Disabling Weather Comp during mid winter?

[Andehh]

We run a Samsung Gen6 ASHP and despite having a 'well' insulated house (very good vs average new build, 'good' vs BuildHub standards) it is still a challenge to really warm up - caused by it being a sprawling bungalow with very very high ceilings (3.5 to 4.5m throughout) and carpeted floors. It was fine during the last cold snap we had (3-4 days of -3 temps) but we needed to run the ASHP all day to keep around 20 degrees, and at night it froze up so we turned it off and only ran it al day.

 

With our current setup we run all zones together, to maximise the 2 x cheap periods with Octopus Cosy. Right now we have 50% of the ASHP in the cheap period and 50% of the usage during the 'normal' period.

 

One frustration I do have, is that for the majority of the heating times, our flow rate is around 30degs which means it takes ages to warm up during cheap & normal rate periods...but oes eventually get there with a 'high' flow rate temp of low mid 30s.

 

I am weighing up for 'winter' periods disabling Weather Comp, setting the flow temp at a flat 37 degrees (so still 'ok' efficiency wise) and using this to get more heat out of the cheap periods, and reduce our usage of non cheap periods.

 

Even if we take a 20% hit on efficiency going from a weather comp'd 30 degs to a 37 degs flat temp.... then the 30% cheaper rate elec still means we are quids in, and have a quicker warm'd up house!

 

Just wanted to test this logic with the team!

 

Cheers,

 

[crispy_wafer]

I'm not running my heatpump yet, but I guess you have to be flexible in your approach, you have to find what works for you in different scenario's.  I've been reading the various threads and trying to take the conclusions and build up my own plan, because I just know this time next year I'll be joining in with the various ASHP threads as I try to find the right balance on my HP install. 

 

As users we will have to come to a compromise by trying to eek out every last drop of efficiency vs  being comfortable, and if that means a couple of quid extra per day when it's baltic outside then so be it.  Life's too short to be freezing in your own home.

[HughF]

Leave it on 24/7 and let it defrost when required.

 

is your Samsung installed per midsummer wholesale instructions or per freedom instructions?

[Conor]

Sounds like you'd be better off on a standard tariff and run ashp 24x7.

 

 

[sharpener]

46 minutes ago, Andehh said:

One frustration I do have, is that for the majority of the heating times, our flow rate is around 30degs which means it takes ages to warm up during cheap & normal rate periods...but oes eventually get there with a 'high' flow rate temp of low mid 30s.

 

I am weighing up for 'winter' periods disabling Weather Comp, setting the flow temp at a flat 37 degrees (so still 'ok' efficiency wise) and using this to get more heat out of the cheap periods, and reduce our usage of non cheap periods.

 

From reading yr post in the UFH thread it would seem you have a lot of setback, 3 deg would be more normal.

 

Also many ppl increase the target by 1 or 1.5 deg during the cheap periods to provide a reserve of heat so the HP runs less in the peak. Whether you can do this with the setpoint or the WC will depend on how yr controls work.

[ProDave]

What is your peak rate vs your cheap rate?

[sharpener]

https://octopus.energy/smart/cosy-octopus/

 

 

So peak is 160/60 = 2.67 x "cosy" rate.

 

 

Edited December 7, 2023 by sharpener

[ProDave]

Sorry it's that peak rate late afternoon / early evening that would rule it out for me.

 

It's 60% above normal rate to that would make it about 44p per kWh to cook my dinner.  No thank you.

[ReedRichards]

Isn't the problem that you have the weather Compensation curve/line set wrongly?  There's not even one right answer to this, if you run your heat pump 24/7 you can get away with lower water temperatures than if you don't and the heat pump is off some of the time.  But it should be possible to adjust the settings if they're not working for you and get settings that do work.  

[Marvin]

Hi @Andehh

 

Thinking which is the right thing to do is excellent, and everybody has excellent suggestions, however as @ProDave is veering towards, it really depends on the maths, and then what controls you have which will allow you to change things when required to the optimum set-up.

 

Remembering my plumbing days, the higher the ceiling the more heat used to achieve the temperature at the height of the temperature controls so your already at a disadvantage.  I hope you have your roof insulated to within an inch of its life (we have a bungalow with ASHP PV, MVHR and good airtightness and insulation).

