Making a cheap electrical energy meter

Very interesting Nick, as you know I built in brick and block (heavy weight) and this was done for several reasons. Brick because I hate render, maintenance, cracking etc. internal heavy block because I hate “hollow” houses and even thermalite blocks are difficult to fix too (IMO). I did however have a large fully filled cavity and fairly airtight. Not that I am going to build another house but if I was I would probably go brick and timber frame with cellulose blown insulation AND line with ply/OSB under the plasterboard to give a more solid feel and be able to hang stuff from it. (I just had a coat rack fall of the wall of my new place because it was fixed to the plasterboard dot and dab only 🤷‍♂️.)

I once had a conversation with a manager of a large wine cellar of a country estate. The cellar was brick built with vaulted ceilings. A dozen rooms in total. 

 

They had detailed records going back several hundred years of conditions in the vaults (only recently controlled with modern techniques) 

 

They filled the racks with dummy bottles of water rather than leave them empty. 

 

He said the practice was done for as long as the records had been kept. In fact some of the fake bottles were older than the wines. 

 

"an empty vault fluctuates in temperature a lot more and will kill the wine" 

 

Know there are other factors info involved here. But just wondering that came to mind. 

@joe90

There are many reasons for choosing building materials, two of the biggest are availability and local skills.

 

What should not be happening is nonsense about how heavy weight materials thermally stabilise a building, that only happens at the very extremes i.e. a deep cave or a single skin tent. And even then, different inputs are interacting differently.

 

Solid masonry walls are not much different in rigidity than properly designed steel or timber walls. 

The key point there is 'properly designed'.

If all design was equal, we would still be driving Austin Allegros.

I agree with you Nick, which is why (a bit late in the day) I have changed my mind, keep banging your drum and things might change (but not quickly).

Well it’s an interesting area, maybe called ‘building dynamics’ rather than ‘building statics’ which 95% of the other modelling is - part O / PHPP etc.

 

I’m not sure I understood all your assumptions or model and I don’t get a 100% intuitive model in my head either - but I feel it’s an important area to explore because it might contribute understanding to some of the design choices we have to make.

 

I guess this comes into play when making decisions e.g. masonry vs. timber frame / wooden deck vs. beam and block / conventional tile vs. metal roof?

I guess it also depends on what heating and cooling control systems you’re looking at. Very fast acting systems might keep the internal environment comfortable despite materials and structure (e.g. loads of glazing) which would tend to make the internal conditions jump around.

1 hour ago, Alan Ambrose said:

guess it also depends on what heating and cooling control systems you’re looking at

Yes, this probably has the greatest effect, along with uncontrolled/un designed solar gain and ventilation.

 

I think the main thing is that if someone says 'we are building heavyweight because it stops temperature variation', they need to be made to stop and think.

If someone says 'we are building heavyweight because we can't find a carpenter' then that is sensible.

Density is a variable of decrement delay. A decrement delay of 12hours will average out the highs of day and lows of night for a more stable internal temperature. I don’t think your experiment factors that in? I’m not suggesting chucking more density in to solve the problem, although you could. A more sensible approach would be to consider decrement delay when choosing the insulation material by having a play on ubakus.

1 hour ago, LiamJones said:

Density is a variable of decrement delay.

It does take that into account, the ⁰C/hour figures are decrement.

This notional 12 hours is of no use in the UK, our latitude is too high.

Don’t we have a 24h wave sitting on a 365 day wave plus a bunch of randomish noise?

12 minutes ago, Alan Ambrose said:

Don’t we have a 24h wave sitting on a 365 day wave plus a bunch of randomish noise

Add in a couple of sin waves for good measure, if only for moon phases.

"regardless of construction type, the air in a building will react more to external inputs than internal inputs i.e. solar gain, ventilation and a heating system versus thick stone, brick or concrete walls." isn't that fairly obvious?

9 minutes ago, Adrian Walker said:

isn't that fairly obvious

Well it is to me, but not to everyone.

Does need a bit more clarification as obviously, directly heating interior air will raise the temperature very rapidly.

Edited February 24 by SteamyTea

3 hours ago, Adrian Walker said:

the air in a building will react more to external inputs than internal

T'other way round?

This just doesn’t match my personal experience.  

My parents years ago had a timeshare in a triple glazed highly insulated wooden house in the UK, which had hollow sounding plasterboard walls.  It was build around 2000, I don’t know what insulation it used.  Many evenings in October it was too hot (either due to cooking or solar gain), windows were opened wide for an hour to decrease the temperature.  After a hot evening it invariably would  be really cold in the morning, so electric heaters were manually switched on as it didn’t have central heating.  We all appreciated how wasteful this was, but had no way to change the property to prevent it, and elec was not separately charged.
Our retrofitted home now is similarly highly insulated, but has solid walls and floor, and the temperature just doesn’t change much over a single day - and we never heat and open windows in the same month let alone day.

46 minutes ago, RobLe said:

This just doesn’t match my personal experience.  

