Can a window-mounted air conditioner suck in air or particulates from outside?

[chirhone]

I read before that room air conditioner is not supposed to suck in air or particulates/dusts from outside but my air quality monitor can detect some increase in pm2.5 particulates when the aircon is opened. Is it because its sucking those particulates from outside or the fan of the air conditioner recirculating the dusts within the room?

This is s 3/4 horsepower window air conditioner:

 

[berkeman]

Unless your air conditioner has a "Recirculate" setting, I would think that all of the air that it pumps in would be outside. Where else would it get it from?

As for particulate matter, that outside air should go through a filter, which would be specified in the datasheet for the A/C unit, no?

 

[hutchphd]

All the ones I have dealt with have separate external and internal airflow system. It would be wildly inefficient to continuously cool (and dehumidify!) new outside air.

 

[chirhone]

My aircon design is just like the one posted by hutchphd. Mine doesn't have any recirculate button nor any filter.

I think the unit outside and inside air compartment is not so air tight hence still acquiring air from outside? Or maybe the dusts in the room is recirculating especially near the ceililng? My electric fan is small and I can't hang it in the aircon level to test.

 

[hutchphd]

There was always a "filter" behind the inside grill on the ones I have opened up. Usually just some cheap open cell foam <1 cm thick that you wash in the dish pan and put back. Maybe that got lost on yours . Also you can usually see the dirty air path if you open up the unit.

 

[Lnewqban]

It seems to me that the main source of pollutants is the wind-driven outside air infiltration trough windows and the gaps around the AC unit opening.
The windward face of a high-rise building experiences wind-driven infiltration, while the opposite face suffers increased exfiltration because the leeward pressure is lower than the internal building pressure.

Some window AC models have intentional ventilation, which uses an adjustable damper that allows fresh air intake.
As the picture shows, it takes advantage of the relatively low pressure created between the air filter and the suction end of the blower.
You may be able to determine if your unit has that feature via visual inspection.
If it has it, check the condition of its soft seal, as well as either or not the damper is fully closing as commanded to do so.

A stand alone HEPA filter unit may help.
Please, see:
https://blissair.com/air-purifying-technology-overview.htm

 

[russ_watters]

There is often (as in the post above mine) a damper that can be opened or closed manually to allow the unit to bring in a small amount of outdoor air.

Otherwise, the seal around the window is a common source of additional infiltration.

 

[chirhone]

All the ones I have dealt with have separate external and internal airflow system. It would be wildly inefficient to continuously cool (and dehumidify!) new outside air.

View attachment 257692

I'd like to inquire something about the humidity influence of an air conditioner.

Whenever I steam food in the kitchen, the humidity increase by about 10% and it becomes hot because the perspiration can't evaporate faster due to the water vapor in the air. How does a room airconditioner help here? Can it lower the humidity? Is there a separate device that can just lower the humidity? The HEPA Air purifier just suck in the pm2.5 particulates. It can't lower humidity.

Thanks.

 

[256bits]

Yes. The air conditioner should remove some of the water content of air.

 

[256bits]

my air quality monitor can detect some increase in pm2.5 particulates when the aircon is opened.

When?
Immediately.
Or some time later when the temperature of the room has dropped?

 

[chirhone]

When?
Immediately.
Or some time later when the temperature of the room has dropped?

A few minutes later the particles count begin to increase. Ill time it next time. I still haven't opened the air conditioner casing and look at any damper because its so heavy.

Too bad i didnt invest in a dehumidifier before. It was only when i used my humidity meter inside and right outside my unit and saw it went down immediately outside when the room got hot after steaming food last week that i realized humidity inside a room can indeed be altered. I should have bought air purifier with build in dehumidifier. Now i have to buy a separate one.

 

[chirhone]

I am thinking whether to just buy an additional air conditioner for the kitchen since its near summer and hot. I noticed my bedroom air conditioner can decrease humidity from 60% to 51% (with no steaming of food). When steaming food. It reaches up to 75%.

If you use a stand alone dehumidifier. Can it make the humidity 20%? What would happen if you make it 5% humidity. Some references I am reading (wikipedia entry on Dehumidifier):

"Makeshift dehumidifiers

Because window air conditioner units have condensers and expansion units, some of them can be used as makeshift dehumidifiers by sending their heat exhaust back into the same room as the cooled air, instead of the outside environment. If the condensate from the cooling coils is drained away from the room as it drips off the cooling coils, the result will be room air that is drier but slightly warmer.

However, many window air conditioners are designed to dispose of condensate water by re-evaporating it into the exhaust air stream, which cancels out the air humidity decrease caused by the condensation of moisture on the cooling coils. To be effective as a dehumidifier, an air conditioner must be designed or modified so that most or all of the water that condenses is drained away in liquid form, rather than re-evaporated. Even if condensate is drained, a modified air conditioner is still less efficient than a single-purpose appliance with a design optimized for dehumidification. Dehumidifiers are designed to pass air directly over the cooling coils and then the heating coils in a single efficient pass through the device.

