Venting an observatory


Eric Claeys
 

I realize this isn't an AP question, but I have an 1000 GTO in my roll-off roof remote observatory in the mountains of New Mexico so it's kinda related...

In the summer my observatory can get to over 100 degrees F (38 C).  Although I'm not particularly worried about the mount, there are other less "robust" electronics, and I'd like to keep the temperature down so everything cools off more rapidly.  The observatory is noticeably warmer the higher up you go.
The observatory's west wall is 9 foot (2.7 m) and the roof goes up another 3 feet (1 m).  The other three walls are about 5 feet (1.5 m).  The roof rolls off to the east.

I made an enclosure with two 9-inch (22 cm), 12-volt fans and a furnace filter since there tends to be a lot of dust.  The fans will be temperature-controlled via a Digital Loggers power switch with temperature sensor.  Although the fans are 4-pin, they'll either be on or off.

A couple questions:
  1. Given the wind usually blows from the west and there tends to be dust, would I be better off with the fans on the east or west side of the roof?
  2. Should the fans blow IN or OUT?
There are currently enough areas where air can come in, e.g., around the wheels, that I'm not worried about how air on the other side will come in or go out.  If need be, I can install a vent on the other side, or maybe even a second fan.

Knowledgeable suggestions appreciated.  Thanks - Eric


Roland Christen
 

Not sure about the fans but I would make sure to paint your roof white. My Hawaii observatory has a green roof (local requirement) and it gets 100F in there during the summer (10 degree F warmer than the outside air). My Illinois observatory has a white roof and on the hottest days the inside temperature is almost always at the same temperature as the outside air, and some times actually cooler.

Rolando

-----Original Message-----
From: Eric Claeys <AstroEric@...>
To: main@ap-ug.groups.io
Sent: Wed, Nov 30, 2022 8:39 pm
Subject: [ap-ug] Venting an observatory

I realize this isn't an AP question, but I have an 1000 GTO in my roll-off roof remote observatory in the mountains of New Mexico so it's kinda related...

In the summer my observatory can get to over 100 degrees F (38 C).  Although I'm not particularly worried about the mount, there are other less "robust" electronics, and I'd like to keep the temperature down so everything cools off more rapidly.  The observatory is noticeably warmer the higher up you go.
The observatory's west wall is 9 foot (2.7 m) and the roof goes up another 3 feet (1 m).  The other three walls are about 5 feet (1.5 m).  The roof rolls off to the east.

I made an enclosure with two 9-inch (22 cm), 12-volt fans and a furnace filter since there tends to be a lot of dust.  The fans will be temperature-controlled via a Digital Loggers power switch with temperature sensor.  Although the fans are 4-pin, they'll either be on or off.

A couple questions:
  1. Given the wind usually blows from the west and there tends to be dust, would I be better off with the fans on the east or west side of the roof?
  2. Should the fans blow IN or OUT?
There are currently enough areas where air can come in, e.g., around the wheels, that I'm not worried about how air on the other side will come in or go out.  If need be, I can install a vent on the other side, or maybe even a second fan.

Knowledgeable suggestions appreciated.  Thanks - Eric


ROBERT WYNNE
 

In or out is the first problem you will need to decide. Ideally you would want positive pressure pulling in filtered air faster than it can escape. Clean rooms all operate at positive pressure. Air is introduced into the clean room from the ceiling and filtered through HEPA filters. The positive pressure is just enough to almost keep the doors blowing open. The ideal pressure is set by trial and error. You haven't mentioned at  what temperature you want to maintain inside the dome. If the ambient temperature is 100 degrees you won't get lower than ambient unless you air condition the space. In this instance you would want to exhaust hot air from the roof and pull filtered air near the floor. -Best, Robert

On 11/30/2022 6:39 PM Eric Claeys <astroeric@...> wrote:


I realize this isn't an AP question, but I have an 1000 GTO in my roll-off roof remote observatory in the mountains of New Mexico so it's kinda related...

In the summer my observatory can get to over 100 degrees F (38 C).  Although I'm not particularly worried about the mount, there are other less "robust" electronics, and I'd like to keep the temperature down so everything cools off more rapidly.  The observatory is noticeably warmer the higher up you go.
The observatory's west wall is 9 foot (2.7 m) and the roof goes up another 3 feet (1 m).  The other three walls are about 5 feet (1.5 m).  The roof rolls off to the east.

I made an enclosure with two 9-inch (22 cm), 12-volt fans and a furnace filter since there tends to be a lot of dust.  The fans will be temperature-controlled via a Digital Loggers power switch with temperature sensor.  Although the fans are 4-pin, they'll either be on or off.

A couple questions:
  1. Given the wind usually blows from the west and there tends to be dust, would I be better off with the fans on the east or west side of the roof?
  2. Should the fans blow IN or OUT?
There are currently enough areas where air can come in, e.g., around the wheels, that I'm not worried about how air on the other side will come in or go out.  If need be, I can install a vent on the other side, or maybe even a second fan.

