Free Storage Heater Experiment

[nowty]

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Gas boiler still switched off since 1st May 2021 here at Nowty Towers, really surprised to have got this far through the winter without gas for heating or hot water in a 1970’s style detached house.

We are very lucky to have the 6kW GSHP taking heat from an underground stream but and running it on an off peak rate at night and the batteries by day. Works ok when its mild 5 to 8 degrees, but cooler we have only managed it by boosting two storage heaters and leaving the kitchen heated floor on overnight. And when it’s been below zero its been a struggle. I keep thinking another storage heater might help but it would only be needed in extreme times now and again.

Today I had a brainwave (or a crazy idea) based on Joeboys thermal mass on his WBS. When we cook chicken dinner in the electric oven it helps heat the house for a while. And it’s got a timer on it which I’ve never bothered using. Towards the end of the cheap rate the car is charged and the house batteries have filled up, so there is some more electrical capacity headroom on the cheap rate to use.

So tonight, its going to be cold, around zero degrees. I’m going to set the oven to come on, say 4am at max temperature (280 degrees) for 1.5 hrs so goes off when the fixed cheapslot ends.

But I’m going to fill it with some bricks I have lying around, 8 of them so around 17kg of mass. Got the OK from SWMBO, in fact she thought it was a good idea.

Not sure whether to have them together as a concentrated mass or leave gaps for them to absorb the heat faster. I’m starting with gaps first. And if there is electrical capacity headroom at 11:30pm, I will turn on to see how long it takes for the oven to achieve its max temp. The specific heat capacity of brick is about 800 J/kg per degree and 1kWh is 3,600,000 J. So for 17kg of brick at around 250 degree increase in temp, that’s approaching 1kWh, should be well over that including the oven itself. The oven takes 2.2kW so 1.5 hours should be enough to attain max heat.

Bricks in Baking Tray


In Oven

[Joeboy]

Nice one, lateral thinking.

[Joeboy]

It comes down to block density and as few air gaps as possible. I would suggest (and I might build this myself). A cube of thermal mass with a couple of elements built in. 2.4kW say with double the storage heater bricks.

Although the answer is another storage heater...on wheels, with a plug.

We are good here until the crossover from 0 to -. In saying that we can literally see a 10 minute gas . I don't hang up on it, in fact happy it's there when we need it.

Always storage heaters knocking about on gumtree for little to no money? Wheeeelllss!

[nowty]

I was going to B&Q as they have 400mm x 400mm x 20mm granite paving slabs which are 8.5kg each. Three of them would fit perfectly, one on the bottom and one on each shelf giving around 25kg.

But this is just a proof of concept experiment as I already had the baking tray and bricks.
Alternatively block paving bricks are cheap and denser than normal bricks.

When we cook a chicken the oven stays hot / warm for 2 to 3 hours. Hoping to extend that for an extra hour or two with the bricks thus extending the heat into the house for several hours after the cheapslot has finished.

[Joeboy]

I was going to B&Q as they have 400mm x 400mm x 20mm granite paving slabs which are 8.5kg each. Three of them would fit perfectly, one on the bottom and one on each shelf giving around 25kg.

But this is just a proof of concept experiment as I already had the baking tray and bricks.
Alternatively block paving bricks are cheap and denser than normal bricks.

When we cook a chicken the oven stays hot / warm for 2 to 3 hours. Hoping to extend that for an extra hour or two with the bricks thus extending the heat into the house for several hours after the cheapslot has finished.

It is an excellent indeed! I continue to be amazed at the slow passive release and its longevity. On the flanks of our WS we see maybe 95 degs falling to 30 degs by morning. On the front face of the thermal mass more exposed to the fire as Is in the moment we see 130 rising to 180 degs. Got to say it is very nice to walk down in the morning and put hand on brick and its still working. Link that to the couple of storage heaters downstairs emitting nicely and its damn excellent
As said earlier, I like and get your thoughts on this one.

[Moxi]

Well Nowty was the brick casserole cooked this morning ?

