Ducted or split system?

The upper floor of my home contains living areas/kitchen plus 3 adjoining bedrooms. During the heat waves in summer the bedrooms are ovens with no a/c and the living area is serviced by a split system a/c which is more than 10 years old but does a good job of cooling and heating.

Which is the cheaper to run, split system for 3 adjoining bedrooms only or ducted system for the whole of the upper floor. The a/c in the bedrooms would only be used during hot summer nights.

Thanks for any advice ...

 

You'd use zoning controls on a ducted system so you can select the areas being conditioned.

 

Mine is zoned, lounge/two beds. The zoning is woolly at best and the system (big heat pump in a hall cupboard) cuts in and out very obviously. I'd rather have 3 x splits running at low speed, just using the one depending one which room I'm using (bed 2 is home office).

 

Thanks everyone for your comments, I am going to install the multi split system to the 3 bedrooms and replace the unit in the living area when it dies ...

 

Three split systems will probably be cheaper to run - logic being that the small splits tend to have very high published EERs and no ductwork to cool.

However, a ducted system should be much quieter and you can use much better air filtration. You wouldn't think that mattered... until you had bushfire air quality.....

 

I did have problems with air quality when the bushfires were raging, I had forgotten! Now you have given me something to think about ...

 

Generally once you have to get 3 splits it's cheaper to go with a ducted system in my experience. I also think that ducted systems in this instance with smart inverters may use less power than the individual systems.

Have you checked out other issues as well such as insulation and window tinting to try and minimise the heat coming in?

 

my PPOR has two levels, and we have three split systems for the top level, and two split systems for the ground floor level.

we prefer splits because of risk diversification - splits systems are pretty rock solid, and I don't want to pay thousands if anything happens to one ducted system.

also you can just turn on the one depends on where you are in the house.

 

Get an AC expert to review your premises and quote. There are many alternatives incl splits, full ducted and split ducted and split -splits (multi head - One compressor) with pro's and cons to each. Multiple splits can be cost efective but can also costs more to run in a busy house. They can also produce multiple noise sources. A ducted system may mean lost cupboard and wardrobe space upstairs and ducting downstairs may be impractical due to access. There are also cheap splits which can be false economy eg too small. The costs to wire and run additional circuits (multiple) is a hidden costs with 2 story dwellings and splits. Ducted may need 3 phase. Many splits can be inverter units which may need less amps on compressor startup but will cost a little more than a budget unit. A good brand (Mirsubishi Heavy Ind) may also have useful apps etc where a cheapier wont and cheapies are notorious as throw aways

 

Ducted all the way where you have access to the roof.
Warms up the whole house instead of just a small part.
Ducted also works better in open plan

 

Thank you all for your comments, much appreciated. I should explain that its only the 3 adjoining bedrooms upstairs I need to cool in summer, as the rest of the house, ground floor & upper floor living/kitchen areas already have a/c ...

 

We have Ducted A/c and here are my tips to avoid the old duct system issues

1. More zone, I have 8 zones so I can close off rooms not in use

2. more temp sensors, most single storey houses only have the one temp sensor at the control panel, double storey usually have 2, its how the A/C installer keep price down, spend the extra $150 and get a sensor away from the control panel, helps even out temperature across the whole house.

3. insulation, the more the merrier, I have roof insulation and I will be embarking on doing under floor insulation as my old house has floor boards which let in cold are, great in summer not so much in winter.

 

Good house design is the answer, it's painful to read that the solution seems to be to throw money at expensive perishable A/C devices.

Your problem upstairs might be due to a lack of ventilation (openable windows) and ceiling fans in the bedrooms.

If you do have opening windows in each bedroom then I'd just install ceiling fans (they last decades). I'd also consider external awnings and shutters than can block sun during the day from entering so you can keep windows open.

If you don't have opening windows upstairs then go with a ducted system because most have fan options that will help with circulating air on an average day.

 

My house is solid brick, built 1980, insulation in roof, tinted windows that open, wide covered verandahs with awnings, and all rooms have ceiling fans. The problem is it is facing north west and it is the bedrooms that receive the last of the summer sun. Its only in the last 3 years when we had those heat waves that we began to feel the uncomfortable heat at night ...
Thanks for your comments...

 

My 2 cents worth

A/C Basics
By design air conditioners don't cool they remove heat from the conditioned space by transferring it through the indoor heat exchanger (Evaporator) into the refrigerant and then expelling it through the outdoor heat exchanger (Condensor) . Heat will transfer from the warmer body (indoor air Temp) to the cooler body (Indoor heat exchanger) and then expel it through the same process at the outdoor unit (Super Heated Refrigerant in outdoor heat exchanger) to the cooler ambient air.

For reverse cycle a 4 way valve turns the indoor heat exchanger into the condensor and outdoor heat exchanger into the evaporator with the same principles applying.
(This is where the name reverse cycle comes from) The 4 way valve reverses the refrigerant cycle.

All A/C units have KW rating (Capacity) which is the amount of heat that unit can remove.


The less heat you have entering the conditioned space the less work the A/C has to do to remove it.

That's why A/C installers will do a Heat Load on a house before sizing the unit.

My point here

Insulation and roof ventilation are key here. Reduce the heat going into the house means the A/C unit doesn't have to remove it which means it works a lot less saving money on energy bills.

House designs also play a part due to heat gains through large windows etc and the direction they face.

For anyone interested

So where does the heat come from on heating?

R32 refrigerant boils at -52 degree's celcius so even at - 6 degrees outside ambient there is a lot of heat in the air that the outdoor heat exchanger transfer from outdoor ambient into the refrigerant and then conditioned space through the indoor heat exchanger.

What does the compressor do ?

It pumps the refrigerant around the system and superheats the refrigerant gas by means of compression before it enters the condensor. Change the pressure of the refrigerant you change the boiling point of it.

Sorry if I bored you.

 

That didn't bore me. My eyes glazed over and it put me to sleep......

 

But how can the west sun be affecting it if you have awnings? It sounds like maybe you need better awnings for those windows. Ones that retract perhaps.

Do you open windows with fans on at night?

 

Ducted tends to make sense by the time you're looking at 4+ zones, especially in a highset home. If you had good access to install the ducted throughout and wanted to futureproof the home, that's not a bad idea. In any other scenario, it makes sense to install splits to the bedrooms.