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Grim Reading - Temp/Hum in Obs, Dec-Jan.

SnakeyJ

By SnakeyJ
in DIY Observatories

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SnakeyJ

SnakeyJ

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Bizibilder's post on mould reminded me to retrieve and download the temp and humidity data from the logger (Lascar EL-USB-2) which has been left out in the obs through Dec and January.

I think I need to raise the priority on the dehumidifier and look at fixing trying to fix a leak I've just discovered on the roof.

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Results are not so surprising given the recent run of bad weather!

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SnakeyJ

SnakeyJ

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Does the dehumidifier actually work?  Humidity levels seem close to ambient....

Chris

Chris  - I haven't actually brought one yet, due to limited funds - but meant I will raise the priority on this!

That just goes to show what we are dealing with - I bet Norfolk is not much different!!

Perhaps a little drier being in the favoured east and a little further from these wet Atlantic fronts - but doubt it will make a whole lot of difference.     I think one of the roof seams is leaking, so will take the roof off and reseal all the panel edges with fresh silicon - it has faired rather well until this point, so the leak may be attributed to the wind lifting a panel edge.

I do have a conventional peltier dehumidifier that I used to use on my boat - not ideal if the temp drops, but might well be better than nothing as a stop gap until I can get a dessicant dehumidifier.     Ideally I would like to get the humidity down to around 60%.

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SnakeyJ

SnakeyJ

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Jake - I had a roof leak that was caused by the panels fitting together too well and the water wicking through the joint by capilliary action - a dollop of silicone sorted it!

It's been very good until this recent spell of bad weather, despite some pretty rough conditions earlier.    I hadn't considered capillary action, but this sounds quite likely - I will lift the panels, clean and re-bed the joins on a good bead of silicon.   Pretty sure this will cure the problem and only a minor job if I can get my step brother up to help with the lift on and off.

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Bizibilder

Bizibilder

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I didn't bother dismantling the roof - just wiped around the joint with some meths on kitchen paper then put a bead of silicone along the inside and outside of the joint. Then run your thumb along firmly to ensure some silicon is squeezed into the joint.  

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SnakeyJ

SnakeyJ

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I installed the small peltier dehumidifier yesterday morning and will run this for a few days (at great expense!) to see if this provides any mitigation.   The data logger was reset to record the new data.     Yesterday afternoon and overnight were very wet, so a definite baptism!

I have been considering making a DIY desiccant cassette system - as this could have much lower running costs only needing a small (120-150mm DC fan for circulation).     The fan would be controlled by a humidity sensor.  Cartridges could be made up from loose silica beads and coarse filters.   Cartridges would have to be visually inspected or swapped out on a regular basis and recharged using a simple rig based on a small fan heater/hair dryer/paint gun, probably in my workshop venting out through a window/door to loose the steam.

Just a few thoughts at present, though the bulk self indicating silica desiccant is probably £ 40-50 for 10kg from flea bay.   This is reputed to absorb 30% by weight, which would be roughly 3L.   Divided and operated as two sets this would give 1.5L absorption per 5Kg, which would for maintenance would probably keep things dry nicely for weeks if the observatory was reasonably air tight and unused.     The reality is that I want to open the roof and observe, I'm replacing 6m3 with fresh damp air which will probably be 80%+.

Not sure of the accuracy, but I found a good table on H20 content in air here.     Relative Humidity of 90% @ 20C equates to something like 16g/m3 and at 5C is 6g/m3.   To reduce this to 60% RH I would need to remove between 5 and 2g/m3 dependent on ambient temp.       Sounds like I could operate with a much smaller quantity of desiccant and relatively long recycling/recharge periods - though will have to allow for the fact the observatory will never be air tight, due to construction and regular human access.

Certainly worth some further thought and investigation.

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pete_l

pete_l

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Is there actually a problem here?

The graph shows T-ambient to be always above the dew point. Although dew point is a calculated value, so long as it does reflect the actual temperature that dew forms (and that you're measuring the temperature of dew-prone surfaces) you shouldn't be seeing any condensation.

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Gina

Gina

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Alternatively.....

