Discussion ... ASHP(Air/Air) with Solar pv ....

mmmmikey

JKenH wrote: »

So I’m not the only one who stands outside watching the meter to see what time it switches to E7.:).. in my case it is 08.36.

It’s my first year with ASHPs and second year with solar. Last year nothing got switched on if the sun wasn’t shining (until the wife protested) but this year I am going to try living a normal life. I got my first ASHP at the end of January and second end of April and am still working out how to get the best out of them. Like you, in the spring, I was operating the kitchen unit on the inbuilt timer to come on at 6.30 am (yes we do have PV at 6.30 from late April) to get the house warm for breakfast then only using them during the day and evening if we felt cold, letting the IBoost take any surplus. Yesterday was a bit of an experiment as It was cool enough to run a heater all day and had limited solar - just over 4kwh (almost typical winter day PV). As a result the IBoost only saw 0.17 kWh and as that had followed a couple of below average days I wasn’t sure if we would have enough hot water this morning for showers but we did - just.

The plan for this winter is to run the ASHPs most of the time (using as much free solar PV as possible) in preference to oil CH and top the water tanks up overnight with E7. That means the IBoost will only be useful on sunnier days but it is cheaper and more efficient (less heat loss) to heat the water overnight and use my ASHPs during the day. As we have a big house and only 2 ASHPs I will probably have to run the oil CH for an hour in the morning and one in the evening as well.

I noted that you were only assuming a COP of 2.4. Is that something you have calculated? The COP of my 3.5 kw heater is supposed to be 4.0 and the 2.0 kw one 4.3 but I have no means of checking if this is true in practice. ( I seem to recall reading they are more efficient when operating at low power and when the temperature differential to outside is not too large).

At an efficiency factor of 2.4 my daytime use would be slightly more expensive, at 6.25 per kWh, than oil at, 5.2p per kWh, but maybe cheaper once I factor in the cost of powering the CH pump. I like your point though about the targeted nature of the heat from ASHP as my wife loves to sit directly underneath the unit and have the vanes forcing the airflow straight at her.

Today with clear blue skies (at the moment) one ASHP is on, building up core temperature, along with the washing machine and the IBoost is still getting fed. Happy days.:)

I established the COP using a technique known as guessing


As you say, all quite absorbing from a technical perspective. Like you, I am starting to try and balance reducing costs with staying comfortable - it's all too easy to get obsessive and only use the heating when the sun is shining, etc.

JKenH

Update; over a week I have run my 3.5kw ASHP for heating 50.9 hours and used 21.1 kwh - an average of 415w per hour on an Eco Automatic setting with the thermostat set at 23, 24 or 25C. I am assuming that as the ASHP is mounted just below the ceiling it will take the temperature measurement there. The equilibrium room temperature achieved with door open measured 1m off the floor has been on average 21C (max22C) from a starting temperature of 17,18, or 19C first thing in the morning. Outside temperatures have ranged from 1.5C at 8am(coldest) to 17.5C at 4pm (warmest).

Edit; room size is 38 sq.m, 91 cu.m

joefizz

JKenH wrote: »

Update; over a week I have run my 3.5kw ASHP for heating 50.9 hours

I might have missed this but is the automatic setting timer related or manual?



Ive been experimenting with my ashp but havent been getting enough solar this last week to get above 40% charge mind drive the ashp.

The week before I was just firing it up for between 1 and 3 hours manually about 8pm but with the temperature set high to 27C, so pretty much running all the time. It feeds the long corridor in a bungalow and with all the doors closed it was enough to keep the bedroom (next to the ashp output but not blown air into it - if I had my time again ;-) ) at above 20C. Really just using the hallway as a large heat store as its very well insulated with no outside walls (triple layer of thermal curtains at front door).
Ive been using it manually as only turning on when battery is above 70% and as a result have had to put the oil on for 1/2 hour around 6am to bring the heat up and heat enough for a shower (not enough in the battery now to do both and unusual amount of work so higher energy use than normal).


Ive considered just letting it run on a timer like that but your figures look really good so might try lower temperature for longer. Eventually Im going to run it on a percentage of battery feed automatically but I might die before I get round to coding and setting all that up!
Mine is a cheap one so its either on or off with a remote which can delay start for a number of hours or turn off after a number of hours.

JKenH

The ASHP has several timer functions but I have been operating it manually. One mild day it was only on for 1.5 hours in the evening, on other days it ran for up to 12 hours or so continuously.

The auto setting relates to the temperature control/fan operation adjusting the heat output to achieve the selected temperature. The Eco function initiates a soft operation to suppress the power to avoid excessive cooling or heating.

