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A/C for a small observatory

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Posts 11
foggyglasses Posted: 11-05-2013 4:35 PM

Hello SB: I'm planning a small observatory in the SW of the USA, featuring  a Paramount of course. I've been watching air temperatures which last summer reached 110 F even in Flagstaff AZ. At the least that must lead to drying of lubricants in a mount, never mind the stresses on an OTA.

Installing an A/C unit inside a dome does not seem like a good idea. What have your customers done?

Thanks!

fg

Top 10 Contributor
Posts 5,025
Software Bisque Employee

I know several customers doing this, A/C unit inside the dome/buildings.

Even if only to run during the day to keep the temperatures inside from going through the roof (literally). I am not sure if any of them also run these during the night - while imaging but that probably doesn't make any sense to do. Outside of this I am not aware of any other better options or alternatives? Maybe others can chime in here.

Depending on the structure, the entire dome/building may retain sufficient enough heat so that a long cool down period is required before optimal viewing conditions exits. Opening the roof/shutter before twilight to expel trapped heat can help.

Thomas M. Bisque

Software Bisque, Inc.

862 Brickyard Circle

Golden, Colorado 80403-8058

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Posts 27,307
Software Bisque Employee

foggyglasses:
What have your customers done?
Hopefully others will chime in.  Here's a related thread on this subject: http://www.bisque.com/sc/forums/p/18265/76912.aspx#76912

Daniel R. Bisque

Software Bisque, Inc.

862 Brickyard Circle

Golden, Colorado 80403-8058

Office Hours: 8 a.m.-5 p.m. Monday-Friday GMT-7:00

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Posts 194
Universal Subscription Licensee

I would suggest looking for a dog house or pet A/C unit. That is what I have installed "outside my OBS. They typically only produce between 2500 to 5000 BTUs so they aren't going to freeze your interior but they will lower the temperature . And since they recirculate the air the tend to be a little more efficient plus they help lower the humidity which is a plus for me. 

 

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Posts 27,307
Software Bisque Employee

Daniel R. Bisque:
Hopefully others will chime in.
See this contribution to your OP: http://www.bisque.com/sc/forums/p/18265/87647.aspx#87647.

Daniel R. Bisque

Software Bisque, Inc.

862 Brickyard Circle

Golden, Colorado 80403-8058

Office Hours: 8 a.m.-5 p.m. Monday-Friday GMT-7:00

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Posts 172

The best way to deal with hot sunny days is to limit heat buildup inside the structure. Roll-off observatories can use foliage shaded walls and double metal roofs with an air space. A simple bathroom-type exhaust fan can lower internal temperatures by 10-20F compared to a structure with no ventilation. Polyethylene domes, even white ones, are highly transparent to long wave infrared and objects inside a single layer dome will heat very quickly. I see that some dome companies now offer black liners and these might be useful to limit IR heat passing into the dome during the daytime.

If you have AC power, then running a small air conditioner on the hottest days might make sense. My 120 square-foot RoR observatory has a vine-shaded West wall, a 80 CFM thermostat controlled exhaust fan set for 75F, and an air conditioner that runs when the inside temperature goes over 90F. I experimented with several types over the years and ended up using a 5K BTU window unit. The portable units I tried were not very efficient and draining the condensate water during our two-month monsoon season was a pain. The small window unit is permanently mounted in a north-facing wall and uses much less power (650W vs. 900W) than the portable A/C it replaced. During the summer months it runs 5-6 hours a day and the inside temperature rarely exceeds 95F. 

If I were building my observatory again, I would definitely opt for a double metal roof to reduce the "broiler effect" where solar heat is absorbed by the roof structure and then radiated down inside the building.

Jim McSheehy

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Posts 11

Thanks for the great advice! I had no idea doghouse A/C was available. HOAs hate domes so if they present thermal problems too then that's two points for  RoRo. I did see a used RoRo for sale and the owner was frank about dust problems. Anyway it seems that a lot of care will be required. Many thanks again to all.

fg

 

Top 10 Contributor
Posts 27,307
Software Bisque Employee

This thread (and the other related thread referenced above) contains a treasure trove of useful information. Nice work.

Daniel R. Bisque

Software Bisque, Inc.

862 Brickyard Circle

Golden, Colorado 80403-8058

Office Hours: 8 a.m.-5 p.m. Monday-Friday GMT-7:00

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