Water "Battery" 20kwh+ of extra storage

graememk

A few of you know what I've been up to as a side project/experiment (with the bonus of burning less stuff and exporting less)

Is to put a buffer tank in my heating system. A 500L one, plumbed (and wired) in as if it was a oil boiler.

Wired in such a way that if the tank is cold it can fall back to oil.

I prefer to maintain a temperature in the house than let it cool and then blast it but that's by the by. I also have a tado heating controls installed so only the rooms that need heat will call for heat. all rads except bathroom & ensuite are on smart trvs.

Now for the fun bit some pics and graphs

500L joule stainless buffer tank, there is dual immersions but unfortunately the bottom temp probe is below the immersion.

Got the tank heated to 55c, used about 21kwh, (still haven't the full monitoring built for it yet)

A call for heat occured at 9am and (actually I think continued for the rest of the day, there was a trv complaining about a low battery and might be full open)

But it's interesting how quickly the tank mixes and not all of the heat is taken out of the water before it returns.

This was the rest of the day. About 16kwh of heat has been put into it.

Still learning and working out the ins and outs of it, may put a flow meter on it, then I could work out the kwh out of it.

Its been a fun project and this is just the start of it.

Also as a side bar, my night rate is currently 5c.. so that's a 1/3 of the price of oil currently! (Its 1.50 currently at the pump and I don't have a new boiler never mind a condensing one!.) We shall see what rate I change to in August.

Got a bunch more temperature probes so should be able to read the temperature of the flow and return water, and maybe get one in that dry pocket above the bottom immersion.

Ubbquittious

How do you heat it? Just electric? Is it something that you could heat using solar tubes as well?

graememk

https://www.boards.ie/discussion/comment/119224835#Comment_119224835

Immersions. But yeah if you got a tank with a coil you could use solar tubes.

But I could stick up another 8kwp SW facing without much hassle. But about 100m away from the tank.

Ubbquittious

https://www.boards.ie/discussion/comment/119224847#Comment_119224847

that is a good bit away. otherwise you'd probably get more bang per m2 with tubes. I like the idea, its something u could combine with solid fuel stove or heat pump. Do u have a means of transferring from the buffer tank to the hot water tank for the taps?

graememk

https://www.boards.ie/discussion/comment/119224902#Comment_119224902

I have plumbed it that I can charge it from the solid fuel stove in the house. But didn't want to complicate the main post with that. This tank is in the garage and reusing the existing heating pipes, I can "back feed it" but that automation is still to be built/figured out but the function/hardware is there. - we still have turbatory rights too

As for a heatpump, yep I should be able to connect one directly to the tank, HP heats tank, and then house uses it as needed. That's the theory anyway.

House when running on the stove generally runs best at a lower temperature rather that cycling on and off when hitting 65 or something, - controlled now via automation. A sharp rise in temperature is enough to trigger it and it stays on for longer than a normal pipe stat would. (Pipe stat still is there as a failsafe)

As for heating the DHW, yes I could but I just run the immersion in the DHW (which is also heated via the solar tubes and the stove). Currently not connected but it is possible.

Fantana2

Interesting project! In winter how long do you think the a full tank would keep the heating running for? Was it a TRV issue or have you the heat on this time of year? We wouldn’t normally have the heat on at all from May to end September.

graememk

https://www.boards.ie/discussion/comment/119254213#Comment_119254213

Heat is "on" mainly for testing but oil is switched off.

