Adding more filtration to "Window" AC - HVAC engineer questions /

[Marctrees]

We are installing two 24k Frigidaire "Window" AC's in wall holes in our shop.

It seems all these "window" Ac's have very basic thin filters, with definite possible gaps on the perimeter.

There is a 1 to 1 1/2" gap between the front face of the filter and the backside of the factory intake grille... space to add media.

Our use will be woodshop... often will have fine wood dust in air when the AC's are running.

I am wanting to buy bulk roll "filter media" to place in that space, to place on top of factory filter.

Then as maintenance either wash or throw out, whatever makes more sense.

Am learning about "MERV", basically the higher the # the finer particles it catches but of course w more resistance to air flow.

Don't know what MERV is overall best to choose.

Any experts on this to suggest best way to keep dust from inside unit... reason being to extend years between removing from wall sleeve and hosing out.

Marc

 

[Marctrees]

Was figuring to put clamp on ammeter on blower motor after I installed extra filtration.. was thinking knee jerk to confirm I did not increase blower motor amp draw more than 10% max more than it was before filter ??????

????

5% ????

Obviously I do not want to overwork/ overheat my blower motor by too much restriction over what it is designed for.

Marc

 

[Marctrees]

Alternate is to duct tape onto to outside face of grille something like below link and then toss out when loaded.

These are the approx ballpark size of the intake opening.

A "pre filter" idea.

Marc

https://www.amazon.com/gp/product/B07FNWB1B5/?tag=atomicindus08-20

 

[Marctrees]

Actually, this same thread questions answer principles would cross apply to ANY air handler filtration restriction.

Marc

 

[jjrbus]

Some time ago I saw someone that had a mini split in his shop and was having dust issues. His approach was to build a large box, I'm talking maybe 8'X2' to hold filters, acted as a prefilter. Seemed like a good idea. Would not be as easy to pull off with a window AC, but something to think about.

As I was typing I remembered it was a video, here you go.

 

[LS6 Tommy]

Adding filtration will not increase blower amperage draw. It will most likely make the coil freeze, however.

Tommy

 

[Bruce Amacker]

Adding filtration will not increase blower amperage draw.

Tommy

It will actually decrease amperage and increase fan RPM. I use a similar model in the classroom for demonstration.

As for filtration, I'm interested in this too, as I also use 2- 24K window AC units in my shop. Auto work/mancave so no big sawdust problem but I clean the filters regularly.

 

[Marctrees]

Well, I could easily build a box that would hold more surface area of filter.
.
Tommy - coil may freeze if I decrease airflow cfm through it ?

Marc

 

[gregs]

I just finished doing this to the two 24k window a/c units in my shop. I built a frame that went around the intake area and used a filter grille that was bigger than the original filter area. I removed the original filter. It allows me to use standard filters and makes it easy to change as well.

 

[Milton Shaw]

If your shop is really that dusty, I hope you are running an air cleaner all the time for your own health. If so direct its output at the front of the unit so the air conditioner is seeing already filtered air. Any thing you add inside the unit is going to increase the problems you get with reduced air flow like coil freezing.

 

[DynoDave]

I just finished doing this to the two 24k window a/c units in my shop. I built a frame that went around the intake area and used a filter grille that was bigger than the original filter area. I removed the original filter. It allows me to use standard filters and makes it easy to change as well.

Do you have some pictures of this setup gregs?

 

[LS6 Tommy]

Well, I could easily build a box that would hold more surface area of filter.
.
Tommy - coil may freeze if I decrease airflow cfm through it ?

Marc

Yup, you got it. Gregs' idea is pretty darn good.

Tommy

 

[gregs]

View media item 105514
Lets see if I can make the picture thing work. This is the before picture. My units are mounted in a 2x frame I built to make a good solid mount in the windows. My walls are 2x6 and with the window the front face of the units are about flush with the interior wall.

 

[gregs]

View media item 105515
This is the finished picture. Not sure why it doesn't look straight. I can get some other pics of the frame if you want me to. I made it so that it has 2 screws on each side to make it easy to remove for service. But I used filter grilles so that I could easily replace the filters without tools. The frame rests on the window sill and there are filler blocks on each side near the top. Then I used foam tape to make a good seal.