Knowledgeable suggestions appreciated.  Thanks - Eric


Eric Claeys
 

Thanks Robert.  I was hoping to have positive pressure.  The ambient rarely gets above 85 F - the observatory heats up (probably) due to the color.  I'd like to get as cool as possible given the fans I have.  I considered 120v fans but feel it's too dangerous since I'll need electrical contacts so the fans get power only when the roof is closed.  I don't want exposed 120v contacts.
Air conditioning is too costly, too complex, and requires more maintenance so I prefer to stay away from that.
I've considered pushing hot air out and adding a filtered vent near the floor.  I assume I'd want the vent on the opposite side from the fans?  Adding a floor vent would be a backup if the current solution isn't enough.

Rolando, I'll need to check with the community covenants to see if I can have a white roof (it's in New Mexico Skies Enclave, next door to Mike Rice's place).  I hesitate to paint anything though (the current siding came colored) since that adds to maintenance. 


weems@...
 

I agree with Roland that it’s best to reduce solar gain than to try to get rid of the energy once it has entered. My white dome with the black interior gets only a few degrees warmer than ambient on the sunniest long days of summer. If you can’t paint the roof white, you could insulate it with reflectix or foil clad foam board just under the metal. Be sure to keep the ridge vent clear.

You can also put reflectix covers over the sensitive electronics.

I would have the fans blow in from the shadiest side, pulling the air through a filter, and just let the air escape through the various gaps that dust would tend to enter through. 

Chip


Eric Claeys
 

Thanks Chip. I'm pretty sure the bottom of the roof is already insulated, at least it has something that looks like there's foam in it.  I've never gotten up there to check it out though.


Christopher Erickson
 

Preserving local seeing is behind many details related to ventilation.

Insulation isn't an ideal solution. You want your observatory parts to have about the same thermal inertia as your environment.

Have a reversible fan mounted low on the observatory. Pulls air in during the day and pushes hot air out of a passive vent at the high point of the observatory. Reverse the fan direction at night. Little fans are mostly useless.

A filter box might be a good thing when pulling air into the observatory.

A reflective roof is VERY desirable. There are special paints available.

Heat can be very hard on lubrications in mounts and focusers. It can age many things quickly. Things like O-rings, gaskets, plastic, etc. It will also accelerate oxidation, contamination and corrosion.

Having two or more reversible fans is way, way better than having just one fan. Redundancy. Avoiding SPoF's (Single Point of Failure.)


-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738
www.summitkinetics.com
   

On Wed, Nov 30, 2022, 8:01 PM Eric Claeys <AstroEric@...> wrote:
Thanks Chip. I'm pretty sure the bottom of the roof is already insulated, at least it has something that looks like there's foam in it.  I've never gotten up there to check it out though.


ROBERT WYNNE
 

I think you should consider solar powered attic fans. They are quite effective. I have several on my home and no longer have a strata of warm air hugging the ceiling. BTW That's quite a set up you have there. -Best, Robert

On 11/30/2022 9:08 PM Eric Claeys <astroeric@...> wrote:


Thanks Robert.  I was hoping to have positive pressure.  The ambient rarely gets above 85 F - the observatory heats up (probably) due to the color.  I'd like to get as cool as possible given the fans I have.  I considered 120v fans but feel it's too dangerous since I'll need electrical contacts so the fans get power only when the roof is closed.  I don't want exposed 120v contacts.
Air conditioning is too costly, too complex, and requires more maintenance so I prefer to stay away from that.
I've considered pushing hot air out and adding a filtered vent near the floor.  I assume I'd want the vent on the opposite side from the fans?  Adding a floor vent would be a backup if the current solution isn't enough.

Rolando, I'll need to check with the community covenants to see if I can have a white roof (it's in New Mexico Skies Enclave, next door to Mike Rice's place).  I hesitate to paint anything though (the current siding came colored) since that adds to maintenance. 


ROBERT WYNNE
 

I second painting the roof white. -Best, Robert

On 12/01/2022 12:36 AM Christopher Erickson <christopher.k.erickson@...> wrote:


Preserving local seeing is behind many details related to ventilation.

Insulation isn't an ideal solution. You want your observatory parts to have about the same thermal inertia as your environment.

Have a reversible fan mounted low on the observatory. Pulls air in during the day and pushes hot air out of a passive vent at the high point of the observatory. Reverse the fan direction at night. Little fans are mostly useless.

A filter box might be a good thing when pulling air into the observatory.

A reflective roof is VERY desirable. There are special paints available.

Heat can be very hard on lubrications in mounts and focusers. It can age many things quickly. Things like O-rings, gaskets, plastic, etc. It will also accelerate oxidation, contamination and corrosion.

Having two or more reversible fans is way, way better than having just one fan. Redundancy. Avoiding SPoF's (Single Point of Failure.)


-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738
www.summitkinetics.com
   

On Wed, Nov 30, 2022, 8:01 PM Eric Claeys <AstroEric@...> wrote:
Thanks Chip. I'm pretty sure the bottom of the roof is already insulated, at least it has something that looks like there's foam in it.  I've never gotten up there to check it out though.




weems@...
 

