Ventilation question

[Brent Brod]

I'm about to purchase a laser, and I have a concern about ventilation. Recommended flows of 400+ cfm seems like it will load up an AC system pretty hard. Are you all running these in a conditioned environment? If so, did you have to oversize your cooling capacity to deal with the air exchange?

I'm thinking of putting this whole operation in a small building (10X15) with its own AC system, but it looks like it will change the air in the building every few minutes when I turn on the ventilation system.

By the way, here in Houston the ambient outside temp in the summer runs around 95F with humidity in the 80% range during the day. That is a lot of latent heat to remove from the "new" air being replaced.

[Jerry Allen]

The 400+ CFM relates to the vent system connected to the laser not the ambient airflow. I think 3/4 HP to 1 HP is what it takes.
However, the ambient air humidity and heat will affect the laser and needs to be controlled to between 60-75 degrees F, and probably 65-70% humidity max.

[Lee DeRaud]

The 400+ CFM relates to the vent system connected to the laser not the ambient airflow. I think 3/4 HP to 1 HP is what it takes.
However, the ambient air humidity and heat will affect the laser and needs to be controlled to between 60-75 degrees F, and probably 65-70% humidity max.
I think Brent's concern is that he's going to be running it in a smallish air-conditioned shop and it will be pumping his expensively-cooled air out the vent at a pretty good clip, as opposed to a DC that leaves the cold air inside.
Hmmm...don't people with humongous DC systems that have the cyclone and bags outside have the same problem?

[Brent Brod]

Lee has the problem pegged. If the total volume of the workroom is 1500 cubic feet, I'll empty the air out of the room one time every 3 minutes or so. The air has to be replaced, or I'll be living in a high altitude/low oxygen environment :) The replacement air will be 95F from the outside coming in around cracks and under the door or via some controlled point.

I spoke with an AC pro today, and he tells me that 500 cfm in our summer environment is equivalent to about 1 ton of AC capacity. So, while the vent is running on the laser I'd need an extra 12,000 btu/hr capacity on the cooling to maintain the temperature. Now I just need to calculate the cost of running that extra cooling to see how it will impact the budget.

[Rick Maitland]

Hi Brent welcome to the site. My day job is as an Air Balancing Technician. I have been adjusting airflows in commercial buildings for about 13 years now. You have a very valid concern. Removing 400 CFM from your shop will cause the room to go negative and allow unconditioned humid air to leak into your shop. I do not have a cheap solution to the problem. You will have to add in 420 cfm of outside air to your existing A/C unit, which may cause loading problems. Or add a 420cfm 100% outside air unit to the shop. The question is how much are you really going to be using the exhaust. I have my Laser Pro in an office and just added a window unit to help out the existing system. I live in Fort Worth Texas and so far have not had any problems. Hope this helps.

[Michael McDuffie]

Brent,
Phil from Pacific Northwest Laser has a plywood cabinet with filters that he uses at woodworking shows. Can't smell any smoke when he is running it. He even used it when he demo'd the machine for us in a motel room a few years back.

Some systems intended for use in kiosks also have filter cabinets. I do vent my DC outside and I open a window so that I won't backdraft the water heater and furnace. AC isn't as much of a concern here in sunny Seattle.;)

Michael

[Brent Brod]

I found this nifty calculation for figuring the cost:

Capacity (Btuh)/SEER X Cooling Load Hrs/1000 X Elec. Rate = Annual Cost of Operation

If I used an extra ton of AC (12,000 btu/hr) while I worked the laser, and I estimate 3 hours per day, I'd have cooling load hours of 750 assuming a 50 week year (at this point you know I'm exaggerating on the high side). Electricity here runs about $0.125/kwh.

12,000 / 12.0 X 750 / 1000 X 0.125 = $93.75

Not enough to be concerned about as long as I can stay comfortable while all this is happening. Thanks for your feedback. I can now feel comfortable believing what I've been hearing. After proving it to myself, of course! I need to work on that some, I guess :)

[Rodne Gold]

We have 3 largish lasers in a small closed airconditioned room , the venting system does not evacuate the room or affect the airconditioning and this is not a humungous aircon either.(small window unit) We installed the aircon cos the sources were shutting down due to overheating.(I live in South Africa , its gets real hot in summer)
The blowers work when the laser is closed , and albeit might be capable of shifting 400cfm , they dont do so in real terms.
I would not be concerned about this at all.
Heres a pic of our laser room
http://www.rodneycanon.fotopic.net/p3203802.html

[Brent Brod]

Thankyou, Rodne. That is very encouraging. By the way, what temperature was your laser room when you had problems with the sources shutting down?

[Rodne Gold]

I would say ambient about 80-85 degrees. The sources get hot here cos we run the lasers almost on a coninuous basis and the temps in the enclosure where the sources are were much higher. We added extra cooling fans to solve the problem asthe Aircon did help but but never solved the problem by it'self , by far the biggest effect of the aircon was to make the 2 operators more comfortable.

[Keith Outten]

When temperatures in my shop office exceed 80 degrees F my Epillog will often dump a running job. I have a 1.5 ton heat pump, central heat and air system, that does a fair job in the summer but needs a little help in the cold winter months keeping up with my exhaust system which dumps outside.

[Brent Brod]

That's good information. Thanks for the follow up.