Energy Assessment: From energy conservation to thermodynamic efficiency

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- CommentAuthorrhamdu
- CommentTimeOct 11th 2012
OK, so let's continue the discussion that we began in the thread "What's the best modelling software?" http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=1427

I asked whether any of the software packages calculate changes in entropy, the related 'free energy' variables, or other indicators of a building's thermodynamic efficiency. It would be good to know how close our buildings are, to the limits set by physics.

Fostertom - who suggested creating this new thread - restated the issue in terms of high-grade vs low-grade energy. Useful concepts, I think.

Barney said that in the chemical industry, thermodynamically wasteful processes are known as pinch points, and chemical engineers have software for analysing them.

Djh pointed out that the term 'exergy' is widely used as a term for available or usable energy, though (thanks, Wikipedia) I understand that different people use the term with different meanings. However, that doesn't stop 'exergy' being a useful button for making governments cough up money.

So here we are on planet Earth, astride a mighty energy-flow, from the sun's surface at 6000K to the depths of space at 3K. We can use it efficiently or we can waste it. The question I would like to ask is: How can we exploit ideas of thermodynamic efficiency, entropy, free energy, exergy - whatever - in the design, construction and use of buildings?
- CommentAuthorSteamyTea
- CommentTimeOct 11th 2012
Posted By: rhamduHow can we exploit ideas of thermodynamic efficiency, entropy, free energy, exergy - whatever - in the design, construction and use of buildings?

Storage seems to be the key, with long term storage being the holy grail.
New housing could/should, as far as possible be orientated to take full advantgae of local solar conditions. Hard in practice without designing towns and cites on a grid system, but I am sure the artistic amongst us may be able to sort this one.
Maybe the traditional house that is longer than it is wide is an old model that needs rethinking.
- CommentAuthorPaul in Montreal
- CommentTimeOct 11th 2012
Posted By: SteamyTeaMaybe the traditional house that is longer than it is wide is an old model that needs rethinking.

Interesting that on this side of the pond, many old houses are like that. Mine, for example, is 20 feet wide and 55 feet long (semi detached) - as a standard lot size here was 25x110 feet. Some houses are wider as they're on double-width lots, and these tend to be detached. For the narrower lot, either you get a full 25-foot wide terrace or a semi that's 20 feet wide with a 5 foot alley to access the garden at the back. Quite efficient against the cold Canadian winter.

Paul in Montreal.
- CommentAuthorSteamyTea
- CommentTimeOct 11th 2012
Posted By: Paul in Montrealas a standard lot size here was 25x110 feet
So you still using feet and inches over there
So 7.6m by 33.5m
We would build 6 'family homes' with gardens on that and expect to house up to 30 people.
- CommentAuthorBrompton
- CommentTimeOct 11th 2012
Setting aside the linking of the insulation with the cavity wall insulation I think you are suggesting that the space between the joists be filled with celotex (or maybe a combination of celotex and quilt) with a layer of celotex under the joists. This is close to the variation suggested by my builder. I am concerned that as moist air will inevitably get into the structure from above and below, condensation will occur and as celotex is impermeable there would be insufficient ventilation to dry it out and in time the joists would rot. I thought your earlier suggestion to use quilt (which I took to be vapour permeable) was to reduce this risk. Am I worrying unnecessarily?
- CommentAuthorfostertom
- CommentTimeOct 11th 2012
Posted By: rhamduhere we are on planet Earth, astride a mighty energy-flow, from the sun's surface at 6000K to the depths of space at 3K
I like that - 'astride'.
The question might be, if astride such a vast flow, why should we bother with trying to use it economically?
The comment on that might be that we've forgotten how to use that bountiful clean flow, instead squandering a finite fossil resource as if it were equally limitless, ignoring that its use is toxifying us to extinction.
- CommentAuthoran02ew
- CommentTimeOct 11th 2012
Posted By: SteamyTeaStorage seems to be the key, with long term storage being the holy grail.
New housing could/should, as far as possible be orientated to take full advantgae of local solar conditions. Hard in practice without designing towns and cites on a grid system, but I am sure the artistic amongst us may be able to sort this one.
thats fine for everything from now on, what about the vast amounts of existing housing stock.
- CommentAuthorfostertom
- CommentTimeOct 11th 2012
Posted By: rhamduDjh pointed out that the term 'exergy' is widely used
And there's 'emergy' too - what's that? Not to mention Negawatts.
- CommentAuthorbarney
- CommentTimeOct 12th 2012
The comment on that might be that we've forgotten how to use that bountiful clean flow, instead squandering a finite fossil resource as if it were equally limitless, ignoring that its use is toxifying us to extinction.

