Octopus ASHP

ninjaef

Well, what can I say. Great service, lots of it, but issues are not getting resolved. 

OCTOPUS ENERGY AIR SOURCE HEAT PUMPS

been through the rigorous process to installation, and had all my rads replaced,HW tank installed, super friendly staff. Electrician was a nightmare.. ruined a lot of deocr.

Notwithstanding, main problem i have is in my main bedroom, north facing, bungalow...the temp doesnt get above 18.5C used to be 17C.but after complaining, fair doos , octopus have visited four times , balancing rads, recommissioned system, inspected pipes and pump ... but still same prob.

the rest of bungalow heats up lovely,but i had to turn the TRVs down to favour the main bedroom  Result..slight difference as i say, it now gets to 18.5 AFTER FIVE HOURS  but now rest of house takes FIVE hours  to go from 17C to 19C when it used to take two hours. and i can't get main room above 18 5C.

heating is set for 17C all day except 4am to 7am and 1pm to 4pm when it is so to 19C.

ambient temp is 10C

mods in tried to no or little effect 
1.The heating emitters was set to FAN COIL so I changed that to RADIATOR.
2. WD heating curve was set to 50,25,-7,15 i changed to 50, 28, -7, 23 to raise leaving tempt by 3C at ambient temps above 10C
3. Turn down all other TRVs from 5 to 1 , brrr cold hone

help 

tacpot12

You need a Heat Geek to review Octopus' work, and configure the system correctly. It sounds like the radiator in the bedroom (or the pipes supplying it) are too small or there is a blockage, but I'm not sure they need to be increased - 18.5C is hot enough for a bedroom, and hotter than recommended for a good nights sleep. (16-18C is recommended).

I wouldn't turn down the TRVs in the rest of the house if they were working correctly and the rest of the house was heating up as expected. The problem is just in one room, and a throw over the bed should be enough to see you through until the source of the problem can be fixed. 

If you have legal expenses insurance as part of your home insurance, you could talk to the Legal hlepline to get advice about getting an expert in, and sending the bill to Octopus. There will be a legal process to follow before you can do this, so take advice about how you do this.

ninjaef

what is a "heat geek"

i don't want to go legal just yet. octopus are trying.... albeit not resolving.

in regard to your comment about 18C being comfortable....NO , you are not sat in the room and its used through the day dor reading and quiet space. 17C ok for sleeping but not when its used IN THE DAY for resding, writing, and relaxing to radio.

ninjaef

I was hoping that someone could offer practical advice please

Scot_39

ninjaef said:

Well, what can I say. Great service, lots of it, but issues are not getting resolved. 

OCTOPUS ENERGY AIR SOURCE HEAT PUMPS

been through the rigorous process to installation, and had all my rads replaced,HW tank installed, super friendly staff. Electrician was a nightmare.. ruined a lot of deocr.

Notwithstanding, main problem i have is in my main bedroom, north facing, bungalow...the temp doesnt get above 18.5C used to be 17C.but after complaining, fair doos , octopus have visited four times , balancing rads, recommissioned system, inspected pipes and pump ... but still same prob.

the rest of bungalow heats up lovely,but i had to turn the TRVs down to favour the main bedroom  Result..slight difference as i say, it now gets to 18.5 AFTER FIVE HOURS  but now rest of house takes FIVE hours  to go from 17C to 19C when it used to take two hours. and i can't get main room above 18 5C.

heating is set for 17C all day except 4am to 7am and 1pm to 4pm when it is so to 19C.

ambient temp is 10C

mods in tried to no or little effect 
1.The heating emitters was set to FAN COIL so I changed that to RADIATOR.
2. WD heating curve was set to 50,25,-7,15 i changed to 50, 28, -7, 23 to raise leaving tempt by 3C at ambient temps above 10C
3. Turn down all other TRVs from 5 to 1 , brrr cold hone

help 

Firstly there is now an ASHP specific sub forum - where this might be better placed.

I am not sure - but isn't this simple a fundamental difference between ASHP and gas boilers - energy vs power - that perhaps no one has bothered to explain fully to you.

Energy (Heat) = (Output Power / Power) * Time.

For best efficiency ASHP should normally be operated at a lower flow temperature - but for longer.  Not sure about the specific recommended setpoints for the Octopus model / vs it's COP ratios.

A quick google of respective likely powers for a 3 bed semi

 

A typical combi boiler might have over 25kW power at peak demand for the heating circuit.

For ASHP

https://heat-pumps.org.uk/best-air-source-heat-pump/

Table suggests - a 3 bed semi - might need just  6-8 kWh output

And a larger detached 4 bed - might have 10-11kW effective output power.

Quite simply that means is going to take 2 or 3 times the time to supply the same energy - heat - as a typical domestic boiler.