In addition, most air conditioners are controlled by a thermostat which senses temperature, rather than a humidistat that senses humidity and is typically used to control a dehumidifier. A thermostat is not designed for the control of humidity, and controls it poorly if at all."

 

[256bits]

To be effective as a dehumidifier, an air conditioner must be designed or modified so that most or all of the water that condenses is drained away in liquid form, rather than re-evaporated.

That's the key.
Most window air conditioners I have known do drain water to the outside.
Floor models would not have that feature, and the condensed water is re-evaporated to the room.

Reason I asked about the time of particulate increase is that with a cooler living space, the infiltration does increase through cracks and the like. But if outside air entering the living space is the cause of the particulate increase, then that would mean the outside air has more particles than inside. perhaps the blow from the air conditioner is moving the drapes or curtains which do collect settled dust. Or something else like that being disturbed.

 

[russ_watters]

I'd like to inquire something about the humidity influence of an air conditioner.

Whenever I steam food in the kitchen, the humidity increase by about 10% and it becomes hot because the perspiration can't evaporate faster due to the water vapor in the air. How does a room airconditioner help here? Can it lower the humidity?

Yes, the discharge air will be saturated; water condenses on the coil just like it does on a cold drink.

Is there a separate device that can just lower the humidity?

Yes, a dehumidifier. But if the room is already warm that will just make it warmer. a second air conditioner would be better.

 

[hutchphd]

I would also point out that there is no reason that steaming vegetables should produce great excess of steam. Tight fitting lid and just hot enough to vent a tiny bit of steam...more steam doesn't help the cooking. Even better is a pressure cooker.

 

[chirhone]

That's the key.
Most window air conditioners I have known do drain water to the outside.
Floor models would not have that feature, and the condensed water is re-evaporated to the room.

Reason I asked about the time of particulate increase is that with a cooler living space, the infiltration does increase through cracks and the like. But if outside air entering the living space is the cause of the particulate increase, then that would mean the outside air has more particles than inside. perhaps the blow from the air conditioner is moving the drapes or curtains which do collect settled dust. Or something else like that being disturbed.

There are more particulates outside because I'm also using an air purifier. The outside particulates is like this:

It's about 20ug/m^3.

It's only 2ug/m^3 in my room. Turning on the aircon makes it 3ug/m^3. An increase of 1 ug/m^3.

If my air purifier is turned off. The room pm2.5 slowly increases as the mist outside diffuses in.

Before last christmas when my cousin gave an air purifier to my parents as present. I didn't even know that without any visible pollution like in the street cars exhaust. There is still pollution even at 35th floor that can diffuse into bedroom. Most didn't know this hence there is no greater awareness to fight against pollution by the public.

I don't know if the aircon blows the dusts around the room or there is some damper in the aircon. I'll test more.

Meanwhile I'm in dilemma. A stand alone dehumidifier costs the same as an air conditioner. They even have the same electrical usage costs. One can make the air cooler, one no effect or hotter (the dehumidifier). But with the dehumidifier, you can control it better like down to 20% humidity. What lowest humidities you guys are still comfortable? I heard too dry and your nose dries up.

 

[russ_watters]

Meanwhile I'm in dilemma. A stand alone dehumidifier costs the same as an air conditioner. They even have the same electrical usage costs. One can make the air cooler, one no effect or hotter (the dehumidifier). But with the dehumidifier, you can control it better like down to 20% humidity. What lowest humidities you guys are still comfortable? I heard too dry and your nose dries up.

See why flu and probably Coronavirus are winter diseases?

 

[chirhone]

View attachment 258535

See why flu and probably Coronavirus are winter diseases?

That settles what to get. An air conditioner that can make the room cool instead of just a dehumidifier that can make it a bit hot. Thanks.

I wonder if humidity levels are related to the levels of the particulates. The humidity is low today. This is the pollution mist or haze when our Coronavirus positives were only 3.

This is when the Coronavirus positive counts increased to 49. The air becomes very clean because of few vehicles in street. All schools closed. Many don't go out. It's taken both early morning at about 6:30AM.

This is first time I get a very low pm2.5 reading. You can look into the far horizon. Air is just so fresh. This should be what cities should look like.

For the rest of the world. Try to notice the pollution is less now. I saw maps of china. It showed much lower pm2.5 levels too during the lockdown.

 

[russ_watters]

I wonder if humidity levels are related to the levels of the particulates.

They are. Higher humidity can make particles heavier and fall faster, and rain (and wet cooling coils) literally wash the air. Where you are it may be humid year-round, but in temperate zones, airborne indoor dust is a much bigger problem in winter (when it is drey) than in summer.

 

[chirhone]

This is the internal of the air conditioner when I asked for cleaning service today. I can't find any damper. Maybe when the condensor fan is running. It can send some air from the sides to the inside?