Well basically Tom, I think because it's easier, cheaper (in the immediate) and for much of what we want in terms of energy, the technology needed to get solar energy in a useable temperature, in quantity and available when required is complex and expensive - more so than just burning fossils fuels requires anyway. Usually we have to convert it to high grade electricity and then reduce that to low or medium grade heat, with the attendant efficiency issues.

Generally the one thing we should avoid doing.

If we take something simple like glass manufacture - how do we do it ?

Regards

Barney
- CommentAuthorfostertom
- CommentTimeOct 12th 2012 edited
That may have been true till a short while ago, but even that was more about 'modernist' fashion, vast profits, and inertia. As you say
Posted By: barneyGenerally the one thing we should avoid doing.
Now, the problem's solved - can readily make electricity from solar energy - the answer to
Posted By: barneytake something simple like glass manufacture - how do we do it ?

Solar, tho the ultimate hi-grade source, can also be gathered as v lo-grade heat for space heating at v high efficiency, thus taking that hugest-single sector off 'fuel' altogether (because such lo-grade heat can't be comoditised/traded as 'energy' but can only be used on the spot). That used to be all there was for space heating, and cob cottages (imitation caves) did that very well. Until 'modernism' and profit deemed that unfashionable, and 9" brick disregarding solar orientation, coal heated (for some), supplanted and extinguished the old wisdom, all a mere 200yrs ago out of our long history. Now the old wisdom is back - in our GBF hands.
- CommentAuthorbarney
- CommentTimeOct 12th 2012
OK Tom, I'm willing to go with it - but we are forgetting that right back to us living in real caves, we've burnt something for heat, light, food preparation, security and well being. Generally we've burnt carbon - we are almost genetically programmed to do so, in my view

Personally speaking, I'm all for passive solar - as a building services engineer, I've spent a considerable amount of time trying to get the message of "Passive before Active" across to design teams and clients. But as an engineer, I also know the practicable limits of using solar directly without throwing loads of technology at the problem to resolve storage, transportation and utilization issues.

And I'm not sure the old wisdom is actually back - because I don't think we had it in the first place - as a species we are good at exploitation - and we've exploited what's easy and cheap. For sure we have an emerging (or maybe a re-emerging knowledge) of how to harness solar energy - but only at a very basic level - to go further needs technology that previous generations never had.

Regards

Barney
- CommentAuthorfostertom
- CommentTimeOct 12th 2012
Posted By: barneyFor sure we have an emerging (or maybe a re-emerging knowledge) of how to harness solar energy - but only at a very basic level - to go further needs technology that previous generations never had.
True - and that technology is emerging at tremendous speed, on a human-history timescale.

Nothing wrong with the collection technology - it's only the vast fossil profits and the inertia (no longer 'modernist' fashion) that's still enforcing '200-yr-old business as usual', mainly by diverting will, therefore attention and awareness, from the one enabling/technology step still unaddressed - that is, 80% demand reduction to make present renewables potential adequate - which is what this thread is about.
- CommentAuthorfostertom
- CommentTimeOct 12th 2012 edited
Posted By: barneyright back to us living in real caves, we've burnt something for heat, light, food preparation, security and well being. Generally we've burnt carbon - we are almost genetically programmed to do so
True, but always renewable carbon.

