Luftutskiftingen kommer an på luftbalansen.

Kommer an på is an idiomatic expression meaning depends on.

So:

• Luftutskiftingen kommer an på luftbalansen.
• The air exchange depends on the air balance.

A very common equivalent is avhenger av:

• Luftutskiftingen avhenger av luftbalansen.

Both are natural, but komme an på is very common in everyday Norwegian.

Because komme an på is a fixed expression.

The parts belong together:

• komme = come
• an på = part of the idiom

You cannot usually drop an here without changing the meaning.
Compare:

• Det kommer an på været. = It depends on the weather.
• Jeg kommer på mandag. = I’m coming on Monday.
• Jeg kommer på en idé. = I think of an idea / an idea occurs to me.

So in your sentence, kommer an på must be learned as one unit meaning depends on.

The ending -en is the definite article attached to the noun, roughly like the in English.

• luftutskifting = air exchange

• luftutskiftingen = the air exchange

• luftbalanse = air balance
• luftbalansen = the air balance

Norwegian usually puts definiteness at the end of the noun instead of using a separate word like English the.

So this sentence is talking about specific or understood things:

• the air exchange
• the air balance

They are compound nouns, which are very common in Norwegian.

luftutskiftingen

This can be broken down as:

• luft = air
• utskifting = replacement / exchange
• -en = the

So luftutskiftingen means the air exchange or the air replacement rate, depending on context.

luftbalansen

This can be broken down as:

• luft = air
• balanse = balance
• -n / -en = the

So luftbalansen means the air balance.

A useful thing to remember: Norwegian often makes one long noun where English might use two or more words.

Because Norwegian usually marks definiteness with an ending on the noun.

So instead of saying:

• the air balance

Norwegian says:

• luftbalansen

The the idea is built into the noun itself.

You do sometimes see both a separate determiner and a definite ending, but that happens in other structures, for example with adjectives:

• den gode balansen = the good balance

In your sentence there is no adjective, so the noun just takes the definite ending by itself.

The basic word order is:

• Luftutskiftingen = subject
• kommer = verb
• an på luftbalansen = rest of the predicate

So literally:

• The air exchange
  • depends
    • on the air balance

This is normal Norwegian main-clause word order: the finite verb comes early, usually in the second position.

Because the full expression is komme an på noe, meaning to depend on something.

So the pattern is:

• Det kommer an på deg. = It depends on you.
• Alt kommer an på prisen. = Everything depends on the price.
• Luftutskiftingen kommer an på luftbalansen.

Even though English uses depend on, Norwegian uses the fixed combination komme an på. So på is required here.

Yes. That is a very natural alternative.

Compare:

• kommer an på
  • noun
• avhenger av
  • noun

So:

• Luftutskiftingen kommer an på luftbalansen.
• Luftutskiftingen avhenger av luftbalansen.

Both mean essentially the same thing: The air exchange depends on the air balance.

A small difference in feel:

• komme an på is often a bit more everyday and conversational
• avhenge av can sound slightly more formal or technical

But both are correct.

It is singular.

You can tell from the form:

• luftutskifting = air exchange
• luftutskiftingen = the air exchange

A plural form would look different, for example:

• luftutskiftinger = air exchanges
• luftutskiftingene = the air exchanges

The same idea applies to luftbalansen:

• luftbalanse = air balance
• luftbalansen = the air balance

A careful approximation is:

LUFT-oot-sheef-ting-en KOM-mer an po LOOFT-ba-lan-sen

A few helpful notes:

• u in luft is not exactly like English oo, but oo is a decent starting point.
• sk before i in utskiftingen is pronounced like sh.
• kommer has a clear double consonant feel: KOM-mer, not KO-mer.
• på has a long vowel, roughly like po with rounded lips.

If you want to sound more natural, the biggest thing is probably learning kommer an på as one rhythm unit.

It works fine, especially in semi-technical or general explanatory writing.

Still, in more formal or technical texts, Norwegian often prefers verbs like:

• avhenger av = depends on
• bestemmes av = is determined by
• påvirkes av = is affected by

So in a technical context, you might also see:

• Luftutskiftingen avhenger av luftbalansen.
• Luftutskiftingen bestemmes av luftbalansen.

Your original sentence is correct and natural, but there may be slightly more formal alternatives depending on the text type.