OR if for example you need 30 kWh heat energy - to get a given space / house to a given temp - a 25 kW boiler can probably deliver that in 1.5 - 2 hour

But a 7kW output ASHP - would need in reality I suspect over 5 hours

(Gas boilers tend to derate / mark space on / off - gas burners quite quickly - often even within 1st hour.  Not sure about ASHP though)

So in short - the most probable solution is you simply need to run at the higher heat setting for longer to achieve it - starting the 19C set-point cycle earlier vs your required time.

PS

A TRV setpoint of 1 might be 10C (BG website - but valve model dependent) - and would make either the 17 or 19 C setting for the main thermostat / pump control -  null and void - in that room- as would switch off that individual radiator flow. 

Too chilly for most people - even for occasional use.

TRV 2-3 (again model dependent  but say 15-20C according to BG website ) should suffice for most in unused / used space - 3-4 if BG 20-25 TRV scale like it toasty warm (or need say NHS / HTA 21 style or even higher for certain ailments / ages) should be more than enough in room / space where master thermostat located - to return control to that over TRV - if set to 19C max.

ninjaef

thank you that's really insightful and educational.

so, are you postulating that, to take the bungalow room from 17C to 19C+ could well take more than 5 hours?
and. 
that it's "normal" for the rest of house to be"fine" apart from this main room that remains stubbornly cold?

you do seem too know what you're talking about so I'm interested to learn!

Reed_Richards

A Heat Geek is somebody who had paid money for a training course in ASHP installation from an organisation called Heat Geeks.  Some people on the forum place huge faith in them; personally I'm sceptical.  Your problem could take time and patience to fix so it would be better if you can get Octopus to do it as part of their package than to pay somebody else by the hour.

Adjusting the TRVs isn't going to solve your problem, that will just make every other room colder.  If you want to try to balance the system you need to adjust the valves at the other end of each radiator; this will reduce the flow rate through the radiator.  But if Octopus has already tried this then you would be lucky to succeed where they failed.

This thing about the power output difference between a heat pump and a conventional boiler is a complete red herring.  Your heat source can only heat the water up to a safe operating temperature no matter how powerful it is.  This might take 15 minutes with a boiler and 30 minutes with a heat pump but after that it's a completely level playing field.     

If one radiator is under-performing whilst all the others are okay then either that radiator is too small (i.e. it doesn't have a big enough surface area) or the flow rate through the radiator is too low, which would imply that there is an obstruction somewhere (if the radiator has been correctly sized).    

FreeBear

Reed_Richards said: If one radiator is under-performing whilst all the others are okay then either that radiator is too small (i.e. it doesn't have a big enough surface area) or the flow rate through the radiator is too low, which would imply that there is an obstruction somewhere (if the radiator has been correctly sized).    

Have seen problems before where multiple radiators are plumbed in on long runs of 15mm pipe. There is a limit as to how much water (and in turn, amount of heat) can be pumped through a pipe. It may be a case that @ninjaef needs to replace some of the pipes with bigger ones.

I replumbed my CH system last year using 22mm for the main feed & returns, and kept the final connections to the radiators as short as possible with 15mm pipe.

Scot_39

I have seen a few examples here of 1/2 hourly meter stats here showing gch boilers can easily consume over c10kWh energy in first hour and upto 20 kWh in first 2 hours.

See just one of many examples here by no means extreme

https://forums.moneysavingexpert.com/discussion/comment/79569437/#Comment_79569437

Assuming thats purely heating - a bit of a stretch admittedly - but also note its entirely possible thr boiler wasn't in fact on for tge full 1st half hour slot - so it's actual power output even higher - as would seem reasonable - but total energy under stating it.

About 11.5kWh in first 2 half hour slots - and note that was despite a 5kWh warm up hours earlier -  a 7kWh output ashp needs c1.6 hours to deliver that energy - so already 40 min behind.

19.5kWh in first 2 hours a 7kWh heat pump now 50 mins behind  hrs if the radiators can support it at potentially low flow temps etc..

and 24 kWh in first 2.5 hours -  7kW ashp needs 3.4 hours - so nearly a whole hour behind.

Before settles to lower then even lower after 3-4 hrs so maintaining output of c1.5kWh per half hour - so ashp can then start to catch up.

But of course there's no guarantee that an ashp of that rating would have been chosen for that property either - it was just one sites estimate of likely power for a 3 bed semi.

But thats only the boiler aspect.

Hardly surprising when you think I I not only raising 10s of litres of water but 100+ kG easily in most homes of radiator metal in that time.

The first radiator I checked detailed specs on a reasonable but not huge 600x1200 double - 2kW effective power at delta T of 50C ( that needs 70C ave water temp input to output) for a 20C room  - contains over 7l water so 7kG and mild steel body etc weighs c35kg.  Multiple that by 3 or 4 or whatever and then calculate energy required to lift that mass of metal and water volume by say 45-50C to get to operating point you might just understand that initial energy requirement.

