Cooling advice for a 40Sq house

Hi,

Wondering if anyone has any advice on the following as we're a bit new to all this.

We're looking at building a dual storey 40SQ house in north Melbourne and are looking to add cooling to the build plan.
I asked for a quote on refrigerative rather than evaporative and the builder has suggested a Brivis Ice add-on to the ducted heating system.

I like this idea, but the thing that worries me is that the cooler they've suggested is only 20.5kw.

Using online calculators, the recommendation seems to be 125kw/sqm for living areas and 80w/sqm for bedrooms.
With about 150sqm per floor, this makes the cooling requirements as follows;

19kw for the ground floor
12kw for the first floor
31kw total.

When I mentioned this to the builder, they said that only 1 floor was intended to be cooled at a time (really?). As we have young children however, this is not an option as they can quite often be in bed for 4 or 5 hrs before we go to bed, therefore either floor going without cooling for that length of time is not acceptable when it's 40degs outside.

They also suggested adding a second cooler, one for each floor. However, as they are going to cost $14k each, spending $28k on cooling seems rather excessive.

My question is would a single 20.5kw adequately cool the whole house? I have a feeling not.

Would there be a better option than what the builder has suggested?

I did wonder about adding split systems to each room rather than the ducted cooling, but doesn't each split system require it's own external fan unit? Not sure where i'd locate 8 or so external fans if this was the case.

Ay idea what kind of setups the builders use in their display homes as they always seem nice and cool?

Thanks.

I'm getting a similar size with my about 40squares double story; check for zoning options as intelligent zoning can help. I'm going the maximum (for the brand they offer) 4 zones, 2 zones up and 2 down; I might have a few days in a year when all four zones would be inhabited and even 3 zones at the same time wouldn't be common. And if it only did two zones on a 40+ degree day, well, I can change my lifestyle for the handful of days involved.

But if that doesn't solve it, consider using splits to supplement the ducted instead of replace it. Also, if locations for the outside units are limited, you can get multi-head units, with multiple indoor units off one outdoor unit. I have a backup plan of 1-2 strategically placed split systems if the ducted proves inadequate or excessive.

And - look at your insulation, orientation and other passive climate-control elements. The recommendations are not based on well insulated houses that are properly orientated with external shade to relevant windows in summer. Get those right and your active heating/cooling requirements can plummet. (for example, I'm moving all possible windows off my west-facing wall and the remaining ones will all be getting external canvas blinds. I'm putting a pergola/veranda up post build at the right height/width to prevent direct summer sun in through my big north facing stacker doors but allow it in during winter. I'm upgrading the wall insulation.)

Lastly, if you want professional advice, take your plan to an independent a/c outfit and ask them what they'd recommend and why.

Just checking you would be prepared to pay the running costs for 30kwatts of cooling. MOst people are not. If I was you I would go with the 20kwatt unit and have the house correctly zoned. If your kids go to sleep when the sun is down you will not have a problem you can run two zones. I have a 36 square house with 30square living and at night I can do the whole house on 15kwatt aircond.

We got 2 separate systems installed in our house a 14kw for the living areas and a 7.1kw for the bedrooms, this is what the installer suggested for us as we didn't change to 3 phase power.

Another suggestion would be install ceiling fans in the bedrooms and beef up your insulation.

You must be running close to maximum current draw on a single phase system with that running there. Must have a 80 amp connection to the street, which is the biggest single phase you can get.

If you can have a look at the Actron ESP + range. You can have up to 8 zones and you only have to run the zones you want and run down to any one zone at a time. There is no "common" zone. We have it and very impressed.
Just as a side issue I presume you 3 phase power?

Thanks guys, zoning may be the way to go.
I like the look of the Actron range and how it scales power dependent on zone usage.

I'd be interested to hear from anyone who has a similar sized house and cooling system to what is being suggested as to how effective it is on the hottest of days.

Thanks.

Out if interest, at what point do u need 3 phase power? 18kw?? Or does this depend in the total draw from all electrical outlets in the house?

And although you can do 4 zones, how many zones or floor space can u effectively cool (provided doors etc seal the zones?

18 kwatt usually require 3 phases. However Lennox make a unit close to 18kwatt that runs on single phase. These days it is not a good idea to over dimension your cooling in fact I would say with all the other energy efficient choices people make around their house you could easly cut down the size of the unit. I run a 15kwatt unit for a house with 30square living and it works on the hotests of days we had last summer. DUring the day I run the living areas only. At night without the sun be present I can run and cool the whole house.

So if a house is double storey with 50 squares of internal dimension (living space), then 3 phases by inference would be a prerequisite - to run one or more likely two units?

Our home is 50sq and we run a ducted aircon/heating unit to the main living areas, theatre room and study. We also have a multi head split system unit to the 3 bedrooms and to downstairs.

For us this was the most economical option that would allow us to have each bedroom set on its own temperature with its own thermostat. Also, if we are watching TV in bed we can simply run our 3.5kw split system head instead of a much bigger unit. Hubby is a shift worker so in summer needs the aircon in the bedroom only.

Yes three phase would be required. You will only need two units if you plan on running both bedrooms and living at the same time.
But you will find double stories are generally very cool on the lower floor anyway. If you want the most flexibility you will have two smaller 3phases (maybe 15 or 18kwatt) or one big unit. But remember in either case you need to be prepared to pay to run the units.

For the record I know someone who was able to run a large double storey house on one 18kwatt unit. However to be effective they need to run the unit from early morning to give it a head start before the hot weather arrived during the day.

Which is the best way to do it anyway.

why do you say that IceMan. I Prefer not to put it on until I need it. My home doesnt get hot until 3 pm somedays. By that time I have hopefully exported some electricity to the grid and I can buy it cheaper.