A cave (or later hi-tech for-all evolution, the dug-into-ground cob thatched cottage) needs negligible heat to maintain year-round comfort temp, once surrounding subsoil mass is up to temp. Light, cooking, security - yes, but all can now be done with by solar alone - this is almost the 22nd century you know. I suspect that 'genetic programming' cd readily give way to greater ease, economy and convenience!
- CommentAuthorEd Davies
- CommentTimeOct 12th 2012
Posted By: barneyPersonally speaking, I'm all for passive solar...

I'm not, for exactly the reasons which are the subject of this thread. Passive solar tends to collect heat in a rather low-grade (i.e., low-temperature) form making storage and control more difficult whereas active solar thermal (solar collectors rather than large windows) gives you higher temperatures with increased flexibility of use.
- CommentAuthordjh
- CommentTimeOct 12th 2012
barney asked: "If we take something simple like glass manufacture - how do we do it ?"

I don't know about glass specifically, but this book - http://withbotheyesopen.com/ - addresses the question for steel, aluminium, cement, plastic and paper. It's free to read online, or you can buy a hardcopy.
- CommentAuthordjh
- CommentTimeOct 12th 2012 edited
Posted By: Ed Davies
Posted By: barneyPersonally speaking, I'm all for passive solar...

I'm not, for exactly the reasons which are the subject of this thread. Passive solar tends to collect heat in a rather low-grade (i.e., low-temperature) form making storage and control more difficult whereas active solar thermal (solar collectors rather than large windows) gives you higher temperatures with increased flexibility of use.

It's horses for courses rather than choose one or the other, isn't it? Passive solar is much cheaper than active solar because you have to have windows anyway, so you may as well optimise the solar gain from them.
- CommentAuthorbarney
- CommentTimeOct 12th 2012
It is Tom,but I also think we should be mindful of inapropriate technology, or incorrect deployment of that technology - let's be careful we don't recreate the 9 inch wall scenario.

Well actually there is something wrong with the technology at a fudamental level - it needs huge resources and often at significant environmental cost - if we are going to heat molten tin (and keep it molten) for float glass production just think of the PV array that needs - it'll be vast, and it will only work if there is another vast array half a world away to keep the power flowing 24/7.

I'm with you on demand reduction - but there is a certain irony that in order to achieve that demand reduction we need to throw, again, vast resources at buildings (and at the component manufacture for buildings) that could easily outweigh the demand reductions we are trying to achieve. It's not easy to have a modern passive solar home without mass and glass is it - both of which take real energy to make - and making them from sunlight is difficult.

OK - back to the thread - at the moment, I'd say our buildings are a long way from theoretical physical limits - often for good reasons. We can only really model them simplistically - but do we actually need the sophistication. We can build for totally passve and active solar operation, for sure - but sometimes the wind turbine or water wheel has greater potential than passive or active solar - there'd be a certain irony in building a thermally massive house on an exposed south facing slope with loads of solar collectors including windows when a thermally lightweight, sealed box on the noth side would make better use of the energy in the stream trickling by the door.

regards

Barney
- CommentAuthorfostertom
- CommentTimeOct 12th 2012
That's right Dave - whether 'passive' (if that means thro windows you've got anyway) or 'active' (using v simple collector technology), ultra-lo-grade solar collection (for space heating) or the familiar fairly-lo-grade collection (for DHW) can be supremely efficient.

At collector flow temp about 23C we reckon to usefully capture 60% of the solar power that actually reaches our collector design (under development) thro Dec/Jan, for space-heating a near-PH building without much reliance on windows as collectors. Then yes it's a storage problem but we naturally have that cracked as well, as often described (most of it) on GBF.

Anyway, this thread isn't about 'passive' vs 'active'. It's about appropriate non-profligate conservation of the grade of the heat (temp if thermal, or any electricity), not just its raw quantity (kWh).

