Di notte chiudo la persiana per non far entrare il freddo.

Di notte is a common Italian time expression meaning at night or during the night.

A few useful contrasts:

• di notte = at night, nights, during the night in a general sense
• la notte = the night, or sometimes at night depending on context, but it can sound a bit less neutral here
• di sera = in the evening, not at night

So in this sentence, Di notte is the most natural way to say that this is what the speaker does at night as a regular habit.

Italian often leaves out subject pronouns when they are not needed. The verb ending already tells you who the subject is.

• chiudo = I close
• chiudi = you close
• chiude = he/she closes

Because chiudo already clearly means I close, adding io is usually unnecessary unless you want emphasis or contrast:

• Io chiudo la persiana, tu apri la finestra.
  = I close the shutter, you open the window.

So the sentence sounds perfectly natural without io.

Persiana usually means a shutter or sometimes a blind, depending on context and region.

It is not the same as:

• tenda = curtain
• tapparella = रोलler shutter / rolling blind
• finestra = window

So chiudo la persiana means the speaker is closing the window shutter/blind, not the window itself.

This is one of those words where the exact English translation depends on what kind of window covering is meant in the real situation.

Italian uses definite articles much more often than English. With things that are understood from context, Italian usually prefers the article.

So:

• chiudo la persiana = I close the shutter/blind

Even though English often uses a possessive like my, Italian often does not if it is obvious whose thing it is. The article is enough.

This is very common in Italian:

• Mi lavo le mani = I wash my hands
• Apro la porta = I open the door
• Chiudo la persiana = I close the shutter

In Italian, the present tense is often used for habits and routines, just like in English:

• Di notte chiudo la persiana = At night I close the shutter

This means I usually / regularly do this at night, not necessarily I am doing it right now.

So the present tense here expresses a general habit.

This is a very common Italian structure.

• per = in order to / to
• non = not
• far = make/let (short form of fare)
• entrare = enter / come in

So per non far entrare il freddo literally means:

in order not to let the cold enter

More natural English:

• to keep the cold from coming in
• so that the cold doesn’t come in

The key idea is that fare + infinitive can mean make/let/have something happen.

Far is just the shortened form of fare used before another infinitive.

So:

• fare entrare
• far entrare

Both are possible, but far entrare is very common and often sounds smoother in everyday Italian.

You will see this shortening a lot:

• far vedere = to show
• far capire = to make someone understand
• far entrare = to let/make come in

So per non far entrare is completely normal.

Because Italian uses fare + infinitive to express causing or allowing an action.

Here:

• far entrare il freddo = to let the cold come in / to allow the cold to enter

Other examples:

• Faccio entrare il cane. = I let the dog come in.
• Non far uscire il gatto. = Don’t let the cat go out.

So entrare stays in the infinitive because it depends on far.

Italian often uses the definite article with abstract nouns or general concepts where English may not.

So:

• il freddo = the cold / cold air / the cold weather, depending on context

In this sentence, il freddo refers to the cold outside, understood as something that could come in.

This is very natural Italian. Compare:

• Non mi piace il caldo. = I don’t like hot weather / the heat.
• Temo il freddo. = I’m sensitive to the cold.

English sometimes drops the article, but Italian often keeps it.

Not in the same way.

Per non far entrare il freddo expresses purpose:

• in order not to let the cold in

Perché non entra il freddo would sound more like a clause about a result or explanation, and in this sentence it would not be the normal choice.

If you want another purpose structure, you could say:

• ...così il freddo non entra.
  = ...so the cold doesn’t come in.

But per non far entrare il freddo is more compact and more idiomatic here.

Yes, you could say Chiudo la persiana di notte. It is grammatically correct.

The difference is mainly one of emphasis and flow:

• Di notte chiudo la persiana...
  puts the time expression first, so it highlights at night
• Chiudo la persiana di notte...
  starts with the action itself

Italian word order is often flexible, especially with adverbial phrases like di notte. The original version sounds very natural because it sets the scene first.

It is a normal way to speak. Italian often uses il freddo this way, just as English can say:

• to keep the cold out
• the cold is coming in

So this is not strange or overly poetic. It simply means that cold air or low temperature from outside is entering the room.

Yes. That would also be correct, but it is a bit more specific.

• il freddo = the cold, cold air, coldness in general
• l’aria fredda = the cold air

The original sentence is more natural and idiomatic in everyday speech. L’aria fredda is fine if you want to emphasize the physical air coming in through the window.