No idea how long it will last.. depends on how cold the house is I suppose. I'll find out when I actually need heat!

the_amazing_raisin

I'd love to do something similar with a heat pump, use it with a large buffer tank to pre heat water on the night rate for space heating during the day

With a reversible pump it could also pre chill the tank in summer using excess solar to help cool the house in the evening

manonboard

Very interested project. Thanks for sharing!

graememk

@SD_DRACULA

Just came across this :

https://youtu.be/NOUDbx1tX-A

Basically it's a thermal battery 40kwh.

graememk

A bit more digging

Charge rate of up to 9.3kw

Cost, gbp : 6k, + install of 1.5-2. so about £187/kwh

3.6kwh pylontech 1300 - €333/kwh

aliexpress cells 32, looking like about 3k now, 20kwh €150/kwh, + bms + building costs

Hot water tank, 500L about 20kwh. coming in around 2k (inc eddi) €100/kwh + my time

bunderoon

https://www.boards.ie/discussion/2058250939/water-battery-20kwh-of-extra-storage

Would you mind sharing the links to the temp probes and circuit board you have? I was planning on using my old pi3B, a '1-wire' probe along with https://www.digitemp.com/.

I have just a basic digital display with wirey temp probe stuck into the top sensor. I see that yours has a white plastic grommet/connector of some sort.

Are these what you used and then pushed the probe tips into them?

Gerry

Very interesting. I wish I could fit enough panels to make something like this a reality. Could I ask how you've wired the immersions for control.. do you have a contactor for the pi to trigger?

graememk

https://www.boards.ie/discussion/comment/119394123#Comment_119394123

yeah the plastic white bit is just a normal stuffing gland/compression gland that screws into the thermopocket.

Im using the ds18b20 temperature sensors. https://www.amazon.co.uk/AZDelivery-Stainless-Temperature-Waterproof-Raspberry/dp/B07KNQJ3D7 but need to cut the heatshrink off to fit into it. the gland stops it from coming out. the probes fit prefectly into it.

The circuit board is just some protoboard with some headers and a 4.7kohm resistor on it. Its running on an ESP8266 wemos d1 board with a0.66" oled screen. The code is something that i threw together.

https://www.boards.ie/discussion/comment/119394222#Comment_119394222

Simply, an eddi runs the immersions.

the_amazing_raisin

@graememk I'd love to hear an update on this project. Have you had need for the heating yet and did the heat battery provide much heat before you needed to switch to oil?

graememk

Haven't had much need for heating just yet. But have been able to cycle it a few times so far it has been a nice boost on the bad days after the good. No proper good runs.

Not put it to the test yet with a full house load. Although running the flow temperature at 45 c out of the tank is working well. (Testing the viability of a heatpump)

Haven't fallen back to oil .. Well there isn't any in the tank 🙂

I have lit the stove the odd evening and can successfully heat it to about 60c, going past that is difficult as the open rads in the bathroom leak heat. 2 bathrooms and a towel rail. Thinking of dropping the 2 bathrooms to smart TRVs and leaving just the towel rail open.

Easy to cycle it down to 30c. Possible to go colder, but house needs to be colder.

Stove is rated at 6(wood)-9(coal) kw to water, depending on the fuel.

When the colder months roll in, stove is usually running 24/7 but just ticking over most of the day and closed down overnight.

But planning on heating the tank on night rate to give a boost in the morning. (Currently 2x cheaper than oil)

I'd say I'd need another 8kwp of panels to be able to heat the tank every day in Sept + Oct.

TLDR no proper test yet, solar can heat it, and I'd estimate a full house load it would last 2 hrs but majority of it goes in the first hour. Winter heating will be solid fuel and night rate electric

graememk

I have sensors on the tank top middle, one between middle and bottom and bottom.

You can "see" the tank depleting as the heating is running. But tends to heat all at once (if using the bottom immersion)

Also have sensors on the flows out of the tank so I can see the flow out of the tank, the mix out and return.

Considering adding a motorized valve to allow the bypass of the mixer valve when temps are below say 40 but unsure if it would make any difference,

the_amazing_raisin

So I'm trying to make sure I've got this right in my head

You've got a big buffer tank which is just a 500l direct tank with immersion heaters

The immersion heaters heat the tank from the night rate or solar PV

Then when your thermostats call for heat it starts the circulation pump which cycles the water from the buffer through the rads

If the tank water is say 50C and your oil boiler is set to 45C then your boiler doesn't kick in because the water is already hot

Then when the tank is "depleted" the oil boiler starts up

Do you then use valves to zone out the buffer, or does it get "recharged" by the oil boiler as well when it heats the rads?

