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?

 

[Tomfh]

That makes a lot of sense. Thanks. I hadn’t really considered that they aren’t working hard most of the time. Realistically for us there are only a few days a year where we really need the AC. Presumably they’re the only times you need the capacity.

 

[LittleInch]

The thing to remember is that even on those really hot days the machine will work but may be get to 25 or 27C, but it will be cool dry air is blowing around and will feel much cooler than the air outside or in the rest of the house.

Trying to design for the worst day means oversized it for 95 or 97% of the time.

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

 

[dbill74]

Ductless split systems don't do well trying to cool multiple rooms. As HVAC-Novice mentioned, you really need to get the cool air into each room.
With ductless split systems, you are best served having one per room. Before you ask about having a bunch of small condensing units outside, you can get systems where 1 outside unit can serve multiple indoor units.
Talk with your local representative/installer.

Do you have any underfloor space?

 

[Tomfh]

Before you ask about having a bunch of small condensing units outside, you can get systems where 1 outside unit can serve multiple indoor units.

I've wondered about these systems. How do they work? Is it a single outside unit, with branching coolant lines? How does the cooling/heating get distributed? Are there valves that shut off different lines as required? Does each line get pumped separately?

 

[MedicineEng]

Tomfh:
Google "how do VRV systems work". You are going to find the info that you are looking for in the first page of the search results

 

[LittleInch]

But basically its one unit, one pump, one header and then a series of pipes to the individual units, either direct from the header to each unit or branching off.

The trick comes in distributing flow evenly and that's where you need things like PICVs = Pressure independent control valves - basically once you set them they adjust to maintain a more or less fixed flow through the branches. Doing that effectively is the key to avoid starving one unit and lots of flow through another. Then how you control the cooling is down to the individual unit - it either shuts off the air or cold water flow or modulates it as required.

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

 

[HVAC-Novice]

I'm under the impression OP is looking at DX systems, like single split or VRF. Those don't have pumps or PICV. They only use the compressor to move the refrigerant, and solenoids (or similar modulating) valves in case of VRF. All the piping between indoor unit(s) and outdoor unit is proprietary and designed by the manufacturer and set up by the contractor. There isn't much for us design engineers to detail out.

I'm not sure why people bring up hydronic system components.

OP: in VRF, each indoor unit has an electronically controlled expansion valve that controls how much refrigerant flows and expands (cools). There are VRF that only cool. There are also heatpump VRF that can cool and heat. Heating only works down to a specific outdoor temperature, though. Commercial VRF also can simultaneously heat and cool different zones and recover heat from a cooling zone to a heating zone. But I doubt they exist in residential, or would be very expensive for little gain in residential scenarios. Different manufacturers (think Mitsubishi, Daikin) have different ways to manifold and distribute. You basically buy the whole system from one manufacturer and they have specific design rules for piping etc. So the Mitsu system will have different piping layout from Daikin etc. The contractor is trained, or would have access to a rep for detailed layout. Refrigerant systems are designed to return the oil to the compressor, so you can't just violate their rules.

 

[LittleInch]

Fair enough, but the same applies. It's one pipe with branches out its a header and individual runs then in the unit each system will control flow. How the system copes with variable load varies.

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

 

[nuuvox000]

I've wondered about these systems. How do they work? Is it a single outside unit, with branching coolant lines? How does the cooling/heating get distributed? Are there valves that shut off different lines as required? Does each line get pumped separately?

It's just a single outdoor unit with multiple connections for multiple indoor units, really just that simple. Then you run the refrigerant to each indoor unit like any other split system.

 

[Tomfh]

Those don't have pumps or PICV. They only use the compressor to move the refrigerant, and solenoids (or similar modulating) valves in case of VRF.

OP: in VRF, each indoor unit has an electronically controlled expansion valve that controls how much refrigerant flows and expands (cools).

Is this how all these residential “multihead” split systems work? A variable valve in the indoor unit?

Is that how single head system work too? A valve throttling the refrigerant at the indoor unit?

Is there any real difference between single and multi, aside from the number of heads?

What I’m really wondering is how much additional complexity and potential points of failure there are in a multihead system, vs a single system.