Below is a link to the technical manual if you are interested.

https://condex.bg/wp-content/uploads/2016/manuals/SRKxxZS.pdf

Edit: Page 91 gives the COP figures at various external temperatures with a maximum of 7.8 at 12C outside and 20C inside (if I have understood that correctly). It has been a more or less consistent 12C outside today and over 8h15m the unit has used 2.1 kWh, an average of 259 watts.

joefizz

JKenH wrote: »

Below is a link to the technical manual if you are interested.

https://condex.bg/wp-content/uploads/2016/manuals/SRKxxZS.pdf

Thanks, definitely interested!
I'll give it a go at a lower temperature,manually starting for longer, tonight. Although the weather forecast doesnt look good for solar charging the battery this week, conversely due to the cloud cover the temperature is higher so I should need less!
I'll see how it goes.

mmmmikey

joefizz wrote: »

Thanks, definitely interested!
I'll give it a go at a lower temperature,manually starting for longer, tonight. Although the weather forecast doesnt look good for solar charging the battery this week, conversely due to the cloud cover the temperature is higher so I should need less!
I'll see how it goes.

Please let us know how you get on.

I've been experimenting with my cheapo Chinese ASHP over the last week or so and found that if I let it run on Auto, every now and again it ramps up the outside compressor to the point where the new battery system can't cope with the surge and fools itself into thinking the batteries are discharged. So for me, putting the ASHP on a low setting an hour before I need the heat works best.

btw mine is a Midea Blanc and some of the features can only be accessed if you install the optional WiFi link and app - this gives me access to one on and one off time per day. tbh I now wish I'd spent a bit more for a higher quality unit with better controls, but happy overall.

JKenH

mmmmikey wrote: »

I now wish I'd spent a bit more for a higher quality unit with better controls, but happy overall.

If you are running yours most of the time on solar and battery the savings from a more sophisticated unit would be a long time coming.

Currently mine is running at about 670watts so it isn’t a steady 250 or 400 watts all day long.

Looking at it purely from a savings point of view, more initial outlay equals longer payback time. I don’t use the unit in the kitchen half as much and a cheaper one would probably have been fine for a quick blast in the morning and at mealtimes but maybe as winter sets in it will be on all the time like the one in the lounge. The colder it gets outside though the less efficient the units are - at 2C the COP for mine is 4.65 and at -7C only 2.65 so it will be cheaper to run the oil central heating if it gets really cold.

1961Nick

JKenH wrote: »

If you are running yours most of the time on solar and battery the savings from a more sophisticated unit would be a long time coming.

Currently mine is running at about 670watts so it isn’t a steady 250 or 400 watts all day long.

Looking at it purely from a savings point of view, more initial outlay equals longer payback time. I don’t use the unit in the kitchen half as much and a cheaper one would probably have been fine for a quick blast in the morning and at mealtimes but maybe as winter sets in it will be on all the time like the one in the lounge. The colder it gets outside though the less efficient the units are - at 2C the COP for mine is 4.65 and at -7C only 2.65 so it will be cheaper to run the oil central heating if it gets really cold.

I noticed that on the very cold days when the COP isn't particularly good, there's often a very clear sky, so even in January there can be a reasonable solar contribution to running an ASHP.

Martyn1981

mmmmikey wrote: »

btw mine is a Midea Blanc and some of the features can only be accessed if you install the optional WiFi link and app - this gives me access to one on and one off time per day. tbh I now wish I'd spent a bit more for a higher quality unit with better controls, but happy overall.

That was my initial thought after going for a quite basic LG model, not the higher spec'd option.

But after a while I came to the conclusion ... Meh!

During the shoulder months you probably have an outside temp around 10C, so potential COP around 4. So even running 100% on import, it'll work out Ok against gas price.

From there, assuming some PV, you win anyway.

No argument that if only for personal satisfaction I'd like to be able to run it in line with PV generation, but economically, I'd probably never get the investment back, and if you want/need the heat, but don't have enough gen, and don't want to heat the whole house, then you'll run it on some import anyway.

joefizz

mmmmikey wrote: »

Please let us know how you get on.

Not great!
Well it was ok the first couple of nights, outside temperature 10-12C turned temp down on the electriq ashp to about 24C,didnt do much other than blow air around, 25C is when it kicked in so thats probably the level for where its situated.
I didnt measure kWh but it was using about 5% of battery per hour (9.6kWh battery) so in the same ballpark as earlier postings.
Little sunshine here earlier in the week so battery didnt get to more than about 60% but 4 hours was enough to get the house to a temperature (bedroom 20C) that would last until the oil kicked in at 6am for 20 mins.
Weds night, almost full battery, but less than 5C outside, just couldnt get the ASHP going enough and ended up sticking a 600W halogen heater in the bedroom for a bit and putting the 60w electric under blanket on (so much for testing each of those in isolation).
Last night battery was about 50% at sundown and outside temp again around 3C so gave up and put the oil heating back on.

That might be me for the winter now.
I'll maybe insulate above the ashp path a bit more cut down the differential losses but given that Ive a drimaster air flow system pumping colder air in now its probably had its time for the year for my usage at least.
I could of course pay for electric, but wheres the fun in that!