Multi Split Air-Conditioning System

There are problems associated with this.

Many people in the US have stopped opening their windows. As a result, the indoor pollution can get much higher than outside and can even lead to illness.

Early in the morning, or whenever the weather allows, turn off the air conditioning and open the windows....................at least for a while to change out the air.

Is this is a larger commercial or institutional facility? In the US there are minimum air change requirements governed by local and State codes based on expected occupancy and square footage, most of which are stated in the ASHRAE standards.

The split application you are referring to is most likely a residential or a small office which, due to the square footage may not fall under the stated codes. The air exchange from opening and closing of the doors is considered adequate. IMO this isn't enough as poster 2 points out open some windows during mild days to create what I call a pluggers econimizer.

This type of A/C system is almost 100% used in residential and small to medium office buildings, at least in this part of the world. My point is , since there are millions people using such A/C everywhere and there is a potential risk of starvation of oxygen, and very likely brain damage due to long term use , how come there is no health warning , from your post , there seems to be no regulation either in your country for residential, certainly none in my country .

If adequate ventilation already exists, it wouldn't need to be added my the split system's evaporator/aid handler section. On the other hand, an outside air ventilation feature would be a nice option if existing ventilation is marginal or low. It depends on the specifics.

Infiltration of outside air is the only solution. If you plan spending long time indoors(night time, holiday), ensure some exhaust is working either thru attatched toilet or kitchen where air travels into toilet/kitchen thru door undercut say 20mm high. Best part is to open windows for cross ventilation on pleasent nights. In India (tropical climate), summer time we sleep outdoors, lawn or roof, which gives most refreshing sleep in 100% fresh air. You will also notice difference in sleep quality between indoors & camps

actually, while infiltration is the most common solution, it is not the only solution. Most modern high efficiency structures that are designed for very tight envelope conditions have an HRV (Heat Recovery Ventilation) which is an air to air heat exchanger that inputs fresh outdoor air into a space while preserving the temperature of the air to preserve energy efficiency. (either heated or cooled air)

with or without A/C, sleeping in an air tight room be it one of several people will increase the CO2 levels, if the room is completely air tight.

AS to the effect of the A/C unit on this room while people are sleeping, I don't see that being a problem as the split units only cool the air within the room. Other than reducing the temp of that air, they change nothing (unless I've missed something).

Working in the desert in numerous locations on different camps, the different accommodation has had window A/C units & split units. during the summer months you have to have the A/C on, and I've slept in these rooms, sometimes two up, with (for me) no ill-effects.

AS for the effects of increase levels of CO2..please see the extract from wikipedia..

CO2 retention is a pathophysiological process in which too little carbon dioxide is removed from the blood by the lungs. The end result is hypercapnia, an elevated level of carbon dioxide dissolved in the bloodstream. Various diseases may lead to this state; disturbed gas exchange may lead to impaired excretion of the gas. In addition, breathing air with a high carbon dioxide concentration may also lead to hypercapnia. The principal result of the increased amount of dissolved CO2 is acidosis (respiratory acidosis when caused by impaired lung function); other effects include tachycardia (rapid heart rate) seizures, coma, respiratory arrest and death.

However no room is really air tight, as previously mentioned.

Options in split acs for fresh air ventilation are minimum. If in filtered are meets the fresh air requirements as per the relevant standards then split acs are ok otherwise prefer ahus associated with refrigeration unit.

This is sketch given in wickipedia. I think now it is clear that in split type AC also outside air is sucked in like window type AC as basic machine is same.

look up mini split. Your diagram is of a window air conditioner.

I agree with you, but please note that basic machine is same only blower part is fixed in the AC which is indoor. I could not get details of Split AC so I posted this sketch.

As an added info on the difference between window type and split package. The Window type AC has a built-in mechanical linkage (exhaust control knob) that can be used to open or close a metal flap, that will vent out stale air or let in fresh air. Unlike the split package type of AC which does not have this feature and the capability to either let in fresh air and/or exhaust stale air.

that is not correct. In a split system, the air handler is remote, on a wall connected by any length of refrigerant you choose, to an outside pad mounted heat pump compressor unit. The system you are envisioning is not a split system. It is a unified ductless, common in motel rooms.

Once in awhile running air-vents in the bathroom, toilet or kitchen will be enough to force fresh air into the room. Having indoor plants will also supplement and balance the 21 % oxygen content of air we need or breath.

In multi split air-conditioning system, there is no provision for fresh air intake. Isn't this a health risk ? What if a number of people sleep inside such an air-conditional room for a long period of time without opening the door and the room is small and quite air-tight? There is no fresh air !

However, I have not heard a single report or problem related to this. This is quite puzzling. Can any one shed a bit of light here?

In Ohio the old schools are slowly being replaced by new buildings that meet the fresh air requirements of today. There doesn't seem to be a rush to correct these problems and no problems have been reported. It is troubling that codes are in place to protect the public and yet noncompliance causes no problems.

Gerald Eagy Jr.
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In industrial, manufacturing, commercial, hospitals and any multi-purpose business buildings, I believe there exist a code requirement of about 30% fresh air by volume is mandated.

In contrast, privately owned residential houses where central AC systems are installed, no provisions for fresh air exchanges are put in place. One possible reasoning for this maybe is that there is no such thing as perfectly enclosed / sealed rooms in existent for this type of constructions.. Also bathrooms and kitchens exhaust requirements always prevails in this type of dwellings. That making it a tightly sealed building becomes irrelevant or are just secondary and never considered nor specified during construction.

It is quite possible to have a room without attached bathroom and with window quite well made. Even it is not air tight, the air flow is negligible. I think the reason that no fresh air intake is not an immediate problem is because human can tolerate much higher CO2 concentration , it is only unclear what health effect there is if human is subject to long term high CO2 concentration air. For me , i have installed a small eexhaust fan in my bedroom and use whenever i sleep with A/C on. Thank you guys for sharing your experience.

Humans will not die in sleep. They will get up as they will feel uneasy first and will open up the windows.

GA.