 

Many, many, many, companies and people, ignore the important design and installation requirements required to achieve the most efficient use of  an ASHP, mainly because each installation design requires individual consideration of the property its to be installed in.

 

Without knowing much about your set-up. I would suggest trial and error. This is what we did. For us it turned out to be more efficient to have the Weather Compensation on and the ASHP on all the time, and adjust our wall thermostat between day temp and lower night temp.

 

I assume you have underfloor heating below your carpet. We have radiators. So I would expect your temperature recovery would be much slower than ours. 

 

If you have a programmable thermostat I would try lowering the temp slightly before each cheap rate and increasing it during the cheap rate, but keeping it on all the time. Not sure why it freezes so badly. I'm sure that last comment will create a plethora of responses.

 

Your comments suggest that the ASHP is struggling to produce the warmth required unless its on all the time topping up your home temperature.

 

Recommended small works to check/improve:  Insulate all pipework/ tanks/ controls (except of electrical elements/wires) outside the building thermal envelope to within an inch of its life. Insulate all primary circuit pipework excessively, insulate any other associated pipework. 

 

And, as  @ReedRichards just commented the Weather Compensation needs to be related to your individual set-up/installation/home.  It maybe fine it may not. I do not know.

 

Good luck

 

Marvin

 

 

 

 

 

 

 

 

 

 

 

 

  

[sharpener]

1 hour ago, ProDave said:

Sorry it's that peak rate late afternoon / early evening that would rule it out for me.

 

It's 60% above normal rate to that would make it about 44p per kWh to cook my dinner.  No thank you.

 

Yes, I am wondering whether plain old Economy 7 will be best for me for that reason. Will have to do some spreadsheet modelling. The 10kWh battery will bridge the gap for usual domestic loads but would not get a 12kW HP through to 0400. Planning to switch to Octopus to give me a choice of tariff when the HP is installed in the spring.

[ProDave]

My gripe is there is not an off peak tariff available that does not in some way penalise you for at least some of the "normal" usage times.

 

And in part my resistance to having a smart meter.  There really is this thing that late afternoon / early evening electricity is expensive, but being all electric I do not want to be forced into a position where I either have to cook and eat outside a time I consider "normal" or pay through the nose for the privilege.   People keep pedalling the  notion that smart meters are for the consumers benefit, where the reality it is for the grids benefit to try and even out demand through time of use charging, i.e force behaviour change, cook your dinner at some other time being just one of them.

 

I also have solar PV so have a natural desire to use as much in the daytime, so do as much of my heating then, heating at night counters that so seems to conflict with having solar PV.

 

So on balance at the moment I will just stick with a single rate tariff on a dumb meter.  Appreciate other views differ.

[JohnMo]

@JamesPa did a spreadsheet a while ago, for setting up a WC curve and comparing the CoP. On a low W/m2 the difference in CoP is very small between set flow temp and WC. The CoP hit from 30 to 37 at 2 Deg is around 0.5.

 

I have been doing the same internal debate on this. We are on E7, DHW uses about an hour of that, so I have 6 hours of charging time, at the moment am using a WC curve, but it not right for batch charging, so have been thinking set temp from HP, and two set points on mixer (electronic), high temperature during E7 and a maintain temp  with a flow of around 28 after. Not sure how it work though, would it be better just switching off.

 

 

[sharpener]

24 minutes ago, JohnMo said:

two set points on mixer (electronic)

 

That's the catch, if you have a fixed (highish) flow temp from the HP and then temper it during the day you will not get the same CoP benefit as lowering the flow temp at source somehow during the daytime.

 

For that reason I would guess that separate timed setpoints or conventional night setback setting would give better CoP. 0.5 is quite a big hit if you were to get that.

 

24 minutes ago, JohnMo said:

would it be better just switching off.

 

If you mean the entire HP I wouldn't have thought so. Recovery from off would take a long time as many ppl have found. Maybe during the 1600 - 1900 peak would be viable for someone on Cosy (which you are not).

