water as thermal mass

[macpavee]

Cheers CP

it was in my initial hypothesis that IES wasn't fit for purpose and if i can get some technical explanations from the engineers that would be very useful.

When considering thermal mass in passive solar design one will choose a dark colour for mass directly exposed to shortwave solar radiation. other wise a light colour will be ok for absorbing longwave radiation. (and comparatively improving daylight factor)_

i assumed that the radiance link might communicate these additional albeit subtle gains.

the thing is, when designing passively the subtle effects from a range of interconnecting parameters are important.

(thought)
it seems modern simulation engines like IES are understandably biased towards the use of heating systems as a primary function in the building rather than as the final resort. my argument (it seems) is that the use of these tools in aiding design may in fact lead us away from more beneficial and arguably truly 'green' practice. (discuss...)

[macpavee]

As a last ditch attempt, i came across this post: http://energy-models.com/forum/ies-ve-r ... re-ceiling

Preferable to having a solid floor (at least in my design) would be to have underfloor vented tanks through which air channels carry either fresh or recycled air for heat exchange.

however the guidance given which includes the use of Microflo (which i haven't touched yet) i think demands to much from me in the time i have left, seeing as i have a deadline fast approaching.

any thought appreciated nonetheless

[Complex Potential]

The issue is one of computing power and the fact that dynamic thermal simulation programs are very much a niche market. There are only about 4-5 main developers and they are all small companies in comparison to the big boys like Microsoft or Apple, any of the AAA gaming houses or, more importantly, the CFD packages who have powerhouses like McLaren, Lockheed Martin, Boeing and AirBus investing and pushing for ever more detailed results. In comparison, we have CIBSE and ASHRAE who aren't quite in the same league.

As such the investment in this "technology" is not advancing as fast as other more mainstream tech. Also, the fact that it is dynamic means that a certain amount of simplification has to be made in order to keep computing times manageable. To do what you are asking would require 8760 individual steady state CFD convergences. With even the fastest desktop computer money can buy each one of those convergences normally takes hours which would translate to years needed.

IES and Tas both run 8760 hour calculations in under 30 minutes for normal sized models so you can imagine the sorts of simplifications that are being made in the background.

Potentially a software designed to run on a render farm cluster might have a chance at running a true annual dynamic CFD calculation but you would still need weeks or months and it would be ruinously expensive.

One day I fully expect this capability will be developed (the new quantum CPUs currently under experimentation look like they could go a very long way to it) but even if the hardware is capable, the software will need a lot more investment before we see it (IES doesn't even utilise multi-core processing yet and that's been around for 10 years!)

[macpavee]

Excellent stuff CP

exactly the limitations i need to know about.

i will be careful not to plagarise you of course.



so, ventilation and shading techniques then. these at least are showing promise.


cheers

[macpavee]

ok

i havent given up on this just yet

i have a roof pond with a down draft windcatcher running through the middle and into the room.

following this recomendation: http://www.iesve.com/support/knowledgebase/faq/2116
i have set the glazing accordingly
next i have a thin room on top with an insulative door providing cover in the winter which is removed in the summer

then in a horse shoe around the whole stucture is a finned dome which shades the pond through out whilst allowing air to the wind catcher.

in all there are some favorable indications. the Mass get good and warm in the winter and helps.

but it doesnt quite cool sufficiently in summer.

i am unsure that IES is really accounting for the radiative cooling appropriately (which in theory would occur day and night) but am not sure how to check

also

i haven't yet programed in the evaporative cooling effect from the pond to the outside air.
i appreciate that this is a dynamic process dependant on fluctuations but still.....

even a bold guess would do, but i cant find the data in the recommended literature (above)
nor (as yet) else where.

now, i havent yet played with apachesim so if any ideas are forthcoming please keep it simple as i have just about ran out of time for play.

& this is only a very conceptual investigation to justify the need/time for future investigation .....aswell as limitations of software.

any thoughts?

[Complex Potential]

Hi Mac

It looks like you've covered most bases I can think of for now, certainly the ones that can be done in any sort of reasonable time frame. At the very least I suspect you will have plenty to write about based on your experiences thus far and it sounds like you have a working model as a bonus, albeit one that doesn't quite show what you were hoping for.

As an aside, IES does account for long wave radiation losses to the sky for solid constructions but I am unsure how this would translate to fluids. A good way to check would be to run two models, one with a clear view of the sky and another with a big shading device across the "pond" and then look at the night time temperature profiles.