I'm contemplating doing something similar with a heat pump at some point and just trying to understand the system

Punchin A Keyboard

The heat geeks do recommend a buffer tank as part of a hp install

mickdw

Alot of people here in mayo have reverted to turf burner furnace in shed for central heating, removing oil burners. They are though doing it without buffer so little to no control over heating.... It fire is strong, heat is strong and no heat in the morning til you get the fire going.

A buffer tank would make that a very good system too being able to release heat to the house in the mornings and soak up that unneeded heat in late evening.

Turf is plentiful here.

the_amazing_raisin

https://www.boards.ie/discussion/comment/119660129#Comment_119660129

True, but typically it's around 50l, not 500l like @graememk has

the_amazing_raisin

https://www.boards.ie/discussion/comment/119660182#Comment_119660182

I've seen a few stove installers with recommendations to install like a 300l buffer, pretty much to absorb the excess heat and release it back slowly

Nelbert

Would this be doable with a heat pump with the internal unit having a 200l tank already built in?

Is it purely a plumbing thing or would it needs it's own pump?

Electrics I'm fine to DIY but water I don't like...

Would be potentially interested in this as a way to avoid running the HP on day rate over winter.

graememk

https://www.boards.ie/discussion/comment/119659685#Comment_119659685

Yep its a Stainless Steel Direct buffer with 2 immersions. no coil, just has 6 1" fittings on it with a few 1/2" for thermostats/etc

I have a tado, but yeah when there is a call for heat, That signal is sent out to the "plant room/energy room/ whatever , Its a room in the garage. So a bit of a leak wouldnt be the end of the world during setup/install.

There is a thermostatic mixer valve on the outflow from the tank and the tank has its own pump.

It is plumbed in parallel to the oil boiler with one way valves to prevent the water going the wrong way.

Currently cannot heat the tank from oil, but with a bit of wiring and another relay I could do it, but theres no real point, better to just heat the house with it.

There is a manual thermostat on the buffer tank so if it drops to below 20c, It switches the call for heat from the tank pump to the oil burner and its pump. It will work even if the automation crashes/fails.

I have tado TRVS on all rads except the bathroom + ensuite, Only really need 1 open radiator for the stove. Might consider changing a valve or 2.

I have a few other pipework/valves to allow back feeding from the stove.

Explained any better? Tank is essentially working as a oil boiler.

graememk

Stove + buffer would be v good, house can call for heat when required, can use it later in the evening/morning.

Buffers with heatpumps seem to help with flow + cycling but with a cost of less efficiency but in reality it wouldn't store that much heat, 500l moved 50c - 30c is about 10kwh of heat.

Would nearly be better to just use batteries.

the_amazing_raisin

https://www.boards.ie/discussion/comment/119660825#Comment_119660825

Gotcha, so the two are essentially like parallel heat sources. Sounds like a good setup being able to switch between the two and not have to lose a whole load of heat from the boiler to heat the buffer

the_amazing_raisin

https://www.boards.ie/discussion/comment/119660854#Comment_119660854

One of the main reasons you need a buffer with a heat pump is to stop the outdoor unit from icing up

Because it's cooling the outside air then condensation can freeze on the outdoor unit when it's cold outside

So it heats up the buffer first and when the outdoor unit gets iced up then it switches off the heating zones and recirculates the warm water from the buffer through the outdoor unit to defrost it

Also it helps to stop short cycling the heat pump and other advantages

I think if I was doing the heat battery idea with a buffer tank, it'd probably need to use the immersion heaters to get the water up to a higher temp. The heat pump probably can't get the water hot enough for it to be worthwhile

graememk

https://www.boards.ie/discussion/comment/119661129#Comment_119661129

I suppose If you were pre charging the tank with a heatpump on night rate, Even if your COP went to 2, its still twice as good as an immersion.