Posted By: Ed Davies... heat in a rather low-grade (i.e., low-temperature) form making storage and control more difficult
Not necessarily, just needs re-thinking - maybe that's difficult?
Posted By: Ed Davies... whereas active solar thermal (solar collectors rather than large windows) gives you higher temperatures with increased flexibility of use
Not necessarily higher, but higher temps do enable lazier but wasteful solutions.
- CommentAuthorrenewablejohn
- CommentTimeOct 12th 2012
Technology in this area is certainly moving fast. Trying not to give to many details away but a 4 tank system solves most of a house energy requirements.

High Temperature Thermal oil 230C

Used for cooking (Already used commercially in bread ovens)
Used for Washing (Already used in commercial washers,dryer, and ironing)
Used for Instantaneous boiling water (Already used commercially for instant steam, boiling water applications)
Used for Power Generation (Tegs already available to produce electric 35C cooling water used for UFH)
Used to heat hot water if insufficient from CSV unit.

Medium Temperature Hot Water 70C

Used for DHW

Low Temperature Warm Water 35C

Used for UFH

Cold Temperature Cold Water 1C

Used as Refrigerator

Only the Infra Red spectrum is used for heating the thermal oil the remaining spectrum is used in a normal CSV unit to provide primary electric. Any excess electric generated by the CSV can be dumped by immersion heater in the thermal oil tank. CSV unit mounted in loft space next to hot water tank so DHW can be used to cool CSV unit.

Heat loss from both the thermal oil and hot water tanks are reduced by the use of vacuum flasks.
- CommentAuthorfostertom
- CommentTimeOct 12th 2012
Posted By: barneyif we are going to heat molten tin (and keep it molten) for float glass production
Once melted, the only input needed depends on how well the process is insulated - don't tell me that can't be reduced to a trickle. For that reason glass is great - new stuff v largely recycled, and in future no doubt carefully saved and re-used. Unlike e.g. Portland cement, whose chemical-embodied energy can't be reduced and should be blacklisted by all greenies. Anyway, silicon/glass PVs will be superseded by organic compounds pretty soon.

Posted By: barneywe need to throw, again, vast resources at buildings (and at the component manufacture for buildings) that could easily outweigh the demand reductions we are trying to achieve
Don't think so - it's clear that even if embodied energy has to rise as you say, the in-use savings vastly outweigh that. However it's true that the embodied input is 'now', when the planet can least tolerate it, while the savings are spread over the next 30, 80 or 200yrs. It's not a lack of technology or organisational ability, just a matter of fossil-profit interests hence lack of will and priority - does the govt want to create a new mass-employment serious-retrofit industry or not? Apparently not.
- CommentAuthorfostertom
- CommentTimeOct 12th 2012
Posted By: renewablejohnthe Infra Red spectrum is used for heating the thermal oil
to that temp right thro Dec/Jan? Really? If not 100% sufficient thro Dec/Jan then you still need boiler etc.
- CommentAuthorEd Davies
- CommentTimeOct 12th 2012
Posted By: djhPassive solar is much cheaper than active solar because you have to have windows anyway, so you may as well optimise the solar gain from them.

Well yes, you have to have some windows so optimizing them for solar gain makes sense.

However, once you have enough for reasonable light levels, a view and means of escape I'd dispute that extra window area (with greater cost than plain wall and greater heat losses when the sun is not shining) is much, if at all, cheaper overall than the marginal cost of extra solar collectors beyond those needed for DHW anyway.

Whatever, I think the cost differential between active and passive is often exaggerated while at the same time the difference in value of high- vs low-grade heat is discounted.

Posted By: fostertomNot necessarily higher, but higher temps do enable lazier but wasteful solutions.

If the sun shining through the window is creating temperatures in the room comparable to those which can be produced by evacuated tubes in even moderate sunshine that'd be a problem.

Isn't allowing relatively high-grade energy in the form of light shining in through the window to spray around the room degrading to lower-temperature energy a lazy and wasteful solution?
- CommentAuthordjh
- CommentTimeOct 12th 2012
Posted By: Ed DaviesHowever, once you have enough for reasonable light levels, a view and means of escape I'd dispute that extra window area (with greater cost than plain wall and greater heat losses when the sun is not shining) is much, if at all, cheaper overall than the marginal cost of extra solar collectors beyond those needed for DHW anyway.