 

24 minutes ago, JohnMo said:

I have been doing the same internal debate on this.

 

Will be interested to learn what your conclusions are in practice for someone on E7.

 

 

Edited December 7, 2023 by sharpener

[Marvin]

23 minutes ago, JohnMo said:

Not sure how it work though, would it be better just switching off.

And what does your ASHP installation instructions say about turning on after leaving it off for hours when below 5 degrees Centigrade.....  Mine says don't do it!

[ProDave]

3 minutes ago, Marvin said:

And what does your ASHP installation instructions say about turning on after leaving it off for hours when below 5 degrees Centigrade.....  Mine says don't do it!

Yes if you want to "turn the heating off" for a period, don't flick the big red switch, turn it "off" via some control input while leaving it still powered.  In my case I use the "room thermostat" input to tell it that it is satisfied when I want the heating "off" but the ASHP is still powered and indeed overnight on a cold night it will still periodically start the water circulating pump to prevent a slug of cold / freezing water being left in the outside unit.

 

Some makes of ASHP use a crankcase heater to warm the compressor before first start up, there was a long thread about this a year or so back as some users were noticing a big unexplained usage even when the ASHP was "off"  but you can't just turn those off at the mains switch without allowing them proper time to warm up before starting.

[JohnMo]

45 minutes ago, Marvin said:

And what does your ASHP installation instructions say about turning on after leaving it off for hours when below 5 degrees Centigrade.....  Mine says don't do it!

Mine has a sump heater, and antifreeze, plus below 5 degs it circulates on and off anyway so no mention anything special.

[Andehh]

Thank for all the comments here, our setup is decidedly awkward & hard work to manage! 

 

ASHP feeding 2 x UFH Manifolds with no blending valve but we are over zoned thoughout (lesson learnt here). Every room having its own stat - 22 of them throughout the house. Due to a c290sqm bungalow and 2 x mono pitch roof we also see very different temperatures throughout the house because of very 'odd' rooms...small floors & high ceilings etc etc

 

This means we have 3 bedrooms which are relatively small floor space with very high ceilings - because they each have a mezzanine & staircase in for sleeping 'up stairs'. Floor being carpeted means these rooms are always 15% colder then the rest of the house based on the small floor vs volume of air inside. Blending valves do not make enough of a difference to balance these rooms vs rest of the house - probably due to our manifold being 11 zones on one pump & flow rates being bottle necked.

 

A night time setup of 2 degrees & operation 24/7 would have these 2 rooms short cycling the ASHP all night & rest of the rooms only needing 1 top up a night. 

 

That being said on average nights - mid single figures no real issue. 2 x 4 hour chunks sitting in the Cosy periods is enough to keep all rooms at 20 degrees and the 'cold bedrooms' around  18 degrees during daytime and  a degree or two lost over night. On very cold nights we need to run for c10 hours to achieve the above, then see temps flow as you'd expect.

 

All of this is done with a flow rate of 28-32 degrees, hence debating flat lining the flow rate at 37 degrees during Dec/jan to keep us warm during the day & maximising cosy cheap rate of 16p and dumping more 'raw heat' into the slab to coast through the real cold snaps.

 

I have lifted up the Weather comp from 2 degrees to 4 degrees (i think).....would a compromise be to lift it up to say 6 degrees? I presume this would lift the flow rate up a few more degrees on the low end, but still have a sort of weather comp to help efficiencies on milder days?

[SteamyTea]

5 hours ago, Andehh said:

caused by it being a sprawling bungalow with very very high ceilings (3.5 to 4.5m throughout)

As warm air rises, have you checked the air temperature up there?

You may find a ceiling fan can shift enough to raise the temperature lower down.

You could try it out with a desk fan first if you have one.

[Marvin]

1 hour ago, JohnMo said:

Mine has a sump heater, and antifreeze, plus below 5 degs it circulates on and off anyway so no mention anything special.

Hi @JohnMo 

 

Yes my comment was if you were turning it off completely....

 

[Marvin]

1 hour ago, Andehh said:

I have lifted up the Weather comp from 2 degrees to 4 degrees (i think).....would a compromise be to lift it up to say 6 degrees? I presume this would lift the flow rate up a few more degrees on the low end, but still have a sort of weather comp to help efficiencies on milder days?