Had a call for heat at 8.. when we got home, possibly left the door open!

I think i might need to tweak the mix out, its running a bit high. Might stick another temperature sensor in the upper dry pocket. as the "middle" could be about 1/3 of the total heigt of tht tank. That was about a 20 mins run time.

graememk

Starting to get a bit colder outside, some graphs from this evening, I am now keeping an eye on calls for heat too.

Living room felt a little bit chilly so I bumped it the thermostat up to 21, that being said I'm still in a t-shirt and shorts!

Stove was not lit today, but all the air is closed on it to limit heat loss.

Not sure what "state of charge" the tank was in, as the middle temp sensor is below the halfway point. Maybe about 40%?

State of play in the house

graememk

Came across this Heat Geek Video.

If you think my setup is unusual, they are running an experiment with

Solar thermal, Sunamp, Buffer tank, Heat pump..

https://www.youtube.com/watch?v=pw4CiawIQgk

The jist is,

Solar PV heats the Sunamp, and DHW comes from that. When that is hot it diverts to the buffer.

Heatpump is connected to the buffer and that heats the space heating.. I think it uses the buffer then the heatpump takes over

If buffer gets completely hot, Its moved out to another storage in the garage, and then also can be moved back if needed to the buffer.

graememk

A further update.

It's working really well, I can either heat it from the stove (takes about 4 hrs, keeping the fire stoked), hard to get past 60ish. It's allowing load shifting, and I'd say more effective use of turf.

Or I've started heating it via the immersion overnight.

Been playing with the temperature in the living room too. Currently set to 22. Usual setpoint is 20/21. Only in the evening, setback rest of the day is 18.

Fire is lit but all closed down today. Bumped the temperature to 22 as I could still feel a very slight "chill" in the air...and I'm in shorts.

I have new window seals on the way for the windows (approx 20 yrs old, and can feel cold breeze at the window when it's windy)

Onto the data:

Put 12kwh into the tank last night and topped up with solar (charging the house batteries to 100% now every day, excess can go to the tank. Started this evening at 70+c.

The majority of the sensors are at bottom of the tank, and the "middle top" is just under the top immersion. Not sure how to monitor the top half of the tank.

You can see the tank being used up, and the heat requirements for the rooms in the house(ensuite window was left open!)

You can see the tado cycling the pump from the tank, only running a flow temperature out of the tank, using a mixing valve turned to 45c, this is my "virtual heatpump"

Rough estimates are looking like the radiators are oversized, having been upgraded over the years.

I basically have a electric boiler that runs on night rate.

graememk

It's got cold, hasn't it?

Was away for just under a week, maintained the temperature at 18c

Didn't want to try to lift the house from cold when I got back.

when it was mild, the 12kwh I was putting in it a night was fine.

When it got cold, it wasn't enough. It never got ahead. (Charging at 3kw).

So was able to run both immersions to heat the tank, that was able to get ahead. But used about 50kwh (would have been 6L of oil though!)

Although by time night rate rolled around again, the house was at about 17c (and dropping) tank was also at about 20.

Now that I'm home, the tank is heating the house in the morning. And also filling in the gaps when the fire dies down.(turf, from less than 2km away.. solar dried!).

Last night 34kwh was put into the tank.

Tank flow out temperature is set at 46c,

If I put a heatpump in, (would be looking at a propane one, as that has a better cop at higher temperatures) a 10kw one should be enough for my house, would be plumbed straight into the buffer tank. Cop of 3 should be obtainable.

Theorycraft, 100kwh of heat/day for nov-jan, 90 days.(no fire) 3000kwh of electric via heatpump vs 9000 using pure electric.

9000kwh, put into perspective you wouldn't have much..if any change from 1000L of oil.

