we are at a stage of about 50 years ago emerging from the era of the K-Jetronic with Lambda from 1976 as things are. Therefore my conjecture is that we are just at the bottom of the S curve with ASHP technology, @ the breakthrough point, where more understanding, better controls, improved materials and better design all round will precipitate a much more rapid growth of capability and uptake. The only thing we risk at the moment is failure because we, the innovators / early adopters, give up on it because without us trying everything the future is bleak. Naturally some political backing may be needed here even if it really wasn't in the development of engine management until the emissions came to the front. 

   

 

Edited May 4 by MikeSharp01
Typo 30 to 50

[sharpener]

Well you seem to have thought about it all very logically so I don't think there is anything different I would propose. Maybe that is some comfort in itself.

 

Having the two systems normally independently controlled and operating separately is sensible inasmuch as it simplifies the control requirements.

 

If there is however some way of linking the F and R pipework, with e.g. normally closed manual lever valves, this might give you a cheapish way of keeping some heating going if one HP breaks down. I can't immediately think how you might configure the sensors though as am not familiar with Daikin controls. Maybe there is some "limp home" mode you can invoke.

 

 

[JohnMo]

20 hours ago, mickeych said:

heat gain of 26.5 kW (for cooling)

I would really challenge that, because it sounds nonsense.

 

1 hour ago, mickeych said:

largest gain is via a 4Mx4M glazed screen

Put internal blinds in that are closed at the worst time, that's 60% of the gain gone.  I managed to keep our sitting room cool enough with blinds, a 6kW heat pump via UFH, with cross ventilation and have about 36m2+ of glazing in that room alone.

[mickeych]

1 hour ago, JohnMo said:

I would really challenge that, because it sounds nonsense.

 

Put internal blinds in that are closed at the worst time, that's 60% of the gain gone.  I managed to keep our sitting room cool enough with blinds, a 6kW heat pump via UFH, with cross ventilation and have about 36m2+ of glazing in that room alone.

Yes I was hoping that internal blinds and solar glass would really nail that and I just feel that if we can go the single ASHP route it has to make sense from all counts. 

[mickeych]

1 hour ago, sharpener said:

Well you seem to have thought about it all very logically so I don't think there is anything different I would propose. Maybe that is some comfort in itself.

👍

[IGP]

@mickeych Might be worth doing a heat loss yourself in heatpunk if you know your build up. Just to see if you’re in the right ballpark. It’s not too difficult and definitely a good use of a few hours. 

[JohnMo]

3 minutes ago, IGP said:

worth doing a heat loss yourself in heatpunk

I lost the will to live using the heatpunk tool, (tried a few times) way easier and accurate is the spreadsheet on here

 

 

 

[IGP]

I get that, it takes a bit of getting used to. But I find it invaluable if I have to show it to anyone else as it’s visual rather than a spreadsheet (seen the eyes glaze over!) but that’s just my 2p. 

[Nick Laslett]

On 03/05/2024 at 22:31, mickeych said:

We have been given a calculated heating loss of 12.2kW and a heat gain of 26.5 kW (for cooling). 

This is not something I am familiar with, but 26.5kW of cooling sounds like a lot. 
 

My physics is pretty sketchy, but I would have thought the temperature deltas for hot and cold would be quite similar. I only need a 5kW ASHP for my heat loss, but made a big assumption that going down from 28° to 22°, would require a lot less energy than going up from -2° to 22°.

 

If the windows are creating that much solar gain, then it might be worth investing in the active glass like @NSS . Not sure if that is what you mean by Solar Glass? We have Suncool SN70/35 coated glass,  which still lets in heat. 

Edited May 5 by Nick Laslett

[SteamyTea]

23 minutes ago, Nick Laslett said:

but I would have thought the temperature deltas for hot and cold would be quite similar

It is how well the ASHP can dispell energy to a hot atmosphere.

 

Say the refrigerant is effectively expanded until it hits -25⁰C and the OAT is -10⁰C, that is ∆15.

Now say the refrigerant is at 25⁰C, and the OAT is 35⁰C, ∆10.

 

Different refrigerant fluids have different temperature/pressure coefficients so can also have different CoPs between heating and cooling 

[TerryE]

I have a passive-class house with a 70 tonne MBC "warm-slab" within the heated fabric of our build.  I went for the deferred option of putting in the 6mm radial from the CU to an outside wall box and a insulated double pipe run from the  UFH cupboard to where I would put the ASHP, but held off installing an ASHP and used a 3kW Willis as an interim means of heating the UFH loops so that we could size the ASHP based on a year or two run rate.

 

The issue that we have is that going from using the Willis (plus Oil filled rad top up Dec/Jan) on an Octopus Agile optimised heating schedule to an ASHP at an average CoP of 3½ say might save us perhaps £300 p.a. in electricity costs.  (We have a handful of days a year when we put in more than 30 kWh heat.) 

 

I'd want at least a 10 year payback so would want my install costs to be at most ~£3K. And then you have the issue that the typical life of an ASHP can be ~10 years.  It's just easier to pay the extra £300.  6 years on, and I still can't make the investment case.  

[MikeSharp01]

4 minutes ago, TerryE said:

I'd want at least a 10 year payback so would want my install costs to be at most ~£3K. And then you have the issue that the typical life of an ASHP can be ~10 years.  It's just easier to pay the extra £300.  6 years on, and I still can't make the investment case.  

How did the SAP assessor 'see' the Willis heater - others on here have said it really hit their SAP outcome having direct electric heating?

