Single AC cooling 2+ rooms?

[Tomfh]

We are installing split system AC in our house. Multi-storey house with partially open plan.

Im trying to understand how open it needs to be between rooms for the cooling effect to reach other rooms (assuming the system is sized large enough).

E.g if you have two 4m x 4m rooms side by side, sealed from each other with a wall, how much of the dividing wall would need to be open to allow the air to mix and cool both rooms? Presumably a single door would provide partial mixing, but not much. What about half the wall open? I.e. at what level of openness is it suitable to use a single larger unit to cool the combined space?

 

[HVAC-Novice]

As large as possible. And aim the airflow so it goes through the opening.

In cooling the solar load can differ a lot between rooms. Large west facing windows will be bad and heat up that room much more.

In general, the more extreme the climate, and the worse the enclosure, the more those rooms will differ.

If noise and draft is acceptable, a fan may help moving air around.

A lot depends. Are you in Alaska or Saudi Arabia? Is the house built like a tent, or like a very efficient passive house?

 

[LittleInch]

My best guess is at least 50% of the area.

A normal door is next to useless in letting a normal wall mounted unit generate enough mixing of the warm and cold air.

But then an 8m x 4m room with a single AHU is pushing it a bit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nuuvox000]

I don't have a scientific answer but I would say that I wouldn't be comfortable cooling an 8x4 meter room with the supply air on one end using a residential system even if there was no wall between your rooms (100% open).

 

[IRstuff]

Some sort of ceiling fan might make it a bit easier

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[Tomfh]

But then an 8m x 4m room with a single AHU is pushing it a bit.

I wouldn't be comfortable cooling an 8x4 meter room with the supply air on one end using a residential system even if there was no wall between your rooms (100% open).

Thanks for this. What is it that makes it a problem? Will the air struggle to reach the far end?

 

[MedicineEng]

Air circulation will be the problem.
One end next to the AC wlll be freezing while the other end will be too hot.

Are some sort of ducts out the question?

 

[Tomfh]

We could duct from one part of the house to the other. But a fully ducted system is too hard.

Can you draw air from an cooled/heated space and duct to another space? Like products promise?

 

[HVAC-Novice]

Fans just transfer air close to room temperature. To cool, cold air has to go in all spaces. A fan will only temper the room. If that secondary room is just storage or something else unimportant with not much load, it may be acceptable. But no real information was given.....

You still haven't revealed climate, construction, and if heating performance also is a concern or cooling only.

Quality of data provided will impact quality of answers. It all matters.

 

[Tomfh]

It’s in Sydney Australia. Temps range from about 5-40C. Brick veneer home with poorly insulated tile roof. Heating too, but the main concern is cooling.

 

[DBronson]

Tomfh:

Have you considered a multizone split system? Link Seems like the simplest way to solve your problem.

Regards,

DB

 

[LittleInch]

A central ceiling AHU might work, but a wall mounted unit at one end just doesn't have the power to circulate enough air without the fan getting very noisy and a noticeable "breeze" in the room.

If you know the insulation is poor why don't you increase it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tomfh]

To properly insulate the house would involve ripping it apart. I'd sooner rebuild the whole thing.

 

[LittleInch]

No access under the roof to insulate in the loft space?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tomfh]

Not without removing the tiles and sarking or the plasterboard ceiling. There is no attic/loft space.

 

[nuuvox000]

Tomfh, after thinking about this again, I think you could definitely shoot the air 8 meters, using the correct grille sizes. We do this all the time in multifamily housing projects. You would, however, need a clear path from the grille to the opposite wall. Put the top of grilles about 6" below the ceiling so that the air can stick to the ceiling (coanda) and make it to the other side. You'll just need to be picky about your grille selection and have an open path. If you have a floorplan, I could take a look and offer some advice.

Sorry, I was imagining typical residential floor registers when I first read through this. If you're willing to do wall grilles with commercial-type diffusers, it should work fine. I like to design around Titus diffusers, but I'm not sure if they're sold in Australia.

 

[Tomfh]

Thanks for the advice.

I’m talking about the normal split system units sold in Australia.

These things:

https://www.voltfixelectrical.com.au/catalogue/daikin-reverse-cycle/

 

[nuuvox000]

Oh ok, gotcha. In that case, you can ask the manufacturer if they have the throw data to see how far it will throw.

 

[Tomfh]

Oh ok, gotcha. In that case, you can ask the manufacturer if they have the throw data to see how far it will throw.

Thanks, I'll have a look.

Another question about these systems. I've heard it's bad to oversize them, and that they misperform in such cases. However I've heard other people say that the problem of oversized systems is largely overstated, and they happily run at a lower level, and that it's only when a system is much bigger than it needs to be (e.g. 3x as big) that it's a problem. What are your thoughts on that?

 

[HVAC-Novice]

They can modulate. But oversizing typically prevents good dehumidification.

Note the unit will already be oversized most the time if it is sized properly for design day. So oversizing for design day wil be even worse.

In residentia you already have a large disadvantage due to relatively low sensible loads.