My parents years ago had a timeshare in a triple glazed highly insulated wooden house in the UK, which had hollow sounding plasterboard walls.  It was build around 2000, I don’t know what insulation it used.  Many evenings in October it was too hot (either due to cooking or solar gain), windows were opened wide for an hour to decrease the temperature.  After a hot evening it invariably would  be really cold in the morning, so electric heaters were manually switched on as it didn’t have central heating.  We all appreciated how wasteful this was, but had no way to change the property to prevent it, and elec was not separately charged.
Our retrofitted home now is similarly highly insulated, but has solid walls and floor, and the temperature just doesn’t change much over a single day - and we never heat and open windows in the same month let alone day.

That will be down to the amount and decrement delay of the insulation.

 

Our house is all timber, plenty of insulation but of a type with a slow decrement delay.  The house only ever heats up or cools down very slowly.  That is not because it has lots of "mass", it doesn't, but because the type of insulation.

23 minutes ago, RobLe said:

This just doesn’t match my personal experience.  

Without do a detailed thermal model it is very easy to attribute the wrong things to the outcomes.

The things that will make the biggest differences are the ventilation rates, the solar gain though windows and the insulation levels, not the difference in the thermal inertia of the walls.

 

There is generally a very large difference between the mass of air in a building (even allowing for air changes), and the mass of the construction.

 

No one goes looking for heavyweight insulation.

To get the equivalent insulation value from a brick wall, compared to 0.25m of mineral wool would mean that the brick would need to be 3.5m thick.

 

How about this thought experiment?

 

Imagine 3 cubic blocks, say 5mx5mx5m sitting on a lovely building plot somewhere with no shade. One block has concrete walls, say 30cm thick, one PIR with the wall thickness set for the same U-value, one say, cellulose fluff held within very thin inconsequential surfaces, again with the same U-Value. No windows or other penetrations.

 

Assume the PIR and the cellulose box are painted the same grey as the concrete (with the same reflectivity etc) and all are airtight - so the only environmental effects are air temperature / radiant heat from the sun / the cooling effects of wind.

 

Which box has the higher air temperature variation inside?

Edited February 26 by Alan Ambrose

15 minutes ago, Alan Ambrose said:

Which box has the higher air temperature variation inside?

Over a typical metrological year, they are same.

 

I did a similar experiment a few years ago and posted the result up on this site predecessor, there was no difference.  Was brick, timber and polystyrene, all coated to the safe reflectivity (albedo).  Was a follow on from "Paint your roof white" I posted up about on the Other Place.

 

Thing is, I was not showing volumetric differences, but specific differences.

 

But how about this for a thought experiment, how much concrete would you have to add to internal walls to stabilise the air temperature to a fixed band i.e. ±1°C?

 

It is easy to create an experiment designed to go looking for anomalies, but that is rather missing the point, as well as bad experiment design.

 

 

 

The masonry one absorbs a lot of heat from the sun's energy and releases some if it by convection and more at night. 

The others resist the heat but don't absorb much. The heat gets through more quickly and more gets through in the day.

At night, the opposite happens so it depends how much sun (location and season) and on day and night temperatures.

 

Can I add to your thought experiment?

In the middle of each room there is a big stack of thermal bricks as used in night storage heaters, laid in a grid for maximum surface. 

They will absorb energy in the day, once the heat gets inside, and hold it into the evening...but I won't dare call it thermal mass.

 

Consider a Spanish villa. Zero insulation other than perforated bricks. In winter we turn up and it's 15C indoors. The fire heats it up to 22C in 3 hours, but overnight it's back to being cold.

Next day repeat, and it remains moderately comfortable overnight. Day 3 and it's cosy. 

Clearly the solid walls and floor are absorbing and retaining the heat. 

 

In summer, it remains cool indoors if blinds and air are managed. Most sun energy stops at the roof tiles and vents.

 

 

 

 

Edited February 26 by saveasteading

1 minute ago, saveasteading said:

In the middle of each room there is a big stack of thermal bricks as used in night storage heaters, laid in a grid for maximum surface. 

They will absorb energy in the day, once the heat gets inside, and hold it into the evening...but I won't dare call it thermal mass.

Call it what is it, thermal effusivity.

 

e = (kpc)^0.5

 

Then just to complicate it, the the temperature differences decrease, the power transfer decreases.

 

T = e^(-kt)

 

The e are has different meanings in each formula.

 

 

51 minutes ago, SteamyTea said:

Call it what is it, thermal effusivity.

I'll never remember that when trying to complicate a discussion.

Some heavy reading is called for later, but Wikipedia says its simple, if we consider two semi-infinite bodies. gulp.

 

  thermoception.... is a particularly important metric for textiles, fabrics, and building materials

 

 

26 minutes ago, saveasteading said:

thermoception.... is a particularly important metric for textiles, fabrics, and building materials

I shall remember that when I next pull my winceyette nightie on.

 

But just last night, I noticed that if I put a bit of pillow case material under my hand, then rest it in the metal bed head, it feels nowhere near as cold, compared to a naked hand on it.

 

Same with socks and a cold floor, even the thinnest of socks impede the energy flow significantly, and the k-value is probably very high for a compressed sock.