House is lovely and warm. Occupants are not complaining 😆.

This is mostly an eddi install, not sure if it's on a buffer tank or DHW, but someone is a crazy as me.. but with a lot more funds!

https://youtu.be/y5bs5TOSSSw

graememk

As mentioned in another thread, and for the ones following (I'm not going to do a full install video a-la Gyln Hudson : https://youtu.be/bHsp7fDw_bg ) worth a watch.

I have a heat pump heating the buffer now, An ecoforest EcoAir+ 3-12kw. Its a R290 ones which can do 60+ for CH and 75 for DHW I think [ but at a cost of efficiency] Not the usual setup, but I'm tinkering with it. 1980's bunglow.

I heat the buffer, buffer heats the house. Currently the HP kicks in at a 5c drop (in a 500L tank). Allows me to keep my current tado system.

I have been heating to 60c overnight, precharging the tank, and the house before night rate ends. Last night was cold, it really hurt the COP, only about 2.4! Have been running the tank at 50c during the day these last few days but have backed it off to 46 today.

Currently running it all on night rate or battery. These freezing conditions, the fire is still on, but majority of heat is coming from the heat pump now.

The living room has been struggling to get up to temperature (without the fire). Rad is currently behind the sofa, with a bit of space but not great. It has never been an issue.. theres always been a fire, Never has been an issue before. While I did have oil, it wasnt used that much. maybe a blast in the morning/night I had never heated only by oil... Or my grandfather didnt either. Radiators have all been changed since the house was built, mostly double radiators now.

Living room radiator is possibly undersized. Going to experiment with radiator fans. More experimentation!

Follow along! : (room temperature is buffer temperature)

https://emoncms.org/app/view?name=EcoAir&readkey=82a75750e2f56ccdc7e96768b9776268

AmpMan

Am I understanding this correctly .

The CH water is just circulating through the coil of the buffer tank?

graememk

https://www.boards.ie/discussion/comment/121452016#Comment_121452016

No, The buffer tank water, is the heating water, and also the HP water. No coils.

edit:

when the heating demand is low, you can see the tank stratifying

If its freeezing outside, the HP will run its circulation pump to prevent freezing, this also will mix the tank

graememk

Rad is coming off tomorrow for cleaning if I get a chance. Suspect it's blocked up

bullit_dodger

https://www.boards.ie/discussion/comment/121454518#Comment_121454518

I think that's sort of normal water flow/temp for a rad. Assuming that the water enters in the left side of that FLIR snap, it will rise up and travel along the top of the radiator and then back down out the exhaust. If it's cold and you open the valve, and have one hand at the top center and the other at the bottom, the bottom will take a long time (if ever) to completely get up to the top temp. Fan close to the entry/exhaust should boost though as you say.

Also, have you considered a radiator reflector ?

volila Radiator Reflector Foil - 5m x 0.6m x 4mm Folded Insulation Foil - Energy Saver Foil Insulation for Radiator Reflector Panels to Cut Your Winter Bills - Easy to Use Radiator Foil : Amazon.co.uk: DIY & Tools

Would help cut down on heat absorbed by the wall, effectively that energy would go into the room instead.

graememk

Wall wouldnt be taking that much heat. also radiators dont radiate, they heat by convection, There isnt much to reflect!

Flow comes in from the right and exits to the left, I had both valves wide open for that photo and the radiator had been on for most of the day before that.

This rad has been on for at least 15 years, and one of the first on its loop.

It has been suspect for a good while, but with the stove, it hadnt been an issue until now.

radiator off, onto the unregulated mains (plenty of pressure here) need to find my rubber mallet to try and dislodge everything and flushed out.

graememk

Rad off, and flushed out a good bit of gunk, Some percussive maintenance with a rubber mallet too.

Back on and heating. we shall see how it goes. (waiting for my buffer to heat up again)

I am getting a line of hot across the bottom that wasnt there before but we shall see.