[George]

5 hours ago, TerryE said:

I have a passive-class house with a 70 tonne MBC "warm-slab" within the heated fabric of our build.  I went for the deferred option of putting in the 6mm radial from the CU to an outside wall box and a insulated double pipe run from the  UFH cupboard to where I would put the ASHP, but held off installing an ASHP and used a 3kW Willis as an interim means of heating the UFH loops so that we could size the ASHP based on a year or two run rate.

 

The issue that we have is that going from using the Willis (plus Oil filled rad top up Dec/Jan) on an Octopus Agile optimised heating schedule to an ASHP at an average CoP of 3½ say might save us perhaps £300 p.a. in electricity costs.  (We have a handful of days a year when we put in more than 30 kWh heat.) 

 

I'd want at least a 10 year payback so would want my install costs to be at most ~£3K. And then you have the issue that the typical life of an ASHP can be ~10 years.  It's just easier to pay the extra £300.  6 years on, and I still can't make the investment case.  

A bit pessimistic on ashp lifespan but otherwise it probably doesn't make sense to use a ashp. If heating with resistance heating is cost effective then ashp does not have a place. How is your hot water heated?

[NSS]

3 hours ago, Nick Laslett said:

This is not something I am familiar with, but 26.5kW of cooling sounds like a lot. 
 

My physics is pretty sketchy, but I would have thought the temperature deltas for hot and cold would be quite similar. I only need a 5kW ASHP for my heat loss, but made a big assumption that going down from 28° to 22°, would require a lot less energy than going up from -2° to 22°.

 

If the windows are creating that much solar gain, then it might be worth investing in the active glass like @NSS . Not sure if that is what you mean by Solar Glass? We have Suncool SN70/35 coated glass,  which still lets in heat. 

Last time I spoke to my SageGlass contacts, they confirmed that they no longer supply for residential projects in the UK. That was a year or so ago, so I guess it may have changed again since then.

[Nickfromwales]

5 hours ago, George said:

A bit pessimistic on ashp lifespan but otherwise it probably doesn't make sense to use a ashp. If heating with resistance heating is cost effective then ashp does not have a place.

Most ASHP's have a 7 year warranty, from the few I've been associated with, and that's even from the likes of Stiebel Eltron who offer 5 iirc. 

Lifespan / longevity is found (promoted) by good design and sizing the unit so that it can live a relaxed and long(er) life. 

[TerryE]

5 hours ago, George said:

How is your hot water heated?

 

We have an OSO UVC which is heated by dual immersion. I also have a couple of digital thermometers on the inner tank, one next to each immersion. 

 

My Node-RED heating control system does a day-ahead heating calcs at 23:00 GMT each night. We have Octopus Agile and the daily half-hour (HH) pricing runs 00:00 - 00:00 C.E.T.  As far as DHW goes, the CH calc takes the average tank temp to work out a slight overestimate of kWh needed to bring it up to 55°C and this get scheduled at the cheapest HH slots with a cut out at 55°C (though at the mo the Immersion thermo cuts out first).

 

We are on a Greek island ATM, so the HW draw is only from one occupant; our son who lives with us in his bed-sit on the 2nd floor.

 

The screen capture below show the last 24hr history for Home Assistant. (BTW, the bottom scale is in local Greek time, sorry.)   He hasn't used much hot water today (mainly just a quick shower, I guess).  The OSO is really well insulated but even so most heating here is loss replacement.  Checking my eventlog table, the total DHW heating used was 1.6 kWh costing 20p (The north sea is dead calm ATM, so the daily low price is quite high at about 13p.)

 

Over the last few months since we commissioned the OSO it's been a lot windier and even though we use more HW with 3 of us in the house, the HH price for DHW has been averaging around 5p so we typically spend maybe 50p a day on DHW.

 

[TerryE]

6 hours ago, MikeSharp01 said:

How did the SAP assessor 'see' the Willis heater - others on here have said it really hit their SAP outcome having direct electric heating?

 

Remember we did our as-built EPC in 2017.  The detailed stuff is back in the UK and not to hand, but IIRC we got marked down for using resistive heating and ended up with a C EPC, but still good enough to make BReg requirements.  That being said, I regarded the whole SAP exercise as a paper one needed to get sign-off.  What I really care about is real-world performance and total levelised cost of heating.

 

Given that we use renewable electricity only, the total doesn't worry me and I suspect that going forward the scoring system will penalise fossil-fuel based heating more than direct electric.   

Edited May 6 by TerryE

[Nickfromwales]

7 hours ago, TerryE said:

but IIRC we got marked down for using resistive heating and ended up with a C EPC

Which just goes to show how under-qualified these bodies are to provide a global summary of an entire property vs just adding the number of ticks in particular boxes and then down-grading you like Neanderthals.

[MikeSharp01]

4 hours ago, TerryE said:

and ended up with a C EPC,

Although it is what it is, the EPC system, but doesn't that make a laughing stock of the whole EPC panjandrum.

[JamesPa]

34 minutes ago, MikeSharp01 said:

Although it is what it is, the EPC system, but doesn't that make a laughing stock of the whole EPC panjandrum.

One might argue that it's the same problem that Ofsted has, ie dumbing down the assessment of something to a level that readers of (insert your choice of 'newspaper') can readily understand and/or make for good headlines.

 

Unfortunately almost nothing in the world isn't as simple as a one word, one dimensional, rating.  But if we want/need such simplicity we have to accept (and preferably be educated about) it's limitations.

Edited May 6 by JamesPa