It’s grey overcast and cold here so the WBS is on and the boss is just knocking out the second batch of madeleines fresh from the oven. They don’t last long on the plate ! Little hands constantly returning to grab another along with bigger hands of course

Moxi

[nowty]

Overall a success with one caveat.

Turned on last night at start of cheapslot to see how long it takes to heat up. It ran for nearly an hour before the thermostat switched off vs about 20 mins when I preheat the oven empty. Temp setting was 250 degrees (but that's air temp), the bricks were about 150 degrees and the metal inside oven casing was about 170 degrees. So that was enough to tell me the extra load was absorbing the heat nicely.

The caveat was it was smelling a bit from some baked potato residues which stick to the racks and are very hard to get off. Its not noticeable at normal cooking temps but on full whack it is, so I have given the rack a good scraping with a knife this morning.

I set the timer for 4:00am to 5:25am and went to bed.

Checked this morning at 9:50am, so nearly 4.5 hrs after the oven switched off. House downstairs definitely felt warmer and the heatpump was off as the house was up to temp, but it wasn't sub zero last night although the temp was only about 3 degrees outside this morning.

Top layer of bricks were 83 degrees and the lower ones were 70 degrees,


The inside oven casing was 64 degrees,


The outside was cool at the bottom, warmer towards the top around 35 degrees maxing out at 45 degrees were there is a cooling vent above the oven door.


The bricks have been sitting outside the oven for 2 more hours now and the top ones are still 30 to 35 degrees. I had to take them out to heat up the croissants.

Weather for rest of week looks like I won't need this, but its another electrical heating resource to battle against the gas boiler in times of sub zero temps. And it takes advantage of electrical capacity headroom towards the end of the cheapslot as battery chargers are ramping down. You can see the increase of consumption at 4:00am as other loads are reducing.

[Joeboy]

Overall a success with one caveat.

Turned on last night at start of cheapslot to see how long it takes to heat up. It ran for nearly an hour before the thermostat switched off vs about 20 mins when I preheat the oven empty. Temp setting was 250 degrees (but that's air temp), the bricks were about 150 degrees and the metal inside oven casing was about 170 degrees. So that was enough to tell me the extra load was absorbing the heat nicely.

The caveat was it was smelling a bit from some baked potato residues which stick to the racks and are very hard to get off. Its not noticeable at normal cooking temps but on full whack it is, so I have given the rack a good scraping with a knife this morning.

I set the timer for 4:00am to 5:25am and went to bed.

Checked this morning at 9:50am, so nearly 4.5 hrs after the oven switched off. House downstairs definitely felt warmer and the heatpump was off as the house was up to temp, but it wasn't sub zero last night although the temp was only about 3 degrees outside this morning.

Top layer of bricks were 83 degrees and the lower ones were 70 degrees,


The inside oven casing was 64 degrees,


The outside was cool at the bottom, warmer towards the top around 35 degrees maxing out at 45 degrees were there is a cooling vent above the oven door.


The bricks have been sitting outside the oven for 2 more hours now and the top ones are still 30 to 35 degrees. I had to take them out to heat up the croissants.

Weather for rest of week looks like I won't need this, but its another electrical heating resource to battle against the gas boiler in times of sub zero temps. And it takes advantage of electrical capacity headroom towards the end of the cheapslot as battery chargers are ramping down. You can see the increase of consumption at 4:00am as other loads are reducing.

Cracking result to have and to be used when you REALLY need it, nice one! You could buy a 2nd hand cheap cooker and load it up with dense storage bricks. One of those bare metal hidden units with a single oven, box it in to make it look decent and its there when you need it?

[Andy]

You probably need to invest in a small forklift to speed up the loading / unloading. It will also allow removal of the bricks whilst really hot.

[Joeboy]

Ground was frozen here this morning yet no gas used. My gas trip temp is 16 degs so that's all good.

Parboiling some of the very last of our homegrown tatties from last year. A filled roll for lunch for my son and then out for a long walk

SWMBO has seriously gotten behind the whole WS cooking and the reality of the thermal mass is now just a given in our daily lives.

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