This is actually a fair bit cheaper than I thought (available for around £ 130) and looks quite favourably reviewed - http://www.dehumidifiers-direct.co.uk/contents/en-uk/d90_ecoair-dd122FW-simple.html?gclid=CKeR6vq86bsCFabLtAod_CkAZA

One thing wrong with this dehumidifier - it only operates down to 1C (not even freezing) so useless for outdoor sheds or observatory scope rooms :(  Pity.

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SnakeyJ

SnakeyJ

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Is there actually a problem here?

The graph shows T-ambient to be always above the dew point. Although dew point is a calculated value, so long as it does reflect the actual temperature that dew forms (and that you're measuring the temperature of dew-prone surfaces) you shouldn't be seeing any condensation.

I am getting some surface rust on screws/bolts, probably from condensation in use,  but mainly keen to keep the electronics (UPS, PSU, mount, dew controller and fixed display screen) damp free.     Lower ambient humidity should also help preserve the optics and prevent mould.

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SnakeyJ

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One thing wrong with this dehumidifier - it only operates down to 1C (not even freezing) so useless for outdoor sheds or observatory scope rooms :(  Pity.

Fair point Gina, though I think sub zero will be a problem for any dehumidifier with iced/blocked drainage hose or cracked tanks.     In use these are supposed to raise temps 3-5C, due to the output from the drier heater element, though they are not running all the time.    Perhaps a thermostatic plug as a safeguard!   If temps drop below zero then the humidity should not be a worry until it starts to warm up again!    These units do benefit from auto restart when the power returns.

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pete_l

pete_l

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I am getting some surface rust on screws/bolts, probably from condensation in use,  but mainly keen to keep the electronics (UPS, PSU, mount, dew controller and fixed display screen) damp free.     Lower ambient humidity should also help preserve the optics and prevent mould.

I think everyone who has a shed gets some rusting of exposed metal. You could give them a quick squirt of WD40 (the WD stands for Water Dispersant). But make very sure you don't spray any electrical contacts or connectors.

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ChrisLX200

ChrisLX200

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I recently installed a small dehumidifier in my shed and it has made a huge difference, hardly surprising since during the first couple of hours it pulled out 2 litres of water. I plumbed it in with a permanent drain and left it running for a week and now it's finally dry in there. The dehumidifier is now left permanently on at its lowest setting in a sort of maintenance role. A wood building like my shed is going to let moisture in, it's unavoidable either through wicking or condensation.

The best chemical protection is offered by modern corrosion inhibitors like ACF50 rather than WD40 (hack, spit). ACF50 as a very thin film offers at least 12months protection. I use it on motorcycles too and get no rust after standing outside over winter (under a cover!).

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SnakeyJ

SnakeyJ

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I recently installed a small dehumidifier in my shed and it has made a huge difference, hardly surprising since during the first couple of hours it pulled out 2 litres of water. I plumbed it in with a permanent drain and left it running for a week and now it's finally dry in there. The dehumidifier is now left permanently on at its lowest setting in a sort of maintenance role. A wood building like my shed is going to let moisture in, it's unavoidable either through wicking or condensation.

The best chemical protection is offered by modern corrosion inhibitors like ACF50 rather than WD40 (hack, spit). ACF50 as a very thin film offers at least 12months protection. I use it on motorcycles too and get no rust after standing outside over winter (under a cover!).

Thanks Chris, I'll look up the ACF50, which I hadn't previously seen/heard - could be quite useful to keep the mount/pier and ancillaries protected.

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SnakeyJ

SnakeyJ

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Dratt and double dratt - just been out to check the data logger to see how things were coming along and found the obs door open to the elements.   Can't have latched it securely, but OTOH better to find out now than tomorrow morning.   I can report the DH was still working full tilt and dripping condensate from the drain pipe!   Might have to give it another 24hrs before checking...

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SnakeyJ

SnakeyJ

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Looking slightly better today with rh down below 80% - hoping this will drop some more over the next 24-48hrs as the structure dries out - particularly under the raised floor and concrete slab.   Might have to lift the tiles and raised floor to ventilate this properly.

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SnakeyJ

SnakeyJ

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http://www.dry-it-out.com/DD822-Graphite-dehumidifier

That got favourable reviews, so I bought one.

Now it's on sale.

There was a voucher that worked for me though - google ukastroimaging dehumidifier

Thanks Dave for the link and info - I will have to wait until next month as have to put road tax out this month, but some nice overtime coming up so should be affordable.

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