how to set the infiltration temperature variation profile?

[macpavee]

i would like to know how to write the formula for more accurately setting the temperature of the infiltration air in my sim.

The building template manager allows for adjustments to be made to the infiltration rate but also the temperature at which it enters by use of the variation profile and adjacent condition.

thats great

i have a passive solar designed double skinned building, top bottom and sides. -there is no heating or cooling 'active' system.

the infiltration rate is lower for the Main central room than the outer buffer zone but this figure must be guessed. no matter.

the temperature in the buffer zone can be seen to be more stable than the external air maintaining the peak of the DBT on average through the heating season.

the summer difference is not so relevant (although it maintains a modulation frequency within 3*C of DBT), as a natural ventilation profile in all likelihood, nullifies any potential benefits.

there are a lot of operators given in the Appro guide (pg. 30) which may work to create the formula i need however, i cant work out how to construct the formula for the variation profile on this effect. i can program in the annual variation just not the daily formula for -the mean of the dry bulb or a similar effect.

any boffins?

[macpavee]

make that the upper peak of the DBT through the winter -not its mean.

[Complex Potential]

I would suggest that this be done by setting up actual cracks lengths into the internal walls through Mocroflow and then allowing the model to calculate the air movement around the building.

The infiltration aux vent is basically there for the benefit of central plant calculations but it's pretty poor for simulating individual rooms.

For example, I had to model a large, leaky national trust property and every room had to have an estimated heating load for radiator sizing. I realised that applying a building average of 1AC/H would be a huge oversimplification and so I included every internal and external window and door throughout and set them them to a small % opening based on how leaky I thought they were going to be in winter.

The result was that the impact of infiltration was reduced the further towards the centre of the building you got, as it should be and that the rates increased on windy days, again as it should be. Additionally, the temperature of the incoming air is far more representative in each case (freezing cold for the external boundary rooms but almost room temperature once it had travelled through 2 or 3).

The only really tricky part is working out a % opening to represent the leakage correctly but I've found looking at the resulting flow rates (external macroflow) through vista after a run and then fine tuning to get the building average you are after is the best way.

CP

[macpavee]

i like the thinking CP

my additional problem is that i am (possibly) using very permeable materials,(as i am looking at temporary structures) the lowest rate could be around 0.5cm3/cm2/s for the canvas so a complete infiltration rate kinda makes sense...but along with big cracks also.
for the area of the space this would work out at around 0.25 - 0.5 ach through the fabric alone. (depending on fabric)

there is the argument to have liners of course. but i would need to compare with some valid figures.

i suppose i could set the infiltration rate at a low rating say 0.5 and include a careful adjustment of the cracks as you advise.
the temperature of the infiltration air, assuming there is no way of setting it to the adjacent room temp, might be set it to the monthly mean temperature of the adjacent room and modulate through the yearly cycle. -but i am not keen on this.

[Complex Potential]

Hi Mac

Actually I think there is a way of setting an air exchanges infiltration temperature to match the adjacent room but you would need a separate profile for every single room around your building which would be a lot of work. I wont go into it unless you need me to because it's quite heavy.

CP

[Complex Potential]

Also, Woohoo! 100 posts! I am now apparently a VE Professor and will presumably be fending off hordes of attractive ladies with a big stick from this point on.

[macpavee]

hi CP

that sounds perfect though.
i would like to know the process, especially as i am effectively working with one room in the middle, -admittedly i have the surrounding area divided into seperate zones for the simulation (so i can better observe the dynamics occuring due to orientation) but this gives me only 12 zones, so not so bad.

shame you probably wont get this till your back at work as i would love to run one last sim with this effect before i submit the work on monday.

nonetheless it will be ongoing so please, when you can spare the time, direct me to this method.

all the best.
m

[Complex Potential]

Hi Mac

Yeah, sorry, didn't see this until just now.

The method actually isn't too bad now that I've just reminded myself about it. If you go into Apache and do an individual room query, then go to Air Exchanges and highlight infiltration, you should have some options further down the screen. Where it says "Adjacent Condition" select "Ventilation from Adjacent Room" and where it then says "Adjacent Room", select the adjacent room that the infiltration will be coming from.

Of course you need to do this individually for all rooms around the building but 12 should be fine.

CP

[macpavee]

excellent stuff CP -thanks.

no worry about the delay -as you can see.

i handed in the thesis and took a much needed LONG break from all this. (smiling sleepy face)

but am about to begin a new redraw and some more (relaxed) testing.

this is a vital parameter to get right as i am sure you are well aware so a very useful tip.