Hmm.. Hi @Andehh

Not sure if the figure you are changing allows for undershoot or overshoot or both....  Think this will depend on the ASHP model. I may be confused...

 

If your floor takes along time to heat back up, personally I would keep the temperatures tight i.e. as soon as the floor slab loses temp reheat, otherwise it would take a long time to reheat??

 

It may also be the lack of a blending valve that's causing you challenges. Thinking how turning all those different zones on and off would effect the return temperature I wouldn't be surprised.

 

Also how are you measuring the temperature in the bedrooms? Surely the air temp is what you want to know?  If the heat from below was heating the air above surely the bedroom heating would only supplement the air temperature from below??

 

What happens when all the zones shut off??

 

Marvin.

 

 

Edited December 7, 2023 by Marvin
further thought

[Beelbeebub]

You can usually unzone UFH fairly easily by unclipping the actuators (normally on return).  The zones are then always on. You can adjust the heating to each room by tweaking the flow rate.

 

I unzoned my house (admittedly fairly open plan) and the UFH runs much better.

 

Also a ceiling fan works well to move the warm air down to ground level. We havea 4.5m high lounge with a mezzanine. When we ran the wood burner we would hit 28C upstairs and 23 on the sofa. Now we turn the fan on and downstairs gets warmer immediately 

[joth]

I recently turned off WC on my ecodan, just during the Octopus Go cheap rate window. Full explanation in the thread linked below. This is extremely effective in reducing costs (or actually, attaining a more comfortable temperature during cheap rate only) during colder days.

 

 

 

[andyj007]

i run my grant arona  10kw heat pump, flat out  , between 12.am and 5am using cheap over night electric..  during that periord at about 0-3 degrees it uses 10-14 kw of power.. 

my thermo stats are all calling for heat higher than it will ever reach .. its just pumping heat into the floors ..  i have the weather  comp set at 50 degress at -3 external ..  this is into my buffer tank , but i have recordeded retirn tems of 40 degrees from teh underfllor loops..  i designed my house to run at Under floor flow temps at 35d at external 3, but this would be leaving it running all the time ..  and it works perfectly, , but its way more cheaper for me to utilse the overnight cheap rate and charge up the floors as much as i can for teh 5 hour period then turn it off  (cost to last year are about a 1/3 )

I have a large 4000 sqft house. all with under floor heating .. during this perior   we heat bathrooms, kitchen , family room , living area .. ( bedrooms dont require heat..they stay warm)  

the charge into the floor make the whole  house snug and warm .. we may light  log burner in the evening but this is more creature comfort rather than nessesity..

at the same time over night we charge our 10kw batteries ,,  this mostly enough to run our house , do our hot water  via teh heap pump and electric cook..  if we get a bit of sun its enough to boost the battery by 30% (7.2kw 5 degree facing west rray)  to last out till the 12am charge time.. if not and we do a big electric cook we may need  couple of imported kw.. 

House is new, i(designed by myself  )contemporay design, open plan iving areas  with solar gain in winter if its sunny ..  floors are  covererd in either amtico , tiles with carpets in bedroom.. (wood floors what ever they are are just terrible for low grade under floor heat efficiency we learned that mistake the hard way in our last house  )  

we basically pay about £2-2.30  - britisg gas 0.09p kwh  (standing charge aside) deending on temp say 5 degree or under to heat and run our 4000 sq ft house per day .. keeping it super comfy toastie thsi way.. we only really need to heat november / december /jan feb march..  

if you woudl like any more details or soe energy graphs  ask away, but using over night to pre wrm your house works brilliant, teh more isnulation and draft proofing you do to retain that heat then it has every chance of being your only heat time required..

kind regards

Andy 

 

 

Edited December 9, 2023 by andyj007

[ReedRichards]

4 hours ago, andyj007 said:

i run my grant arona  10kw heat pump, flat out  , between 12.am and 5am using cheap over night electric..  during that periord at about 0-3 degrees it uses 10-14 kw of power.. 

 

You get up to 14 kW out of what is nominally a 10 kW heat pump?