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2005-03-06, 2006-05-20, -5-22, -07-23, 2006-10-27, 2009-06-14
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|Cold Air Intake|
|Fans, Blowers, and Compressors|
The purpose of this page is to discuss some of the needs and principles of ventilating a glass blowing studio, including comments based on visits to many studios and online comments in various discussion boards. Several references are made to my hot walls page, so you may wish to start a new browser window (Ctrl-N in Explorer) and load it in that window.
Many studios are overly hot, making it uncomfortable to work if not actually risking heat exhaustion. The best design seems to be to have separate exhaust fans with separate air supply for the furnaces and the blowing floor and to insulate the metal panels between the two so the heat does not radiate from them.
However, one particularly nice design that took a lot of planning, involves bringing the makeup air out to the floor and blowing it down on the work floor. This is shown at the right in the setup from Vetro Glass Art in Grapevine Texas. This studio also has air conditioning for the next door gallery which blows chilled air down on the bleacher seating at the camera position. 2005-03-06
Note that in the discussion that follows, it is assumed that there is NO air conditioning. If there is then it should be completely obvious that everything is done to keep the AC air where the people are and the hot air where the furnaces are and to avoid releasing the furnace air into the cool stuff or sucking the cool stuff into the furnace space. The setup at Bowling Green State U (right) is inside the arts building and is heated/air conditioned with the rest of the building. As you can see, the entire hot wall is an encased box with large vent stack going off the top (the smaller tubes in the back are filtered exhausts for fuming with noxious chemicals.) If this place has a flaw, it is the limited intake air - when the shipping bay doors are opened a crack, really cold air comes past the camera position in winter.
VENTILATION - A studio's ventilation system should, if possible, not include free standing fans to shift glass dust around the shop. The exhaust point of the system should be near or above the hottest part of the shop to move both heat and furnace fumes out of the shop. A planned entry point for air should be used and when possible two or more should be provided: one which provide for the best air flow across the work area and another which supplies air during winter to ventilate without chilling the workers. Only one input should normally be used at a time so that air flow velocity is as high as possible for best cooling and removal of dust and fumes. The input should be chosen so that it does not normally pull in dust or exhaust from parking cars. If several openings are provided, normally air will flow over the shortest possible route from input to exhaust, including along walls, bypassing the people in the center. A fan blowing into a building normally provides poor ventilation except for the direct air flow within a few feet of the fan; there are many dead pockets where fumes and dust may collect. Heat shields in front of furnaces may also help control the air flow - with enough surface before the furnace area, it may be possible to have two exhaust fans, one primarily for heat and fume control and one for work area air flow. When possible, work with the prevailing wind, setting exhaust fans into the downwind side of the building and intakes on the upwind side. Drawing air from the shadier side or from under a building may result in cooler air for much of the day. 5/30/95 from Hot Glass Bits #25
Air can be moved by sucking it or blowing it. While standing in a fan feels good, blowing air into a space is not the best way to ventilate it - sucking air out is much better. Controlling where the air comes in with vent panels (windows) is much easier than other ways. In the sketch at the right I have placed three "windows" A, B, & C, a door, a work bench and a wall between the work space and the hot wall space. Think of the "windows" as places that can either hold a fan/blower or allow the intake or exhaust of air. The door can obviously also do that also, depending on where it leads. Be aware that adding screening will cut down on the free air flow, by as much as 50% depending on the screening. 2005-03-06
To state it up front, my recommendation is that exhaust fans should be placed at B and C, taking air from A and the Door. (Better would be an intake separate from the door, but I didn't offer that.) Let's look at other choices and see what is usually wrong.
A very common choice is to put an exhaust fan at A and take the air in at C (with B not even being provided.) This works under ideal conditions, because air is crossing the room diagonally and air is being taken out from the hottest area. By placing panels or baffles in the hot wall, it can be kept from being too hot in any one place. It becomes a problem when the air being drawn in C is either already hot (late spring in Texas, not to speak of summer) or so cold it freezes the worker (winter up north.) Shutting down C or if C is too small, results in lack of ventilation, hot spots, etc.
Blowing air in through C produces a good air flow just in front of C, which could be aimed at the bench, but the moving air can be felt for only 5-10 feet in front of the fan and there will be dead spots, especially in the area from the word Door to just below the word Bench in the drawing.