The linear 30kWh divided by rated is simplistic - but was simply to demonstrate the point - that if you have less power - it rakes longer to deliver the required heat.

And one of the most significant differences likely your experiencing could well be the flow temp setpoint of old gch boiler vs Ashp floe setpoints required for efficiency.

Do you know what they are nominally now (probably variable by comp curve) and were before when you measured your timings for gas .

And the impact that has on effective radiator power.

Viessman for instance recommended 75C.  Govt suggested we all drop to 60C last winter at height of crisis etc

That first radiator spec I checked quoted c2kW power at delta T of 50C - thats about matching a reqt for around 75 C boiler output in a 20C room.

An ASHP might for instance quote its efficiency and nominal output performance at say 7/45C (outside vs flow).

If were to fix at 45C then essentially radiator delta T drops from 50 to 20C - so greatly impacting the effective radiator power - again from online data source not verified - to 0.328x2kW - 0.656kW.

Or in other words needing three times as long to heat the same space to a given temperature if even gets there it wont if room losses exceed that effective power.

And the problem with increasing many heat source pump flow temps - is it impacts efficiency - and so in limit output power -  in one example online looking at one ashp brand data  -


https://www.firepowerheating.co.uk/heat-pump-outputs-explained-pumps-help-and-advice

Again that may be atypical and might have own reasons for using etc - but it's supposedly actual data..


Moving from 45 to 60C flow - dropped COP ratio from 3.53 at 7/45  to 2.48 at 7/60,  and to maintain at 60C on a sub zero day when it might really be required say a rare  -2/60 - drops it back to 1.81.  Costing nearly twice - twice the electrical input you pay for - per kWh of actual heat output.

And that article interprets the powers tabled  drops the potential  power for that model from 12.4 kW at 7/45 to 8.7kW at -2/ 60.

So either radiator powers drop at lower flow temps or max available power and efficiency drops leading to increased running costs in that example.

It's why many may need to significantly resize rads and improve home insulation to maximise performance of ashp.

Less power for whatever reason - in this case boiler and / or radiators = longer running times to supply the same energy - in this case to raise room temperatures.

Basic physics.

Edit : if the problem with the one room not reaching setpoint cannot be easily resolved by adjustments and you don't want to fit a bigger radiator - you could consider a radiator fan - which aims to boost air flow  / heat exchange.

MP1995

Slower (lower flow temp) for longer is the mantra for heat pumps so extend your heat times.

You won't get that blast of gas firing full blast and a radiator you can't touch.

Reed_Richards

There's a lot of fallacious thought around heat pumps.

If you have a gas boiler and old radiators that are sized for 80 C flow and 60 C return then if the heating was off and the water in the radiators was say 15 C then the temperature needs to be raised by 65 C to get the leaving water temperature to 80 C.  Suppose the boiler outputs 20 kW and the volume of water in the system is such that it takes 30 minutes to reach temperature.  So you used 10 kWh of gas/oil in the first half hour.  The boiler does not want to get any hotter so after that it will modulate down its output or cycle to maintain the 80 C leaving water temperature (or 60 C return water temperature depending on the mode of control).  The radiators are now at their maximum output.  If the house is still cold you can't warm it any faster.

If you have a heat pump and radiators designed for 50 C flow and 40 C return but the same volume of water in the system you only need to heat that water up to 50 C, so the temperature needs to be raised by only 35 C instead of 65 C to get the maximum output from the radiators.  Lets say it's a 7 kW heat pump, at maximum output it will take 46 minutes to get the radiators up to their maximum output.  So that's 16 minutes longer than the gas boiler.  But after that the radiators are at their maximum output.  If the house is still cold you can't warm it any faster.  But these are bigger radiators and if correctly sized then their heat output will be the same as the old ones that were replaced.  So now you are not warming the house any slower than you were before

Some modern gas boilers have a feature called Load Compensation.  Let's assume you have a more modern system with radiators designed for 60 C flow and 40 C return.  Your gas boiler still maintains a 20 kW output but it only needs to raise the temperature by 45 C so that only takes 21 minutes.  But the room thermostat sees that the room has not yet warmed up completely so it communicates this to the boiler and the boiler takes the water temperature up past the normal operating point, maybe as high as 80 C.  This boosts the output of the radiators beyond their normal maximum and heats the room more quickly.  Now the boiler will stop condensing for a while whilst this is happening so you are sacrificing economy for speed of warming.  But if you want to warm up a house really fast then get a modern gas boiler and make sure your heating controls support Load Compensation.

Actually, some heat pumps can do Load Compensation but it's much less common than with gas boilers and there usually isn't so much headroom to raise the water temperature beyond its normal maximum.