air conditioner location

[jared herbert]

I am in the process of building a 20x24 addition on to my existing 16x24 shop. I am going to install a window airconditioner to cool the new room. I will mount it through the wall. I can either put it below a window, close to the floor, or the other alternative is to mount it high on the wall. The room to be cooled has 9 foot ceilings. Either location will get the unit out off the way of my work areas but I got to thinking that a location high on the wall might give better air circulation. At the stage of construction that I am in it doesn't make any difference where I mount it. Any thoughts or experience on this sort of thing.
thanks in advance. Jared

[Frank Pratt]

Higher is better for cooling. The opposite for heating.

[Steve Peterson]

I suspect that a window mounted air conditioner should be more effective if the outdoor section is not in the direct sun. A north or east wall would be shaded in the late afternoon.

My only other thought is to let it work together with a ceiling mounted air cleaner if you have one. The air currents should flow around the room rather than fighting each other.

Steve

[Howard Acheson]

Here is some info that may be helpful. It's primarily focused on air cleaners but includes info on placement and circulation that would be applicable to air conditioners.

Be aware that you must consider that AC units can quickly become dust clogged in a very short time. AC units are not designed to deal with clogged filters or clogged cooling coils or with heavy dust. In my prior shop, we built some pre-filter enclosures containing as much square area as possible. We also designed the filters to be easily removed and cleaned. This was in addition to some good air cleaners and good dust collectors.

Here are some general rules based on Nagyszalanczy's "Workshop Dust Control" and some of my own experiences and thoughts.

The two most important criteria for an air cleaner are the CFM and the filters. You want a CFM factor that will clean the size of your shop and a filter that removes the particle size that you are concerned about.

To determine the size or required air flow, use this formula: Volume of your shop (Length x width x Height) times Number of air changes per hour (typically 6 - 8) divided by 60. This will give you an answer in Cubic Feet per Minute which is how air cleaners are measured. MOST AIR CLEANER MANUFACTURERS RATE THE CFM OF THE FAN ONLY, but there are losses due to the filters. If you are building your own or if the air cleaner you are purchasing rates only the fan, figure you will lose about 25 - 40% for filtering losses.

As important as the air cleaner size is how and where you mount it. Try to mount at about 8-10 feet above the floor (no lower than 6'or 2/3 of the floor to ceiling distance if less than 8' ceiling). Mount along the longest wall so the intake is approximately 1/3 the distance from the shorter wall. Mount no further than 4-6 inches from the wall.

The exhaust is the largest determiner of the circulation pattern. You are trying to encourage circulation parallel to the floor/ceiling so ceiling mounting is not recommended. Use a smoke stick (or a cigar) to observe and maximize circulation. Use a secondary fan to direct air to the intake if necessary. Also, consider that a standard 24" floor fan moves a lot of air and, in some shops, just positioning it in a doorway with a window or other door open can accomplish as much or more than an air cleaner. It's all in the circulation patterns.

The exhaust is the clean air so that is where you want to position yourself. Do not place the air cleaner over the a dust producer. That will guarantee that the operator will be in direct line between the dust producer and the air cleaner. The operator wants to be in the clean air stream. If the dust has to pass your nose to get to the air cleaner, you get no benefits. If you have an odd shaped shop, two smaller units may be better than one large one.

DO NOT RELY ON A AIR CLEANER TO ACT AS A DUST COLLECTOR. The purpose of and air cleaner is to keep airborne dust in suspension and reduce airborne dust as quickly as possible AFTER THE DUST PRODUCER HAS BEEN TURNED OFF.

Finally, if you are looking for health benefits, you will not find any air cleaner manufacturer that makes health claims because there are few health benefits. CATCHING DUST AT IT'S SOURCE IS THE BEST LONG TERM GOAL. Rick Peters', author of "Controlling Dust in the Workshop", makes the point that spending your money getting the dust at its source is a better investment than trying to capture it after it is already airborne. If the dust is in the air, it's going to be in your nose and lungs too. Robert Witter of Oneida Air Systems has noted that "overhead cleaners can only lower ambient dust levels AFTER THE SOURCE OF EMISSIONS IS SHUT DOWN, and they take several hours to do this. This is why they are not used in industry." The absolute best answer, if health is the primary concern, is to use a NIOSH approved respirator. The dust cleaner will help keep your shop cleaner but have minimal or no health benefits. OSHA takes this position too. They measure the number of particles per a volume and most air cleaners will not satisfy their specs.