Blowing air in through B produces even less flow because the flow is broken up by the hardware behind the wall. Even if A is open as exit, air flow will be diffuse from the center on unless the wall is almost sealed, which is very awkward in use. The higher pressure behind the wall will force hot air out into the work space.
Exhausting air at C produces an air flow across the whole
room, strongest across the center and stronger near C but most of
the air will be moving. It is important that C (and any exhaust
fan) be shrouded* so that power going into the fan will not be
wasted with air simply moving in a short circuit around the fan.
I have been in a couple of studios where a fan on brackets has
been stuck in a window opening and without a piece of plywood or
metal cut to surround the blades, almost all the electricity
going into the fan is merely pushing air in a donut shape, about
1 foot outside the window, turn outward radially a foot, head
back into the building to be sucked out again, pulling almost
nothing from the inside of the building.
If an exhaust fan is used at A, then air sucked in at B and through any gaps in the hot wall, will flow to the left, taking hot air with it. Ideally A should be higher up, since hot air rises and in the ultimate can be overhead exhaust as long as there is air supplied behind the wall from an intake like B. Many studios use a hood and take the hot air up and out and this is an excellent choice if available.
The air safety and ventilation industry people discuss air changes per hour [AC/hr]. The box below has a suggestion of up to 30 AC/hr which would only be necessary with rather toxic materials. Another source, soon to be published, suggests 1 to 1.25 AC/hr. I think I would be happier with 2-4 AC/hr. To get from AC/hr to air flow per minute, you have to know the cubic feet of the room (height x length x width). Divide that by 60 minutes per hour to get cubic feet per minute (cfm) for 1 air change, then multiply by the number of air changes. If you want to see what the make up air flow will be, you divide the cubic feet per minute by the square feet of the intake opening(s). The cubic feet per minute can used to select one or more air movers (fans, blowers). 2005-03-06
COLD AIR INTAKE - One problem of studios in
northern climes is that the winter air being drawn in can be very cold.
The drafts of this cold air can be very uncomfortable and cold reduces the
efficiency of the furnace that has to heat air an additional 60F degrees.
The solution goes by the name of
heat-recovery ventilator (good
article) which have become a lot more available with the construction
of sealed homes. [There is also recuperation
which is done with much higher heated air and special furnace
The solution is to draw cold air in over an air-to-air heat exchanger where thin metal plates divide the outgoing warm air from the incoming cold air, heat moving through the plates as it will. Such a unit could be home built in several ways including metal tubes inside a box or sheet metal assembled like a commercial box (image from article) If built as part of a ventilation system using blowers that would be used anyway, the added cost would be much lower. 6009-06-14
|Reply to e-mail about ventilation. Unless you can live with the sound of a high speed blower, you are going to have to get at least two additional openings, probably at least 2x2 feet each, one for intake air and one for the exhaust, depending on the blower you get. I would take out a window or take off a door and replace it with another with a hole cut in it to get the changes of air you need. Pete on the group mentions a change of air in the room every two minutes - a room 20x20 with 10 foot ceilings would be 4000 cubic feet so ventilation would have to be 2000 cfm. In a room with this change and air moving through 2x2 foot openings, the air would be moving at 500 feet per minute (2000 cubic feet divided by 4 sq.ft.) or 30,000 ft/hr or 5.7 miles per hour. A 6 inch round opening has only 0.196 sq.ft of opening so air velocity would have to be 10,185 feet per minute, or 611154 feet per hour or 115.7 miles per hour!!!!!!!!|
Reply to e-mail question below 2002-08
Furnace Glass Web Site/Hot Glass Bits
Condensing Heat Output
ELEMENTS OF COMBUSTION
OF NATURAL GAS
Composition of METHANE:
A mole is defined in S.I. as Avogadro's number of particles of any kind of substance (atoms, ions, molecules, or formula units). In S.I., this unit is abbreviated mol. The mole is the basic unit of amount of substance. Wikipedia
q = DHvap (mass / molar mass)
The meanings are as follows:
1) q is the total amount of heat involved
1 kilojoules = 0.94781712 Btu
Conversion 1000 MJ = 1 gigajoule (GJ)
There are three groups of devices for dealing with air as stated in the title of this section. They differ by the path of the air and the pressure they will work against.
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