That may just be a sound absorbing layer, to reduce drumming in the rain. Insulation isn’t the best solution, but if painting the roof isn’t an option, it will help reduce solar gain and lower the load on the fans. Since the roof rolls off, it shouldn’t affect seeing. It will slow radiative cooling after the sun goes down, so may necessitate opening earlier. 

Chip 


Dean S
 

My south wall gets very warm from the sun during the summer.   I hang a solar shade on the wall and it cuts the heat tremendously.   Lasts about 5 years before it needs replaced.  image0.png


On Dec 1, 2022, at 4:44 AM, ROBERT WYNNE <robert-wynne@...> wrote:


I think you should consider solar powered attic fans. They are quite effective. I have several on my home and no longer have a strata of warm air hugging the ceiling. BTW That's quite a set up you have there. -Best, Robert
On 11/30/2022 9:08 PM Eric Claeys <astroeric@...> wrote:


Thanks Robert.  I was hoping to have positive pressure.  The ambient rarely gets above 85 F - the observatory heats up (probably) due to the color.  I'd like to get as cool as possible given the fans I have.  I considered 120v fans but feel it's too dangerous since I'll need electrical contacts so the fans get power only when the roof is closed.  I don't want exposed 120v contacts.
Air conditioning is too costly, too complex, and requires more maintenance so I prefer to stay away from that.
I've considered pushing hot air out and adding a filtered vent near the floor.  I assume I'd want the vent on the opposite side from the fans?  Adding a floor vent would be a backup if the current solution isn't enough.

Rolando, I'll need to check with the community covenants to see if I can have a white roof (it's in New Mexico Skies Enclave, next door to Mike Rice's place).  I hesitate to paint anything though (the current siding came colored) since that adds to maintenance. 

<Observatory.png>


Jeff B
 

One thing I learned with roll off roofs is that when I really insulate the walls, ceiling and door, the interior temperature will always track below, sometimes well below,ambient, right up until sunset.  The 22' x 32' ROR we house the big 11" achromat in tracks a good 5-6 degrees F under ambient.  Its wall and ceiling are super insulated, running clearances low.  My recent 13' x 13' ROR for my personal big refractor runs a solid 3-4 degrees lower than ambient with R11 in the walls and R20 in the "attic".  Both observatories have vents in their attics.

I have found it a tremendous advantage to have both scopes, particularly my big LZOS triplet, at or a little below ambient temperature when deployed, preferably the later.  We can use high powers immediately, especially during that really nice window from just before sunset to about an hour after sunset when the upper atmosphere is really calm.  Plus, after that, the scopes are much better positioned to track the falling ambient temperature.  No boiling thermal soups in the out of focus images!

Jeff

On Thu, Dec 1, 2022 at 7:55 AM Dean S <dean@...> wrote:
My south wall gets very warm from the sun during the summer.   I hang a solar shade on the wall and it cuts the heat tremendously.   Lasts about 5 years before it needs replaced.  image0.png


On Dec 1, 2022, at 4:44 AM, ROBERT WYNNE <robert-wynne@...> wrote:


I think you should consider solar powered attic fans. They are quite effective. I have several on my home and no longer have a strata of warm air hugging the ceiling. BTW That's quite a set up you have there. -Best, Robert
On 11/30/2022 9:08 PM Eric Claeys <astroeric@...> wrote:


Thanks Robert.  I was hoping to have positive pressure.  The ambient rarely gets above 85 F - the observatory heats up (probably) due to the color.  I'd like to get as cool as possible given the fans I have.  I considered 120v fans but feel it's too dangerous since I'll need electrical contacts so the fans get power only when the roof is closed.  I don't want exposed 120v contacts.
Air conditioning is too costly, too complex, and requires more maintenance so I prefer to stay away from that.
I've considered pushing hot air out and adding a filtered vent near the floor.  I assume I'd want the vent on the opposite side from the fans?  Adding a floor vent would be a backup if the current solution isn't enough.

Rolando, I'll need to check with the community covenants to see if I can have a white roof (it's in New Mexico Skies Enclave, next door to Mike Rice's place).  I hesitate to paint anything though (the current siding came colored) since that adds to maintenance. 

<Observatory.png>


Astrobob
 

My ROR has 2X6 rafters fully covered by 1/4" plywood. Attached to that is bright silver aluminum roofing. The exterior walls are covered with light colored siding. The bottom of the 16" square pier has a space in the floor (to prevent vibrations) that has screening to prevent critters from getting in. The perimeter of the roof has a one-inch space all around to ventilate rising heat. The whole observatory acts like a chimney when closed. I rarely see the temperature over 80 during the hottest days. In the spring, I spray the interior perimeter of the roof with a house friendly bug killer. I have no trouble with rain or snow except for brushing it off the roof. I built the observatory in 2000. I've never had critters or a leak except (on two occasions) a 3-foot Rat snake (excellent climbers) that I put out the door. They live under my observatory and they're not poisonous. They are welcome! I've never seen a mouse in the observatory in 22 years.

Bob