Radiator is quite old and the first on the line so very likely has caught a lot of sludge over the years. we are now thinking 20+ years now. It predates the renovations in 2006-2008ish.

DC999

https://www.boards.ie/discussion/comment/121457665#Comment_121457665

Fair play. I'd procrastinate for weeks, watch a million videos and then lose interest and never do it :)

graememk

https://www.boards.ie/discussion/comment/121458731#Comment_121458731

Well, Its been on my to-do list for the last year or so lol. Was always a bit suspect of it. With it struggling now it gave me the push needed to do it.

10-10-20

https://www.boards.ie/discussion/comment/121457665#Comment_121457665

That lower heat-line is the path of least resistance for the flow. That's why vertical (designer) radiators are commonly fitted with a flow diverter so that the main body of the radiator isn't bypassed.

https://www.bestheating.ie/milano-flow-diverter-15mm-inlet-chrome-63476

graememk

https://www.boards.ie/discussion/comment/121460672#Comment_121460672

Yeah, especially in high flow systems. Seen that mentioned in a skill builder video

It ain't a designer rad by any means 😂

I still think it's under performing, I've got the bottom clear but I think there's still stuff stuck in the middle of the panel.

unkel

https://www.boards.ie/discussion/comment/121454892#Comment_121454892

Always frown when people put the foil behind radiators. That measure has an infinite payback time (as it costs you money and the savings is zero)

"percussive maintenance" 😁

graememk

After another couple of days, the radiator was still struggling.

I have upgraded the blocked 1400*500 double with an 1800*600 double.

These are the outputs of a new radiator: (firefly compact, Double)

I pulled the D50 stats and the conversion from this pdf https://www.thermtek.ie/pdf/compact-radiators-delta-t50.pdf

JayBee66

There's a recent Skill Builder/Heat Geek video where it is recommended that the home owner gets rid of his buffer and heats the radiators direct. I assume you use the buffer so that you can heat it from a variety of sources. However, the homeowner in the video has both heat pump and gas.

DC999

https://www.boards.ie/discussion/comment/121472894#Comment_121472894

What is D50? Is that a delta of 50C from the heat at the top of the rad to the bottom? I assume it's that and not the temp of water in and out of the rad. I see the table in that pdf shows D50 as the benchmark of 1.00.

But when YouTube installers talk about a D5 on a 35C flow rate to get a really good COP, does that D5 mean the difference between out and return temp back to the heat pump?

10-10-20

https://www.boards.ie/discussion/comment/121474252#Comment_121474252

When talking about a rad, D50 should be DT50 (delta temperature 50) of the feed and return as measured at the radiator tails. When talking about a boiler then it's at the boiler tails.

They are essentially the same for most intents.

graememk

I thought D50 on a radiator is the difference between flow temperature and room temperature. Hotter room, Less heat that can be pushed into it.

Suppose its much of the same.

The radiator values in that document is at d50

Heatpumps like a difference of 5c, but can handle more.

This has implications for the flow rate through the system as

power(kWh) = flow rate (L/s) x temp difference in c x 4.18(specific heat of water)

So the smaller the difference in temperature the higher the flow rate needs to be to maintain a certain power.

In my house, It comes in on 1", But drops to 3/4" at the T for the DHW, Then splits into a 3/4" T between the loop at the front and the back of the house.

The flow is easily accessible, Return is behind the DHW tank. I can see it, and just about reach in and get at it, but not worth annoying it right now.

https://www.boards.ie/discussion/comment/121473989#Comment_121473989

Mines not the normal buffer though. instead of 50L, Its 500L and acts like a thermal store. I do gain a little bit of efficiency when the tank gets cold but drawback is responsiveness. I am toying with an idea of being able to do both, But would need to switch both flow and return. Enjoying tinkering with it and experimenting.

manonboard

This has been an excellent and very enjoyable thread OP. Thanks a lot.