Whatever, I think the cost differential between active and passive is often exaggerated while at the same time the difference in value of high- vs low-grade heat is discounted.

I'd agree with that and as things are, with the playing field tipped by government decree, people are encouraged to buy PV rather than either passive solar or solar thermal.
- CommentAuthordjh
- CommentTimeOct 12th 2012
Posted By: fostertomHowever it's true that the embodied input is 'now', when the planet can least tolerate it, while the savings are spread over the next 30, 80 or 200yrs. It's not a lack of technology or organisational ability, just a matter of fossil-profit interests hence lack of will and priority - does the govt want to create a new mass-employment serious-retrofit industry or not? Apparently not.

It's not just fossil profits. The economic inputs have the same difficulty as the emissions. Somebody has to pay now if you want to save later. I don't think it's a question of whether the government wants to create a new mass-employment serious-retrofit industry or not. It's a question of whether they can find a way to pay for one.
- CommentAuthorbarney
- CommentTimeOct 12th 2012
Well Tom, I guess you've never been involved in glass production or you would realise the futility of that statement

Glass is not largely recyled and we don't have a shortage of sand anyway - a max of about 10% recycled glass in the furnace is a resonable limit and reduces the energy demand by about 2%. The high cost items are energy in the furnace and the molten tin float pond and the soda ash used in the glass. The cost of providing the nitrogen blanket to avoid tin oxidization is also not cheap.

As for cement - well, if we use it properly (like over say 100 years in concrete structures for example) then the energy burden is not that problematic.

My point however, was that without fossil fuels we cannot easily get solar energy to make glass, refine gasses or make cement - modifying about 0.01% of the UK housing stock through pasive and active solar design becomes a bit - well you know.

I'm not so sure that this is all about the fossil - profit conspiracy, if we want the material technology that we currently enjoy we need energy to achieve that - and there are practicable limits on using solar energy for that.

A tonne of glass emits about a tonne of CO2 - probably a bit worse than cement production. It's interesting though that we feel OK about that - we even say that it's repayed within a year based on the energy loss through a single glazed window compared with that through our new double glazed window. We don't follow the same lines of thought for cement very often though.

Regards

Barney
- CommentAuthorfostertom
- CommentTimeOct 12th 2012
Posted By: djhI don't think it's a question of whether the government wants to create a new mass-employment serious-retrofit industry or not. It's a question of whether they can find a way to pay for one
Well, fiscal Tories say no, trapped as they are by their artificial 'Money' construct/concept. Keynsians say print the money (if you must) and go for it - didn't do US any harm in the 30s, in fact all that new infrastructure and wage-led domestic spending quantum-leaped them into pole position come WW2.
- CommentAuthorfostertom
- CommentTimeOct 12th 2012 edited
Posted By: barneyWell Tom, I guess you've never been involved in glass production or you would realise the futility of that statement
I've noticed that rank-and-file insiders in any industry (incl architecture and building), who are immersed in how it's done, are least able to imagine quantum-leap changes - but those do keep on happening, overturning conventional wisdoms. And you're extending that to pour cold water on the practicability of much that's mentioned about both the subject of this topic (conservation of energy-grade rather than just energy) and also about the possibilities for radical energy-demand reduction in industry. We on GBF seem to agree the latter is essential - well this is what it will take, and is how it can happen.

You started talking about the crippling environmental impact of glass for major PV installations.
First, they won't be made of either rare elements or glass for much longer;
Second, glass, needing lots of heat but only for melting, not for endothermic chemical reaction (Portland cement), is a prime candidate for massive energy savings, whereas Portland cement is irredeemable.
Third, glass doesn't have to be brand-new hi-spec, except for present uses like PV, which can be superseded, and coated window glasses, which can afford to lose some performance, in the interest of recycling every last scrap of glass (as well as careful recovery for re-use). Hi-tech can and will get applied to recycled glass too. !00% recycling (solar powered) and/or re-use of everything is undoubtedly the future, and glass is a 'low hanging fruit' candidate for that.