By Robert Witter, Oneida Air Systems, Chief Engineer
"Air quality tests show that Source collection (dust collection) can lower the dust loading in a wood shop by a factor of 5 to 20 times over a shop with no or bad dust collection. The goal is to lower the dust level below 5 milligrams per cubic meter(OSHA reg). A good DC system can keep the dust loading down to 1-2 mgM3. This means you inhale the quantity of dust in ten years that might have inhaled in 1 year. A little dust is OK. Overhead cleaners can only lower ambient dust levels after the source of emission is shut down, and they take several hours to do this. This is why they are not used in industry.Cloth filters can accomplish 99.9 % submicron filtration. For example, carbon black can be filtered with cloth but at a 2:1 air to cloth ratio. That's allot of filter bags. Good Felt filters 16oz will filter 99.5% of material between 0.2-2.0 micron at 10:1 air to cloth ratio. Cartridges pleat more cloth area into a smaller space, that's all. In the air sample tests i have seen only a negligible % of wood flour is as small as 1-2 microns, so a filter efficiency of 99% @ 1-2 microns is more than sufficient, and ostensibly represents 100% filtraton for wood dust."

[Charles Lent]

I live just North of Charlotte, NC so we usually have moderate Winters, with temperatures usually to +10 Deg F, and long hot Summers, sometimes with temps of 100+ deg F. My window style heat pump is mounted high (7' to top of unit) through the North wall of my 14 X 26' shop with 8' ceilings, and it does a great job of both heating and cooling my insulated detached shop building. I put it there because I felt that I needed the best air flow in the air conditioning mode when the cool air is heavier and wants to settle, pushing the warmer air higher in the space. The heated air, will circulate better on it's own than the cooler air, so I mounted the unit high to favor the cooling mode.

My unit is rated at 22,000 BTU. I replaced the typical 1/8" foam filter with a 12 X 24 X 1" pleated furnace filter that just fits under the front panel of the unit and covers the coil completely. This keeps the sawdust out of the unit's coils and also makes my heating/cooling system double as a whole shop air cleaner. If the temperatures will be at the extreme ends of the range above it helps to leave the unit on over night if I want it in the 70-75 range, but most of the time I only run it while working in there. I also run the unit all night when the temperatures will be below freezing during the night to keep my glue, batteries, and finishing products from freezing. The unit was installed about 15 years ago, so I will likely be replacing it within the next couple of years. When I do, I'm planning to buy the next larger size unit. This one has been great, but I think a little bit more cooling capability would be better for my situation.

This was not a direct answer to your question, but I hope it helps. You did not include where you live and this makes a big difference.

Charley

[jared herbert]

I live in northwest Iowa, I neglected to mention that in the first post. I had already planned on installing the AC on the east wall so it would not get hit with the hot afternoon sun. We don't get a lot of superhot days here, that being said there are a lot of days in the 80s with very high humidity that makes it uncomfortable to say the least. The more I think about it the more inclined I am to mount the unit high on the wall to avoid as much of the dust as possible, as logic tells you, the dust will settle to the lower levels fairly fast I think. Jared

[John K Jordan]

Jared,

I don't have an opinion or advice about the window/wall AC but wondered, did you consider installing a central unit?. I put HVAC in my shop and I'm very happy with it - the shop is comfortable year around. I live in TN so a heat pump is practical.

The entire cost was less than I thought it would be and the inside space needed was quite small. The outside half is away from any dust. The inside part uses standard filters on the air returns. I wired and installed everything for a significant cost savings. (The HVAC company supplied all the components and materials and did the plumbing, freon charge, and programming. I understand the window/wall units are not as efficient.

JKJ