Am I over-complicating things... Data Logger and Air Conditioner Control

[slimplynth]

However you want to word it, heat rises/hot air travels upwards in a house.. that's why the cellar is a cool place, as opposed to having a "wine-loft".

Dippy, I am the wind in so many different ways to so many different people - I get paid to be like a bad smell that will not go away.. i am here also like a bad smell

Anyway, common sense tells me that the room will begin to return it's equilibrium as soon as the door is shut again - even wafting the door like a deranged maniac for 10 mins is going to have very little effect on a thermal mass the size of a basement? I put a question mark because I really, really want to see the results on a graph, posted by Fizzzit, showing the recovery time of the room and a youtube (timestamped) video of someone wafting the door - seeing is believing

 

[boriz]

“opening the door for seconds possibly many minutes would have very little impact on overall conditions”

I agree. Once the door has closed and the air has had enough time to circulate and equalize, the overall change will be very small.

However, 0.1 Degrees C is very very small, and maintaining that stability throughout the room CONSTANTLY without local variations, will be impossible without an airlock.

But forget that. It’s not going to be a problem.

What about getting hold of temperature sensors that can measure accurately to within 0.1c, and guarantee that accuracy for long periods?

In fact, in order to maintain the 0.1c air temperature, the sensor itself would need to be accurate to a fraction of 0.1c. (0.05c or better at the very least.)

You will find that such a sensor will be expensive and delicate. It will need proper laboratory calibration and special transport arrangements. It will need constant monitoring with similar parallel redundant sensors and regular visits to the lab for re-calibration.

But forget that. It’s not going to be a problem.

What about the aircon unit itself? It can only be on or off. So when it’s on, the air just downstream will be much cooler than the air on the other side of the room. And when the temperature at the other end is perfect, the temperature near the unit will be far too low. Using only one on/off cooler will only work well in a fairly small space. To maintain a globally stable temperature, you will probably need several units, all over rated so they can quickly overcome the thermal inertia of such a large space, and all modulated for detailed control.

I think what we need here is a sense of perspective.

In practical terms, I would expect the temperature in a well insulated, shaded from daylight, cellar with a single cooler to be maintainable to within maybe 1 to 2c overall with possible 2c temporary local variations. Much better than that and we’re looking at some real money.

As to whether a Picaxe can do it THAT. Very probably. But is the cooler/heater up to it?

(How cold is the winter? Do you need a heater?)

 

[Jeremy Leach]

Just for interest ...
http://www.instructables.com/id/How-to-convert-a-closet-into-a-mini-wine-cellar/

 

[eclectic]

It probably doesn't matter any more, but

post #8
"so at the moment my cellar keeps things very stable around 18 degrees C,”

And post #26

"The air conditioning unit is in there already and is doing a great job of holding the temperature stable around 18 degrees C having recorded it for the past twelve months with a less than desirable unit. I don't need to calculate the heat load, I have done that when I sized the unit.”


What was the measurement method?
What were the results?
e

 

[BCJKiwi]

OP has indicated that this wine 'cellar' has been constructed in the 'middle' of the house.
From this I presume it is not in the cellar (basement) and most likely on the same level as other regular use parts of the house.

The corollary to hot air rises is that cold air falls. In this instance the cooler air being heavier will definitely spill out through the door along the floor and hotter air will enter through the top of the door to replace it - neither are likely to have any serious affects unless the the door is open for a long enough time for a significant part of the cool air volume inside the cellar to be exchanged for warmer air.

 

[slimplynth]

Sorry, i am like a (warm) bad smell

Last week i was looking at chart records for a CMM inspection room. We use the CMM room to measure machined aircraft parts, approx. 2m cubed in size with tolerances of ±30 microns. Our customers require we control the room's temp at 20°C (±2°C)

The room is approx. 4m (w) x 8m (l) x 5m (h). There is a smaller, standard door and a larger barn type door. The barn door is only opened to allow parts to be loaded onto rollers outside, preapred for quick loading on to the measuring table. (this still takes sevral minutes.)

A standard 2m airconditioning unit, like most that you see in shops, offices etc is used to control temp. Over a week period of plotted data i witnessed no out of tolerance condition in the room.

It's A-level physics surely... the hotter or colder something is, relative to it's environment.. the faster it will cool or warm up (its exponential).

I can see the advantage of controlling humidty in this application as, from the little i've read, it can affect taste. Temperature should be straightforward (possibly ignored until it's quantified by continous logging and/or shown to be an issue).

Maintaining stable temps significantly above and below ambient (say 50°C) are surely trickier and require quicker response times, accuracy and higher quality (expensive) equipment? (well it does in my experience)