Posted By: barneyThe high cost items are energy in the furnace ...
Once melted, isn't temp maintenance say 50% a problem of effective insulation?
Posted By: barney... and the molten tin float pond ...
Is the tin consumed?
Posted By: barney... and the soda ash used in the glass
What if much higher recycled %age?
- CommentAuthorrenewablejohn
- CommentTimeOct 12th 2012
Posted By: fostertom
Posted By: renewablejohnthe Infra Red spectrum is used for heating the thermal oil
to that temp right thro Dec/Jan? Really? If not 100% sufficient thro Dec/Jan then you still need boiler etc.

Its all down to volume of thermal oil once you eliminate heat losses by using vacuum flasks.
- CommentAuthorbarney
- CommentTimeOct 12th 2012
I dn't work in the glass industry Tom, although i have been involved in the design of systems for glass manufacture.

If we want good quaility float glass there isn't much alternative to the current process - although we may not actually need glass I accept

as for pouring cold water, actually the opposite - I was simple looking at how very high grade energy is reduced to something that generally deals with very low grade energy control - ie windows and heat gain or loss etc

I raised some points initially about energy grade and Pinch thinking - and was wondering how we can move from high grade to low grade energy from solar technology.

Personally, I don't see much move away from glass technologies for a very long time to come - it's an excellent material and has some fantastic benefits in low energy or low carbon bulding strategies - but we won't be able to make by chucking sand out in the sun - otherwise our deserts would be full of the stuff by now

I guess we'll disgaree about the actual carbon content in cement - if i use it in enough concrete to provide enoufgh mass so that night cooling eliminates say refrigerant based cooling and I do that in buildings that are recyclable/re usable on a long time cycle then it's perhaps not the demon it's made out to be.

I agree we could re use a lot of glass - but most people don't want it in thier new 3g systems - and in reality, just how much glass is available to recycle as windows without crushing it and throwing it in a furnace with the attendant energy burden.To put this low hanging fruit into perspective - energy costs for glass production using recycled glass as feedstock has reduced by about 50% in the last 30 years - you'll know how the laws of diminishing returns work, so it'll be more than a few decades before it halves again.

As I mentioned solar powered glass making is not going to be easy due to the temperatures involved - probably around 150c in the furnace and then to about 1200C dropping to about 600c in a float bath and then further controlled cooling (by heating!) to avoid cracking etc - it's a hell of an energy hungry process.

Insulation is and will continue to be important in glass making - but it only delays the heat loss - essentially all of the energy runs down hill to atmospheric temperatures no mater how thick you make it - and maintaining even partial vacuums over equipment that's several hundred metres long is not easy either. The tin isn't consumed, or at least not in great quantities as the nitrogen shroud keeps oxidization at bay, but maintaining it in a molten form takes the energy.

The soda ash is generally the flux in the process

Regards

Barney
- CommentAuthorWillInAberdeen
- CommentTimeOct 13th 2012
Lets try a list of energy carriers in order of exergy (no data, I'm ad libbing, maybe the forum will correct me)

Highest grade:
Electricity
Gas
Oil
Coal
Wood
Hydro
Tidal
Wind
Active solar
Heat pump
People
Waste heat from lighting, appliances, cooking etc
Passive solar
: lowest grade

Now lets try a list of functions in order of the exergy required:

Highest grade:
Appliances/electronics etc
Manufacturing/smelting/etc
Transport
Lighting
Cooking
Hot water
Space heating
: lowest grade

So in a world of physicist s, the highest grade energy would be reserved for the highest grade functions and v v.

Is striking that 99% of houses have this completely the other way round, using highest grade electric gas or oil for lowly space htg.

What order would yhe forum put those lists?

1 to 30 of 34



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Energy Assessment: From energy conservation to thermodynamic efficiency